剪切速率对各向异性不排水剪强度影响分析

在各向异性弹粘性本构关系基础上，推导考虑粘性各向异性不排水剪强度表达式，探讨剪切速率与不排水剪强度之间的关系，并从理论上解释各向异性不排水剪强度的速率相关性，最后将理论计算值与试验结果进行比较，验证理论的合理性。     

On the effective behavior of nonlinear inelastic composites: I. Incremental variational principles

A new method for determining the overall behavior of composite materials comprised of nonlinear inelastic constituents is presented. Upon use of an implicit time-discretization scheme, the evolution equations describing the constitutive behavior of the phases can be reduced to the minimization of an incremental energy function. This minimization problem is rigorously equivalent to a nonlinear thermoelastic problem with a transformation strain which is a nonuniform field (not even uniform within the phases). In this first part of the study the variational technique of Ponte Castañeda is used to approximate the nonuniform eigenstrains by piecewise uniform eigenstrains and to linearize the nonlinear thermoelastic problem. The resulting problem is amenable to simpler calculations and analytical results for appropriate microstructures can be obtained. The accuracy of the proposed scheme is assessed by comparison of the method with exact results.     

Estimates for the overall linear properties of pointwise heterogeneous solids with application to elasto-viscoplasticity

New estimates are derived for the overall properties of linear solids with pointwise heterogeneous local properties. The derivation relies on the use of ‘comparison solids’ which, unlike comparison solids considered previously, are themselves pointwise heterogeneous. The estimates are then exploited within an incremental homogenization scheme to determine the overall response of multiphase elasto-viscoplastic solids under arbitrary loading histories. By way of example, the scheme is applied to incompressible Maxwellian solids with power-law plastic dissipation; particularly simple estimates of the Hashin–Shtrikman type are obtained. Predictions are confronted with full-field simulations for particulate composites under cyclic and rotating loading conditions. Good agreement is found for all cases considered. In particular, elasto-plastic transitions, tension-compression asymmetries (Bauschinger effect) and stress-path distortions induced by material heterogeneity are all well-captured, thus improving significantly on commonly used elastic-plastic decoupled schemes.     

Elasto-viscoplastic behaviour of a polyvinylidene fluoride (PVDF) in tension

The present paper is concerned with the plasticity of a polyvinylidene fluoride (PVDF) in tension. Strain rate strongly influences the plastic behaviour, but the variation of the elastic properties is almost negligible within the range of strain rates considered in the study (from 1.6 × 10⁻⁴ s⁻¹ up to 1.6 × 10⁻¹ s⁻¹). In particular, the yield stress and the ultimate tensile strength are strongly rate-dependent. A one-dimensional elasto-viscoplastic phenomenological model is proposed and analysed. Despite the nonlinearity of the model equations, only one tensile test performed with variable strain rate is sufficient to identify all material parameters. Model predictions are compared with experiments showing good agreement.     

Analysis of the cyclic tensile behaviour of an elasto-viscoplastic polyamide

The present paper is concerned with the experimental and theoretical investigation of the progressive accumulation of inelastic deformation observed in cyclic tension tests performed on a particular polyamide. The elastic properties are not strongly affected by the strain rate, but the strain hardening induced by the plastic deformation is rate-dependent. Thus, the material behaviour is elasto-viscoplastic rather than viscoelastic or elasto-plastic. For the polymer studied in this paper, the kinematic hardening is much more significant than the isotropic hardening, and a negative plastic strain rate may occur even with a positive stress. The kinematic hardening is strongly dependent, not only on the accumulated plastic strain, but also on the loading rate. An elasto-viscoplastic mechanical model able to describe the cyclic inelastic behaviour for an arbitrary loading history is proposed. All parameters that arise in the theory are identified experimentally. The preliminary theoretical results concerning the modelling of cyclic load-unload tests are in good agreement with the experiments.     

软土三维各向异性弹粘塑性本构关系

结合真三轴试验所得到的破坏面在Л平面的形状，提出能够反映应力诱发各向异性的体积蠕变方程及弹粘塑性本构模型，并对模型进行试验验证     

Temperature and variable strain rate sensitivity in recycled HDPE

The recycling of post-consumer plastics and their utilization as raw materials to develop value-added products has become an important goal worldwide. The present work is concerned with the thermo-mechanical analysis of recycled high-density polyethylene (HDPE) under uniaxial tensile loading. The main focus is to propose a one-dimensional phenomenological model able to describe the influence of temperature and strain rate on the mechanical behavior. Tensile tests were performed over a wide range of temperatures (from 25°C to 100°C). Each experiment was performed under controlled strain rate varying from 7.25 × 10⁻⁵ s⁻¹ to 7.25 × 10⁻³ s⁻¹ in steps. It is shown that only one tensile test performed at three different temperatures is necessary to fully identify experimentally all material parameters that arise in the theory. Thus, with this experimental procedure, the number of tests used to evaluate the mechanical properties of recycled HDPE is significantly reduced. The experiments are compared with the model predictions and show good agreement.