Issue 16

G. Pesquet et alii, Frattura ed Integrità Strutturale, 16 (2011) 18-27; DOI: 10.3221/IGF-ESIS.16.02 27 C ONCLUSIONS he effect of thermally expandable microcapsules (TEMs) on structural adhesives was investigated in terms of mode I fracture toughness. The single-edge-notch-bending (SENB) test was used. Three adhesives were selected (AW106 that is very ductile, 2015 that is ductile and AV138M that is brittle) and different mass fraction of TEMs were studied. Firstly, a standard fracture test was conducted. Secondly, since TEMs expands start their expansion at about 60ºC, specimens fatigue testing was performed expecting a local heating of the notch. Then, the specimen was statically tested. Thirdly, the specimen was heated locally in its notch at 90ºC to lead to a local expansion of the particles. Then, the specimen was loaded for fracture toughness determination. The following conclusions can be drawn. 1. The fracture toughness increased as the mass fraction of TEMs increased. However, the very ductile adhesive AW106 did not show clearly this increase in terms of toughness. 2. The two local heatings tested did not heal TEMs-modified adhesives. 3. A parallel could be drawn between TEMs and rubber incorporation since the sizes of the particles are comparable and both are barely compressible. Indeed, stress-strain curves for TEMs-modified and rubber-modified exhibit similarities. 4. As rubber particles, TEMs-induced shear yielding of the epoxy matrix is believed to be the dominant toughening mechanism. However, since TEMs are a shell filled with liquid, they may not exhibit the crack-bridging mechanism. 5. The specimens were successfully simulated using linear elastic fracture mechanics (LEFM) approximation. The bending test was simulated with the virtual crack closure technique (VCCT) using the experimental strain energy release rate. 6. TEMs have been developed for recycling purpose by allowing joints to be dismantled. However, TEMs also increase the fracture toughness of adhesives Therefore, TEMs-modified adhesives could be used on a larger scale. R EFERENCES [1] Y. Nishiyama, N. Uto, C. Sato, H. Sakurai, Int J Adhesion and Adhesives, 23 (2003) 377. [2] Y. Nishiyama, C. Sato, In: Adhesion - Current Research and Applications, W. Possart (editor), Wiley, Weinheim, (2005) 555. [3] H. Ishikawa, K. Seto, S. Shimotuma, N. Kishi, C. Sato, Int J Adhesion and Adhesives, 25 (2005) 193. [4] J.-Y. Cognard, R. Créachcadec, J. Maurice, P. Davies, M. Peleau, L.F.M. da Silva, J Adhesion Science and Technology, 24 (2010) 1977. [5] S.R. White, N.R. Sottos, P.H. Geubelle, J.S. Moore, M.R. Kessler, S.R. Sriram, E.N. Brown, S. Viswanathan, Nature, 409 (2001) 794. [6] R.S. Trask, H.R. Williams, I.P. Bond, Bioinspir. Biomim., 2 (2007) 1. [7] M.R. Kessler, N.R. Sottos, S.R. White, Composites Part A, 34 (2003) 743. [8] I.P. Bond, J.W.C. Pang, Compos Part A, 36 (2005) 183. [9] L.F.M. da Silva, R.D. Adams, J. Adhesion Science and Technology, 19 (2005) 109. [10] Z. Chen, R.D. Adams, L.F.M. da Silva, Int J Fracture, 167 (2011) 221. [11] J. Du, M.D. Thouless, A.F. Yee, Int J Fract, 92 (1998) 271. [12] A.F. Yee, R.A. Pearson, J Mater Sci, 21 (1986) 2462. [13] Y. Huang, A.J. Kinloch, J.Mater Sci, 27 (1992) 2753. [14] M. Imanaka, D. Yamashita, Y. Suzuki, A. Fujinami, Polymer & Polymer Composites, 13 (2005) 765. [15] ABAQUS Analysis User’s Manual. ABAQUS 6.9 (2009). T