PSI - Issue 47

R. Nobile et al. / Procedia Structural Integrity 47 (2023) 176–184 R. Nobile et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Subsequently, the resistance values show a rapid increase from about 5-30 % of the fatigue life due to the early nucleation of the damage. Starting from about 60 -70 % of the fatigue life, the electrical resistance undergoes a further rapid increase in the damage propagation phases, before the sudden failure of the specimen. This latter result is in good agreement with the stiffness degradation obtained by processing fatigue data of the tested specimens. The processed thermal data, expressed through the damage dissipative parameter (D diss ), generally showed for specimens A3 and A6 a similar trend to the stiffness degradation expressed through the D k parameter. The thermal profiles related to the studied parameter Ddiss, show a progressive increase up to about 80 % of the fatigue life, followed by a further increase in the final stages of damage propagation before the sample failure. In particular, the obtained thermal results showed that the increase of the dissipative damage parameter Ddiss is in good agreement with the observed increase of the electrical resistance variation ( ΔR damage ) in the range from 5 to 30 % of the fatigue life. Starting from 60 % of the useful life, the trends of the dissipative parameter and of the variation of the electrical resistance both showed a rapid increase. For A5 specimen, starting from 60 % of the fatigue life, the general trends of the thermal profiles relating to the D diss parameter decrease because of the considerable surface damage of the composite which determines a reduction of the temperatures in the selected ROIs, while in this phase, the electrical resistance further increases as observed. In conclusion, Non-Destructive methods applied for structural health monitoring appear to be valid for detecting progressive fatigue damage in composite materials and constitute a valid alternative to the use of piezoelectric ultrasonic sensors. References Coron, P. C., Owston, C. N., 1969. Electrical resistance of single carbon fibres. Nature 223, 1146-1147. Dattoma, V., Nobile, R., Panella, F. W., Saponaro, A., 2019. Real -time monitoring of damage evolution by nonlinear ultrasonic technique. Procedia Structural Integrity 24 , 583-592. De Baere, I., Van Paepegem, W., Degrieck , J., 2010. Electrical resistance measurement for in situ monitoring of carbon fabric composites. International Journal of Fatigue 32 , 197- 207. Dulieu- Barton, J.M., Crump, D.A., 2011. Analysis of large scale composite components using TSA at low cyclic frequencies. In: Proulx, T. (Eds.) Experimental and Applied Mechanics, Volume 6. Conference Proceedings of the Society for Experimental Mechanics Series. Spring er, New York (2011). Grilo, T. J., Paulo, R. M. F., Silva, C. R. M., Davim, J. P., 2013. Experimental delamination analyses of CFRPs using different drill geometries. Compos ites Part B : Engineering 45, 1344– 1350. Irving, P. E., Thiagarajan , C., 1998. Fatigue Damage Characterization in Carbon Fibre Composite Materials using an Electrical Potential Technique. Smart Materials and Structures 7 ( 4 ), 456–466. Nobile, R., Panella, F. W., Pirinu, A., Saponaro, A., 2022. Full - field monitoring methods for damaged analysis on aeronautical CFRP specimens under fatigue loads. IOP Con ference Ser ies : Mater ial Sci ence and Engineering 1214 (1) , 012008. Nobile, R., Saponaro, A., 2021. Real - time monitoring of fatigue damage by electrical resistance change method. International Journal of Fatigue 151, 106404. Omari, M. A., Sevostianov, I., 2013. Estimation of changes in the mechanical properties of stainless steel subjected to fatigue loading via electrical resistance monitoring. International Journal of Engineering Science 65 , 40 -45. Palit Sagar, S., Das, S., Parida, N., Bhattacharya, D. K. , 2006. Non- linear ultrasonic technique to asses fatigue damage in structural steel. Scripta Materialia 55 (2) 199 - 202. Park, J. M., Lee, S.I. , DeVries, K. L. , 2006. Nondestructive sensing evaluation of surface modified single- carbon fiber reinforced epoxy composites by electrical resistivity measurement. Compos ites Part B : Engineering 37, 612-626. Seo, D. C., Lee, J. J., 1999. Damage Detection of CFRP Laminates using Electrical Resistance Measurement and a Neural Network. Composite Structures 47 (1 - 4) , 525– 530 . Skorupa, M., Machniewicz, T., Skorupa, A. Korbel, A., 2017. Fatigue life predictions for riveted lap joints. Int ernational Journal of Fatigue 94 , 41– 57. Xia, Z., Okabe, T., Park, J.B., Curtin, W. A. , Takeda , N., 2003. Quantitative damage detection in CFRP composites: coupled mechanical and electrical models. Compos ites Sci ence and Technol ogy 63, 1411-1422.