Determination of the deformation and the failure mechanisms of thermoplastics under unidirectional compressive stress
Walter Michaeli, Thorsten Krumpholz*
Institute of Plastics Processing (IKV) at the
RWTH Aachen University
Pontstraße 49, 52062 Aachen, Germany
Fax.: +49 (0) 241 80 92 262
Email: zentrale@ikv.rwth-aachen.de
Abstract:
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.