Depth-sensing indentation at macroscopic dimensions
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A macroscopic-scale depth-sensing indentation apparatus with the ability to be mounted on an inverted microscope for in situ observation of contact events was calibrated using the Oliver and Pharr [J. Mater. Res. 7, 1564 (1992)] procedure with a two-parameter area function. The calibrated Vickers tip was used to determine the projected contact area at peak load and the modulus and hardness of a variety of non-metallic materials through deconvolution of the measured load-displacement traces. The predicted contact area was found to be identical to the measured area of residual contact impressions. Furthermore, for transparent ceramic materials the projected contact area during loading was found to be the same as the area measured from the diagonal of post-indentation residual contact impressions. The modulus and hardness values deconvoluted from the load–displacement traces were compared with independent measurements. The effects of sample clamping, column compliance, and tip radius on the load–displacement data and inferred materials properties were also examined. It is suggested that the simplicity of instrumentation and operation, combined with the ability to observe indentations optically, even in situ, makes macroscopic-scale depth-sensing indentation ideal for fundamental studies of contact mechanics.
I. INTRODUCTION A. Motivation
Depth-sensing indentation (DSI) has in recent years become a common technique for characterization of metals,1 ceramics,2 and polymers.3 In particular, small-load indentations are being used to characterize thin film and surface layer properties4 and small-scale deformation phenomena.5 Analysis of the load–displacement (P-h) data recorded continuously throughout the load–unload cycle provides information about the projected contact area at peak load, which is coupled with the measured unloading stiffness to provide estimates of the elastic modulus and hardness. The analysis method, however, requires careful calibration to determine the column compliance and indenter tip shape. The most popular calibration technique is that of Oliver and Pharr,6 which is based on the elastic solution of Sneddon7 for indentation by an axisymmetric body. It is the purpose of this work to examine this calibration technique at large loads and macroscopic length scales at which the indentation impressions can be examined optically. The calibration
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Present address: Seagate Technology, Bloomington, Minnesota 55435 J. Mater. Res., Vol. 17, No. 10, Oct 2002
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and analysis procedures of Oliver and Pharr are used to examine a variety of nonmetallic materials with a twoparameter area function introduced previously.8 The indentation impression area, elastic modulus, and hardness are determined from the P-h traces, and the areas are compared with those determined from direct optical measurements of the residual indentation impression. The post-indentation corner-to-corner area is shown to be equivalent to the contacted indentation area at peak load for th
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