Modelling the Shear Banding in Gradient Nano-Grained Metals

Area of Science:

• Materials Science
• Mechanical Engineering
• Computational Modeling

Background:

• Gradient nano-grained metals show a promising combination of strength and ductility.
• Deformation mechanisms in these materials, especially at the nanocrystalline surface, remain unclear.
• Recent experiments suggest surface shear bands form even at low strains, contradicting uniform deformation theories.

Purpose of the Study:

• To investigate shear band evolution in gradient copper using a computational model.
• To clarify the debate on deformation mechanisms in gradient metals.
• To understand the role of microstructure in shear band formation and material ductility.

Main Methods:

• Development of a dislocation density-based computational model.
• Utilizing Voronoi polygons to simulate irregular grain structures with gradient grain sizes.
• Analysis of shear band initiation and propagation under applied strain.

Main Results:

• Shear bands initiate at small applied strains in the surface region of gradient copper.
• Multiple shear bands form with increasing load due to the constraint of the interior coarse grains.
• The number of shear bands correlates positively with uniform elongation, influenced by grain size distribution and gradient layer thickness.

Conclusions:

• Gradient deformation-induced stable shear band evolution is key to the enhanced ductility of gradient metals.
• The computational model accurately predicts experimental observations of stress-strain responses and shear band evolution.
• Understanding shear band dynamics is crucial for designing high-performance gradient materials.