While the introduction of a graded interface may enhance the structural integrity of a material joint, the benefits that may be obtained by a crack deflecting into a more compliant and often tougher material, may be not fully realised. This is because crack bridges, inherent to a crack propagating in a composite of two materials with different failure strains, may reduce the extent of crack deflection such that the crack propagates through a more brittle region of the gradient structure. Figure 6 Effect of fibre (a) diameter and (b) modulus upon crack deflection (in degrees) as a function of phase angle (in degrees) of applied stress intensity factors. CONCLUSIONS From this work a number of conclusions can be made in regards to crack deflection of a crack propagating perpendicular to the direction of spatial material gradient which incorporates a stiffness gradient: 1. Crack bridging leads to a reduction in the extent of crack deflection and that 2. This is dependent upon the (a) diameter, (b) stiffness, (c) bridging length of the bridging fibres and also upon the (d) applied stress intensity factor. ACKNOWLEDGEMENTS A/Prof. Don Kelly of the Department of Mechanical Engineering, University of NSW, is thanked for his assistance with the FEM package. This work was supported by an Australian Research Council Large Research Grant. REFERENCES 1. F. Delale and F. Erdogan (1983) J. Appl. Mechanics, 50 609-14 2. N. Noboru and F. Erdogan (1994) Eng. Fracture Mechanics, 47[4] 533-545 3. H. Li, J. Lambros, B. A. Cheeseman, M. H. Santare, Int. J. Solids Structures (2000) 37, 3715-32 4. Z.-H. Jin and R.C. Batra (1998) Mat. Sci. & Eng. A, 242 70-6 5. T.-J. Chung, A. Neubrand, J. Roedel, and T. Fett. to be published in Proceedings of FGM2000, Estes Park, CO, USA 2000 0 2 4 6 8 10 0 10 20 30 40 50 60 200 300 500 1000 Crack phase angle, ÷÷ ø ö çç è æ y= - I II 1 K K tan Change in crack deflection angle due to crack bridging, br q-q Increasing fibre diameter (a) Fibre diameter, mm 0 2 4 6 8 10 0 10 20 30 40 50 60 0.1 1 5 10 Crack phase angle, Increasing fibre modulus (b) Fibre Modulus, Ef, [GPa]
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