Wedge tension test of a high-strength bolt of fully pearlitic high-carbon steel

Using a wedge tension test for service and safety reasons, this study determines the fracture location of a previously developed high-strength M8 bolt with a tensile strength of 1600 MPa. The strength distributions of the manufactured bolt are examined in compression and microhardness tests to ensure a better understanding of the experimental results of the wedge tension test. The strength variations of the manufactured bolt were confirmed through scanning electron microscope measurements of the interlamellar spacing of the pearlite. Because of the strength condition in the neck of the bolt and the geometry-induced stress concentration, the head of the manufactured bolt can be separated from the neck during the wedge tension test. In this study, stress analyses were therefore conduced to prevent the head separation. That is, the stress concentration on the neck of the bolt was checked by varying the fillet radius for a given pitch size of the bolt. The numerical findings were subsequently validated by the wedge tension test. The findings are the basis of practical industrial design guidelines on the fillet radius to prevent the head of the manufactured bolt from being separated.