摘要
针对工程结构共振疲劳问题,提出一种激励频率跟踪随裂纹扩展变化的固有频率的加载方法,并对共振频带激励的裂纹悬臂杆进行理论分析。分析过程中,采用线性弹簧等效裂纹单元,复弹性模量考虑阻尼行为,得到考虑激励幅值、激励频率、阻尼以及裂纹长度等因素的动应力。利用Paris方程模拟裂纹扩展过程,分析阻尼对共振结构疲劳裂纹扩展寿命的影响。结果显示:裂纹扩展使结构共振频率下降;阻尼较小时,阻尼变化对疲劳裂纹扩展寿命的影响并不显著;阻尼达到一定值后,裂纹扩展速率迅速下降,可能发生止裂现象;越低阶模态振动,裂纹扩展速率越大,对应的疲劳裂纹扩展寿命越短。
According to the resonance fatigue problem of the engineering structure, the loading method for the natural frequency is proposed. The frequencies are changed with crack propagation by the excitation frequency based on the modified natural frequency equation, and the law of fatigue crack growth for the cracked cantilever beam under the longitudinal resonance is studied. The crack element is replaced by the linear spring and the damping loss factor is introduced by complex elastic modulus on vibration stress analysis. So that the loading amplitude and the crack length together with the excitation frequency and damping are considered in the dynamic stress. The Paris equation is used to simulate the crack prop- agation for analyzing the fatigue life of the cantilever beam. Results indicate that the propagating crack introduces the flexibility to the continuous system, thus resulting in gradual shifting away of the reso- nance result in smaller loading of the cracked section. This reduces, the growth rate to be dropped and brings eventually the system to a certain value of the crack propagation rate below a conventional thresh- old rate which can be interpreted as dynamic crack arrest. Different laws of the crack propagation on dif- ferent modes, thus the crack propagation speed on the low mode is faster than that of the high mode and that needs less time to spend for propagating certain crack length.
出处
《南京航空航天大学学报》
EI
CAS
CSCD
北大核心
2010年第3期298-302,共5页
Journal of Nanjing University of Aeronautics & Astronautics
关键词
振动疲劳
共振
阻尼
裂纹扩展
vibration fatigue
resonance
damping
crack propagation
