This study aims to determine the stress components of the multiaxial stress state in the load-bearing thread area of a M8 stainless-steel bolt using X-ray diffraction, which is otherwise impossible without an intervention in the stress states using any known non-destructive method. For steels, high X-ray energy at about 80 keV is required to penetrate the material. For this reason, these experiments were carried out at the DESY Hamburg. Measuring the stress tensor's six components requires a long time under the given conditions (sample material, geometry, surface structure, alignment).The limited measurement time at the DESY requires that this study examines the difference between the axial and radial stress components σ11 and σ33.

The stress difference from production-induced residual compressive stress (RCS) and mechanical load stresses applied to the longitudinal section of the thread shows in all states a heterogeneous stress field with transition boundaries from negative to positive areas. Negative components dominate the thread base in the “no load” state. With increasing load, the resulting axial stresses in the bolt appear and the areas of negative stress difference disappear. The data show that the areas with RCS almost completely convert from negative to positive stress differences at 10 Nm. So, it can be suggested that RCS have a significant influence on the level of tensile stresses in the root of the thread and consequently on the material's load reserves.