Stress development in supported polymer films during thermal cycling

A simple and in‐situ bending‐beam technique has been used to investigate the stress‐temperature relationships for three different polymer coatings (viz, poly(methyl methacrylate), FR‐4 epoxy resin, and an amide‐imide polymer) during thermal cycling. With this technique, we were able to detect stress relaxation near the polymer's glass transition or caused by cracking of the polymer. Knowing the Poisson's ratio and Young's modulus for the polymer, this technique also allows calculation of the polymer's thermal expansion coefficient from measured thermal stress data. The calculated thermal expansion coefficient of poly(methyl methacrylate) (7 × 10−5/°C) is in good agreement with literature values (5 to 9 × 10−5/°C). Copyright © 1986 Society of Plastics Engineers