Deformation Behaviour in Tensile and Burst Testing

Even with this correction the entirety of the mechanical behaviour of plastic geomembranes is not yet fully described. Isothermal conditions and an approximately constant deformation rate were assumed in the previous considerations. The model can be extended in such a way that also non-isothermal conditions and dynamic effects due to time-dependent deformation rates can be considered. For this, however, one should refer to the special literature (Bonten et al. 2000 Schoche 1997 Wanders 1999). 

In the burst test, where a plane state of stress is forced upon the geomembrane test specimen, the maximum in the stress-strain curve, i.e. the yield point, is less pronounced and a tear occurs rapidly within the yielding region of the test specimen (see Sect. 3.2.9, Fig. 3.12). 

From what has already been diseussed in the sections above, it is sufficiently clear that all eharacteristie parameters derived from a stress-strain diagram (Young s modulus, (upper and lower) stress at yield and elongation at yield, stress at break and elongation at break) are functions of the deformation rate, test temperature and imposed state of stress. 

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