Wavy Contact Research Articles

Interaction of a shock front with a wavy contact discontinuity

The excitation of Richtmayer-Meshkov instability fora0λ−1>1 (a0λ are the amplitude and wavelength of the initial contact discontinuity) is experimentally and numerically investigated. The effect of the curvature of the initial contact discontinuity on the development of the instability is determined.

Peridotite sills and metasomatic gabbros in the Eastern Layered Series of the Rhum complex

Mapping of the Eastern Layered Series (ELS) of the Rhum ultrabasic complex on the northern flank of Hallival shows that peridotite and allivalite (troctolite or gabbro) layers are laterally discontinuous and vary both in thickness and lithology. Peridotite generally has sharp upper and lower contacts against the allivalites, which sometimes cut across the layering in the allivalite. Reaction, dissolution and hybridization effects between peridotite and allivalite are developed locally. Some troctolite layers terminate as isolated, fingered blocks in peridotite. There are many small peridotite bodies which are clearly intrusive into allivalite and have previously been identified as distinct peridotite sheets and plugs. They are petrographically almost identical to the major stratiform peridotites and in some cases are apophyses from them. We propose that many of the peridotite layers in the ELS formed as thick sills of picritic magma emplaced into a partly solidified, layered troctolite complex. The stratiform gabbros of the ELS are heterogeneous, layered rocks that commonly contain relicts of troctolite and anorthosite. Wavy (metre-scale) contacts between gabbro and troctolite cut across pre-existing grain-size, modal and rhythmic layering with little disruption. These metasomatic gabbros mimic the textures, grain-size and rhythmic layering of their troctolitic protoliths. We propose that many of the ELS gabbros formed as a result of interaction between porous troctolites and a low-temperature basaltic melt. Residual basaltic melt segregated from solidifying peridotite may have caused this metasomatism.

The hysteresis loop of a fixing element. Influence of contact surface waviness.

The stiffness and energy losses at a fixing element, which has a contact surface and is subjected to oscillating tangential loads, are studied. They are calculated using two different kinds of calculation model. One model has a flat contact surface and the other has a wavy contact surface. The results are compared with experimental results and it is shown that by using a wavy contact surface, the numerical results are similar to the experimental ones. Because of flatness inaccuracies on the actual surfaces, the real contact areas are much smaller than that of the apparent contact areas. From the numerical results, as waviness increases and the height of the waviness becomes lower, the stiffness increases and the energy loss decreases, becoming more similar to that of a flat contact surface.