312 International ournal of Applied Ceramic Technolog-Nozawa and Tanigawa Vol.7,No.3,2010 3.5 DNT-2a(W=10mm, t=1.7mm, ao/w=0. 20) DNT-2b(W=10mm, t=1.7mm, a0/w=0. 36) DNT-2c(W=10mm, t=1.7mm, a/=0.58) PIP- Coat 0.35 Crack opening displacement (mm r DNT-3a(W=4mm, t=1. 5mm, ao/w=0. 30) DNT-4(W=7.5mm, t=1.5mm, ao/W=0.51 DNT-3b(W=4mm, +1.5mm, a/=0.60)./ NITE-Thick-Coat NITE-Thin-Coat Fig 9. Load versus crack opening displacement curves in double-notch tensile(DNT) tests the contribution from the F/M interfacial interaction was huge enough to increase the total work. New surface cre- NTE- Thick-o on by crack branching might also influence the results PIP-Coat(W-1Omm) Failure Energy Analysis by Nonlinear fracture 个个 Mechanics Appr As aforementioned, test results apparently show quasi-ductility of composites, that is, energy consump tion during irreversible damage accumulation beyond matrix cracking. Therefore, considering the contribu- tions separately from irreversible energies such as inter- facial friction, thermal-residual strain energy, and fiber breaks become a key. Because of this quasi-ductility king an analytical model based on the nonlinear frac ture mechanics is reasonable and the analytical 1-a0/w method has been developed by the e authors. In this Fig. 10. Strengths as a function of the notch depth to width ratio model, the total work during tched specimen in double-notch tensile(DNT) tests.the contribution from the F/M interfacial interaction was huge enough to increase the total work. New surface cre￾ation by crack branching might also influence the results. Failure Energy Analysis by Nonlinear Fracture Mechanics Approach As aforementioned, test results apparently show quasi-ductility of composites, that is, energy consump￾tion during irreversible damage accumulation beyond matrix cracking. Therefore, considering the contribu￾tions separately from irreversible energies such as inter￾facial friction, thermal-residual strain energy, and fiber breaks become a key. Because of this quasi-ductility, taking an analytical model based on the nonlinear frac￾ture mechanics11,12 is reasonable and the analytical method has been developed by the authors.18 In this model, the total work during the notched specimen Fig. 9. Load versus crack opening displacement curves in double-notch tensile (DNT) tests. Fig. 10. Strengths as a function of the notch depth to width ratio in double-notch tensile (DNT) tests. 312 International Journal of Applied Ceramic Technology—Nozawa and Tanigawa Vol. 7, No. 3, 2010