An automated system is developed to perform fatigue crack growth tests under constant effective stress intensity factor range $ΔK_eff$. In the system, crack length and crack opening load are measured in real-time by using the unloading elastic compliance method.
The system consists of two personal computers, an analogue electrical subtraction circuit, a stepping motor, a stepping motor driver, a PIO board, and the application software used to integrate the whole system.
The performance of the developed system was tested and discussed performing constant $ΔK_eff$ crack growth tests on a CT specimen of 7075-T6 aluminum alloy. The performance of the system is found to be strongly dependent on the accuracy of measurements of crack opening load.
Besides constant $ΔK_eff$ testing, the system is expected to be successfully applied for automation of various fatigue tests.
