20#钢构件应力疲劳检测的新技术及试验研究

Studies on new testing technique and experiment of stress fatigue damage for 20# steel component

灵敏微分磁导率检测技术是通过对试件微分磁导率极大值的检测,对构件的应力集中状况和疲劳损伤程度进行早期评价的新方法。研究分析了灵敏微分磁导率检测技术的相关基础问题,推导证明了检测信号与微分磁导率有关,分析了磁轭与待检试件之间的空气间隙及其变化对检测信号的影响。结果表明,检测信号可以正确反映待测试件微分磁导率的变化。研制了灵敏微分磁导率检测的试验平台,优化了激励频率。建立了检测信号与微分磁导率的关系算法,为信号的反演奠定了基础.试验发现,对20#钢构件,检测信号随拉应力的增加而减少,当拉应力超过屈服强度时,检测信号急剧下降;当卸载后测量残余应力对检测信号的影响时,拉应力在较小的应力范围增加时,检测信号几乎保持不变,当拉应力超过屈服强度时,检测信号急剧下降;疲劳对检测信号的影响与应力的影响相反,随着疲劳循环次数的增加和疲劳损伤程度的加深,检测信号逐渐增加.可见灵敏微分磁导率检测技术是一种新的可反映试件的受力状况、疲劳程度和受拉力历史的检测方法,具有广阔的应用前景。

Sensitive differential magnetic permeability testing technique is based on testing the maximum value of differential magnetic permeability,which is a new early evaluating method of stress concentration situation and fatigue damage degree for ferromagnetic component.The basic issues of the sensitive differential magnetic permeability detection technology were studied.It is deduced and proved that the testing signal is correlative to the differential magnetic permeability,the influences of air gap between the yoke and specimen and its variation on test signal were analyzed.The results show that the test signal can correctly reflect the change of differential magnetic permeability.A test detecting platform of the sensitive differential magnetic permeability was successfully developed,and the excitation frequency was optimized.The arithmetic of the relation between the test signal and differential magnetic permeability was established,which lays a foundation for the signal reversal.The experiment results show that for 20# steel,the testing signal decreases with the increasing of the stress.When the stress exceeds the yield intensity the testing signal decreases sharply.While studying the influences of remainder stress on testing signal in unloaded condition,when the stress increases in a small range,the testing signal almost remains constant,when the stress exceeds the yield intensity,the testing signal decreases sharply.The influences of fatigue on testing signal is just opposite to that of the stress,the testing signal will gradually increase with the increasing of the number of the fatigue cycles and the degree of the fatigue damage.Therefore,the sensitive differential magnetic permeability detection technology is a new kind of test technique,which can reflect the stress status,fatigue degree and stress history of the specimens,and has broad application prospect.