拉压性能不同纤维增强复合材料的非线性本构模型

为满足在工程应用中对建立拉压性能不同纤维增强复合材料的非线性本构理论的需要,考虑静水压影响的Drucker-Prager屈服准则与各向异性的Hill屈服准则相结合,提出了广义Hill屈服准则,并推广到Sun-Chen的单参数塑性模型中,建立了考虑拉压异性复合材料的非线性统一本构方程.实验验证结果表明,运用本文中所建立的本构模型能够很好地描述碳纤维/环氧(IM600/Q133)复合材料在偏轴拉伸和压缩载荷作用下的非线性响应.     

拉压性能不同纤维增强复合材料的非线性本构模型

为满足在工程应用中对建立拉压性能不同纤维增强复合材料的非线性本构理论的需要, 考虑静水压影响的Drucker-Prager屈服准则与各向异性的Hill屈服准则相结合, 提出了广义Hill屈服准则, 并推广到Sun-Chen的单参数塑性模型中, 建立了考虑拉压异性复合材料的非线性统一本构方程。实验验证结果表明, 运用本文中所建立的本构模型能够很好地描述碳纤维/环氧(IM600/Q133)复合材料在偏轴拉伸和压缩载荷作用下的非线性响应。     

基于率相关三维弹塑性损伤模型的复合材料渐进失效分析

建立了一个同时考虑复合材料非线性力学响应、应变率效应和损伤累积导致材料属性退化的弹塑性三维损伤本构模型。采用改进的塑性力学模型表征材料在动态荷载下的非线性力学行为。为准确预测复合材料在动态荷载下的弹塑性力学响应,引入了率相关放大系数对准静态下的塑性强化函数进行修正。采用“断裂带模型”对已开发的本构模型软化段进行规则化,以减轻有限元分析结果的网格敏感性。采用分区反抛物线插值法对基体损伤初始断裂面角度及纤维扭结/劈裂平面角度进行求解。开发包含数值积分算法的用户材料自定义子程序VUMAT,并嵌于有限元程序ABAQUS V6.14中,对力学行为展现显著非线性力学效应和应变率效应的IM7/8552碳纤维/环氧树脂复合材料层合板进行了渐进失效分析,验证本文提出的材料本构模型的有效性。结果显示,预测结果与已报道的试验结果吻合良好,表明已建立的率相关三维弹塑性损伤本构模型能准确预测此类复合材料层合板的在动态荷载下的力学行为,为复合材料构件及其结构设计提供了一种有效的分析方法。     

钢-混凝土组合简支梁滞回性能非线性有限元分析

为实现钢-混凝土组合简支梁滞回性能三维非线性有限元分析,该文提出混凝土在单轴拉、压应力下的损伤变量计算方法,给定了混凝土的卸载规则,完善并提出混凝土应力-应变滞回本构关系和钢材循环本构关系,应用ABAQUS有限元软件建立混凝土棱柱体试件、钢材试件和钢-混凝土组合简支梁有限元三维非线性有限元模型,对混凝土棱柱体试件在单轴受压和受拉反复荷载下的试验结果进行分析,对钢材试件在单轴拉压循环荷载下的试验结果进行分析,对钢-混凝土组合简支梁在循环荷载下的荷载-挠度滞回关系、梁端荷载-滑移滞回关系以及栓钉的荷载-侧向变形滞回关系曲线等试验结果进行分析,计算结果与试验结果符合较好。     

二维编织C/SiC复合材料非线性损伤本构模型与应用

基于二维编织C/SiC复合材料的基本力学性能试验, 建立了该材料的宏观正交各向异性非线性损伤本构模型。模型中以可检测的应变作为变量, 采用形式简单的函数分别描述了单轴拉伸和剪切加载下的材料损伤演变下的应力-应变关系, 以及卸载状态的刚度变化规律。同时, 考虑了材料的单边效应以及拉压应力状态转换时的损伤钝化行为。将此本构模型编写成UMAT子程序并引入ABAQUS有限元软件, 可以完整描述该材料的加载非线性和卸载线性的应力-应变关系特征, 及其加卸载历史。通过对带孔板的拉伸模拟, 孔边应变分布与试验结果吻合较好, 验证了本构模型的有效性。     

纤维缠绕壳体材料非线性及大变形分析计算

论述了Jones-N elson-Morgan 模型的构成原理及其参数的确定方法, 利用这个模型研究了纤维缠绕复合材料的非线性本构关系。推导和建立了纤维缠绕壳体大变形有限元公式和有限元模型。在同时考虑材料非线性和大变形情况下对纤维缠绕壳体内压进行了有限元分析计算, 获得了与实验结果符合较好的理论预报结果。      

反映阻尼影响的混凝土弹塑性损伤本构模型

通过引入有效阻尼应力和阻尼应力,提出了一种基于损伤的阻尼模型,并与混凝土弹塑性损伤本构模型相结合,建议了一类可以直接在材料层次考虑阻尼耗能影响的弹塑性损伤本构模型。当材料处于线弹性阶段,该阻尼模型退化为经典的Rayleigh刚度比例阻尼;同时,还可以描述材料非线性阶段损伤演化引起的耗能能力降低、裂缝闭合后耗能能力(部分)恢复等典型的非线性结构阻尼行为。利用建议的本构模型,通过HHT-α方法可以将结构的动力非线性分析转化为常规的无阻尼结构动力学问题来处理,十分方便有限元方法实现。对Koyna大坝的地震动时程分析结果表明了建议模型及其数值算法的有效性,可以应用于混凝土结构的非线性动力反应分析。     

基于弹塑性损伤本构模型的复合材料层合板破坏荷载预测

在连续损伤力学和塑性力学框架内,建立一个同时考虑塑性效应和损伤累积导致材料属性退化的复合材料弹塑性损伤本构模型。基于最近点投影回映算法,开发本构模型的应变驱动隐式积分算法以更新应力及与解答相关的状态变量,并推导与所开发算法相应的数值一致性切线刚度矩阵,保证有限元分析采用NewtonRaphson迭代法解答非线性问题的计算效率。采用断裂带模型对已开发的本构模型软化段进行规则化,以减轻有限元分析结果的网格相关性问题。对损伤变量进行粘滞规则化,并推导出相应的粘滞规则化数值一致性切线刚度张量,解决了在有限元隐式计算程序中采用含应变软化段本构关系的数值分析由于计算困难而提前终止的问题。开发包含数值积分算法的用户材料子程序UMAT,并嵌于有限元程序Abaqus v6.14中。通过对力学行为展现显著塑性效应的AS4/3501-6V型开口复合材料层合板的渐进失效分析,验证本文提出的材料本构模型的有效性。结果显示,预测结果与已报道的试验结果吻合良好,并且预测精度高于其他已有弹性损伤模型。表明已建立的弹塑性损伤本构模型能够准确预测力学行为,展现显著塑性效应的复合材料层合板的破坏荷载,为其构件和结构设计提供一种有效的分析方法。     

三维四向编织复合材料界面损伤机理数值分析

考虑界面脱粘表面压应力下摩擦力对材料界面力学性能的影响,建立损伤-摩擦相结合的界面本构模型,编写用户材料子程序VUMAT,实现其在有限元软件ABAQUS中的嵌入。基于周期性胞元分析思想,在单胞模型中纤维束/基体、纤维束/纤维束分界面引入界面单元,结合损伤-摩擦相结合的界面本构模型,建立含界面相三维四向编织复合材料的细观有限元模型。模拟典型载荷下界面损伤的起始和扩展过程,分析界面应力传递和界面破坏机理,研究界面性能对复合材料宏细观力学性能的影响规律,为实现三维四向编织复合材料界面性能优化设计和控制提供参考。      

纤维增强复合材料本构模型研究进展

本文对纤维增强复合材料的本构模型最新研究成果进行简要阐述和归纳,并结合实例进行了相关数值模拟计算。文中阐述的复合材料为纤维增强树脂复合材料、纤维增强金属基复合材料和纤维编织复合材料。目前,关于纤维增强金属基复合材料的研究较少,大多数研究集中在纤维增强树脂复合材料和纤维编织复合材料。许多学者在经典弹性本构模型和连续介质力学基础上,推导出了一些弹塑性、粘弹性和考虑损伤的非线性本构模型。通过实例计算结果表明,考虑损伤导致刚度退化的复合材料弹塑性本构模型计算得到的拉伸应力应变曲线与测试结果基本一致。本文通过对复合材料本构模型的最新研究成果的归纳和数值模拟实例计算,为后续研究工作提供借鉴,推动其在实际工程中的应用。     

单向纤维增强聚合物复合材料压缩渐进破坏单向纤维增强聚合物复合材料压缩渐进破坏

复合材料结构在承压时破坏如何演化,是其强度破坏分析的基础和核心任务。本文提出了基于连续介质损伤力学（CDM）的单向纤维增强聚合物复合材料压缩破坏渐进损伤分析（PDA）模型。建模中考虑了材料非线性行为、失效判断及损伤演化中材料性能退化等基本问题,分别对应于拉压不对称弹塑性本构关系、Puck准则、LaRC05准则及考虑破坏面方向的刚度退化方法。该模型通过用户材料子程序接口VUMAT引入到有限元软件ABAQUS中实现了有限元求解。对文献中提供的纵向、横向及偏轴压缩案例进行了数值计算并与试验数据对比。数值分析结果与试验数据吻合较好,证明了该方法的合理性和有效性,对开展多向层合板压缩破坏分析富有参考价值。      

Multiscale finite element modeling of failure process of composite laminates

A multiscale nonlinear finite element modeling technique is developed in this paper to predict the progressive failure process for composite laminates. A micromechanical elastic–plastic bridging constitutive model, which considers the nonlinear material properties of the constituent fiber and matrix materials and their interaction and the damage and failure in fibrous composites at the fiber and matrix level, is proposed to represent the material behavior of fiber-reinforced composite laminates. The micromechanics constitutive model is employed in the macroscale finite element analysis of structural behavior especially progressive failure process of the fiber-reinforced composites based on a 4-node 24-DOF shear-locking free rectangular composite plate element.     

Failure analysis of fiber-reinforced composite laminates subjected to biaxial loads

A nonlinear constitutive model for a single lamina is proposed for the failure analysis of composite laminates. In the material model, both fiber and matrix are assumed to behave as elastic-plastic and the in-plane shear is assumed to behave nonlinearly with a variable shear parameter. The damage onset for individual lamina is detected by a mixed failure criterion, composed of the Tsai-Wu criterion and the maximum stress criterion. After damage takes place within the lamina, the fiber and in-plane shear are assumed to exhibit brittle behavior, and the matrix is assumed to exhibit degrading behavior. The proposed nonlinear constitutive model is tested against experimental data and good agreement is obtained. Then, numerical analyses are carried out to study the failure behavior of symmetric angle-ply composite laminates and symmetric cross-ply composite laminates subjected to biaxial loads. Finally, the conclusions obtained from the numerical analysis are given.     

A stochastic plasticity approach to strength modeling of strand-based wood composites

A 3 dimensional stochastic finite element technique is presented herein for simulating the nonlinear behaviour of strand-based wood composites with strands of varying grain-angle. The approach is based on the constitutive properties of the individual strands to study the effects of varying strand characteristics (such as species or geometry) on the performance of the member. The constitutive properties of the strands are found empirically and are subsequently used in a 3 dimensional finite element program. The program is formulated in a probabilistic manner using random variable material properties as input. The constitutive model incorporates classic plasticity theory whereby anisotropic hardening and eventual failure of the material is established by the Tsai–Wu criterion with an associated flow rule. Failure is marked by an upper bound surface whereupon either perfect plasticity (i.e. ductile behavior) or an abrupt loss of strength and stiffness (i.e. brittle behavior) ensues. The ability of this technique to reproduce experimental findings for the stress–strain curves of angle-ply laminates in tension, compression as well as 3 point bending is validated.     

On the use of a multilayer higher-order theory for the stress analysis around a circular hole of laminates under tension

Many single layer and multilayer higher-order theories were recently proposed for the analysis of the three-dimensional stress field that usually occurs in composite laminates especially in critical areas such as free edges. In this paper a finite element analysis based on a multilayer theory is performed in order to predict the complicated pattern of the stress field around the hole of laminates under tension. The numerical results are compared with the ones obtained with other modelling approaches, including single layer higher-order theories. The analysis shows that multilayer-theory-based finite elements can be effectively used in the prediction of the stress response of composite structures in cases of practical interests.     

Progressive damage analysis and testing of composite laminates with fiber waves

In this work, the Progressive Damage Analysis (PDA) of composite laminates with waves was developed, experimentally validated, and discussed. PDA using Continuum Damage Modeling (CDM) and Discrete Damage Modeling (DDM) was conducted. In CDM, the material continuum constitutive properties are updated to incorporate the influence of progressive damage. In DDM, the actual damage is modeled, consistent with the progressive damage model analysis and observations. A commercial finite element code ABAQUS was used for all of the analysis with specialty user subroutines for the CDM and DDM. The laminate wave parameters (wavelength and amplitude) were determined from a statistical analysis of as-manufactured laminates from failed composite wind turbine blades. Laminates with waves under tension and compression loading were considered to create a benchmark set of tests for laminates and waves, and to provide an unambiguous comparison between CDM and DDM for this type of defect. Both methods (CDM and DDM) are compared and contrasted with experimental data. It is important to note that no assumed damage (such as a crack or other discontinuity) was necessary for the analysis. The failure mode and progressive damage is a consequence of the analysis. Correlations are found with each, and the pros and cons are evaluated and discussed. Better correlations were found with DDM, but accounting for nonlinear shear in the stress–strain response using CDM in the analysis provided numerical stability and the best experimental/analytical correlations.     

螺栓夹持填充孔复合材料层压板层间应力分析

为了研究含螺栓复合材料层压板连接接头的层间应力分布规律,提出了采用填充孔形式和虚拟界面层方法求解层间应力,并建立了三维有限元模型对受面内压缩载荷的螺栓夹持填充孔层压板进行分析。结果表明:层压板层间应力集中不仅发生在孔边,还会在螺栓头边缘附近出现,且夹持力越大螺栓头边缘附近的层间应力集中越严重;合理的螺栓夹持力能改善孔边应力状态,提高孔边抵抗分层的能力,但无法改善螺栓头边缘附近的层间剪切应力集中状态。因此,在进行含螺栓夹持的层压板机械连接结构孔边层间强度设计时,也要考虑螺栓头边缘的层间剪切应力集中问题,以提高复合材料结构的安全性。     

Nonlinear analysis of interlaminar stress in graphite/epoxy laminates with and without delamination cracks

A quasi three-dimensional yield function, which is quadratic in stresses except for σ₁₁, is proposed for graphite/epoxy composites. The elastic-plastic interlaminar stress response near a free edge in the [90/0]_s, [0/90]_s, and [45/−45]_s laminates with and without delamination cracks was investigated using the pseudo three-dimensional finite element technique. The plasticity model was evaluated by comparison with off-axis experimental data. Since shear response is the key element for nonlinear stress-strain behavior of graphite/epoxy composites, the plasticity theory predicts interlaminar stresses in the [45/−45]_s laminate significantly different from linear elasticity. Moreover, the existence of a delamination crack caused more plasticity effects on interlaminar stresses.     

不同形状弹体高速冲击下复合材料层板损伤分析

根据纤维增强复合材料宏细观结构,基于纤维的线弹性假设和基体的粘弹性假设,推导了单向复合材料粘弹性损伤本构关系。在此基础上,结合Hashin失效准则进行单层板面内损伤识别,通过界面单元模拟层间分层损伤,采用非线性有限元方法,建立了复合材料层板高速冲击损伤有限元分析模型。利用该模型,深入研究了不同形状弹体高速冲击下复合材料层板的弹道性能和损伤特性,探讨了相关参数对冲击损伤的影响规律,获得了一些有价值的结论。     

基于剪切非线性三维损伤本构模型的复合材料层合板失效强度预测

基于连续损伤力学,建立了同时考虑复合材料剪切非线性效应和损伤累积导致材料属性退化的三维损伤本构模型。模型能够区分纤维损伤、基体损伤和分层损伤不同的失效模式,并定义了相应损伤模式的损伤变量。复合材料层合板层内纤维初始损伤采用最大应力准则判定,基体初始损伤采用三维Puck准则中的基体失效准则判定,分层初始损伤采用三维Hou准则中的分层破坏准则判定,为了计算Puck失效理论中的基体失效断裂面角度,本文提出了分区抛物线法,通过Matlab软件编写计算程序并进行分析。结果表明,与Puck遍历法和分区黄金分割法对比,本文提出的分区抛物线法有效地降低了求解断裂面角度的计算次数,提高了计算效率和计算精度。推导了本构模型的应变驱动显式积分算法以更新应力和解答相关的状态变量,开发了包含数值积分算法的用户自定义子程序VUMAT,并嵌于有限元程序Abaqus v6.14中。通过对力学行为展现显著非线性效应的AS4碳纤维/3501-6环氧树脂复合材料层合板进行渐进失效分析,验证了本文提出的材料本构模型的有效性。结果显示,已提出的模型能够较准确地预测此类复合材料层合板的力学行为及其失效强度,为复合材料构件及其结构设计提供一种有效的分析方法。