Applying a non-hydrostatic stress to solids containing intergranular liquid films (internally wetted polycrystals, liquid-saturated porous media etc) may lead to a considerable increase in the solid deformability. Such a liquid-enhanced deformation mechanism (aka pressure solution) involves the dissolution of solids at grain-to-grain contacts into the liquid in areas of relatively high stress, diffusion of solutes along the grain boundaries or pore space and the re-precipitation at stress-free or hydrostatically stressed sites. The slowest of the three serial processes controls the overall deformation rate. This phenomenon has been extensively studied by many geologists considering it as a major deformation process of sedimentary and metamorphic rocks in Earth’s crust and, to a lesser extent, in liquid phase sintering studies.
Previously, we have investigated pressure solution creep of various materials trying to find ways for controlling the strain rate in order to intensify this process for some technological procedures or to avoid its injurious effects (monuments degradation etc), as well as to get a better insight into the coupling of physicochemical and tectonophysical factors in Earth’s history. Various effects of liquid composition [1] and a really dramatic impact of cyclic loading [2] were found. Earlier, an arguable increase of intergranular mass transport capabilities as a result of stress relaxation was assumed by other authors [3], who pointed out that cyclic variations of stress might provide an efficient deformation enhancement. In our experiments, each transition from static to cyclic regime produced an increase — sometimes manifold — in creep rate which lasted over the whole time of cyclic impact. After returning to static regime, the initial creep rate reappeared. Any noticeable changes in strain rate were absent in a pure inert medium (paraffin oil).
In this paper, we are reporting some new results on loading-unloading effects. The experiments were carried out on polycrystalline alkali halides intergranurally wetted with saturated aqueous solution. Cyclic loading-unloading impact was observed in specimens containing an intrinsic continuous network (quasi-infinite percolation cluster) of wetted boundaries, or in the cases when such a cluster appeared as a result of applied stresses. Single crystals indentation with ball and cylindrical glass indenters was also used. The thickness of liquid interlayers was measured under loading and unloading phase and their structure was investigated. A mechanism for effects observed has been proposed.
1. Traskine V., Skvortsova Z., Muralev A.(2008) Intergranular pressure solution in internally wetted polycrystals: Effect of additives. Materials Science and Engineering: A, v.495, Issues 1-2, p.132-137November 15, 2008
2. Traskine V., Skvortsova Z., Muralev A., Zubov D. (2009) Pressure solution creep under cyclic loading. Miner.Petrol., v. 97, 3-4, p.265-274.
3. Jordan G., Aldushin K., Lohkämper T., Schmahl W. (2005) Dissolution-precipitation creep under cyclic stress. Geochim.Cosmochim.Acta 69(Suppl): A314