Transient Response Of Structures With Cracks And Crack Identification

Cracks present a serious threat to the performance of structures since most of the structural failures are due to material fatigue. For this reason, methods allowing early detection of cracks have been the subject of intensive investigation, which help management the structure and reducing the cost of refinement. Defects in the structure will cause some changes in the dynamic character, such as frequency, mode shape and damp, which can be used to indicate the state of the structure.In this paper, transient response of structures with cracks and crack identification are studied. First it changes the question of transient response into a frequency-domain question by using Fourier Transform, second the injury unit stiffness matrix based on line-spring model and dynamic stiffness FEM equations can be derived according to the fracture mechanics theory, the solutions of the equations will be the response of structures with cracks in a frequency-domain. The inverse Fourier Transform gives the transient response of structures. The transient response of three typical structures will be discussed, and the effects of crack location, severity of cracks and multiple cracks on the dynamic behaviors will be analyzed.Wavelet analysis can characterized local features of space, frequency domain signal make it a way to identify injury. According to the singularity of wavelet theory the non-consecutive points and its derivative of non-consecutive points of a signal can be identified. Finally in this paper wavelet analysis are used to analysis the difference of displacement response between damaged and undamaged structures.