Rotation field in wedge indentation of metals
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Tejas G. Murthy Department of Civil Engineering, Indian Institute of Science, Bangalore 560 054, India
Chris Saldana Department of Industrial and Manufacturing Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802
Srinivasan Chandrasekara) Center for Materials Processing and Tribology, Purdue University, West Lafayette, Indiana 47907 (Received 26 May 2011; accepted 17 August 2011)
A study is made of the rotation field in wedge indentation of metals using copper as the model material system. Wedges with apical angles of 60° and 120° are used to indent annealed copper, and the deformation is mapped using image correlation. The indentation of annealed and strain-hardened copper is simulated using finite element analysis. The rotation field, derived from the deformation measurements, provides a clear way of distinguishing between cutting and compressive modes of deformation. Largely unidirectional rotation on one side of the symmetry line with small spatial rotation gradients is characteristic of compression. Bidirectional rotation with neighboring regions of opposing rotations and locally high rotation gradients characterizes cutting. In addition, the rotation demarcates such characteristic regions as the pile-up zone in indentation of a strain-hardened metal. The residual rotation field obtained after unloading is essentially the same as that at full load, indicating that it is a scalar proxy for plastic deformation as a whole.
I. BACKGROUND AND INTRODUCTION
The deformation field obtained in metal indentation has been the subject of numerous investigations, both theoretical and experimental, due largely to its relevance for studying elastic and plastic properties of solids.1–4 In this context, hardness numbers and force–displacement curves obtained from instrumented indentation may be considered to provide a global picture of the indentation process. While such information is adequate for engineering purposes, the integrated nature of these quantities means that they do not reveal sufficient information about the underlying details of plastic flow, kinematics of material displacement, and self-similarity of deformation. Early work to study deformation in wedge indentation directly was carried out by Hill et al5 using slip-line field theory to analyze frictionless wedge indentation. The analysis provided a characterization of the mean contact pressure in terms of yield strength and indenter angle. In the same work, the deformation was studied using split lead specimens. A grid was inscribed on one-half of the lead specimen, and the two halves were held together during indentation. The postindentation deformation pattern was examined after separating the two halves to assess a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.294 284
J. Mater. Res., Vol. 27, No. 1, Jan 14, 2012
http://journals.cambridge.org
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the nature of the deformation. Mulhearn6 investigated the deformation pattern produced by indentation of cold-rolled st
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