PLASTIC DEFORMATION AND ROUGHNESS OF FREE METAL SURFACES

Relationships between roughening of plastically deforming free metal surfaces and phenomenological, mechanistic and continuum mechanics aspects of uniform and localized modes of plastic deformation were studied with a special emphasis on developing a comprehensive, unified framework for further research in this area.; Extensive critical literature reviews of the following areas were developed: (i) random process theory description of roughness; (ii) theoretical and experimental aspects of roughness measurements by means of stylus profilometry and laser light scattering methods; (iii) roughening kinetics descriptions of a wide variety of metals and alloys identifying the key variables controlling roughening; (iv) mechanistic roles of crystal plasticity, surface instability, shear bands, diffuse and localized necking, voids and cracking in the roughening process; (v) continuum theory bifurcation, post-bifurcation and imperfection/damage sensitivity descriptions of the different localization modes in the forming limit diagram framework.; The main new developments resulting from the work include: (i) an "excess" roughness-based criterion for defining experimental localization strains from objectively measured roughening kinetics data; (ii) a simple slip/shear model to describe the crystal plasticity controlled roughening behavior of single crystals and shear band controlled roughening behavior of polycrystalline materials; (iii) a composite grain structure/double pileup model to describe the role of grain size, position and orientation in both roughening and localization processes; (iv) enhanced understanding of the J{dollar}sb{lcub}2{rcub}{dollar} corner theory localization predictions by means of post-maximum strain and other analyses; (v) linking of the Clausing plane strain sensitivity results to the J{dollar}sb{lcub}2{rcub}{dollar} corner theory localization predictions by means of a new material property correlation; (vi) corrected comparisons between experimental and J{dollar}sb{lcub}2{rcub}{dollar} corner theory surface instability and shear band formation strains for three steels showing that the disagreement between the two increases with increasing yield stress; (vii) a laser camera for surface roughening studies; (viii) a triple-N power law stress vs. strain model for the spheroidized AISI 1090 steel tested in uniaxial and Clausing-typeplane strain tension; (ix) existence of a coupling with the laser camera-based surface roughness observations and the characteristics of the bulk deformation field for spheroidized AISI 1090 steel; (x) absence of "excess" roughness, and thus of an objectively determined surface instability strain for spheroidized AISI 1090 steel in plane strain tension; (xi) a detailed program for near-future work.