Definitions

Stress = load / area

Strain = deformation / gage length = &Delta L / L_o

Modulus of Elasticity, E = slope of intial linear part of the stress-strain curve

Proportional Limit Stress, &sigma_pl = stress value at which the stress-strain curve goes nonlinear

Yield Point Stress, &sigma_y = stress value at which the stress-strain curve goes horizontal (for many steels)

0.2%-Offset Yield Stress, &sigma_{0.2% y} = the stress value at which a line drawn with slope E starting at 0.002 strain intersects the stress-strain curve

Ultimate Tensile Stress, &sigma_ult = largest stress on the stress-strain curve (top of the curve)

Engineering Fracture Stress = fracture load / original area

True Fracture Stress = fracture load / fracture area

Energy at Yield = area under the elastic portion of the load-deformation curve

Energy at Break = area under the entire load-deformation curve

Modulus of Resilience, U_r = area under the elastic portion of the stress-strain curve = &sigma_pl² / 2E = the amount of energy (or work) stored per unit volume at the elastic limit

Modulus of Toughness, U_t = area under the entire stress-strain curve = the amount of energy absorbed per unit volume at fracture -- a measure of the material ductility

Percent Elongation = (L_f - L_o) / L_o x 100%

• Percent Elongation of 2" Gage Length = ΔL₂ / 2" x 100%

• Percent Elongation of 8" Gage Length = &DeltaL₈ / 8" x 100%

Percent Reduction in Area = (A_f - A_o) / A_o x 100%