Experimental Evaluation of Nonlinear Parameters in Fatigue Crack Growth Using Digital Image Correlation

Area of Science:

• Materials Science and Engineering
• Mechanical Engineering
• Fracture Mechanics

Background:

• Accurate characterization of the crack-tip region is crucial for understanding fatigue crack propagation.
• Traditional methods often lack the resolution to precisely measure small-scale plastic deformation at the crack tip.
• Nonlinear parameters like plastic crack-tip opening displacement (CTODp) and cyclic plastic zone size are key indicators of fatigue behavior.

Purpose of the Study:

• To present an experimental methodology for high-resolution characterization of the crack-tip region using Digital Image Correlation (DIC).
• To evaluate the correlation between nonlinear parameters (CTODp, cyclic plastic zone size) and fatigue crack propagation.
• To validate the proposed DIC methodology for fatigue life assessment under complex loading.

Main Methods:

• Utilized a stereoscopic microscope setup for high-resolution imaging.
• Employed 3D-Digital Image Correlation (DIC) analysis for precise crack-tip measurements.
• Conducted constant-ΔK fatigue testing on AISI 1020 steel compact tension specimens.

Main Results:

• Demonstrated a strong correlation between CTODp, cyclic plastic zone size, and stable fatigue crack propagation.
• Validated the proposed high-resolution DIC methodology through consistent results.
• Verified the significance of crack-tip plasticity in fatigue crack growth under the tested conditions.

Conclusions:

• The developed high-resolution DIC methodology effectively characterizes crack-tip plasticity.
• CTODp and cyclic plastic zone size are reliable indicators of fatigue crack propagation.
• The methodology offers utility for fatigue life assessment in complex loading scenarios.