M.L. Antti et al. Journal of the European Ceramic Society 24(2004)565-578 4. Results heat-treated at 1000 oC. after 100 hours at 1100 oc the strength fell to less than one third of the as-received 4.. Stress-strain behaviour strength. The 0/90 material lost stiffness when tested at 1100oC, but after heat-treatment the stiffness at room Tables I and 2 summarise the tensile strength, stiff- temperature increased. The strain to failure of the sam- ness, strain to failure and matrix hardness values of the ples with 0/90 fibre orientation was severely decreased tested samples for 0/90 and +45 orientation, respec- after heat-treatment indicating embrittlement of the tively. Each set of tensile bars contained a replicate material samples to assess reproducibility. This was found to be The +45 material increased in strength after heat atisfactory treatment, but the fracture sequences were abrupt and Representative sets of stress-strain curves for samples violent compared to the as-received fracture which was with a width of 12.5 mm and an a/w ratio of 0. 25 are a gradual process, indicating an embrittlement after shown in Fig. 3(0/90 fibre orientation) and Fig. 4 heat-treatment. The stiffness also increased significantly (+45 fibre orientation). It can be seen that the material as a result of heat-treatment. It is to be noted that with with 0/90 fibre orientation lost some strength when thermal exposure the properties of the 0/90 and +45 Table 2 Properties of±4s° fibre orientation@ plate C Net-section strength [MPa] Stiffness [ GPa Strain to failure [% As-received (RT) 0.10 200hat500°C 10 0.29 l00hatl000°C 0.09 66.5 0.24 0.29 0.40 62.5 3240hatl000°C 0.10 0.29 0.40 0.17 100hatl100°C 0.10 0.29 93.5 0.40 0.15 As- rec test at I000°C 0.10 0.20 Failed at grips, because plate C was not perfectly flat which induced bending forces when clamped 装150 目 200hrs500 50 OOhrs10 00,0sD,10,1s Strain % o] Fig 3. Representative stress-strain curves of 0/90 samples4. Results 4.1. Stress–strain behaviour Tables 1 and 2 summarise the tensile strength, stiff- ness, strain to failure and matrix hardness values of the tested samples for 0/90 and 45 orientation, respec￾tively. Each set of tensile bars contained a replicate samples to assess reproducibility. This was found to be satisfactory. Representative sets of stress–strain curves for samples with a width of 12.5 mm and an a/w ratio of 0.25 are shown in Fig. 3 (0/90 fibre orientation) and Fig. 4 (45
fibre orientation). It can be seen that the material with 0/90 fibre orientation lost some strength when heat-treated at 1000
C; after 100 hours at 1100
C the strength fell to less than one third of the as-received strength. The 0/90 material lost stiffness when tested at 1100
C, but after heat-treatment the stiffness at room temperature increased. The strain to failure of the sam￾ples with 0/90 fibre orientation was severely decreased after heat-treatment indicating embrittlement of the material. The 45
material increased in strength after heat￾treatment, but the fracture sequences were abrupt and violent compared to the as-received fracture which was a gradual process, indicating an embrittlement after heat-treatment. The stiffness also increased significantly as a result of heat-treatment. It is to be noted that with thermal exposure the properties of the 0/90 and 45 Table 2 Properties of 45
fibre orientation (plate C) Sample a/w Net-section strength [MPa] Stiffness [GPa] Strain to failure [%] As-received (RT) 0.10 64 57 0.28 0.24 61 52 0.19 0.43 69 47 0.16 200 h at 500
C 0.10 61 53 0.25 0.29 64.5 51 0.17 100 h at 1000
C 0.09 66.5 56.5 0.24 0.29 66 57 0.14 0.40 62.5 49 0.15 3240 h at 1000
C 0.10 91 62 0.27 0.29 91 63 0.16 0.40 96.5 58 0.17 100 h at 1100
C 0.10 94 69 0.25 0.29 93.5 66 0.16 0.40 87 56 0.15 As-rec test at 1000
C 0.10 68a 48 0.20 0.30 81a 45 0.22 0.40 95 40 0.41 a Failed at grips, because plate C was not perfectly flat which induced bending forces when clamped. Fig. 3. Representative stress–strain curves of 0/90 samples. M.-L. Antti et al. / Journal of the European Ceramic Society 24 (2004) 565–578 569