Stress-Strain curve

Stress-Strain curve

Definition: The relationship between the stress and strain that a particular material display is known as that particular material's stress–strain curve.

Proportional limit:

Proportional limit is the point on a stress-strain curve at which it begins to deviate from the straight-line relationship between stress and strain.(OA)

Elastic limit:

Maximum pressure (stress) that a piece of material can withstand without being permanently deformed.elastic limit is the maximum stress to which a specimen may be subjected and still return to its original length upon release of the load.(A)

Yield point:

The yield point is a point on the stress-strain curve at which there is a sudden increase in the strain without a corresponding increase in stress.

Yield strength:

Yield strength, Sy, is the maximum stress that can be applied without permanent deformation of the test specimen. This is the value of the stress at the elastic limit for materials for which there is an elastic limit.

Modulus of elasticity: 

the ratio of the stress applied to a body or substance to the resulting strain within the elastic limit.Also called: elastic modulus.

The constant, E, is the modulus of elasticity, Young's modulus or the tensile modulus and is the material's stiffness. Young's modulus is in terms of 10⁶ psi or 10³ kg/mm².

Proportional limit:

The greatest stress at which a material is capable of sustaining the applied load without deviating from the proportionality of stress to strain. Expressed in psi (kg/mm²).

Ultimate strength (tensile):

The maximum stress a material withstands when subjected to an applied load. Dividing the load at failure by the original cross-sectional area determines the value.

Elastic limit: 

The point on the stress-strain curve beyond which the material permanently deforms after removing the load.

Yield strength:

The point at which material exceeds the elastic limit and will not return to its original shape or length if the stress is removed.

Poisson's ratio:

The ratio of the lateral to longitudinal strain is Poisson's ratio for a given material.

Bending stress:

When bending a piece of metal, one surface of the material stretches in tension while the opposite surface compresses. It follows that there is a line or region of zero stress between the two surfaces, called the neutral axis.the following assumptions in simple bending theory:

1. The material of the beam is homogeneous and isotropic.
2. The value of Young's Modulus of Elasticity is same in tension and compression.
3. The transverse sections which were plane before bending, remain plane after bending also.
4. The beam is initially straight and all longitudinal filaments bend into circular arcs with a common center of curvature.
5. The radius of curvature is large as compared to the dimensions of the cross-section.
6. Each layer of the beam is free to expand or contract, independently of the layer, above or below it.

Notes: Homogeneous means the material is of the same kind throughout. Isotropic means that the elastic properties in all directions are equal.

Yielding:

Yielding occurs when the design stress exceeds the material yield strength. Design stress is typically maximum surface stress (simple loading) or Von Mises stress (complex loading conditions).