Strains beneath washers in thick single-lap composite bolted joint using embedded DSPI and RSG's

摘要

In this pilot study, Digital Speckle Pattern Interferometry (DSPI) is employed to analyze the stress distribution near and beneath the washer of a single-lap, bolted joint between composite and aluminum plates. A transparent fastener was developed in order to obtain strain data close to the bolt in the area covered by the washer and nut. The new fastener had to perform the function of a normal washer and nut, but also be optically clear so that the area under the washer may be illuminated with the laser and imaged with a CCD camera. These requirements led to the development of the 'washer-nut,' a circular nut with the diameter of the washer manufactured from a thick transparent sheet material. Dimensions of the washer-nut were chosen so that its stiffness matched the stiffness of the normal steel components. Using this washer-nut, it is possible to see how the clamping force affects the strain field under the washer of the joint. This study will add to the comprehensive knowledge base of orthotropic joint behavior, and the results serve to guide and validate FEA analysis.