A sensitive pyramidal-diamond tool for indentation measurements

Abstract

A sensitive diamond indenting tool was developed which gives indentations of accurately measurable length in the most resistant steels with loads of less than 1 kg. It was found that the use of these light loads permits extension of indentation tests to small specimens and to tests of brittle materials, such as glasses, which shatter under the heavy loads required by present indenters. The indenter is pyramidal in form, giving a diamonn-shaped (rhomb) indentation of which the diagonals have an approximate ratio of 7 to 1 instead of 1 to 1 for the square-based pyramid. Such indenters were duplicated to the required accuracy and showed no discernible wear with use. Elastic recovery of indentations with this indenter takes place in a transverse rather than a longitudinal direction, and, consequently, from the measured length of the long diagonal and the constants of the indenter, unrecovered dimensions of an indentation are obtained. Results of tests are expressed as indentation numbers which relate the applied load in kilograms to the unrecovered projected area in square millimeters. Recovered projected areas also, may be determined with an added measurement of the short diagonal. Since knowledge of both recovered and unrecovered dimensions may be obtained, the indenter offers possibilities for study of the fundamentals involved in indentation testing that are not afforded by ball, cone, and square-based pyramidal indenters, which, because of their symmetrical form, yield recovered dimensions only. The performance of seven indenters of different angular formation was investigated to determine their relative sensitivity and adaptability for use in different materials and to determine also the effect of load and of different dimensional bases of computation on indentation number. Consideration of the results led to the selection of an indenter which gives excellent performance in many materials. Comparison is made of indentation numbers given by this indenter and corresponding Brinell and Vickers numbers for the same specimens. CONTENTS Faga 1. Introduction _________________________. ___ __ __ ___ ___ _ _ _ _ _ ____ _ _ 40 1. Indentation testing ________. ______. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 40 2. Forms of indenters ____ _______ ___ __ ______ __ ._ _ ___ _ __ _ __ _ _ 41 (a) Indenters in common use____ __ ______ __ _ _ _ _ _ _ _ __ _ _ 41 (b) Development of the diamond-based pyramid indenter. 41 3. Purpose of this investigation__ __ __ __ _ __ __ _ _ __ __ _ _ _ _ _ _ _ __ __ 41 II. Diamond-based indenting tooL__ ____ __ ___ ___ _ __ _ _ _ _ __ _ __ _ _ ____ _ _ 42 1. Description_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 42 2. Production, duplication, and weaL________________________ 43 III. Preliminary considerations for the indentation tests _______________ \.. 43 1. Various indenters used _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 43 2. Indenting and measuring apparatus __ ______________________ ' 44 (a) Mechanisms for applying loads_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 44 (b) Apparatus for measuring indentations_ _ _ _ _ _ _ _ _ _ _ _ _ _ 44 3. Specimens______________________ __ ______________________ 45 (a) Materials and specimens selected_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 45 (b) Size___ _______________ __ ________________________ 45 (c) Preparation___ _ __ ___ _______ _ _ __ __ __ __ __ __ __ _ ____ 45