Thermoplastic tensile specimens under one-sided thermal load – temperature evaluation and failure after cooling

A thorough understanding of polymer behavior under asymmetric thermal loading is a prerequisite for assessing the fire resistance of polymer structures. Yet, despite the widespread use of both fiber-reinforced and unfilled thermoplastics, their performance under such conditions remains insufficiently studied. In the present study polyoxymethylene (POM) tensile test specimens are exemplarily studied, the high thermal load is applied by a laser. Whereas on the irradiated front side temperatures considerably above the melting temperature occurred, temperatures on the back side were below. Quasistatic uniaxial tensile tests at room temperature after cooling showed that the elongation at break is strongly reduced by the irradiation, for stiffness and strength only a minor decrease could be observed. The transient temperature field inside the specimens was simulated by finite element analysis. This temperature was used to introduce a temperature dependent damage thickness which describes the thickness of the zone assumed to be irreversibly damaged by the thermal load. Based on this, an empirical model for the decrease of elongation at break of the investigated POM specimens is proposed.