2 TENSILE TESTThe purpose of TENSILE TEST is to check the strength of any metal.Before understanding the test, following definition are required to know.Engineering Stress:Ratio of the applied force to the initial area.
3 Where F is the applied force in newton or in pound. is the cross section area of the test piece in m2 or in inch2.The unit for the Engineering Stress ispascals(N/m2) or PSI (lb/ inch2)
4 Engineering Strain:Ratio of the change in length (elongation) to the original length.WhereChange in length because of the force applied.Where is the original length.
7 Zone IRelation between stress and stain is linear and the curve is a straight line.Where E is proportionality constant and called YOUNG’S MODULUS.Deformation is Elastic in this zone, means No permanent deformation.
8 Zone IIDeformation is permanent. Stress and Strain are not linear. This zone starts from end of the first zone and ends at the highest point of the curve which is called NECKING POINT. This point corresponds to the maximum force applied during the test.The deformation in this zone is called PLASTIC DEFORMATION.
9 Zone IIIAfter necking point, the area of the specimen decreases and hence load carrying capacity of the sample also decreases. Load decreases in the zone and after some time sample fail (fracture) from necking point.
10 Yield Strength (sy): Stress corresponds to the Elastic Limit (up to where, the curve is linear, called yield point).If two limits, Lower will be yield point.
12 ULTIMATE TENSILE STRENGTH (su) Also called Tensile Strength (TS), or Engineering Tensile Strength (suts).Stress at highest point of the curve or at necking point.
13 ENGINEERING FRACTURE STRENGTH (sF) Stress at the last point of the curve. This point is the fracture point.
14 DUCTILITYAbility of a material to deform plastically without fracture. Measure in two terms.Percentage Elongation (%EL)Percentage Reduction in Area (%RA)
15 RESILIENCE & MODULUS OF RESILIENCE (UR) The ability of a material to absorb energy when deformed elastically and to return it when unloaded is called resilience. Modulus of Resilience is the energy per unit volume stored in the specimen while deform elastically. It is area under the curve up to elastic region and can be obtain from
16 TOUGHNESS & MODULUS OF TOUGHNESS (UT) Ability of the material to absorb energy in elastic region. This is the energy stored in the specimen during the test and can be expressed in energy per unit volume.It is the area under the hole curve and can be approximated byFor ductile materialFor brittle material
17 TRUE STRESS (st)Ratio of the instantaneous load and instantaneous (actual) Area.Area conserved during the test up to necking point.