Bioinspiration:Pull-Out Mechanical Properties of the Jigsaw Connection of Diabolical Ironclad Beetle’s Elytra

In engineering,connections between components are often weak areas.Unreasonable connection methods can easily reduce the strength of components,resulting in unpredictable failure modes.In nature,numerous connection methods for biological structures with excellent mechanical properties have evolved.Studying the connection methods of organisms in nature can inspire new ideas for bionic connection methods.When the diabolical ironclad beetle is under pressure,the elytra are not easy to separate,which ensures the stability of the beetle’s external structure,thus making the beetle extremely resistant to pressure.The reason for this is the interlocking and toughening effect of the unique jigsaw connection between the elytra.Therefore,in this paper,a theoretical analysis model is established and used to analyze the mechanical behavior of the diabolical ironclad beetle’s jigsaw connection during the drawing process and determine the influences of factors such as quantity,angle,and geometric characteristics on the mechanical properties of the jigsaw connection.The results of the theoretical analysis are then compared with the results of experiments and ABAQUS finite element simulation.

Theoretical Characterization of Indentation Depth-Dependent Creep Behavior of CoCrFeNiAl_(0.3) High-Entropy Alloy

The effects of indentation loading depth and dynamic pre-compression on the creep behavior of CoCrFeNiAl_(0.3) high-entropy alloy(HEA)were studied through a series of indentation creep tests.Results show that the creep displacement,creep stress exponent and creep strain rate are all sensitive to loading depth.A phenomenological model based on the holding time and loading depth was established by studying the characteristic relation between the loading depth and the creep displacement of CoCrFeNiAl_(0.3) HEA.The phenomenological model was used to analyze the creep behavior of the alloy under dynamic pre-compression(i.e.,dynamic compressive deformation caused by Hopkinson bar impact).

A Supersonic Aerodynamic Energy Harvester:A Functionally Graded Material Beam with a Giant Magnetostrictive Thin Film

In this study,a simply supported functionally graded material beam with a giant magnetostrictive thin film(GMF)was selected as an energy harvester.Based on the theory of large deformation and the Villari effect of GMF,piston theory was used to simulate the dynamic equation of the whole structure under supersonic aerodynamic pressure and in a thermal environment by using Hamilton^principle,and the energy harvesting effect of GMF was simulated by using a Runge-Kutta algorithm.Below the critical flutter velocity,the maximum voltage output and energy harvesting results were discussed as they were affected by external factors such as the geometric model of structure parameters,slenderness ratio,gradient index,number of turns of an electromagnetic coil,airflow velocity,and temperature.The electromechanical coupling coefficient/C33 was 71%.The results show that this proposed harvester can achieve an optimal harvesting effect by adjusting the parameters appropriately,and collect energy in thermal and supersonic environments using the GMF,which provides power to sensors of the health monitoring system of the aircraft’s own structure.

Transient Response in a Bi-material Cylinder of Soft Ferromagnetic Material Subjected to Magnetic Shock

The transient response in a bi-material cylinder of soft ferromagnetic material under magnetic shock is investigated in this study.The analytical solutions for displacement and stress have been derived using the finite Hankel transform and the Laplace transform.The numerical examples show that the displacement and stress fields respond dynamically in the bi-material cylinder under magnetic shock.The derived displacement at the center and radial stress on the surface of the cylinder satisfy the boundary conditions,showing the correctness of calculation.The displacement and stress waves propagate from the surface to the center of the cylinder when the magnetic field is loaded.The stress fields increase from the center to the surface of the cylinder and are much larger than the quasi-static state since the waves reflect,collide and concentrate in the body of the cylinder.The method of this paper can be used in the design of soft ferromagnetic structures.

Mechanical Analysis and Strength Checking of Current Collector Failure in the Winding Process of Lithium-Ion Batteries

The current collector fracture failure of lithium-ion batteries(LIBs)occurs during its winding production process frequently,and the consequent damages are usually large,but little research has been conducted on this phenomenon.This work stems from the difficulty and obstacles in the winding process of actual production of LIBs.The fracture failure of the current collectors is easily caused by the evolution and mutation of the mechanical behavior during the winding process,resulting in safety hazards and poor efficiency.The purpose of this work is to reveal the evolution and distribution mechanism of circumferential strain of the current collectors on the fracture failure under the constraint of winding process.Experimental tests,finite element calculations and theoretical model are used to study the evolution and distribution of circumferential strain.The dynamic evolution process of circumferential strain is tested accurately,and the mechanism of fracture failure of current collectors is revealed.The criterion for current collector strength is proposed based on the results of strain analysis and SEM observation.

Modeling the Damage and Self-healing Behaviors of Plasticized PVC Gels

Plasticized polyvinyl chloride(PVC)gel is a type of electroactive polymers,which has potentials to be applied as soft actuators.However,few studies have been performed to investigate the mechanical responses of PVC gels in cyclic loading conditions.In this work,we combined experiments and theory to characterize the mechanical responses of two plasticized PVC gels.The gels were subjected to different types of loading-unloading-reloading cycles.The experimental results showed that the plasticized PVC gels exhibited stress softening response(the Mullins effect)in the cyclic tests.Meanwhile,the gels regained some strength after annealing at room temperature for several hours,indicating the self-healing ability of gels.We further extended the eight-chain model with incorporation of the chain dissociation and reassociation mechanism.The developed constitutive model is able to reproduce the Mullins effect and the recovery of the Mullins effect observed in the experiments.Our results clearly show that understanding the complex mechanical response is crucial for the applications of plasticized PVC gels.

Numerical Investigation of the Cushion and Size Effects During Single-Particle Crushing via DEM

This paper uses the discrete element method to model the size and cushion effects during single-particle crushing tests.We propose simplified numerical modeling to examine the effects of particle size and coordination number on particle breakage behavior.We validate the proposed modeling by comparing the numerical results with the experimental data reported in the literature,in terms of the variability of particle tensile strength and axial force-displacement responses.Based on the numerical results,it is clear that a larger particle size entails a higher tensile strength with a larger discreteness.In addition,the characteristic tensile strength increases linearly with an increasing coordination number.Moreover,smaller particles are more susceptible to the cushion effect than larger particles.The numerical results also indicate that an increasing coordination number induces a more ductile mode of failure.Based on these results,we propose an empirical equation for calculating tensile strength,incorporating both the cushion effect and the size effect.

Correction To: Finite Indentation of Pressurized Elastic Fluid Nano vesicles by a Rigid Cylindrical Indenter

Correction To:Acta Mechanica Solida Sinica https://doi.org/10.1007/s10338-019-00107-5 Unfortunately due to a typesetting mistake in the caption of Fig.1,fourth line,仏has been displayed wrongly as/2-The original article has been corrected.

A Multi-scale Corrosion Fatigue Damage Model of Aluminum Alloy Considering Multiple Pits and Cracks

A multi-scale model is developed to link the continuum damage variable in macroscale to the number density of multiple pits and cracks in microscale for studying the corrosion fatigue of aluminum alloy from multi-scale viewpoint.The developed model is used to predict the coherent multi-scale corrosion fatigue process of aluminum alloy component in the 3.5 wt% NaC1water solution under constant stress amplitude at a nominal frequency of 5Hz, and the numerical prediction results are compared with the experimental results.It shows that the model is effective and can be used to study the corrosion fatigue mechanisms of alurninum alloy from both macro and microscale viewpoints.

Structural Damage Recognition Based on Perturbations of Curvature Mode Shape and Frequency

A new method for structural damage identification is presented based on perturbations of curvature mode shape and frequency.Firstly,the structure's mass and stiffness matrices are expressed as functions of its elements'physical parameters,which reflect their damage states. According to differences in the curvature mode shape of the structure in undamaged and damaged states,possible damage equations and determined damage equations are established and used to solve for the elements'damage parameters.Then,to ensure the accuracy of the recognition result,a reasonable solution is substituted into a damage-checking equation based on the change of frequency of the damaged structure.Numerical examples are used to show that,to identify the damage,only one order mode needs to be tested.When the degree of damage is low, first-order perturbation equations can be used to recognize the damage with sufficient accuracy. If the extent of the damage is high,second-order perturbation equations can be used to provide more accurate identification results.

Heterogeneous Fracture Simulation of Three-point Bending Plain-concrete Beam with Double Notches

Plain concrete is regarded as a two-phase material comprising randomly distributed aggregates and mortar matrix. A series of three-point bending concrete beams with symmetric or asymmetric double notches are modeled using the modified random aggregate generation and packing algorithm. The cohesive zone model is used as the fracture criterion and the cohesive el- ements are inserted into both the mortar matrix and the aggregate-mortar interfaces as potential micro-cracking zones. The dead and alive crack phenomena are studied experimentally and nu- merically; and the influences of notch location, aggregate distribution and gradation on fracture are numerically evaluated. Some important conclusions are given.

COMPUTER PROGRAM FOR DIRECTED STRUCTURE TOPOLOGY OPTIMIZATION

To compensate for the imperfection of traditional bi-directional evolutionary structural optimization, material interpolation scheme and sensitivity filter functions are introduced. A suitable filter can overcome the checkerboard and mesh-dependency. And the historical information on accurate elemental sensitivity numbers are used to keep the objective function converging steadily. Apart from rational intervals of the relevant important parameters, the concept of distinguishing between active and non-active elements design is proposed, which can be widely used for improving the function and artistry of structures directly, especially for a one whose accurate size is not given. Furthermore, user-friendly software packages are developed to enhance its accessibility for practicing engineers and architects. And to reduce the time cost for large timeconsuming complex structure optimization, parallel computing is built-in in the MATLAB codes. The program is easy to use for engineers who may not be familiar with either FEA or structure optimization. And developers can make a deep research on the algorithm by changing the MATLAB codes. Several classical examples are given to show that the improved BESO method is superior for its handy and utility computer program software.

NONLINEAR VIBRATION OF THE COUPLED STRUCTURE OF SUSPENDED-CABLE-STAYED BEAM-1:2 INTERNAL RESONANCE

Through the Galerkin method the nonlinear ordinary differential equations （ODEs） in time are obtained from the nonlinear partial differential equations （PDEs） to describe the mo- tion of the coupled structure of a suspended-cable-stayed beam. In the PDEs, the curvature of main cables and the deformation of cable stays are taken into account. The dynamics of the struc- ture is investigated based on the ODEs when the structure is subjected to a harmonic excitation in the presence of both high-frequency principle resonance and 1：2 internal resonance. It is found that there are typical jumps and saturation phenomena of the vibration amplitude in the struc- ture. And the structure may present quasi-periodic vibration or chaos, if the stiffness of the cable stays membrane and frequency of external excitation are disturbed.

CELL AND MOLECULAR BIOMECHANICS: PERSPECTIVES AND CHALLENGES

As an intriguing interdisciplinary research field, cell and molecular biomechanics is at the cutting edge of mechanics in general and biomechanics in particular. It has the potential to provide a quantitative understanding of how forces and deformation at tissue, cellular and molecular levels affect human health and disease. In this article, we review the recent advances in cell and molecular biomechanics, examine the available computational and experimental tools, and discuss important issues including protein deformation in mechanotransduction, cell deformation and constitutive behavior, cell adhesion and migration, and the associated models and theories. The opportunities and challenges in cell and molecular biomechanics are also discussed. We hope to provide readers a clear picture of the current status of this field, and to stimulate a broader interest in the applied mechanics community.

FORMULATION AND EVALUATION OF AN ANALYTICAL STUDY FOR CYLINDRICAL HELICAL SPRINGS

The free vibration analysis of cylindrical helical springs is carried out by means of an analytical study. In the governing equations of the motion of the springs, all displacement functions are defined at the centroid axis and also the effects of the rotational inertia, axial and shear deformations are included in the proposed model. Explicit analytical expressions which give the vibrating mode shapes are derived by rigorous application of the symbolic computing package MATHEMATICA and a process of searching is used to determine the exact natural frequencies. Numerical examples are provided for fixed-fixed boundary conditions. The free vibrational pa- rameters are chosen as the number of coils （n = 4- 14）, the helix pitch angle （a = 5 - 30°） and as the ratio of the diameters of the cylinder and the wire （D/d = 4 - 18） in a wide range. Validation of the proposed model has been achieved through comparison with a finite element model using two-node standard beam elements and the results available in published literature, which in these cases indicates a very good correlation.

STUDY OF NUMERICAL AND PHYSICAL FRACTURE WITH SPH METHOD

Two kinds of fractures can be observed in the SPH （smoothed particle hydrodynamics） simulations, which are the physical fracture and the numerical fracture. The physical one exists in reality, while the numerical one is fictitious. This paper presents the effects of both fractures and proposes a simple adding particle technique to avoid the numerical fracture. The real physical fracture is then figured out by using an applicable fracture criterion. Firstly, the effect of the numerical fracture on the computational accuracy is investigated by introducing the artificial fracture in a model of wave propagation. Secondly, a simple adding particle technique is proposed and validated by a three dimensional bending test. Finally, the experiments of penetration on the skin of aircrafts are simulated by both the initial SPH method and the improved method with the adding particle technique. The results show that the improved SPH method can describe the physical fracture very well with better accuracy.

ULTRASONIC INFLUENCE OF POROSITY LEVEL ON CFRP COMPOSITE LAMINATES USING RAYLEIGH PROBE WAVES

It was found that a pitch-catch signal was more sensitive than normal incidence backwall echo of longitudinal wave to subtle flaw conditions in the composites （damages, fiber orientation, low level porosity, ply waviness, and cracks）. Both the strength and stiffness depend on the fiber orientation and porosity volume in the composites. The porosity content of a composite structure is critical to the strength and performance of the structure in general. The depth of the sampling volume where the pitch-catch signal came from was relatively shallow with the head- to-head miniature Rayleigh probes, but the depth can be increased by increasing the separation distance of the transmitting and receiving probes. Also, a method was utilized to determine the porosity content of a composite lay-up by processing micrograph images of the laminate. A free software package was utilized to process micrograph images of the test sample. The results from the image processing method were compared with existing data. Beam profile was characterized in unidirectional CFRP（carbon fiber reinforced plastics） using pitch-catch Rayleigh probes and the one-sided pitch-catch technique was utilized to produce C-scan images with the aid of the automatic scanner.

INTERACTION OF A DISLOCATION DIPOLE WITH A MODE III INTERFACE CRACK

Interaction between a screw dislocation dipole and a mode III interface crack is investigated. By using the complex variable method, the closed form solutions for complex potentials are obtained when a screw dislocation dipole lies inside a medium. The stress fields and the stress intensity factors at the tip of the interface crack produced by the screw dislocation dipole are given. The influence of the orientation, the dipole arm and the location of the screw dislocation dipole as well as the material mismatch on the stress intensity factors is discussed. The image force and the image torque acting on the screw dislocation dipole center are also calculated. The mechanical equilibrium position of the screw dislocation dipole is examined for various material property combinations and crack geometries. The results indicate that the shielding or anti-shielding effect on the stress intensity factor increases abruptly when the dislocation dipole approaches the tip of the crack. Additionally, the disturbation of the interface crack on the motion of the dislocation dipole is also significant.

WAVE LOCALIZATION IN RANDOMLY DISORDERED PERIODIC PIEZOELECTRIC RODS

在周期、混乱的周期的压电的杆的波浪繁殖在这篇论文被学习。在二个连续单位房间之间的转移矩阵根据连续性条件被获得。压电的材料的机电的联合被考虑。根据矩阵特征值的理论，在周期的结构的频率乐队被学习。而且，由在两个介绍混乱尺寸更少长度和压电的陶艺的有弹性的常数，在混乱周期的结构的波浪本地化被使用矩阵特征值方法和 Lyapunov 代表方法也学习。调节了周期的结构，这被发现让频率通带和站乐队和本地化现象能发生在错误调子周期的结构。由于压电的效果，而且，为不能通过结构宣传的波浪的频率区域稍微随压电的常数的增加被增加。

THE CONSTRUCTION OF WAVELET-BASED TRUNCATED CONICAL SHELL ELEMENT USING B-SPLINE WAVELET ON THE INTERVAL

Based on B-spline wavelet on the interval （BSWI）, two classes of truncated conical shell elements were constructed to solve axisymmetric problems, i.e. BSWI thin truncated conical shell element and BSWI moderately thick truncated conical shell element with independent slopedeformation interpolation. In the construction of wavelet-based element, instead of traditional polynomial interpolation, the scaling functions of BSWI were employed to form the shape functions through the constructed elemental transformation matrix, and then construct BSWI element via the variational principle. Unlike the process of direct wavelets adding in the wavelet Galerkin method, the elemental displacement field represented by the coefficients of wavelets expansion was transformed into edges and internal modes via the constructed transformation matrix. BSWI element combines the accuracy of B-spline function approximation and various wavelet-based elements for structural analysis. Some static and dynamic numerical examples of conical shells were studied to demonstrate the present element with higher efficiency and precision than the traditional element.