Determining the Mode II Intra-Ply Energy Release Rate of Composites Made of Prepreg

Authors: Philip Rose, Markus Linke, David Busquets

Abstract:

The distinction between interlaminar and intralaminar fracture toughness is challenging. For loading mode I, the double cantilever beam specimens were often used for the interlaminar fracture toughness and the compact tension specimen for the intralaminar fracture toughness. For the analysis of interlaminar properties regarding energy release under different loading modes, the geometry of the DCB specimen can also be tested under three-point bending for Mode II characteristics. The same specimen can also be tested with defined superimposed loading conditions (mixed mode) using the Mixed Mode Bending test apparatus. However, this approach has not been applicable for intralaminar characteristics, as crack initiation in a single layer for laminates made out of prepreg, has not been feasible. The method presented in this work enables differentiation of interlaminar and intralaminar energy release rates in Mode II loading with nearly identical specimen geometry. With this, a practically identical energy release rate is observed in Mode II for the investigated material IM7/8552.

Keywords: Fibre reinforced plastics, end-notched flexure, energy release rate, fracture toughness, intralaminar, interlaminar.

References:

[1] Sachse, R. (2019). Untersuchungen zur Auslegung von schadenstoleranten Klebeverbindungen durch mechanische Riss-Stopper-Elemente. Dissertation, University of Stuttgart, Stuttgart.
[2] Girolamo, D., Dávila, C., Leone, F. A., Lin, S. Y. (2015). Cohesive Laws and Progressive Damage Analysis of Composite Bonded Joints, a Combined Numerical/Experimental Approach. 56th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference. 10.2514/6.2015-1578.
[3] Leone, F. A., Girolamo, D., Dávila, C. (2012). Progressive Damage Analysis of Bonded Composite Joints. Report number: NASA/TM-2012-217790, L-20210, NF1676L-15757 Affiliation: NASA.
[4] Benzeggagh, M.L., Kenane, M. (1996). Measurement of mixed-mode delamination fracture toughness of unidirectional glass/epoxy composites with mixed-mode bending apparatus, Composites Science and Technology, Volume 56, Issue 4, pp. 439-449, ISSN 0266-3538, https://doi.org/10.1016/0266-3538(96)00005-X.
[5] Borg, R., Nilsson, L., Simonsson, K. (2002). Modeling of delamination using a discretized cohesive zone and damage formulation. Composites Science and Technology - COMPOSITES SCI TECHNOL. 62. 1299-1314. 10.1016/S0266-3538(02)00070-2.
[6] Sato, N., Hojo, M., Nishikawa, M. (2014) Novel test method for characterizing accurate intra-laminar fracture toughness in CFRP. Composites Part B, Vol. 65, pp. 89–98.
[7] Czabaj, M. W., Ratcliffe, J. G. (2013). Comparison of intralaminar and interlaminar mode I fracture toughnesses of a unidirectional IM7/8552 carbon/epoxy composite. Composites Science and Technology, Vol. 89, pp. 15–23.
[8] Rose, P., Linke, M., Busquets, D. (2022). A novel approach for determining the intra-ply energy release rate of composites made of prepreg. 25th International Conference on Composite Structures, Porto, Portugal.
[9] Hansen, P and Martin, R. (1999). DCB, 4ENF and MMB Delamination Characterisation of S2/8552 and IM7/8552. United States Army, European Research office of the US Army. London, England.
[10] Gutkin, R., Laffan, M.L., Pinho, S.T., Robinson, P., Curtis, P.T. (2011). Modelling the R-curve Effect and its Specimen-Dependence. International Journal of Solids and Structures, 48(11-12):1767-1777.
[11] ASTM D7905/D7905M: Standard Test Method for Determination of the Mode II Interlaminar Fracture Toughness of Unidirectional Fiber-Reinforced Polymer Matrix Composites. American Society for Testing and Materials (ASTM).
[12] DIN EN 6034:2015: Aerospace series - Carbon fibre reinforced plastics – Test method - Determination of interlaminar fracture toughness energy - Mode II – GIIC. DIN Deutsches Institut für Normung e. V.