Strength and Lifetime of Bolted Laminates

An extensive experimental program was conducted to investigate the effects of various parameters on the strength and lifetime of bolted laminates. The tested joint specimens were composite-to-metal joints where a single fastener transferred the load from one plate to the other. The various test variables were the bolted plate geometry, laminate lay-ups, stacking sequences and thicknesses, fastener material, diameter, fastener head type (protruding or countersunk), fastener torque, joint configuration (single lap or double lap), load type (tensile or compressive under static and fatigue loading conditions), and test environment conditions (room or ambient temperature and dry; elevated temperature and wet). All the laminates were fabricated using AS1/3501-6 graphite/epoxy prepreg material. Static tests reproduced the general trends reported in the literature for the effects of plate edge distance and plate width on the strengths of laminates and the corresponding failure modes. Constant-amplitude fatigue tests were conducted at a frequency of 10 Hz, maintaining a constant minimum-to-maximum cyclic load ratio. The effect of the maximum cyclic load amplitude, as a fraction of the corresponding static strength, on the number of cycles to failure was recorded. Hysteresis plots, hole diameter, and fastener torque loss measurements were also obtained during fatigue. The obtained results complement data available in the literature.