J.C. McNulty et al. /Composites Science and Technolog y 61(2001)1331-1338 calibrated using the results of tensile tests performed both into account [5, 35]. Furthermore, previous studies have along one of the fiber axes(in the 00/90 orientation) and revealed that the characteristic distance inferred from at 45 to the fiber axes. The constitutive law is then the model and the experiment is rather insensitive to the implemented in a finite-element code for the purpose of details of the composite microstructure, falling in the calculating stress and strain fields in non-uniform spe narrow range of 0.5-0.75 mm for SiC/SiC [5], SiC/ men or component geometries. The capability of the MAs [5] and an all-oxide CFCC [35] model to predict the latter response has been validated This approach has been used to model the strength of through comparisons with strain measurements on spe- the center-hole specimens of the SylramicM/SiC com- cimens containing notches and circular holes [5, 35]. The posite tested at room temperature, using a characteristic model tacitly assumes that the material response is distance, d=0. 75 mm. The effects of inelastic straining on scale-independent. This presents some limitations on the the stress distribution ahead of a hole are illustrated by the size-scale of features that can be accurately simulated, as results plotted in Fig. 7(a). The strength predictions are discussed in Section 4.2. Additional details of the imple- plotted in Fig 3, for comparison with the experimental mentation and calibration procedures are described in measurements. Excellent agreement between experiment Refs. [36] and [5] and theory is obtained. Furthermore, the inferred char- he effects of stress gradients on fracture are less well acteristic distance is remarkably similar to the values nderstood. Nevertheless, a simple fracture criterion obtained in other CFCCs, indicating a commonalty in based on the attainment of a critical stress( taken as the the factors controlling fracture of the various composite unnotched strength)over a characteristic distance d along systems the incipient fracture plane has been found to adequately The same approach has been used to rationalize the describe notched strength of CFCCs, provided the effects effects of both notches and holes on the strength at 815oC. of inelastic straining on the stress distribution are taken In this case, the characteristic distance was inferred 2.0 g =75 MPa 150M g15 0.10 Distance from hole edge, X/(W-a) m tch length, 2a=6. 35 mm EM model predictions 00002 0060.080.10 Fig. 7. Typical stress distributions for(a) center-hole and(b)center- 10m notched specimens of the SylramicTM/SiC composite, calculated using the nonlinear constitutive law of Genin and Hutchinson [36]. Also shown for comparison are the corresponding elastic predictions. The Fig. 6. Fracture surface of a center hole specimen tested in fatigue at results demonstrate the role of inelastic straining in mitigating stress ap=85 MPa at8l5°Ccalibrated using the results of tensile tests performed both along one of the fiber axes (in the 0
/90
orientation) and at 45
to the fiber axes. The constitutive law is then implemented in a finite-element code for the purpose of calculating stress and strain fields in non-uniform speci￾men or component geometries. The capability of the model to predict the latter response has been validated through comparisons with strain measurements on spe￾cimens containing notches and circular holes [5,35]. The model tacitly assumes that the material response is scale-independent. This presents some limitations on the size-scale of features that can be accurately simulated, as discussed in Section 4.2. Additional details of the imple￾mentation and calibration procedures are described in Refs. [36] and [5]. The effects of stress gradients on fracture are less well understood. Nevertheless, a simple fracture criterion based on the attainment of a critical stress (taken as the unnotched strength) over a characteristic distance d along the incipient fracture plane has been found to adequately describe notched strength of CFCCs, provided the effects of inelastic straining on the stress distribution are taken into account [5,35]. Furthermore, previous studies have revealed that the characteristic distance inferred from the model and the experiment is rather insensitive to the details of the composite microstructure, falling in the narrow range of 0.5–0.75 mm for SiC/SiC [5], SiC/ MAS [5] and an all-oxide CFCC [35]. This approach has been used to model the strength of the center-hole specimens of the SylramicTM/SiC com￾posite tested at room temperature, using a characteristic distance, d=0.75 mm. The effects of inelastic straining on the stress distribution ahead of a hole are illustrated by the results plotted in Fig. 7(a). The strength predictions are plotted in Fig. 3, for comparison with the experimental measurements. Excellent agreement between experiment and theory is obtained. Furthermore, the inferred char￾acteristic distance is remarkably similar to the values obtained in other CFCCs, indicating a commonalty in the factors controlling fracture of the various composite systems. The same approach has been used to rationalize the effects of both notches and holes on the strength at 815
C. In this case, the characteristic distance was inferred Fig. 6. Fracture surface of a center hole specimen tested in fatigue at
p ¼ 85 MPa at 815
C. Fig. 7. Typical stress distributions for (a) center-hole and (b) center￾notched specimens of the SylramicTM/SiC composite, calculated using the nonlinear constitutive law of Genin and Hutchinson [36]. Also shown for comparison are the corresponding elastic predictions. The results demonstrate the role of inelastic straining in mitigating stress concentrations. J.C. McNulty et al. / Composites Science andTechnology 61 (2001) 1331–1338 1335