厚钢板疲劳裂纹扩展前缘应力状态试验与数值仿真

复杂的环境载荷不可避免地会造成海洋结构物的疲劳损伤,而高强度厚钢板典型的三向应力状态会增加结构脆性,更加缩短结构的疲劳寿命。为研究厚板裂纹前缘应力状态沿板厚方向的分布,完成了3组36 mm板厚Q370QE高强度钢的标准疲劳裂纹扩展速率试验,得到了材料参数C,m以及应力强度因子门槛值。接着,应用有限元方法分别基于线弹性分析和塑性分析计算裂纹尖端应力强度因子和裂纹尖端局部约束因子,并解释试验中裂纹前缘由倾斜趋于平直的现象。计算所得裂纹尖端应力强度因子可描述板厚中心部分裂纹前缘的应力状态,但在试件表面处结果失真,而裂纹前缘局部约束因子因考虑了厚板的厚度效应,故沿板厚方向分布的裂纹尖端局部约束因子可有效量化裂纹尖端的应力状态分布。

Investigation on the stress state along the crack front in the fatigue crack growth rate test for thick high strength steel plates

Complex environmental loads would unavoidably lead to the fatigue damage in marine structures, and the case worsens in high strength steel thick-welded structures which have typical tri-axial stress and the feature of brittleness.To study the stress state along the crack front, a standard fatigue crack growth rate test for high strength steel Q370QE with a thickness of 36 mm is conducted, and the corresponding material parameters and the threshold of stress intensity factor are obtained.Next, the abnormal behavior of a crack front during crack growth and the stress state along crack front during crack growth are analyzed with the finite element method.Accordingly, the varying tendency of crack front shape could be qualitatively defined.Finally, local constraint factors are introduced in order to quantitatively describe the stress state along the crack front with the growth of fatigue crack based on plasticity analysis, which provides proper explanation to why the crack front changes from slant to flat with the crack growing.The calculated stress intensity factor could only describe the stress state in the center area, but distortion is inevitable on the surface, while the local constraint factor can fully describe the stress state along the crack tip zone.