Direct Observation of the Mechanics of Friction at a Single Asperity on Mineral Surfaces

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9706580 Kohlstedt The PI proposes a study that will contribute to our understanding of the frictional behavior of rocks, particularly the deformation processes occurring at asperities between sliding rock surfaces. Insight into this process will be elucidated from an experimental investigation of the deformation mechanisms and rheology at a single asperity sliding on the surface of the same or a different mineral. By examining the frictional response at a single asperity, the PI can directly interpret the measured mechanical properties in terms of the observed microstructural damage. Experiments will be performed on a suite of minerals including olivine, calcite and halite surfaces which exhibit a range of brittleness versus plasticity at room temperature. Both static indentation and dynamic scratch experiments will be carried out using two unique micro/nanomechanical testing apparatuses that have been recently developed. The partitioning of strain between brittle fracture and plastic flow processes and the dependence of this partitioning on slip rate, penetration rate and humidity will be determined. The coefficient of friction in slide-hold-slide tests and velocity-step tests to constrain its evolution will also be measured. Microstructures will be characterized using optical, scanning electron, transmission electron, and atomic force microscopy techniques. ***