Pull-Through Mechanical Behavior of Composite Fastener Threads

A method was proposed to test the pull-through mechanical behavior of fastener threads, which were fabricated from weave carbon/carbon (C/C) composites. The damage morphologies of the C/C fastener threads were observed through an optical microscope and high-resolution micro-CT systems. The acoustic emission (AE) technique was utilized to track the damage progression of threads during loading up to fracture in terms of AE event rate which has an exponential type profile. Finally, A 3D finite element damage evolution model of composite threads was established based on continuum damage mechanics to calculate the thread load distribution and damage progression. The relations between the pitch and the load distribution, as well as between different fabrication directions and ultimate loads, were investigated by using this model. The stress in the first thread was analyzed based on the tapered cantilever assumption. The results show that, the first thread is brittle fracture at the root where is the higher stress level region of the threads and it is the initial damage. The load distribution in C/C threads is not uniform and not improved as the value of pitch decreases. Load capacity of C/C threads is different result from the fabrication direction. Numerical results agree well with experimental results.