Mechanical response of neo-Hookean fiber reinforced incompressible nonlinearly elastic solids

The mechanical behavior of an incompressible neo-Hookean material, directionally reinforced by neo-Hookean fibers, is examined under homogeneous deformations. A composite model for this transversely isotropic material is developed based on a multiplicative decomposition of the deformation gradient which considers interaction between the fiber and the matrix. The so-called standard reinforcing model exhibits non-monotonic behavior in compression. The present composites-based approach leads to a modification of the standard reinforcing model in which monotonic behavior in compression is observed. This stems from the micromechanical basis of the model in which the fiber is treated as a neo-Hookean material. The conditions for loss of monotonicity and positivity in the stress-shear behavior in off-axis simple 2D shear are also obtained.     

The elastostatic plane strain mode I crack tip stress and displacement fields in a generalized linear neo-Hookean elastomer

A general asymptotic plane strain crack tip stress field is constructed for linear versions of neo-Hookean materials, which spans a wide variety of special cases including incompressible Mooney elastomers, the compressible Blatz–Ko elastomer, several cases of the Ogden constitutive law and a new result for a compressible linear neo-Hookean material. The nominal stress field has dominant terms that have a square root singularity with respect to the distance of material points from the crack tip in the undeformed reference configuration. At second order, there is a uniform tension parallel to the crack. The associated displacement field in plane strain at leading order has dependence proportional to the square root of the same coordinate. The relationship between the amplitude of the crack tip singularity (a stress intensity factor) and the plane strain energy release rate is outlined for the general linear material, with simplified relationships presented for notable special cases.     

丙烯酸弹性体的率相关分数阶黏弹性模型研究

丙烯酸弹性体VHB 4910作为一种重要的介电弹性体,在软体机器人、致动器、俘能器和智能隔振器等领域有很好的应用前景.但材料的非线性黏弹性对其力学行为有显著影响.近来分数阶模型在复杂材料的建模中取得了成功.本文基于分数阶有限变形Kelvin-Voigt流变学模型建立弹性体的三维张量本构,并进一步推导单向拉伸情况下的本构...     

Membrane Curvatures and Stress-strain Full Fields of Axisymmetric Bulge Tests from 3D-DIC Measurements. Theory and Validation on Virtual and Experimental results

The bulge test is mostly used to analyze equibiaxial tensile stress state at the pole of inflated isotropic membranes. Three-dimensional digital image correlation (3D-DIC) technique allows the determination of three-dimensional surface displacements and strain fields. In this paper, a method is proposed to determine also the membrane stress tensor fields for in-plane isotropic materials, independently of any constitutive equation. Stress-strain state is then known at any surface point which enriches greatly experimental data deduced from the axisymmetric bulge tests. Our method consists, first in calculating from the 3D-DIC experimental data the membrane curvature tensor at each surface point of the bulge specimen. Then, curvature tensor fields are used to investigate axisymmetry of the test. Finally in the axisymmetric case, membrane stress tensor fields are determined from meridional and circumferential curvatures combined with the measurement of the inflating pressure. Our method is first validated for virtual 3D-DIC data, obtained by numerical simulation of a bulge test using a hyperelastic material model. Afterward, the method is applied to an experimental bulge test performed using as material a silicone elastomer. The stress-strain fields which are obtained using the proposed method are compared with results of the finite element simulation of this overall bulge test using a neo-Hookean model fitted on uniaxial and equibiaxial tensile tests.     

具有线性介电常数的Ogden型介电弹性体的本构关系和机电稳定性

应用多材料常数的Ogden弹性应变能函数分析了介电弹性体的力学行为,研究了介电弹性体的机电稳定性.数值结果表明,通过对材料系数(如材料常数比和电致伸缩系数等)的恰当调节可以使得介电弹性体材料或介电弹性体结构更趋稳定.这些有益于深入理解介电弹性体的机电稳定性行为,进而设计恰当的介电弹性体器件.     

柔性硅泡沫薄片的短时松弛行为研究

根据多孔硅泡沫材料的单轴压缩和应力松弛实验,利用最小二乘法的LM法拟合得到硅泡沫材料的本构关系.基于上述模型开展了组合结构中多孔泡沫薄片应力松弛行为的数值模拟,得到了短时松弛过程中硅泡沫结构件的应力变化规律.     

A theoretical analysis for the dynamic axial crushing behaviour of aluminium foam-filled hat sections

A theoretical analysis was performed to predict the dynamic axial crushing behaviour of aluminium foam-filled top hat and double hat sections made from mild steel material. The deformation mode from the test results was used to create a deformation model for the theoretical analysis. According to the energy method and the superfolding element theory, the mean dynamic crushing loads of the aluminium foam-filled hat sections and the interactive effect between the aluminium foam and hat sections were theoretically predicted. The mean dynamic crushing loads and the interactive effect predicted by this theoretical analysis were in good agreement with the experimental results. The theoretical prediction results showed that the interactive effect was mainly from the aluminium foam.     

Study of bifurcation in a pressurized hyperelastic membrane tube enclosed by a soft substrate

We model a perivascular supported arterial tube as a uniform cylindrical membrane tube enclosed by a soft substrate, and derive the solution bifurcation criterion. We assume the surrounding soft substrate as an elastic foundation with distributed stiffness. We consider the tube to be a neo-Hookean material with isotropic and anisotropic (orthotropic) properties, and study solution bifurcation at a constant axial stretch. In the isotropic case, the surrounding soft substrate can substantially delay the onset of bifurcation through a subcritical jump in circular distension at bifurcation with increasing substrate stiffness. Introduction of anisotropy can significantly change the jump behavior from subcritical to supercritical.     

Kelvin结构开孔泡沫材料的弹性性能研究

采用一修正的十四面体结构模型(Kelvin结构模型)对开孔泡沫金属的弹性性能进行研究,对低密度开孔泡沫材料表现出不可压的特性进行了分析。该模型考虑作用在泡沫筋条上的弯矩、剪力和轴向力,以及轴向力的平衡。修正模型的数值计算结果与实验结果及其他模型的结果进行了对比,结果表明修正模型计算的杨氏模量比原有模型的略有提高,筋条截面为星形的修正模型计算的结果与实验比较符合。在密度等同的条件下,筋条截面惯性矩越大的开孔泡沫材料,其弹性模量也越大,而泊松比则越小。Kelvin结构的开孔泡沫材料的泊松比随相对密度的减小而趋于0.5。     

聚氨酯泡沫塑料压缩杨氏模量的理论预测

通过微分法导出了泡沫塑料剪切模量和体积模量所满足的微分方程组，再利用联系泡沫塑料泊松比和孔隙比的Ｋｅｒｎｅｒ－Ｒｕｓｃｈ经验关系及泡沫塑料弹性常数间满足足的关系，在基体材料不可压缩的假设下，确定了泡沫塑料的杨氏模量。本文针对几种密度的泡沫塑料，分别对它们的杨氏模量进行了理论预测和实验测定，结果表明：理论预测的模量在较高密度下与实验符合的很好，在低密度下也给出相当好的近似值。此外，本文的结果同其他理     

复合泡沫塑料力学行为的研究综述

复合泡沫塑料是一种重要的防护材料,它在国防工业和民用工业各部门均有许多重要的应用,对这类材料的力学行为进行研究具有重要的学术价值和应用前景.本文对复合泡沫塑料力学行为的研究文献进行了综述.首先,对复合泡沫塑料力学行为研究的早期工作进行了简介.然后,重点介绍了复合泡沫塑料力学行为研究的最新进展,其中也包括作者近期在该领域开展的一些工作;对复合泡沫塑料进行了静、动态压缩实验和细观加载实验,研究了材料的宏观变形规律和细观失效机制;在理论研究方面,探讨了复合泡沫塑料的能量吸收和缓冲特性,从宏、细观力学分析出发研究了复合泡沫塑料有关力学性能的理论预测问题;还利用计算机和通用软件对高密度复合泡沫塑料进行了有限元分析,研究了高密度复合泡沫塑料的失效行为.最后,给出对该领域研究工作的一些展望.      

Dynamic non-linear energy absorbers based on properly stretched in-plane elastomer structures

Traditionally, elastomers are considered to be one of the best material candidates for the design of energy absorbing devices, due to their remarkable visco-elastic and extensibility material properties. This capability can be further enhanced by the design of appropriate Dielectric Elastomer Generators (DEGs). The present paper proceeds to another alternative direction, which consists of the design of appropriate elastomer structures with enhanced energy absorption capabilities, are attributed more to the appropriate non-linear design of the elastomer structure itself, than to the hyperelastic material properties of the elastomer members. For this reason, a simple chi-shaped in-plane elastic structure is considered, comprising one proof mass with four elastomer members attached to it, placed in a chi-shaped configuration, and being properly stretched. A systematic analysis is carried out, with respect to the variation of two basic structure design properties on the dynamic behavior: the orientation angle of the members and their initial pre-stress. The obtained results show that the variation of just these two basic parameters of the structure may lead to a quite rich and interesting non-linear dynamic behavior. More specifically, the traditional always-in-tension concept leads to a linear dynamic system response, even though the elastomer members are considered to have been made of a non-linear hyper-elastic material. Alternatively, a new partially-loose-member operating concept is analyzed. This concept suggests that some individual elastomer members be allowed to become loose for some period of the operating cycle, (but not all of them simultaneously), strongly enhancing the broadband energy absorbing capability of the structure itself.     

Elastic displacements along the flanks of internal cracks in rubber

Biaxial tensile experiments with thin rubber sheets, containing an internal crack, reveal the possibility to simulate and readily check the exact linear-elastic crack-flank displacements. The resulting deformed shape and the final position during loading of an internal inclined crack in an infinite, biaxially loaded elastic plate, was defined by measuring the crack-flank displacements, and the deformation features of the internal crack in rubber sheets. The results were compared with the linear-elastic displacements and the respective features, which have been obtained from an infinitesimal elasticity theory.The calculation of these displacement and deformation properties for a given crack presupposes the determination of two parameters, which characterize the loading conditions of the boundaries of the elastic cracked plate. These parameters have been determined as Lagrangian or Eulerian ones from the homogeneous strains at the boundaries of the elastic sheet, assuming either a Hookean, or a neo-Hookean or a Mooney material behavior for the elastic sheet.It has been shown that, except for the vicinities of the crack tips and for the regions of the imposed boundary strains in the experiments, the observed crack-flank displacements agree satisfactorily with the respective displacements obtained from the infinitesimal theory, if the material behavior is assumed as a neo-Hookean one, and the boundary-loading parameters are calculated as Eulerian ones.     

Finite amplitude oscillations of a simple rubber support system

Exact solution of the nonlinear problem of undamped, finite amplitude, free vertical oscillations of a mass supported by a rubber spring made of a neo-Hookean material is presented for both suspension and compression supports. The motion in the special case of free fall of the mass from rest at the unstretched state is characterized in terms of elliptic integrals, and it is shown that the periodic time may be expressed universally in terms of the tabulated Heuman lambda-function. The finite amplitude, free vibrational frequency and the dynamic deflection of a neo-Hookean oscillator are compared with those for a linear spring oscillator having the same constant stiffness; and both upper and lower bounds on the ratio of these frequencies are presented. Numerical values for several cases are illustrated, and the physical results are described graphically. General solutions for the free vibrations with arbitrary initial data are obtained in terms of certain generalized lambda and beta-functions, and some transformation identities relating these functions are derived.     

Influence of Thermally Induced Chemorheological Changes on the Inflation of Spherical Elastomeric Membranes

When an elastomeric material is deformed and subjected to temperatures above some chemorheological value T _cr (near 100°C for natural rubber), its macromolecular structure undergoes time and temperature dependent chemical changes. The process continues until the temperature decreases below T _cr. Compared to the virgin material, the new material system has modified properties (often a reduced stiffness) and permanent set on removal of the applied load. A recently proposed constitutive theory is used to study the influence of chemorheological changes on the inflation of an initially isotropic spherical rubber membrane. The membrane is inflated while at a temperature below T _cr. We then look at the pressure response assuming the sphere's radius is held fixed while the temperature is increased above T _cr for a period of time and then returned to its original value. The inflation pressure during this process is expressed in terms of the temperature, representing entropic stiffening of the elastomer, and a time dependent property that represents the kinetics of the chemorheological change in the elastomer. When the membrane has been returned to its original temperature, it is shown to have a permanent set and a modified pressure-inflated radius relation. Their dependence on the initial inflated radius, material properties and kinetics of chemorheological change is studied when the underlying elastomeric networks are neo-Hookean or Mooney–Rivlin.     

Remarks on the Instability of an Incompressible and Isotropic Hyperelastic, Thick-Walled Cylindrical Tube

The problem of instability of a hyperelastic, thick-walled cylindrical tube was first studied by Wilkes [1] in 1955. The solution was formulated within the framework of the theory of small deformations superimposed on large homogeneous deformations for the general class of incompressible, isotropic materials; and results for axially symmetrical buckling were obtained for the neo-Hookean material. The solution involves a certain quadratic equation whose characteristic roots depend on the material response functions. For the neo-Hookean material these roots always are positive. In fact, here we show for the more general Mooney–Rivlin material that these roots always are positive, provided the empirical inequalities hold. In a recent study [2] of this problem for a class of internally constrained compressible materials, it is observed that these characteristic roots may be real-valued, pure imaginary, or complex-valued. The similarity of the analytical structure of the two problems, however, is most striking; and this similarity leads one to question possible complex-valued solutions for the incompressible case. Some remarks on this issue will be presented and some new results will be reported, including additional results for both the neo-Hookean and Mooney–Rivlin materials. This revised version was published online in August 2006 with corrections to the Cover Date.     

Radial oscillations of nonhomogeneous,thick-walled cylindrical and spherical shells subjected to finite deformations

The infinitesimal breathing motions of long cylindrical tubes and hollow spherical shells of arbitrary wall thickness subjected to a finite deformation field caused by uniform internal and/or external pressures are investigated. A neo-Hookean material with a material constant varying continuously along the radial direction is used. The shell is first subjected to finite static deformations and is then exposed to a secondary dynamic displacement field. Based on the theory of small deformations superposed on large deformations, closed form expressions are obtained for the frequency of small oscillations about the highly prestressed state. Frequency versus initial deformation parameter curves are given for several nohomogeneity functions and for various wall thicknesses.     

Qualitative study of cavitated bifurcation for a class of incompressible generalized neo-Hookean spheres

IntroductionIn 1 958,GentandLindleyobservedthephenomenonofsuddenvoidnucleationinsolidsexperimentallyintensioningahomogenousclose_grainedvulcanizedrubbercylinderforthefirsttime.ButthemathematicalmodelonvoidnucleationandgrowthhasnotbeendescribedasabifurcationproblembasedonthetheoryofnonlinearelasticmechanicsbyBall[1]until1 982 .Inrecentyears,manyinvestigationshavebeenmadeonthisaspect.Theproblemofcavitatedbifurcationforincompressibleisotropichyperelasticmaterialswithpower_lawtypehasbeeninvestig…     

A Eulerian approach to the finite element modelling of neo-Hookean rubber material

A Eulerian approach is applied to the finite element modelling of neo-Hookean rubber material. Two major problems are encountered. The first problem is the construction of an algorithm to calculate stresses in the rubber material from velocities instead of displacements. This problem is solved with an algorithm based on the definition of the velocity gradient. The second problem is the convection of stresses through the finite element mesh. This problem is solved by adapting the so-called Taylor-Galerkin technique. Solutions for both problems are implemented in a finite element program and their validity is shown by test problems. Results of these implementations are compared with results obtained by a standard Lagrangian approach finite element package and good agreement has been found.     

Stresses near a crack in a rubber sheet

The principal stresses in the vicinity of the crack tip in a rubber sheet have been determined experimentally by measuring the strain field with the aid of an imprinted grid work and calculating the stresses by assuming neo-Hookean material behavior. The principal stresses in the crack-tip vicinity are presented graphically. A correlation between the measured maximum tensile stress on the crack axis and that obtained from infinitesimal-elasticity theory is established. Information is given which provides bounds on the loading and deformation within which a large-deformation elastic analysis is valid before geometric deformations due to tearing must be considered.