Penetrating Impact Strength of Sandwich Panels — Meaningful Test Method and Simplified Prediction
This paper proposes a test method which is comprehensive enough to be able to quantify the impact strength, according to various definitions, of a sandwich and, most importantly, be applicable to sandwich panels of various types and scales. These findings are based on the results of a penetrating impact test series using three different test methods: The standardised ISO 6603 method and two non-standardised methods. The first non-standardised method uses a pyramid-shaped impactor instead of the cylindrical impactor used in the ISO 6603 method and in the second the impact test is performed quasi-statically using a cylindrical impactor.
The results obtained with the three test methods lead to a different ranking in impact strength of the panels. Hence, impact test results obtained with different test methods are not even qualitatively comparable.
The pyramid-shaped impactor is able to generate clearly more failure modes than the cylindrical impactor in the ISO 6603 method. Therefore, it is considered to be of more practical value for determining the impact strength of FRP-sandwich structures.
Additionally, a simplified approach to predict the impact strength of FRP-sandwich panels in respect to full penetration is presented. The method is semi-empirical and allows one to predict the absorbed energy at penetration of the inner face without the need for exotic input values. The empirical part of the method lies in the fact that certain damage modes are assumed to occur during the impact. These assumed damage modes have been observed in many earlier experiments. The accuracy of the method is reasonably high, in most cases better than ±30%.
The semi-empirical prediction method is particularly useful during the design stage of sandwich structures due to its reasonable accuracy and the fact that the needed input values are usually known at this stage.
KeywordsFailure Mode Impact Strength Transverse Shear Sandwich Structure Sandwich Panel
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- 1.Gaarder, R. H. 1995. Methods to predict impact performance of sandwich structures. Espoo: Nokos Second Composites and Sandwich Meeting, 4.–5. 4. 1995. Pp. 25–27.Google Scholar
- 2.Brevik, A. F. 1995. Sandwich constructions for subsea applications. Presented at the third international conference on sandwich construction. 9 p.Google Scholar
- 3.Grenestedt, J. & Kuttenkeuler, J. 1995. Slow impact on Sandwich panels. Espoo: Nokos Second Composites and Sandwich Meeting, 4.–5. 4. 1995. Pp. 35–37.Google Scholar
- 4.Olsson, R. 1995. Prediction of impact damage in sandwich panels. Presented at the third international conference on sandwich construction. 10 p.Google Scholar
- 5.Lönnö, A. & Håkanson, P. 1995. Development of a super tough FRP-sandwich concept for the 10.8 m combat craft 90E. Presented at the third international conference on sandwich construction. 12 p.Google Scholar
- 6.Hildebrand, M. 1994. The effect of raw-material related parameters on the impact strength of sandwich boat-laminates. Espoo, Technical Research Centre of Finland, VTT Publications 211. 36 p. + app. 19 p.Google Scholar
- 7.Auerkari, P. & Pankakoski P. H. 1995. Strength of sandwich panels with impact defects. Espoo: VTT Technical Report VAL B 75. 19 p. + app. 4 p.Google Scholar
- 8.Burchardt, C., et al. 1993. Slagpåvirkning af sandwichplader. Aalborg: M.Sc. Thesis, Aalborg Universitets Center. 90 p. + app. 82 p.Google Scholar
- 9.Aamlid, O. 1995. Oblique impact testing of aluminium — and composite panels. Hovik: Det Norske Veritas Research, Technical Report No. 95–2042. 36 p.Google Scholar
- 10.Marum, S.E. 1993. Impact testing of GRP/PVC sandwich panels (In Norwegian). Mandal: Kvaerner Mandal test report EO 094. 23 p. + app. 49 p.Google Scholar
- 11.Nilsen, P.E., Moan, T., Gustafson, C.-G. 1992. Dynamic and quasi-static indentation of PVC/GRP sandwich plates. Warley: Proceedings of the second international conference on sandwich construction. EMAS. Pp. 121–137.Google Scholar
- 12.Kivelä, J. 1992. The determination of local impact strength for small-craft sandwich structures (in Finnish). Espoo: Helsinki University of Technology. M.Sc. Thesis. 62 p. + app. 19 p.Google Scholar
- 13.Hildebrand, M. 1996. Improving the impact strength of FRP-sandwich panels for ship applications. Technical Research Centre of Finland, VTT Technical Report VAL B 138.Google Scholar
- 14.ISO 6603/2–1989. Plastics — Determination of multiaxial impact behaviour of rigid plastics — Part 2: Instrumented puncture test.Google Scholar
- 15.Hildebrand, M. 1996. A comparison of FRP-sandwich penetrating impact test methods. Espoo, Technical Research Centre of Finland, VTT Publications 281. 33 p. + app. 1 p.Google Scholar
- 16.Hildebrand, M. 1996. Penetrating impact strength of FRP-sandwich panels — empirical and semi-empirical prediction methods. Technical Research Centre of Finland, VTT Technical Report VAL B 154.Google Scholar