Because of clear trend in the world to design lighter plastic products, the phenomenon of creep buckling of visco-elastic solids becomes increasingly important. This paper reports the intermediate results of the research project on loading capability and buckling of plastic containers, carried out in the Laboratory of Mechanical Reliability (LMB) of TU Delft. Based on the earlier developed non-linear visco-elasticity model for engineering plastics, the FE simulation of the delayed in time buckling of plastic strips have been performed as a first step toward the understanding and predicting creepbuckling behaviour of plastic carriers.

For reasons of reliability, stability, safety and economy, controlling and monitoring the response of structures during the time of use, either permanently or temporally, is of increasing importance. Experimental methods enable in-situ measuring deformations of any kind of structures and enable drawing conclusions over the actual state of the structures. However, to obtain reliable knowledge of the real internal conditions like the strength of materials and the actual stress-state, as well as of their changes over time, caused by ageing, fatigue and environmental influences, always an inverse problem must be solved. That requires special mathematical algorithms. Especially for time-depending material response it might be quite important to know the material parameters at any time and furthermore the internal stress-state also. Therefore, a method will be presented to solve the inverse problem of parameter identification with reference to linear visco-elastic materials.

A crucial feature in health monitoring of already existing structures is to be seen particularly in identifying their topical internal structural parameters and controlling their remaining bearing capacity in the course of ageing processes. This is commonly carried out by measuring the deformations/strains caused by test-loading and calculating the parameters on the basis of the metered data.

In the case of elastic response of materials, the information on the parameters is directly related to the time of measurement; in the case of visco-elastic response, however, the history of the time-depending structural response during the period between initial loading and initiating the test-measurements is generally unknown. The problem exists, then, to separate the superimposed strains due to the existing state and to the test-load. For solving the problem, at first the relevant relations between stress/strain and the visco-elastic parameters are considered. Then a procedure will be described how to determine the strain state owing to the test-load only and to calculate the relevant parameters as functions of time. According to the principle of time-shift invariance, the results describe the time-depending response of the viscoelastic material, no matter at which time the loads are applied.

The presented method will be illustrated by two simple but instructive examples.

The purpose of this paper is to study the thermoviscoelastic interactions in a homogeneous, isotropic semi-infinite solid under two-temperature theory with heat source. The Kelvin-Voigt model of linear viscoelasticity which describes the viscoelastic nature of the material is used. The bounding plane surface of the medium is subjected to a non-Gaussian laser pulse. The generalized thermoelasticity theory with dual phase lags model is used to solve this problem. Laplace transform technique is used to obtain the general solution for a suitable set of boundary conditions. Some comparisons have been shown in figures to estimate the effects of the phase lags, viscosity, temperature discrepancy, laser-pulse and the laser intensity parameters on all the studied fields. A comparison was also made with the results obtained in the case of one temperature thermoelasticity theory.