Load-deformation, paper testing

ABSTRACT To identify the relationship between the development of surface discontinuities and the stress-strain state of rocks, we introduce a paper, which is based on laboratory experiments. Artificial (a mixture of cement and sand) and natural rock specimens (marble, dolerite, sandstone) were made in the form of disks with thickness of 10 mm and diameter of 30 mm. Mechanical Brazilian tests were performed by servo-hydraulic press Instron 8802. The crack propagation during the mechanical tests was recorded with industrial camera Pixelink. The plots identifying stages of loading and depending on the behavior of the summed surface deformation pattern of the fracture were drawn. Study allowed to get a more detailed description of rock deformation and prediction of discontinuities (cracks) formation through the observed surface deformations. 

There are relatively few papers that have explored the viscoelastic response of UHMWPE to indentation. Typically, indentation tests of viscoelastic materials have included a pause in the load-unload curves at the maximum load to allow creeplike deformation to occur [21]. Researchers have typically inserted a hold time of between 10 and 100... 

In paper [43] acceleration of the stress relaxation process was found at loading of epoxy polymers under the conditions similar to those described above (Figure 6.8, curves 2-4). The authors [43] explained the observed effect by the partial rupture of chemical bonds. In order to check this conclusion in paper [39] repeated tests on compression of samples, loaded up to the cold flow plateau and then annealed at T < T, were carried out. It has been established that in the diagram o-e tooth of yield is restored. This can occur at the expense of the restoration of unstable clusters, since the restoration of failed chemical bonds at T < is scarcely probable. In this connection it is also necessary to note that yield tooth suppression as a result of preliminary plastic deformation was observed earlier for linear amorphous polymers, for example, polycarbonate [44], for which the chemical bonds network is obviously absent. 

The tensile behaviour of concrete is determined by the complete stress-deformation relation under tensile loading. Previously, it has been assumed that the 0-6 relation obtained from a deformation controlled tensile test directly yields the material property. Recently, however, it has been demonstrated by experiments [1] and by finite element analyses [2] that the post-peak behaviour can be affected by a (macro-)structural behaviour of such a specimen. In this paper it will be demonstrated that this phenomenon can also be studied by means of a simple numerical model. 

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