Issue 48

J.P.S.M.B. Ribeiro et alii, Frattura ed Integrità Strutturale, 48 (2019) 332-347; DOI: 10.3221/IGF-ESIS.48.32 345 C ONCLUSIONS he proposed work aimed at experimentally defining the most suitable  parameter for the mixed-mode crack propagation prediction of three structural adhesives. With this purpose, pure and mixed-mode fracture tests were undertaken that enabled building the fracture envelopes of the three adhesives. Brittle crack propagation issues were detected in some specimens bonded with the Araldite ® AV138, due to its brittleness. On the other hand, the Araldite ® 2015 and Sikaforce ® 7752 revealed a ductile failure, which, together with the G I / G II and G IC / G IIC values obtained, confirmed their expected ductile behaviour. The R -curves enabled estimating the data points that were on the basis of the built fracture envelopes. The experimental data points revealed a different mixed-mode behaviour, with  =0.5 giving a close match for the Araldite ® AV138 and Araldite ® 2015, while  =2 closely represented the Sikaforce ® 7752. Validation of this data was undertaken with SLJ and DLJ. However, a previous experimental data discussion was presented, enabling to realize that the lap-joints’ behaviour is highly dependent on the adhesive type and L O . More particularly, it was found that strong yet brittle adhesive behave well for short L O , while this is not true for large L O . For these geometries, less strong but ductile adhesives take advantage, on view of the ability to endure loads after damage onset takes place. After this analysis, numerical simulations of the SLJ and DLJ were made with different  , and P m was compared with experiments. For the Araldite ® AV138 and Araldite ® 2015, the energetic criterion resulting from the experimental work provided matching numerical results and, thus, the fracture envelopes were validated. For these two adhesives and the chosen  , the deviations were mostly under 10%. The Sikaforce ® 7752 results were slightly offset due to CZM law shape issues. In the end, this work made possible, by CZM, to estimate the most suitable  parameter to use in crack propagation of adhesive joints under mixed-mode conditions. R EFERENCES [1] da Silva, J.F.M.G., Öchsner, A., Adams, R.D. Handbook of Adhesion Technology. Heidelberg: Springer; 2011. [2] Loureiro, A.L., da Silva, L.F.M., Sato, C., Figueiredo, M.A.V. (2010). Comparison of the Mechanical Behaviour Between Stiff and Flexible Adhesive Joints for the Automotive Industry. J Adhesion. 86, pp. 765-87. DOI: 10.1080/00218464.2010.482440. [3] Petrie, E.W. (1999). Handbook of adhesives and sealants. 2nd ed ed. New York: McGraw-Hill. [4] Adams, R.D. (2005). Adhesive bonding: science, technology and applications. Cambridge: Woodhead Publishing Limited. [5] Kinloch, A.J. (1987). Adhesion and Adhesives: Science and Technology. Heidelberg: Springer. [6] He, X. (2011). A review of finite element analysis of adhesively bonded joints. Int J Adhes Adhes. 31, pp. 248-64. DOI: 10.1016/j.ijadhadh.2011.01.006. [7] Barenblatt, G.I. (1959). The formation of equilibrium cracks during brittle fracture. General ideas and hypotheses. Axially-symmetric cracks. Journal of Applied Mathematics and Mechanics. 23, pp. 622-36. DOI: 10.1016/0021-8928(59)90157-1. [8] Dugdale, D.S. (1960). Yielding of steel sheets containing slits. J Mech Phys Solids. 8, pp. 100-4. DOI: 10.1016/0022-5096(60)90013-2. [9] Jung Lee, M., Min Cho, T., Seock Kim, W., Chai Lee, B., Ju Lee, J. (2010). Determination of cohesive parameters for a mixed-mode cohesive zone model. International Journal of Adhesion and Adhesives. 30, pp. 322-8. DOI: 10.1016/j.ijadhadh.2009.10.005. [10] Andersson, T., Stigh, U. (2004). The stress–elongation relation for an adhesive layer loaded in peel using equilibrium of energetic forces. Int J Solids Struct. 41, pp. 413-34. DOI: 10.1016/j.ijsolstr.2003.09.039. [11] Pandya, K.C., Williams, J.G. (2000). Measurement of cohesive zone parameters in tough polyethylene. Polymer Engineering & Science. 40, pp. 1765-76. DOI: 10.1002/pen.11308. [12] Banea, M.D., da Silva, L.F.M., Campilho, R.D.S.G. (2011). Mode I fracture toughness of adhesively bonded joints as a function of temperature: Experimental and numerical study. Int J Adhes Adhes.31, pp. 273-9. DOI: 10.1016/j.ijadhadh.2010.09.005. [13] BS 7991:2001 Standard. Determination of the mode I adhesive fracture energy, GIC, of structural adhesives using the double cantilever beam (DCB) and tapered double cantilever beam (TDCB) specimens. London, United Kingdom: British Standards Institution; 2001. [14] ASTM D3433-99 Standard. Standard test method for fracture strength in cleavage of adhesives in bonded metal joints. West Conshohocken, PA: ASTM International; 2012. T