Bolt-hole tightening effects in single-lap composite bolted joints

The weight and fuel savings offered by composite materials make them attractive not only to the military, but also to the civilian aircraft, aerospace, and automotive industries, where bolting joints are extensively used as a primary method of forming structural joints. Single-lap joints have good accordance with real conditions in comparison with other joint types. Therefore, the main objective of this paper is to investigate the behavior of single-lap joints in glass fiber reinforced epoxy (GFRE) composites under tension and pure bending loading conditions, with a constant W/D ratio (3) and variable the E/D ratios (3, 4, 5) and tightening torque values (0, 3 and 6 Nm). First, the mechanical properties of the composite were determined experimentally using the ASTM testing standards. Bending properties were determined using four-point bending test. Finally, special test fixtures were designed to facilitate the study of the effect of bending on the composite bolted joints.The experimental results show that in the tension tests, with increasing E/D ratio and tightening torque, the value of failure bearing stress increased. But, it seems that, this is not always true for continuous increase of these parameters. And in the bending tests, it is seen that at zero torque, with the increase of the E/D ratio the bending strength value increases, but this increase is small at T=3, 6 Nm torques. And in these tests, the joint failed at the center, near the bolt, because of the excessive delaminations on the compressive side.