正在加载图片...
1568 v.A. Krab et al. Composites Science and Technology 61(2001)1561-1570 breakage may occur within the first tow adjacent to the 0 fiber pullout lengths were a2-3 mm. Fiber pullout notch. However, fiber breakage beyond the first tow lengths were consistently smaller than that suggested by results in specimen failure the C-scans. This result indicates that fiber breakage The region of higher attenuation in the C-scan [Fig. 5(d) does not occur at the end of the damage zone was also compared to the length of 0 fibers, which exten ded from fracture surfaces of failed specimens shown in [8]. 3. 2. Edge notched fracture test at 950C C-scans of post peak fracture specimens suggested damage zone approximately 6 mm in height. Examina The load-CMOD response for the edge notched frac- tion of fracture surface profiles showed that maximum ture test at 950C, is shown in Fig 9. Similar to the frac ture behavior at 23C, nonlinear loading behavior was 100 observed prior to and after the peak load. At 950C 6543.2 however, linear loading was exhibited up to only n=30 MPa. Similarly, at 950C On peak=62 MPa, a reduction of 50% from the value at 23C. The reduction in peak stress indicated a change in damage mode with tem- perature During the fracture test at 950C, optical inspection of the notch tip region revealed a dominant matrix crack at an applied load of 3.0 kN. Increasing load-line displace- ment resulted in extension of the dominant crack as it grew and linked with other preexisting surface matrix cracks. When the test was stopped, the continuous matrix Fig9. Typical load-CMOD response for an edge notched specimen, crack extension from the notch tip, measured on the spe- W=25.4mm,a/W=0.2,950°C cimen surface, was equal to 9 mm [Fig. 10(b). Fig. 10(a) 50% 5 mi notch 100% 11 mm dominant matrix crack extensin Fig. 10.(a)C-scan of entire gage section, and (b)optical micrograph of the edge notched specimen after reaching the peak load. W=25.4 mm, ao W=0.2.950°Cbreakage may occur within the first tow adjacent to the notch. However, fiber breakage beyond the first tow results in specimen failure. The region of higher attenuation in the C-scan [Fig. 5(d)] was also compared to the length of 0 fibers, which extended from fracture surfaces of failed specimens shown in [8]. C-scans of post peak fracture specimens suggested a damage zone approximately 6 mm in height. Examination of fracture surface profiles showed that maximum 0 fiber pullout lengths were 2–3 mm. Fiber pullout lengths were consistently smaller than that suggested by the C-scans. This result indicates that fiber breakage does not occur at the end of the damage zone. 3.2. Edge notched fracture test at 950 C The load-CMOD response for the edge notched fracture test at 950 C, is shown in Fig. 9. Similar to the fracture behavior at 23 C, nonlinear loading behavior was observed prior to and after the peak load. At 950 C however, linear loading was exhibited up to only n=30 MPa. Similarly, at 950 C n,peak=62 MPa, a reduction of 50% from the value at 23 C. The reduction in peak stress indicated a change in damage mode with temperature. During the fracture test at 950 C, optical inspection of the notch tip region revealed a dominant matrix crack at an applied load of 3.0 kN. Increasing load-line displacement resulted in extension of the dominant crack as it grew and linked with other preexisting surface matrix cracks. When the test was stopped, the continuous matrix crack extension from the notch tip, measured on the specimen surface, was equal to 9 mm [Fig. 10(b)]. Fig. 10(a) Fig. 9. Typical load-CMOD response for an edge notched specimen, W=25.4 mm, a/W=0.2, 950 C. Fig. 10. (a) C-scan of entire gage section, and (b) optical micrograph of the edge notched specimen after reaching the peak load. W=25.4 mm, a0/ W=0.2, 950 C. 1568 V.A. Kramb et al. / Composites Science and Technology 61 (2001) 1561–1570