Device for Testing at Combined Cyclic Fatigue Loading by Tensile and Torsion, Attachable to the Universal Testing Machine

To designing various types of components that work in operation under the simultaneous effect of normal stresses, σ, and shear stresses, τ, is important to determine and know the behavior of materials under fatigue compound stress states. A device constructed to introduce into a specimen a state composed of normal and shear stresses is presented herein. The device is intended for performance under fatigue tests under combined tensile and torsional loading and can be mounted on a monoaxial fatigue machine. Variation of the combinations of normal and shear stresses is given by the possibility to change the cams to different inclination angles. We present a method of calculating the normal and shear stresses based on the parameters provided by a universal testing machine. Fatigue data for 6061 aluminum alloy are presented for several combinations of tensile and torsional loading. The fatigue limits, σ0–τ0, obtained by biaxial testing of the cylindrical specimens, were used to construct the σ–τ diagram. The calculation relations resulting from the use of the device for normal and shear stresses are deduced and presented. The calibration of the device is presented by means of a sample on which two electrotensometric transducers are mounted. The main feature of the device is its simplicity, based on the original idea of using a rigid cam that forces the central shaft to transform a translational movement received from the testing machine into rotational and translational movements using the inclined channel in the cam.