This document summarizes key concepts in mechanics of materials including: - Normal stress is defined as force per unit area. Stress can be tensile or compressive. - Shear stress is defined as the tangential force per unit area. Shear strain is the deformation under shear stress. - Normal strain is the fractional change in length. Hooke's law defines the proportional relationship between stress and strain in the elastic region. - Stress-strain curves illustrate the elastic region, yield point, work hardening, and elastic break. - Bulk modulus relates pressure change to fractional volume change. Poisson's ratio relates lateral to normal strain. - Double index notation is used to represent normal and shear stress components. Equ