MATERIAL SCIENCEFTB 11203

TENSILE AND HARDNESS

Muhammad Ikhwan Bin Banis 50213215241Hidayat Bin Johari 50213215337

INTRODUCTION Two basic quantities:

•Stress

Measures the force required to deform or break a material.

•Strain

Measures the elongation for a given load.

3 TYPE OF STRESSThere are three types of stress:

•Tensile

•Compression

•Shear

The tension and compression are called direct stresses.

STRAIN Strain is defined as the ratio of increase in length to original length.

•Specifically, when force is applied to the wire, its length L increases, while its cross-sectional area A decreases, as sketched:

•The dimensions of strain are unity, i.e. strain is non dimensional.

WHAT IS TENSILE•Tensile strength is a measurement of the resistance to being pulled apart when placed in a tension load.

•The tensile strength of a material is the maximum amount of tensile stress that it can be subjected to before failure.

•There are three typical definitions of tensile strength:

1. Yield strength

The stress at which material strain changes from elastic deformation to plastic deformation, causing it to deform permanently.

2. Ultimate strength

The maximum stress a material can withstand.

3. Breaking strength

The stress coordinate on the stress-strain curve at the point of rupture.

TENSILE TEST•Tensile test are carried out on standard size and shape(dog bone).

Example of tensile test specimen (ASTM E8)

• Engineering stress = Force/Original cross Sectional Area (Newtons/ σ=

• Engineering strain = Extension / Original gauge length (mm/mm)

STRESS AND STRAIN FOR TENSILE

•Used to describe the effects of an increasing tensile force on a material during a tensile test.

•Stress relates the force on specimen to the cross-sectional area of the specimen.

•Strain relates the elongation of a specimen to the original gauge length of the specimen.

HARDNESS TESTING

Hardness is the property of a material that enables it to resist plastic deformation, usually by penetration.The term hardness may also refer to resistance to bending, scratching, abrasion or cutting.

HARDNESS TESTING METHODS:

•Rockwell Hardness Test

•Rockwell Superficial Hardness Testing

•Brinell Hardness Test

•Vickers Hardness Test

•Knoop Hardness Testing

The usual method to achieve a hardness value is to measure the depth or area of an indentation

left by an indenter of a specific shape, with a specific force applied for a specific time. There are

three principal standard test methods for expressing the relationship between hardness and the

size of the impression, these being Brinell, Vickers, and Rockwell. For practical and calibration

reasons, each of these methods is divided into a range of scales, defined by a combination of

applied load and indenter geometry.

BRINELL HARDNESS TEST

•used to test materials that have a structure that is too coarse or that have a surface that is too rough to be tested using another test method, e.g., castings and forgings.

•often use a very high test load (3000 kgf) and a 10mm wide indenter.

Brinell Hardness Test With the Brinell test, a hardened steel ball or tungsten carbide ball is pressed for a time of 10 to 30 seconds into the surface of specimen by a standard load F (kgf). After the load and the ball have been removed, the diameter of the indentation, d (mm) is measured. The Brinell hardness number (BHN or HB), is obtained by dividing the size of the load applied by the surface area of the spherical indentation A (mm2).

Where b (mm is the depth of indentation, D (mm) is the diameter of the ball. The Brinell test cannot be used with very soft or very hard materials with hardnesses up to 450HB with a hardened steel ball and 600 HB with a tungsten carbide ball.

VICKERS HARDNESS TEST

•referred as a microhardness test method,used for small parts, thin sections, or case depth work.

•useful for testing on a wide type of materials as long as test samples are carefully prepared.

•A square base pyramid shaped diamond is used for testing in the Vickers scale.

•Typically, a load of 30kg is used for steels and cast iron, 10kg for copper alloys, 5kg for pure copper

and aluminum alloys, 2.5kg for aluminum and 1kg for lead, tin and tin alloys. Up to a hardness value

of about 300 HV, the hardness value number given by the Vickers test is the same as that given by

the Brinell test.

•The Vickers hardness number (VHN or VH) is obtained by dividing the size of the load F (kgf), is

applied by the surface area, A (mm2), of the indentation. Thus, the VHN or HV is given by

VHN =Load (kg)/Surface Area (mm2)

: 1.85 F/ d^2

ROCKWELL HARDNESS TEST

•used on all metals, except in condition where the test metal structure or surface conditions would introduce too much variations; where the indentations would be too large for the application; or where the sample size or sample shape prohibits its use.

•Formula : HR= E-e

>Differs from the Brinell and Vickers test in not obtaining a value for the hardness in terms of an

indentation but using the depth of indentation, this depth being directly indicated by a pointer

on a calibrated scale. The tests use either a diamond cone or a hardened steel ball as the

indenter.