Influence of Porosity on the Interlaminar Shear Strength of Fibre-Metal Laminates

Abstract:

Structures manufactured in fibre-metal laminates (e.g. Glare) have been designed considering ideal mechanical properties determined by the Classical Lamination Theory. This means that among other assumptions, perfect bonding conditions between layers are assumed. However, more than often, perfect interfaces are not achieved or their quality is not guaranteed. When in laboratory, high-quality fibre-metal laminates are easily fabricated, but in the production line the complicated manufacturing process becomes difficult to control and the outcome products may not meet the quality expected. One of the consequences may be the poor adhesion of metalprepreg or prepreg-prepreg as the result of porosity. The interlaminar shear strength of fibre-metal laminates decreases considerably, due to porosity, as the result of insufficient adhesion between layers. Small voids or delaminations lead to stress concentrations at the interfaces which may trigger delamination-propagation at the aluminiumprepreg and prepreg-prepreg interfaces at load levels significantly lower than what is achievable for perfectly bonded interfaces. Mechanical experiments show a maximum drop of 30% on the interlaminar shear strength. In the present work, the effects of manufacturing-induced porosity on the interlaminar shear strength of fibre-metal laminates are studied using a numerical approach. The individual layers are modelled by continuum elements, whereas the interfaces are modelled by cohesive elements which are equipped with a decohesion law to simulate debonding. Porosity is included in the geometry of the interface by setting some of these elements to a pre-delaminated state.

• Periodical: Key Engineering Materials (Volume 383)
• Pages: 35-52
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.383.35
• Online since: June 2008
• Authors: Cláudio S. Lopes, Joris J.C. Remmers, Zafer Gürdal
• Keywords: Cohesive Element, Delamination, Fibre Metal Laminates, Fracture Toughness, GLARE, Porosity

References

[1] A.M. Rubin and K.L. Jerina (1994), Evaluation of Porosity in Composite Aircraft Structures, Mechanics of Composite Materials, Vol. 30, No. 6, pp.587-600.

DOI: 10.1007/bf00821276

[2] H. Jeong (1997), Effects of Voids on the Mechanical Strength and Ultrasonic Attenuation of Laminated Composites, Journal of Composite Materials, Vol. 31, pp.276-292.

DOI: 10.1177/002199839703100303

[3] M.L. Costa, S.F.M. de Almeida and M.C. Resende (2001), The influence of Porosity on the Interlaminar Shear Strength of Carbon/Epoxy and Carbon/Bismaleimide Fabric Laminates, Composite Science and Technology, Vol. 61, pp.2101-2108.

DOI: 10.1016/s0266-3538(01)00157-9

[4] Z. Gürdal, A. P. Tomasino and S.B. Biggers (1991), Effects of Processing Induced Defects on the Laminate Response: Interlaminar Tensile Strength, SAMPE Journal, Vol. 27, No. 4, pp.39-49.

[5] A. Mobuchon and Z. Gürdal (1991), Effects of Processing-Induced Defects on Failure of Graphite/Epoxy Angles, Mechanics and Mechanisms of Damage in Composites and MultiMaterials, ESIS11, Mechanical Engineering Publications, London, pp.95-115.

[6] ABAQUS, Inc (2007), ABAQUS Version 6. 7 User's Manual, Pawtucket, RI, USA.

[7] J.C.J. Schellekens and R. de Borst (1994), Free Edge Delamination in Carbon-Epoxy Laminates: a novel numerical/experimental approach, Composites and Structures, Vol. 28, pp.357-373.

DOI: 10.1016/0263-8223(94)90118-x

[8] P.P. Camanho, C.G. Dávila and M.F. Moura (2003), Numerical Simulation of Mixed-mode Progressive Delamination in Composite Materials, Journal of Composite Materials, Vol. 37, No. 16, pp.1415-1438.

DOI: 10.1177/0021998303034505

[9] A. Turon, P.P. Camanho, J. Costa and C.G. Dávila (2004), An Interface Damage Model for the Simulation of Delamination Under Variable-Mode Ratio in Composite Materials. NASA/TM-2004- 213277.

DOI: 10.1016/j.mechmat.2005.10.003

[10] A. Turon, P.P. Camanho, J. Costa and C.G. Davila (2006), A Damage Model for the Simulation of Delamination in Advanced Composites under Variable-Mode Loading. Mechanics of Materials, Vol. 38, pp.1072-1089.

DOI: 10.1016/j.mechmat.2005.10.003

[11] M. Vesco and J. Sinke (2005), Response and damage evolution in GLARE laminates under indentation loads - Experimental results, Report B2V-05-01, Faculty of Aerospace Engineering - TUDelft.

[12] M.L. Benzeggagh and M. Kenane (1996), Measurement of Mixed-Mode Delamination Fracture Toughness of Unidirectional Glass/Epoxy Composites with Mixed-Mode Bending Apparatus, Composite Science and Technology, Vol. 56, pp.439-49.

DOI: 10.1016/0266-3538(96)00005-x

[13] Y. Mi and M.A. Crisfielfd (1996), Analytical Derivation of Load/Displacement relationship for the DCB and MMB and Proof of the FEA Formulation, Department of Aeronautics, Imperial College, London.

[14] A. Korjakins (1997), Interlaminar Fracture Toughness of Glass Fibre Reinforced Polymeric Composites Influenced by Fibre Surface Treatment. Ph. D Thesis. Riga Technical University.

[15] C. Schuecker and B.D. Davidson (2000), Evaluation of the accuracy of the four-point bend end-notched flexure test for mode II delamination toughness determination, Composites Science and Technology, Vol. 60, pp.2137-2146.

DOI: 10.1016/s0266-3538(00)00113-5

[16] Ad. Vlot (2001), Fibre Metal Laminates (An Introduction), Kluywer Academic Publishers.

[17] A. Turon, C.G. Davila, P.P. Camanho and J. Costa (2005), An Engineering Solution for using Coarse Meshes in the simulation of Delamination with Cohesive Zone Models, NASA Technical Memorandum, NASA/TM-2005-213547.