Tensile tests and fatigue tests on differently heat-treated low carbon (non- and low-alloy) steels were conducted and accompanied by non-destructive electrical resistometric (ER) and magnetic Barkhausen noise (MBN) measuring devices, in order to establish an improved short-time fatigue life estimation method according to StressLife. MaRePLife (Material Response Partitioning) is the hereby proposed method for calculating S–N curves in the HCF regime, based on the partitioning of material responses acquired during the above-mentioned mechanical tests. The rules were set to make use of the information gathered from pre-conducted tensile tests, which helps to determine the parameters of two load increase tests (LIT) and two constant amplitude tests (CAT). The results of the calculated S–N curves were satisfactory and could be verified by more separately conducted fatigue tests on specimens under different material conditions.

This research provides a method for a reliable fatigue life estimation at high testing frequencies. The investigations are based on the lifetime prediction method StressLife_HCF considering test frequencies of 80 and 260 Hz for normalized SAE 1045 (C45E, 1.1191) steel. Therefore, load increase tests and constant amplitude tests were carried out using a resonant testing rig. To ensure a mechanism-oriented lifetime prediction, the material response to dynamic loading is monitored via temperature and electrical resistance measurements. Due to the higher energy input per time unit, when the test frequency is increased, the heat dissipation also increases. For this reason, a precise differentiation between frequency- and temperature-related effects for adequate fatigue assessment is challenging. To evaluate the temperature’s influence on electrical resistance, an electrical resistance-temperature hysteresis is measured, and the frequency influence is analyzed by considering cyclic deformation curves. In addition to an extension of the fatigue life due to an increased test frequency, the lifetime prediction method was validated for high frequencies. The generated S-N curves show a reliable agreement with the data points from conventional constant amplitude tests. In this context, the temperature correction of the electrical resistance proved to be an important input variable for a reliable lifetime prediction.

Investigations on low carbon (non- and low-alloy) steels were conducted in form of load increase tests (LIT) and constant amplitude tests (CAT) to find the correlation among material behaviour, mechanical load, and the type of NDT method. With the help of preprogrammed load-free sequences, the thermal impact on magnetic Barkhausen noise (MBN) measurement can be avoided, so that the cyclic deformation properties of material responses can be interpreted more precisely. The results indicate differences between the change in temperature and the MBN-derived variable during LITs and CATs regarding the demonstration of the incubation stage and the cyclic hardening behaviour.

Magnetic Barkhausen Noise measurements are advantageous for the fatigue characterisation of ferromagnetic materials since they can provide information regarding microstructure, residual stresses, hardness and the presence of microstructural defects. The fatigue characterisation of a quenched and tempered SAE 4140 steel was realised using a servo-hydraulic fatigue testing rig instrumented with an infrared camera and a Magnetic Barkhausen Noise sensor for capturing the material response. Magnetic Barkhausen measurements require correlation against a standardised measurement method such as X-ray diffraction technique. Therefore, micromagnetic measurements were carried out ex-situ at different fatigue stages and then correlated with X-ray diffraction data as well as thermographic data. Since the measured parameters correspond to the induced partial damage, they can be used in lifetime prediction methods and enable an accelerated estimation of the lifetime of materials, thus proving to be effective in monitoring the structural integrity of the material.

A reliable design of dynamically loaded components requires a thorough understanding of the fatigue properties of metallic materials. This article focuses on extending conventional methods to include non-destructive testing (NDT)-based methods, which enable a process-oriented evaluation of fatigue behaviour instead of a lifetime driven approach. The use of NDT-generated data to describe cyclic deformation curves not only enables a significant increase in information, but also a generation of virtual S-N curves with a significantly reduced number of specimens. Therefore, synergies between the two disciplines of NDT-based and conventional destructive materials testing are used to enable a better understanding of ongoing processes. The main focus lies on the development of thermographic evaluation approaches, whereby further methods such as resistance measurements are used additionally. The test materials are two unalloyed steels of grade SAE 1020 and SAE 1045, as well as the low-alloyed 20MnMoNi5-5 steel.