EXPERIMENTAL STUDY OF THE INFLUENCE OF INCIDENTAL OVERLOADS ON THE FATIGUE BEHAVIOR OF SHEETS ASSEMBLED BY SPOT WELDS

The assembly of steel sheets using the spot-welding process is commonly used in the automotive industry - notably at Renault - for the production of the chassis. The stresses encountered in service due to rough roads or driving conditions are transmitted between assembled components via the welded points. Understanding their fatigue behavior under incidental overloads is therefore essential for ensuring their service life and permanently dimensioning the structure. In the present study, an experimental test campaign was conducted to analyze the fatigue failure modes of two identical steel plates joined by welded points and loaded in tension-shear. Two high-strength steel grades (HE360D and XE360D) and one mild steel grade for deep drawing (XES) were tested either at constant amplitude, or with incidental stresses occurring at a rate of one overload cycle for every 100 cycles applied. All cycles had a load ratio of 0.1 (undulating tension). The assembly of steel sheets using the spot-welding process is commonly used in the automotive industry - notably at Renault - for the production of the chassis. The stresses encountered in service due to rough roads or driving conditions are transmitted between assembled components via the welded points. Understanding their fatigue behavior under incidental overloads is therefore essential for ensuring their service life and permanently dimensioning the structure. In the present study, an experimental test campaign was conducted to analyze the fatigue failure modes of two identical steel plates joined by welded points and loaded in tension-shear. Two high-strength steel grades (HE360D and XE360D) and one mild steel grade for deep drawing (XES) were tested either at constant amplitude, or with incidental stresses occurring at a rate of one overload cycle for every 100 cycles applied. All cycles had a load ratio of 0,1 (undulating tension). The experimental results show that periodic overloading is beneficial to fatigue life in the case of high-strength steels, whereas the effect recorded is, on the contrary, a very marked collapse in fatigue properties in the case of mild steels.