Mechanical testing of plastics - Long-term characteristics and toughness

This second article on Mechanical testing of plastics presents the :

• long-term behaviour tests, such as dynamic fatigue, creep, stress cracking, etc., which generate the data needed for design calculations (engineering) and for predicting service life, information which is unfortunately still too rarely available in the technical literature;

• fracture mechanics tests, to determine quantities characterizing the resistance of materials to crack initiation and propagation, which can also be taken into account in structural calculations. Relatively new in terms of concepts and methodologies, these tests are not yet widely used on polymers, but are developing at such a pace that we can expect to see the corresponding characteristics appearing in the catalogs and databases of the many commercial grades of industrial polymers in the near future.

Attention is drawn to the special nature of these tests, which in both cases provide access to data that can be used for design purposes, engineering calculations and material selection, unlike, strictly speaking, instantaneous mechanical characteristics (AM 3510) and thermomechanical characteristics of volume or surface (AM 3511). In practice, however, while the results of long-term tests are increasingly taken into account in industrial design offices, crack initiation and propagation characteristics derived from fracture mechanics tests are still rarely considered, mainly in industrial fields with an aeronautical background.