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An Analysis on Multiaxial Loading Fatigue through Constitutive Equation Derived in Terms of Dislocation Dynamics

基于位错动力学推导的本构方程分析多轴加载疲劳

基本信息

批准号：
11450046
负责人：
HATANAKA Kenji
金额：
$ 9.6万
依托单位：
Ube National College oft, Technology (2001)Yamaguchi University (1999-2000)
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2001
项目状态：
已结题

项目摘要

Multiaial stress is induced around stress-concentrated location such as notch root and crack tip. In the present study, the cyclic strain, crack opening displacement and cyclic stress-strain response were calculated in the vicinity of crack tip by means of elastic-plastic finite element method in annealed copper, where the constitutive equation derived from using the concept of dislocation dynamics was employed. Furthermore, strain was measured by the grid method : the displacement of the grid was measured through the laser microscope observation around the crack tip.Firstly, the analysis was made for the cyclic deformation around the crack tip in the through-thickness center-cracked specimen subjected to the model loading.Secondly, the similar calculation was achieved for the pre-cracked compact tension/shear specimen under the mode II loading.Main results obtained are summarized as follows.(1)Load-displacement response calculated for the through-thickness center-cracked specimen under the mode I loading expressed well the cyclic hardening behavior in the early cyclic deformation process, being in good agreement with the experimental data.(2)The measured crack opening displacement tends to reach the stabe state through it's early increasing stage under the load-controlled condition, which is well expressed by the calculation.(3)The variation range of the cyclic strain during one load cycle and the amount of strain concentration tend to decrease with increasing number of cyclic loading around the crack tip. The Calculation describes quite well such cyclic strain behaviors.(4)The strain calculated around the crack tip in the compact tension/shear specimen subjected to the mode II loading developes in the diredction of θ=0゜just ahead of the crack tip and in the direction of θ= -30゜ in the region distant from the crack tip.

在缺口根部和裂纹尖端等应力集中部位产生多点应力。采用位错动力学的概念推导出的本构方程，采用弹塑性有限元法计算了退火铜裂纹尖端附近的循环应变、裂纹张开位移和循环应力应变响应。此外，通过网格法测量应变：通过激光显微镜观察裂纹尖端附近网格的位移，首先分析了中心穿透裂纹试件在模型载荷作用下裂纹尖端附近的循环变形，其次，对Ⅱ型加载下的预裂纹紧凑型拉剪试件进行了类似的计算，所得主要结果如下。（1）对中心穿透裂纹试件在Ⅰ型载荷作用下的载荷-位移响应进行了计算，计算结果较好地反映了循环变形早期的循环硬化行为，与试验结果吻合较好。（2）在荷载控制条件下，实测裂纹张开位移经过早期的增长阶段，趋于稳定状态，计算结果与实测值吻合较好。（3）随着循环加载次数的增加，裂纹尖端周向应变的变化范围和应变集中量有减小的趋势。该计算很好地描述了这种循环应变行为。（4）在Ⅱ型载荷作用下，计算得到的紧凑型拉剪试件裂纹尖端附近的应变沿裂纹尖端正前方θ=0 °方向发展，而远离裂纹尖端的区域沿θ= -30 °方向发展。