Note that in the discussion above, the original cross-sectional area and length (before any deformation had taken place) were used to calculate stress and strain, respectively. But regardless of the property being described, “strength” typically refers to a material’s resistance to failure, either through fracture or excessive deformation. The term “strength” can be used with various material properties (tensile strength, yield strength, shear strength, etc.). This point denotes the maximum stress that can be applied to a material in tension before failure occurs. The point where this line intersects the stress-strain curve is the offset yield point.įinally, at point “D,” where the curve begins to fall, the material’s ultimate tensile strength has been reached. It is found by drawing a line that crosses the X (strain) axis at 0.002 and runs parallel to the stress-strain line (slope = E). Offset yield strength is the stress that will cause a specified amount of permanent strain (typically 0.2 percent). The yield point, shown here as point “C,” is the point where strain increases faster than stress (referred to as “strain hardening”), and the material experiences some amount of permanent deformation.įor materials that do not have a well-defined yield point, or whose yield point is difficult to determine, an offset yield strength - shown here as point “B” - is used. (In the stress-strain curve shown here, the proportional limit and the elastic limit are assumed to be the same.)Īs long as the applied stresses are below the proportional limit, stress-strain relationships are the same whether the material is under tension or compression. For many materials, the proportional limit and the elastic limit are the same or nearly equal. Just beyond the proportional limit is the elastic limit, at which point the material transitions from elastic behavior, where any deformation due to applied stress is reversed when the force is removed, to plastic behavior, where deformations caused by stress remain even after the stress is removed. The modulus of elasticity is essentially a measure of stiffness and is one of the factors used to calculate a material’s deflection under load. Many materials exhibit a proportional relationship between stress and strain up to certain point, referred to as the proportional limit, shown here as point “A.” This stress-strain relationship is known as Hooke’s Law, and in this region, the slope of the stress-strain curve is referred to as the modulus of elasticity (aka Young’s modulus), denoted E. The stress-strain diagram provides valuable information about how much force a material can withstand before permanent deformation or failure occurs. The most common way to analyze the relationship between stress and strain for a particular material is with a stress-strain diagram. Note: A material’s change in length (L – L 0) is sometimes represented as δ. Strain is the deformation or displacement of material that results from an applied stress. Stress is the force applied to a material, divided by the material’s cross-sectional area.Ī 0 = original cross-sectional area (m 2) There are five fundamental types of loading: compression, tension, shear, torsion, and bending. The component’s reactions to these loads are described by its mechanical properties.įor components subjected to tension or compression - such as load-carrying balls and rollers, shafts mounted vertically, or fastening and joining hardware - the mechanical properties of stress and strain play an important role in determining whether the component can withstand the application’s loading conditions.
Every component in a linear motion system experiences some form of loading due to applied forces or motion.