Distributional analysis of residual stresses with the Ti-6Al-4V internal trapezoidal thread torsional vibration extrusion

The aim of this study is to actively explore the quantitative measurement of residual stress of trapezoidal internal threads after extrusion processing. In this paper, innovative stress test specimens of the Ti-6Al-4V alloy disc with a diameter of 86 mm and a thickness of 20 mm were designed, and vibration extrusion tapping was carried out with a Tr14*2 extrusion tap in the center of the disc. Then, based on the elastic principle and the linear superposition principle, the incremental slicing method or crack flexibility method was applied to retrieve the residual stress distribution from the strain measurement. The stress distributions along the axial direction of the threaded hole and along the tangential and normal directions of the threaded hole were measured. The redistribution law of internal residual stress of extruded internal threaded parts was explored and studied, which provides a basis for studying the fatigue resistance of materials. In addition, the three-dimensional finite element method was used innovatively to calculate the stress flexibility factor of circular pie specimens with finite boundary constraints as not used the previous two-dimensional plane strain approximation.