A unified expression to estimate the stress-strain curve of polyamides at different temperatures

Abstract

The present paper proposes a unified expression to estimate the mechanical behaviour of polyamides in tensile tests at different temperatures. The goal is to present an algebraic equation able to describe the stress-strain curves that would be obtained using the ASTM D638-14 standard for a wide range of temperatures (roughly from -30 °C to 90 °C, even above the Glass Transition Temperature). This expression is valid for different kinds of polyamides. It is shown that with a minimum of three tests performed at different temperatures, it is possible to obtain a reasonable approximation of the stress-strain curve for this range of temperatures. Examples are presented considering different types of polyamides-PA11, PA12 and PA66-GF30 (PA66 reinforced with 30 wt% of short glass fibres). Although the mechanical behaviour is strongly affected by temperature variation, the estimates of the material behaviour are in good agreement with experiments in all cases studied in this paper. Such a procedure can be a practical tool for designers, used to obtain a reasonable approximation of tensile tests and thus reducing the need of performing many complex experiments.