Plastic deformation microstructural features

As a result of this process, a joint is produced in solid state. Because of various geometrical features of the tool, the material movement around the pin can be quite complex. During FSW process, the material undergoes intense plastic deformation at elevated temperature, resulting in generation of line and equiaxed recrystallized grains. The fine microstructure in friction-stir welds produces good mechanical properties of the joints, both static and dynamic. 

Time-independent or plastic deformation refers to a material performance that results from relatively fast loading rates. In the laboratory, time-independent deformation is typically generated by the stress-strain experiments. The tests are carried out under either strain-rate control or stress-rate control, but most often, the experiments are performed under strain-rate control. An approximate boundary between time-independent deformation and time-dependent deformation for solders are strain rates of s . The test sample dimensions are typically large, relative to the microstructural features of the material. However, there is a growing need to understand size or length-scale effects on these properties as solder interconnections become increasingly smaller, particularly solder joint dimensions less than 100 pm. 

As we have emphasized aheady, the study of plasticity is one of the centerpieces of the mechanics of materials. A wide array of technologies depend upon the ability to deform materials into particular desirable shapes, while from a scientific perspective I personally find the subject of great interest because it is an intrinsically dissipative process featuring history dependence and is a strong function of the material s microstructure. In addition, from the effective theory perspective, the study of plasticity is built around the motion and entanglement of dislocations which requires the construction of theories of lines and their interaction thus ushering in a certain nonlocality to the phenomenon right from the outset. 

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