DYNAMIC RESPONSE OF STRUCTURE CONTAINING CRACKS

Abstract

Structural faults are introduced in vibrating structures. If left unchecked, they may be lead to unexpected failures. For ensuring the safety and reliability of structure, the changes in its static and dynamic behaviour must be monitored with great care. These changes are often caused by local reduction of stiffness of the structure caused by defects in the structure. The presence of the crack does not necessary mean that the structure will collapse, but it is a signal that the behaviour of the structure should be monitored more carefully. An accurate prediction of the initiation of cracks and the subsequent monitoring of their behaviour play a significant role in ensuring the safety of the structure. Methods based on vibration responses (Modal analysis, frequency response functions (FRF's) etc.) are important tool for detecting damages and prediction of static and dynamic behaviour of structure. Modal parameters such as natural frequencies, magnitude of frequency response functions, displacement mode shapes and strain mode shapes can be obtained in terms of the crack present in the structure. It has been established that the surface crack in the structure affects most of the modal parameters, such as the natural frequencies of the structure, amplitudes of the response and mode shapes. This study presents a damage detection technique based on time response monitoring using contact element approach, which can identify damage in structures and may be implemented as a continuous structural health monitoring technique. The technique is based on breathing crack models, i.e. a crack which opens and closes during vibration. The present model takes care of transition stage of crack. Monitoring changes in time responses, natural frequency and mode shapes indicate the damage in Structure.