Session: 03-06-01: Damage, Fatigue, and Fracture

Paper Number: 162481

162481 - Predictive Modeling and Fatigue Characteristics on the Delamination of L-Shaped Cfrp Laminates With Varying Inter-Ply Angle Orientation 

L-shaped composite structures are widely used in aerospace industries for reinforcing load-bearing components. However, their structural integrity is challenged with the introduction of delamination when subjected to high bending loads. This research introduces a cohesive zone modeling (CZM) strategy to accurately predict the progressive delamination in L-shaped laminates with varying inter-ply angle differences. Unlike the conventional approach of assigning a constant interfacial strength parameter based on unidirectional laminates, the CZM's interfacial strength incorporates the interlaminar tensile strength (ILTS) from experimental data for each inter-ply angle difference. Four stacking sequences, categorized as unidirectional (UD, 0°), helicoidal (HC, 15°), quasi-isotropic (QI, 45°), and cross-ply (CP, 90°), were evaluated under quasi-static four-point bending to measure force-displacement behavior, initial stiffness, peak load capacity, and ILTS. The quasi-isotropic laminate demonstrated the highest peak load, indicating superior delamination resistance, while the unidirectional laminate exhibited the highest initial stiffness but lower peak load, highlighting a trade-off between stiffness and delamination resistance. The proposed modeling strategy effectively predicted peak loads and delamination locations across configurations, with discrepancies within a 7% margin when compared to experimental results. Based on the quasi-static results, fatigue behavior was further explored by subjecting samples to cyclic loading at 3 Hz under various amplitudes of the ultimate failure displacement. A linear relationship was observed between the logarithm of cycles to first delamination and increasing fatigue stress. Interrupted nondestructive testing has been conducted after the appearance of first and second delamination in order to find out the 3D sequence of the delamination using X-ray Computed Tomography. Laminates with 45° inter-ply angle difference demonstrated superior fatigue life under applied loading conditions. By successfully integrating experimental data with cohesive modeling, this study not only improves the predictive accuracy of finite element models for complex composite structures under loading but also provides critical insights into the fatigue behavior of L-shaped laminates, optimizing the design of more durable components for aerospace and structural applications.

Presenting Author: Kirtunia Rahul Baylor University

Presenting Author Biography: Kirtunia Rahul has received his B.Sc. in Engineering in Naval Architecture and Marine Engineering from Bangladesh University of Engineering and Technology. After working several years as Assistant Naval Architect and later as Territory Manager in Industrial Coatings, he joined Baylor University to pursue Ph.D. in Mechanical Engineering under the supervision of Dr. David Jack. Along the way, he also received his master’s in mechanical engineering from Baylor University. His research area is focused on the damage assessment using Non-Destructive Testing (Ultrasound) and implementing Ultrasound information for generating predicting models of composite materials through Finite Element Analysis. He has published several peer reviewed journal papers, conference papers, and presented posters at different conferences.