地磁场环境下烧结钕铁硼疲劳破坏在线监测方法研究

Research on On-line Monitoring of Fatigue Damage for Sintered NdFeB Magnet in Geomagnetic Field

作为一种典型的硬磁材料,烧结钕铁硼在疲劳断裂时具有突发性、不确定性和紧迫性等特性,难以对其疲劳破坏变化过程进行在线监测.为了实现对烧结钕铁硼零构件在长期服役期间疲劳破坏全过程的在线监测,论文根据力磁耦合效应构建了地磁场环境下烧结钕铁硼的疲劳状态演变方程,将烧结钕铁硼的磁感应强度值作为描述疲劳破坏的状态参数.利用高精度测磁传感器采集微磁信号,通过获取的磁感应强度值对烧结钕铁硼疲劳破坏过程进行在线监测.疲劳试验结果表明:磁感应强度信号曲线的变化可以无失真地反映烧结钕铁硼在应力作用下产生疲劳破坏的全过程.同时,磁感应强度值与多项式拟合曲线之间的残差值变化趋势能够准确地预测烧结钕铁硼疲劳破坏过程中脆性疲劳断裂的产生.

The fatigue cracking of sintered NdFeB magnet,a typical hard magnetic material,is usually unexpected,uncertain,and urgent.Therefore,it is difficult to monitor its fatigue damage propagation process online.In order to realize the online monitoring of the whole process of fatigue damage for sintered NdFeB magnet during its service life,the fatigue state evolution equation of sintered NdFeB magnet in the geomagnetic field is constructed using the magneto-mechanical coupling effects.Within this theory,magnetic induction is used as the state parameter to describe the fatigue damage.The magnetic induction intensity in the weak magnetic field collected by a high-precision magnetic sensor is used to monitor the fatigue damage propagation process online.The fatigue test results show that fracture can be accurately predicted in time during the fatigue damage propagation process of sintered NdFeB magnet with the trends of magnetic induction intensity and residual value of the polynomial fitting curve.Furthermore,the variation of magnetic induction signal curve reflects the whole process of NdFeB fatigue damage propagation under stress without distortion.A long-term monotonic increase in the residual value means the growth of fatigue cracks in the sintered NdFeB magnet.Moreover,the sintered NdFeB magnet tends to induce fatigue fracture when the magnetic anomaly reaches its maximum value.Therefore,the proposed on-line monitoring method based on magnetic induction intensity can not only reflect stress concentration,but also monitor the brittle fracture of NdFeB magnet when fatigue failure occurs.Specifically,in the early stage,the accumulation process of fatigue failure can be qualitatively analyzed based on the variation trends of magnetic induction intensity.Then,in the fatigue failure stage,the sudden fracture can be timely captured by the maximum value of magnetic induction intensity.The method described in this paper realizes the in-service and real-time monitoring of sintered NdFeB mechanical components,for ensuring the safety and reliability of mechanical equipment.