What are stress and strain?
Definition: Stress is a force over an area (units are lbs/in2 or psi, N/m2 or Pa) Stress and pressure have the same units. Tensile stress tends to elongate something. Compressive stress (a.k.a. pressure) tends to shorten something. Definition: Strain is a shape change, usually described as a fraction or percent change calculated from dividing the change in a dimension by its original, unstressed dimension. When you tension a web, it gets longer in the machine direction. If you stretch a 10-inch sample to 10.1 inches, you have strained it 1 percent.
