Session: 01-06-01: Impact, Fatigue, Damage and Fracture of Composite Structures

Paper Number: 138366

138366 - Digital Volume Correlation Analysis of Progressive Failure in a Laminated Composite Structure 

Fiber-reinforced composite materials exhibit complex damage behavior involving the interaction of multiple-scale damages. Commonly observed damage modes in laminated composites include fiber/matrix debonding, fiber fracture, fiber splitting, intralaminar matrix cracking, and delamination. These damages interact in three dimensions, leading to the degradation and ultimate failure of the composite structure. In order to enhance the fidelity of predictive models for capturing such microscopic damage behavior, it is crucial to have a thorough understanding of the underlying failure mechanisms. Recently, in-situ experiments utilizing high-resolution X-ray CT have emerged as powerful tools for characterizing the damage and its progression in three dimensions under increasing external loads. However, the observation of damage patterns in CT images has limitations in providing a detailed understanding of damage interactions.

In this study, we performed in situ experiments using synchrotron radiation tomography (SRCT) on cross-ply single edge-notched (SEN) specimens. The damage progression mechanisms were investigated with a particular focus on the interaction between intralaminar fracture modes and delamination. High-resolution 3D CT images of the sequentially loaded sample were obtained and segmented for better visualizing the occurrence and growth of intralaminar matrix cracks, fiber splitting, and delamination. The high-resolution images were used for digital volume correlation (DVC) calculations. The DVC data have been primarily utilized for damage detection based on the deformation behavior of the constituents or localized strain concentration. DVC analysis detected significant deformations in the regions of each fracture mode. It was found that, for the intralaminar matrix cracks and fiber splitting, the in-plane strain along the tensile direction and the in-plane strain perpendicular to the tensile direction, respectively, were locally increased. Prior to the occurrence of fiber splitting, in-plane shear strain was concentrated, while out-of-plane shear strain was concentrated at the interfaces where intralaminar cracks intersect. This indicates that fiber splitting and delamination were mainly driven by shear.

The CT-reconstructed microstructure with cracks were overlayed with DVC-calculated volumetric strain fields for the investigation of the strain behavior affected by damage. The intralaminar cracks enhanced shear deformation at the interfaces and relaxed strains in the surrounding regions. In particular, it was observed that the strain relaxation characteristics varied depending on the presence of damage at the interfaces. Interfacial delamination relieved stress in the nearby region and made it more difficult for intralaminar damage to occur in that area. As a result, new intralaminar cracks were initiated at the tips of the delamination. These cracks eventually triggered new delamination. The DVC technique was instrumental to explain the failure mechanism in detail. The results in the presentation are expected to provide valuable insights into the interactive damage mechanisms in laminated composite materials and contribute to the development of reliable and accurate failure prediction models. The appropriate radiation setup for the material, in situ experimental methods, CT image processing techniques, and qualitative and quantitative analysis of segmented cracks will also be presented in the conference.

Acknowledgement: This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Science and ICT (MSIT) of the Republic of Korea (Grant No.: 2021R1A2C2013545).

Presenting Author: Wooseok Ji Ulsan National Institute of Science and Technology

Presenting Author Biography: Dr. Wooseok Ji is an associate professor in the Department of Mechanical Engineering at Ulsan National Institute of Science and Technology. He received his bachelor' degree from Seoul National University in 1999. After working as a tooling engineer for Korean Air Aerospace Division (currently Korean Air TechCenter) from 1999 to 2003, he pursued a postgraduate diploma and earned MS and PhD degrees in the major of Aerospace Engineering from University of Michigan in 2005 and 2008, respectively. His research efforts are put into the promotion of advanced composites for practical applications based on the fundamental understanding of their mechanics. He is a member of American Institute of Aeronautics and Astronautics (AIAA) and an associate editor of Journal of Reinforced Plastics and Composites and Functional Composites and Structures.