wwceramics. org/ACT SiC Fiber-Reinforced MI SiC Composites 155 (b)600 00 232GP SYL-iBN fo=020&0.1 400 o=0.18&0.14区 E=210 GPa E=210 GPa E=210 GPa Hysteresis Loops Removed Hysteresis Loops Removed 0 0.20.4 12 Strain. % Fig. I. Representative stress-strain curves from different woven composite systems. Figure 3 shows the ae data from different speci- composite. In essence, the curves in Fig. 3 show the mens for each family of composites, collected during the relative distribution of matrix cracks as stress is increased tensile test. The aE parameter of interest is the energy of in the different composite specimens, and complement E events that occur in the gauge section. A single event the tensile stress-strain data in further understanding was captured on two different sensors. The average en- fiber effects on matrix cracki ergy from each event was determined and used to com- The ae onset stress has been shown to pute the cumulative energy of the events starting from to the onset of fiber-bridged matrix crack formation an the initial event until the final event. Figure 3 shows the is one measure of"matrix cracking stress. "The AE normalized cumulative AE energy(Norm CumAE), onset stress is the onset of a high rate of high-energy AE which is the cumulative energy divided by the total cu- events and determined by extrapolating the steep mulative energy at the final event, plotted versus com- sle tion of the norm Cumae versus stress curve posite stress. It has been shown that for MI composites, back to the zero axis. Table II shows the average values Norm CumAE is directly related to matrix crack den- for the AE onset stress. Also shown are the 0.005% off- sity.The decrease in the rate of Norm CumAE at high set stresses. from the stress-strain curves. a common stress is indicative of matrix crack saturation in the technique for determining the proportional limit, and often associated with matrix cracking strengths for these u0.7 E 02 0.6 Strain. 50100150200250300350400 Fig. 2. Initial part of unload-reload stress-strain curves showing residual stress(circles) for representative specimens from each Fig 3. Acoustic emission behavior during room temperature tensile tests on different fiber-containing MI composites.Figure 3 shows the AE data from different speci￾mens for each family of composites, collected during the tensile test. The AE parameter of interest is the energy of AE events that occur in the gauge section. A single event was captured on two different sensors. The average en￾ergy from each event was determined and used to com￾pute the cumulative energy of the events starting from the initial event until the final event. Figure 3 shows the normalized cumulative AE energy (NormCumAE), which is the cumulative energy divided by the total cu￾mulative energy at the final event, plotted versus com￾posite stress. It has been shown that for MI composites, NormCumAE is directly related to matrix crack den￾sity.7 The decrease in the rate of NormCumAE at high stress is indicative of matrix crack saturation in the composite. In essence, the curves in Fig. 3 show the relative distribution of matrix cracks as stress is increased in the different composite specimens, and complement the tensile stress–strain data in further understanding fiber effects on matrix cracking. The AE onset stress has been shown to correspond to the onset of fiber-bridged matrix crack formation and is one measure of ‘‘matrix cracking stress.’’7 The AE onset stress is the onset of a high rate of high-energy AE events and is determined by extrapolating the steep slope portion of the NormCumAE versus stress curve back to the zero axis.7 Table II shows the average values for the AE onset stress. Also shown are the 0.005% off￾set stresses, from the stress–strain curves, a common technique for determining the proportional limit,15 and often associated with matrix cracking strengths for these 0 100 200 300 400 500 600 0 0.2 0.4 0.6 0.8 1 1.2 Strain, % Stress, MPa SA fo = 0.18 & 0.14 [x] SYL-iBN fo = 0.20 & 0.18 ZMI-1 fo = 0.14 E = 210 GPa HN fo = 0.14 E = 220 GPa Hysteresis Loops Removed 0 100 200 300 400 500 (a) 600 (b) 0 0.2 0.4 0.6 0.8 1 Strain, % Stress, MPa SA-2 fo = 0.18 E = 254 GPa SYL-2 fo = 0.20 E = 283 GPa ZMI-1 fo = 0.14 E = 210 GPa HN fo = 0.14 E = 210 GPa Hysteresis Loops Removed HNS-2 fo = 0.17 E = 232 GPa Fig. 1. Representative stress–strain curves from different woven composite systems. –50 0 50 100 150 200 250 300 0 0.2 0.4 0.6 Strain, % Stress, MPa ZMI fo = 0.14 HN fo = 0.14 SA fo = 0.18 fo = 0.2 Syl-iBN Fig. 2. Initial part of unload–reload stress–strain curves showing residual stress (circles) for representative specimens from each composite system. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 50 100 150 200 250 300 350 400 Composite Stress, MPa Norm Cum AE ZMI SA Syl-iBN HN HNS Fig. 3. Acoustic emission behavior during room temperature tensile tests on different fiber-containing MI composites. www.ceramics.org/ACT SiC Fiber-Reinforced MI SiC Composites 155