J.. Haslam et al. / Journal of the European Ceramic Society 20(2000)607-618 constrained by the fibers, would produce regions that are dense and others that are less dense. Eventually crack-like voids form if it is heated to a high enough 4. Discussion 10 mm 4. Interlaminar shear strength According to finite element analysis, the shear stresses are much higher than calculated by the classical beam theory equation 25 They are higher principally at the loading lines and along almost a diagonal line between that was tested with a notch in the upper load point and the lower load points. Close to the in-plane 3-point bending configuration. The sample still holds together due to interlocking fibers even after considerable permanent below the surface(approximately 0. 13-0. 2 of the normal ized sample height). 5 It is suggested that the localized 1m 100u 81 100 Fig. 9. Fracture surface near the tensile surface of a 0/90 fiber orientation composite containing 70v% cubic ZrO2(8m%Y2O3)/30v% sintered at 1200C for 5 h inHCL. The composite was tested in the in-plane 3-point bending configuration. Large amounts of fiber pullout are with little coordinated fracture. (a) Low magnification showing general extent of fiber pullout. (b) Higher magnification, arrows show fibers that failed independently and pulled free with disintegration of the surrounding matrix.(c)Micrograph showing fiber pullout and showing portions of the matrix bonded to the fibers indicating a strongly bonded matrix. Matrix between the fiber disintegrated during the fracture process. (d) Micr graph showing a region of fairly coordinated fiber fracture in the 0/90 composite sample although, except for fibers that were bonded together (arrows), the crack plane is unique implying that a continuous crack plane did not exist during fracture even in this regionconstrained by the ®bers, would produce regions that are dense and others that are less dense. Eventually, crack-like voids form if it is heated to a high enough temperature.8,24 4. Discussion 4.1. Interlaminar shear strength According to ®nite element analysis, the shear stresses are much higher than calculated by the classical beam theory equation.25 They are higher principally at the loading lines and along almost a diagonal line between the upper load point and the lower load points. Close to the top anvil, the maximum shear stress occurs just below the surface (approximately 0.13±0.2 of the normal￾ized sample height).25 It is suggested that the localized Fig. 8. Photograph of 0/90 composite that was tested with a notch in the in-plane 3-point bending con®guration. The sample still holds together due to interlocking ®bers even after considerable permanent strain, a/W0.5. Fig. 9. Fracture surface near the tensile surface of a 0/90 ®ber orientation composite containing 70v% cubic ZrO2 (8m% Y2O3)/30v% mullite sintered at 1200C for 5 h inHCl. The composite was tested in the in-plane 3-point bending con®guration. Large amounts of ®ber pullout are evident with little coordinated fracture. (a) Low magni®cation showing general extent of ®ber pullout, (b) Higher magni®cation, arrows show ®bers that failed independently and pulled free with disintegration of the surrounding matrix. (c) Micrograph showing ®ber pullout and showing portions of the matrix bonded to the ®bers indicating a strongly bonded matrix. Matrix between the ®ber disintegrated during the fracture process. (d) Micro￾graph showing a region of fairly coordinated ®ber fracture in the 0/90 composite sample although, except for ®bers that were bonded together (arrows), the crack plane is unique implying that a continuous crack plane did not exist during fracture even in this region. 614 J.J. Haslam et al. / Journal of the European Ceramic Society 20 (2000) 607±618