棘轮应变累积广泛存在于压力容器和管道轮轨接触疲劳、紧固连接和密封技术等工程问题中，是工程设计中必须考虑的重要因素。棘轮可以表现为单轴棘轮效应或多轴棘轮效应，材料的棘轮效应或结构的棘轮效应，本文介绍近年来棘轮效应的最新研究进展，对近年提出的描述材料棘轮效应的循环本构理论作了较详细的评述，对模型的预测能力和存在的问题进行了讨论，并对今后的工作提出了建议。

This paper evaluates the performance of four Ohno-Wang type constitutive models in predicting ratcheting responses of medium carbon steel S45C for a set of axial/torsional loading paths. Suggestions are also made for further modification. The four models are the Ohno-Wang model, the McDowell model, the Jiang-Sehitoglu model and the AbdelKarim-Ohno model. It is shown that the Ohno-Wang model and the McDowell model overestimate the multiaxial ratcheting. Whereas, the Jiang-Sehitoglu model yields good predictions for most loading conditions used in this study with an appropriate modification of the dynamic recovery term. The AbdelKarim-Ohno model gives acceptable predictions for all considered multiaxial conditions when used with an evolution function for li, but gives poor predictions of uniaxial ratcheting if the parameter li is determined from a multiaxial ratcheting response. A new modified Ohno-Wang hardening rule is proposed for better adaptability under diverse situations by multiplying a factor to the dynamic recovery term, which is dependent on noncoaxiality of the plastic strain rate and back stress. This new model predicts ratcheting strain reasonably well for the test cases.

A modified kinematic hardening rule is proposed in which one biaxial loading dependent parameter δ'0 connecting the radial evanescence term [(α:n)ndp] in the Burlet-Cailletaud model with the dynamic recovery term of Ohno-Wang kinematic hardening rule is introduced into the framework of the Ohno-Wang model. Compared with multiaxial ratcheting experimental data obtained on 1Cr18Ni9Ti stainless steel in the paper and CS1026 steel conducted by Hassan et al. [Int. J. Plasticity 8 (1992) 117], simulation results by modified model are quite well in all loading paths. The simulations of initial nonlinear part in ratcheting curves can be improved greatly while the evolutional parameter δ'0 related to plastic strain accumulation is added into the modified model.

Solder joint fatigue failure is a serious reliability concern in area array technologies, such as flip chip and ball grid array packages of integrated-circuit chips. The selection of different substrate materials could affect solder joint thermal fatigue life significantly. The mechanism of substrate flexibility on improving solder joint thermal fatigue was investigated by thermal mechanical analysis (TMA) technique and finite element modeling. The reliability of solder joints in real flip chip assembly with both rigid and compliant substrates was evaluated by accelerated temperature cycling test. Finite element simulations were conducted to study the reliability of solder joints in flip chip on flex assembly (FCOF) and flip chip on rigid board assembly (FCOB) applying Anand model. Based on the finite element analysis results, the fatigue lives of solder joints were obtained by Darveaux s crack initiation and growth model. The thermal strain/stress in solder joints of flip chip assemblies with different substrates were compared. The results of finite element analysis showed a good agreement with the experimental results. It was found that the thermal fatigue lifetime of FCOF solder joints was much longer than that of FCOB solder joints. The thermal strain/stress in solder joints could be reduced by flex buckling or bending and flex substrates could dissipate energy that otherwise would be absorbed by solder joints. It was concluded that substrate flexibility has a great effect on solder joint reliability and the reliability improvement was attributed to flex buckling or bending during temperature cycling.

A series of multiaxial low-cycle fatigue experiments was performed on 45 steel under non-proportional loading. The present evaluations of multiaxial low-cycle fatigue life were systematically analysed. A combined energy density and critical plane concept is proposed that considers different failure mechanisms for a shear-type failure and a tensile-type failure, and from which different damage parameters for the critical planestrain energy density are proposed. For tensile-type failures in material 45 steel and shear-type failures in material 42CrMo steel, the new damage parameters permit a good prediction for multiaxial low-cycle fatigue failure under non-proportional loading. The currently used critical plane models are a special and simple form of the new model.