13th International Conference on Fracture June 16–21, 2013, Beijing, China -10- Fulfillment of the condition, f fr y induced f fr y total σ σ ) ) ( ( , , , , > , in bridging zone of fibre layer convincingly confirms load transfer towards fibre. Also, al fr y induced al fr y total σ σ ) ) ( ( , , , , << , around cracked area of aluminum hints at the shielding effect. Although the presence of crack, as a free surface, in itself dips the load line stress field in shielded area of aluminum, the magnitude of { } al fr y induced al fr y total σ σ ) ) ( ( , , , , − is found to be high enough to include both the compressive effects i.e. due to the crack and due to shielding by fibre bridging. Similar trends are observed in laminates with cracks of other sizes as well. Again from the experimental results in Table 2, the finding, d C al C lam tip C lam K K K K , , , or > > , adequately proves crack tip shielding and enhanced fracture toughness of the laminates vis-à-vis corresponding plain aerospace aluminum alloy specimens. Experimental and numerical results of tip K are compared in Figure 8. They are close to each other. The error is attributed to slight difference between theoretical and experimental values of residual stress in aluminum layer of the laminate. The experimental values are lower than the theoretical ones. Fibre bridging effect, br K , is quantified by{ } tip C lam K K− , . The effect, in general, is found to increase with increase in crack size in aluminum layers. Absence of delaminations intensifies the effect. Acknowledgements The author is grateful to Science and Engineering Research Council, Department of Science and Technology, The Government of India for funding the project. Support received from the School of Mechanical and Building Sciences, VIT University, Vellore, India during the course of this work is acknowledged. References [1] Y.J. Guo, X.R. Wu, Bridging stress distribution in center-cracked fibre reinforced metal laminate: Modeling and Experiment. Eng Fra Mech, 63 (1999) 147-163. [2] R.C. Alderliesten, Analytical prediction model for fatigue crack propagation and delamination growth in Glare, Int J Fat, 29 (2007) 628-646. [3] G.R. Irwin, NRL Report 6598, 1967. [4] J.R. Rice, A path independent integral and approximate analysis of strain concentration by notches and cracks. J App Mech, 35 (1968) 379-386. Y Y 0 20 40 60 80 100 0 5 10 15 20 25 Series1 Series2 Series3 Series 1 - C lam K , Series 2 - tip K (Experimental) Series 3 - tip K (Numerical) Crack length (mm) Fibre bridging effect, br K MPa m 1 2 3 4 5 1 to 5 - Laminate No’s tip K zone zone ,C lam K Figure 8. Comparison between experimental and numerical estimations of fibre bridging
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