Time-dependent stress behavior: A study on creep and relaxation performance for heat treatment-free fasteners

Abstract

The increasing demand for sustainable manufacturing processes has driven the company Bulten to develop new fasteners (BUFOe), which are heat treatment-free, to minimize its carbon footprint. This thesis examines the time-dependent stress behavior of BUFOe fasteners (non-heat-treated) in comparison to regular heat-treated fasteners under ambient and elevated temperature conditions. It is essential to quantify the mechanical stability of the new fasteners during thermal loading to give clear recommendations regarding suitable service conditions. To achieve this goal, a testing procedure was established to measure creep strain over short periods at both ambient and elevated temperatures. The comparison between BUFOe fasteners and regular heat-treated fasteners indicates that BUFOe800X fasteners exhibit excellent performance in resisting creep deformation (0.07%), which is superior to their counterpart 8.8 fasteners and comparable to that of regular heat-treated fasteners (10.9) at room temperature. This shows that non-heat-treated fasteners may be a viable alternative in engineering applications at room temperature. However, at higher temperatures, all fasteners of BUFOe exhibited increased susceptibility to creep deformation compared with regular heat-treated fasteners within the same propertyclasses. These findings provide valuable references for optimizing the reliability and integrity of fasteners under various industrial conditions in the continually evolving field of fastener design and manufacturing processes