基于红外热成像的镁合金疲劳裂纹扩展的研究

采用红外热成像技术监测疲劳裂纹扩展过程中试件表面温度的变化情况,对AZ31B镁合金板材室温下的疲劳裂纹扩展特征进行研究。分析疲劳裂纹尖端温升值与裂纹长度的对应关系,试件表面温度分布差异与裂纹扩展趋势的关系,探索镁合金材料疲劳裂纹扩展的规律。试验结果表明,疲劳裂纹扩展过程中,镁合金表面温度变化经过一个升温、降温的过程,在稳定扩展阶段,温度变化不大,在快速扩展阶段,温度呈明显上升趋势。三组试件最高温升值分别为A试件10.89℃、B试件15.19℃、C试件12.37℃。裂纹尖端及其附近组织观察发现,裂纹尖端发生转向,裂纹总体为穿晶断裂,并伴随少量沿晶断裂,在裂纹附近区域有少量塑性变形。疲劳试件表面的最高温度区域与材料的疲劳损伤机制相关,该区域对应材料的应力集中区,是疲劳微裂纹形成与扩展的部位,温度变化与试件的最终断面相吻合。

Study on Fatigue Crack Propagation of AZ31B Magnesium Alloy Based on Infrared Thermographic Technology

Fatigue crack propagation of AZ31B magnesium alloy in room temperature is studied.And the temperature on the surface of the samples is tested by infrared thermographic technology.The mechanism of magnesium crack propagation is studied according to the relationship between the temperature of crack tip and crack length,and the relationship between temperature distribution on the surface and the trend of crack propagation in this test.Results show that the temperature on the surface of the samples increases in the beginning and then decreases during the process of fatigue crack propagation,the temperature changes a little in the stabilize phase and obviously in the rapid phase.The highest temperature rise of three group samples is sample A 10.89 ℃,sample B 15.19 ℃ and sample C 12.37 ℃.By observing the crack tip and vicinity region of crack tip,the orientation of crack tip changed,most of the crack is transgranular fracture with some intergranular fracture.There is some plastic deformation in the vicinity region of crack tip.The maximum temperature area on the surface of samples is related to the damage mechanisms of materials.This area corresponding to the stress concentration zone,it is the site of which the fatigue micro-crack formation and expansion,the temperature change and the final section of the specimen is consistent.