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Cite this document
Bolts are commonly used in many structures to transfer loads from one component to another. When the structural components are fabricated using heterogeneous, fiber-reinforced composite materials and the magnitudes of the load transferred directly through the bolt vary, concerns regarding structural integrity arise. A change in the failure mode due to a change in the bolt load could be detrimental to the strength of the bolted joint. Results are available in the literature for the extreme cases where the bolt load is zero (unloaded hole) and where the total applied load is resisted by a bolt. This paper summarizes the results from an experimental-analytical program that investigated the effect of transferring an arbitrary fraction of the applied load through the bolt. In the analytical part of the program, a two-dimensional finite-element analysis was carried out, using NASTRAN, to predict the stress state around the bolted joint and the average stress failure criterion used to predict the joint strength and failure modes. The experimental program was conducted under room temperature dry and wet (1.2 percent moisture by weight) conditions. Experiments were conducted on AS/3501-6 graphite/epoxy specimens in test fixtures designed to transfer variable loads through the bolt. Identical specimens were subjected to static tensile and compressive loads, and to two lifetimes of tension and compression-dominated F-5 fatigue spectrum load conditions. Design curves were generated for the different test cases.
composite materials, AS/3501-6 graphite/epoxy, bolts, variable bolt loads, finite-element analysis, average stress failure criterion, tension, compression, static fatigue loads, spectrum fatigue loads
Senior engineer, Structural Mechanics Research, Northrop Corp., Hawthorne, Calif.