Determination of Material Parameters of EVA Foam under Uniaxial Compressive Testing Using Hyperelastic Models

The objective of this research was to determine the mechanical parameter from EVA foam and also investigate its behavior by using Blatz-Ko,Neo-Hookean,Mooney model and experimental test.The physical characteristic of EVA foam was also evaluated by scanning electron microscopy(SEM).The results show that Blatz-Ko and Neo-Hookean model can fit the curve at 5%and 8%strain,respectively.The Mooney model can fit the curve at 50%strain.The modulus of rigidity evaluated from Mooney model is 0.0814±0.0027 MPa.The structure of EVA foam from SEM image shows that EVA structure is a closed cell with homogeneous porous structure.From the result,it is found that Mooney model can adjust the data better than other models.This model can be applied for mechanical response prediction of EVA foam and also for reference value in engineering application.

An alternative form of energy density demonstrating the severe strain-stiffening in thin spherical and cylindrical shells

The present article investigates an elastic instability phenomenon for internally pressurized spherical thin balloons and thin cylindrical tubes composed of incompressible hyperelastic material.A mathematical model is formulated by proposing a new strain energy density function.In the family of limited elastic materials,many material models exhibit strain-stiffening.However,they fail to predict severe strainstiffening in a moderate range of deformations in the stress-strain relations.The proposed energy function contains three material parameters and shows substantially improved stain stiffening properties than the limited elastic material models.The model is further applied to explore the elastic instability phenomenon in spherical and cylindrical shells.The findings are compared with other existing models and validated with experimental results.The model shows better agreement with experimental results and exhibits a substantial strain-stiffening effect than the current models.

LARGE DEFORMATION OF INCOMPRFSSIBLE RUBBER CYLINDER UNDER PLANE STRAIN

The large deformation of incompressible rubber cylinder under inner pressure is ana- lyzed by a kind of new rubber materials strain energy function.The theory formulation for the dis- placement and stress is presented.The penalty finite element formulation is established in order to ana- lyze nonlinear rubber materials,and the results of finite element method agree well with theoretical ones.A new method for controlling the calculating stability and convergence rates is put forward.The selection of the appropriate penalty factor and its influence on calculated results are discussed.

The 4-D integrated geodesy and strain analysis

Research of the practical 4-D integrated geodesy(IG) and strain analysis is presented in this paper.The practical model and basic observation equation are established by using IG and dynamic adjustment.Furthermore,the observation equations about gravity vector,zenith distance,azimuth angle,difference are derived and determination of local gravity field covariance solved.The 3-D strain formular is derived and the strain parameters calculated from it.The improvement of the OPERA software of Landan and Hem etc,FRG has been done to get a new software in Fortran Language which implements in MASSCOMP computer.Using the software,the integrated adjustment of two term observation data of triangle chain, triangle net,gravity,level,astronomic observation and strain analysis are established.The result is satisfactory.

Diet and Rat Strain as Factors in Nervous System Function and Influence of Confounders

The necessity for understanding normal human cognitive processes and behavior, and themechanisrns which result in dysfunction in these processes are dependant on utilization of a suitable animal model. In order to develop pharmaceutical agents to alleviate mental disturbances and enable the individual to cope within the norms of society, it is incumbent upon investigators to choose a species in which pharmacokinetic principles are established and resemble those of hurnans. The choice of rats in cognition research studies has specific advantages in that these anirnals possess similar pharrnacodynamic parameters to hurnans. Further advantages include availability, low cost, ease of breeding, maintenance and an extensive literature database which enable comparisons to present findings. However, there are substantial differences in the perforrnance of various rat strains in tasks of learning, memory, attention, and responses to stress or drugs. In addition to rat strain, quantity of thed also exerts profound consequences on animal behavior. The aim of this review is to demonstrate that there are differences in the central nervous systern responsivencess of rat strains to chemicals and these could be related to factors such as source of supplier, type and quantity of feed, or season of the year. It is also evident that the genotype differs amongst strains and this may be responsible for the observed differences in CNS sensitivity to chemicals. Strain differences must be identified and taken into consideration in interpretation of assessrnent of neurobehavioural functions. It is also incumbent upon the investigators to utilize healthy (diet-controlled) animal models.

THE INTEGRAL AS A FUNCTION OF THE UPPER LIMIT AND AN ANALYTICAL SOLUTION TO PLANE STRAIN DRAWING AND EXTRUSION

A kinematically admissible velocity field which is different from Avitzur's is established in Cartesian Coordinates. An upper-bound analytical solution to strip drawing andextrusion is obtained by using the integral as a function of the upper limit in this paper.

Pilot regulation of MnP-SA for treating PTA wastewater

In the pilot study of treating the purified terephthalic acid(PTA) wastewater with the functional Strain Fhhh in the carrier activated sludge process(CASP), the ratio of COD∶TN∶TP and the concentrations of Cu, Mn, Se and Zn were controlled to improve the manganese peroxidase(MnP) levels for increasing the treatment efficiency. When the ratio of COD∶TN∶TP was 100∶0.36∶0.15 and the concentrations of Cu, Mn, Se and Zn were 0.54, 5.07, 0.00 and 0.08 mg/L, the MnP specific activity(MnP-SA) reached 689 U/L, and the sludge loading rate to COD(SLRC) was 1.09 d -1, which was 4—7 fold of that in other processes reported. The data indicated that improving MnP level could enhance the degradability of Fhhh. And the potentials of Fhhh and CASP will be also discussed in this paper.

Growth of a Void in a Rubber Rectangular Plate under Uniaxial Extension

The finite deformation and stress analyses for a rectangular plate with a center void and made of rubber with the Yeoh elastic strain energy function under uniaxial extension were studied in this paper. An approximation solution was obtained from the minimum potential energy principle. The numerical results for the growth of the cavitation and stresses along the edge of the cavitation were discussed. In addition, the stress concentration phenomenon was considered.

Void Formation and Growth for a Class of Compressible Hyper-Elastic Sphere

In this paper, the strain energy function proposed by Shang and Cheng was generalized by introducing a nonlinear term. Void formation and growth in the interior of a sphere composed of compressible hyper-elastic material, subjected to a prescribed uniform displacement, was examined. A parametric cavitated bifurcation solution for the radial deformed function was obtained. Stability of the solution of the cavitated bifurcation equation was discussed. With the appearance of a cavity, an interesting feature of the radial deformation near the deformed cavity wall is the transition from extension to compression.

A comparative study of 85 hyperelastic constitutive models for both unfilled rubber and highly filled rubber nanocomposite material

Nonlinear finite element analysis is widely used for structural optimization of the design and the reliability analysis of complex elastomeric components.However,high-precision numerical results cannot be achieved without reliable strain energy functions(SEFs)of the rubber or rubber nanocomposite material.Although hyperelastic constitutive models have been studied for nearly 80 years,selecting one that accurately describes rubber's mechanical response is still a challenge.This work reviews 85 isotropic SEFs based on both the phenomenological theory and the micromechanical network theory proposed from the 1940s to 2019.A fitting algorithm which can realize the automatic fitting optimization and determination of the parameters of all SEFs reviewed is developed.The ability of each SEF to reproduce the experimental data of both the unfilled and highly filled rubber nanocomposite is quantitatively assessed based on a new proposed evaluation index.The top 30 SEFs for the unfilled rubber and the top 14 SEFs for the highly filled rubber nanocomposite are presented in the ranking lists.Finally,some suggestions on how to select an appropriate hyperelastic constitutive model are given,and the perspective on the future progress of constitutive models is summarized.

Constitutive modeling of particle reinforced rubber-like materials

The present study is focused on the constitutive modeling for the mechanical behavior of rubber reinforced with filler particles.A filler-dependent energy density function is proposed with all the continuum mechanics-based necessities of an effective hyperelastic material model.The proposed invariant-based energy function comprises a single set of material parameters for a material subjected to several modes of loading conditions.The model solution agrees well with existing experimental results.Later,the effect of varying concentrations of filler particles in the rubber matrix is also studied.

AN ANALYSIS MODEL OF PULSATILE BLOOD FLOW IN ARTERIES

Blood flow in artery was treated as the flow under equilibrium state (the steady flow under mean pressure)combined with the periodically small pulsatile flow.Using vascular strain energy function advanced by Fung,the vascular stress_strain relationship under equilibrium state was analyzed and the circumferential and axial elastic moduli were deduced that are expressed while the arterial strains around the equilibrium state are relatively small, so that the equations of vessel wall motion under the pulsatile pressure could be established here.Through solving both the vessel equations and the linear Navier_Stokes equations,the analytic expressions of the blood flow velocities and the vascular displacements were obtained.The influence of the difference between vascular circumferential and axial elasticities on pulsatile blood flow and vascular motion was discussed in details.

Mechanical performance and negative pressure instability for venous walls

Mechanical properties, such as the deformation and stress distributions for venous walls under the combined load of transmural pressure and axial stretch, are examined within the framework of nonlinear elasticity with one kind of hyper-elastic strain energy functions. The negative pressure instability problem of the venous wall is explained through energy comparison. First, the deformation equation of the venous wall under the combined loads is obtained with a thin-walled circular cylindrical tube. The deformation curves and the stress distributions for the venous wall are given under the normal transmural pressure, and the regulations are discussed. Then, the deformation curves of the venous wall under the negative transmural pressure or the internal pressure less than the external pressure are given. Finally, the negative pressure instability problem is discussed through energy comparison.

Two-dimensional arsenic monolayer sheet predicted from first-principles

Using first-principles calculations, we investigate the two-dimensional arsenic nanosheet isolated from bulk gray arsenic. Its dynamical stability is confirmed by phonon calculations and molecular dynamics analyzing. The arsenic sheet is an indirect band gap semiconductor with a band gap of 2.21 e V in the hybrid HSE06 functional calculations. The valence band maximum（VBM） and the conduction band minimum（CBM） are mainly occupied by the 4p orbitals of arsenic atoms,which is consistent with the partial charge densities of VBM and CBM. The charge density of the VBM G point has the character of a π bond, which originates from p orbitals. Furthermore, tensile and compressive strains are applied in the armchair and zigzag directions, related to the tensile deformations of zigzag and armchair nanotubes, respectively. We find that the ultimate strain in zigzag deformation is 0.13, smaller than 0.18 of armchair deformation. The limit compressive stresses of single-layer arsenic along armchair and zigzag directions are-4.83 GPa and-4.76 GPa with corresponding strains of-0.15 and-0.14, respectively.

Effects of uniaxial compressive strain on the electronic- transport properties of zigzag carbon nanotubes

Recently, substantial attention has been paid to the strain sensitivity of the carbon nanotubes＇ （CNTs＇） electronic properties. In this study, the relationships between the geometric structures and electronic states of zigzag CNTs under uniaxial compressive strain were investigated. We found that different factors dominate the electronic states of zigzag CNTs depending on the strain regions： the initial stage of the strain loading, which lasts until column-buckling deformation begins, and the strain regions corresponding to column- and shell-buckling deformations. Because shell-buckling deformation significantly increases the re-orbital angle, the angle between the π orbital axis vectors of adjacent atoms, strong localization of the density of states （LDOS） occurs in the buckled area. We also analyzed the current able to pass through deformed CNTs using a tight-binding-based Green＇s function approach and determined that the current can be significantly suppressed by applying uniaxial compressive strain. Our method of predicting the electronic state of a deformed CNT based on the π-orbital angle is expected to be useful for predicting the electronic properties of CNT-based electronic devices and sensors.

Improved Carroll’s hyperelastic model considering compressibility and its finite element implementation

In engineering component design,material models are increasingly used in finite element simulations for an expeditious and less costly analysis of the design prototypes.As such,researchers strive to formulate models that are less complex,robust,and accurate.In the realm of hyperelastic materials,phenomenological-based Carroll’s model is highly promising due to its simplicity and accuracy.This work proposes its further improvement by modifying the strain energy density function to comply with the restriction that it should vanish at reference configuration and adding a compressible term to capture the practical behavior of elastomeric materials and to avoid numerical problems during finite element implementation.The model constants for both the original and the modified versions were obtained by fitting their respective expressions to the classical Treloar’s experimental data using the Levenberg-Marquardt algorithm.The modified model was implemented using Abaqus CAE 2016 via a vectorized user material(VUMAT)subroutine.Comparisons of the model predictions with Treloar’s experimental data demonstrated the superiority of the modified version particularly in the equibiaxial loading mode.Moreover,the simulated and the experimentally observed behavior agreed to a great accuracy thus making the modified model suitable for simulating the loading response of components fabricated of elastomeric materials.