Composite materials are increasing in popularity for use in various industries. Recently the size of structures produced from these materials has begun to increase. As the size and thickness of such structures increase, it is inevitable that joints will be necessary. Mechanical fastening is a popular choice in joining composites because of the ability to transfer high loads and the ease of assembly and disassembly. However, drilling operations expose the fibers to environmental factors, and the high contact stresses between the bolt and the hole lead to localized delaminations, decreasing the joint strength. In this thesis, the effects of using isotropic inserts and varying the preload of thick composites in a single lap joint are examined. In addition to failure testing, a specialized sensor to accurately measure preload with the use of a Fiber Optic Strain Gage is proposed and created. This sensor is produced for the current experiments but can be expanded to other applications. Testing methods are initially developed and a sample size of .5" thick is decided upon. The tests then performed are on non-reinforced joints and joints reinforced with both machined isotropic inserts and the novel design. The amount of preload is also varied for tests. All of the joints described are tested to ultimate failure to determine any trends. From these tests, it can be seen that the inserts and preload improve stiffness of thick composite joints. Preload also increases the initial failure load of the joints.
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