An improved NG-F model for capturing the three types of indentation size effect

Area of Science:

• Materials Science
• Mechanical Engineering
• Solid Mechanics

Background:

• Experimental studies identify three types of Indentation Size Effect (ISE).
• Modeling these three ISE types presents a significant challenge in materials science.
• Existing models struggle to capture the complex, nonlinear relationship between indentation parameters.

Purpose of the Study:

• To systematically analyze the relationship between k (plastic zone to contact radius ratio) and h (indentation depth).
• To develop an improved NG-F model capable of capturing three types of ISE.
• To validate the model's predictive capabilities across different materials.

Main Methods:

• Systematic analysis of the k-h relationship.
• Modification of an exponential decay function to describe k-h.
• Improvement of the NG-F model using the modified exponential decay function.
• Qualitative parameter analysis to understand model behavior.
• Validation against experimental data for three ISE types.

Main Results:

• A modified exponential decay function accurately describes the nonlinear k-h relationship.
• The improved NG-F model successfully captures three types of ISE.
• Model validation shows accurate prediction of ISE for various materials.
• The competition between the relative rates of change of k^3 and h underlies the model's mechanism.
• Predictive accuracy varies, with lower DC values for NR-ISE and C-ISE materials due to differing dislocation mechanisms.

Conclusions:

• The improved NG-F model offers a robust framework for predicting three types of ISE.
• The model's success is attributed to capturing the interplay between k and h.
• Further research is needed to address variations in predictive accuracy for specific material types.