Understanding subsurface integrity in machining of cellular solids
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Thermomechanical loading during surface severe plastic deformation in machining is marked by the generation of high and graded strains, strain rates and temperatures in bulk materials. The present study examined the surface integrity of cellular solids processed by machining-based processing at full volume using x-ray micro-computed tomography. The structural parameters of the strut-pore network were characterized as a function of controllable parameters of cutting speed, feed rate and depth of cut. The resulting surfaces were shown to be comprised of density gradients directly controlled by the processing parameters employed. A series of in situ compressive loading experiments was conducted to evaluate the effect of the structural gradation on mechanical response and showed enhanced plateau stress levels at low strains for the graded surfaces. Direct measurements of incremental strain using digital volume correlation identified the role of the gradation in arresting deformation at low strains. Implications of these results for using surface deformation processing in achieving specific properties by functional gradation were briefly discussed.