Grain size-dependent crystal plasticity constitutive model for polycrystal materials.

Area of Science:

• Materials Science
• Mechanical Engineering
• Solid Mechanics

Background:

• Constitutive models for polycrystal materials often use a core-mantle grain configuration to account for grain size-dependent mechanical properties.
• Current methods for defining mantle properties are typically arbitrary, relying on experimental validation rather than physical principles.
• This arbitrary approach limits the predictive power and fundamental understanding of grain size effects.

Purpose of the Study:

• To develop a physics-based method for creating grain size-dependent crystal plasticity constitutive models using a core-mantle grain configuration.
• To establish a framework where mechanical properties in the mantle region are intrinsically linked to material physics, not arbitrarily assigned.
• To provide a more accurate and fundamentally grounded approach to modeling polycrystal plasticity.

Main Methods:

• The study assumes that resistance to dislocation nucleation and motion directly influences yield strength and strain-hardening modulus.
• A physics-based approach introduces shear flow strain and dislocation density distributions to model variations in mechanical properties within the grain boundary influence region (mantle).
• The model ensures that changes in yield strength and strain-hardening modulus are mutually related through inherent, grain size-independent plastic properties of the material.

Main Results:

• A novel physics-based core-mantle constitutive model for polycrystal materials was developed.
• The model successfully links grain size-dependent mechanical properties to fundamental material physics, specifically dislocation behavior.
• Validation using polycrystal copper under uniaxial loading showed excellent agreement between the model's predictions and experimental stress-strain data.

Conclusions:

• The developed physics-based method provides a more robust and accurate way to model grain size-dependent plasticity in polycrystal materials.
• This approach moves beyond arbitrary parameter fitting, offering deeper physical insight into grain boundary effects.
• The validated model can be applied to predict the mechanical behavior of various polycrystal materials with improved fidelity.