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The uniaxial tension test is the primary experimental method used to directly measure a material's stress–strain behavior, providing valuable insights into its strain-hardening behavior. [1] The strain hardening exponent is sometimes regarded as a constant and occurs in forging and forming calculations as well as the formula known as Hollomon ...
Work hardening, also known as strain hardening, is the process by which a material's load-bearing capacity (strength) increases during plastic (permanent) deformation. This characteristic is what sets ductile materials apart from brittle materials. [1] Work hardening may be desirable, undesirable, or inconsequential, depending on the application.
Alternatively, if the yield stress, , is assumed to be at the 0.2% offset strain, the following relationship can be derived. [5] Note that is again as defined in the original Ramberg-Osgood equation and is the inverse of the Hollomon's strain hardening coefficient.
Thus the basic influence parameters for the forming limits are, the strain hardening exponent, n, the initial sheet thickness, t 0 and the strain rate hardening coefficient, m. The lankford coefficient, r, which defines the plastic anisotropy of the material, has two effects on the forming limit curve. On the left side there is no influence ...
The index n usually lies between the values of 2, for fully strain hardened materials, and 2.5, for fully annealed materials. It is roughly related to the strain hardening coefficient in the equation for the true stress-true strain curve by adding 2. [1] Note, however, that below approximately d = 0.5 mm (0.020 in) the value of n can surpass 3.
An empirical equation is commonly used to describe the relationship between true stress and true strain. = Here, n is the strain-hardening exponent and K is the strength coefficient. n is a measure of a material's work hardening behavior.
Where is flow stress, is a strength coefficient, is the plastic strain, and is the strain hardening exponent. Note that this is an empirical relation and does not model the relation at other temperatures or strain-rates (though the behavior may be similar).
The normalized strain-rate and temperature in equation (1) are defined as ... The strain hardening function ... is the drag coefficient. Zerilli–Armstrong flow ...