试样厚度对船用钢疲劳裂纹扩展速率影响的试验

为研究试样厚度对船用钢疲劳裂纹扩展速率的影响，设计并实施两组不同厚度的紧凑拉伸试样进行疲劳裂纹扩展速率试验，同时建立了三维疲劳裂纹扩展有限元模型，分别基于线弹性理论和弹塑性理论对应力强度因子进行了计算，并分析了试样厚度对裂纹扩展速率的影响。试验与计算结果的综合分析表明：相同应力水平下，薄试样裂纹尖端的塑性区明显大于厚试样，且裂纹尖端应力强度因子值大于理论经验计算结果可达23.25%，因此，在材料裂纹扩展速率试验前，特别是试样厚度尺寸较小时，应充分考虑试样的厚度效应，参考基于弹塑性理论计算得到的应力强度因子结果，同时有必要针对当前试样及材料进行专门的裂纹扩展速率试验，以得到准确裂纹扩展参数结果。

Experiment Study of the Specimen Thickness Effect on Fatigue Crack Growth Rate of Ship Hull Steel

In order to study the influence of the specimen thickness to fatigue crack growth rate (FCGR), two groups of Compact Tension specimens with different thickness were designed and the FCGR tests were conducted. The 3D fatigue crack growth finite element models for calculating SIF were established. Both linear elasticity theory and elastoplasticity theory are introduced to calculate the stress intensity factors. The influence of specimen thickness to FCGR was analyzed. According to the comprehensive comparison of test and calculation results, under the same stress level, the plastic zone at the crack tip of the thin specimen is obviously larger than that of the thick specimen. The stress intensity factor at crack tip of thin specimen is also larger than the theoretical experience calculated one, and the results can reach 23.25%. Therefore, the thickness effect should be fully considered and the stress intensity factor calculated based on the elastic-plastic theory should be consulted before the material crack growth rate test, especially when the thickness of the specimen is small. At the same time, it is necessary to carry out the crack growth rate test for current specimens in order to obtain accurate results of crack growth parameters.