Investigative Method for Fatigue Crack Propagation Based on a Small Time Scale

Area of Science:

• Materials Science
• Mechanical Engineering
• Fracture Mechanics

Background:

• Traditional fatigue crack growth studies often use a cycle-based approach, which can overlook critical time-dependent phenomena.
• Understanding the influence of microstructure, crack closure, and applied loading on crack growth is crucial for material design and safety.

Purpose of the Study:

• To develop and validate an in-situ scanning electron microscopy (SEM) testing methodology based on a small time scale for investigating fatigue crack growth behavior and mechanisms.
• To comprehensively analyze the effects of microstructure, crack closure, and applied loading on fatigue crack growth.
• To correlate crack tip opening displacement (CTOD) with the stress intensity factor (SIF) and predict CTOD variation.

Main Methods:

• Utilizing in-situ scanning electron microscopy (SEM) for real-time observation of fatigue crack growth at a small time scale.
• Acquiring high-resolution images to measure crack tip opening displacement (CTOD).
• Developing an experimental data-driven model to predict CTOD variation and analyzing the correlation between CTOD and stress intensity factor (SIF).

Main Results:

• The proposed time-scale SEM method allows for detailed observation of fatigue crack growth at any point within a loading cycle.
• It enables a comprehensive analysis of how microstructure influences crack growth.
• The study successfully investigated the unstable crack growth of aluminum alloy 7050-T7451, demonstrating the method's efficacy.

Conclusions:

• The novel time-scale SEM approach provides a more integral investigation of fatigue crack growth mechanisms compared to traditional cycle-based methods.
• This methodology holds significant potential for advancing fatigue crack growth research and material performance analysis.