Techshore Institute Blogs about Best Technical and Management Courses: TECHSHORE INSPECTION SERVICES-KOCHI-KERALA | STRESS

Ductile materials, in which includes structural steel and alloys of other metals, are regarded as their ability to yield at normal temperatures.

Refer to the Fig.1&2, illustrates the stress-strain relationship and pointed out the deformation of material under stress and regions. The different regions in the curve are,

Ultimate strength

Yield strength or yield point

Rupture

Strain hardening region

Necking region

Apparent stress

Actual stress

Low carbon steel generally demonstrates a very linear stress–strain relationship up to yield point. The linear portion of the curve is the elastic region and the slope is called the Young’s Modulus or modulus of elasticity. Young's Modulus is defined as the ratio between the compressive stress and longitudinal strain. After the yield point, the curve typically decreases slightly because of dislocations escaping from Cottrell atmospheres. As deformation stays, the stress increases on account of strain hardening until it can reaches the ultimate tensile stress which obeys Hooks law. Until this point, the cross-sectional area will decrease uniformly and randomly because of Poisson contractions (as per Poisson’s ratio). The actual fracture point which is in the same vertical line as visual fracture point.

However, further than this point a neck forms where the local cross-sectional area becomes ominously smaller than the original. The ratio of the tensile force to the true cross-sectional area i.e., at the narrowest region of the neck is called the true stress. The ratio between the tensile force to the original cross-sectional area of the specimenis called the engineering stress. If the stress–strain curve is schemed in relationships of true stress and true strain the stress will increase or rise until failure. Ultimately the neck becomes unstable and the specimen undergone fractures.

If the specimen is subjected to progressively raising tensile force it reaches the ultimate tensile stress and then necking and elongation occur quickly until fracture. If the specimen is undergone to progressively increasing length it is possible to perceive the progressive necking and elongation, and to measure the reducing tensile force in the specimen. Civil structures such as bridges are loaded that applies progressively increasing forces. Sheet-metal pressing operation subjects the work-piece to gradually increasing deformation. In order to perfectly record the enactments of materials between ultimate tensile stress and fracture, most of the tensile-testing machines load the specimen with a steadily increasing length.

Techshore Institute Blogs about Best Technical and Management Courses

Tuesday, March 28, 2017

TECHSHORE INSPECTION SERVICES-KOCHI-KERALA | STRESS – STRAIN CURVE FOR DUCTILE MATERIALS

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