Abstract
<title>Abstract</title> <p>Residual stresses (RS) are known to critically influence the mechanical performance of cold-formed components, particularly in fatigue loading scenarios. This study focuses on enhancing fatigue life, with particular emphasis on the low-cycle fatigue (LCF) regime in which cyclic stresses exceed the material's yield strength. The approach involves targeted control of RS in a modified forward extrusion process, achieved by applying variable counterforces during forming. The investigation was carried out in two stages. In the first stage, workpieces were produced under different counterforce levels, which allowed the RS state to be tailored by promoting a more homogeneous material flow and a locally increased hydrostatic pressure during the forming process through optimized counter punch support. Experimental measurements and numerical simulations showed that increasing the counterforce up to \SI{80}{\kilo\newton} led to a consistent reduction of tensile RS near the surface. In the second stage, rotating bending fatigue tests were conducted to assess the fatigue performance. The maximum number of cycles to failure was observed at a counterforce of \SI{60}{\kilo\newton}, while higher counterforces resulted in a decline in fatigue life. This behavior is explained by the interaction between the RS state and the externally applied bending load, which diminishes the beneficial effects of RS optimization at higher load levels. The trend was confirmed by numerical analysis and an analytical model for fatigue life prediction based on the local approach, utilizing results obtained from finite element simulations. The study demonstrates that increasing the counterforce improves the fatigue life of cold-formed components by promoting a more favorable RS state. However, this effect is limited by a process-specific threshold, which becomes evident through combined evaluation of internal and external stress contributions.</p>