Mechanical Tests - Materials

G.GopinathAssistant Prof - Mechanical

(b)

Tensile testing

Tensile testing

Engineering Stress• The engineering stress, or

nominal stress, is defined as the ratio of applied load to original area of the specimen,

0AP

Ductility• 2 quantities commonly used to define ductility

in a tension test are known as elongation and reduction of area.

• Elongation is defined as

• A second measure of ductility is known as a reduction of area, defined as

100 Elongation0

0

lll f

100 area ofReduction 0

0

AAA f

True stress and true strain• Similar to stress definition, true stress is

defined as

where A is the actual area supporting the load (Instantaneous)

• True strain is defined as

AP

0

ln0

ll

ldll

l

Toughness• Energy needed to break a unit volume of material. • Area under stress strain curve.

Effect of Temperature

Various materials

Various materials

Compressive test

Compressive test

Shear testing

Hardness

• Hardness is the ability to resist plastic deformation, usually by penetration/ Indentation load.

• This may also refer to resistance to scratching, abrasion or cutting.

Brinell Hardness Test

Rockwell Hardness Test

Rockwell hardness test

Vickers hardness test

• Vickers hardness test uses a square-base diamond pyramid as the indenter with the included angle between opposite faces of the pyramid of 136 0.

• This angle approximately the most desirable ratio of indentation diameter to ball diameter in the Brinell Hardness test.

• Diamond pyramid hardness Test.

VHN• It is defined as the load divided by the surface

area of the Indentation. • This area is calculated from microscopic

measurements of the lengths of the diagonals of the impression.

VHN

Impact testing

• To measure the toughness, or energy absorption capacity of the materials.

• Charpy impact test • Izod impact Test

•The Specimen is held horizontally – between two supports•The notch on the specimen faces away from the pendulum•The striking energy of the pendulum is 300 Joules

Pendulum

Support

Specimen

Charpy Impact test

•The Specimen is held vertically in a vice

•The notch on the specimen faces the pendulum

•The striking energy of the pendulum is 167 Joules

Pendulum

Vice

Specimen

Izod impact test

DBTT ( Ductile to Brittle Transition Temperature )

DBTT ( Ductile to Brittle Transition Temperature )