含剪胀效应界面张力-位移关系的一种构造方法

为了研究异种材料界面的开裂过程,在Srensen等人工作的基础上,给出一种含剪胀效应张力-位移关系的构造方法。在界面受拉状态下,通过预先给定的剪胀函数及法向张力-位移关系导出切向张力-位移关系;在界面受压状态下,将切向张力分解为粘结力和摩擦力,摩擦力的大小与法向压力和粘结界面的破坏程度相关。该方法的结果解释了Srensen模型中切向张力-位移关系不连续及其不符合一致关联准则的原因。为便于进行数值计算,给出了用于三维有限元模型的界面刚度矩阵计算方法。选取了一种特定形式的剪胀函数,并将法向张力-位移关系假定为分段线性形式和指数形式,分别求得对应的切向张力-位移关系。最后给出了两个工程应用的例子,数值模拟结果与试验数据吻合较好。     

CRTS Ⅱ型轨道板/CA砂浆界面内聚力模型研究

轨道板与CA砂浆层间离缝是CRTS Ⅱ型板式无砟轨道结构的主要病害之一。为描述轨道板-CA砂浆层间界面本构行为、揭示层间离缝机理,该文提出了一种改进指数型界面内聚力模型,并基于理论分析和试验数据确定了改进模型的参数取值。该模型为含有指数系数的分段函数,可以表征层间界面拉力-位移关系的非线性特征。研究结果表明:改进指数型内聚力模型可以高效计算轨道板-CA砂浆界面内聚强度、损伤萌生时界面相对位移和界面临界断裂能,结果与试验值基本一致;改进指数型模型可以较为准确地模拟轨道板-CA砂浆界面的法向和切向开裂行为。     

循环荷下层间界面反平面剪切破坏的解析解：2.再加载及综合响应分析

本研究利用“剪切梁”模型,研究了在定常侧压力和周期性的反平面剪切载荷共同作用下,层间界面的破坏规律。本文为本研究的第二部分。对应一个完整的载荷周期,解析地给出了界面层上剪应力及位移场在再加载过程中的分布规律及演化规律。计算结果表明,由于裂纹前方损伤过程区的存在,当再加载过程不能覆盖卸载过程造成的损伤区时,会产生新的“应力锁死”现象。文末对结构整体的载荷-位移行为的分析,揭示了周期载荷作用下的两种结构响应模式：1)接触塑性安定：2)增量破坏。     

岩体结构面切向循环加载本构关系研究

回顾岩体结构面切向循环加载的力学试验和数值模型,并建立新的本构模型。在粘接状态下,结构面切向本构关系表示为由双曲线和直线段组成的滞回曲线。在接触状态由粘接变为滑移的过程中,峰值摩擦角以双曲线函数逐渐降低至残余摩擦角,体现出峰值剪切特性。考虑结构面切向与法向耦合的剪胀关系,建立相应的接触刚度矩阵,并引入初始剪胀角和残余剪胀角来建立分段抛物线形式的剪胀曲线。循环加载导致的磨损对结构面的摩擦和剪胀特性均产生影响,通过以切向塑性功指数函数表示摩擦角和剪胀角的磨损过程。模型在物理意义上反映了切向循环加载的特性,计算结果能较好地拟合试验曲线。     

循环载荷下层间界面反平面剪切破坏的解析解:2.再加载及综合响应分析

本研究利用“剪切梁”模型,研究了在定常侧压力和周期性的反平面剪切载荷共同作用下,层间界面的破坏规律。本文为本研究的第二部分。对应一个完整的载荷周期,解析地给出了界面层上剪应力及位移场在再加载过程中的分布规律及演化规律。计算结果表明,由于裂纹前方损伤过程区的存在,当再加载过程不能覆盖卸载过程造成的损伤区时,会产生新的“应力锁死”现象。文末对结构整体的载荷－位移行为的分析,揭示了周期载荷作用下的两种结构响应模式：１）　接触塑性安定;２）　增量破坏。     

FRP-混凝土三点受弯梁损伤粘结模型有限元分析

该文采用双线形损伤粘结模型研究带切口FRP-混凝土三点受弯梁(3PBB)I型加载下的界面断裂性能。通过有限元参数分析,详细讨论了界面粘结强度、界面粘结能、混凝土抗拉强度、混凝土断裂能对3PBB受力性能的影响。数值模拟表明,FRP-混凝土界面有两种破坏形式,包括FRP-混凝土界面的损伤脱粘和界面混凝土的损伤脱粘破坏,与实验所观察到的现象一致。两种破坏形式尽管在宏观上均表现为界面脱粘,但破坏机制却不同。FRP-混凝土界面的损伤粘结模型与混凝土的拉伸塑性损伤模型相结合,不但再现了3PBB的宏观力学性能,数值分析得到的荷载-位移曲线接近实验结果,而且还能详细展示FRP-混凝土界面的损伤、断裂破坏过程以及损伤在FRP-混凝土界面和界面混凝土之间的转移,能够预测构件的承载力,有助于界面优化设计,这是单纯以能量判据预测裂纹发展的经典断裂力学方法所无法做到的。     

定侧压混凝土双压疲劳损伤模型

基于边界面概念和损伤力学理论,建立了一向定侧压混凝土双轴压各向异性损伤模型。加载面、边界面方程均以损伤能量释放率表示。在能量释放率空间内,由加载面与初始损伤面、边界面之间的位置描述损伤状态。通过建立累积损伤与相应循环损伤能量释放率阈值之间的关系,确定了疲劳加载中极限断裂面尺寸的变化规律,由此模拟混凝土在循环荷载作用下的刚度退化过程。结合已有的试验结果,确定了理论模型中的计算参数。经比较,理论模型预测的应力-应变数值、疲劳寿命和试验结果吻合较好。     

混凝土拉-压疲劳损伤模型及其验证

基于连续损伤力学理论,提出了混凝土单轴拉-压疲劳损伤模型。模型中采用了拉和压两个边界面。加载面、边界面方程均以损伤能量释放率表示。在能量释放率空间内,由加载面与初始损伤面、边界面之间的位置描述损伤状态。通过建立累积损伤与相应循环损伤能量释放率阈值之间的关系,确定了疲劳加载中极限断裂面尺寸的变化规律,由此模拟混凝土在循环荷载作用下的刚度退化过程。结合作者完成的疲劳试验结果,确定了理论模型中的计算参数。经比较,理论模型预测的应力-应变数值、疲劳寿命和试验结果吻合较好。     

岩石类脆性材料动态压剪耦合特性研究

岩石具有复杂的细微观结构,其宏观力学性能表现出明显的加载路径敏感性和应变率效应。应用基于改进的SHPB装置,对花岗岩、大理岩和砂岩等三类岩石进行了五种倾角的准静态和动态压剪联合加载实验,较系统地讨论了与岩石应力应变关系曲线的拟线性阶段的斜率、破坏强度等有关的加载路径敏感性和应变率效应。结果表明:岩石的法向模量、切向模量和破坏强度都有明显的压剪耦合效应(即加载路径敏感性)和应变率效应;比较而言,法向模量对剪切应力的依赖性强于剪切模量对法向应力的依赖性。基于Drucker-Prager(D-P)准则和考虑压剪耦合效应的修正的DP准则拟合岩石的动静态破坏面,拟合结果表明:岩石的内黏聚力有一定的应变率效应,内摩擦角的应变率效应不明显;修正的D-P准则可以描述压剪耦合效应。并探讨了大理岩的后继屈服面和岩石应力应变关系的描述问题。此研究提供了一种确定岩石动态强度参数的方法,表明进行压剪联合加载实验研究有助于揭示复杂应力状态下岩石的动静态力学性能。     

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。     

A calibrated frature process zone model for thin film blistering

The purpose of this work was to examine the feasibility of using fracture process zone models for extracting the adhesive fracture energy of thin films on a thick substrate from circular blister experiments that involve a substantial amount of inelastic deformation in the thin film. The interface produced by vapor depositing polyimide on aluminum formed the basis of the experiments that were conducted. The experiments were conducted in volume control while the pressure history and the corresponding three dimensional blister shape were measured. The analysis accounted for the nonlinear kinematics and material behavior of the polyimide film and included a traction-separation law for the interface. The traction-separation law for the interface was calibrated in an iterative manner by comparing measured pressure-volume responses and crack opening displacements. The adhesive fracture energy obtained from the selected traction-separation law was reasonable considering that fracture occurred in an interphase region. It was bounded by values that were obtained from elastic analyses (with updated kinematics) of the type performed by Gent and Lewandowski (1987) and Chu et al. (1992 a, b). This revised version was published online in July 2006 with corrections to the Cover Date.     

On the interfacial constitutive laws of mixed mode fracture with various adhesive thicknesses

Interfacial toughness and interfacial strength, as two critical parameters in an interfacial traction–separation law, have important effect on the fracture behaviors of adhesively bonded joints. In this work, the global and local fracture tests are employed to investigate the effect of adhesive thickness on interfacial energy release rate, interfacial strength, and shapes of the interfacial traction–separation laws under the mixed I/II mode loading condition. Basically, the measured interface laws based on the single leg bending (SLB) specimens reflect the equivalent and lumped interfacial fracture behaviors which include the cohesive fracture, damage and plasticity. Several new and interesting experimental results were obtained. The experimentally determined interfacial traction–separation laws may provide valuable baseline data for the parameter calibrations in numerical models. The current experimental results may also facilitate the understanding of adhesive thickness-dependent interface fracture of bonded SLB joints.     

Mixed mode cohesive law

A traction-separation relation to model the fracture process is presented. The cohesive law captures the linear elastic and softening behaviour prior to fracture. It also allows for different fracture parameters, such as fracture energy, strength and critical separation in different mode mixities. Thus, the fracture process in mode I (peel), in mode II (shear) or in mixed mode (a combination of peel and shear) can be modelled without the limitation of a common fracture energy in peel and shear. Examples are given in form of FE- implementations of the normalised cohesive law, namely for the Unsymmetrical Double Cantilever Beam (UDCB) specimen and the Mixed-mode double Cantilever Beam (MCB) specimen. Both specimens are adhesively bonded and loaded in mixed-mode.     

A Stochastic XFEM Model to Study Delamination in PPS/Glass UD Composites: Effect of Uncertain Fracture Properties

A nonlinear extended finite element (XFEM) modeling framework under a stochastic cohesive zone is presented for realistic prediction of delamination in polyphenylene sulfide (PPS)/glass composites in mode I of fracture. The cohesive zone model adopts damage evolution of the material based on a bilinear traction-separation law, the critical energy release rate and the J-integral method to formulate the delamination interface under stochastic fracture properties. To demonstrate the application of the approach, numerical predictions are compared to experimental data using Double Cantilever Beam (DCB) tests. In particular, it is shown how the XFEM model can be used to capture test non-repeatability due to uncertain fracture properties, which is often the case during the characterization of composites using standard fracture tests.     

界面脱粘对正交铺设SiC/CAS复合材料基体开裂的影响

采用细观力学方法研究了正交铺设SiC/CAS复合材料在单轴拉伸载荷作用下界面脱粘对基体开裂的影响。采用断裂力学界面脱粘准则确定了0°铺层纤维/基体界面脱粘长度, 结合能量平衡法得到了主裂纹且纤维/基体界面发生脱粘(即模式3)和次裂纹且纤维/基体界面发生脱粘(即模式5)的临界开裂应力, 讨论了纤维/基体界面剪应力、 界面脱粘能对基体开裂应力的影响。结果表明, 模式3和模式5的基体开裂应力随纤维/基体界面剪应力、 界面脱粘能的增加而增加。将这一结果与Chiang考虑界面脱粘对单向纤维增强陶瓷基复合材料初始基体开裂影响的试验研究结果进行对比表明, 该变化趋势与单向SiC增强玻璃陶瓷基复合材料的试验研究结果一致。     

分层界面角度对CFRP层板Ⅱ型分层的影响

Ⅱ型层间断裂韧度是复合材料结构损伤容限设计的关键力学参数。针对5种具有不同预置分层界面的国产T300复合材料端部缺口弯曲(ENF)实验件,开展Ⅱ型分层测试,获得预嵌薄膜末端开裂的Ⅱ型层间断裂韧度 G Ⅱc,NPC 和预开裂裂纹处扩展的Ⅱ型层间断裂韧度 G Ⅱc,PC 。结果表明:5种分层界面下 G Ⅱc,NPC 均比 G Ⅱc,PC 高,并且对于 G Ⅱc,NPC 值,0°/0°分层界面的最高,0°/90°分层界面的最低;而对于 G Ⅱc,PC 值,0°/45°分层界面的最高,0°/90°分层界面的最低。同时,采用虚拟裂纹闭合技术(VCCT)模拟不同分层界面处的Ⅱ型分层扩展,获得了分层扩展过程中分层前缘应变能释放率分布,结合实验结果分析了分层界面角度对Ⅱ型断裂韧度测量值的影响。     

Computational homogenization of discrete fracture in fibre-epoxy systems

In the present paper the effective mesoscale failure response of a fibre-epoxy sample is computed from its complex microscale fracture behaviour. The mesoscale failure response is represented by a traction-separation curve derived from numerically homogenizing the fracture response of a periodic fibre-epoxy microstructure loaded under uniaxial tension. The traction-separation curve can be applied in material points of interface elements that are used for simulating mode I mesoscopic fracture in macroscopic laminate failure problems. The effect of the size of the microscopic fibre-epoxy sample on the mesoscale failure response is examined, as well as the effect of local imperfections at fibre- epoxy interfaces.     

Numerical simulation of fatigue‐driven delamination using interface elements

This paper presents a computational technique for the prediction of fatigue‐driven delamination growth in composite materials. The interface element, which has been extensively applied to predict delamination growth due to static loading, has been modified to incorporate the effects of cyclic loading. Using a damage mechanics formulation, the constitutive law for the interface element has been extended by incorporating a modified version of a continuum fatigue damage model. The paper presents details of the fatigue degradation strategy and examples of the predicted fatigue delamination growth in mode I, mode II and mixed mode I/II are presented to demonstrate that the numerical model mimics the Paris law behaviour usually observed in experimental testing. Copyright © 2005 John Wiley & Sons, Ltd.     

Cohesive zone representations of failure between elastic or rigid solids and ductile solids

A cohesive zone model that describes tangential separation as well as normal separation along an interface is reviewed. The model is based on nonlinear traction-separation relations between the normal and tangential components of the interface tractions and relative displacements. To illustrate the application of the cohesive zone model in studies of material failure or crack growth, analyses of matrix-fibre debonding in metal matrix composites are presented, taking into account effects of residual stresses or of nonlocal plasticity for the matrix. Also studies of interface crack growth under mixed mode conditions are discussed.