Investigation of bolt clamping force on the fatigue life of double lap simple bolted and hybrid (bolted/bonded) joints via experimental and numerical analysis

• Effects of torque tightening on the fatigue strength of simple and hybrid joints have been studied.
• The fatigue life improvement is related to the created compressive stresses.
• Hybrid joints have longer fatigue lives compared to the simple joints.
• There is a linear relation between the clamping force and the applied torque.

In this research, the effect of bolt clamping force on the fatigue life of double lap simple bolted and hybrid (bolted/bonded) joints have been studied both experimentally and numerically. To do so, two kinds of joints, i.e. double lap simple and hybrid (bolted/bonded) joints were studied. For each kind of the joints, three sets of specimens were prepared and subjected to tightening torque of 1, 2.5 and 5 N m and then fatigue tests were carried out at different cyclic longitudinal load levels. Experimental tests revealed that the hybrid joints have higher fatigue life in comparison with the simple bolted joints. In the numerical method, finite element code was used to obtain stress distribution in the joint plates due to clamping force and longitudinal applied loads. Numerical simulation and experimental results showed that the fatigue life of specimens was improved by increasing the clamping force due to compressive stresses created around the hole. In addition, the investigation revealed the positive role of clamping force resulting from torque tightening on the fatigue life of both simple and hybrid joints.