Issue 41

S.M.J. Razavi et alii, Frattura ed Integrità Strutturale, 41 (2017) 424-431; DOI: 10.3221/IGF-ESIS.41.53 430 A synthesis in terms of the square root value of the considered parameter, that is the sum of the weighted energy contributions related to mode I and mode III loading, is shown in Fig. 3 as a function of the notch root radius ρ . The obtained trend is very promising. Many of the results are inside a scatter band ranging from 0.9 to 1.1 with only few exceptions. The fracture model proposed in this paper can be used for predicting the onset of brittle fracture in notched graphite components which are subjected to a combination of tension and torsion loadings. Such criterion would be very useful for designers and engineers who should explore the safe performance of graphite components particularly under complex loading conditions. C ONCLUSIONS rittle fracture in V-notched polycrystalline graphite specimens was investigated both experimentally and theoretically under combined tension and torsion loading. Fracture tests were conducted on notched round bar graphite specimens. Different notch depths, notch radii and opening angles were considered in the test specimens as well as different combinations of the mode mixity ratio σ nom / τ nom . The new set of data provided in the paper is unique because no previous papers have been devoted to similar topics dealing with graphite components. The SED criterion was used for the first time in order to estimate the fracture load of notched graphite components under mixed mode I+III static loading. A new formulation of the SED criterion was proposed showing the capabilities of the suggested method to assess the fracture behaviour of polycrystalline graphite under the considered loading conditions. The results estimated by the SED approach were found to be in good agreement with the experimental results. The criterion based on the elliptic expression described above seems to be very advantageous because it requires, as experimental parameters, only the critical energies from unnotched graphite specimens under pure tension and pure torsion. R EFERENCES [1] Sakai, M., Urashima, K., Inagaki, M., Energy Principle of Elastic-Plastic Fracture and Its Application to the Fracture Mechanics of a Polycrystalline Graphite, J. Am. Ceram. Soc., 66 (1983) 868–874. DOI: 10.1111/j.1151-2916.1983.tb11003.x. [2] Ayatollahi, M.R., Razavi, S.M.J., Rashidi Moghaddam, M., Berto, F., Mode I fracture analysis of Polymethylmetacrylate using modified energy—based models, Phys. Mesomech., 18(5) (2015) 53-62. DOI: 10.1134/S1029959915040050. [3] Ayatollahi, M.R., Rashidi Moghaddam, M., Razavi, S.M.J., Berto, F., Geometry effects on fracture trajectory of PMMA samples under pure mode-I loading, Eng. Fract. Mech., 163 (2016) 449–461. DOI: 10.1016/j.engfracmech.2016.05.014. [4] Rashidi Moghaddam, M., Ayatollahi, M.R., Razavi, S.M.J., Berto, F., Mode II Brittle Fracture Assessment Using an Energy Based Criterion, Phys. Mesomech. (in press). [5] Hess, P., Graphene as a model system for 2D fracture behavior of perfect and defective solids, Frattura ed Integrita Strutturale, 9(34) (2015) 341-346. DOI: 10.3221/IGF-ESIS.34.37. [6] Vo, T.T.G., Martinuzzi, P., Tran, V.X., McLachlan, N., Steer, A., Modelling 3D crack propagation in ageing graphite bricks of Advanced Gas-cooled Reactor power plant, Frattura ed Integrita Strutturale, 9(34) (2015) 237-245. DOI: 10.3221/IGF-ESIS.34.25. [7] Doddamani, S., Kaleemulla, M., Experimental investigation on fracture toughness of Al6061–graphite by using circumferential notched tensile specimens, Frattura ed Integrita Strutturale, 11(39) (2017) 274-281. DOI: 10.3221/IGF-ESIS.39.25. [8] Bazaj, D.K., Cox, E.E., Stress-concentration factors and notch-sensitivity of graphite, Carbon, 7 (1969) 689–697. DOI: 10.1016/0008-6223(69)90524-7. [9] Kawakami, H., Notch sensitivity of graphite materials for VHTR, Trans. Atomic Energy Soc. Jpn., 27 (1985) 357–364. DOI: 10.3327/jaesj.27.357. [10] Sato, S., Awaji, H., Akuzawa, H., Fracture toughness of reactor graphite at high temperature, Carbon, 16 (1978) 95– 102. DOI: 10.1016/0008-6223(78)90004-0. [11] Ayatollahi, M.R., Berto, F., Lazzarin, P., Mixed mode brittle fracture of sharp and blunt V-notches in polycrystalline graphite, Carbon, 49 (2011) 2465–2474. DOI: 10.1016/j.carbon.2011.02.015. B