Understanding the correlation between wrinkle morphology, fracture and fatigue of plain woven CFRP laminates through mechanical and ultrasonic characterization.

Wrinkles, often perceived as manufacturing defects in carbon fiber-reinforced polymer (CFRP) laminates, can significantly alter the fracture and fatigue behavior of composite structures. This dissertation presents a comprehensive experimental investigation into the influence of out-of-plane wrinkles on interlaminar fracture toughness under both Mode I and Mode II loading conditions, along with the development of a novel ultrasonic characterization technique for wrinkle detection and quantification. In the first part of the study, a co-curing-based fabrication technique was developed to embed controlled wrinkle topologies at the ply interface in double cantilever beam (DCB) specimens. These wrinkles, characterized using ultrasonic testing and optical microscopy, were quantified by peak-to-valley and peak-to-base amplitudes using an 8-point Gaussian fitting method. Mode I fracture testing revealed a strong positive correlation between wrinkle amplitude and energy release rate (ERR), with up to a 60% increase in ERR for high-amplitude wrinkles. This enhancement was attributed to crack deflection and increased fracture surface area due to the wrinkled interface. The second phase of the research extended this understanding to Mode II conditions by evaluating both static and fatigue-driven crack propagation in specimens with varying wrinkle morphologies. Moderate wrinkle amplitudes were found to improve initial interlaminar shear strength and stiffness, enhancing Mode II ERR at initiation. However, higher amplitudes led to unstable crack propagation, both in static and fatigue conditions. Fatigue testing showed accelerated crack growth rates and increased Paris law slopes for high-amplitude wrinkles, indicating reduced long-term durability. Furthermore, wider wrinkle spacing disrupted stress continuity, resulting in stepwise, staircase-like crack paths. To support this experimental work, the final part of the dissertation introduces a high-resolution algorithm for wrinkle characterization using full-waveform ultrasonic scan data. The method reconstructs the 3D geometry of each lamina interface, enabling precise measurement of wrinkle amplitudes. Validation against microscopic sectioning confirmed the reliability of the approach, with deviations within 0.06 mm. Together, these findings offer new insights into how wrinkle morphology affects interlaminar toughness and fatigue resistance in CFRP composites and provide a foundation for designing defect-tolerant laminates through controlled interface tailoring and advanced non-destructive evaluation.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Doctoral

Grantor

Baylor University.

Year dc:date.issued

2025

Author dc:creator

• Amif, Md Admay, 1995-

Advisor dc:contributor.advisor

• Jack, David Abram, 1977-

• Carbon fiber reinforced polymer (CFRP)
• Wrinkles.
• Fracture and fatigue.
• Ultrasonic testing.

Statement dc:rights

• Baylor University works are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. Contact libraryquestions@baylor.edu for inquiries about permission.

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/2104/14071

OAI identifier oai:identifier

oai:baylor-ir.tdl.org:2104/14071