G H. Min et al. /Ceramics International 29(2003)323-326 Table I Properties evaluation of the Al2O3/SiC prismatic composites Interlayer thickness(um) Fracture work (m-) Fracture toughness(MPa m/) Bending strength (MPa) 794.6 .70 685 253.1 15.6 481.6 5.02 210.3 0 0,000200.400600801.001.20 Fig. 3. Crack route on the side surface of the prismatic ceramics with SiC boundaries in various thickness of (a)4.4 um, (b) ceramics with SiC boundaries in thickness of 9.3 um 9.3 um, and(c)15.6 um propagation exists near the notch tip, the cracks deflect alumina-based multilayered ceramics, in which dis- but do not cause a longer delamination. However, placement showed value of 0.4-0.6 mm, similar to those of cracks occur also quickly on the multi-portions or else the prismatic ceramics in the earlier stage [11, 12, 14-16 over the entire section near or far from the main route Generally, two factors govern the fracture properties which plays an important role in the further improve of the composites: the fracture resistance of the cell and ment for crack path. Then, those cracks with small-scale cell boundary(load-carrying capacity in Fig. 2), and deflection result in long-distance delamination by inter weaker cell boundaries in comparison to the cells acting with the main route in a bridging manner, some (developed crack routes or displacement in Fig. 2) delaminations stretching up to two outer loading points of the tested sample 33. Fracture characteristics A more detailed observation is seen in Fig. 4. in which sev eral typical manners of crack growth can be As analyzed above, the controlled structure of the lyzed. While going across a fibrous layer, a crack is cellular ceramics is closely related to their mechanical deflected into a weak interface layer, causing a delani- properties, including fracture features. Fig 3 shows the nation. However, some delaminations grow only a finite crack propagating paths on the side-surface of a sample distance and deflect in the next fibrous layer or deflect after the notched bending test. The main route of crack ing and delaminating occur at same time(Fig 4A). The A FI? Fig 4. Propagating manners of cracks nearby the interlayer showing deflecting and delaminating(A)and bridging(B)alumina-based multilayered ceramics, in which dis￾placement showed value of 0.4–0.6 mm, similar to those of the prismatic ceramics in the earlier stage [11,12,14–16]. Generally, two factors govern the fracture properties of the composites: the fracture resistance of the cell and cell boundary (load-carrying capacity in Fig. 2), and weaker cell boundaries in comparison to the cells (developed crack routes or displacement in Fig. 2). 3.3. Fracture characteristics As analyzed above, the controlled structure of the cellular ceramics is closely related to their mechanical properties, including fracture features. Fig. 3 shows the crack propagating paths on the side-surface of a sample after the notched bending test. The main route of crack propagation exists near the notch tip, the cracks deflect but do not cause a longer delamination. However, cracks occur also quickly on the multi-portions or else over the entire section, near or far from the main route, which plays an important role in the further improve￾ment for crack path. Then, those cracks with small-scale deflection result in long-distance delamination by inter￾acting with the main route in a bridging manner, some delaminations stretching up to two outer loading points of the tested sample. A more detailed observation is seen in Fig. 4, in which several typical manners of crack growth can be ana￾lyzed. While going across a fibrous layer, a crack is deflected into a weak interface layer, causing a delami￾nation. However, some delaminations grow only a finite distance and deflect in the next fibrous layer or deflect￾ing and delaminating occur at same time (Fig. 4A). The Table 1 Properties evaluation of the Al2O3/SiC prismatic composites Interlayer thickness (mm) Fracture work (Jm
2 ) Fracture toughness (MPa m1/2) Bending strength (MPa) 4.4 794.6 2.70 164.4 9.3 1221.4 6.85 253.1 15.6 1481.6 5.02 210.3 Fig. 2. Load–displacement curves of of the alumina-based prismatic ceramics with SiC boundaries in various thickness of (a) 4.4 mm, (b) 9.3 mm, and (c) 15.6 mm. Fig. 3. Crack propagation route on the side surface of the prismatic ceramics with SiC boundaries in thickness of 9.3 mm. Fig. 4. Propagating manners of cracks nearby the interlayer showing deflecting and delaminating (A) and bridging (B). G.H. Min et al. / Ceramics International 29 (2003) 323–326 325