Strain

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.

A measure of a material's stiffness, defined as the ratio of stress to strain in the elastic region of loading. A higher modulus means less deflection under a given load; for plastics and composites it is typically measured in tension to ISO 527.

The strain at which a specimen ruptures in a tensile test, expressed as a percentage of its original length. High values indicate a ductile or flexible material such as an elastomeric roofing membrane, while rigid laminates typically fail at low elongation.