纤维增强橡胶复合材料界面力学性能有限元分析

基于剪滞理论,引入双线性内聚力模型研究了纤维与基体界面应力传递机理.采用ABAQUS模拟了非理想界面在单纤维拔出过程中的脱粘失效,分析了不同脱粘阶段界面剪应力分布情况,以及界面刚度和纤维长径比对界面应力传递和拔出载荷的影响规律.结果表明,在纤维受载失效过程中,纤维的拔出过程可分为4个阶段,即界面的完全粘结、损伤演化、逐渐脱粘、完全脱粘.界面的刚度和纤维长径比对界面应力传递与最大拔出力均有一定的影响.界面刚度、纤维长径比主要影响纤维的最大拔出载荷以及界面脱粘失效位移.     

基于弹性-塑性内聚力模型的纤维拔出界面宏观行为分析

用解析法分析了单纤维从聚合物基体中的拔出过程,采用弹性—塑性内聚力模型模拟裂纹的扩展和界面失效,确定了临界纤维埋入长度,该值区分两种不同长度的纤维拔出过程. 在纤维拔出过程,界面经历不同的阶段. 纤维埋长小于临界长度时,界面的脱粘载荷与纤维的埋长成正比;超过临界长度后,界面的脱粘载荷近似为常数. 分析了界面参数对脱粘载荷的影响:增加界面的剪切强度和界面的断裂韧性,或减小界面裂纹萌生位移,均能提高界面的脱粘载荷;界面脱粘后无界面摩擦应力时,拔出载荷—位移曲线的峰值载荷等于界面的脱粘载荷;界面摩擦应力存在时,使峰值载荷大于脱粘载荷,需要较长的纤维埋入长度和较大的界面摩擦应力.      

柔性基层合柱瞬态响应的有限元分析

良好的尺寸设计可优化结构的力学性能,为了研究几何参数对柔性基底结构抗冲击性能的影响,本文运用ABAQUS软件,计算了柔性基底层合柱受冲击载荷时的瞬态响应,对比分析了不同基底厚度、截面尺寸的柔性基底层合柱的动态力学性能。给出了层合柱上端面中心点的位移、速度、加速度等响应,以及接触面中心点处的应力、应变响应,发现冲击过程中柔性基层合柱出现了大变形。结果表明:柔性基底对中间层的缓冲保护起到了较大的作用,减少了冲击力对中间层的破坏;柔性基层合柱瞬态响应随基底厚度的增加而减小。均布载荷冲击下,截面尺寸为10mm或7.5mm的层合柱瞬态响应平缓且出现一定幅度的波动;截面尺寸为4mm、5mm、5.2mm层合柱出现失稳现象,发生失稳的时刻分别为7.8ms、11.4ms、13.6ms。     

弱界面端初始失效位置的试验初探

通过双材料受压试验研究了弱奇异性界面端的界面初始脱粘点的位置问题。实验材料采用钢和有机玻璃,根据弱奇异性要求和界面端应力分布特征,设计、制作了试件,并进行了初始脱粘实验。由实验发现楔形角为30°、45°和55°试件的界面初始脱粘点位置均在界面内部,脱粘是由有限应力引起的。63°是个临界角楔形角,大于63°试件,脱粘多会从界面端开始,即脱粘由奇异的界面应力引起的。此外界面正应力若为拉应力时,它对界面脱粘有很大的贡献。     

金瓷界面力学特性的数值分析

建立不同金属厚度的金瓷试件梁有限元力学模型,分析界面处应力分布,利用真实口腔修复体的金属和瓷的力学参数,分别对常用的三种不同厚度为基底的金属梁试件进行了瓷层以0.2mm为梯度进行加厚,计算各梁的界面应力和位移,同时也对力学性能较好的金属层和瓷层一组进行了全瓷梁应力、位移计算分析.为了更加真实的反映计算结果,部分试件的数值分析与实验进行了比较.通过分析比较,结果显示金瓷界面处应力较大,是脱剥瓷常发生部位;金属层较薄的烤瓷体有更高的韧性,力学性能较金属基底厚的有更强的抗脱瓷能力;金属作为基底大大提高了试件的抗弯曲能力,比全瓷梁更增强了试件破坏能力.     

纤维压出实验双向脱粘现象的数值研究

本文利用轴对称边界元程序，对影响纤维同界面剪面应力分布的材料和几何参数；纤维与基体的弹性模量比，纤维体积分数，试件厚度和支撑孔尺寸进行了数值分析工作，找出了纤维压出实验中导致界面双向脱粘的主要影响参数，给出了关于性暮一经和纤维体积分数的两界面端初始剪切脱粘的发生区域。     

混凝土断裂过程及尺寸效应分析

为研究混凝土裂纹断裂过程和最大承载力计算方法,通过实验机对四种不同尺寸混凝土紧凑拉伸断裂试件进行了加载过程实验,并对其中一个试件进行应变片跟踪测试.由实验结果分析得到了一系列关系曲线,如试件的载荷-加载点位移关系曲线,断裂损伤区变形随载荷变化曲线;并且计算了不同尺寸断裂试件的应力强度因子.结合计算粘聚裂纹应力强度因子的公式与断裂准则,完成了对承载力理论值的计算,并将其与实验峰值平均值进行对比,其结果是两者相比误差较小,表明此种计算裂纹结构最大承载力方法是可行的.     

纤维复合材料界面横向拉伸分析

以单纤维十字型横向拉伸试验为研究对象,对纤维/基体界面采用弹性-软化双线性内聚力模型,建立了纤维复合材料在横向拉伸作用下界面法向失效过程的解析模型。得到了沿纤维/基体圆周界面的法向应力分布,纤维/基体界面的状态与界面承载力和单纤维复合材料承载力的关系,以及内聚力参数和试件几何尺寸对它们的影响。结果表明:纤维/基体圆周界面在脱粘前经历全部弹性及弹性+软化两种状态;当界面为弹性状态时,界面法向应力随界面强度线性增加;当界面为弹性+软化状态时,界面软化范围随界面裂纹萌生位移的增加而增大;界面初始脱粘位置与拉伸荷载方向重合;界面初始脱粘时的界面承载力随界面强度及界面裂纹萌生位移的增加而增加,随界面裂纹生成位移的增加而降低;单纤维复合材料的脱粘荷载受基体截面尺寸的影响,当纤维体积含量相同时,沿荷载方向截面尺寸的增大对提高脱粘荷载更显著。     

微纳米尺度膜/基结构界面性能的实验研究

为了研究铜膜/有机玻璃结构的界面性能,首先对沉积在有机玻璃基底上300nm厚的铜膜进行了单轴压缩实验,部分区域的薄膜因屈曲而脱离基底。选择在膜/基粘接良好区域、膜/基脱粘区域分别进行等位移纳米压痕实验。利用膜/基粘接良好区域处硬度/弹性模量与压痕位移的关系来确定膜/基结构的临界脱粘位移。基于宏观力学中表征界面性能的能量法,利用两个区域等位移的塑性功差值来确定界面能量释放率。研究结果表明:当压痕位移约450nm时,膜/基结构开始出现界面脱粘,实验测得铜膜/有机玻璃结构的界面能量释放率值在6.81~10.32J/m2之间。     

冲击载荷下钨合金圆台试件绝热剪切变形局部化的数值模拟

采用有限元计算编码ABAQUS模拟了钨合金圆台试件在冲击载荷下的变形和剪切局部化行为.计算采用二维轴对称应变条件下的绝热模型.钨合金的本构方程采用热粘塑性形式的Johnson-Cook模型.为了得到不同尺度的变形信息,计算中用了两种网格;先用粗糙网格分析试件变形局部化的概貌;接着,用细密网格(在变形局部化区域,网格尺寸达到10μm)分析绝热剪切带的形成和发展.有限元模拟得到的绝热剪切带位置和方向与实验一致.计算结果表明,绝热剪切带的形成和发展与试件的应力状态密切相关.     

Interfacial stress analysis and prediction of debonding for a thin plate bonded to a curved substrate

This paper focuses on the analytical and numerical modeling of the interface between a rigid substrate with simple constant curvature and a thin bonded plate. The interfacial behavior is modeled by independent cohesive laws in the normal and tangential directions, coupled with a mixed-mode fracture criterion. The newly developed analytical model determines the interfacial shear and normal stress distributions as functions of the substrate curvature, during the various behavioral stages of the interface prior to the initiation of debonding. The model is also able to predict the debonding load and the effective bond length. In the numerical model the interface is modeled by zero-thickness node-to-segment contact elements, in which both the geometrical relationships between the nodes of the discretized problem and the interface constitutive laws are suitably defined. Numerical results and comparisons between the predictions of the two models are presented.     

Debonding of FRP-plated reinforced concrete beam,a bond-slip analysis. I. Theoretical formulation

External bonding of FRP plates or sheets has emerged as a popular method for strengthening reinforced concrete. Debonding along the FRP–concrete interface can lead to premature failure of the structure. In this study, a bond-slip model is established to study the interface debonding induced by a flexural crack in a FRP-plated concrete beam. The reinforced concrete beam and FRP plate are modeled as two linearly elastic Euler–Bernoulli beams bonded together through a thin layer of FRP–concrete interface. The interface layer is essentially modeled as a large fracture processing zone of which the stress–deformation relationship is described by a nonlinear bond-slip model. Three different bond-slip models (bi-linear, triangular and linear-damaging) are used. By dividing the debonding process into several stages, governing equations of interfacial shear and normal stresses are obtained. Closed-form solutions are then obtained for the interfacial shear and normal stresses and the deflection of the beam in each stage of debonding. In such a way, the proposed model unifies the whole debonding process, including elastic deformation, debonding initiation and growth, into one model. With such a superior feature, the proposed model provides an efficient and effective analytical tool to study FRP–concrete interface debonding.     

固化温度对碳纤维/环氧基体界面行为影响的分析

对界面粘结性能及热残余应力影响下的单纤维复合材料的界面行为进行了分析。采用界面的弹性-软化内聚力模型,用解析法对单纤维复合材料由固化引起的热残余应力、以及单纤维碎断过程纤维的轴向应力分布进行了模拟,得到了碳纤维/环氧树脂在常温和高温固化两种情况的界面粘结性能。结果表明：与常温固化相比,高温固化后,界面的剪切强度增幅不大,界面的断裂韧性显著增加;高温固化后形成的界面,使界面的软化提前、界面的脱粘延迟;高温固化产生的纤维轴向和界面径向热残余应力对界面的软化均有延迟作用;界面径向热残余应力还对界面的脱粘有延迟作用。     

Delamination of an elastic film from an elastic–plastic substrate during adhesive contact loading and unloading

Adhesive contact between a rigid sphere and an elastic film on an elastic–perfectly plastic substrate was examined in the context of finite element simulation results. Surface adhesion was modeled by nonlinear springs obeying a force-displacement relationship governed by the Lennard–Jones potential. A bilinear cohesive zone law with prescribed cohesive strength and work of adhesion was used to simulate crack initiation and growth at the film/substrate interface. It is shown that the unloading response consists of five sequential stages: elastic recovery, interface damage (crack) initiation, damage evolution (delamination), film elastic bending, and abrupt surface separation (jump-out), with plastic deformation in the substrate occurring only during damage initiation. Substrate plasticity produces partial closure of the cohesive zone upon full unloading (jump-out), residual tensile stresses at the front of the crack tip, and irreversible downward bending of the elastic film. Finite element simulations illustrate the effects of minimum surface separation (i.e., maximum compressive surface force), work of adhesion and cohesive strength of the film/substrate interface, substrate yield strength, and initial crack size on the evolution of the surface force, residual deflection of the elastic film, film-substrate separation (debonding), crack-tip opening displacement, and contact instabilities (jump-in and jump-out) during a full load–unload cycle. The results of this study provide insight into the interdependence of contact instabilities and interfacial damage (cracking) encountered in layered media during adhesive contact loading and unloading.     

Theoretical analysis on the local critical stress and size effect for interfacial debonding in particle reinforced rheological materials

The mechanisms of interfacial debonding of particle reinforced rheological materials are studied. Based on an energy criterion, a simple formula of local critical stress for interfacial debonding is derived and expressed in terms of the interfacial energy. The particle size effect on interface debonding can then be analyzed easily owing to the fact that critical stress is inversely proportional to the square root of particle radius. By taking PP/CaCO₃ system as an example, the present energy criterion is compared with the mechanical debonding criterion, and it is found that under the condition that bond strength is equal to matrix strength and particle radius not over 0.2μm, the mechanical debonding criterion can be automatically satisfied if the energy criterion is satisfied. A relation between critical time and interface energy is calculated by using the energy criterion. The influences of the particle volume fraction and the parlicle size, the loading rate and the relaxation time of the matrix on the critical time of interfacial debonding are also discussed. Supported by the National Natural Science Foundation of China (19632030 and 19872007) and Natural Science Foundation of Jiangsu Province.     

INTERFACIAL BEHAVIOR OF PIPE JOINTS UNDER TORSION LOADS

The interfacial behavior of pipe joints is studied in this paper. Firstly, through nonlinear fracture mechanics, the analytical expressions of interfacial shear stress and the loaddisplacement relationship at loaded end of pipe joints under torsion loads are obtained. Thus the shear stress propagation and the debonding process of the whole interface for different bond lengths can be predicted. Secondly, through the analytical solutions, the influences of different bond lengths on the load-displacement curve and the ultimate load are studied. The stress transfer mechanism, the interface crack propagation and the ductility behavior of the joints can be explained.     

微粒填充流变材料界面开裂的局部临界应力及尺寸效应的理论分析

研究了以等轴粒子填充流变材料的边界开裂机理，采用能量准则导出了以界面能表示的界面开裂局部临界应力的简洁表达式。由于临界应力正比于１√α，从而可以非常方便地研究粒子开裂的尺寸效应，以碳酸钙微粒填充的聚丙烯复合材料为例进行了理论分析，通过比较界面开裂的能量准则和张应力准则得出结论：即使按照保守的方法估算，即在界面强度等于基体强度的条件下，只要粒径不超过０．２微米，若能量准则得到满足，则张应力准则也会得