Indentation

About: Indentation is a research topic. Over the lifetime, 13002 publications have been published within this topic receiving 340476 citations.

On Brinell and Boussinesq indentation of creeping solids

Abstract: As an alternative to traditional tensile testing of materials subjected to creep, indentation testing is examined. Axisymmetric punches of shapes defined by smooth homogeneous functions are analysed in general at power law behaviour both from a theoretical and a computational point of view. It is first shown that by correspondence to nonlinear elasticity and self-similarity the problem to determine time-dependent properties admits reduction to a stationary one. Specifically it is proved that the creep rate problem posed depends only on the resulting contact area but not on specific punch profiles. As a consequence the relation between indentation depth and contact area is history independent. So interpreted, the solution for a flat circular cylinder (Boussinesq) is not only of intrinsic interest but serves as a reference solution to generate results for various punch profiles. This is conveniently carried out by cumulative superposition and in particular ball indentation (Brinell) is analysed in depth. A carefully designed finite element procedure based on a mixed variational principle is used to provide a variety of explicit results of high accuracy pertaining to stress and deformation fields. Universal relations for hardness at creep are proposed for Boussinesq and Brinell indentation in analogy with the celebrated formula by Tabor for indentation of strain-hardening plastic materials. Quantitative comparison is made with a diversity of experimental data attained by earlier writers and the relative merits of indentation strategies are discussed.

The Elastoplastic Response of Poly(Methyl Methacrylate) to Indentation

Abstract: This paper describes an experimental and analytical study of the contact compliance and hardness of a glassy polymer, poly (methyl methacrylate), which has an elastoplastic response to indentation using rigid conical and spherical indenters. The experimental method and the associated intrinsic errors are described. The nature and importance of these errors are reviewed and a variety of corrections are applied. The potential errors addressed include the zero error, the indenter tip defect correction and the problems associated with various extrapolations and interpolations of the experimental data necessary in order to abstract the material characteristics of the polymer. The analytical description of the data has been facilitated by an adaptation of the Box-Cox transformation (Box, G. E. P. Sz Cox, D. R. 1964 J. R. Statist. Soc. 26, 211), which is shown to be a most effective way of abstracting the required material characteristics data and minimizing the influence of the intrinsic errors inherent in the compliance method. The deduced material response characteristics of the polymer, in particular the Young’s modulus and the yield stress, are shown to be consistent with data obtained by conventional mechanical testing methods.