wwceramics. org/ACT Cracking Resistance of Silicon Carbide Composites 313 where load-line displacement is x. Note that the crack surface formation energy includes micro-and macro- E: SENB-2 d SENB-3 Following the definition specified in Fig. 12, the ■SENB4 rack surface for rmation energy was plotted as a function of displacement(Fig. 13). From Fig. 13, it is apparent that the crack surface formation energy rapidly increased when damage accumulated. Specifically, the crack sur face formation energy seems proportional to the load- line displacement in the second stage. A constant crack surface formation energy rate is then obtained by linear SU fit. In contrast, the crack length change as a function of load-line displacement was obtained from Fig. 7. Sub- iting these data into the Eq. (4), a fracture Coat. Note that no significant size effect was obtained 0. 3 0.4 0.5 Of particular emphasis is that the result clearly indicates good coincidence with the critical value of the J integral Fig I1. )integral versus crack extension when Aa/W=0 in Fig. 11, which was determined by test(w) is expressed as the work until the peak load. For both cases, these en- ergy parameters assigned to the crack surface formation w=Ue+ Ur+Ur+r icrocrack formation but no contribution from interfacial friction was considered where elastic energy(Ue), friction energy at the interface One drawback of this analysis is that the fracture re- (Uf), residual strain energy(Ur), and crack surface for- sistance( G) defined in this study cannot perfectly distin mation energy(T)are defined in Fig. 12. Then, the ImIcro- and fracture resistance(G can be defined as G、or1orax 0.15 tda t ax da DOABC: Crack formation energy (r) AOCP: Residual strain energy (U) O SENB APCQ: Friction energy (U) E SENB-2 △QcR: Elastic 1 SENB-3 ■SENB4 B: initiation of macro-cracking Micro- crack formation energy 品005 P R S 0.2 0.3 040.5 0.6 Fig 12. Definition: (a)elastic energy, (b) permanent strain Fig 13. Crack surface formation energy consumed by single-edge energy,(c) friction energy, and (d) crack surface formation energ. notched bend (SENB)tests.test (w) is expressed as w ¼ Ue þ Ufr þ Ur þ G ð3Þ where elastic energy (Ue), friction energy at the interface (Ufr), residual strain energy (Ur), and crack surface for￾mation energy (G) are defined in Fig. 12. Then, the fracture resistance (G) can be defined as G ¼ ›G t›a ¼ 1 t ›G ›x ›x ›a ð4Þ where load-line displacement is x. Note that the crack surface formation energy includes micro- and macro￾crack-forming energies together. Following the definition specified in Fig. 12, the crack surface formation energy was plotted as a function of displacement (Fig. 13). From Fig. 13, it is apparent that the crack surface formation energy rapidly increased when damage accumulated. Specifically, the crack sur￾face formation energy seems proportional to the load￾line displacement in the second stage. A constant crack surface formation energy rate is then obtained by linear fit. In contrast, the crack length change as a function of load-line displacement was obtained from Fig. 7. Sub￾stituting these data into the Eq. (4), a fracture resistance of B3.8 kJ/m2 was finally obtained for NITE-Thick￾Coat. Note that no significant size effect was obtained. Of particular emphasis is that the result clearly indicates good coincidence with the critical value of the J integral when Da/W 5 0 in Fig. 11, which was determined by the work until the peak load. For both cases, these en￾ergy parameters assigned to the crack surface formation including microcrack formation but no contribution from interfacial friction was considered. One drawback of this analysis is that the fracture re￾sistance (G) defined in this study cannot perfectly distin￾guish contributions from micro- and macrocrack Fig. 11. J integral versus crack extension length to width ratio. Fig. 12. Definition: (a) elastic energy, (b) permanent strain energy, (c) friction energy, and (d) crack surface formation energy. Fig. 13. Crack surface formation energy consumed by single-edge notched bend (SENB) tests. www.ceramics.org/ACT Cracking Resistance of Silicon Carbide Composites 313