During cyclic mechanical loading, fatigue failure eventually occurs. Built-in residual stress (RS) is a component of the total loading condition that is not directly observable and can therefore be underestimated in fatigue lifetime estimations. It is generally known that tensile RS shortens fatigue life, while compressive RS prolongs it. However, quantifying these effects is challenging because extensive experimental work is required. The present contribution focuses on the detrimental influence of tensile RS and demonstrates how the fatigue crack growth rate (FCGR) may vary under tensile residual-stress field.

Figure 1 presents a schematic illustration of the procedure used in this work. All specimens were extracted directly from a single railway axle after induction hardening, with built-in residual stresses. First, the depth-dependent microstructure and tensile mechanical properties were characterised. Afterwards, RS measurements were performed. With known RS field, the design of the FCGR experimental campaign was carried out to obtain the required results.

Reliable RS determination is essential when evaluating tensile RS effects. Therefore, three different RS field determination techniques were applied to specimens manufactured from the induction hardened railway axle, whose RS field had been previously characterised [1, 2]. X-ray diffraction, relaxation method and numerical modelling were used to determine the RS field. The three methods showed consistency and repeatability in the obtained RS profiles.

The FCGR experiments were performed under different loading conditions. Three load ratios were considered: a high ratio R = 0.8, where crack closure effects are minimal; an intermediate ratio R = 0.1, where crack closure is active; and a low load ratio R = −1.0, where crack closure is even more pronounced. The maximum stress intensity factor (Kmax) at the beginning of crack growth was kept constant for all load ratios (R). The results confirm that RS significantly affects FCGR, but its influence depends on the applied loading ratio. The obtained result will enable a more accurate estimation of the magnitude of the effect of residual stresses on the resulting fatigue crack propagation rate at various loading conditions.