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Results of a design data development program involving hundreds of graphite epoxy bolted joint tests are summarized. Emphasis was on obtaining information for HMF330C/34 cloth material at room temperature, 394, and 450 K; however, many specimens made from T300/5208 and AS/3501 tape laminates were tested to provide correlating information on bearing behavior and the importance of hole-bolt tolerances. Bearing strengths for quasi-isotropic laminates made from these three prepregs were similar. Complete removal of bolt torque was shown to reduce the bearing strength relative to fully torqued bolts by approximately 40 percent. Multiple bolt joints were tested using three different hole-bolt tolerances. Resulting strengths were encouragingly similar, indicating the materials were less brittle than might have been expected. This was particularly true for bearing failures. Loaded-bolt and open-hole tests on cloth laminates indicated a greater degree of effective ductility than indicated by available data for similar tape laminates. Layups with no 45-deg plies exhibited markedly greater brittleness than their quasi-isotropic brethren. The higher the temperature, the less was the ductility for both layups. Bolt head details were shown to exercise a strong influence on bearing strength for single lap joints.
composite materials, bolted joints, high temperature strength
Senior staff engineer, Lockheed Missiles and Space Co., Inc., Sunnyvale, Calif.
Measurement Technology, Inc., Palo Alto, Calif.
Earl and Wright, Inc., San Francisco, Calif.
Structures engineer, Lockheed Missiles and Space Co., Inc., Sunnyvale, Calif.