Effect of residual stresses on crack behaviour in single edge bending specimens

Residual stresses due to manufacturing processes, such as welding, change the load bearing capacity of cracked components. The effects of residual stresses on crack behaviour in single edge bending specimens were investigated using Finite element analyses. Three parameters (J, Q and R) were used to study the crack behaviour. The J‐integral predicts the size scale over which large stresses and strains exist, the constraint parameter Q describes the crack‐tip constraint as a result of geometry, loading mode and crack depth and the constraint parameter R is used to describe the constraint resulting from residual stresses. To carry out a systematic investigation on the effect of residual stresses on the J‐integral and crack‐tip constraints, models under different combinations of residual stresses and external loads with different crack depths were analysed. It has been shown that the crack‐tip constraint R increased by tensile residual stresses around the crack‐tip. On the other hand, the constraint parameter R decreased and tended to zero at high external load levels.     

全自动引线键合机送丝系统受力模型及实验

丝线传输的阻力控制和张紧力控制是引线键合机送丝系统的关键技术之一,对键合质量有着重要的影响．为了解决当前全自动引线键合机送丝系统中的传输阻力大、传输张力不稳定等问题,根据引线键合工艺过程和系统的技术要求,设计了由气体导轨和真空张紧装置组成的低摩擦送丝系统,来实现金丝的低阻传输．建立了金线在气体导轨和真空张紧装置内的受力模型,得出了二者的控制参数与金线作用力的关系;分别对金丝在气体导轨和真空张紧装置内的受力模型进行了实验验证,实验结果表明达到了所要求的低摩擦力要求．     

包装机送丝导路结构分析与设计

介绍了冶金厂矿高温线材(小盘卷)在线快速包装中送丝导路的方案形成和工作原理,并从包装机送丝导路的理论探导入手,设计了相关参数,分析了导路结构,经样机试验和现场使用,该导路结构能满足打捆要求,达到了设计目的.     

Effect of a variation in material properties on the crack tip opening displacement

This paper investigates the effect of a variation in material properties on the crack tip opening displacement, a parameter often used in the prediction of fatigue and fracture. This situation is typical when a component is subjected to a relatively slow temperature fluctuation or the material properties undergo direct changes, such as due to a phase transformation. An analytical strip‐yield model is developed using the small‐scale yielding assumption and theory of complex potentials. Four cases of crack tip plasticity behaviour are identified for the different combinations of parameters controlling the variation in material properties. Results of calculations over a wide range of material properties are presented and show a significant effect on the crack tip opening displacement. Finite element simulations are conducted to verify the analytical findings. The implications of the outcomes in relation to several practical situations are also discussed.     

Elastic T stress estimates for circumferential surface‐cracked cylinders*

On the basis of detailed three‐dimensional (3D) elastic finite element (FE) analyses, this paper provides tractable approximations for elastic T stress solutions for circumferential inner‐surface cracks in cylinders. Internal pressure and global bending moment were considered. The FE model and analysis procedure employed in the analysis were verified using existing solutions for both elastic stress intensity factor and T stress. To cover a practical range, three different values of the ratio of the mean radius of cylinder to the thickness, R_m/t, were selected; furthermore, four different values of the ratio of the crack depth to the thickness, a/t, ranging from 0.1 to 0.75 and three different values of θ/π ranging from 0.1 to 0.4 were selected. On the basis of FE analyses results, polynomial approximations were proposed at three different locations: surface point, middle point and deepest point. On the basis of the detailed 3D elastic FE analysis, the solutions presented are believed to be the most accurate, and thus provide valuable information for structural integrity assessment considering a crack‐tip constraint.     

Fatigue growth prediction of center slant crack in rectangular plate

This paper presents a numerical prediction model of mixed‐mode crack fatigue growth in a plane elastic plate. It involves a formulations of fatigue growth of multiple crack tips under mixed‐mode loading and a displacement discontinuity method with crack‐tip elements (a boundary element method) proposed recently by Yan is extended to analyse the fatigue growth process of multiple crack tips. Due to an intrinsic feature of the boundary element method, a general growth problem of multiple cracks can be solved in a single‐region formulation. In the numerical simulation, for each increment of crack extension, remeshing of existing boundaries is not necessary. Crack extension is conveniently modelled by adding new boundary elements on the incremental crack extension to the previous crack boundaries. At the same time, the element characters of some related elements are adjusted according to the manner in which the boundary element method is implemented. As an example, the present numerical approach is used to analyse the fatigue growth of a centre slant crack in a rectangular plate. The numerical results illustrate the validation of the numerical prediction model and can reveal the effect of the geometry of the cracked plate on the fatigue growth.     

A numerical method for evaluation of J‐integral in plates made of functionally graded materials with sharp and blunt V‐notches

The main purpose of the paper is to propose a numerical method for evaluation of J‐integral in plates made of functionally graded materials (FGM) with sharp and blunt V‐notches under Mode I loading. The material properties have been assumed to be varied exponentially along the specimen width (notch direction). Using the proposed method, the effect of material gradient on the J‐integral for two cases of sharp and blunt V‐notches has been studied. The results have shown that in FGMs with sharp V‐notches, the J‐integral is not proportional to . So, the parameter J_L is path dependent. It has been observed that the material gradient has larger effect on the J‐integral in sharp V‐notch compared with that in blunt V‐notch.