Primary creep behaviour of polyester resins from multiple relaxation curves

摘要

Typical primary creep behaviour of a viscoelastoplastic material is shown when varying the temperature and the time rate of strain (of a previous tension). The creep behaviour is obtained from the tension test with multiple relaxations, where a numerical procedure is used in order to obtain creep curves from a series of relaxation curves. This test methodology allows interrelated tension, relaxation and creep behaviours to be obtained from one single test. The materials tested are proportional to the weight mixtures of rigid/flexible polyester resins with hardeners, generally used as model materials in photomechanics. With the increase in temperature, there is a decrease in the time needed to reach a given creep strain. The time rate of the strain, used in the tensions prior to the relaxations, has a considerable influence on the beginning of the relaxations. Since the creep curve is obtained from these relaxations, the rate of strain is shown to have an influence on creep behaviour, depending on the portion of the relaxation curve from where values are taken for calculation of creep.