Finite element modeling and optimization of load transfer in multi-fastener joints using structural elements

A computationally effective model of a multi-fastener, single-lap, composite-to-aluminium joint has been developed by means of structural finite elements. The model is geared towards accurate predictions of load distribution between the fasteners and accounts for bolt-hole clearances, bolt clamp-up and member plate friction. Comparisons with previously conducted experiments and detailed finite element analyses validated the accuracy of the model. A parametric study was conducted where it was found that an increased stiffness mismatch between the plates generates a more uneven load distribution, while reducing the length of the overlap region has the opposite effect. Increasing the stiffness of a fastener shifts some of the load from the nearest fasteners to that particular fastener. An idealized optimization study was conducted in order to minimize bearing stresses in the joint with restrictions on the increase of joint weight and net-section stresses. Maximum bearing stress was reduced from 220 to 120 MPa and both weight and net-section stresses were decreased.