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.     

拉压异性纤维增强树脂基复合材料弹塑性问题的有限元分析

为了对复杂的非线性问题进行便捷求解,首先提出了考虑拉压异性的纤维增强树脂基复合材料统一非线性本构模型;然后,在此基础上进一步导出了本构模型的三维表现形式,以适用于非线性有限元分析工具的开发;随后,利用有限元软件ABAQUS提供的用户自定义子程序UMAT,自编了在二维和三维情况下的弹塑性应力分析程序;最后,应用程序对复合材料单向板和复合材料斜交板在偏轴拉伸/压缩下应力-应变曲线的预测与测试结果进行了比较,探讨了复合材料悬臂梁的弹塑性问题,并分析和比较了有无考虑拉压异性情况下应力分布和挠度响应的差异。结果表明:运用所提出的本构模型对考虑拉压不对称问题的弹塑性变形分析十分有效,这一本构模型有望成为实用数值分析工具,进而指导工程实践。     

Koyna混凝土重力坝的塑性地震损伤响应分析

考虑了混凝土拉压异性损伤变量，根据相关流动法则推导了混凝土的损伤本构方程。通过有限元方法模拟坝体在地震激励下的非线性损伤演化过程，数值计算过程中考虑了库坝动力耦合及混凝土后继屈服的强化效应，采用四参数Ottosen屈服准则及相应的损伤型本构，算例验证了Koyna混凝土重力坝在竖向和横向实测地震激励下的非线性损伤响应特性。     

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。     

正常使用状态下RUHTCC梁的弯曲变形预测

该文以有效截面惯性矩为参数,提出了正常使用状态下钢筋增强超高韧性水泥基复合材料(RUHTCC)梁的挠度简化计算方法。与钢筋混凝土梁不同,RUHTCC梁需要考虑受拉区UHTCC在弯曲开裂后的承载能力,理论分析表明基于拉压区面积矩平衡与基于内力平衡且假定压应力线性分布所得的中和轴高度计算公式不同,而后者符合中和轴的物理意义。采用UHTCC的非线性拉、压本构模型以及受压区边缘压应变对应的割线模量,得到基于内力平衡的RUHTCC梁完全开裂截面的中和轴高度以及惯性矩公式。其次,有效惯性矩公式中的常系数m修正为随配筋率变化的函数,得到适用于RUHTCC梁的有效惯性矩公式。采用该文提出的挠度简化计算方法,对比预测与实测的屈服前荷载-挠度曲线,两者基本一致。     

基于应变空间的碾压混凝土各向异性损伤本构模型

根据碾压混凝土材料的力学特性和损伤拉压显著不同的特点,分别在拉应变和压应变空间建立了碾压混凝土的本构关系和损伤演化方程。在拉应变空间,碾压混凝土的变形特性表现为脆弹性,考虑弹性与损伤耦合,应用正交各向异性损伤理论描述碾压混凝土的刚度退化和应变软化;在压应变空间,考虑弹塑性与损伤耦合,应用内时理论来描述碾压混凝土的弹塑性特性,正交各向异性损伤理论来描述微裂缝扩展引起的刚度退化和应变软化,内时理论没有屈服面,使模型的参数和方程大大减少,从而简化了非线性计算过程。计算结果表明,该模型能够较好地描述碾压混凝土在单轴和多轴加载下的性质。     

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。      

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。      

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。     

TATB基PBX在不同围压下的Boltzmann-P本构模型及其数值计算方法

围压对于PBX材料的力学性能影响显著,围压影响的实质为静水压力的影响。该文基于Boltzmann本构模型,建立了考虑静水压力影响的TATB基PBX准静态Boltzmann-P非线性弹性本构模型,提出了针对该本构模型的非线性计算方法,采用Mises等效应力-应变并引入泊松比提出了一维本构模型转化为三维模型的数值方法,然后通过二次开发实现了本构模型以及相应算法的实际应用。通过对单位体积单元进行计算,在无围压条件以及围压两种条件下Boltzmann-P模型描述精度均高于Boltzmann模型,验证了Boltzmann-P本构模型及相应算法与所开发程序的正确性。     

Constitutive modeling of woven composites considering asymmetric/anisotropic, rate dependent, and nonlinear behavior

The mechanical performance of woven composites was analyzed focusing on their nonlinear and rate dependent asymmetric/anisotropic deformation behavior. Three key characteristics were identified which are indispensable for realistically simulating the mechanical performance of woven composites: the asymmetric material behavior between tension and compression, its anisotropic and nonlinear evolution and rate dependency. To include all three characteristics into the nonlinear finite element analysis for woven composites, a phenomenological constitutive equation was developed based on an elasto-viscoplastic theory using the modified Drucker–Prager yield criterion and, in particular, developing the anisotropic nonlinear hardening law. A characterization method using both uniaxial tensile and compressive tests at different strain rates was proposed to determine the material properties for the constitutive equation. Then, the developed constitutive equation was incorporated into a finite element code and was validated by comparing the finite element simulation of the three points bending test with experiments.     

Nonlinear constitutive models for FRP composites using artificial neural networks

This paper presents a new approach to generate nonlinear and multi-axial constitutive models for fiber reinforced polymeric (FRP) composites using artificial neural networks (ANNs). The new nonlinear ANN constitutive models are complete and have been integrated with displacement-based FE software for the nonlinear analysis of composite structures. The proposed ANN constitutive models are trained with experimental data obtained from off-axis tension/compression and pure shear (Arcan) tests. The proposed ANN constitutive model is generated for plane–stress states with assumed functional response in some parts of the multi-axial stress space with no experimental data. The ability of the trained ANN models to predict material response is examined directly and through FE analysis of a notched composite plate. The experimental part of this study involved coupon testing of thick-section pultruded FRP E-glass/polyester material. Nonlinear response was pronounced including in the fiber direction due to the relatively low overall fiber volume fraction (FVF). Notched composite plates were also tested to verify the FE, with ANN material models, to predict general non-homogeneous responses at the structural level.     

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.     

考虑双拉耦合的复合材料编织物各向异性超弹性本构模型

为了准确描述复合材料编织物的各向异性力学特性,首先,基于纤维增强复合材料连续介质力学理论提出了一种考虑纤维双拉耦合的复合材料编织物各向异性超弹性本构模型,该模型中单位体积的应变能被解耦为便于参数识别的纤维拉伸变形能、双拉耦合引起的挤压变形能和纤维间角度变化产生的剪切变形能;然后,给出了模型参数的确定方法,并通过拟合单轴拉伸、双轴拉伸和镜框剪切实验数据得到了本构模型参数;最后,利用该模型对双轴拉伸和镜框剪切实验进行了数值仿真,并将模拟结果与实验结果对比分析。结果表明:提出的本构模型适用于表征复合材料编织物在成型过程中由于大变形引起的非线性各向异性力学行为。所得结论表明提出的本构模型具有简单、实用的优点,且材料参数容易确定,可为复合材料编织物成型的数值模拟和工艺优化奠定理论基础。      

混杂纤维增强应变硬化水泥基复合材料的拉伸本构关系

钢纤维与聚乙烯醇纤维混杂增强应变硬化水泥基复合材料(SF-PVA/SHCC)的力学性能研究是近年来的热点问题之一,但目前依然欠缺能够完整描述SF-PVA/SHCC拉伸本构关系的理论模型。本文基于混凝土断裂力学和细观力学理论,通过考虑拉伸应力-应变曲线软化段及SF-PVA混杂纤维对SHCC拉伸性能的影响,提出一种新的可适用于SF-PVA/SHCC材料的单轴拉伸本构模型。为了验证模型的有效性,开展了SF-PVA/SHCC单轴拉伸性能试验,分析了纤维种类和掺量对SHCC拉伸强度、拉伸应变及拉伸韧性的影响。通过与试验数据对比发现,本文所提出的拉伸本构模型可以较好地预测SF-PVA/SHCC的拉伸应力-应变关系。      

Meso-Scale Progressive Damage Behavior Characterization of Triaxial Braided Composites under Quasi-Static Tensile Load

Based on continuum damage mechanics (CDM), a sophisticated 3D meso-scale finite element (FE) model is proposed to characterize the progressive damage behavior of 2D Triaxial Braided Composites (2DTBC) with 60° braiding angle under quasi-static tensile load. The modified Von Mises strength criterion and 3D Hashin failure criterion are used to predict the damage initiation of the pure matrix and fiber tows. A combining interface damage and friction constitutive model is applied to predict the interface damage behavior. Murakami-Ohno stiffness degradation scheme is employed to predict the damage evolution process of each constituent. Coupling with the ordinary and translational symmetry boundary conditions, the tensile elastic response including tensile strength and failure strain of 2DTBC are in good agreement with the available experiment data. The numerical results show that the main failure modes of the composites under axial tensile load are pure matrix cracking, fiber and matrix tension failure in bias fiber tows, matrix tension failure in axial fiber tows and interface debonding; the main failure modes of the composites subjected to transverse tensile load are free-edge effect, matrix tension failure in bias fiber tows and interface debonding.     

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。     

Evaluation of constitutive models for textured aluminium alloys using plane-strain tension and shear tests

The constitutive modelling of the strongly textured aluminium alloys AA6063-T6 and AA7003-T6 is studied. The materials were delivered in the form of flat extruded profiles. Plane-strain tension and shear tests in the plane of the flat profiles are performed. The tests are then used to evaluate a constitutive model including an anisotropic yield function, the associated flow rule and a nonlinear isotropic work-hardening rule. The parameters of the yield criterion and the work-hardening rule were identified primarily from uniaxial tension tests in different in-plane directions. It is suggested how analytical considerations and the results from the plane-strain tension and shear tests may be used to obtain a more accurate calibration of the anisotropic yield criterion. To further assess the constitutive model, finite element simulations of the plane-strain tension and shear tests are carried out and the results compared with the experimental force-elongation curves. Significant deviations in the experimental and predicted results are disclosed, and attributed partly to the parameter identification, primarily based on uniaxial tension tests, and partly to the assumption of isotropic work-hardening. Polycrystal plasticity calculations are carried out for simple shear of the AA7003-T6 material, indicating that texture evolution plays an important role in determining the response in this test already at moderate strains.     

Progressive damage modeling for large deformation loading of composite structures

A nonlinear constitutive model for large deformation loading at different strain rate condition was developed to represent tensile progressive damage of the nonlinear large deformation rate dependent behavior of polymer-based composite materials. The material was characterized by using off-axis composite specimens at different strain rates. A new failure criterion was proposed for the analysis of different loading directions and strain rates. Based on a method of combining the nonlinear constitutive theory and the proposed failure criterion for different strain rates, the progressive damage behavior of large deformation composites was represented. The strength of the material was also successfully represented with a single material constant.