The stress-strain diagram is generally accepted as the plotted results of a tensile test completed under carefully controlled conditions on a speciman of a metal. The stress-strain diagram important for design engineers in that it establishes the physical properties of the material under test including the yield strength, the ultimate strength, the elongation at fracture, the elastic limit etc. Ductile materials, which includes structural steel, as well as many alloys of other metals, are characterized by their ability to yield at normal temperatures. Materials that are ductile, or have the property of ductility, will stretch and deform when they are pulled, rather than breaking. Gold, silver, copper, iron, and lead are common examples of ductile materials.
Brittle materials, which includes cast iron, glass, and stone, are characterized by the fact that rupture occurs without any noticeable prior change in the rate of elongation. Brittle materials such as concrete or carbon fiber do not have a yield point, and do not strain-harden. Therefore the ultimate strength and breaking strength are the same
An elastic modulus, or modulus of elasticity, is the mathematical description of an object or substance's tendency to be deformed elastically (i.e., non-permanently) when a force is applied to it. The elastic modulus of an object is defined as the slope of its stress–strain curve in the elastic deformation region: As such, a stiffer material will have a higher elastic modulus.
where lambda (λ) is the elastic modulus; stress is the restoring force caused due to the deformation divided by the area to which the force is applied; and strain is the ratio of the change caused by the stress to the original state of the object. If stress is measured in pascals, since strain is a dimensionless quantity, then the units of λ are pascals as well. ELASTIC LIMIT. The maximum stress that can be applied to a metal without producing permanent deformation....
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