The Response of Composite Joints with Bolt-Clamping Loads, Part II: Model Verification

Abstract

Extensive experiments were performed to characterize the material response due to bearing failure in composite bolted joints with and without lateral clamp-up supports. Composite plates made of T800H/3900-2graphite/epoxy were selected in the tests, and various washer sizes and clamping forces were used in the study. The clamping force in the bolt was found to vary with the applied load, and may increase significantly due to a sudden through-the-thickness expansion of the laminate under the washers where bearing failure occurred. Experiments showed that the joint strength and response can be significantly affected by the bolt clamp-up, and the bolt bearing failure is a 3-D phenomenon. The results of the tests were utilized to verify the model predictions proposed in Part I of the study. The model predicts both the failure load and response of bolted composite joints very well for various clamping forces and washer sizes. The predicted bolt clamp-up load as a function of the applied load agreed also well with the data, which validates that the proposed incompressibility assumption in the model for bearing-damaged material. Based on the model, a parametric study was performed to evaluate the sensitivities of bearing load to bolt stiffness, clamping force, washer size, joint geometry such as width, edge distance and bolt sizes.