An investigation was performed to study the bearing failure of mechanically fastened fiber-reinforced laminated composite joints. Only double-lap metal/composite/metal bolted joints were investigated. The results of this study will be presented in two parts: experimental characterization and analytical prediction. This paper summarizes the experimental work. The major focus of the experiments was to characterize the bearing failure mechanism and mechanics, and to evaluate the effect of clamping pressure on the bearing response and bearing strength of bolted joints. The bearing damage was characterized either as pure bearing, which had no lateral supports, or as bolt bearing, which contained lateral supports with various degrees of clamping pressure. A specially designed semi-circular notched specimen was proposed to characterize pure bearing damage. For bolt bearing, a load cell was designed and manufactured which was mounted on the fastener to monitor the bolt clamping pressure as a function of the applied load. T800/3900-2 graphite/epoxy prepregs were selected to fabricate the specimens. All the specimens were x-rayed and sliced at different load levels to examine internal damage. Based on the experiments, it could be concluded that lateral support is crucial for bolted laminated composite joints. Bearing damage can be catastrophic if there is no lateral support. Shear cracks induced by accumulated compression failure appeared to be the primary failure mode of the bearing damage. Lateral supports could suppress the shear crack propagation and change failure from a catastrophic to a progressive failure mode. Clamping pressure could increase bearing strength.

An investigation was performed to study the bearing failure and response of a mechanically fastened laminated composite joint. The experimental work of the study was presented in Part I, and this paper summarizes the analytical work. An accumulative damage model based on the damage mechanisms observed from the experimental study was developed to simulate the bearing failure in the laminated composite joints. The model consists of two parts: damage prediction and constitutive modeling. Damage accumulation criteria by modifying Hashin criteria were proposed to predict the mode and extent of bearing damage as a function of the stress state, and the relationships between material properties and bearing damage were established based on failure mechanisms. A nonlinear finite element analysis based on the model was developed. Data obtained from this study and existing literature were used to validate the model. Overall, the predictions agreed with the data very well.

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An investigation was performed to study the strength and failure of bolted composite joints subjected to bypass loads. The damage accumulation models developed previously by the authors were implemented in a nonlinear finite element code, designated "BJSTAT," for predicting failure and response of bolted composite joints. Utilizing the code, numerical simulations were conducted to generate the strength envelope for a bolted composite joint under multi-axial bypass loads. The predictions of bolted joints subjected to an axial bypass load were compared with available experimental data. The prediction agreed with the data very well. The envelope can provide information on the strength as well as the failure type of the joint as functions of the bypass loads and, therefore, is very useful in joint design.