Determining Mechanical Properties with a Tensile Test
Tensile properties indicate how the material will respond to forces being applied in tension. A tensile test is an essential mechanical test where a thoroughly prepared specimen is loaded in a controlled technique while measuring the applied load and the elongation of the specimen over some distance. The diagram here shows the results of a tensile test. Diagrams like this are used to determine the modulus of elastic limit (Young's Modulus), elasticity, proportional limit, elongation, reduction in area, tensile strength, yield strength, yield point, and other tensile properties.
The yield strength or yield point of a material is defined in materials and engineering science as the stress at which a material starts to deform plastically - meaning the material deforms permanently. Preceding to the yield point, the material will deform elastically and will come back to its original shape when the stress is removed. The slope of the elastic deformation region is actually the Young's Modulus of the material, a measure of its elastic deformation. When the yield point is crossed some part of the deformation will be permanent and non-reversible. Details regarding the yield point is important when designing a component since it normally represents an upper limit to the load that can be applied. It is also important in many materials production techniques such as rolling, forging, or pressing. In structural engineering, this is a soft mode of failure which is not usually a source of catastrophic failure or ultimate failure.
Ultimate Tensile Strength
It is the maximum stress that a material can undertake. It measures the magnitude of stress applied to a material at its breaking point or the point at which it fails. The tensile strength of a material is the point at which a material, under the stress of an applied force, breaks or can no longer maintains its structural reliability. It is, in other words, the extent of force the material can resist without breaking.
Under constant tensile deformation, some materials (especially polymers) may deform disproportionately, forming a "neck".
After necking, the applied stress will result in the breaking of the material (point of fracture).