Tensile testing

Formular for %EL

%EL = ((Lf-Lo)/Lo) x 100 Lf = length between gauge marks after fracture. Lo = original gauge length.

Formular for %R of A

%RA = ((Ao-Af)/Ao) x 100 Ao = original cross-sectional area. Af = cross-sectional area at the fracture.

Three types of hardness testers?

1. Brinell 2. Vickers 3. Rockwell

Two types of Impact testing.

1. Charpy notched-bar impact test. 2. Izod notched-bar impact test.

What encourages Brittle failure?

1. Dynamic (impact) loads. 2. Low temperatures. 3. The presence of stress concentrations.

2 advantages of Brinell test.

1. Gives good indication of the properties of the whole material, rather than just the surface. 2. Less sensitive to surface condition.

3 points for the Vickers test

1. Much smaller loads are used 2. Uses a dimond square-based pyramid indentor. 3. The penetrator makes a square impression

What are the two ways ductility can be measured?

1. Percentage elongation, %EL 2. Percentage reduction of area, %RA

Disadvantages of Brinell and Vickers

1. Requires a semi-skilled operator. 2. Designed for testing wide rang of materials. Not needed.

Advantages of Rockwell hardness test.

1. Requires less skill to operate. 2. Wide range of hardness. 3. Very quick and easy to operate.

Three reasons why you would want to do hardness testing on materials

1. To check the acceptability for use. 2. Quality control. 3. To control uniformity of properties.

Advantages of Vickers hardness test

1. Uses small indentor, so it can test thin samples. 2. Uses a dimond as indentor, can test very hard materials. 3. More accurate results.

What type of testing is done on brittle materials?

Compression testing.

Characteristics of tough materials

High levels of ductility coupled with strength.

Tensile strength

Is a measure of the ability of a material to resist a force that tends to pull it apart.

Brittle behaviour

Is when fracture takes place at the end of plastic deformation.

Modulus of elasticity (E)

It is the linear relationship between the stress on the metal and the strain that is produced. Stress/Strain Pg 43-45 of lecture slide

What does hardness tests check?

It only checks the surface characteristics of the material

What is Brinell hardness number (BHN) defined as?

Load on ball/ Area of impression

Definition of Vickers hardness test.

Load on ball/Area of impression

Ultimate strength

Maximum stress that can be obtained before fracture occurs.

What is the Modulus of elasticity a measure of?

Measure of ridigity or stiffness.

Definition of hardness

Resistance to permanent deformation under a static load.

Ductility

The abilityof a metal to be drawn.

How can you determine the proof stress or proof strength of a metal?

The load that causes the deformation divided by the original cross-sectional area.

Elastic limit

The point where the linear relationship of stress and strain stops for elastic deformation.

Yield point

The transition from elastic to plastic deformation.

What are we trying to find out when carrying out tensile testing?

The ultimate strength of the material.

Proof stress or proof strength

The value of transition from elastic to plastic behaviour. This value is normally a plastic deformation of 0.2% of the specimen length. Pg 40 of slide

Brinell hardness equation

_______________P___________ (πD/2)(D-sqrt(D^2-d^2) P = load D = diameter of the indentor d = diameter of the impression