Thermal Mechanical Testing of Low Density Thermoplastic Foam

Abstract

Foams made from engineered thermoplastic resin systems possess high glass transition temperatures. When compared to most thermoset resins, it was anticipated that lightly cross-linked foam candidates might survive high temperature/ pressure cures. This is especially true if the viscosity decline (i.e., loosening of weak secondary bonds) during sandwich bond cycles were found to be gradual enough to be controllable. To test this supposition, a low-cost five-step screening down-select methodology was utilized: (a) survey and evaluate vendor data, (b) pre-screen candidate foams using a vertical flame test, (c) characterize basic material properties using room temperature quasi-static compression testing, (d) evaluate failure mechanisms via elevated temperature compression testing, and (e) validate material functionality by conducting flat and contoured autoclave sandwich panel bond trials. None of the three candidate materials evaluated individually met all research requirements. Still, the population taken as a whole exhibited the potential for fulfilling the study's objectives. It is hypothesized that foam chemistry modifications, cell structure manipulation, and/or additional cure cycle process parameter management could lead to extended usage of foam in structurally demanding applications.