PSI - Issue 28

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Evangelia Nektaria Palkanoglou et al. / Procedia Structural Integrity 28 (2020) 1286–1294 E. Palkanoglou et al. / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 7: Evolution of von Mises stresses with temperature in matrix (i), graphite (ii) and interface (iii) for two different unit cells.

4. Conclusions Debonding as the main mechanism of fracture in the microscale is investigated in this research, following a micromechanical approach. A two-dimensional unit cell was generated, based on statistical results of microstructure characterisation. The effect of boundary conditions and incorporation of a layer around graphite to represent the interface are studied. The elastoplastic behaviour for both constituents was assumed and a damage criterion was used for either graphite or interface to simulate degradation due to debonding. The numerical results were primarily affected by the choice of boundary conditions. Although the developed stresses in the matrix were at similar levels for both fully fixed and periodic BCs, the size of plastic zone differed significantly, and the magnitude of plastic deformations was two orders of magnitude in the former case. In addition, the incorporation of an interfacial layer around graphite can model debonding more accurately. In this case, graphite exhibited elastic behaviour, a performance that is consistent with its brittle nature and was observed experimentally. The deletion of elements in the interfacial layer corresponds to the loss of contact between graphite and matrix and can be characterised as partial debonding. In conclusion, a methodology to simulate debonding under thermal loading was presented suitable for further research on decohesion when interaction of particles takes place. References Andriollo, T., Thorborg, J., Tiedje, N. S., Hattel, J., 2015. Modeling of Damage in Ductile Cast Iron - The Effect of Including Plasticity in the Graphite Nodules. IOP Conference Series: Materials Science and Engineering 84. Andriollo, T., 2016. Modeling the Elastic Behavior of Ductile Cast Iron Including Anisotropy in the Graphite Nodules. International Journal of Solids and Structures 100-101, 523-35. Cocco, V.D., Iacoviello, F., Rossi, A., Iacoviello, D., 2014. Macro and Microscopical Approach to the Damaging Micromechanisms Analysis in a Ferritic Ductile Cast Iron. Theoretical and Applied Fracture Mechanics 69, 26–33. Drago, A., Pindera, M.J., 2007. Micro-Micromechanical Analysis of Heterogeneous Materials: Macroscopically Homogeneous vs Periodic Microstructures. Composites Science and Technology 67, 1243–63. Greenstreet, W.L., Yahr, G.T., Valachovic, R.S., 1973. The Behavior of Graphite under Biaxial Tension. Carbon 11, 43-57. Hill, R. 1963. Elastic Properties of Reinforced Solids: Some Theoretical Principles. Journal of the Mechanics and Physics of Solids 11, 357–72. Hjelm, H.E., 1994. Yield Surface for Grey Cast Iron under Biaxial Stress. Journal of Engineering Materials and Technology 3, 465–72. Josefson, B.L., Stigh, U., Hjelm, H.E., 1995. A Nonlinear Kinematic Hardening Model for Elastoplastic Deformations in Grey Cast Iron. Journal of Engineering Materials and Technology 117, 145-50. Kanit, T., Forest, S., Galliet, I., Mounoury, V., Jeulin, D. 2003. Determination of the Size of the Representative Volume Element for Random Composites: Statistical and Numerical Approach. International Journal of Solids and Structures 40, 3647–79. Kanouté, P., Boso, D. P., Chaboche, J. L., Schrefler, B.A., 2009. Multiscale Methods for Composites: A Review. Archives of Computational Methods in Engineering 16, 31–75. Lim, C. H., Goo, B.C., 2011. Development of Compacted Vermicular Graphite Cast Iron for Railway Brake Discs. Metals and Materials International 17, 199–205. Matsushita, T., Ghassemali, E., Saro, A.G., Elmquist, L., Jarfors, A.E.W., 2015. On Thermal Expansion and Density of CGI and SGI Cast Irons. Metals, 1000-19.