States of Stress and Strain in Adhesive Joints Including Photoelastic Imaging of Defects in Adherends

摘要

Water migration across the thin epoxy layer in model adhesive joints causes strongly inhomogeneous swelling. The swelling is the principal cause of stress systems which are being examined by analysis of the patterns of Newton's rings formed between a glass cover slip and an optical flat. Enhancement of water migration by normal stresses of the order of a kilobar is reported. The development of a self-stressed fracture mechanics test piece, designed to investigate water uptake by adhesives, is reported. Photoelastic imaging of ultrasonic waves can be utilized to investigate defects in opaque solids. Instead of using a piezoelectric detector, the reflected sound from a defect is actually observed in a visualizing block of quartz, after propagating from the specimen to the block across an acoustic coupling. Experiments and a computer model are described. (Author)