B G. Nair et al. Materials Science and Engineering 4300 (2001)68-79 The fact that the creep results presented in Fig. 5 indicate the 2D material, a necessary first step is to understand intermediate behavior of the 2D material compared to the significance of the results for the ID composite orresponding ID specimen suggests that the 2D com- posite behaves as a laminate, i. e. the applied stress 4.1. ID Composite rheology distributed among the constituent plies, based on the effective viscosities of each. To investigate the possibility The inelastic response of the present CAS-II/SiCr ID of laminate theory to composites displayed behavioral trends that were pre- dictable based on our earlier experimental work on a similar anorthite-matrix/SiCr composite [10]. The previ- 5F1D:=20° ous study, which emphasized only off-axis loading with cp>30%, demonstrated(a) the maximum strain rate n=3.7 occurring for 50 and(b) substantial stress and orientation effects on the apparent activation energy, results qualitatively identical to those presented here for similar values of cp in Figs. 6, 7 and 9. The previous data n=53 were analyzed by the articulation of three modes of T=1325°c inelastic response [15] that were defined /identified by the -8.5 T=1300°c strain/strain-rate effects of specific components of the stress tensor -(1)the load-transfer(LT)mode for the 16 normal-stress component parallel to the fibers, (2)the Log F-a. (MPa) transverse-shear(TS)mode for the normal-stress compo- nent perpendicular to the fibers and ( 3)the longitudinal- Fig. 8. Stressstrain-rate relationships for 9=20 ID specimens at shear(LS)mode for the shear-stress component parallel to the fibers (and its complementary component, required for equilibrium). In the LT mode of deformation, stress ID is continuously transferred from the matrix to the fiber -o1 =40 MPa as deformation proceeds In the ts mode, deformation primarily occurs by shear flow of the matrix around the -6.0 fibers resulting in very little improvement in creep properties over the unreinforced matrix. The terminology used for these modes of deformation is based on our previous work [15]. Both the LT and the TS modes of deformation have been studied in detail previously in ID T=1275°c ceramic composites [6, 17]. Application of the mode analysis to the off-axis-loading ID composite flow is 8.0 analogous to the use of the Levy-Mises flow rules in continuum plasticity. From this analysis, and from p Degree knowing the structure and resultant flow behavior of the Fig. 9. Strain-rate as a function of o for ID specimens deformed at fiber-matrix interface(flow on the thin, amorphous -O,=40 MPa silicate interlayer), one realizes that considerable, tem perature-sensitive sliding can occur on the interface Matrix Unreinforced) Thus, a substantial magnitude for the LS component of the applied stress (e.g. x45%) promotes significant 1300°c displacement across the interface (modeling suggests 1310°c some 40%/ of the accumulated strain results from interfa- 1310° cial displacement when x 40-500), which turn. affects greatly the state of stress in the matrix [18]. The result overall is both the optimization of steady-state D5.0 strain rate at =50%(it is the TS component that moves 3.0 the maximum away from =45%)as well as(because of the temperature sensitivity of the interface response) the dramatic, high apparent activation energy for composite Log F-C,(MPa) New in these ID composite experiments (i studied experimentally previously) is the data for com- 10. Steady-state creep response of unreinforced CAS.lI matri pression creep with p=0 and 20. The steady-state flowB.G. Nair et al. / Materials Science and Engineering A300 (2001) 68–79 75 The fact that the creep results presented in Fig. 5 indicate intermediate behavior of the 2D material compared to corresponding 1D specimen suggests that the 2D com￾posite behaves as a laminate, i.e. the applied stress is distributed among the constituent plies, based on the effective viscosities of each. To investigate the possibility of a straight forward application of laminate theory to the 2D material, a necessary first step is to understand the significance of the results for the 1D composite. 4.1. 1D Composite rheology The inelastic response of the present CAS-II/SiCf 1D composites displayed behavioral trends that were pre￾dictable based on our earlier experimental work on a similar anorthite-matrix/SiCf composite [10]. The previ￾ous study, which emphasized only off-axis loading with 8]30°, demonstrated (a) the maximum strain rate occurring for 8=50° and (b) substantial stress and orientation effects on the apparent activation energy, results qualitatively identical to those presented here for similar values of 8 in Figs. 6, 7 and 9. The previous data were analyzed by the articulation of three modes of inelastic response [15] that were defined/identified by the strain/strain-rate effects of specific components of the stress tensor — (1) the load-transfer (LT) mode for the normal-stress component parallel to the fibers, (2) the transverse-shear (TS) mode for the normal-stress compo￾nent perpendicular to the fibers and (3) the longitudinal￾shear (LS) mode for the shear-stress component parallel to the fibers (and its complementary component, required for equilibrium). In the LT mode of deformation, stress is continuously transferred from the matrix to the fiber as deformation proceeds. In the TS mode, deformation primarily occurs by shear flow of the matrix around the fibers resulting in very little improvement in creep properties over the unreinforced matrix. The terminology used for these modes of deformation is based on our previous work [15]. Both the LT and the TS modes of deformation have been studied in detail previously in ID ceramic composites [6,17]. Application of the mode analysis to the off-axis-loading 1D composite flow is analogous to the use of the Levy-Mises flow rules in continuum plasticity. From this analysis, and from knowing the structure and resultant flow behavior of the fiber-matrix interface (flow on the thin, amorphous silicate interlayer), one realizes that considerable, tem￾perature-sensitive sliding can occur on the interface. Thus, a substantial magnitude for the LS component of the applied stress (e.g. 845°) promotes significant displacement across the interface (modeling suggests some 40% of the accumulated strain results from interfa￾cial displacement when 840–50°), which, in turn, affects greatly the state of stress in the matrix [18]. The result overall is both the optimization of steady-state strain rate at 8=50° (it is the TS component that moves the maximum away from 8=45°) as well as (because of the temperature sensitivity of the interface response) the dramatic, high apparent activation energy for composite flow. New in these 1D composite experiments (i.e. not studied experimentally previously) is the data for com￾pression creep with 8=0 and 20°. The steady-state flow Fig. 8. Stress/Strain-rate relationships for 8=20° 1D specimens at 1300 and 1325°C. Fig. 9. Strain-rate as a function of 8 for 1D specimens deformed at −s1=40 MPa. Fig. 10. Steady-state creep response of unreinforced CAS-II matrix.