Accelerated multi-axial fatigue experiments: test rig design and first results

This work describes the design, implementation and first results of a fatigue test rig capable of subjecting cylindrical specimens of different sizes and materials to complex real-life loading conditions. The resulting test rig can be used to combine a rotating bending load with a fluctuating torsional load. Due to a closed electromechanical loop, power consumption is limited and a maximum test frequency of 50Hz can be obtained for both the bending and the torsion. In addition, the optimal control strategy is determined using analytical techniques in order to simulate the test rig and to further reduce the power requirements for both electrical motors. Bending moments of 5–150 Nm can be combined with torsional moments of 5– 100 Nm at test frequencies between 2 and 50 Hz, leading to a significant advantage with respect to conventional fatigue testing techniques. In general, the presented test rig concept allows accelerated multi-axial fatigue tests on steel specimens, leading to a reduction of the time and cost needed for experimental validation of analytical and numerical fatigue calculations. Additionally, multi-axial fatigue criteria will be studied for different specimen sizes, geometries and materials. Furthermore, the test rig concept consists of conventional mechanical components making it relatively straightforward to implement and economically feasible.