Hardness Testing of Engineering Materials: A Technical Report

Types of Hardness Tester

Introduction

Hardness testing can be used to identify the mechanical properties of engineering materials, and unlike tensile testing which requires specific dimensions on Its test specimens, it relies on pushing a hard indenter with a known force into the surface of the materials in question. As such it is a quick test to perform on engineering materials/ products in several applications (such as quality check on the surtace of a case-hardened specimen, or products having followed a specific heat treatment procedure) and its results can be co-related to strength values (e.g.. the UTS) of the tested materials. 

There are primarily 3 types of hardness tester namely the Brinell, rockers  and Rockwell, which the University of South Wales has in its Materials Laboratory in G118 which are calibrated annually to ensure their proper functioning according to their respective British Standards. The hardness number for both the Brinell and Vickers tests can be derived by dividing the indentation force (it kgf) with the resulting surface area of their indents/ impression on the surface of the tested specimen. The Rockwell's number however is identified by subtracting the depth of penetration from a known constant. 

Please note that the unit of the hardness number has no direct correlation to strength. Hardness numbers can be used as a relative indication of material strength but do not replace tensile test results,Therefore: 

I. The Aims of the laboratory session is to:

(a) establish the hardness number for a range of carbon steels using standard hardness tester under the relevant British Standard;

(b) develop an understanding of the relationship between material's strength with the said parameters. It. The Objectives are:

(c) conduct hardness tests under the relevant British Standards on a range of materials namely low carbon steel, medium carbon steel, and high carbon steel;

(d) gather the test results, produce the necessary hardness numbers. and discuss the results. 

Laboratory Set-Up & Method I

I. You will be provided with 3 steel specimens of varying carbon content, namely: low carbon steel, medium carbon steel, and high carbon steel. Place the specimens one at a time on the test platform of the hardness tester and carry out the test procedure according to the relevant British Standard:

II. Derive or read in the case of Vickers Hardness tester, the Hardness value from the relevant table. You should carry out several tests on a specimen to obtain a representative average hardness reading. You will need to specify the type of hardness tester used, and the condition of the test (type of indenter, load). 
III. Repeat with the remaining test specimens.

IV. If in doubt, please ask the lab technician.

Test Results & Discussion 

I. Tabulate the results and arrange the information in ascending order — softest to strongest. Validate your findings against published data and identify/ correlate where possible the strength values for the tested materials. II. Compare the mechanical properties of the various materials and in particular comment on the effect of increasing the carbon content in steel.  comment on the effect of increasing the carbon content in steel. Compare your empirical results with published data and comment on them. Identify the example applications in which each type of steel specimen can be used. Please note that you must reference any published information which is used in your report.

Conclusion 

I. Conclude what was presented In the Results and Discussion sections. Do not conclude anything that had not been discussed. Think of the conclusion as a short restatement of important findings from the experiment.