复合材料非线性本构关系的机算机模拟

本文对单向连续纤维增强复合材料的弹塑性本构关系进行了数值模拟。首先提出了基于统一弹粘塑性本构理论的有限无法,然后利用微观力学模型研究了弹性纤维增强弹粘塑性基体的复合材料应力——应变关系。     

板壳非线性分析的新理论新方法

提出了板壳非线性分析的新理论新方法。首先建立了下列几个新的本构关系:塑性应变向量增量与总应变向量增量的新关系,热塑性应变向量增量与总应变向量增量及温度应变向量增量的新关系,粘塑性应变向量增量与总应变向量增量的新关系,热粘塑性应变向量增量与总应变向量增量及温度应变向量增量的新关系。这些关系分别称为弹塑性应变增量理论、热弹塑性应变增量理论、弹粘塑性应变增量理论及热弹粘塑性应变增量理论,避开了屈服曲面、加载曲面、流动法则及复杂的非线性应力应变关系。其次建立了非线性样条无网格法,这种方法是以新的本构关系、几何非线性理论、变分原理、广义变分原理、加权残数法及样条离散化为基础建立的,避免了经典本构关系及有限元法带来的巨大困难及缺陷,不仅计算简便,而且精度高,收敛速度很快。建立了板壳非线性分析的统一格式,对板壳的几何非线性分析、材料非线性分析及双重非线性分析都适用。     

沥青砂混合料粘弹塑力学特性研究

在0.1MPa、0.15MPa、0.2MPa、0.25MPa和0.3MPa下进行了沥青砂试样单轴压缩和蠕变实验,分析了其压缩和蠕变性质,根据变形机理提出了粘弹塑本构模型可由粘弹性和粘塑性的两个子模型串联构成,通过对粘塑性子模型中粘性系数进行改进,理论推导了模型蠕变本构方程,确定了模型参数,并求得模型参数与加载应力函数关系。进行模型预测与实验结果对比,结果表明:该模型能够描述沥青砂试样在不同应力下蠕变变形的3个阶段,反映了沥青砂混合料粘弹塑变形特点。     

岩体粘塑性模型参数的反分析

基于弹—粘塑性有限元方法,探讨了通过反分析来确定P.Perzyna粘塑性本构模型中反映岩体粘塑性变形的流动系数和屈服函数的函数的方法,并用实测数据检验了这一反分析方法的可行性。     

复合材料蠕变本构关系及实验测定Ⅰ.本构关系

蠕变是复合材料最重要的力学性能之一,实验表明:复合材料在蠕变条件下的变形可以分为弹性变形、粘弹性变形和粘塑性变形.应用不可逆过程的热力学和广义变量的概念可以分析材料的蠕变变形.本文首先回顾了热力学的基本方程;基于Schapery本构关系的假设和思路推导了蠕变本构关系的一般形式,其中包括弹性变形、粘弹性变形和粘塑性变形;考虑到广义力选取的不唯一性,本文提出了广义力选取的原则以使得到的本构关系尽可能地简单;由此本文给出了复合材料的一维蠕变,各向同性复合材料的二维蠕变和纤维增强复合材料平面内的蠕变的本构关系.     

树脂基三维编织复合材料粘弹性能的数值预报

建立了基于三细胞模型数值预报三维编织复合材料粘弹性能的方法。首先构造了三维编织复合材料的三细胞模型并施加周期性边界条件,随后利用标准线性固体模型模拟树脂基体的粘弹性能,导出基体的松弛模量,再通过有限元计算及Prony级数拟合,得到三种胞元的粘弹性参数。然后根据三种胞元的体积分数和粘弹性参数,利用三个标准线性固体模型并联,模拟得到三维编织复合材料沿编织方向的粘弹性参数和蠕变本构关系。最后,分析了编织角和纤维体积含量对粘弹性能的影响。     

率相关饱和多孔介质动力响应的数值分析

在基于混合物理论的多孔介质模型的基础上,将固体相视为弹粘塑性体,建立了饱和多孔介质的弹粘塑性模型。模型的基本思想是在无粘弹塑性本构关系中引入-时间参数,使固体骨架具备了粘性效应。利用Galerkin加权残值法推导得到了罚有限元格式,并采用Newmark预估校正法求解率相关饱和多孔介质的非线性有限元动力方程,此算法可以很...     

复合材料蠕变本构关系及实验测定Ⅱ实验测定

在前一部分,本文得到复合材料蠕变的本构关系,在此基础上,本文进一步分析了复合材料蠕变本构关系的具体形式,实验测得了长纤维增强复合材料在蠕变、恢复两个阶段的应变,以用来确定本构关系中的待定参数,考虑到本构关系为复杂的非线性方程,本文提出了用离散变量和最小二乘法联合的方法确定参数,进而拟合蠕变本构关系的理论公式,分离出了蠕变过程中的弹性变形、粘弹性变形和粘塑性变形,对本构关系中的几个参函数,本文根据有限的实验数据拟合了其函数。      

复合材料蠕变本构关系及实验测定 Ⅱ实验测定

在前一部分,本文得到复合材料蠕变的本构关系,在此基础上,本文进一步分析了复合材料蠕变本构关系的具体形式,实验测得了长纤维增强复合材料在蠕变、恢复两个阶段的应变,以用来确定本构关系中的待定参数,考虑到本构关系为复杂的非线性方程,本文提出了用离散变量和最小二乘法联合的方法确定参数,进而拟合蠕变本构关系的理论公式,分离出了蠕变过程中的弹性变形、粘弹性变形和粘塑性变形,对本构关系中的几个参函数,本文根据有限的实验数据拟合了其函数.     

颗粒增强复合材料刚塑性细观损伤本构模型的验证

验证已建立的刚性颗粒增强复合材料刚塑性细观损伤本构理论的合理性和可靠性。将上述本构理论的数值计算结果与SiC颗粒增强的铝基复合材料单轴拉伸实验结果进行比较。结果表明:由此本构模型得到的应力-应变理论曲线与拉伸实验所得的应力-应变曲线基本吻合,从而验证了该本构模型的合理性和可靠性。因此已建立的刚塑性细观损伤本构模型可用于数值计算,在一定程度上可预测颗粒增强复合材料的力学特性。在此基础上对大、小颗粒增强复合材料的延展性、空洞和颗粒体积分数演化规律等作了讨论。      

The effect of plasticity on dynamic crack growth across an interface

The effect of plasticity on the growth of a crack originating in an elastic solid across an interface and into an elastic-viscoplastic solid is analyzed numerically. The analyses are carried out within a framework where the continuum is characterized by two constitutive relations; one relating the stress and strain in the bulk material and the other relating the traction and separation across a specified set of cohesive surfaces. Crack initiation, crack growth and crack arrest arise naturally as a consequence of the imposed loading, without a priori assumptions concerning criteria for crack growth and for crack path selection. Full transient analyses are carried out. Various values of initial flow strength and cohesive strength of the elastic-viscoplastic solid and of cohesive strength of the interface are considered. With the ratio of cohesive strength of the elastic-viscoplastic solid to cohesive strength of the interface fixed, increasing the ratio of cohesive strength to initial flow strength for the elastic-viscoplastic solid is found to promote crack deflection into the interface.     

短纤维增强金属基复合材料的细观塑性变形与宏观性能

本文研究单向短纤维增强金属基复合材料的细现弹塑性变形和宏观弹塑性响应。假设纤维是弹性体,基体是弹性粘塑性体。利用有限元法分析了复合材料可周期性重复的单胞的细观弹塑性应力场;利用体积平均的均匀化方法研究了复合材料的弹塑性应力-应变关系。本工作着重分析复合材料中纤维与纤维、纤维与周围基体的相互作用机理。     

Birefringent effects in the cyclic loading for an elastic-viscoplastic polymer

The general plastic deformation should be considered by the elastic-viscoplastic theory, which contains the viscosity in addition to the elastic am plastic properties. In this paper, the birefringen effects are experimentally investigated by using celluloid as elastic-viscoplastic polymer under cyclic loadings. The optical relations in the loading and the unloading processes are semi-empirically deduced for the elastic-viscoplastic solid. The deduced optical relations give good agreement with the actual observations under the cyclic loadings for various cyclic conditions.     

A hardness law for inelastic deformation

Certain formulations of elastic-viscoplastic constitutive equations lead to inelastic deformations being governed by a functional relation between the plastic deformation rate and the stress. A parameter that appears in certain forms of this equation can be interpreted as an internal variable measure of the overall resistance of the material to plastic flow. In this paper, it is taken to be a second order tensor and designated the “hardness stress.” A procedure for calculating changes in the hardness stress parameter for general multiaxial loading histories is proposed in this paper. These evolutionary equations lead to induced plastic anisotropy. Stress-strain relations that would be predicted by this procedure appear to be consistent with experimental results for various multiaxial loading histories including proportional and non-proportional cyclic loading.     

Arrest of fast mode-i fracture in an elastic-viscoplastic transition zone

Arrest of a rapidly propagating Mode-I crack has been investigated for a crack which initially propagates in an elastic solid, and then enters a region of viscoplastic material properties. The transition to the viscoplastic behavior has been modeled by a gradual process which starts at a certain time at which the constitutive relations change in a time-wise manner from elastic to elastic-viscoplastic. The solution to the transient problem has been obtained numerically by a finite-difference procedure. Arrest of a crack in a perfectly elastic material has been treated as a special case. Field quantities such as the effective plastic strain, and the plastic work, have been computed, and their relation to arrest criteria have been explored. Both deformations in plane stress and plane strain have been considered.     

SMA长纤维增强弹塑性基体复合材料的力学性能

本文从作者建立的SMA本构模型出发,推导出增量型的SMA本构关系;借助于细观力学的方法,推导出了新的长纤维SMA复合材料的增量型细观本构模型;应用此模型分析了该复合材料的力学性能,得出了一些定量的结论,尤其是计算了复合材料中各相的残余应力的变化,这对智能复合材料的设计提供了很大帮助。     

Modeling of continuum damage for application in elastic-viscoplastic constitutive equations

A procedure is described for including isotropic and directional damage as load-history dependent softening variables in a set of elastic-viscoplastic constitutive equations. The evolution equation proposed for isotropic damage integrates to an exponential form for the case of constant stress. Directional damage is represented as a second-order symmetric tensor with a scalar effective value used in the constitutive equations. A method is proposed for treating directional damage in the case of non-proportional loading histories. Comparisons are given of uniaxial creep test results for an alloy at high temperatures with calculations based on the constitutive equations with the inclusion of isotropic damage.     

复合材料螺栓连接松弛的弹-黏塑性分析方法

预紧力松弛是影响复合材料螺栓连接结构耐久性的主要原因之一。本文重点讨论导致预紧力松弛的材料蠕变与粗糙表面接触蠕变的相互影响。内容包括建立了以弹-黏塑性理论为基础的复合材料蠕变本构模型,并结合考虑粗糙表面的分形接触理论,将其推广到与时间相关的弹-黏塑性接触问题。数值结果与实验结果对比表明,考虑粗糙表面接触效应时,计算误差从2.87%~4.37%降至0.04%~0.5%,预测准确性有显著提高。表面分形参数D和G的讨论结果表明,接触表面越粗糙,预紧力越容易松弛。这对工程上通过控制表面形貌参数来改善表面接触性质具有指导意义。     

A finite element comparison between short and long cracks within a plastic zone due to a notch

This paper considers the finite element characteristics of a crack growing within an area affected by a small notch. It is a continuation of an investigation leading from the development of a finite element program which considers elastic-viscoplastic constitutive relations to the actual features present in modelling a crack growth within a specimen. A final paper actually compares given parameters developed within this paper with experimental findings. The material considered is IN 718 at a temperature of 1200°F. A compact tension with a blunt notch is the specimen eventually tested. The findings relate to the most effective technique for allowing the crack to grow within a specimen. A trace is carried out on stress and strain functions as the crack grows with a consideration of the closure phenomenon. Parameters such as the J range, COD, maximum stress and strain range, stress intensity, and effective stress intensity range are shown to be potential candidates for crack growth as short and long cracks are compared.