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Large-stroke snap-through instability in the axial direction of a bi-stable structure with high slenderness

Huan Zhou, Qian Sun, Haibin Xia, Yiwei Xiong, Youchao Yuan, Yin Huang, Jianghong Yuan

Accepted Manuscript , doi: 10.1016/j.taml.2024.100561

[Abstract] (4) [PDF 1201KB] (0)

Abstract:
Mechanical snap-through instability of bi-stable structures may find many practical applications such as state switching and energy transforming. Although there exist diverse bi-stable structures capable of snap-through instability, it is still difficult for a structure with high slenderness to undergo the axial snapthrough instability with a large stroke. Here, an elastic structure with high slenderness is simply constructed by a finite number of identical, conventional bistable units with relatively low slenderness in series connection. For realizing the axial snap-through instability with a large stroke, common scissors mechanisms are further introduced as rigid constraints to guarantee the synchronous snapthrough instability of these bi-stable units. The global feature of the large-stroke snap-through instability realized here is robust and even insusceptible to the local out-of-synchronization of individual units. The present design provides a simple and feasible way to achieve the large-stroke snap-through instability of slender structures, which is expected to be particularly useful for state switching and energy transforming in narrow spaces.

Numerical study on micro-fracture mechanism of rock dynamic failure induced by abrupt unloading under high in-situ stresses

Yuezong Yang, Anye Li, Zhushan Shao, Kui Wu, Wei Wei, Wenhui Du, Yujie Wang

Accepted Manuscript , doi: 10.1016/j.taml.2024.100558

[Abstract] (18) [PDF 2431KB] (0)

Abstract:
Rock burst is a kind of severe engineering disaster resulted from dynamic fracture process of rocks. The macro failure behaviors of rocks are primarily formed after experiencing the initiation, propagation, and coalescence of micro-cracks. In this paper, the grain-based discretized virtual internal bond model is employed to investigate the fracturing process of unloaded rock under high in-situ stresses from the micro-fracture perspective. The simulated micro-fracturing process reveals that the longitudinal stress waves induced by unloading lead to the visible unloading effect. The influences of in-situ stresses, mineral grain sizes, and grain heterogeneity on rock macro and micro fracture are investigated. Micro-crack areas of tensile and shear cracks and micro-crack angles are statistically analyzed to reveal the rock micro-fracture characteristics. The simulated results indicate that the combined effect of the stress state transition and the unloading effect dominates the rock unloading failure. The vertical and horizontal in-situ stresses determine the stress state of surrounding rock after unloading and the unloading effect, respectively. As the vertical stress increases, the stress level after unloading is higher, and the shear failure characteristics become more obvious. As the horizontal stress increases, the unloading effect increases, leading to the intensification of tensile failure. The mineral grain size and grain heterogeneity also have nonnegligible influences on rock unloading failure. The micro-fracture perspective provides further insight into the unloading failure mechanism of deep rock excavation.

Determination of angle of attack and dynamic stall loop in the complex vortical flow of a vertical axis wind turbine

Wenzhong Shen, Tao Xie, Lingpeng Ge, Jiamin Yin, Zhenye Sun

Accepted Manuscript , doi: 10.1016/j.taml.2024.100560

[Abstract] (16) [PDF 1218KB] (0)

Abstract:
To improve the vertical axis wind turbine (VAWT) design, the angle of attack (AOA) and airfoil data must be treated correctly. The present paper develops a method for determining AOA on a VAWT based on computational fluid dynamics (CFD) analysis. First, a CFD analysis of a two-bladed VAWT equipped with a NACA 0012 airfoil is conducted. The thrust and power coefficients are validated through experiments. Second, the blade force and velocity data at monitoring points are collected. The AOA at different azimuth angles is determined by removing the blade self-induction at the monitoring point. Then, the lift and drag coefficients as a function of AOA are extracted. Results show that this method is independent of the monitoring points selection located at certain distance to the blades and the extracted dynamic stall hysteresis is more precise than the one with the “usual” method without considering the self-induction from bound vortices.

Numerical investigation on transonic flutter characteristics of an airfoil with split drag rudder

Yongchang Li, Yuting Dai, Chen Song, Chao Yang, Guangjing Huang

Accepted Manuscript , doi: 10.1016/j.taml.2024.100554

[Abstract] (16) [PDF 1347KB] (0)

Abstract:
In this paper, a series of flutter simulations are carried out to investigate the effects of split drag rudder (SDR) on the transonic flutter characteristic of rigid NACA 64A010. A structural dynamic model addressing two-degree-of-freedom pitch-plunge aeroelastic oscillations was coupled with the unsteady Reynolds-averaged Navier-Stokes equations to perform flutter simulation. Meanwhile, the influence mechanism of SDR on flutter boundary is explained through aerodynamic work and the correlated shock wave location. The results show that the SDR delays the shock wave shifting downstream, and the Mach number corresponding to reaching freeze region increases as the split angle increases. Therefore, the peak value of aerodynamic moment coefficient amplitude and the sharp ascent process of phase occurs at higher Mach number, which leads to the delay in the occurrence of the transonic dip. Besides, before the transonic dip of airfoil without SDR occurs, the aerodynamic moment phase of airfoil with the SDR decreases slowly due to the decrease in the speed of shock wave moving downstream. This results in an increased flutter speed when employing the SDR before the transonic dip of airfoil without SDR occurs. Meanwhile, the effects of asymmetric split angles on the transonic flutter characteristics are also investigated. Before the transonic dip of airfoil without SDR occurs, the flutter characteristic is dominated by the smaller split angle.

Topology transition description of horseshoe vortex system in juncture flows with velocity characteristic lines

Bo Hu, Hua Zhang, Ran Li, Qingkuan Liu

Accepted Manuscript , doi: 10.1016/j.taml.2024.100557

[Abstract] (59) [PDF 1225KB] (1)

Abstract:
Particle image velocimetry and numerical simulation results of juncture flows were analyzed to parametrically investigate topology transition. The vortex system evolutions from non-vortex to multi-vortex with variations in obstacle bluntness, obstacle width, flow velocity and boundary layer thickness are discussed from the perspective of velocity characteristic lines. The velocity characteristic lines of u = 0, v = 0, and ▽²v = 0 are adopted to describe the vortex system evolution. The motions of the characteristic lines with juncture flow parameters are described in detail, and the corresponding reflections of the vortex system patterns are illustrated. A panoramic picture of the development of velocity characteristic lines corresponding to the HSV topology transition from a non-vortex to a multi-vortex system with variations in the juncture flow parameter is established. Two methods for determining the attachment/separation pattern of the most upstream singularity are proposed. One method is based on the number of intersections of the u = 0 and v = 0 velocity characteristic curve lines, and the other is based on the relative positions of the most upstream feet of the u = 0 and v = 0 loop curves with both feet attached to the wall.

Regularized Dynamic Mode Decomposition Algorithm for Time Sequence Predictions

Xiaoyang Xie, Shaoqiang Tang

Accepted Manuscript , doi: 10.1016/j.taml.2024.100555

[Abstract] (105) [PDF 3081KB] (1)

Abstract:
Dynamic Mode Decomposition (DMD) aims at extracting intrinsic mechanism in a time sequence via linear recurrence relation of its observable, thereby predicting later terms in the sequence. Stability is a major concern in DMD predictions. We adopt a regularized form and propose a Regularized DMD (ReDMD) algorithm to determine the regularization parameter. This leverages stability and accuracy. Numerical tests for Burgers’ equation demonstrate that ReDMD effectively stabilizes the DMD prediction while maintaining accuracy. Comparisons are made with the truncated DMD algorithm.

Reduction in wave shoaling over a linear transition bottom using a porous medium

I. Magdalena, Ivan Jonathan Kristianto, Hany Q. Rif'atin, Amila Sandaruwan Ratnayake, Cherdvong Saengsupavanich, I. Solekhudinn, M. Helmi

Accepted Manuscript , doi: 10.1016/j.taml.2024.100556

[Abstract] (54) [PDF 1790KB] (0)

Abstract:
Wave shoaling, which involves an increase in wave amplitude due to changes in water depth, can damage shorelines. To mitigate this damage, we propose using porous structures such as mangrove forests. In this study, we use a mathematical model to examine how mangroves, acting as a porous breakwater, can reduce wave shoaling amplitude. Shallow water equations are used as the governing equations and are modified to account for the presence of porous media. To measure the wave reduction generated by the porous media, the wave transmission coefficient is estimated using analytical and numerical approaches. The separation of variables method and the staggered finite volume method are utilized for each approach, respectively. The numerical results are then validated against the previously obtained analytical solutions. We then vary the friction and porosity parameters, influenced by the presence and extent of porous media, to evaluate their effectiveness in reducing wave shoaling.

Spatially-graded 3D-printed viscoelastic truss metamaterials for impact trajectory control and energy absorption

Kaoutar Radi, Raphaël N. Glaesener, Siddhant Kumar, Dennis M. Kochmann

Accepted Manuscript , doi: 10.1016/j.taml.2024.100553

[Abstract] (149) [PDF 6604KB] (0)

Abstract:
We demonstrate that two- and three-dimensional spatially-graded truss-based polymeric-material metamaterials can be designed for beneficial impact mitigation and energy absorption capabilities. Using numerical and experimental techniques, we highlight the broad property space of periodic viscoelastic trusses, realized through 3D printing using selective laser sintering. Going beyond periodic designs, we present the impact response of spatially variant viscoelastic lattices in two and three dimensions. We show that introducing spatial variations in the lattice topology admits redirecting the impact trajectory and opens up new opportunities for the engineering and tailoring lightweight materials with a target impact functionality, which is made possible through the combined choice of base material and metamaterial design.

Penetration resistance of Al₂O₃ ceramic-ultra-high molecular weight polyethylene (UHMWPE) composite armor: Experimental and Numerical Investigations

Wencheng Lu, Yiding Wu, Minghui Ma, Yilei Yu, Xuan Zhou, Guangfa Gao

Accepted Manuscript , doi: 10.1016/j.taml.2024.100550

[Abstract] (151) [PDF 2383KB] (0)

Abstract:
To enhance the protective performance of ceramic composite armor, ballistic penetration experiments were conducted on Al₂O₃ ceramic-ultra-high molecular weight polyethylene (UHMWPE) composite armor with different thickness configurations. The damage and failure modes of hard projectiles and ceramic-fiber composite targets were analyzed. The recovered projectiles and ceramic fragments were sieved and weighed at multiple stages, revealing a positive correlation between the degree of fragmentation of the projectiles and ceramics and the overall ballistic resistance of the composite targets. Numerical simulations were performed using the LS-DYNA finite element software, and the simulation results showed high consistency with the experimental results, confirming the validity of the material parameters. The results indicate that the projectile heads primarily exhibited crushing and abrasive fragmentation. Larger projectile fragments mainly resulted from tensile and shear stress-induced failure. The failure modes of the composite targets included the formation of ceramic cones and radial cracks under high-velocity impacts. The UHMWPE laminated plates exhibited interlayer separation caused by tensile waves, permanent plastic deformation of the rear surface bulging, and perforation failure primarily due to shear forces.Through extended numerical simulations, while maintaining the same areal density and configuration of 9 mm Al₂O₃ ceramic + 12 mm UHMWPE laminated composite armor, the thickness configurations of the Al₂O₃ ceramic and UHMWPE laminated backplates were varied, and various thicknesses of UHMWPE laminates were simulated as the cover layer for the ceramic panels. The simulation results indicated that the composite armor configuration of 10 mm Al₂O₃ ceramic + 8 mm UHMWPE composite armor increased energy absorption by 13.48%. When altering the cover layer thickness, a 4 mm UHMWPE + 9 mm Al₂O₃ + 8 mm UHMWPE composite armor demonstrated a 27.11% improvement in energy absorption, showing a relatively significant enhancement.

Study of the fatigue fractography of Dual phase low carbon steel used in automotive industry

Ahmed A. Zainulabdeen, Bahaa Sami Mahdi, Jabbar H. Mohmmed, Niveen Jamal Abdulkader, Muslim Ali, Mujtaba A. Flayyih

Accepted Manuscript , doi: 10.1016/j.taml.2024.100552

[Abstract] (144) [PDF 2854KB] (0)

Abstract:
Fatigue properties play a crucial role as they are vital to ensuring the durability and integrity of components subjected to repeated loading conditions over long periods. The main objective of this work is to investigate the fatigue behavior of dual-phase low-carbon steels used in automotive applications using a rotating bending fatigue machine. Heat treatments were carried out to analyze the microstructure's effect on the fatigue properties, including quenching lowcarbon steel samples at 800 ℃ and 900 ℃. Hardness and tensile tests were performed, and the microstructure was inspected to examine the constitute phases. With the assistance of a scanning electron microscope, fractographic analyses were carried out to reveal the fracture features of the samples at different lifetime ranges. The results show that various failure mechanisms occur depending on the stress levels. Additionally, the specimens quenched at 900 ℃ exhibited higher fatigue strength.

Elastodynamic behaviors of steady moving straight dislocation within thin nano film

Ran Tao, Yehui Hong, Li Zheyu, Wenwang Wu

Accepted Manuscript , doi: 10.1016/j.taml.2024.100551

[Abstract] (140) [PDF 1567KB] (0)

Abstract:
The elastodynamic dislocation behaviors are of great interest for understanding the performances of structural alloys under intense dynamic loading conditions. The formation, propagations， and interactions of dislocations (such as injected dislocation, accelerating dislocation, steady moving dislocation at high constant speed) are quite different from static dislocations. For steady-moving dislocation within the isotropic infinite medium, the effects of surface and interface on steadymoving dislocations within limited space are still known. In this paper, we investigate the elastodynamic image stress simulation of steady moving dislocation within film of limited thickness at constant speed using Eigenstrain theory, Lorentz transformation, and steady dynamic equilibrium equations. We propose an efficient solution method that involves complex Fourier series, transforming partial differential equations into ordinary differential equations, and ultimately into a set of algebraic equations in spectral space. The effects of dislocation speed and position near the free surface on the image stress of steady-moving climbing and gliding dislocations within the thin film are examined. The results show that relativistic effects are significant for certain dislocation configurations and stress components, whereas other stress components are less sensitive to relativistic effects near the transonic speed region.

Data-model coupling driven stress field measurements

Guangbo Wang, Jian Zhao, Jiahui Liu, Dong Zhao

Accepted Manuscript , doi: 10.1016/j.taml.2024.100549

[Abstract] (138) [PDF 1808KB] (0)

Abstract:
This paper presents a method for measuring stress fields within the framework of coupled data models, aimed at determining stress fields in isotropic material structures with localized deterioration behavior without relying on constitutive equations in the deteriorated region. This approach contributes to advancing the field of intrinsic equation-free mechanics. The methodology combines measured strain fields with data-model coupling driven algorithms. The gradient and Canny operators are utilized to process the strain field data, enabling the determination of the deterioration region's location. Meanwhile, an adaptive model building method is proposed for constructing coupling drive models. To address the issue of unknown datasets during computation, a dataset updating strategy based on a differential evolutionary algorithm is introduced. The resulting optimal dataset is then used to output stress field results. Validation against finite element method calculations demonstrates the accuracy of the proposed method in obtaining fullfield stresses in specimens with local degradation behavior.

Dynamic Response of Armor-piercing Bullets to Blunt and Penetration with Protective Gelatin

Rui Yuan, Yaoke Wen, Weixiao Nie, Dongxu Liu, Zhouyu Shen, Haoran Xu

Accepted Manuscript , doi: 10.1016/j.taml.2024.100548

[Abstract] (139) [PDF 1476KB] (0)

Abstract:
To investigate the coupled damage mechanism of blunt impact and bullets penetration after penetrating ballistic plates against human body targets, experiments were conducted using 6.8 mm caliber armor-piercing bullets against gelatin targets with protective coatings. A numerical analysis model was developed to simulate bullet penetration into gelatin with protective coatings, obtaining endpoint characteristic quantities such as bullet velocity changes, changes in energy distribution, pressure, stress, and stress wave variations within the gelatin target after protection. The results indicate that at a velocity of 640 m/s, the 6.8 mm caliber armor-piercing round failed to penetrate the ballistic plate yet still caused a blunt impact depression of 37 mm in depth. Under conditions where the bullet did not penetrate the ballistic plate, approximately 80% of the bullet's kinetic energy was absorbed by the ballistic plate. At a velocity of 740 m/s, the bullet penetrated the ballistic plate, resulting in a blunt impact depression depth of 56 mm and an instantaneous cavity with a maximum diameter of 60 mm. During the process of penetrating the ballistic plate, approximately 50% of the bullet's kinetic energy was absorbed by the ballistic plate, and about 40% of the remaining kinetic energy transferred into the gelatin during the penetration of the target.

Learning active flow control strategies of a swept wing by intelligent wind tunnel

Yusi Wu, Tingwei Ji, Xinyu Lv, Changdong Zheng, Zhixian Ye, Fangfang Xie

Accepted Manuscript , doi: 10.1016/j.taml.2024.100543

[Abstract] (196) [PDF 5136KB] (6)

Abstract:
An intelligent wind tunnel using an active learning approach automates flow control experiments to discover the aerodynamic impact of sweeping jets on a swept wing. A Gaussian process regression model is established to study the jet actuator’s performance at various attack and flap deflection angles. By selectively focusing on the most informative experiments, the proposed framework was able to predict 3,721 wing conditions from just 55 experiments, significantly reducing the number of experiments required and leading to faster and cost-effective predictions. The results show that the angle of attack and flap deflection angle are coupled to affect the effectiveness of the sweeping jet. Meanwhile, increasing the jet momentum coefficient can contribute to lift enhancement; a momentum coefficient of 3% can increase the lift coefficient by at most 0.28. Additionally, the improvement effects are more pronounced when actuators are placed closer to the wing root.

A Kresling origami metamaterial with reprogrammable shock stiffness

Ruiwei Liu, Yantong Huang, Manjia Su, Chenxiao Li, Beibin Liang, Chunlong Wang

Accepted Manuscript , doi: 10.1016/j.taml.2024.100546

[Abstract] (179) [PDF 1419KB] (4)

Abstract:
Using origami folding concepts to design novel mechanical metamaterials has recently become a prevalent framework. Inspired by the Kresling origami structure, this study proposes a doublelayer Kresling origami metamaterial with reprogrammable shock stiffness. Two combination strategies are constructed, each with different geometric constraints and kinematic compatibility. They are identified as assigned with same torsion direction (ASTD) and assigned with opposite torsion direction (AOTD), respectively. The shock stiffness of two double-layer Kresling origami metamaterials is analyzed using the finite element method, and results indicate that the AOTD metamaterial has superior impact resistance. Furthermore, the programmability of shock stiffness of the metamaterial is carried out comprehensively, and the influence of each design parameter is exhibited in detail. Finally, two prototypes of ASTD and AOTD metamaterials are fabricated, and experimental tests verify the analysis outcomes. This study provides a new approach to constructing mechanical metamaterials with reprogrammable shock stiffness for applications in energy absorption and vibration isolation engineering.

Finite element modeling and injury criteria investigation for the lower leg of the Chinese human body under impact loads

Xianping Du, Xizheng Zhao, Jianyin Lei, Guanjun Zhang

Accepted Manuscript , doi: 10.1016/j.taml.2024.100547

[Abstract] (145) [PDF 2739KB] (0)

Abstract:
The widely used human body injury criteria were established based on the biomechanical response of the Euro-American human body, without considering the difference in the body anthropometry and injury characteristics among different races, particularly the Chinese human body that has the smaller body size. The absence of such race specific design considerations negatively influences the injury prevention capability for these populations, and weakens the applicability of injury criteria. To resolve these issues, this study aim to develop a lower leg finite element model of a 50th percentile Chinese male. The model is built based on the medical images of an average size Chinese male with detailed ankle ligaments and lower leg muscles modeled. Sixty experiments available in the literature are used to validate its biofidelity. Using the validated model, the lower leg model is subjected to combined axial compression and bending loads to evaluate its injury criteria. Compared with a typical Euro-American human body mode, the Chinese lower leg presents lowered mechanical tolerance, and the revised tibia index may be an option to be the injury criteria for the Chinese lower leg. Additionally, the validated model reproduces the pedestrian lower leg fracture in a domestic accident.

Strain concentration factor of heterogeneous materials and analytical influence functions based on Eshelby tensor

Shanqiao Huang, Zifeng Yuan

Accepted Manuscript , doi: 10.1016/j.taml.2024.100542

[Abstract] (165) [PDF 6732KB] (1)

Abstract:
In this manuscript, Eshelby tensor is employed to assess the strain concentration that arises in the matrix phase at the interface, offering precise values and locations of maximum strain under specific loading conditions for both spherical and cylindrical inclusions. When compared to numerical simulation results, the analytical predictions grounded in the Eshelby tensor exhibit satisfactory accuracy. Then an analytical calculation method based on Eshelby tensor for the elastic strain influence functions of reduced-order homogenization (ROH) method is developed and adopted on particle-reinforced and fibrous composites, presenting its feasibility and advantage on off-line stage calculation of ROH method. The error analyses between analytical and numerical results are conducted. The numerical results also exhibit the necessity of finer interface partitioning to obtain the response on micro-scale with higher resolution.

In vivo imaging and computational modeling of nonlinear shear waves in living skeletal muscles

Yuxi Cao, Chunpeng Chai

Accepted Manuscript , doi: 10.1016/j.taml.2024.100545

[Abstract] (160) [PDF 2146KB] (0)

Abstract:
How the muscle state of living muscles modulates the features of nonlinear elastic waves generated by external dynamic loads remains unclear because of the challenge of directly observing and modeling nonlinear elastic waves in skeletal muscles in vivo, considering their active deformation behavior. Here, this important issue is addressed by combining experiments performed with an ultrafast ultrasound imaging system to track nonlinear shear waves (shear shock waves) in muscles in vivo and finite element analysis relying on a physically motivated constitutive model to study the effect of muscle activation level. Skeletal muscle was loaded with a deep muscle stimulator to generate shear shock waves (SSWs). The particle velocities, second and third harmonics, and group velocities of the SSWs in living muscles under both passive and active states were measured in vivo. Our experimental results reveal, for the first time, that muscle states have a pronounced effect on wave features; a low level of activation may facilitate the occurrence of both the second and third harmonics, whereas a high level of activation may inhibit the third harmonic. Finite element analysis was further carried out to quantitatively explore the effect of active muscle deformation behavior on the generation and propagation of SSWs. The simulation results at different muscle activation levels confirmed the experimental findings. The ability to reveal the effects of muscle state on the features of SSWs may be helpful in elucidating the unique dynamic deformation mechanism of living skeletal muscles, quantitatively characterizing diverse shock wave-based therapy instruments, and guiding the design of muscle-mimicking soft materials.

Investigating the mechanical properties of cortical bone under dynamic torsional loading

Jianyin Lei, Zhiyang Li, Hengru Su, Shiqiang Li, Zhifang Liu

Accepted Manuscript , doi: 10.1016/j.taml.2024.100544

[Abstract] (187) [PDF 1143KB] (0)

Abstract:
Bone is a multi-phase, non-homogeneous material that exhibits strain rate sensitivity, and the bone may fail under compression, tension, torsion, or a combination of these loading. The mechanical properties of cortical bone with strain rate effect under compression and tension have been obtained through the application of the split Hopkinson pressure/tension bar technique, but no such studies have been reported for determining the strain rate behavior properties of bony materials under torsion. In our study, the shear stress-strain curves with the rate-dependent cortical bone under dynamic torsional loading were first obtained using a torsional split Hopkinson bar system. Based on the experiments, an improved mathematical model consisting of elastic, viscoelastic, and viscoplastic components was used to identify the material parameters of the cortical bone. Detailed material properties are derived through constitutive relations. The results may assist researchers in developing more accurate depictions of cortical bone under different load conditions.

Sidewall influence of varying free stream Mach number in ramp induced shock wave boundary layer interactions

Raja Mangalagiri, Satya P Jammy

Accepted Manuscript , doi: 10.1016/j.taml.2024.100541

[Abstract] (185) [PDF 2400KB] (3)

Abstract:
This study investigates the 3D effects introduced by the end walls for an aspect ratio 1 in ramp-induced shock wave boundary layer interactions. The simulations are performed using symmetry boundary condition in spanwise at free-stream Mach num- bers in three dimensions. The simulations are done using an in-house compressible supersonic solver “OpenSBLIFVM”[1]. Two free stream Mach numbers 2.5, and 3 are utilised in the current work, the simulated results are compared with the aspect ratio 1 simulations of Mangalagiri and Jammy [2]. The inflow is initialized with a similarity solution; its Reynolds number based on the boundary layer thickness is adjusted such that the Reynolds number at the starting of the ramp is kept at 3 × 10⁵ for all simu- lations. From the results, it is evident that the introduction of sidewalls resulted in a shorter centerline separation length when compared with the 2D simulations. This is contradictory to the results at Mach 2 by [2]. The vortex observed at Mach 2 by Man- galagiri and Jammy [2], in the central separation region, has vanished with increasing the free-stream Mach number. Also, the topology of interaction has changed from owl- like separation of the second kind to the first kind when the freestream Mach number has increased from 2 to 2.5. It can be concluded that, the topology of interaction is key to the increase or decrease of the central separation length when compared to 2D.

shInvestigation on flight load calibration of aircraft composite wing base on strain gauge measurement

Xiajun Zhao, Yazhi Li, Zhaoxin Yun, Wei Zhang

Accepted Manuscript , doi: 10.1016/j.taml.2024.100540

[Abstract] (214) [PDF 2141KB] (4)

Abstract:
A computational and test method for calibrating the flight loads carried by aircraft wings is proposed. The wing load is measured in real-time based on the resistance and fiber Bragg grating strain gauges. The linear stepwise regression method is used to construct the load equations. The mean impact value algorithm is employed to select suitable bridges. In the ground calibration experiment, the wing load calculation equations in both forward and reverse installation states are calibrated. The correctness of the load equations was verified through equation error and inspection error analysis. Finally, the actual flight load of the wing was obtained through flight tests.

A finite element model of the eye matched with in vitro experiments for the prediction of traumatic retinal detachment

Duo Chen, Xiaona Sun, Yuan Wu, Min Tang, Jinghui Wang, Xiaofeng Qiao, Yuanjie Zhu, Zhiyang Zhang, Xin Du, Jieyi Guo, Yepu Chen, Linyuan Fan, Xiaoyu Liu

Accepted Manuscript , doi: 10.1016/j.taml.2024.100539

[Abstract] (205) [PDF 1312KB] (1)

Abstract:
This study aimed to conduct finite element (FE) analysis matched with an in vitro experiment to analyze traumatic retinal detachments (TrRD) resulting from blunt trauma and provide stress and strain thresholds to predict the occurrence of TrRD. The in vitro experiment was performed on forty-eight porcine eyes using a pendulum device. We examined dynamic mechanical responses at four energy levels. A FE model, based on experimental results and published data, was used to simulate TrRD. Fiftyone additional eyes underwent immediate pathological examination following blunt impact. A dynamic variation of velocities was observed post-impact, displaying an approximate cosine oscillation-attenuation profile. Energy absorption increased as the initial energy and differed significantly at four energy levels (p ＜ 0.001). FE simulation showed a peak strain of 0.462 in the anterior vitreous body and a peak stress of 1.408 MPa at the cornea at the high-energy level. During the energy transfer, the stress was initially observed in retinal region along the impact direction at the separation. TrRD were observed in injured eyes, where a few detachments were detected in control eyes. Correlations were performed between the proportion of pathological outcomes and FE results. In conclusion, this study suggests that stress contributes to the development of retinal detachment, providing an indicator to distinguish the occurrence of TrRD.

Effect of flight helmet mass characteristics and neck stress postures on pilot neck impact injury

Peng Wang, Han Peng, Jinzhi Huang, Yuan Li, Qingbo Dou, Tao Suo

Accepted Manuscript , doi: 10.1016/j.taml.2024.100538

[Abstract] (223) [PDF 2573KB] (1)

Abstract:
Pilots’ ability is significantly improved by using night vision goggles and other equipment built on the flight helmets. Still, excessive helmet mass and centroid deviation caused by the integration of external equipment may increase the risk of neck injury of pilots during takeoff and landing. To reduce the risk of pilots’ neck injuries under impact load, it is urgent to study the law of related factors on pilot’s neck injury and provide theoretical support for the design of flight helmets. This paper establishes a finite element model of the pilot-seat-restraint system, and the effects of helmet masses, helmet centroids, and neck stress postures on the pilot’s neck injury are systematically studied. The function rules of these factors on the neck load are clarified. This research can provide an essential reference for designing and optimizing flying helmets.

Head injury mechanisms of the occupant under high-speed train rear-end collision

Zhenhao Yu, Lin Jing

Accepted Manuscript , doi: 10.1016/j.taml.2024.100537

[Abstract] (212) [PDF 3358KB] (3)

Abstract:
To improve the passive safety of high-speed trains, it is very important to understand the mechanism of head injury in high-speed train collisions. In this study, the head injury mechanisms of occupants in high-speed train rear-end collisions were investigated based on the occupant-seat coupling model, which included a dummy representing the Chinese 50th percentile adult male. The typical injury responses in terms of skull fractures, brain contusions, and diffuse axonal injury (DAI) were analyzed. Meanwhile, the influences of collision speed and seat parameters on head injury response were examined. The simulation results indicate that the skull fractures primarily occur at the skull base region due to excessive neck extension, while the brain contusions and DAI result from the relative displacement of different brain regions. The increase in collision speed will promote the probability of skull fracture, brain contusion, and DAI. Seat design modifications, such as reduced seat spacing, increased seat backrest angles, and selecting the appropriate cushion angle (76°) and friction coefficient (0.15), can effectively mitigate probably occupant’s head injury.

PLA-based additively manufactured samples with different infill percentages under freeze-thaw cycles; mechanical, cracking, and microstructure characteristics

Reza Ale Ali, Hamid Reza Karimi, Razie Mohamadi

Accepted Manuscript , doi: 10.1016/j.taml.2024.100536

[Abstract] (207) [PDF 1122KB] (1)

Abstract:
The layered nature of the parts produced by 3D printing makes them susceptible to freezethaw damage. This research investigates the effect of the freeze-thaw cycles on the tensile, bending, and fracture resistance of samples made of Polylactic acid (PLA) material. For this purpose, the samples with 100, 75, 50, and 25 infill percentages were subjected to 4, 8, and 12 freeze-thaw cycles. The results show that the infill percentage and cycle affect freeze-thaw resistance. So, although for 100% infill samples, the 4, 8, and 12 cycles averagely reduce the tensile strength by 5, 15, and 25. The same trends can also be seen for flexural strength and, more severely, fracture resistance. Reviewing the microstructure with a Scanning electron microscopy (SEM) device shows freeze-thaw’s destructive effect (both the strand’s surface and their joints). In the end, simple statistical analyses were presented to evaluate a model for anticipating the effect of freeze-thaw on mechanical resistance.

Complex Dynamics of a Magnetic Microrobot Driven by Single Deformation Soft Tail in Random Environment

Xinpeng Shi, Yongge Li, Yong Xu, Qi Liu

Accepted Manuscript , doi: 10.1016/j.taml.2024.100534

[Abstract] (184) [PDF 22238KB] (0)

Abstract:
This study focuses on exploring the complex dynamical behaviors of a magnetic microrobot in a random environment. The purpose is to reveal the mechanism of influence of random disturbance on microrobot dynamics. This paper establishes the stochastic dynamic models for the microrobot before and after deformation, considering the influence of Gaussian white noise. The system responses are analyzed via steady-state probability density functions and first deformation time. The effects of different magnetic field strengths and fluid viscosities on the movement speed and angular velocity of the microrobot are studied. The results indicate that random disturbances can cause deformation of microrobots in advance compared to the deterministic case. This work contributes to the design and motion control of microrobots and enhances the theoretical foundation of microrobots.

Modeling and characterization of contact behavior of asperities with irregular shapes

Jiaxin Huanga, Chen Suna, Jubing Chena

Accepted Manuscript , doi: 10.1016/j.taml.2024.100535

[Abstract] (227) [PDF 23416KB] (2)

Abstract:
This paper introduces a model for characterizing the contact behavior of irregular asperities, transforming it into a superposition of sinusoidal asperity contact behaviors. A new sinusoidal asperity model is developed for bilinear hardening under plane strain conditions. Empirical equations are proposed, considering geometric shapes, tangent modulus, and Young's modulus. The frequency of asperity height is extracted through Fourier transform for irregular asperities. Contact area and pressure are predicted using the sinusoidal asperity model, and the behavior of irregular asperities is obtained by superimposing those with the first three frequencies. Experimental validation is conducted with milling and knurling-formed asperities, showing good alignment between the model and experimental results. In rough surface models, the proposed irregular asperity model exhibits greater accuracy in predicting contact behavior than a single sinusoidal asperity when interference exceeds 10% of the amplitude.

Evaporation Mechanisms during Droplet Levitation and Coalescence Based on Molecular Dynamics

Fengming Chen, Tieqiang Gang, Lijie Chen

Accepted Manuscript , doi: 10.1016/j.taml.2024.100533

[Abstract] (270) [PDF 2706KB] (2)

Abstract:
Droplet levitation and coalescence mechanisms have consistently been a focal point in scientific research. From the perspective of molecular interactions, we investigated the influence of vapor pressure on the levitation and coalescence of droplets. The evaporation of nanodroplets and liquid pools under different initial environments was simulated by nonequilibrium molecular dynamics. The study analyzed the effects of evaporation during the processes of droplet levitation and coalescence and determined the existence of the Knudsen layer. Knudsen layers consisting of water molecules rather than clusters are generated during the evaporation. The definition, properties, and mechanisms of the layers were investigated.

Multi-objective optimization of a bistable curved shell with controllable thickness based on machine learning, Theoretical and Applied Mechanics Letters

Shiqing Huang, Chenjie Zhao, Xiaoqian Ning, Wenhua Zhang, Huifeng Xi, Zhiwei Wang, Changxian Wang

Accepted Manuscript , doi: 10.1016/j.taml.2024.100532

[Abstract] (219) [PDF 1134KB] (2)

Abstract:
Bistable curved shells have become a promising low-cost application in energy absorption fields owing to recent advances in material and technology. Significant research has been conducted to improve their energy absorption effect through forward prediction and singleobjective optimization. However, these approaches may not fully explore their functional potential. In this study, we propose a multi-objective optimization framework based on the principle of main objective optimization that combines neural networks and genetic algorithms. The energy absorption effect and backward snapping force of the bistable curved shell are improved synchronously. Meanwhile, a reverse design algorithm is developed to generate the preset load-displacement curve, which further expands the application of machine learning methods in the field of multi-objective optimization. The combination of machine learning and multi-objective optimization is highly effective for building meta-structures with specific performance requirements and has potential applications in solving complex optimization tasks in various fields.

A New Cyclic Cohesive Zone Model for Fatigue Damage Analysis of Welded Vessel

Changyuan Shen, Xiaozhou Xia, Dake Yi, Zhongmin Xiao

Accepted Manuscript , doi: 10.1016/j.taml.2024.100531

[Abstract] (254) [PDF 2857KB] (1)

Abstract:
A new cyclic cohesive zone fatigue damage model is proposed to address the fatigue problem spanning high and low cycle stages. The new damage model is integrated with the damage extrapolation technique to improve calculation efficiency. The model's effectiveness in regulating the low-cycle fatigue evolution rate, overall fatigue damage evolution rate, and stress level at the fatigue turning point is assessed through the comparison of the S-N curves. The fatigue damage model's high precision is proved based on the minor deviation of stress at the turning point of the S-N curve from the actual scenario. Finally, the fatigue damage evolution is simulated considering the effects of pre-load pressure and welding residual stress. It is observed that laser welding induces a significant residual tensile stress, accelerating fatigue damage evolution, while compressive loading impedes fatigue damage progression.

An Implicit Factorized Transformer with Applications to Fast Prediction of Three-dimensional Turbulence

Huiyu Yang, Zhijie Li, Xia Wang, Jianchun Wang

Accepted Manuscript , doi: 10.1016/j.taml.2024.100527

[Abstract] (259) [PDF 6789KB] (1)

Abstract:
Transformer has achieved remarkable results in various fields, including its application in modeling dynamic systems governed by partial differential equations. However, transformer still face challenges in achieving long-term stable predictions for three-dimensional turbulence. In this paper, we propose an implicit factorized transformer (IFactFormer) model, which enables stable training at greater depths through implicit iteration over factorized attention. IFactFormer is applied to large eddy simulation of three-dimensional homogeneous isotropic turbulence (HIT), and is shown to be more accurate than the FactFormer, Fourier neural operator (FNO), and dynamic Smagorinsky model (DSM) in the prediction of the velocity spectra, probability density functions of velocity increments and vorticity, temporal evolutions of velocity and vorticity root-mean-square value and isosurface of the normalized vorticity. IFactFormer can achieve long-term stable predictions of a series of turbulence statistics in HIT. Furthermore, IFactFormer showcases superior computational efficiency compared to the conventional DSM in large eddy simulation.

Motion of a small bubble in forced vibrating sessile drop

Jia-Qi Cheng, Fei Zhang, Chun-Yu Zhang, Hang Ding

Accepted Manuscript , doi: 10.1016/j.taml.2024.100529

[Abstract] (258) [PDF 16530KB] (8)

Abstract:
In this letter, the motion of small gas bubbles within sessile water drops on a vibrating substrate is investigated numerically using a two-phase diffuse interface method. Depending on the amplitude of the plate vibration, the motion of the gas bubbles falls into three distinct regimes: oscillating within the drop, sticking to the substrate, or escaping from the drop. In particular, the motion of oscillating bubbles follows a harmonic function, and is found to be closely related to a combined effect of the deformation of the sessile drop and the vibration of the plate. To interpret the underlying mechanism, we analyze the dominant forces acting on the bubbles in the non-inertial framework fixed to the plate, and take account of the periodic deformation of the drop, which effectively induces flow acceleration inside the drop. As a result, we establish a theoretical model to predict the bubble motion, and correlate the amplitude and phase difference of the bubble with the Bond and Strouhal numbers. The theoretical prediction agrees with our numerical results. These findings and theoretical analysis provide new insights into controlling bubble motion in sessile drops.

Cut layout optimization for design of kirigami metamaterials under large stretching

Chen Du, Yiqiang Wang, Zhan Kang

Accepted Manuscript , doi: 10.1016/j.taml.2024.100528

[Abstract] (246) [PDF 1608KB] (6)

Abstract:
Kirigami metamaterials have gained increasing attention due to their unusual mechanical properties under large stretching. However, most metamaterial designs obtained with trial-and-error approaches tend to lose their desirable properties under large tensile strains due to occurrence of instability caused by out-of-plane buckling. To cope with this limitation, this paper presents a systematic approach of cut layout optimizing for designing kirigami metamaterials working at large tensile strains by fully exploiting their out-of-plane buckling behaviors. This method can also mitigate the local stress concentration issue at the hinges of conventional kirigami designs working at in-plane deformation modes. The effectiveness of the proposed method is demonstrated through several examples regarding metamaterial design with negative Poisson's ratio and specified flip angle pattern. It is shown that the proposed method is capable of addressing the highly nonlinear deformation impacts on the mechanical performance under large stretching, to meet the growing and diverse demands in the field of kirigami metamaterials.

A two-scale method to include essential behavior of bolted connections in structures including elevated temperatures

Qingfeng Xu, Hèrm Hofmeyer, Johan Maljaars

Accepted Manuscript , doi: 10.1016/j.taml.2024.100526

[Abstract] (237) [PDF 14816KB] (1)

Abstract:
A two-scale method is proposed to simulate the essential behavior of bolted connections in structures including elevated temperatures. It is presented, verified, and validated for the structural behavior of two plates, connected by a bolt, under a variety of loads and elevated temperatures. The method consists of a global-scale model that simulates the structure (here the two plates) by volume finite elements, and in which the bolt is modelled by a spring. The spring properties are provided by a small-scale model, in which the bolt is modelled by volume elements, and for which the boundary conditions are retrieved from the global-scale model. To ensure the small-scale model to be as computationally efficient as possible, simplifications are discussed regarding the material model and the modelling of the threads. For the latter, this leads to the experimentally validated application of a non-threaded shank with its stress area. It is shown that a non-linear elastic spring is needed for the bolt in the global-scale model, so the post-peak behavior of the structure can be described efficiently. All types of bolted connection failure as given by design standards are simulated by the two-scale method, which is successfully validated (except for net section failure) by experiments, and verified by a detailed system model, which models the structure in full detail. The sensitivity to the size of the part of the plate used in the small-scale model is also studied. Finally, multi-directional load cases, also for elevated temperatures, are studied with the two-scale method and verified with the detailed system model. As a result, a computationally efficient finite element modelling approach is provided for all possible combined load actions (except for nut thread failure and net section failure) and temperatures. The two-scale method is shown to be insightful, for it contains a functional separation of scales, revealing their relationships, and consequently, local small-scale non-convergence can be handled. Not presented in this paper, but the two-scale method can be used in e.g. computationally expensive two-way coupled fire-structure simulations, where it is beneficial for distributed computing and densely packed bolt configurations with stiff plates, for which a single small-scale model may be representative of several connections.

Effective Permittivity of Compacted Granular Materials: Effects of Interfacial Polarization and Pore-filling Fluids

Xu Wang, Chongpu Zhai, Yixiang Gan

Accepted Manuscript , doi: 10.1016/j.taml.2024.100525

[Abstract] (240) [PDF 1401KB] (9)

Abstract:
Interfacial polarization dominates the permittivity spectra of heterogeneous granular materials for the intermediate frequency range (i.e., from kHz to MHz). In this study, we examine the corresponding dielectric responses of compacted glass sphere packings saturated with pore-filling fluids under various compressive stresses. The effective permittivity spectra are observed to exhibit consistently a plateau-to-plateau drop, described by low-frequency permittivity, characteristic frequency, and high-frequency permittivity. The permittivity spectra under different compressive levels are found to be influenced by the packing structure, compressive stress, and electrical property contrasts between solid and fluid (specifically permittivity and conductivity). For considered measurement conditions, the variation of packing structure and its associated porosity is found to be more significant than the stress evolution in controlling the interfacial polarization, thus the permittivity spectra, as supported by analytical and numerical results for unit cells. Furthermore, to gain a general rule for dielectric responses for saturated granular materials, we train multi-layer artificial neural network (ANN) models based on a series of simulations for unit cells with various structures, stresses, and electrical and dielectric properties. The predictions with two-layer ANN agree well with experimental measurements, presenting errors smaller than 5% for both low-frequency and high-frequency permittivity. This study offers an effective predicting approach for the dielectric behaviour of heterogeneous and multiphase materials.

Tunable Supra-Transmission of a Stacked Miura-Origami Based Meta-Structure

Qiwei Zhang, Hongbin Fang

Accepted Manuscript , doi: 10.1016/j.taml.2024.100523

[Abstract] (269) [PDF 2295KB] (9)

Abstract:
The origami-based meta-structure has wide application in areas such as energy and wave transmission. Existing research has demonstrated the occurrence of supra-transmission in origami meta-structures and revealed its underlying mechanism. However, studies on how to regulate the phenomenon of supra-transmission are still very limited. In this work, we choose the meta-structure composed of stacked-Miura ori (SMO) as the subject. The SMO unit possesses two topologically distinct stable configurations, enabling the meta-structure to possess a rich variety of periodic layouts. Based on the established equivalent dynamic model of the SMO-based meta-structure, we employ numerical simulation methods and find that the supra-transmission threshold could be adjusted by tuning the periodic layout of the meta-structure. Furthermore, the probability of supra-transmission is also highly dependent on the periodic layout. Increasing the number of SMO units under the bulged-out configuration in each periodic layout decreases the likelihood of supratransmission occurring. The findings of this study yield an extensive array of foundational insights into the wave dynamics of origami structures. Furthermore, these insights translate into practical guidelines for designing origami-based meta-structure with tunable and programmable dynamic characteristics.

On the impact of debris accumulation on power production of marine hydrokinetic turbines: Insights gained via LES

Mustafa Meriç Aksen, Kevin Flora, Hossein Seyedzadeh, Mehrshad Gholami Anjiraki, Ali Khosronejad

Accepted Manuscript , doi: 10.1016/j.taml.2024.100524

[Abstract] (298) [PDF 5464KB] (1)

Abstract:
We present a series of large-eddy simulations to systematically investigate the impact of debris accumulation on the hydrodynamics and power production of a utility-scale marine hydrokinetic (MHK) turbine under various debris loads lodged on the upstream face of the turbine tower. The turbine blades are modeled using turbine resolving, actuator line, and actuator surface methods. Moreover, the influence of debris on the flow field is captured by directly resolving individual logs and employing a novel debris model. Analyzing the hydrodynamics effects of various debris accumulations, we show that an increase in the density of debris accumulation leads to more flow bypassing beneath the turbine blade. This, in turn, reduces the flow momentum that reaches the MHK blades at the lower depths, inducing significant fluctuation in power production. Further, it is shown that debris-induced turbulent fluctuations contribute to significant variability in the MHK turbine's power production.

The Significant Contribution of Stochastic Forcing to Nonlinear Energy Transfer in Resolvent Analysis

Youhua Wang, Ting Wu, Guowei He

Accepted Manuscript , doi: 10.1016/j.taml.2024.100521

[Abstract] (406) [PDF 1959KB] (25)

Abstract:
Nonlinear energy transfer is represented through eddy viscosity and stochastic forcing within the framework of resolvent analysis. Previous investigations estimate the contribution of eddyviscosity-enhanced resolvent operator to nonlinear energy transfer. The present article estimates the contribution of stochastic forcing to nonlinear energy transfer and demonstrates that the contribution of stochastic forcing cannot be ignored. These results are achieved by numerically comparing the eddy-viscosity-enhanced resolvent operator and stochastic forcing with nonlinear energy transfer in turbulent channel flows. Furthermore, the numerical results indicate that composite resolvent operators can improve the prediction of nonlinear energy transfer.

A Real Space Moiré Inversion Technique and Its Practical Applications in Real Space for Lattice Reconstruction

Bo Cui, Hongye Zhang, Miao Li, Dong Zhao, Huimin Xie, Zhanwei Liu

Accepted Manuscript , doi: 10.1016/j.taml.2024.100518

[Abstract] (314) [PDF 1551KB] (0)

Abstract:
Distinct physical properties emerge at the nanoscale in Moiré materials, such as bilayer graphene and layered material superposition. This study explores similar structural features within a second-generation nickel-based superalloy, unveiling potential formation mechanisms. Introducing the real space Moiré inversion method (RSMIM) for nanoscale imaging, combined with the transmission electron microscopy (TEM) nano-Moiré inversion method, we reveal spatial angles between specimen and reference lattices in 3D. Simultaneously, we reconstruct the Moiré pattern region to deepen us understand the phenomenon of Moiré formation. Focused on face-centered cubic structures, the research identifies six spatial angles, shedding light on Moiré patterns in the superalloy. The RSMIM not only enhances understanding but also expands 3D structure measurement capabilities. The RSMIM served to validate TEM nano-Moiré inversion results, ascertaining the spatial relative angle between lattices, and establishing a theoretical simulation model for Moiré patterns. This study marks a substantial step toward designing high-performance nanomaterials by uncovering dynamic Moiré variations.

Analysis of pulse-wave propagation characteristics in abdominal aortic sclerosis disease

Xuehang Sun, Bensen Li, Yicheng Lu, Xiabo Chen, Wenbo Gong, Fuxing Miao

Accepted Manuscript , doi: 10.1016/j.taml.2024.100507

[Abstract] (313) [PDF 1495KB] (1)

Abstract:
In this work, a bidirectional fluid‒structure coupling finite element analysis model of the abdominal aorta was established with the various vascular elastic modulus as the main parameter of atherosclerosis, in consideration of blood dynamic viscosity and compressibility. Pressure and velocity pulse-wave propagation were investigated by the application of full-coupling analysis algorithm. The effect of atherosclerosis degree on the propagation characteristics of pulse waves in the bifurcated abdominal aorta was quantitatively analyzed. Arterial bifurcation can cause a substantial attenuation on the peak of pressure pulse waveform and an increase in wave velocity during the cardiac cycle. The elastic modulus and bifurcation properties of the arterial wall directly affected the peak value and wave propagation velocity of the pressure pulse wave. The preliminary results of this work will be crucial in guiding the evolution of the pressure pulse wave and the initial diagnosis of atherosclerotic disease through the waveform.

Quantification and reduction of uncertainty in aerodynamic performance of GAN-generated airfoil shapes using MC dropouts

Kazuo Yonekura, Ryuto Aoki, Katsuyuki Suzuki

Accepted Manuscript , doi: 10.1016/j.taml.2024.100504

[Abstract] (317) [PDF 2212KB] (2)

Abstract:
Generative adversarial network (GAN) models are widely used in mechanical designs. The aim in the airfoil shape design is to obtain shapes that exhibits the required aerodynamic performance, and conditional GAN is used for that aim. However, the output of GAN contains uncertainties. Additionally, the uncertainties of labels have not been quantified. This paper proposes an uncertainty quantification method to estimate the uncertainty of labels using Monte Carlo dropout. In addition, an uncertainty reduction method is proposed based on imbalanced training. The proposed method was evaluated for the airfoil generation task. The results indicated that the uncertainty was appropriately quantified and successfully reduced.

Magnetically-actuated Intracorporeal Biopsy Robot Based on Kresling Origami

Long Huang, Tingcong Xie, Lairong Yin

Accepted Manuscript , doi: 10.1016/j.taml.2024.100500

[Abstract] (308) [PDF 2324KB] (0)

Abstract:
The introduction of wireless capsule endoscopy has brought a revolutionary change in the diagnostic procedures for gastrointestinal disorders. Biopsy, an essential procedure for disease diagnosis, has been integrated into robotic capsule endoscopy to augment diagnostic capabilities. In this study, we propose a magnetically driven biopsy robot based on a Kresling origami. Considering the bistable properties of Krelsing origami and the elasticity of the creases, a foldable structure of the robot with constant force characteristics is designed. The folding motion of the structure is used to deploy the needle into the target tissue. The robot is capable of performing rolling motion under the control of an external magnetic drive system, and a fine needle biopsy technique is used to collect deep tissue samples. We also conduct in vitro rolling experiments and sampling experiments on apple tissues and pork tissues, which verify the performance of the robot.

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Simulation of wave scattering over a floating platform in the ocean with a coupled CFD-IBM model

Pengxuan Luo, Jingxin Zhang, Yongyong Cao, Shaohong Song

Theoretical and Applied Mechanics Letters 14 (2024) 100516. doi: 10.1016/j.taml.2024.100516

[Abstract] (368) [PDF 2195KB] (17)

Abstract:
A numerical study of linear wave scattering over a floating platform has been simulated by an efficient numerical model in this letter. The non-hydrostatic model is used to simulate the free surface and the uneven bottom. For the solid body modelling, the immersed boundary method (IBM) is implemented by introducing a virtual boundary force into the momentum equations to emulate the boundary conditions. This implementation enhances the ability of the model to simulate interactions between waves and floating structures. A numerical case involving wave interactions with a floating platform is studied to validate the numerical model. By simulating the wave propagation, the numerical model captures the variation of the wave scattering very well, which verifies the performance of the numerical model and the robust strategy of the IBM.

A sub-grid scale model for Burgers turbulence based on the artificial neural network method

Xin Zhao, Kaiyi Yin

Theoretical and Applied Mechanics Letters 14 (2024) 100519. doi: 10.1016/j.taml.2024.100519

[Abstract] (328) [PDF 2040KB] (14)

Abstract:
The present study proposes a sub-grid scale (SGS) model for the one-dimensional Burgers turbulence based on the neural network and deep learning method. The filtered data of the direct numerical simulation is used to establish the training data set, the validation data set, and the test data set. The artificial neural network (ANN) method and Back Propagation method are employed to train parameters in the ANN. The developed ANN is applied to construct the sub-grid scale model for the large eddy simulation (LES) of the Burgers turbulence in the one-dimensional space. The proposed model well predicts the time correlation and the space correlation of the Burgers turbulence.

Vibration of Black Phosphorus Nanotubes via Orthotropic Cylindrical Shell Model

Minglei HE, Lifeng WANG

Theoretical and Applied Mechanics Letters 14 (2024) 100513. doi: 10.1016/j.taml.2024.100513

[Abstract] (330) [PDF 2312KB] (10)

Abstract:
Black phosphorus nanotubes (BPNTs) may have good properties and potential applications. Determining the vibration property of BPNTs is essential for gaining insight into the mechanical behaviour of BPNTs and designing optimized nanodevices. In this paper, the mechanical behaviour and vibration property of BPNTs are studied via orthotropic cylindrical shell model and molecular dynamics (MD) simulation. The vibration frequencies of two chiral BPNTs are analysed systematically. According to the results of MD calculations, it is revealed that the natural frequencies of two BPNTs with approximately equal sizes are unequal at each order, and that the natural frequencies of armchair BPNTs are higher than those of zigzag BPNTs. In addition, an armchair BPNTs with a stable structure is considered as the object of research, and the vibration frequencies of BPNTs of different sizes are analysed. When comparing the MD results, it is found that both the isotropic cylindrical shell model and orthotropic cylindrical shell model can better predict the thermal vibration of the lower order modes of the longer BPNTs better. However, for the vibration of shorter and thinner BPNTs, the prediction of the orthotropic cylindrical shell model is obviously superior to the isotropic shell model, thereby further proving the validity of the shell model that considers orthotropic for BPNTs.

Study on cumulative effects of biological craniocerebral trauma under repeated blast

Xingyuan Huang, Bingchen Xia, Lijun Chang, Zhikang Liao, Hui Zhao, Zhihua Cai

Theoretical and Applied Mechanics Letters 14 (2024) 100514. doi: 10.1016/j.taml.2024.100514

[Abstract] (309) [PDF 4044KB] (5)

Abstract:
Repeated blast impacts on personnel in explosive environments can exacerbate craniocerebral trauma. Most existing studies focus on the injury effects of a single blast, lacking in-depth analysis on the injury effects and cumulative effects of repeated blasts. Therefore, rats were used as the experimental samples to suffer from explosion blasts with different peak air overpressures (167 kPa~482 kPa) and varying number of repeated blasts. The cumulative effect of craniocerebral trauma was most pronounced for moderate repeated blast, showing approximately 95% increase of trauma severity with penta blast, and an approximately 85% increase of trauma severity with penta minor blast. The cumulative effect of craniocerebral trauma from severe, repeated blast has a smaller rate of change compared to the other two conditions. The severity of trauma from penta blast increased by approximately 69% compared to a single blast. Comprehensive physiological, pathological and biochemical analysis show that the degree of neurological trauma caused by repeated blasts is higher than that of single blasts, and the pathological trauma to brain tissue is more extensive and severe. The trauma degree remains unchanged after double blast, increases by one grade after triple or quadruple blast, and increases by two grades after penta blast.

Physics-data coupling-driven method to predict the penetration depth into concrete targets

Qin Shuai, Liu Hao, Wang Jianhui, Zhao Qiang, Zhang Lei

Theoretical and Applied Mechanics Letters 14 (2024) 100495. doi: 10.1016/j.taml.2024.100495

[Abstract] (341) [PDF 1991KB] (3)

Abstract:
The projectile penetration process into concrete target is a nonlinear complex problem. With the increase of experiment data, the data-driven paradigm has exhibited a new feasible method to solve such complex problem. However, due to poor quality of experimental data, the traditional machine learning (ML) methods, which are driven only by experimental data, have poor generalization capabilities and limited prediction accuracy. Therefore, this study intends to exhibit a ML method fusing the prior knowledge with experiment data. The new ML method can constrain the fitting to experimental data, improve the generalization ability and the prediction accuracy. Experimental results show that integrating domain prior knowledge can effectively improve the performance of the prediction model for penetration depth into concrete targets.

Design and Mechanical Properties Analysis of a Cellular Waterbomb Origami Structure

Yongtao Bai, Zhaoyu Wang, Yu Shi

Theoretical and Applied Mechanics Letters 14 (2024) 100509. doi: 10.1016/j.taml.2024.100509

[Abstract] (368) [PDF 3091KB] (13)

Abstract:
Cellular structures are commonly used to design energy-absorbing structures, and origami structures are becoming a prevalent method of cellular structure design. This paper proposes a foldable cellular structure based on the Waterbomb origami pattern. The geometrical configuration of this structure is described. Quasi-static compression tests of the origami tube cell of this cellular structure are conducted, and load-displacement relationship curves are obtained. Numerical simulations are carried out to analyze the effects of aspect ratio, folding angle, thickness and number of layers of origami tubes on initial peak force and specific energy absorption (SEA). Calculation formulas for initial peak force and SEA are obtained by the multiple linear regression method. The degree of influence of each parameter on the mechanical properties of the single-layer tube cell is compared. The results show that the cellular structure exhibits negative stiffness and periodic load-bearing capacity, as well as folding angle has the most significant effect on the load-bearing and energy-absorbing capacity. By adjusting the design parameters, the stiffness, load-bearing capacity and energy absorption capacity of this cellular structure can be adjusted, which shows the programmable mechanical properties of this cellular structure. The foldability and the smooth periodic load-bearing capacity give the structure potential for application as an energy-absorbing structure.

A symmetric substructuring method for analyzing the natural frequencies of conical origami structures

Chenhao Lu, Yao Chen, Weiying Fan, Jian Feng, Pooya Sareh

Theoretical and Applied Mechanics Letters 14 (2024) 100517. doi: 10.1016/j.taml.2024.100517

[Abstract] (325) [PDF 2793KB] (7)

Abstract:
Conical origami structures are characterized by their considerable out-of-plane stiffness and energy-absorption capacity. Previous investigations have commonly focused on the static characteristics of these lightweight structures. However, efficient analysis of the natural vibrations of these structures is pivotal for designing conical origami structures with programmable stiffness and mass. In this paper, we propose a novel method to analyze the natural vibrations of such structures by combining a symmetric substructuring method (SSM) and a generalized eigenvalue analysis. SSM exploits the inherent symmetry of the structure to decompose it into a finite set of repetitive substructures. In doing so, we reduce the dimensions of matrices and improve the computational efficiency by adopting the stiffness and mass matrices of the substructures in the generalized eigenvalue analysis. The simulated results of pin-jointed models implemented using finite element analyses are used to validate the computational results of the proposed approach. Moreover, the parametric analysis of the structures demonstrates the influences of the number of segments along the circumference and the radii of the cone on the structural mass and natural frequencies of the structures. Furthermore, a comparison between six-fold and four-fold conical origami structures and the influence of various geometric parameters on their natural frequencies is presented. This work provides a strategy for efficiently analyzing the natural vibration of symmetric origami structures and has the potential to contribute to the efficient design and customization of origami structures with programmable stiffness.

A New Strain-Based Pentagonal Membrane Finite Element for Solid Mechanics Problems

Koh Wei Hao, Logah Perumal, Kok Chee Kuang

Theoretical and Applied Mechanics Letters 14 (2024) 100499. doi: 10.1016/j.taml.2024.100499

[Abstract] (326) [PDF 1128KB] (6)

Abstract:
Polygonal finite elements remain an attractive option in finite element analysis due to their flexibility in modeling arbitrary shapes compared to triangles. In this study, a pentagonal membrane element was developed with the strain approach for the first time. The element possesses invariance, and the equilibrium constraint was applied to the assumed strain field using corrective coefficients. Inspired by the advancing front technique, a pentagonal mesh was generated, and the mesh quality was enhanced with Laplacian smoothing. The performance of the developed pentagonal element was assessed in a few numerical tests, and the results revealed its suitability in modeling the bending of beams. Besides, the numerical results are enhanced when pentagonal elements are used in mesh transitions along boundaries to smoothen curved edges and capture distributed loads.

A theoretical model for impact protection of flexible polymer material

Huifeng Xi, Hui Pan, Song Chen, Heng Xiao

Theoretical and Applied Mechanics Letters 14 (2024) 100506. doi: 10.1016/j.taml.2024.100506

[Abstract] (366) [PDF 1887KB] (6)

Abstract:
The relationship between the protective performance of flexible polymer material and material parameters (elastic modulus, viscosity coefficient) is explored, an impact collision motion equation between two bodies is established from the viscoelastic material constitutive, and the relationship between the kinematic response and the material parameters is obtained. Based on the Kelvin constitutive model, a theoretical model for impact between the protective body and the protected body is established, then the dynamic response is obtained. The feasibility of the model was verified by drop hammer experiment, and the material parameters (elastic modulus, viscosity coefficient) were obtained by formula. The model is discretized and the relationship between local impact response and material parameters is analyzed. The discussion results on the relationship between the impact response and the protective material performance indicate that adjusting the elastic modulus, viscosity coefficient, and thickness of the protective material can effectively improve protective effect.

Analysis and optimization of stamping and forming process of bearing outer ring

Shichao Zhu, Yulu Ding, Bing Long, Hun Guo, Linhan Ouyang, Wengang Chen, Zhengyi Jiang

Theoretical and Applied Mechanics Letters 14 (2024) 100522. doi: 10.1016/j.taml.2024.100522

[Abstract] (350) [PDF 6121KB] (9)

Abstract:
To address the common issues of wrinkling, tearing, and uneven wall thickness in the actual sheet metal stamping process of the outer ring of needle roller bearings, this study analyzes critical technical indicators such as forming limits, thickness distribution, and principal strains in the forming process in detail. Three-dimensional models of the concave and convex dies were constructed. The effects of different process parameters, including stamping speed, edge pressure, sheet metal thickness, and friction coefficient, on the quality of the forming parts were investigated by varying these parameters. Subsequently, the orthogonal experimental method was used to determine an optimal experimental group from multiple sets of experiments. It was found that under the process parameters of a stamping speed of 3000 mm/s, edge pressure of 2000 N, sheet metal thickness of 0.9 mm, and friction coefficient of 0.125, the forming quality of the outer ring of the bearing is ideal.

Crack propagation simulation in brittle elastic materials by a phase field method

Xingxue Lu, Cheng Li, Ying Tie, Yuliang Hou, Chuanzeng Zhang

2019, 9(6): 339-352 doi: 10.1016/j.taml.2019.06.001

[Abstract](2665) [FullText HTML](1459) [PDF 3845KB](110)

Investigation on Savonius turbine technology as harvesting instrument of non-fossil energy: Technical development and potential implementation

Aditya Rio Prabowo, Dandun Mahesa Prabowoputra

2020, 10(4): 262-269 doi: 10.1016/j.taml.2020.01.034

[Abstract](2472) [FullText HTML](1203) [PDF 3192KB](103)

Mechanistic Machine Learning: Theory, Methods, and Applications

2020, 10(3): 141-142 doi: 10.1016/j.taml.2020.01.041

[Abstract](10226) [FullText HTML](1268) [PDF 4844KB](99)

On the Weissenberg effect of turbulence