Influences of the Process Chain on the Fatigue Behavior of Samples with Tension Screw Geometry

Abstract

To analyze the influence of the material batch, the structure of the manufacturing process chain, and the process parameters, four different material batches of the quenched and tempered steel SAE 4140 were used to manufacture samples with tension screw geometry. Five different, manufacturing process chains, consisting of the process steps heat treatment, turning, and grinding, were applied. After selected process steps, light and SEM micrographs as well as fatigue experiments were performed. The process itself as well as the process parameters influences the properties of the surface layers and the fatigue behavior in a characteristic manner. For example the variation of the feed rate and cutting speed in the hard‐turning process leads to significantly different mechanical properties of the surface layers and residual stress states, which could be correlated with the fatigue behavior. The cyclic deformation behavior of the investigated components can be benchmarked equivalently with stress–strain hysteresis as well as high precision temperature and electrical resistance measurements. The temperature and electrical resistance measurements are suitable for component applications and provide an enormous advantage of information about the fatigue behavior. The temperature changes of the failed areas of the samples with tension screw geometry were significantly higher, a reliable identification of endangered areas is thereby possible. A new test procedure, developed at the Institute of Materials Science and Engineering of the University of Kaiserslautern, with inserted load‐free‐states during constant amplitude loading, provides the opportunity to detect proceeding fatigue damage in components during inspections.

Innovative Experimental Approaches and Physical Measurement Methods for Fatigue Monitoring and Life Assessment

“…These experiments yield characteristic cyclic deformation, temperature and electrical resistance curves representing the actual fatigue state. In contrast to the plastic strain amplitude, the physical measurements do not need a defined gauge length, can also be applied on more complex geometries and can be performed continuously, even during variable amplitude loading [6].…”