R Venkatesh/Ceramics International 28(2002)565-573 material to be tested. The fibres were center-line moun- coeffecient of variation were then evaluated by Weibull ted on a paper frame. The fibres were centered over the analysis [39] frame and lightly stretched. A small amount of adhesive Alumina fiber reinforced glass matrix composites was then carefully placed at each end of the fibre. The were fabricated by a slurry impregnation technique [40] specimen gage length for all the fibres tested was 17 m The slurry consisted of glass frit, 2-propanol and an An Instron tensile testing machine (model 1 120)was organic binder to impart green strength to the tapes and used with a 5 N load cell. Before fibres were loaded onto facilitate their handling. For fabrication of alumina/ the machine, the diameter of the individual fibres was glass composites, a continuous process was employed to measured with an optical microscope. The frame was make unidirectional tapes. For fabrication of alumina, then gripped in the jaws of the testing machine and the SnO2/glass composites, the coated fibers were dipped in mounting frame was burned on the sides. The fibres the slurry and laid on mylar tapes to form prepeg tape were successively stressed to failure with a crosshead These unidirectional tapes were heated to 500oC in air peed of 0.25 mm/min. An average of 80 fibres in each to remove the binder and then hot pressed. The hot group, i.e. as-received, heat treated at 500, 600 and pressing was performed in a graphite lined die in argon 900oC and Sno, coated were tested. The mean tensile atmosphere at 925C and 3 MPa. strength, Weibull modulus, standard deviation and a Optical microscopy was used to evaluate the volume action and fiber distributions in the composites. The fracture surfaces of the composites were characterized using SEM. Three point bending tests on the glass matrix composites were conducted in the longitudinal direction. Bending tests were carried out on specimens having a span length(S) to thickness(W) ratio >8 and thickness(W) to breadth(B)ratio of 0.75. The three point bending tests were conducted on an Instron machine(model 1102)with a crosshead speed of 0.05 10 slope=B 7 slope= 0.10 Tensile Strength, a;( MPa) Tensile Strength, O:(MPa) Fig 3. Weibull plots (a) as-received PRD-166 fibres;(b)SnO2 coated PRD.166 fibres Table 2 Estimated Weibull parameters of as-received and heat treated alumina (PRD. 166)fibres Standard strength(MPa) deviation(MPa) variation(%) As-received 1375 418 1313 Fig. 2. Microstructure of as-received fibres (a)Rough longitudinal 600°C 1283 urface of the fibres:(b) zirconia particles dispersed throughout the 900°C 29material to be tested. The fibres were center-line moun￾ted on a paper frame. The fibres were centered over the frame and lightly stretched. A small amount of adhesive was then carefully placed at each end of the fibre. The specimen gage length for all the fibres tested was 17 mm. An Instron tensile testing machine (model 1120) was used with a 5 N load cell. Before fibres were loaded onto the machine, the diameter of the individual fibres was measured with an optical microscope. The frame was then gripped in the jaws of the testing machine and the mounting frame was burned on the sides. The fibres were successively stressed to failure with a crosshead speed of 0.25 mm/min. An average of 80 fibres in each group, i.e. as-received, heat treated at 500, 600 and 900
C and SnO2 coated were tested. The mean tensile strength, Weibull modulus, standard deviation and coeffecient of variation were then evaluated by Weibull analysis [39]. Alumina fiber reinforced glass matrix composites were fabricated by a slurry impregnation technique [40]. The slurry consisted of glass frit, 2-propanol and an organic binder to impart green strength to the tapes and facilitate their handling. For fabrication of alumina/ glass composites, a continuous process was employed to make unidirectional tapes. For fabrication of alumina/ SnO2/glass composites, the coated fibers were dipped in the slurry and laid on mylar tapes to form prepeg tapes. These unidirectional tapes were heated to 500
C in air to remove the binder and then hot pressed. The hot pressing was performed in a graphite lined die in argon atmosphere at 925
C and 3 MPa. Optical microscopy was used to evaluate the volume fraction and fiber distributions in the composites. The fracture surfaces of the composites were characterized using SEM. Three point bending tests on the glass matrix composites were conducted in the longitudinal direction. Bending tests were carried out on specimens having a span length (S) to thickness (W) ratio > 8 and thickness (W) to breadth (B) ratio of 0.75. The three point bending tests were conducted on an Instron machine (model 1102) with a crosshead speed of 0.05 Fig. 2. Microstructure of as-received fibres. (a) Rough longitudinal surface of the fibres; (b) zirconia particles dispersed throughout the fibre. Fig. 3. Weibull plots (a) as-received PRD-166 fibres; (b) SnO2 coated PRD-166 fibres. Table 2 Estimated Weibull parameters of as-received and heat treated alumina (PRD- 166) fibres Fibre Mean tensile strength (MPa) Standard deviation (MPa) Coefficient of variation (%) As-received 1375 418 30 500
C 1313 386 29 600
C 1283 440 34 900
C 1083 320 29 R. Venkatesh / Ceramics International 28 (2002) 565–573 567