In this thesis, an automatic computer based system has been developed to measure the crack length and the crack opening load from test specimens. The system has been developed to operate in real time without the need of changing test conditions by using the unloading elastic compliance method. A unique method of using differential displacement of signal data has been used to determine the crack opening load. The performance of the developed system was verified through a series of constant-amplitude crack growth tests.
The system consists of simple components; a personal computer, an analogue electrical subraction circuit, a stepping motor, a stepping motor driver, a PIO board, and the application software used to integrate the whole system.
The proposed system can contribute to researches on similar grounds in the following way. The system can be used to measure crack length and crack opening load for different test specimens under random loading. Also, short crack growth studies and effective stress intensity factor range $\DeltaK_{eff}$ controlled tests can now be done fully automated and without supervision from fellow researchers.
