Bulk mechanical properties Stiffness Strength Elasticity Ductility Brittleness

Bulk mechanical properties • Stiffness • Strength • Elasticity • Ductility • Brittleness • Malleability • Toughness • Resilience • Hardness

Stress-Strain curve Unique for every material Pulling force applied The amount of elongation (stretch)

Initial response is linear Stress and strain are proportional to one another Elastic Range Proportional Limit (The stress at which proportionality ceases)

Modulus of Elasticity (E) The proportional constant (ratio of stress and strain) A measure of stiffness – The ability of a material to resist stretching when loaded An inherent property of a given material

Elastic Limit Uppermost stress of elastic behavior

Yield Point When the elastic limit is exceeded A very small increase in stress produces a much greater strain Most materials do not have a welldefined yield point

Plastic Deformation Unrecoverable elongation beyond the elastic limit When the load is removed, only the elastic deformation will be recovered

Stiffness The ability to resist deflection Sigma = stress or load; Epsilon = strain or deflection

Strength The ability of a material to resist deformation. The maximum load before failure. stiffness ≠ strength • Y = Yield strength • U = Ultimate strength • R = Rupture (failure)

Elasticity The ability of a material to resume its normal shape after being stretched or compressed

Ductility • The ability of a material to undergo considerable plastic deformation under tensile load before rupture • The ability to stretch without breaking

Tensile Test – Stress-Strain Curve Ductility Amount of plasticity before fracture The greater the ductility, the more a material can be deformed

Brittleness • Absence of any plastic deformation prior to failure • Lack of ductility; not necessarily a lack of strength

Malleability • The ability of a material to undergo considerable plastic deformation under compressive load before rupture. • The ability to be hammered into shapes.

Toughness l l A combination of strength and ductility. The ability to absorb punishment without breaking in two.

• Toughness Work per unit volume required to fracture a material Total area under the stress-strain curve from test initiation to fracture (both strength and ductility)

Resilience l The ability of a material to spring back into its original shape.

Tensile Test – Stress-Strain Curve Resilience The amount of energy per unit volume that a material can absorb while in the elastic range Area under the stress-strain curve Why would this be important to designers? Hint: car bumper

Hardness • The ability of a material to resist scratching, wear, or penetration