Effects of Coating Tribology on Fastener Single and Double Shear Strength 2006-01-3155

In aerospace fastener industry, all materials used or being considered for fastener applications must meet specified minimum shear strength values. It is widely known that shear strength is dependant on the type of shear test. However despite the suspected test dependencies, no detailed open research literature on the fastener shear test, especially shear strength variation via single and double shear approaches, and factors including surface coatings that affect tested shear values, has been conducted. Thus, the objective of this program is to systematically evaluate the effect of coating tribology on the threaded fasteners shear property tested via single shear and double shear testing methods. Five most common fastener finishes were selected, including uncoated, Aluminum CVD, Hi-KOTE, MoS₂ coated, and Anodized. To determine if correlation exist between surface properties and shear strength, detailed physical property measurements on each individual fastener including surface friction coefficients, surface roughness, coating thickness, and diameter were conducted. Detailed statistical analysis was conducted to identify relationship between surface coating tribology and shear strength. In addition, finite element analysis (FEA) was used to simulate the shear testing process in order to explore the effects of surface friction and fastener diameter on shear strength. Experimental results, statistical analysis and FEA confirmed that fastener surface tribology have significant effect on tested shear values.