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The Effects of Fastener Hole Defects

The influence of drilling-induced defects, such as delamination, on the fa tigue life of a pin bearing joint in a toughened carbon epoxy system was investigated. In a pin bearing joint, the parameters of interest are the bearing stress and the pin position or tolerance. Tension bearing by-pass tests were conducted on coupons under ambient and elevated temperature wet conditions. Specimens were tested in a bearing tension frame to static failure in order to measure the failure load and to calculate pin bearing stress. From static test results, a fatigue load was selected as 66% of the static pin bearing failure load. Coupons were then tested under pin bearing fatigue loading at ambient and elevated tem perature wet conditions. Two-dimensional finite element models were used to simulate the pin and tension loads applied to the coupons. These models simulated the stress distribu tion around the loaded pin. The loads in the finite element models represented the failure load incurred in the static pin bearing tests as well as the maximum load during a selected cycle of the pin bearing fatigue tests. Experimental results showed the pin movement to vary with respect to delamination diameter, specimen thickness, and configuration. Numerical results compared with the static failure levels and indicated the form of the delaminated regions. Results give an indication of the effects of environment and hole quality under pin bearing load. Large variations in drilling-induced damage tended to cause variations in the pin bearing response of like specimens.