Modelling the damage formation of bolted carbon fiber reinforced epoxy composite joints at increasing strain rates

The bearing strength of a carbon fiber reinforced/epoxy unidirectional composite joint incorporating a single hex bolt fastener was investigated under quasi-static and dynamic loads experimentally and numerically with two different bolt torques, 2.5 N m and 10 N m. The tests were conducted with neat fit clearance and without washer. The quasi-static tests were conducted at 3.33x10-5 and 1.66 x10-3 m s-1 according to the ASTM D5961 Procedure C. The dynamic tests were conducted in at Tension Split Hopkinson Pressure Bar (TSHPB) at 12.68 m s-1 using a specially designed specimen grip to ensure the same conditions as the quasi-static tests. Three dimensional explicit finite element models of bearing tests were developed in the LS-DYNA and the composite was modelled using the MAT_162 composite material model incorporating the strain rate effects. At the quasi-static velocities, a relatively low strain rate dependence of bearing peak force was found with almost no effect of applied bolt torque. In the TSHPB tests, the bearing force increased by 57% of those of quasi-static tests. The deformation mode also altered in dynamic tests and the increase of the bolt torque resulted with increasing the bearing peak force by 5%.