Characterization of deformation field in plane-strain indentation of metals

Abstract

A study has been made of the deformation field in plane-strain indentation of metals with a flat punch. Deformation field parameters such as velocity and strain rate have been measured using the technique of particle image velocimetry. For this purpose, images of the indentation region were recorded in situ during the deformation process, and motion of ‘asperities’ specially introduced onto a side of the sample being indented was analysed. The velocity and strain rate fields in and around the indentation zone were obtained from an analysis of the asperity motions. The measurements have shown, among other things, the presence of a dead metal zone underneath the indenter, the formation and evolution of regions of intense strain rates or shear bands and a linear variation of the strain rate with indentation speed. Many of the characteristics of the deformation field, e.g. slip lines and dead metal zone, compare favourably with those inferred from classical solutions for this indentation problem. Extensions of the technique for the study of strain field around indentations and deformation in plane-strain indentation by wedges and cylinders are discussed.

Enhanced subsurface grain refinement during transient shear-based surface generation

“…These crystallographic textures reveal a near 2 m symmetry about the X-direction with high concentrations of orientations along fibers outlined using dashed lines. These fibers were coincident with those exhibited by conventional surface generation within experimental error and the intensities exhibited by the ODFs(8,26) were also within a similar range[23]. However, qualitative examination of the present crystallographic textures suggests a degree of variation within the deformation mechanics during transient surface generation.…”

Deformation field heterogeneity in punch indentation

“…In prior work, these in situ methods were used to measure strain and strain-rate in flat punch indentation of a perfectly plastic, non-strain-hardening material (e.g. lead) [1]. The studies revealed the location of primary and secondary shear bands in the plastic zone and were consistent with Prandtl's framework for describing the deformation field [2], wherein material in the region immediately underneath the indenter moves as a rigid body during indentation.…”

“…no hardening) [1], wherein the deformation is far more localized and occurs in a pattern with three distinct regions: a dead zone, a transition zone and an exit zone. In this case, the hardening causes a semicircular dead zone that is abutted by a deformed zone to form.…”

“…This was not possible in previous PIV studies [1,16], as these studies focused on understanding the deformation field in indentation of pure lead, which does not show appreciable microstructure/strength changes with plastic straining. In the ensuing, the evolution of the deformation field in punch indentation of OFHC copper is measured using both PIV and conventional post-mortem characterization of microstructure and hardness.…”

“…strain rate) difficult to obtain. This has been addressed with the application of image-based deformation measurements, for example particle image (or tracking) velocimetry (PIV/PTV), to map strain and strain-rate fields in indentation problems [1,16]. In these methods, surface asperities are tracked during deformation to yield displacement and velocity fields from which strain rate and strain maps are derived using continuum mechanics formulations [2].…”