The effect of clamping compressive stresses on the fatigue life of Al 7075-T6 bolted plates at different temperatures

In this paper, a finite element stress analysis has been carried out to study the effect of flight temperatures on the clamping compressive stresses around aluminium bolted holes subjected to cyclic loads. A holed plate of aluminium alloy 7075-T6 was clamped with two different tightening torques of 2 and 7 Nm and then simultaneously subjected to both longitudinal cyclic loads and flight representative temperatures. Three-dimensional (3D) clamping stress distributions around the bolt-filled hole were numerically estimated at three different temperatures of −50 °C, 25 °C and 60 °C using ABAQUS software. Numerical simulation and experimental results confirmed that at a constant temperature, the 7 Nm tightening torque could considerably prolong the fatigue life of the bolted plates as a result of introducing more compressive stresses around the plate hole. Moreover, under a constant tightening torque, the bolted plates tested at the low temperature showed a significant improvement in fatigue life because of an increase in the tensile properties of the aluminium plate caused by the temperature effect. This was in spite of less compressive stresses being found near the hole edge. Nonetheless, at the high temperature of 60 °C, different fatigue responses were observed from the lightly and firmly bolted holes.

► Stress analysis of bolted holes at different temperatures for assessing fatigue life.
► Added compressive stresses around bolted holes due to thermal expansion of the plate.
► Fatigue life improvement in both lightly and firmly clamped plates at low temperature.