Author:

Keywords:

Science & Technology, Technology, Engineering, Civil, Engineering, Fatigue test rig, Multi-axial loading, Torque introducing concept

Abstract:

This paper describes the development of a novel experimental concept for high frequency multi-axial fatigue analysis of cylindrical specimens. The resulting test rig applies a combination of bending and torsional stress to test specimens with critical diameters ranging from 2 to 15mm at test frequencies up to 50Hz. Furthermore, the amplitude and frequency of both loadcases can be controlled independently. This enables the use of a broad range of test conditions. Test data will be generated which can be used to study and validate multi-axial fatigue criteria for synchronous and asynchronous loading conditions. Furthermore, the test rig will be used to study the effect of size on the fatigue life of metal and plastic components. The test setup consists of a closed mechanical loop which is driven by an electromotor. The primary shaft contains the cylindrical test specimen and is modified to impose rotating bending loads. The secondary shaft is adjusted to introduce fluctuating torque in the transmission loop. Both shafts are connected by means of two double link mechanisms to minimize the clearance and the inertia of the system. The time-varying multi-axial stress state in the cylindrical specimen is analyzed as a function of the amplitudes and frequencies of both bending and torsional loadcases. This is verified by a numerical fatigue analysis in MSC-Patran and MSC-Fatigue. Finally the dynamical behavior of the test rig is studied using a 5 DOF torsional mass-spring representation and the Lagrangian method. A more complex model with 20 DOF is implemented in SimDriveLine and solved via Matlab to analyze the kinematical and dynamical properties more accurately. Both studies take the mechanical properties of steel or plastic test specimens of different size into account.