| The use of mechanically fastened joints is unavoidable in aerospace structures due to serviceability requirements. Because of the low efficiencies of mechanical joints, considerable effort is put into their design. Conventional design methodologies use uniaxial strength data and isotropic failure criteria to predict joint strength. However, these methodologies result in poor strength predictions when applied to fibre reinforced plastic laminates. To improve results, orthotropic failure criteria were developed, but the use of uniaxial allowables remained.; The primary objective of this thesis was to obtain bearing failure data under various states of plane stress to improve joint strength predictions. This was achieved through an experimental test program which investigated the effects of biaxial and bypass stress states on the bearing strength of a graphite/epoxy laminate. Results were compared against uniaxial data, and showed that the application of a biaxial load caused a decrease in the bearing strength. The addition of a bypass load was also found to lower the strength at which bearing failure began. The magnitudes of these strength losses were dependant on the biaxial stress state.; Further to the experimental program, 2-D and 3-D finite element analyses were performed to supplement experimental findings. The 3-D model was determined to be more representative of the present problem, as it demonstrated fastener and joint deformation consistent with that of single shear lap joints. Both 2-D and 3-D models overpredicted the theoretical peak bearing stress.; Experimental, numerical, and analytical results were used to develop an empirical failure prediction technique. This technique relied upon three factors which accounted for joint configuration, stress state, and fastener preload. Strength predictions for various load cases resulted in good agreement with experimental findings. |
