Bend strength of AG and ASG composites versus temperature M Temperature(°Cv(%) ASG 222 Ⅴ iscous flow Viscous flow terface. They have described three regions namely an unslipped region ahead of matrix crack tip(I), a com- pletely debonded region (III)and a region (II) which m extends with increasing misfit strain from end of region I to the beginning of region II. The effective normal stress, on at the interface in region ill due to roughness and residual stresses has been given as [26]. Fig 10. Morphology of interfaces in(a)alumina/glass(b) Saphikon 20 on=i-qEmEJEdl+vm)+ Em(I-vollAoAT+ A/r] where Ao is the mismatch between the thermal expan- sion coefficients of the fiber and matrix. at is the temperature change during cooling, q is an adjustable parameter(equal to l for an infinite matrix), Em, Im, Er and vr are the Youngs modulus and Poisson ratio of the matrix and fiber respectively, A is the amplitude of f the fiber The amplitude of fiber roughness have been experi mentally determined from fiber surface profiles using atomic force microscopy [29-32], profilometry [33], and terference [34]. In the pre ase. sem of longitudinal section of the fibers has been used [24] 20 gm Roughness parameter and thermal stress contribution PRD-166/SnO, interfa Saphikon/SnO, interfac Fig 9. High temperature (400 C)tested composites (a)Alumina/ AxAT 0.0013 glass.(b) Alumina/SnO2/glass.R. Venkatesh Venkatesh / Materials Science and Engineering A Materials Science and Engineering A268 (1999) 47–54 268 (1999) 47–54 53 Table 6 Bend strength of AG and ASG composites versus temperature Temperature (°C) ASG Vf (%) AG 25 200 42 230 200 42 180 200 400 175 150 42 600 42 Viscous flow Viscous flow Fig. 10. Morphology of interfaces in (a) alumina/glass; (b) Saphikon/ SnO2/glass. terface. They have described three regions namely an unslipped region ahead of matrix crack tip (I), a com￾pletely debonded region (III) and a region (II) which extends with increasing misfit strain from end of region I to the beginning of region II. The effective normal stress, sn at the interface in region III due to roughness and residual stresses has been given as [26], Fig. 9. High temperature (400°C) tested composites. (a) Alumina/ glass. (b) Alumina/SnO2/glass. sn={−qEmEf /[Ef (1+nm)+Em(1−nf )]}[DaDT+A/r] (4) where Da is the mismatch between the thermal expan￾sion coefficients of the fiber and matrix, DT is the temperature change during cooling, q is an adjustable parameter (equal to 1 for an infinite matrix), Em, nm, Ef and nf are the Young’s modulus and Poisson ratio of the matrix and fiber respectively, A is the amplitude of roughness and r is the radius of the fiber. The amplitude of fiber roughness have been experi￾mentally determined from fiber surface profiles using atomic force microscopy [29–32], profilometry [33], and optical interference [34]. In the present case, SEM of longitudinal section of the fibers has been used [24]. Table 7 Roughness parameter and thermal stress contributions PRD-166/SnO2 interface Saphikon/SnO2 interface A/r 0.026 0.003 DaDT 0.0013 0.001