Study of fatigue damage behavior in off-axis CFRP composites using digital image correlation technology

Area of Science:

• Materials Science
• Mechanical Engineering
• Polymer Composites

Background:

• Off-axis carbon fiber reinforced polymer (CFRP) composites are susceptible to fatigue damage under cyclic loading.
• Understanding fatigue behavior under different loading modes (tensile-tensile vs. compressive-compressive) is critical for structural integrity.
• Previous research has not fully elucidated the distinct damage mechanisms and failure pathways in these composites.

Purpose of the Study:

• To investigate and compare the fatigue behavior of off-axis CFRP composites under tensile-tensile and compressive-compressive loading.
• To analyze energy dissipation, stiffness degradation, and failure mechanisms.
• To identify critical parameters influencing fatigue life and failure modes.

Main Methods:

• Experimental fatigue testing of off-axis CFRP composites under controlled stress levels.
• Utilized digital image correlation (DIC) for in-situ monitoring of crack propagation and deformation.
• Analyzed energy dissipation and stiffness changes throughout fatigue life.

Main Results:

• Tensile-tensile fatigue: Characterized by interlaminar shear cracks, fiber/resin debonding, and fiber pull-out.
• Compressive-compressive fatigue: Dominated by central intralaminar shear cracks, fiber buckling, and progressive edge propagation.
• Identified a critical compressive strain threshold as a key indicator for compressive fatigue failure.

Conclusions:

• Off-axis CFRP composites exhibit fundamentally different fatigue damage mechanisms under tensile and compressive loading.
• Fiber deflection plays a significant role in the recovery of tensile-tensile fatigue properties.
• The identified critical compressive strain threshold provides a valuable metric for predicting compressive fatigue failure in these materials.