Evaluation of Thermal and Mechanical Behaviors of Bolted Joints Made of Titanium and Titanium Alloy and its Application to Robust Joint Design

Abstract

Titanium and titanium alloys have some excellent characteristics when used for the parts and components of machines and structures. As for bolted joints, however, they are limitedly used mainly due to the high cost. Its specific characteristics, e.g., low weight and high resistance to corrosion, are highly attractive from the engineering point of view. In this paper, thermal and mechanical behaviors of the bolted joints made of titanium or titanium alloy are comprehensively evaluated by finite element analysis, aiming at its broader use by utilizing the distinctive features of small coefficient of linear expansion and Young’s modulus. As a first step, thermal contact coefficients at the interface composed of titanium, titanium alloys and other engineering materials are measured, and then the empirical equations for evaluating the coefficients are derived in the same form proposed in the previous papers. In the next place, numerical analyses are executed by incorporating the thermal contact coefficients into the finite element formulation. Numerical results suggest that threaded fasteners made of titanium alloys are favorably applied to the joints whose clamping forces are likely to decrease when subjected to thermal load. It was also found that the aforementioned threaded fasteners are effective, owing to its low Young’s modulus, for reducing the stress amplitude generated by alternating external forces.