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11.
We investigate the evolution of wear and friction along experimental faults composed of solid rock blocks. This evolution is analyzed through shear experiments along five rock types, and the experiments were conducted in a rotary apparatus at slip velocities of 0.002–0.97 m/s, slip distances from a few millimeters to tens of meters, and normal stress of 0.25–6.9 MPa. The wear and friction measurements and fault surface observations revealed three evolution phases: A) An initial stage (slip distances <50 mm) of wear by failure of isolated asperities associated with roughening of the fault surface; B) a running-in stage of slip distances of 1–3 m with intense wear-rate, failure of many asperities, and simultaneous reduction of the friction coefficient and wear-rate; and C) a steady-state stage that initiates when the fault surface is covered by a gouge layer, and during which both wear-rate and friction coefficient maintain quasi-constant, low levels. While these evolution stages are clearly recognizable for experimental faults made from bare rock blocks, our analysis suggests that natural faults “bypass” the first two stages and slip at gouge-controlled steady-state conditions. 相似文献
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Yuval Cohen 《Marine pollution bulletin》1984,15(6):234-235
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Vladimir Lyakhovsky Amir Sagy Yuval Boneh Ze’ev Reches 《Pure and Applied Geophysics》2014,171(11):3143-3157
Slip along faults generates wear products such as gouge layers and cataclasite zones that range in thickness from sub-millimeter to tens of meters. The properties of these zones apparently control fault strength and slip stability. Here we present a new model of wear in a three-body configuration that utilizes the damage rheology approach and considers the process as a microfracturing or damage front propagating from the gouge zone into the solid rock. The derivations for steady-state conditions lead to a scaling relation for the damage front velocity considered as the wear-rate. The model predicts that the wear-rate is a function of the shear-stress and may vanish when the shear-stress drops below the microfracturing strength of the fault host rock. The simulated results successfully fit the measured friction and wear during shear experiments along faults made of carbonate and tonalite. The model is also valid for relatively large confining pressures, small damage-induced change of the bulk modulus and significant degradation of the shear modulus, which are assumed for seismogenic zones of earthquake faults. The presented formulation indicates that wear dynamics in brittle materials in general and in natural faults in particular can be understood by the concept of a “propagating damage front” and the evolution of a third-body layer. 相似文献
14.
The surface runoff system is often represented by a single-input single-output model in which the rainfall excess x(t) is defined as the input function and the direct surface runoff y(t) is the output. The problem considered is the optimal identification of the system from given records of several independent storm events each consisting of an input and the corresponding output function. The system is represented by a discrete-time second-order Volterra series. The method is a point by point identification which can be extended to Volterra systems of order higher than a second order. The identified system is required to be conservative as in a previous work of Diskin & Boneh [1973]. In this study the identified system is further required to be copositive. Therefore the notion of copositivity is introduced and an example of a watershed system in Southern Illinois is identified with variable copositivity threshold constraints. 相似文献