MECHANICAL PROPERTIES OF MATERIALS

1. MECHANICAL PROPERTIES

ØTensile, Compressive, Shear & Bulk Strength

ØDuctility

ØYield Strength

ØToughness

ØAnelasticity

ØViscoelasticity

ØHardness

ØCreep

ØFatigue

ØStress Relaxation

ØImpact Strength

TENSILE, COMPRESSIVE, SHEAR & BULK STRESS

ØUnder Tensile Stress, load increases length of material, whereas under Compressive Stress, load decreases length of material. In both cases, nature of stress-strain curve remains same

ØShear Stress is force per unit area parallel to surface area of specimen as shown in figure, which is measured in terms of angle of shear

ØShear stress (t) and shear strain (g) are related with each other by ‘Shear Modulus of Rigidity (G)’ 

   and given as t = G g

ØBulk Stress is force per unit area applied on material uniformly in all directions (hydrostatic pressure), so that material changes its volume without changing its shape

ØRatio of bulk stress to bulk strain is known as ‘Bulk Modulus’   [-dp / (dV/V)], where negative sign implies that as pressure increases, volume decreases

ØReciprocal of bulk modulus is known as ‘Compressibility’

ØPoisson’s Ratio is ratio of strains in x or y-directions to that of in z-direction, i.e. u = - (ex / ez) = - (ey / ez) (normally lies in range of 0.25 – 0.35 for metals)

ØElongation in one direction (z-direction) produces compression in other two directions (x and y-directions)

DUCTILITY

ØMaximum percentage elongation for a material or maximum percentage reduction in cross-sectional area (normal to tensile stress) for a material without fracture

ØDuctility = % EL = [(change in length / original length) * 100]

ØDuctility = [(change in diameter / original diameter) * 100]

ØPure metals generally have ductility in range of 35 – 50 %

YIELD STRENGTH

ØStrength of material after which it starts yielding plastically without any appreciable increase in applied stress (perfectly plastic material)

ØDue to strain hardening, yield strength / stress of material goes on increasing up to maximum tensile / compressive strength after which, necking and subsequently fracture takes place