1. Determining long-term mechanical behavior

The mechanical tests presented in the article Mechanical testing of plastics. Instantaneous characteristics are instantaneous tests used to determine the short-term characteristics of materials, without necessarily taking into account the effect of permanent physical, chemical, thermal or mechanical stresses, or even their combinations, occurring under actual conditions of use. As a result, long-term tests are increasingly being developed in order to obtain the characteristics essential for predictive calculations of in-service behavior (or engineering calculations), leading to the determination of genuine design characteristics such as creep modulus, static or dynamic fatigue strength, and resistance to stress cracking in various environments. These tests enable us to measure :

• loss of stiffness as a function of time, due...