N = 1 elastic solid For most metals, 0.1< n < 0.5
The flow curve of many metals in the region of uniform plastic deformation can be expressed by the simple power law. In true stress-strain curve, the stress however increases after necking since the cross sectional area of the specimen decreases rapidly after necking. In engineering stress-strain curve, stress drops down after necking since it is based on the original area. True stress-strain curve gives a true indication of deformation characteristics because it is based on the instantaneous dimension of the specimen. The true stress-strain curve is also known as the flow curve. When the specimen is gradually loaded the curve follows path BC, resulting in a residual strain OC or permanent strain.Ĭomparison of engineering stress and the true stress-strain curves shown below: In figure (b), the specimen is loaded upto point B beyond the elastic limit E. Such a behavior is known as the elsastic behavior. In figure (a), the specimen is loaded only upto point A, is gradually removed the curve follows the same path AO and strain completely disappears. There is no yield point and no necking takes place. In brittle materials there is no appreciable change in rate of strain. The stress-strain diagram is shown in the figure. The volume of the specimen is assumed to be constant during plastic deformation. Where σ and ε is the engineering stress and engineering strain respectively. The volume of the solid is not changed by shear strain.īulk Strain True Stress and True StrainThe true stress is defined as the ratio of the load to the cross section area at any instant. Shear strain Note 1: The angle is radians, not degrees. As Pascal is a small quantity, in practice, multiples of this unit is used. It usually represents the displacement between particles in the body relative to a reference length.į is expressed in Newton (N) and A, original area, in square meters (m 2), the stress σ will be expresses in N/ m 2. Strain: It is the deformation produced in the material due to simple stress. 
The internal resistance force per unit area acting on a material is called the stress at a point. Stress: When a material in subjected to an external force, a resisting force is set up within the component.
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