Young's modulus

The resistance of a material or structure to elastic deformation under load, governed by the elastic modulus and by geometry. Stiffness is distinct from strength: a component can be stiff yet weak, or flexible yet strong, and the two must be considered separately in design.

The internal force carried by a material per unit of cross-sectional area. Stress may be tensile, compressive or shear, and comparing the applied stress with the material's strength is the basis of structural design.

The deformation of a material in response to stress, expressed as change in length divided by original length. Strain is dimensionless, often quoted as a percentage, and may be elastic (recoverable) or plastic (permanent).

The ratio of lateral contraction to axial extension when a material is stretched. It describes how a material thins as it is pulled and is needed alongside the elastic moduli for stress analysis, particularly in laminate calculations.

The maximum tensile stress a material can withstand before failure, determined by pulling a specimen to rupture in a tensile test. It is one of the most widely quoted mechanical properties on datasheets for metals, plastics, laminates and membranes.