基于红外热像法的AZ31B镁合金疲劳寿命预测

采用红外热像法测量AZ31B镁合金板材在疲劳过程中表面温度场的变化,结果表明,当疲劳载荷大于疲劳强度时,镁合金试样表面的温度变化经历5个阶段:温度上升阶段、温度下降阶段、稳定阶段、断裂前的温升阶段和断裂后温度下降阶段。通过疲劳过程中镁合金试样表面的温度变化规律,基于不同的理论提出了2种预测疲劳寿命的方法:由试验过程中试样表面温升(?TM)特征确定其疲劳寿命,?TM–Nf曲线拟合结果表明,?TM=3.89℃为温升极限值,即?TM>3.89℃时,试样会发生断裂,与实测疲劳试样的温升值(3.68℃)相比,误差为5.7%;利用能量法提出了镁合金疲劳寿命的计算公式,用能量法和传统试验方法分别绘制S-N曲线,结果具有很好的一致性,用2种方法分别计算了循环次数为1×107时的疲劳强度ΔσeΦ=99.3 MPa、ΔσeSN=99.8 MPa,误差为0.5%。采用红外热像法估算疲劳寿命具有简单、省时等优势。

Prediction of AZ31B Magnesium Alloy Fatigue Life Based on Infrared Thermography

The surface temperature field change of AZ31B magnesium alloy was measured by infrared thermography during fatigue testing. Fatigue life of an extruded AZ31B alloy was predicted using different methods. Results show that the temperature evolution mainly undergoes five stages when the cycle loading is higher than the fatigue strength: temperature rising, the steep decrease, the constant value on temperature, abrupt temperature rise before specimen fracturing and final temperature drop. According to the temperature field change law, two methods were proposed to predict the fatigue life. The fatigue lives are obtained according to the temperature rise characteristics (?TM) in the course of fatigue test. The curve of ?TM-Nf shows that ?TM=3.89 oC is the maximum temperature increment, i.e. failure will occur when ?TM is more than 3.89 oC, and compared with the measured 3.68 oC, the error is smaller, 5.7%. Energy method is used to determine the fatigue life and draws the S-N curve. Fatigue strength is 99.3 MPa from the curve, and the error is 0.5 % compared with the measured result 99.8 MPa. The method of infrared thermography is convenient and time saving for evaluating the fatigue life of magnesium alloy.