纤维增强复合材料界面疲劳裂纹扩展的模拟研究

脱粘是纤维增强复合材料界面裂纹扩展的主要表现形式.基于剪切筒模型和常用的实验加载方式,研究了纤维增强复合材料中纤维与基体界面在拉-拉循环荷载作用下的裂纹扩展.借助描述疲劳裂纹扩展的Paris公式,得到了疲劳裂纹扩展速率、扩展长度以及界面上摩擦系数与加载次数的关系.在分析中,考虑了疲劳加载引起的脱粘界面的损伤及损伤分布的不均匀性,同时还考虑了材料的泊松效应.     

界面性质对颗粒增强复合材料破坏模式影响的数值模拟分析

运用材料破坏过程分析M FPA2D 系统, 对颗粒增强复合材料的变形、损伤及破坏过程进行了数值模拟分析。主要分析了界面性质对破坏模式的影响。模拟结果表明, 增强颗粒与基体的界面对复合材料的宏观性能有很大影响。在理想界面条件下, 破坏模式以界面附近基体的破裂为主, 在非理想界面(且为弱界面) 条件下, 破坏模式以颗粒与基体的脱粘较为明显。      

短纤维复合材料宏微观内聚力模型参数测量的实验与数值混合法

提出了一种改进的实验与数值混合法。该方法采用随机短纤维增强复合材料的紧凑拉伸实验,首先得到材料的宏观内聚力模型,进而确定该材料纤维基体界面微观内聚力模型参数。通过有限元法和基于场投影的反解法得到了宏观内聚力模型结果,对比分析这两个方法的结果,得出该反解法对误差的容忍度较低。随后采用改进的反解法,用数字图像相关法(DIC)直接获取宏观内聚力模型分离量,减少了该反解法未知数的数量,提高了容错率。再将DIC和改进的反解法结合,对该材料裂纹尖端宏观内聚力区的牵引力进行了反解。采用双线性内聚力模型,根据Mori-Tanaka方法,将求得的宏观内聚力定律与纤维基体界面微观内聚力定律关联起来,从而求得了纤维基体界面微观内聚力模型参数。该方法和结果可为短纤维增强复合材料纤维基体界面的微观力学分析提供实验基础。     

短纤维增强金属基复合材料的多重损伤分析

用细观计算力学的方法分析了短纤维增强金属基复合材料(MMC)多重损伤的相互作用及对拉伸强度的影响。采用唯象的内聚力模型模拟界面的脱粘;G-T模型描述延性基体的损伤。在胞元模型的基础上研究了界面强度、纤维长径比等细观参数对材料损伤模式及强韧性的影响。研究表明,界面较弱时,损伤以界面脱粘为主,界面的强度决定了材料强度;当界面较强时,晶须将发生断裂,材料的最终强度由晶须的强度决定。不同界面强度条件下基体中损伤的分布不同。      

多轴向玻璃纤维增强树脂基复合材料的破坏特性和损伤机制

通过对玻纤增强环氧乙烯基酯树脂(GF/EVE)和玻璃纤维增强不饱和聚酯树脂(GF/UP)复合材料的多轴向铺层设计试件进行低速冲击、弯曲和剪切破坏性力学试验,分析了不同铺层方式的GF/EVE和GF/UP复合材料冲击、弯曲和剪切载荷作用下产生的损伤及失效模式。结果表明:在铺层设计与工艺相同的情况下,CF/EVE的弯曲强度、冲击韧性均优于CF/UP;[0,90]6试件冲击能量吸收性能优于其他五种铺层方式;铺设角设计、树脂基体类型、铺层厚度对层合板剪切力学性能的影响较小。并基于SEM与超声C扫描成像检测(C-SAM)对复合材料的微观界面脱粘机制及损伤演化行为进行阐释。     

聚合物基形状记忆合金复合材料研究进展

本文对聚合物基形状记忆合金复合材料的研究及应用进展进行了综述。着重介绍了该复合材料在结构设计、制备工艺技术以及应用等方面的研究成果以及发展概况,并对其发展前景进行了展望。     

树脂基复合材料抗弹性能数值模拟

使用ANSYS/LS-DYNA大型动力学有限元分析软件,采用正交各向异性材料模型、最大应力和CHANG-CHANG逐渐损伤破坏准则,对不同弹体、不同弹速条件下的芳纶纤维增强复合材料层压板的抗弹性能进行了显式有限元分析。计算结果和实测结果对比表明:在高速冲击条件下,抗弹极限(V50)的模拟计算结果和试验结果误差均在10%以内。说明数值模拟方法可以对复合材料抗弹性能进行有效评估和预测,达到减少实弹试验数量、节约经费、缩短研制周期的目的,研究成果有较高的工程实用价值。     

纤维增强复合材料的细观力学模型以及数值模拟进展

纤维增强复合材料是一类高比强度、高比刚度的新兴结构材料.开展该材料的强度分析和破坏过程模拟具有重要的科学意义和工程价值.介绍了纤维增强复合材料的细观力学模型的发展过程,综述了引入统计概念的复合材料力学行为有限元分析的研究现状,并展望了其发展趋势.     

纤维增强热塑性树脂基复合材料界面研究进展

纤维增强热塑性树脂基复合材料具有优良的耐化学药品性、生产周期短、可二次加工等特点,克服了热固性树脂基复合材料韧性差,断裂延伸率低,易发生早期应力开裂等缺点,可在使用环境苛刻,承载能力要求高的场合得到应用.本文从复合材料界面设计思想入手,评述了纤维/热塑性复合材料界面的最新研究进展,并结合剪滞法对微复合材料的界面测试方法进行了分析讨论.     

短纤维增强树脂基复合材料强度和模量的各向异性

研究了短纤维增强聚合物复合材料(SFRP)的强度和模量的各向异性。纤维的平均长度l_(mean)对纤维增强有效因子有很大的影响。在Φ=0°,纤维增强有效因子随着l_(mean)的增加而增加;当Φ=90°,纤维有效因子在Θ不太大时随着l_(mean)增加而增加,当Θ很大时,纤维有效因子值变成零。θ_(mean)对纤维有效因子也有很重要的影响。在Φ=0°,Θ不太大(<40°)时,纤维有效因子随着θ_(mean)增加而减小;而当Θ很大(>50°)时,则随着θ_(mean)的增加而增大。在Φ=90°,Θ不太大时,纤维有效因子随着θ_(mean)增加而减小;而当Θ很大时,纤维有效因子值为零。模式纤维长度对复合材料的强度无明显影响。大l_(mean)对应高的复合材料模量。当Θ接近60°时,平均纤维长度对模量的影响不大。模式纤维长度对模量的影响相对比较小,而对于一个很小的l_(mean),影响则比较明显。当Θ很小时,θ_(mean)值越小,模量值越高;相反,Θ很大时,θ_(mean)值越小,模量值越低。     

Simulation and analysis of shape memory alloy fiber reinforced composite based on cohesive zone model

Shape memory alloy (SMA) composite has been wildly used in engineering fields as a smart structure. The interface between SMA fiber and matrix plays an important role in determining the effective response of the composites, since it is the medium through which stress transfer occurs. Therefore, it is necessary to investigate how the variation of interfacial properties affects the overall behavior of the composites. In this paper, the interfacial shear strength and ultimate strength of composites are evaluated based on pull-out tests and uniaxial tensile tests, respectively. An algorithm for the automatic generation of unidirectional random distribution short-fiber reinforced composites is developed by using Monte-Carlo method and boundary condition control equation via ANSYS Parameter Design Language (APDL). Cohesive zone model (CZM) approach is used to characterize the interfacial traction separation relationships. Uniaxial tensile test is simulated using finite element method to study the overall macroscopic behavior of the composite through varying fiber ratios and ambient temperatures. The effects of interfacial debonding process, fiber ratios and ambient temperatures on the response of composites are discussed under the same fiber volume fraction.     

基于粘聚区模型的含填充区复合材料接头失效数值模拟

建立了Ⅰ型与Ⅱ型失效模式耦合的粘聚单元本构模型, 并通过模拟双悬臂梁实验进行了验证。将粘聚单元插入填充区任何2 个实体单元之间, 预测填充区的随机裂纹, 模拟了接头在拉伸载荷下的失效。计算了复合材料基体、界面胶膜、填充物3 者不同强度、填充区半径、填充物刚度等多种情况下接头的拉伸失效。计算结果表明: 复合材料基体、界面胶膜、填充物3 者的强度显著影响接头的承载能力与失效模式; 随着填充区半径增大, 结构承载能力也随之提高。试验结果验证了模拟结果。      

Application of cohesive zone model in crack propagation analysis in multiphase composite materials

A nonlinear cohesive stress distribution function is employed by relating the cohesive stress to the cohesive zone size (CZS) and the distance from the crack tip to investigate the elastic-plastic fracture behaviors. A crack-inclusion interaction problem is taken as an example to explore the fracture process in the cohesive zone area. The CZS and crack surface opening displacement are evaluated numerically. It is found that for different cohesive parameter combinations, the normalized CZS and crack surface opening displacements change drastically. By reducing the current model to the famous Dugdale model, the results obtained match well with the existing ones.     

基于小波内聚力模型的界面裂纹扩展

利用区间B样条小波良好的局部化性能,将内聚力模型（CZM）引入小波有限元法（WFEM）数值分析中,以区间B样条小波尺度函数作为插值函数,构造小波内聚力界面单元,推导了小波内聚力界面单元刚度矩阵,基于虚拟裂纹闭合技术（VCCT）计算界面裂纹应变能释放率（SERR）,采用β-Κ断裂准则,实现界面裂纹扩展准静态分析。将WFEM和传统有限元法（CFEM） 的SERR数值分析结果与理论解进行比较,结果表明:采用WFEM和CFEM计算的SERR分别为96.60 J/m2 和 101.43 J/m2,2种方法的SERR数值解与理论解相对误差分别为1.85%和3.06%,这明确表明WFEM在计算界面裂纹扩展方面能用较少单元和节点数获得较高的计算精度和效率。在此基础上,探讨了界面裂纹初始长度和双材料弹性模量比对界面裂纹扩展的影响,分析结果表明:界面裂纹尖端等效应力随界面裂纹初始长度的增加而增加;双材料弹性模量比相差越大,界面裂纹越易于扩展,且裂纹扩展长度也越大,因此可通过调节双材料弹性模量比来延缓界面裂纹扩展。      

一种改进的内聚力损伤模型在复合材料层合板低速冲击损伤模拟中的应用

针对传统内聚力损伤模型(CZM)无法考虑层内裂纹对界面分层影响的缺点,提出了一种改进的适用于复合材料层合板低速冲击损伤模拟的CZM。通过对界面单元内聚力本构模型中的损伤起始准则进行修正,考虑了界面层相邻铺层内基体、纤维的损伤状态及应力分布对层间强度和分层扩展的影响。基于ABAQUS用户子程序VUMAT,结合本文模型及层合板失效判据,建立了模拟复合材料层合板在低速冲击作用下的渐进损伤过程的有限元模型,计算了不同铺层角度和材料属性的层合板在低速冲击作用下的损伤状态。通过数值模拟与试验结果的对比,验证了本文方法的精度及合理性。     

The proper generalized decomposition for the simulation of delamination using cohesive zone model

The use of cohesive zone models is an efficient way to treat the damage especially when the crack path is known a priori. It is the case in the modeling of delamination in composite laminates. However, the simulations using cohesive zone models are expensive in a computational point of view. When using implicit time integration or when solving static problems, the non‐linearity related to the cohesive model requires many iteration before reaching convergence. In explicit approaches, an important number of iterations are also needed because of the time step stability condition. In this article, a new approach based on a separated representation of the solution is proposed. The proper generalized decomposition is used to build the solution. This technique coupled with a cohesive zone model allows a significant reduction of the computational cost. The results approximated with the proper generalized decomposition are very close the ones obtained using the classical finite element approach. Copyright © 2014 John Wiley & Sons, Ltd.     

A superimposed cohesive zone model for investigating the fracture properties of concrete–asphalt interface debonding

A cohesive zone model is proposed to simulate the interface debonding, a preponderant cause of failure for bonded concrete overlay of asphalt (BCOA). The model is constructed by superimposing four root models, each representing the mechanism of one subcritical failure at the interface zone observed in laboratory experiments. The model parameters are established through an inverse analysis of wedge splitting tests performed on BCOA specimens. These inputs are mainly a function of the materials at the interface zone, such as microtexture and macrotexture, and thus can be expected to be applicable to the numerical simulation of a full scale BCOA slab. For modeling across scales, the impact of specimen size, milling depth and initial flaw size on the model, in terms of peak traction and fracture energy, is also discussed.     

Prediction of interfacial fracture between concrete and fiber reinforced polymer (FRP) by using cohesive zone modeling

Interfacial debonding between concrete and fiber reinforced polymer (FRP) is investigated through integrating experiments and computations. An experimental program is designed to evaluate interfacial fracture parameters of mode-I through cutting and bonding specimens with an FRP sheet. The evaluated fracture parameters, i.e. the fracture energy and the bonding strength, are confirmed by predicting FRP debonding failure with the cohesive zone modeling approach. In the cohesive zone model, a traction-separation relation for FRP debonding is proposed with a shape index while providing various initial descending slopes. Computational results of the cohesive zone model agree well with three-point bending test results for both FRP debonding and plain concrete fracture. Furthermore, both experimental and computational results demonstrate that the fracture energy and the cohesive strength are essential fracture parameters for the prediction of FRP debonding behavior.     

Effect of residual stress on cleavage fracture toughness by using cohesive zone model

This study presents the effect of residual stresses on cleavage fracture toughness by using the cohesive zone model under mode I, plane stain conditions. Modified boundary layer simulations were performed with the remote boundary conditions governed by the elastic K‐field and T‐stress. The eigenstrain method was used to introduce residual stresses into the finite element model. A layer of cohesive elements was deployed ahead of the crack tip to simulate the fracture process zone. A bilinear traction–separation‐law was used to characterize the behaviour of the cohesive elements. It was assumed that the initiation of the crack occurs when the opening stress drops to zero at the first integration point of the first cohesive element ahead of the crack tip. Results show that tensile residual stresses can decrease the cleavage fracture toughness significantly. The effect of the weld zone size on cleavage fracture toughness was also investigated, and it has been found that the initiation toughness is the linear function of the size of the geometrically similar weld. Results also show that the effect of the residual stress is stronger for negative T‐stress while its effect is relatively smaller for positive T‐stress. The influence of damage parameters and material hardening was also studied.