Modeling Mechanical Fasteners in Single-Shear Lap Joints
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One central issue in damage tolerance analysis is the evaluation of stress intensity factors for cracks at fastener holes in mechanically fastened joints. Accurate solutions for stress intensity factors may be difficult to determine due to geometric complexity, along with variations in fastener load transfer and fastener interference. Detailed finite element models that include specific aspects of fastener geometry may be developed for lap joint analysis, but such representations are often impractical for large lap joints involving many fasteners. A methodology is derived that efficiently depicts mechanical fasteners in lap joints using finite elements. Fastener material properties are determined, based on an empirical force-displacement relationship, for highly refined fastener models, as well as for idealized spring element representations of fasteners. The two fastener characterizations are used in combination to develop computationally efficient models for determining loads, stresses, and stress intensity factors for cracks in lap joints. Parametric studies involving single-shear lap joints with three rows of fasteners indicate that both fastener representations provide comparable load transfer and relative displacement between mating sheets for a variety of fasteners. These studies also suggest that the particular fastener material has relatively little effect on stress intensity solutions, whereas the fastener diameter has a significant effect. Residual strength predictions are obtained for large bolted lap joints with multiple site damage, which are consistent with experimental results from the literature.
author list (cited authors)
Cope, D. A., & Lacy, T. E.