RS TENSILE PVT IN INDIA The ultimate strength is more important because non-uniform plastic deformation starts at necking. Tensile strength resists tension (being pulled apart), whereas compressive strength resists compression (being pushed together). A material is gripped at both ends by an apparatus, which slowly pulls lengthwise on the piece until it fractures. The pulling force is called a load, which is plotted against the material length change, or displacement. The load is converted to a stress value and the displacement is converted to a strain value.