2598 N. Eswara Prasad et al. Engineering Fracture Mechanics 71(2004) 2589-2605 This is the case in the present CFCC materials. As stated earlier, the increasing contributions from mode Il or in-plane shear fracture during mode I fracture toughness evaluation using specimens of varied crack length, require the adoption of such an energy concept. Li and coworkers [29] have clearly shown that the total fracture energy release rate(they referred to this parameter as the global or over-all fracture energy elease rate, J, and we designate this term as /c, the(critical) total fracture energy release rate; see Fig. 6c) corresponding to the far field loading for discontinuous CFCCs and is given as Jc=jb+ where b is the energy consumed by the development of fracture process zone and tip can be obtained from the stress intensity factor at the crack tip, Ktip using the equation K The overall fracture energy release rate c)could be obtained from [31, 32](using an equation similar to (1): J={-(△Em/Aa)}/B AEfr/Aa is the slope of the linear regression curve fit between the total energy for fracture(Err)and the crack length(a). The Aa here is actually the difference in the crack lengths(such as ay-ay or a3 -ai, where aj, ay and a] correspond to the initial crack lengths of different specimens) but not crack extension. Once the two terms of Jc and Jtip are calculated individually, the third term Jb can be computed from Eq(2) The procedure involved for the evaluation of Jc is illustrated schematically in Fig. 7. Specimens of varied crack length(three crack lengths, al, a2 and a3, in which a1 a2 a3 as in the present case of crack arrester orientation) are pulled in tension in ramp control. These values of (Efr) vary with the chosen value of displacement(6, in this case 81, 82, and d3(and 81<82<83)as shown in Fig. 7). Ideally, the displacement value is chosen in such a way that it encompasses all the events that significantly influence the fracture process and hence, reflected in the determined total fracture energy release rate In the present study, three grossly different displacement values(81, 82, and 83)are chosen for the evaluation of J e. The first chosen value of the displacement(S1) essentially encompasses the elastic region and in this case even the peak load 616 DISPLACEMENT 61 load-displacement curves showing the procedure adopted for the evaluation of total fracture energy release rateThis is the case in the present CFCC materials.As stated earlier, the increasing contributions from mode II or in-plane shear fracture during mode I fracture toughness evaluation using specimens of varied crack length, require the adoption of such an energy concept.Li and coworkers [29] have clearly shown that the total fracture energy release rate (they referred to this parameter as the global or over-all fracture energy release rate, Ja and we designate this term as Jc, the (critical) total fracture energy release rate; see Fig.6c) corresponding to the far field loading for discontinuous CFCCs and is given as Jc ¼ Jb þ Jtip; ð2Þ where Jb is the energy consumed by the development of fracture process zone and Jtip can be obtained from the stress intensity factor at the crack tip, Ktip using the equation: Jtip ¼ K2 tipð1  m2 Þ=E: ð3Þ The overall fracture energy release rate (Jc) could be obtained from [31,32] (using an equation similar to (1)): Jc ¼ fðDEfr=DaÞg=B: ð4Þ DEfr=Da is the slope of the linear regression curve fit between the total energy for fracture (Efr) and the crack length (a).The Da here is actually the difference in the crack lengths (such as a2  a1 or a3  a1; where a1, a2 and a3 correspond to the initial crack lengths of different specimens) but not crack extension.Once the two terms of Jc and Jtip are calculated individually, the third term Jb can be computed from Eq.(2). The procedure involved for the evaluation of Jc is illustrated schematically in Fig.7.Specimens of varied crack length (three crack lengths, a1, a2 and a3, in which a1 < a2 < a3 as in the present case of crack arrester orientation) are pulled in tension in ramp control.These values of (Efr) vary with the chosen value of displacement (d, in this case d1, d2, and d3 (and d1 < d2 < d3) as shown in Fig.7).Ideally, the displacement value is chosen in such a way that it encompasses all the events that significantly influence the fracture process and hence, reflected in the determined total fracture energy release rate.In the present study, three grossly different displacement values (d1, d2, and d3) are chosen for the evaluation of Jc.The first chosen value of the displacement (d1) essentially encompasses the elastic region and in this case even the peak load Fig.7.Representative load–displacement curves showing the procedure adopted for the evaluation of total fracture energy release rate (Jc). 2598 N. Eswara Prasad et al. / Engineering Fracture Mechanics 71 (2004) 2589–2605