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The strain hardening exponent (also called the strain hardening index), usually denoted , is a measured parameter that quantifies the ability of a material to become stronger due to strain hardening. Strain hardening (work hardening) is the process by which a material's load-bearing capacity increases during plastic (permanent) strain , or ...
This phenomenon of soil behaviour can be included in the Hardening Soil model by means of a dilatancy cut-off. In order to specify this behaviour, the initial void ratio, e i n i t {\displaystyle e_{init}} , and the maximum void ratio, e m a x {\displaystyle e_{max}} , of the material must be entered as general parameters.
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.
This behavior, critical state soil mechanics simply assumes as a given. For these reasons, critical-state and elasto-plastic soil mechanics have been subject to charges of scholasticism; the tests to demonstrated its validity are usually "conformation tests" where only simple stress-strain curves are demonstrated to be modeled satisfactorily.
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.
For annealed materials the Meyer hardness increases continuously with load due to strain hardening. [2] Based on Meyer's law hardness values from this test can be converted into Brinell hardness values, and vice versa. [3]
The strain can be decomposed into a recoverable elastic strain and an inelastic strain (). The stress at initial yield is σ 0 {\displaystyle \sigma _{0}} . For strain hardening materials (as shown in the figure) the yield stress increases with increasing plastic deformation to a value of σ y {\displaystyle \sigma _{y}} .
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.