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Digital Image Correlation (DIC) Validation of Engineering Approaches for Bending Stiffness Determination of Damaged Laminates

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During the last decade new models for bending stiffness prediction of damaged composite laminates have been proposed in the literature advancing the earlier developed engineering approaches in accuracy and in complexity. However, experimental data for validation of complex analytical or engineering models are almost non-existent in the literature. In the present work a detailed experimental study was performed to investigate the bending stiffness reduction of composite cross-ply laminates with evolving micro-damage. Intralaminar cracks and local delaminations in the bottom surface 90-degree layer of carbon/epoxy and glass/epoxy cross-ply laminates were introduced in 4-point bending tests. Digital Image correlation (DIC) technique was used to experimentally determine the midplane curvature. The accuracy of beam theory for bending stiffness determination was assessed. The measured bending stiffness reduction with respect to transverse crack density was also compared with FEM predictions. The results show that the beam theory gives slightly underestimated curvature at low deflections, whereas at large deflections the beam theory overestimates the curvature and the moment–curvature relation becomes nonlinear. Nevertheless, the overall agreement between beam theory and DIC-based results is still very good, which leads to conclude that beam theory based data reduction schemes have sufficient accuracy for predicting bending stiffness even for highly damaged laminates.

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Data Availability

The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.


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All authors contributed to the study conception and design. Material preparation, data collection were performed by Andrejs Pupurs and Mohamed Loukil. Data analysis was performed by Andrejs Pupurs and Janis Varna. The first draft of the manuscript was written by Andrejs Pupurs and Janis Varna and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

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Correspondence to Andrejs Pupurs.

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Pupurs, A., Loukil, M. & Varna, J. Digital Image Correlation (DIC) Validation of Engineering Approaches for Bending Stiffness Determination of Damaged Laminates. Appl Compos Mater 29, 1937–1958 (2022).

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