Determining the mechanical properties of small volumes of material from submicrometer spherical indentations
- PDF / 1,468,301 Bytes
- 12 Pages / 576 x 792 pts Page_size
- 103 Downloads / 246 Views
The stress/strain behavior of bulk material is usually investigated in uniaxial tension or compression; however, these methods are not generally available for very small volumes of material. Submicrometer indentation using a spherical indenter has the potential for filling this gap with, possibly, access to hardness and elastic modulus profiles, representative stress/strain curves, and the strain hardening index. The proposed techniques are based on principles well established in hardness testing using spherical indenters, but not previously applied to depth-sensing instruments capable of measurements on a submicrometer scale. These approaches are now adapted to the analysis of data obtained by stepwise indentation with partial unloading, a technique that facilitates separation of the elastic and plastic components of indentation at each step and is able to take account of the usually ignored phenomena of "piling up" and "sinking in".
I. INTRODUCTION 1
Indentation with a steel ball, introduced by Brinell early this century to provide a means of quantifying the different qualities of iron and steel, engendered considerable interest at the time due to its ability to allow a number of materials properties to be investigated through a simple test. This ability arose from the strain hardening behavior of elastic/plastic materials and a simple relationship that exists between strain and the size of spherical indentations. Due to the ease with which stress strain curves can be obtained in uniaxial tension or compression, the use of spherical indentation for this purpose has been largely ignored and its use limited to bulk hardness testing in a form that minimizes the effects of strain variation. Limited in this way, the Brinell hardness test is not free of problems, among which are dependence of hardness number on test conditions, the large size of indentations that is unacceptable in precision engineering, and deformation of the steel balls used as indenters. This latter limits its application to soft materials. The Vickers, Knoop, and Rockwell tests, which use small diamond pyramids or cones, were introduced to avoid these problems and have become industry standards. The two former tests have also been used at very low loads to measure the nominal hardness of thin films or small volumes of materials. More recently, instrumented micromechanical probe systems using Berkovich indenters have been developed that enable the nominal hardness and modulus of localized volumes or thin films to be investigated. Unfortunately, uniaxial tension or compression testing is not readily accessible to the developing field of surface engineering where the properties of thin J. Mater. Res., Vol. 10, No. 1, Jan 1995
surface layers and small volumes of individual material phases are of great importance. This need may be addressed by use of spherical indentation using small, very precise, diamond spherocones, as recently proposed by the authors.2 Such an approach coupled with submicrometer penetration, stepwise loading, and measurement of p
Data Loading...
