S. i et al. / Journal of the European Ceramic Society 25(2005)301-311 No significant difference in water content of samples Qtz aggregates before and after experimental deformation, indicat- 1000 P=300 MPa ing no detected loss of water species such as hy Strain rate =10-/s drogen through the Fe jacket during the mechanical tests. 6 If the water content were higher than 0.5 wt% creep mechanism in fine-grained feldspar / s ate as a solution-precipitation processes might oper 巴巴 3. Mechanical data All axial compressive tests(oI >02= 03>0)were 0.10 performed at 300 MPa confining pressure in a Paterson-type gas-medium apparatus(GFZ-Potsdam, Germany). Temper- ature varied from 1173 to 1473K and axial strain rate from Fig. 7. Stress-strain curves for pure quartz aggregates deformed under 10- to 10-s. Cylindrical specimens of 10 mm diameter at a confining pressure of 300 MPa, a constant strain nd temperatures of 1373 and 1473 K. Note that the and 20 mm length, fabricated from HIP, were jacketed in iron quartz could not yield at 1373K or lower temperatures under with 0.23 mm thick wall. The tests were carried out at con- the expe conditions stant strain rates. In this case, the sample flow strength cor- responds to a differential stress of magnitude(o=01-o3) hich is superimposed upon a state of hydrostatic stress or 300 MPa at temperatures from 1273 to 1473K. The shape confining (o2=03). In other words, a differential of the stress-strain curves is characterized by an initial rapid stress(o) is the difference between the maximum and min- strength increase followed by a slow strain hardening. At an imum compressive principal stresses(o1 -o3). Thus it is axial strain of 0.25, the CAs polycrystal has flow strength always a positive scalar quantity. The axial compression is of 16.6, 60.8 and 115.4 MPa at 1473, 1373 and 1273K, re- frequently used in laboratory experiments on the high tem- spectively rocks. Differential stresses and axial strains were derived, porosity up to 5-6%, do not yield at 1273 and 1373K at respectively, from measured loads and displacements after the conditions of confining pressure 300 MPa and strain correcting for the load supported by the Fe jacket, rig distor- rate 10-5s-l(Fig. 7). Even at a temperature as high as tion and change in sample cross-sectional area and length. 1473 K, the quartz aggregate still has its strength higher than The uncertainty in stress measurements is estimated within 600 MPa. Under the same conditions(1473 K, 300 MPa and regates from the sequence of axial compression tests at CAS ("soft"component). It is ern ("hardo, thus a clor t5 MPa. Temperature control was +3 K along the gauge 10-3s-), quartz is stronger than CAS by a factor of 40 length of specimens (E=0.15)to 51(E =0.05). There is thus a large Fig 6 shows differential stress-strain curves for CAS ag- ological contrast between quartz ("hard"component)and a constant rate of 10-s and a confining pressure of hard quartz into a soft matrix of Cas should produce sig- nificant effects on improving the mechanical properties of CAS-matrix ceramic composite Fig 8 displays typical stress-strain curves for particulate CAS aggregates composite that is a homogeneous mixture of equal volume Strain rate 10-s fractions of Qtz and CAs. Three aspects of the mechanical P=300 MPa data are striking: (i) Steady-state flow is only att in sample J9 which deformed at 1473 K and 10-5s-l.(i) J31(1273K a drastic drop in stress occurs immediately after a strength peak at a strain of approximately 0.04 for sample J26 that J5(1373K deformed at 1373 K and 10-s-I. The abrupt decrease in the level of stress supported from 389 MPa at E=0.04 to 160 MPa at e=0.29 is due to strong strain localization into a J38(1473K semi-brittle shear zone aligned at about 300 to the maximum compression stress(o1).(iii)st rain so 0.000.050.10 and 1.0 x 10-to 2.5 10-s. For example, the strength Fig. 6. Stress-strain curves for pure CAS ag 9Binuau-20 0 25 0.30 .3s peak takes place in all samples deformed at 1173-1373K of sample J25, deformed at 1373 K and 2.5 x 10->s-is ompression at a confining pres nstant strain rate o 59,214,183andl54 MPa at o.10,0.35,0.50and0.65 10-Ss-I and temperatures of 1273, 1373 and 1473K strain, respectively. From 0. 10 to 0.65 shortening strain, theS. Ji et al. / Journal of the European Ceramic Society 25 (2005) 301–311 305 No significant difference in water content of samples before and after experimental deformation, indicat￾ing no detected loss of water species such as hy￾drogen through the Fe jacket during the mechanical tests.16 If the water content were higher than 0.5 wt.%, solution-precipitation processes might operate as a creep mechanism in fine-grained feldspar.15 3. Mechanical data All axial compressive tests (σ1 > σ2 = σ3 > 0) were performed at 300 MPa confining pressure in a Paterson-type gas-medium apparatus (GFZ-Potsdam, Germany). Temper￾ature varied from 1173 to 1473 K and axial strain rate from 10−5 to 10−4 s−1. Cylindrical specimens of 10 mm diameter and 20 mm length, fabricated from HIP, were jacketed in iron with 0.23 mm thick wall. The tests were carried out at con￾stant strain rates. In this case, the sample flow strength cor￾responds to a differential stress of magnitude (σ = σ1 − σ3) which is superimposed upon a state of hydrostatic stress or confining pressure (σ2 = σ3). In other words, a differential stress (σ) is the difference between the maximum and min￾imum compressive principal stresses (σ1 − σ3). Thus it is always a positive scalar quantity. The axial compression is frequently used in laboratory experiments on the high tem￾perature, high pressure properties of materials, minerals and rocks. Differential stresses and axial strains were derived, respectively, from measured loads and displacements after correcting for the load supported by the Fe jacket, rig distor￾tion and change in sample cross-sectional area and length. The uncertainty in stress measurements is estimated within ±5 MPa. Temperature control was ±3 K along the gauge length of specimens. Fig. 6 shows differential stress–strain curves for CAS ag￾gregates from the sequence of axial compression tests at a constant rate of 10−5 s−1 and a confining pressure of 0 40 80 120 160 200 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 Axial strain Differential stress, MPa J31 (1273 K) CAS aggregates Strain rate = 10-5 /s P = 300 MPa J5 (1373 K) J38 (1473 K) Fig. 6. Stress–strain curves for pure CAS aggregates deformed under axial compression at a confining pressure of 300 MPa, a constant strain rate of 10−5 s−1 and temperatures of 1273, 1373 and 1473 K. 0 200 400 600 800 1000 0.00 0.05 0.10 0.15 0.20 0.25 Axial strain Differential stress, MPa Qtz aggregates P = 300 MPa Strain rate = 10-5 /s J39 (1473 K) J20 (1373 K) Fig. 7. Stress–strain curves for pure quartz aggregates deformed under axial compression at a confining pressure of 300 MPa, a constant strain rate of 10−5 s−1 and temperatures of 1373 and 1473 K. Note that the quartz aggregate could not yield at 1373 K or lower temperatures under the experimental conditions. 300 MPa at temperatures from 1273 to 1473 K. The shape of the stress–strain curves is characterized by an initial rapid strength increase followed by a slow strain hardening. At an axial strain of 0.25, the CAS polycrystal has flow strength of 16.6, 60.8 and 115.4 MPa at 1473, 1373 and 1273 K, re￾spectively. The polycrystalline aggregates of quartz, in spite of its porosity up to 5–6%, do not yield at 1273 and 1373 K at the conditions of confining pressure 300 MPa and strain rate 10−5 s−1 (Fig. 7). Even at a temperature as high as 1473 K, the quartz aggregate still has its strength higher than 600 MPa. Under the same conditions (1473 K, 300 MPa and 10−5 s−1), quartz is stronger than CAS by a factor of 40 (ε = 0.15) to 51 (ε = 0.05). There is thus a large rhe￾ological contrast between quartz (“hard” component) and CAS (“soft” component). It is expected that the addition of hard quartz into a soft matrix of CAS should produce sig￾nificant effects on improving the mechanical properties of CAS–matrix ceramic composites. Fig. 8 displays typical stress–strain curves for particulate composite that is a homogeneous mixture of equal volume fractions of Qtz and CAS. Three aspects of the mechanical data are striking: (i) Steady-state flow is only attained only in sample J9 which deformed at 1473 K and 10−5 s−1. (ii) A drastic drop in stress occurs immediately after a strength peak at a strain of approximately 0.04 for sample J26 that deformed at 1373 K and 10−4 s−1. The abrupt decrease in the level of stress supported from 389 MPa at ε = 0.04 to 160 MPa at ε = 0.29 is due to strong strain localization into a semi-brittle shear zone aligned at about 30◦ to the maximum compression stress (σ1). (iii) Strain softening after a strength peak takes place in all samples deformed at 1173–1373 K and 1.0 × 10−5 to 2.5 × 10−5 s−1. For example, the strength of sample J25, deformed at 1373 K and 2.5 × 10−5 s−1, is 259, 214, 183 and 154 MPa at 0.10, 0.35, 0.50 and 0.65 strain, respectively. From 0.10 to 0.65 shortening strain, the