Thermoplastics: a wealth of mechanical behaviors

A synthetic way of illustrating the range of behaviors available to plastics is to observe the effect of temperature on mechanical stress. Consider the multiaxial impact test (dart test), which involves impacting an embedded plate around its entire circumference. At the end of the impact, the impactor is removed immediately before the specimen is cooled, in order to highlight the springback mechanism at the end of the test at test temperature. The result of the experiment is therefore an evolution of the impact force as a function of time and, of course, the fracture surface. Figure 1 is an example of results obtained with polystyrene...