A study of dynamic characteristics for crack identification

Experimental modal analysis has become a commonly-used technique for studying the dynamical behaviour of mechanical and civil structures. During a modal test, both the applied forces and vibration responses of the structure are measured when excited in one or more locations. Based on this data, a modalmodel of the structure, that essentially contains the same information as the original vibration data, is derived by means of system identification. The objective of this project is to detect crack using dynamic characteristics. Four set of specimen were tested with three of them have a different depth of crack which is 10%, 20% and 50%. The healthy specimen was used as baseline data to compare with the crack specimen. The aim of this thesis was to use the modal testing methods as a starting point to develop more advanced modal parameteridentification techniques.The data was collected usingDasylab software with a specified block diagram. First, the data of the beam will be used to simulate in the Algorsoftware in order to determine the natural frequency and mode shape of the beam. Experiment was done and the data will analysed by using ME Scope software. From the result, mode shape and natural frequency plays an important role in supporting result analysed by usingAlgor that will be used on Me Scope software.The data of simulation results will be guidelines for interpret data from experiment of modal testing. Five modes were determined and the value of natural frequency in each mode was increased respectively. If the value of natural frequency shifted means that the specimen was having crack on it. If the shifted is too much means that the specimen having a deeper crack. Then mode shape was used in order to validate whether the specimen is having crack or not. Mode shape 5 was too significant which is first bending mode in y direction compared to the other mode. If the mode shape is a 1st bending mode in y direction, and also natural frequency was shifted, then it shows that the specimen is having a crack on it.Finally, the modal testing method proves to be an effective method for crack identification