电磁谐振式疲劳裂纹扩展试验固有频率跟踪系统

为保证电磁谐振式疲劳裂纹扩展实验工作载荷的稳定性,提出了基于裂纹长度在线测量的自适应改进爬山法固有频率跟踪方法,建立了相应的固有频率跟踪系统。采用自行设计的裂纹长度测量系统测得实验过程中不同时刻的裂纹长度,根据固有频率和裂纹长度的理论关系计算出此时系统的固有频率值,并将此值设定为频率跟踪的初始值,在初始值左右小范围区域内采用自适应改进爬山法搜索系统精确固有频率值。建立了双自由度双质量块电磁谐振式疲劳裂纹扩展实验振动系统数学模型和CT 紧凑拉伸试件刚度模型,从理论上推导出了固有频率随裂纹尺寸变化的规律,并通过实验进行了验证。实验结果表明:文中方法固有频率跟踪精度为0郾3 Hz,跟踪时间为3郾5 s,和一般爬山法相比,跟踪精度高、速度快、过程稳定可靠,很好地满足了疲劳裂纹扩展实验的要求。

Nature Frequency Tracking System for the Electromagnetic Resonance Fatigue Crack Propagation Test

A nature frequency tracking system based on the crack on-line measurement is established to ensure the stability of test load in the resonance fatigue crack propagation test, and its applied method which is an improved adaptive hill climbing nature frequency tracking method for crack length on-line measuring is proposed. First, the designed crack on-line measuring system is used to acquire the crack length, the related nature frequency is calculated according to the theoretical relationship between crack length and nature frequency, and then the theoretical nature frequency value is set as an original frequency point to track the accurate nature frequency. The accurate nature frequency near the original frequency point can be obtained by applying the proposed nature frequency tracking method. A vibrating system mathematical model with two degrees of freedom and double mass and a sample stiffness model are established, and the law of nature frequency changing with crack length is theoretically obtained and verified by experiment. The experimental results show that the nature frequency tracking accuracy is 0-3 Hz, the tracking time is 3-5 s, the proposed method has the higher tracking accuracy, faster tracking speed , and more stable and reliable tracking process compared with the general hill climbing nature frequency tracking method. It can meet the resonance fatigue crack propagation test requirements.