PSI - Issue 50

Alexander Eremin et al. / Procedia Structural Integrity 50 (2023) 73–82 Alexander Eremin / Structural Integrity Procedia 00 (2019) 000 – 000

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more severe and all extensometers demonstrate very sharp and high jumps. Two bottom extensometers are migrated from the compressive to tensile strained areas. This evidences a massive delamination in the plate and a reduction of the stiffness of the loaded plate. 4. Conclusions The paper demonstrates the impact and compression after impact behavior of carbon-fiber reinforced composites with epoxy matrix. Three specimens were impacted with the energies of 8.55 J, 17.1 J and 25.65 J which result in the formation of barely visible damages. The damaged area was determined by digital shearography and was the following: 14.9×26.9 mm after the 8.55 J impact, 17.0×45.4 mm after 17.1 J and 18.7×52.4 mm after 25.65 J. Corresponding residual strength after impact was measured as 253.4 MPa, 173.2 MPa and 192.0 MPa for each specimen. Under compression loading the plates demonstrate different behavior due to different impact damages. These values are lower than the solid strength (657±81 MPa) due to the presence of impact and buckling. The latter seems to be a major reason for strength reduction in the experiment. DIC measurements show the initiation of buckling at ~0.15% of longitudinal strain. The buckling plate theory allows estimation of stress and strain values at buckling point. They are 240.5 MPa and 0.37%, which is quite close to first specimen with small damage. The presence of large damage reduces stiffness and also reduce load bearing capacity initiating buckling at lower stress levels. The technique proposed for the thinner plates should be verified more carefully to optimize the specimen stability and avoid buckling. Or it potentially could work only for low strength materials when critical buckling stress is higher than ultimate compression stress. Acknowledgements This work has been supported by the Russian Science Foundation, grant 21-79-10385. References Luyckx, G., Voet, E., Lammens, N., Degrieck, J., 2011. Strain measurements of composite laminates with embedded fibre bragg gratings: Criticism and opportunities for research. Sensors 11, 384 – 408. Ružek, R., Tserpes, K., Karachalios, E., 2015. Compression after impact and fatigue behavior of CFRP stiffened panels. Intern ational Journal of Structural Integrity 6, 176 – 193. Ostré, B., Bouvet, C., Minot, C., Aboissière, J., 2016. Experimental analysis of CFRP laminates subjected to compression after edge impact. Composite Structures 152, 767 – 778. Bogenfeld, R., Gorsky, C., Wille, T., 2022. An experimental damage tolerance investigation of CFRP composites on a substructural level. Composites Part C: Open Access 8, paper #100267. Kim, G., Hong, S., Jhang. K.Y., Kim, G.H., 2012. NDE of low-velocity impact damages in composite laminates using ESPI, digital shearography and ultrasound C-scan techniques. International Journal of Precision Engineering and Manufacturing 13, 869 – 876. Linke, M. , García -Manrique, J.A., 2018. Contribution to reduce the influence of the free sliding edge on compression-after-impact testing of thin walled undamaged composites plates. Materials (Basel) 11, paper #1708. Linke, M. , Flügge , F., Olivares-Ferrer, A.J., 2020. Design and validation of a modified compression-after-impact testing device for thin-walled composite plates. Journal of Composites Science 4, 126. Rees, D.W.A., 2009. Mechanics of Optimal Structural Design: Minimum Weight Structures. John Wiley & Sons, Ltd, Chichester, UK, pp. 560.