This document covers topics related to stress and strain including: - Definitions of stress as force per unit area and strain as deformation per original length. Stress is proportional to strain below the proportional limit according to Hooke's law. - The stress-strain diagram shows elastic behavior, yield point, plastic deformation, strain hardening, necking and fracture. - Shear stress is defined as force per unit area applied sideways. Shear strain is the ratio of deformation to original height. Shear modulus relates shear stress and strain. - Materials have ultimate tensile, compressive and shear stresses at which they fail. Design allows only a fraction of these stresses for safety.