孔边循环应变与疲劳循环次数相关性实验研究

Experimental Study on Correlation of Cyclical Strain on the Side of Hole with Fatigue Life Cycle

材料的应变疲劳寿命与裂端的塑性应变有关。研究孔边循环应变与疲劳循环次数的相关性,对于研究材料损伤及微裂纹的产生,预防宏观裂纹的产生及扩展具有十分重要的意义。所以本文对有限宽板中心带孔试件进行了拉伸疲劳试验,用以研究这种相关性。在疲劳试验前首先进行逐级的加、卸载缓慢循环实验,同时利用数字图像相关技术测量孔周的位移场,进而求出孔边应变。在疲劳试验过程中,每当疲劳循环1500次就停机,进行同样的缓慢循环实验,并测量出孔周的位移场及孔边应变。实验研究中获得了一些很重要的结果。

The strain-fatigue-life of materials is related to the plastic strain at the crack-tip. It is very important to study the correlation of cyclical strain on the side of hole with fatigue life cycle for understanding the material damage and micro-crack initiation, and for preventing macro-crack initiation and propagation. So the tensile fatigue tests of the limited width specimen with center-hole were performed for studying the correlation. Before fatigue tests, the gradual cyclic experiments by loading with the same increment step by step to the maximum and then unloading to zero step by step were carried out, the whole displacement distribution around the hole were measured by using digital image correlation, and the strains at the side of hole were calculated. In fatigue tests, the fatigue test was paused whenever fatigue life cycle was reached to 1500, then similar gradual cyclic experiment was retried, the displacement distribution around the hole and the strains at the side of hole were measured. Some significant results are gained in the study.