Introduction. The weakness of composites to impact load is a well known problem. In particular, their impact damaging happens through complex mechanisms which are still not completely understood also because of the multitude of materials that can be created by changing: matrix, reinforcement and/or stacking sequence. It is enough to change the direction of a layer of fibres to have a new composite material. Once a new material is created, it is important to assess its performance under impact, or its impact resistance. The scope of this work is to show how advantageous may be to use infrared thermography to monitor impact tests, which are performed to ascertain the resistance-to-impact of a new composite material. Methods. Infrared thermography (IRT) and phased array ultrasonic testing (PAUT) are used. IRT is used with a twofold function: • on-line monitoring the impact event to visualize thermal signatures which bear the witness for the existence of any occurred damage; • non-destructive evaluation with lock-in thermography (LT) of the impacted specimens. Results. Some results are reported in terms of: • thermal images taken during impact tests on carbon/epoxy specimens; • phase images taken on the impacted specimens with lock-in thermography; • C-scan images taken with PAUT on the impacted surface of one specimen are compared with phase images obtained with lock-in thermography and also with thermal images taken during the impact. Discussion. Both LT and PAUT are effective in detecting the impact damage; LT is fast and more effective to map large surfaces, conversely PAUT is better to get information along the thickness especially in case of thick parts. Then, an integrated use of both techniques would be advantageous. However, they are characterized by some uncertainty in discriminating very thin delaminations when they are compared with the thermal signatures visualized during monitoring of the impact event, especially in presence of composites with complex stacking sequence. Conclusion. The obtained results show that, if the aim is to assess the performance under impact of composite materials for design purposes, monitoring the impact with an infrared imaging device appears to be the fastest and better solution.
composites, impact tests, impact monitoring, infrared thermography, phased array ultrasonic testing
1. Soutis C. Fiber reinforced composite in aircraft construction. - Progr. Aerosp. Sci. 2005. V. 41. P. 143-151.
2. Richardson M. O. W., Wisheart M. J. Review of low-velocity impact properties of composite materials. - Composites. Part A. 1996. V. 27. P. 1123-1131.
3. Meola C., Raj B. Nondestructive Testing and Evaluation: Overview. (Saleem Hashmi Editor-in-chief), Reference Module in Materials Science and Materials Engineering. - Oxford: Elsevier; 2016, p. 1-10.
4. Meola C., Carlomagno G. M. Infrared thermography to impact-driven thermal effects. - Applied Physics A. 2009. V. 96. P. 759-762.
5. Meola C., Carlomagno G. M. Impact damage in GFRP: new insights with Infrared Thermography. - Composites Part A. 2010. V. 41. No. 12. P. 1839-1847.
6. Meola C., Carlomagno G. M. Infrared thermography to evaluate impact damage in glass/epoxy with manufacturing defects. - Internat. J. Impact Eng. 2014. V. 67. P. 1-11.
7. Carlomagno G. M., Meola C., Ricci F. Infrared thermography and piezoelectric patches for impact damage detection in composite structures, IWSHM 2011. - In: International Workshop on Structural Health Monitoring 2011. - Stanford: Stanford University, 2011.
8. Meola C., Carlomagno G. M., Ricci F. et al. Investigation of Impact Damage in Composites with Infrared Thermography. - In: 6th NDT in Progress / Ed. by P. Mazal. - Prague: 2011, p. 175-182.
9. Meola C., Carlomagno G. M., Ricci F. Monitoring of impact damage in Carbon Fibre Reinforced Polymers. - In: QIRT 2012, Napoli, June 11-14, 2012, paper n. 374, p.8.
10. Meola C., Carlomagno G. M. Monitoring materials under impact with infrared thermography. - In: Residual Stress, Thermomechanics & Infrared Imaging, Hybrid Techniques and Inverse Problems. Vol. 8 / Conf. Proc. of the Society for Experimental Mechanics Series, Chicago, June 3-6, 2013, Springer 2014, pp. 177-185.
11. Meola C., Boccardi S., Boffa N.D. et al. Infrared thermography to evaluate impact da maging of composites. In: Proc. of ECCM16. Paper 0318 / Program book. -Seville (Spain): 22-26 June 2014.
12. Boccardi S., Carlomagno G. M., Meola C. Infrared thermography to evaluate impact damaging of thermoplastic composites. In: Proc. QIRT 2014. Paper 214. - Bordeaux (France), 7-11 July 2014.
13. Meola C., Boccardi S., Carlomagno G. M. et al. Nondestructive evaluation of carbon fibre reinforced composites with infrared thermography and ultrasonics. - Composite Structures. 2015. V. 134. P. 845-853.
14. Boccardi S., Carlomagno G. M., Meola C. et al. Monitoring impact damaging of thermoplastic composites. - J. Phys.: Conf. Ser. 658 (1):012005, 2015.
15. Boccardi S., Boffa N. D., Carlomagno G. M. et al. Infrared thermography and ultrasonics to evaluate composite materials for aeronautical applications. - Ibid. 012007, 2015.
16. Meola C., Boccardi S., Boffa N. D. et al. New perspectives on impact damaging of thermoset- and thermoplastic-matrix composites from thermographic images. - Composite Structures.2016. V. 152. P. 746-754.
17. Boccardi S., Carlomagno G. M., Simeoli G. et al. Evaluation of impact affected areas of glass fibres thermoplastic composites from thermographic images. - Measurement Sci. & Technology. 2016. V. 7. No. 7, 075602 (12 p).
18. Meola C., Boccardi S., Boffa N.D. et al. Learning more on impact damaging of composites with infrared thermography. - In: Proc. ICILSM 2016. - Torino: 22-26 May, 2016.
19. Meola C., Boccardi S., Carlomagno G.M. et al. Experimental Investigation of Impact Damaging of Carbon Fibre Reinforced Composites. - In: Proc. 19th WCNDT. Paper We.2.I.3. - Munich (Germany), 2016.
20. Boccardi S., Boffa N. D., Carlomagno G. M. et al. Visualization of Impact Damaging of Carbon/Epoxy Panels. - In: Proc. the 8th Conf. on Times of Polymers (TOP) & Composites. - Ischia (Italy): 19-23 June 2016.
21. Boccardi S., Carlomagno G. M., Meola C. Post-processing of time-sequences acquired during impact tests with the aid of a reference area. - In: Proc. QIRT 2016. - Gdańsk (Poland): 4-8 July 2016.
22. Naika N. K., Chandra Y. S., Sailendra M. Damage in woven-fabric composites subjected to low-velocity impact. - Composites Sci. & Techn. 2000. V. 60. P. 731-744.
23. Naika N.K., Ramasimhaa R., Aryaa H. et al. Impact response and damage tolerance characteristics of glass-carbon/epoxy hybrid composite plates. - Composites Part B: Engineering. 2001. V. 32. P. 565-574.