DETERMINATION OF THE DEFORMATION AND THE FAILURE MECHANISMS OF THERMOPLASTICS UNDER UNIDIRECTIONAL COMPRESSIVE STRESS

Today, the usage fields of plastics extend in an increasing way to fields, where they have to stand high compressive stresses. It is often a problem to dimension these parts in a technically safe and economically meaningful way so far. The essential reason for this is the lack of suitable values, which can describe the time and temperature dependent deformation and failure behaviour of the used plastics under compressive stress. Due to this reason, also parts, which are only stressed by compression, will be designed with characteristic values determined by unidirectional tensile tests. Though, investigations have shown that in contrast to tensile loads for parts under compressive stress much higher deformations and loads are allowed without material damage. The possibility to design these parts with compressive values will result in reduced wall thickness (regarding to pipes for example) and because of that in considerable material savings. Therefore, the aim of the current investigations at the IKV is to establish a guideline for the determination of characteristic compression values for plastics. Initially, a test procedure, which will be able to determine unidirectional values by using conical clamping devices for cylindrical test specimen, has been developed. Further, the failure limits and the time-temperature behaviour of selected thermoplastics will be determined.