有机玻璃YB-DM-11的疲劳裂纹扩展特性研究

研究了试样类型、应力比对有机玻璃YB-DM-11疲劳裂纹扩展速率、疲劳裂纹扩展平均寿命的影响。结果表明：试样类型对有机玻璃疲劳裂纹扩展速率影响很小,但紧凑拉伸试样的寿命大于中心裂纹拉伸试样;对于中心裂纹拉伸试样,当应力比为正时,应力比增大,疲劳裂纹扩展速率增加,疲劳裂纹扩展平均寿命减小;应力比为负时,裂纹闭合效应导致裂纹扩展加速;负应力比时的裂纹扩展速率大于正应力比,但疲劳裂纹扩展平均寿命明显小于正应力比。     

16MnR钢表面裂纹的疲劳扩展

报告了在 P_x∶P_y=0,0.5和1三种双轴载荷作用下,对倾斜角等于0°、30°和45°的表面裂纹所作的疲劳扩展研究。讨论了表面裂纹扩展速率的计算方法,指出必须考虑不同的裂纹倾斜角和不同的双轴载荷比造成的裂纹扩展驱动力的变化对斜表面裂纹扩展速率的影响。因而采用裂纹投影法来处理斜表面裂纹的疲劳扩展问题并提出了修正的 Paris 方程。按照修正的 Paris 方程,根据不同的双轴载荷比和裂纹倾斜角分组整理了试验数据,并作了回归分析、假设检验,给出了含表面裂纹的16MnR 板材在三种不同的双轴载荷比情况下的裂纹扩展速率方程。     

07MnCrMoVR钢焊件疲劳裂纹扩展速率

为鉴定０７ＭｎＣｒＭｏＶＲ钢焊件的疲劳性能，通过试验得到了焊接接头以及焊接热影响区的疲劳裂纹扩展速率，同时给出了它们存活率为９７．７３％时的各自疲劳裂纹扩展速率，并对焊接接头与焊接热影响区疲劳裂纹扩展速率进行比较。最后还把结果与“在役含缺陷压力容器安全评定规程”［１］和ＢＳＩＰＤ６４９３［２］推荐结果进行了对比，认为该钢种疲劳裂纹扩展速率在其容许范围内慢于１６ＭｎＲ钢的疲劳裂纹扩展速率     

压力容器裂纹疲劳寿命预测的Pairs公式材料常数的相关性分析

介绍了计算疲劳裂纹亚临界扩展速率中常用的Pairs公式、最小二乘法的一般原理和相关系数r的概念。以07MnCrMoVR钢为例运用最小二乘法得出了lgC和m的线性关系,并利用相关系数r判断其相关程度,得出了两者具有极强相关性的结论。基于Pairs公式中材料常数m服从正态分布这一知识,利用lgC和m的线性关系以及正态分布的相关知识,参考压力容器安全评估的方法,探讨了对疲劳裂纹的亚临界扩展速率和疲劳寿命近似预测的方法。     

含裂纹压力容器的寿命预测方法研究进展

介绍了疲劳裂纹扩展速率计算的3个比较著名的公式以及公式中的各参数,尤其对应力强度因子K的计算进行了深入探讨;综述了概率统计应用于裂纹扩展计算的最新方法;介绍了新技术和压力容器寿命预测的结合。     

增压锅炉耐火砖疲劳裂纹扩展特性研究

基于陶瓷材料断裂力学理论,将影响疲劳裂纹应力强度因子的裂纹尺寸作为评价耐火砖安全使用的依据,通过研究陶瓷材料裂纹扩展的一般规律,建立了耐火材料的裂纹扩展模型,逐一计算两个影响因素对于裂纹应力强度因子的影响,得到裂纹尺寸与应力强度因子的关系曲线,可得出在一定范围内,裂纹应力强度因子随裂纹尺寸的增加而增加,但随后会逐渐降低,由此可预估含裂纹缺陷耐火砖的剩余使用寿命。     

链板式连续运输机械中焊趾表面裂纹扩展形态检测

针对链板式连续运输机械滚动压力增大引起的裂纹扩展问题，提出焊趾表面裂纹扩展形态检测方法，并应用到链板式连续运输机中。我们构建了焊趾表面裂纹图像的尺度空间函数，并计算特征点的梯度幅值与方向，完成焊趾表面裂纹区域的SIFT(Scale Invariant Feature Transform)定位。以裂纹区域定位结果为基础，明确扩展应力强度因子与能量释放之间关系，并引入裂纹开张比的概念，计算裂纹扩展的有效能量。根据裂纹纵、横比与深度比的关系，结合板厚得到裂纹半轴长度的函数关系，从而实现裂纹扩展形态的检测。以链板式连续运输机为例，实验结果表明，本文针对连续滚动机械设备裂纹区域的定位精度比传统的检测方法更高，且裂纹深度检测结果与实测结果基本一致，说明所研究检测方法的裂纹扩展形态检测性能得到了提升，具有较高的实际应用价值。     

轮胎橡胶材料裂纹开裂方向的研究

用断裂力学的方法分析了二维板状试样轮胎橡胶材料的裂纹扩展特性。建立了二维轮胎橡胶材料的有限元模型，用应变能密度这个参数模拟了试样承受单向拉伸时裂纹的扩展方向。模型中考虑了橡胶材料的非线性和不可压缩性，以及断裂奇异单元的收敛性。通过有限元分析，得出了橡胶材料单向拉伸时的裂纹扩展方向，并将计算结果与试验结果进行比较，两者吻合得很好。实验证明：应变能密度是解决橡胶断裂问题的一个有效参数。     

基于疲劳裂纹扩展理论的轮胎橡胶疲劳寿命预测

建立了轮胎断面模型和三维有限元模型,模拟了轮胎稳定滚动时断面上各部件橡胶材料的负荷情况。基于橡胶疲劳裂纹扩展理论和临界平面法,计算了轮胎模型滚动情况下橡胶材料的疲劳寿命,并研究了轮胎橡胶材料疲劳寿命随负荷的变化情况,同时比较了不同负荷下轮胎各部件橡胶材料疲劳危险点的分布。     

焊件疲劳裂纹扩展速率的预测

疲劳是工程中最常见的现象之一,焊件的疲劳裂纹扩展速率的研究为进行疲劳寿命预测提供了基础。本文通过对一定存活率下的疲劳裂纹扩展速率的预测回归分析,得到一个既准确又简便的方法求解 Paris 公式。     

Modelling Damage and Failure in Adhesive Joints Using A Combined XFEM-Cohesive Element Methodology

In recent years, cohesive elements based on the cohesive zone model (CZM) have been increasingly used within finite element analyses of adhesively bonded joints to predict failure. The cohesive element approach has advantages over fracture mechanics methods in that an initial crack does not have to be incorporated within the model. It is also capable of modelling crack propagation and representing material damage in a process zone ahead of the crack tip. However, the cohesive element approach requires the placement of special elements along the crack path and is, hence, less suited to situations where the exact crack path is not known a priori. The extended finite element method (XFEM) can be used to represent cracking within a finite element and hence removes the requirement to define crack paths or have an initial crack in the structure. In this article, a hybrid XFEM-cohesive element approach is used to model cracking in the fillet area using XFEM where the crack path is not known and then using cohesive elements to model crack and damage progression along the interface. The approach is applied to the case of an aluminium–epoxy single lap joint and is shown to be highly effective.     

基于分形理论和扩展有限元法的钢纤维混凝土损伤破坏机理

为研究钢纤维混凝土损伤破坏过程和裂纹发展演化机理,基于分形理论和扩展有限元法,建立钢纤维混凝土立方体抗拉试验细观有限元模型和切口梁三点弯曲试验有限元模型,以相关试验测试结果为基础,比较验证了所建有限元分析模型的可靠性。以裂纹分形维数表征钢纤维混凝土损伤演化过程,考察不同钢纤维体积掺量和长度、粗骨料形状等重要因素对钢纤维混凝土损伤演化过程的影响。结果表明,基于裂纹分形维数的损伤值可以较好地反映钢纤维混凝土的损伤演化过程及特征,钢纤维体积掺量、长度的增加和骨料形状的不规则化会延缓钢纤维混凝土立方体试件的损伤演化过程,钢纤维体积掺量、初始裂纹距跨中距离的增加和初始裂纹缝高比的减小可在较小程度上延缓钢纤维混凝土切口梁的损伤演化过程。     

Comparison of cohesive zone elements and smoothed particle hydrodynamics for failure prediction of single lap adhesive joints

This research investigates the use of a meshless smoothed particle hydrodynamics (SPH) method for the prediction of failure in an adhesively bonded single lap joint. A number of issues concerning the SPH based finite element modelling of single lap joints are discussed. The predicted stresses of the SPH finite element model are compared with the results of a cohesive zone based finite element model. Crack initiation and crack propagation in the adhesive layer are also studied. The results show that the peel stresses predicted by the SPH finite element model are higher and the shear stresses are lower than those predicted by the cohesive zone finite element model. The crack initiation and propagation response of the two models is similar, however, the SPH finite element model predicted a lower failure load than the cohesive zone finite element model. It is concluded that the current implementation of SPH method is a promising method for modelling cohesive failure in bonded joins but requires further development to allow for interfacial crack growth and better stress prediction under tensile loading to compete with existing methods.     

内压作用下斜接弯管纵向半穿透裂纹应力强度因子研究

采用三维有限元技术,应用ANSYS对内压作用下含纵向半穿透裂纹斜接弯管的应力强度因子进行了系统的分析。建立了三维有限元裂纹模型,对裂纹前沿应力强度因子的影响因素进行了研究,分析了不同内压下无量纲参数裂纹相对深度a/t、裂纹相对形状b/a、管壁相对厚度Do/t对应力强度因子的影响。     

Extension of a one-dimensional finite element model program for analysing elastic-plastic stresses and progressive failure of adhesive bonded joints

A program for stress analysis of adhesive bonded joints within an elastic range was extended to consider the elastic-plastic stress state in an adhesive layer and its progressive failure. The program is based on the one dimensional finite element method. The von Mises yield criterion and the Mohr-Coulomb failure criterion are used in the program. Numerical analysis of a single lap joint subjected to four-point bending load was conducted and its result was compared with the experimental result. Good agreements were obtained between both results except for the final failure load. The present extension has some advantages. The stress singularity in the adhesive layer at the lap end or crack tip can be avoided due to the simple assumption for adhesive strains. Shorter computing time by the present method than by other general two- or three-dimensional finite element model programs should be much emphasized as one of the advantages.     

Finite element analysis of failure mechanisms in HDPE/CaCo3 particulate composite

Abstract

A finite element analysis of crack propagation in an HDPE/CaCo₃ composite was carried out using a combination of the extended finite element method (XFEM) and the cohesive zone method (CZM). A unit cell of an entire composite consisting of one particle was chosen as the study zone. The interphase was assumed as a cohesive surface between the matrix and the particle. Variable parameters were the interface adhesion, position of initial crack, volume fraction, and size of the particle. The results showed that, the energy release rate increases when increasing the particle size. Increasing the volume fraction from 5 to 10% has positive effects in decreasing the strain energy release rate; however, the effects of 10 and 15% of volume fraction on the energy release rate are almost the same. Increasing the values of interfacial adhesion strength increases the strength of composite.     

Double cantilever beam fracture toughness measurement method for glass

A simple method of measuring Mode I fracture toughness, K_IC, of glass using the double cantilever beam (DCB) geometry is presented. An inert atmosphere is created at the crack tip to prevent subcritical crack growth and enable “pinning” the crack while the specimen is loaded to failure. This was achieved experimentally using liquid toluene or a glovebox with dry argon. K_IC values measured by this method showed good agreement with published literature values for selected glasses. Applicability of the analytical stress intensity factor solution based on crack length, crack front curvature, and the height of the crack guiding groove are confirmed through experimental data and finite element analysis. The experimentally observed crack front curvature, which leads near the edges for small groove heights and leads in the center for larger groove heights, is predicted from the geometry of the DCB specimen for a linear elastic solid through finite element modeling.     

3D microstructure model and thermal shock failure mechanism of a Si3N4-bonded SiC ceramic refractory with SiC high volume ratio particles

In this study, an efficient method was proposed to establish 3D microstructure model of a Si₃N₄-bonded SiC ceramic refractory with SiC high volume ratio particles and its failure mechanism under thermal shock was studied based on the established microstructure model. The proposed modeling method based on modified 3D Voronoi tessellation method and “precise shrinkage ratio method” was able to establish 3D geometric model of a SiC ceramic refractory with SiC high volume fraction particles more quickly than usual methods. The modified 3D Voronoi tessellation method generated Voronoi polyhedrons (VPs) limited in finite space perfectly. The proposed “precise shrinkage ratio method” achieved a precise volume fraction of SiC particles in the established microstructure model. The crack initiation and propagation under thermal shock were calculated by employing the extended finite element method (XFEM) on the established microstructure model. The results showed the failure mode on micro-scale clearly and efforts of interface strength on the failure mode were also explored. The proposed modeling method was especially suitable for establishing 3D microstructure models of ceramic composites or isotropic metal-ceramic particle composites with high volume fraction particles and extended the use of VPs.     

Role of bond thickness on adhesive failure

An analytical, numerical and experimental program is described which establishes the basic fracture mechanics properties of an adhesive joint. A finite element analysis of a homogeneous finite tapered double cantilever beam is first presented and the results compared with elasticity and strength of materials solutions. Using analytical results developed in another paper, a finite bond line thickness correction factor is introduced to determine the crack tip stress intensity factor as a function of crack length. An experimental program is described wherein the crack tip stress intensity factor for the cantilever beam adhesive joint is measured by the compliance method and the results compared with those obtained by analytical and numerical methods. Finally, the critical value of the adhesive crack tip stress intensity factor is determined using the analytical and experimental techniques presented.