100 po 50 10 50m Fig. 8. Fracture Fig. 7. Fracture surface of Saphikon fiber/SnO,/glass composite(a) (a) Note fiber breakage.(b)Porosity in high volume fraction com- Neat fiber pullout. (b) Debonding at the fiber/coating interface. posites. hat the radial thermal stress in both the composites Jero and Kerans and modeled the effect of fiber rough- were tensile in nature and had a maximum value of 109 ness on the fracture behavior of CMCs [26-31].Kerans and 50 MPa at the fiber/SnO2 interfaces in PRD-166/ and Parthasarathy (26, 31] have described the contribu- SnO2 glass and Saphikon/SnO2/glass composites,re- tion of interfacial roughness with relative fiber/matrix pectively [24]. This radial stress combined with weak displacement during debonding at the fiber-matrix in- interfacial bonding between alumina and SnO2 are de sirable attributes from a toughness point of view [ll Table 5 Once we eliminate interfacial chemical bonding in a Chevron notch fracture toughness of AG and ASG composites CMC, interfacial roughness assumes an important role Fiber volume (% Kl(MPa m) Work of fracture (/m) in controlling the fracture of the CMC. Recent studies on the importance of fiber roughness have evolved since AG the first paper by Jero and Kerans [25]. They reported the importance of fiber roughness using fiber pushout experiments on thin slices of Sic monofilaments in a borosilicate glass matrix composite in which residual 24 compressive stresses existed perpendicular to the inter- 36 3.3 face. Other researchers have confirmed the results of52 R. Venkatesh Venkatesh / Materials Science and Engineering A Materials Science and Engineering A268 (1999) 47–54 268 (1999) 47–54 Fig. 7. Fracture surface of Saphikon fiber/SnO2/glass composite. (a) Neat fiber pullout. (b) Debonding at the fiber/coating interface. Fig. 8. Fracture surface of transverse tested alumina/glass composites. (a) Note fiber breakage. (b) Porosity in high volume fraction com￾posites. Jero and Kerans and modeled the effect of fiber rough￾ness on the fracture behavior of CMCs [26–31]. Kerans and Parthasarathy [26,31] have described the contribu￾tion of interfacial roughness with relative fiber/matrix displacement during debonding at the fiber–matrix in￾that the radial thermal stress in both the composites were tensile in nature and had a maximum value of 109 and 50 MPa at the fiber/SnO2 interfaces in PRD-166/ SnO2/glass and Saphikon/SnO2/glass composites, re￾spectively [24]. This radial stress combined with weak interfacial bonding between alumina and SnO2 are de￾sirable attributes from a toughness point of view [11]. Once we eliminate interfacial chemical bonding in a CMC, interfacial roughness assumes an important role in controlling the fracture of the CMC. Recent studies on the importance of fiber roughness have evolved since the first paper by Jero and Kerans [25]. They reported the importance of fiber roughness using fiber pushout experiments on thin slices of SiC monofilaments in a borosilicate glass matrix composite in which residual compressive stresses existed perpendicular to the inter￾face. Other researchers have confirmed the results of Table 5 Chevron notch fracture toughness of AG and ASG composites K1c (MPa m 1 2 ) Work of fracture (J/m2 Fiber volume (%) ) AG 16 2 50 26 2.3 120 36 2.6 150 ASG 24 160 2.8 36 3.3 220