N. Eswara Prasad et al. Engineering Fracture Mechanics 71(2004)2589-2605 Table 2 Total fracture energy release rate (c)of the CFCC material in crack divider and crack arrester orientations Nature Displacement (o) Slope of the Err -a Jc Operative crack bridging mechanisms kJ/m) Crack divider (A)in Fig. &a 81=130 Matrix cracking (B)in Fig. Sa 52=250 2.16 Matrix cracking, fibre/matrix debonding (C)in Fig. &a 53=720 3.56 Matrix cracking, fibre/matrix debonding fibre breakage and pull-out Crack arrester (A)in Fig. 8b 81=150 Matrix crackin (B)in Fig. 8b 02=400 0.68 Matrix cracking, fibre/matrix debonding (C)in Fig. 8b 53=660 6.8 ).79 Matrix cracking, fibre/matrix debonding, ibre breakage and pull-out obtained for the specimen with smallest crack length, a,, is not exceeded. Such low displacement values presumably include the fracture event of matrix microcracking and hence, would indicate the matrix fracture resistance. As would be seen in the following paragraphs this fracture energy [(c)a=(c)matri is more than 50% lower than the overall fracture energy((Jc))of the composite. The disparity in the Jc values at 8 and 83 displacements is significantly higher in the crack divider direction as compared to the crack arrester direction(see data in Table 2). The second chosen displacement, 82, corresponds to the pe load and hence, encompasses the matrix cracking and the fibre/matrix debonding. However, the most cating fibre bundle breakage. Such large displacement effectively would include all the fracture events of significance and hence, provides the highest values of Jc to evaluate the total energy release rate (c)of the present CFCC material. The variation of fracture energy (Ef)determined for the CFCC material is shown as a function of ack length in Fig. &a and b, respectively for crack divider and crack arrester orientations. The Efr values derived here are similar to the Eini values, derived for Jic evaluation(see previous section). In the former case, the Efr is energy till a certain displacement value, while, the latter Eini is the energy till the specimen attains peak load. In both the notch orientations, the higher values of displacements considered yielded higher fracture resistance, Je. The slope values(Efr/Aa)and the corresponding Jc values vary significantly with the value chosen for the displacement 8(see data in Table 2). The fracture energy progressively 003 自oaA M t\t 2 Crack Length(a),mm Crack Length(a), mm Fig. 8. Variation of fracture energy (Er)with the crack length for three different crack displacement values(01, 02 and a, for cases of A B and C, respectively; for details see Table 2) for the CFCC material in(a)crack divider and (b)crack arrester orientations. Note the increase in the slope of the linear curve fit with increasing 6, indicating the increase in the value of total fracture energy release rate withobtained for the specimen with smallest crack length, a1, is not exceeded.Such low displacement values presumably include the fracture event of matrix microcracking and hence, would indicate the matrix fracture resistance.As would be seen in the following paragraphs this fracture energy [ðJcÞd1 ¼ ðJcÞmatrix] is more than 50% lower than the overall fracture energy (ðJcÞd3) of the composite.The disparity in the Jc values at d1 and d3 displacements is significantly higher in the crack divider direction as compared to the crack arrester direction (see data in Table 2).The second chosen displacement, d2, corresponds to the peak load and hence, encompasses the matrix cracking and the fibre/matrix debonding.However, the most appropriate case is the third chosen displacement, d3, which encompasses the first major load drop indi￾cating fibre bundle breakage.Such large displacement effectively would include all the fracture events of significance and hence, provides the highest values of Jc. The above procedure has been followed to evaluate the total energy release rate (Jc) of the present CFCC material.The variation of fracture energy (Efr) determined for the CFCC material is shown as a function of crack length in Fig.8a and b, respectively for crack divider and crack arrester orientations.The Efr values derived here are similar to the Eini values, derived for JIc evaluation (see previous section).In the former case, the Efr is energy till a certain displacement value; while, the latter Eini is the energy till the specimen attains peak load.In both the notch orientations, the higher values of displacements considered yielded higher fracture resistance, Jc.The slope values (Efr=Da) and the corresponding Jc values vary significantly with the value chosen for the displacement d (see data in Table 2).The fracture energy progressively Table 2 Total fracture energy release rate (Jc) of the CFCC material in crack divider and crack arrester orientations Orientation Nature shown in Displacement (d) (lm) Slope of the Efr  a regression line (J/m) Jc (kJ/m2) Operative crack bridging mechanisms Crack divider (A) in Fig.8a d1 ¼ 130 4.9 0.67 Matrix cracking (B) in Fig.8a d2 ¼ 250 15.8 2.16 Matrix cracking, fibre/matrix debonding (C) in Fig.8a d3 ¼ 720 26.0 3.56 Matrix cracking, fibre/matrix debonding, fibre breakage and pull-out Crack arrester (A) in Fig.8b d1 ¼ 150 3.0 0.35 Matrix cracking (B) in Fig.8b d2 ¼ 400 5.8 0.68 Matrix cracking, fibre/matrix debonding (C) in Fig.8b d3 ¼ 660 6.8 0.79 Matrix cracking, fibre/matrix debonding, fibre breakage and pull-out Fracture Energy (Efr), J Fracture Energy (Efr), J 0 0.02 0.04 0.06 0.08 0.10 0.12 2 4 C (a) B A 0.01 0.02 0.03 0.04 0 2 (b) C B A Crack Length (a), mm Crack Length (a), mm 3 5 6 7 3 4 5 Fig.8.Variation of fracture energy (Efr) with the crack length for three different crack displacement values (d1, d2 and d3 for cases of A, B and C, respectively; for details see Table 2) for the CFCC material in (a) crack divider and (b) crack arrester orientations.Note the increase in the slope of the linear curve fit with increasing d, indicating the increase in the value of total fracture energy release rate with crack extension. 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