Question

Brief Background Penetration hardness is a measure of a materials resistance to indentation. The Rockwell Hardness test is a standard method for characterizing this property of a material. It uses a small indenter, either a hardened ball or diamond cone (Brale), which is pressed into the sample while measuring depth of penetration. There are several scales to select from as indicated in textbook or the chart found in lab. Each scale refers to the type of indenter used and the minor/major loads applied. In some cases it is helpful to measure hardness in a very small region of the material. As an example, you may need to determine if the surface of a piece is harder than it's interior. In that case, microhardness tests are performed and the size of the indentation is used to calculate a hardness value of the material. The Brinell test is similar in that an indentation is made, and the dent size is measured and then hardness calculated. But, Brinell is not a microhardness test, it is a macro test like the Rockwell. When evaluating plastic materials, a common test is the Shore Hardness. There are several scales of Shore hardness, a common one being Shore-D hardness. It works similar to Rockwell in that the penetration depth of a small indenter is measured. The farther the penetration, the lower the hardness value obtained. Answer the questions below. 1. (p174) Hardness testing is considered non-destructive and inexpensive. True or False 2. (p175) Give three types of indentation hardness techniques:1) 3) . For the Rockwell method, identify the indenter (penetrator) and major load used for the following scales: (p176) a) G-scale b) C-scale c) B-scale 4. (p179) Given that the Brinell hardness (BH) for a steel is measured to be 210 (BH 210), what tensile strength would you estimate it to have? . A Vickers microhardness test produced two different size indentations as shown (greatly magnified). Which one indicates a lower hardness, Left or Right ?

Answer 1

Anser 1

The statement is partly true because it is in expensive as long as indentator used are cheap

and partly false because hardness test is of both type Destructive as well as Non Destrutive because in Rockwell, Brinell's, Vicker, Knoop and Shore Hardness techniques the testing leaves a permanent mark on the material or part under testing and if that part is of atmost important for eg. Turbine Blade, Airospace part then it becomes destrutive but if part under testing is to go further processing then it can be used so it becomes NDT.Also there are Non destructive Testing like Eddy Currents Testing, Utrasonic Testing, Rebound testing etc.

Answer 2

here in background Talked about

a) Rockwell Hardness

b) Brinell's Hardness

c) Shore Hardness

d) Knoop Hardness

e) Vickers Hardness

Answer 3

Rockwell hardness Grades

Grade G Indentator Max Load 150Kgf and Indentator size 1/16 inch diameter.

Grade C Indentator Max Load 150Kgf and Indentator 120° diamond spheroconical.

Grade B Indentator Max Load 100Kgf and 1/16 inch-diameter steel sphre.

Answer 4

One widely used HV ≈ 3 *Tensile strength

tensile strength=210/3=70BH