The Strain Behavior of Polymer Materials as a Consequence of One and Two-Axis Creep
Following the tendency of plastics to creep over prolonged periods is not only expensive and time-consuming, it also does not guarantee any acceptable time for the use of the new products in practice.
The numerical description of the non-linear viscoelastic behaviour of plastics by means of empirical approaches enables a reliable extrapolation of 10,000 hours (and longer) with a test period of just 1,000 hours.
Through the linking of three state variables "stress, strain and time" by such approaches, it is possible to plot isochronous stress-strain curves for a specified time. For practical computational procedures a time and temperature-dependent design value has been proposed which permits non-elastic elongation of 0.5% for non-reinforced and short glass fiber-reinforced thermoplastics. For glass fibre-reinforced UP resins this limiting value is reduced to 0.3%.
In order to create single-axis or any desirable plane loads, two test facilities have been developed for static tension/compression torsion loads and internal pressure torsion loads. A shock-free loading device makes it possible to apply the load components simultaneously or according to a specified sequence with a defined rate of increase.
On the basis of experimental results from two-axis loads it has been found that load components do not influence one another only within the linear viscoelastic range. In contrast, in the non-linear viscoelastic range the anisotropic deformation behaviour becomes ever clearer with increasing load duration.
Material strain in the case of multi-axis creep exposure is described by the combination of the stress tensor and the tensor of the rate of deformation via the plastic potential. Any combination of shear and normal stresses can be brought together to create comparative stress for predetermined times and compared with the material resistance from a single-axis tensile-creep test.Lesen Sie die deutsche Zusammenfassung auf Kunststoffe.de
extrapolation of creep curve, isochron stress strain diagram, admissible load for long term loading, multy axial long term loading, comparison stress
Institute / chair: Institut für Werkstofftechnik der Universität - Gesamthochschule Kassel
Technical consultant for expert services: Prof. Dr.-Ing. Dr. h.c. Gottfried W. Ehrenstein (Betreuer), Prof. Dr.-Ing. O. T. Bruhn, Dr.-Ing. Anton Weber
Publication year: 1984
Provider: Wissenschaftlicher Arbeitskreis Kunststofftechnik (WAK) / Kunststoffe.de
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