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Chemist20
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Anyone know the difference¿¿¿¿¿¿¿¿
Bavid said:They are just different models. Depending on the length scale of interest and the application one of them will be more appropriate.
Work Hardening is a simple (i.e., it does not require one to know the material's internal structrue) mathematical model of the hardening phenomena observed in a material's plastic stress-strain behaviour. According to this model, the hardening of the material is described as some function of the plastic work done. Work hardening models do not care if dislocations exist or not.
Forest hardening assumes the existence of dislocations; and the density of these dislocations increases as plastic deformation progresses. Consequently, it becomes harder to move new dislocations across this "forest" of pre-existing dislocations, resulting in hardening of the material. You can now choose to describe hardening as the increase in shear stress required to move a dislocation through the 'forest' as a function of the dislocation density in the forest. Physically, the observation of "work hardening" at the scale of the specimen is the overall effect of "forest hardening" due to dislocations at the micron scale.
Therefore when hardening=func(plastic work done) --> work hardening
and when hardening=func(forest dislocation density) --> forest hardening
See also - http://aero.caltech.edu/~ortiz/talks/tms-04.pdfSTAGE II: FOREST THEORY
The consequence of this secondary slip for the flow stress is that the dislocations produced are mostly "forest" dislocations with respect to the primary slip system. The term "forest" refers to the concept that the flow stress on a given slip plane is determined by the short range interaction of mobile.
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Bavid said:Yeah, you got that all right.
Work hardening, also known as strain hardening, is a process in which a metal or alloy is subjected to plastic deformation, resulting in an increase in its strength and hardness. This occurs due to the dislocations created in the crystal structure of the material.
Work hardening increases the strength and hardness of a metal, making it less ductile and more resistant to deformation. It also results in an increase in the yield strength of the material, meaning it can withstand higher levels of stress before it permanently deforms.
Work hardening and forest hardening are both processes that increase the strength and hardness of a metal. However, work hardening occurs due to plastic deformation, while forest hardening occurs due to the formation of fine precipitate particles within the metal's microstructure.
Work hardening is commonly used in metalworking processes such as rolling, forging, and drawing to increase the strength and durability of the final product. Forest hardening is often used in heat treatments to improve the strength and wear resistance of materials, particularly in the aerospace and automotive industries.
Work hardening can be partially reversed through a process called annealing, which involves heating the metal to a high temperature followed by slow cooling. This allows the dislocations to rearrange and decreases the material's strength and hardness. Forest hardening, on the other hand, is a permanent change and cannot be reversed without melting and reforming the material.