B G. Nair et al. Materials Science and Engineering 4300 (2001)68-79 40/-500 and the 20/-700 composites showed non-New- tonian creep behavior with n increasing from about 2 at 2D 1275° c to about3atl300°C.Theo/-90°spec showed Newtonian behavior in the temperature range 200-+0/m0 1300-1325C. Fig. 4 illustrates the variation of @a with -a, for specimens with different values of y. The 1500 0/-90o composites had an activation energy of about 480 k mol-I. The increase in n with t for othe 。1000 loading configurations (y+O) results in @app having a 500 very strong dependence on the applied stress; @ a 2D 4. Variation of Oapp with for 2D T〓1275c different values of y 8.0 increased from 650 to 1400 kJ mol- for 40/ and from x 1500 to 2400 kj mol 20/-70° composites. 3. 2. Creep experiments on ID composites and on the 20°/70";n=21 unreinforced CAS- matrix 1.5 A comparison of the creep data of y(y-90%)2D Log F-o.(MPa) composite specimens to the data for ID composites with y and p=(90%-p) is presented in Fig. 5 4.5F2D For all values of y, the values of n for 2D composites are intermediate to those for the ID composites, where pp corresponds to either y or(90-y) As such a result suggests an application of laminate theory to the under tanding of 2D behavior, it is nessasary to provide here comprehensive results for the ID material -65 Creep data for ID composite specimens with differ ent values of at 1300 and 1275C are shown in Fig 6a and b respectively. For =0, the observed theol- v0"/90°;n=13 ogy was Newtonian (n A 1). For specimens with values 1112131.41.51.61.718 of op ranging from 40 to 90, n was consistently between Log I-o, (MPa)l 1.9 and 2.7 in the temperature range 1275-1300oC. Fig 7 shows the variation of @app with applied stress for vanous specimen ge metre es. For off-axis'geometries with (p=20-90, @app was significantly higher(> 1000 kJ mol-)than for =0(@app 400-440 kJ mol-) 1300°c The behavior of specimens with 20, both in 。1275°c terms of stress and temperature sensitivity is in striking 6.0 contrast to the general trend. The p= 20 specimens displayed the highest values of n for ID composites Further. n decreased from 5.3 at 1300oc to 3.6 at 1325C(Fig. 8). @app decreased from 2200 kJ mol-I at -a1=20 MPa to 900 kJ mol- at -a1=40 MPa(Fig. 7) Fig.9 illustrates the dependence of iss on at 1275 DEgrees and 1300oC. The =50 specimens consistently dis- Fig3.Stress/strain-rate relationships for 2D composites as a function played the highest strain-rates at all temperatures and of v(a)1275oC:(b)1300C(c) Strain-rate as a function of y for a stresses- at 1300C and 40 MPa, the steady-state constant stress of 40 MPa(the 0/90 data point is extrapolated based strain-rate for p= 50 was two orders of magnitude Eq.(1) higher than the strain-rate of the on-axis, =0 speci72 B.G. Nair et al. / Materials Science and Engineering A300 (2001) 68–79 40/–50° and the 20/–70° composites showed non-New￾tonian creep behavior with n increasing from about 2 at 1275°C to about 3 at 1300°C. The 0/–90° specimens showed Newtonian behavior in the temperature range 1300–1325°C. Fig. 4 illustrates the variation of Qapp with −s1 for specimens with different values of c. The 0/–90° composites had an activation energy of about 480 kJ mol−1 . The increase in n with T for other loading configurations (c"0) results in Qapp having a very strong dependence on the applied stress; Qapp Fig. 4. Variation of Qapp with −s1 for 2D composite specimens for different values of c. Fig. 3. Stress/strain-rate relationships for 2D composites as a function of c. (a) 1275°C; (b) 1300°C. (c) Strain-rate as a function of c for a constant stress of 40 MPa (the 0/90° data point is extrapolated based on Eq. (1)). increased from 650 to 1400 kJ mol−1 for 40/–50° compsites and from 1500 to 2400 kJ mol−1 for 20/–70° composites. 3.2. Creep experiments on 1D composites and on the unreinforced CAS-II matrix A comparison of the creep data of c(c−90°) 2D composite specimens to the data for 1D composites with 8=c and 8=(90°−c) is presented in Fig. 5. For all values of c, the values of n for 2D composites are intermediate to those for the 1D composites, where 8 corresponds to either c or (90°−c). As such a result suggests an application of laminate theory to the under￾standing of 2D behavior, it is nessasary to provide here comprehensive results for the 1D material. Creep data for 1D composite specimens with differ￾ent values of 8 at 1300 and 1275°C are shown in Fig. 6a and b respectively. For 8=0°, the observed theol￾ogy was Newtonian (n1). For specimens with values of 8 ranging from 40 to 90°, n was consistently between 1.9 and 2.7 in the temperature range 1275–1300°C. Fig. 7 shows the variation of Qapp with applied stress for various specimen geometries. For ‘off-axis’ geometries with 8=20–90°, Qapp was significantly higher (\1000 kJ mol−1 ) than for 8=0° (Qapp400–440 kJ mol−1 ). The behavior of specimens with 8=20°, both in terms of stress and temperature sensitivity is in striking contrast to the general trend. The 8=20° specimens displayed the highest values of n for 1D composites. Further, n decreased from 5.3 at 1300°C to 3.6 at 1325°C (Fig. 8). Qapp decreased from 2200 kJ mol−1 at −s1=20 MPa to 900 kJ mol−1 at −s1=40 MPa (Fig. 7). Fig. 9 illustrates the dependence of o; ss on 8 at 1275 and 1300°C. The 8=50° specimens consistently dis￾played the highest strain-rates at all temperatures and stresses — at 1300°C and 40 MPa, the steady-state strain-rate for 8=50° was two orders of magnitude higher than the strain-rate of the on-axis, 8=0° speci-