Numerical studies on microparticle impact/contact with smooth and rough surfaces.

摘要

Two related problems are studied by analysis and numerical simulation: the impact of microparticles with surfaces and rough surface contact in the presence of molecular adhesion. Molecular adhesion here implies short-range interaction of the Lennard-Jones type.; A three-dimensional impact model was developed for arbitrarily shaped particles with nominally smooth surfaces and spherical contact regions. Numerical and analytical results show that the solution paths on the phase portrait (curves of velocity versus displacement) are determined by initial conditions and physical parameters representing material stiffness, surface energy and damping coefficients. Microparticle bounce or capture is delineated by different solution paths. Numerical simulations are compared with the results of oblique impact experiments. Acquired physical parameter values then are used in the model to predict more general impact scenarios. In this manner the numerical model is validated and shown to predict realistic situations. Additional simulations were conducted to investigate the effects of changes in microparticle shape and initial conditions.; Rough surface contact behavior was investigated using two approaches. In one approach, currently available contact models were used with rough surface reconstruction. Surface reconstruction was achieved through an aggregation method of overlapping parabolas representing surface asperities. The second approach taken was the direct simulation of rough surface contact without surface reconstruction. A self-consistent model was used to simulate random surface roughness. The model is self-consistent in that surface deflection is computed by half-space elastic theory and the resulting interfacial force from the Lennard-Jones law. The pseudo arc-length path-following method is used to jump over “turning points” and find multiple solutions. Finally, both linear-elastic, rough-surface contact and adhesive contact were simulated in a comparative manner to elucidate the salient features of rough surface contact in the presence of molecular adhesion.