July 2007 Thermal Cycling Damage in Ceramic Matrix Composites Under a Constant Stress 2141 It can also be observed from Fig. 1l that thermal cycling can M. C. Halbig. D. N. Brewer, and A J. Eckel, " Degradation of Continuo result simultaneously in the initiation of the new cracks and nposites Under Constant Load Conditions": NASA ultiplication of the preexisting cracks n the co expected, the coating cracks of the thermally cycled C/Sic com- Mechanisms in Ceramic Matrix Composite Under Longitudinal Tensile Loading. posites, as well as the matrix cracks(e. g, Figs. 6(a) and(b), ater.29,1946-6l(19 could initiate and propagate with increasing thermal cycles, ar can eventually attain stability for a given applied condition. In Emission During Tensile Testing of SiC-Fibre-Rein forced BMAS Glass- Ceramic Composites, " Comp. Part. A. 28A. 473-80(1997) Fig. ll, the crack density can be determined approximately: (a) M. E. Walter and G. Ravichandran. "" Experimental Investigation of Damage 1.8 ter five cycles, (b)3.5 mm- after 10 cycles, (c)4.9 ASME n 7. 101-8 995, Matrix Composite,". Eng. Mater. Technol. Trans tively. After 15 cycles, the crack density almost reaches a con G Morscher and A L Gyekenyesi, ""The Velocity and Attenuation of Acous- Emission Waves in SiC/SiC Composites Loaded in Tension, Compos. Sci. stant value of about 5.0 mm. Obviously, the macroscopic Techno., 62, 1171-80(2002) TCC strain and the real-time ae data correspond extremely wel "Modal Acoustic Emission of d with the microstructural changes. These results suggest that K. Sato, Y. Kagawa, H Iba, SO.Guo, H. Ka thermal cycling damage to the composites is limited and there Acoustic Emission and fracture Behavior of sic Fibe Composite Fabricated by PIP Process, "Ceram. Eng. Sci. Proc. 21 [3]407-14 tend toward a negligible level for a given applied condition R. Dharani. J. E. Goethe. S B Haug. w. P. Cai and M.A. Lankiord, Com (go Hybrid Ceramic Matrix Composites, "Ceram. Eng Under a thermal cycling between 700 and 1200C with a con- stant stress of 50 MPa, cyclic thermal strains of a 3D C/SiC Harrigan, J. Strife and A. K Dhingra. Warrendale, PA, 1985 composite with a range of 0. 2 have been measured on a pro- of the Failure Modes in Hybrid Ceramic Matrix Composites. ". Compos. Tech- gressively increasing baseline strain. The temperature dependence nol.Res,18[3]194201(1996) M. Enoki. S. Ohtake and T. Kishi. "Classification of microfracture Process of the strain in a single cycle resulted in a substantial strain hys- Type in Glass Matrix Composites by Quantitative Acoustic Emission Method, teresis. a distinct knee occurred on the strain hysteresis loop during heating, which was in large part ascribed to thermal stress M. K each, and R. D. Rawlings. "Acoustic Emission Studies (e, 900.C). No further increase in TCC strain was observe re redistribution in composites above the crack closure temperatur Fatigue-Loaded Sic Platelet-reinforced Y-TZP, J. Mater. Sci. Lett. 13, 211- the crack density became saturated after 15 cycles M. Drissi-Habti and D. Rouby, "Assessment of the Static Fatigue Beha uring testing, the monitored AE signals(hits and energy),as of the SiC Fibre- Reinforced Lithium Magnesium Aluminosilicate Glass -Cerami well as the measured strain, were found to follow a strict per dicity over the same period as their excitation temperature. AE aque and M. Rahman. ""Durability and Damage Development in w appears in certain temperature ranges, being much less during heating than during cooling. A stepwise increasing AE energy is evated Temperatures,"J.Eng Mater. Techimol Trans ASME,122,394-401(2000). aya. F. Kaya and H. Mor, "Damage Assessment of Alumina Fibre- ature cycle. moreover, the incremental amount of ae energy Ambient and Elevated Tem)2出题 per cycle gradually decreased with increasing cycles until it V Kostopoulos, Y. Z Pappas, and Y. P. Markopoulos, "Fatigue Damage tion in 3-Dimensional SiC/iC Composites. " J. Euro. Ceram. Soc.. finally nearly disappeared after 15 cycles. AE responses also 207-15( 99/E. G Henneke, and K L Reifsnider, "Damage Chara exhibited the apparent Felicity effect, and the Felicity ratio increased as the thermally induced stress was gradually relaxed a Cross-Ply SiC/CAS-Il Ceramic Composite Under Fatigue Loading Using during repetitive cooling by the deformation mechanism of ma- Real- Time Acousto-Ultrasonic NDE Technique,"J. Compos. Technol Res, 17, trix cracking. The decreasing AE energy per cycle and increasing Felicity ratio indicated that thermal cycling damage gradually Kaya, F. Kaya, and H. Mori, ""Non-Destructive Damage Evaluation of diminished with cycles until final saturation. As expected, the Using Forced Resonance and Acoustic Emission Techniques, . Mater. Sci. Lett coating and matrix cracks were observed to initiate and prop- agate with cycles, and could eventually attain stability beyond N. Morscher and A Room Temperature Creep of SiC/Sic the critical number of 15. Thus, the measured macroscopic TCC strain and the monitored real-time Ae data correspond extreme. Rupturcora sve 81- Llon BN- nterphase, SiC-Matrix Composite in Air imply that thermal cycling damage to the composite, in the form N. Morscher and J. Hurst, "Stress-Rupture and Stress-Relaxation of SiC/ SiC Composites at Intermediate Temperature, Ceram. Eng. Sci. Proc., 22. 539-46 of significant matrix cracking, mainly takes place during the(2001 cooling stage in each single cycle and before 15 cycles for a given G.N.Morscher,J. Martinez-Fernandez, and M. J. Purdy, "Determination hermal and mechanical applied condition. AE methodology nterfacial Properties Using a Single-Fiber Microcomposite Test. J Am. Ceram. that gives in situ information can be advantageously used to M. Park, E M. Chong. D. J. Yoon, and J H. Lee. "Interfacial Properti understand comprehensively the damage process of the ther- of Two SiC Fiber-Reinforced Polycarbonate Composites Using the Fragmenta- mally cycled ceramic matrix composites on Test and Acoustic Emission, Polym. Compos., 19, 747-58(1998). 2T. Kishi a.Eng,A143.103-10(199 27Y. Yamade. Y. Kawaguchi, N. Takeda, and T Kishi. "Interfacial Debondin Acknowledgments Behavior of Mullite/ SiC Continuous Fiber Composite, "J. Am. Ceran. Soc. The Program for Changjiang Scholars and Innovative Research Team in 320416(1995) university(PCSIRT) is appreciated greatly of Microcracks, "Key Eng. Mater. 127-131, 63-72(1997) 2Y. H. Yu, J. H Choi, J. H. Kweon, and D. H. Kim, "A Study on the Failure References os and y Ke Fabrication and Application of C/C, C/SiC and SiC/Sic Analysis of 2D Carbon/Carbon Using Acoustic Emission Monitoring. " NDT&E emperature Ceramic Naslain, and H. Schneider. Wiley-VCH Press, m13131576 haracterization and Acoustic Emission Monitoring of a 2-D Carbon/Carbon Composite, "Eng Fract. Mechan. R Advanced Ceramic Matrix Composite Materials for Current and Future T. Kishi and J. H. Koo,"Non-Destructive Evaluation of Engineering Propulsion Technology Applications, Acta Astronautica, 55, 409-20(2004) Ceramics, Key Eng. Mater. 2. 587-92(1999)It can also be observed from Fig. 11 that thermal cycling can result simultaneously in the initiation of the new cracks and multiplication of the preexisting cracks in the composites. As expected, the coating cracks of the thermally cycled C/SiC com￾posites, as well as the matrix cracks (e.g., Figs. 6(a) and (b)), could initiate and propagate with increasing thermal cycles, and can eventually attain stability for a given applied condition. In Fig. 11, the crack density can be determined approximatily: (a) 1.8 mm1 after five cycles, (b) 3.5 mm1 after 10 cycles, (c) 4.9 mm1 after 15 cycles, and (d) 5.1 mm1 after 25 cycles, respec￾tively. After 15 cycles, the crack density almost reaches a con￾stant value of about 5.0 mm1 . Obviously, the macroscopic TCC strain and the real-time AE data correspond extremely well with the microstructural changes. These results suggest that thermal cycling damage to the composites is limited and there exists a critical cycle number Nc beyond which the damage will tend toward a negligible level for a given applied condition. IV. Conclusions Under a thermal cycling between 7001 and 12001C with a con￾stant stress of 50 MPa, cyclic thermal strains of a 3D C/SiC composite with a range of 0.2% have been measured on a pro￾gressively increasing baseline strain. The temperature dependence of the strain in a single cycle resulted in a substantial strain hys￾teresis. A distinct knee occurred on the strain hysteresis loop during heating, which was in large part ascribed to thermal stress redistribution in composites above the crack closure temperature (i.e., 9001C). No further increase in TCC strain was observed as the crack density became saturated after 15 cycles. During testing, the monitored AE signals (hits and energy), as well as the measured strain, were found to follow a strict peri￾odicity over the same period as their excitation temperature. AE appears in certain temperature ranges, being much less during heating than during cooling. A stepwise increasing AE energy is found to be only enhanced at the cooling stage of each temper￾ature cycle. Moreover, the incremental amount of AE energy per cycle gradually decreased with increasing cycles until it finally nearly disappeared after 15 cycles. AE responses also exhibited the apparent Felicity effect, and the Felicity ratio increased as the thermally induced stress was gradually relaxed during repetitive cooling by the deformation mechanism of ma￾trix cracking. The decreasing AE energy per cycle and increasing Felicity ratio indicated that thermal cycling damage gradually diminished with cycles until final saturation. As expected, the coating and matrix cracks were observed to initiate and prop￾agate with cycles, and could eventually attain stability beyond the critical number of 15. Thus, the measured macroscopic TCC strain and the monitored real-time AE data correspond extreme￾ly well with the observed microstructural changes. These results imply that thermal cycling damage to the composite, in the form of significant matrix cracking, mainly takes place during the cooling stage in each single cycle and before 15 cycles for a given thermal and mechanical applied condition. AE methodology that gives in situ information can be advantageously used to understand comprehensively the damage process of the ther￾mally cycled ceramic matrix composites. Acknowledgments The Program for Changjiang Scholars and Innovative Research Team in university (PCSIRT) is appreciated greatly. References 1 F. Christin, ‘‘Design, Fabrication and Application of C/C, C/SiC and SiC/SiC Composites’’; pp. 731–43 in High Temperature Ceramic Matrix Composites, Vol. 4, Edited by W. Krenkel, R. Naslain, and H. Schneider. Wiley-VCH Press, Weinheim, 2001. 2 S. Schmidt, S. Beyer, H. Knabe, H. Immich, R. Meistring, and A. Gessler, ‘‘Advanced Ceramic Matrix Composite Materials for Current and Future Propulsion Technology Applications,’’ Acta Astronautica, 55, 409–20 (2004). 3 M. C. Halbig, D. N. Brewer, and A. J. Eckel, ‘‘Degradation of Continuous Fiber Ceramic Matrix Composites Under Constant Load Conditions’’; NASA/ TM-209681, January, 2000. 4 J. J. Luo, S. C. Wooh, and I. M. Daniel, ‘‘Acoustic Emission Study of Failure Mechanisms in Ceramic Matrix Composite Under Longitudinal Tensile Loading,’’ J. Comp. Mater., 29, 1946–61 (1995). 5 M. Surgeon, E. Vanswijgenhoven, M. Wevers, and O. Van Oer Biest, ‘‘Acous￾tic Emission During Tensile Testing of SiC-Fibre-Reinforced BMAS Glass￾Ceramic Composites,’’ Comp. Part. A., 28A, 473–80 (1997). 6 M. E. Walter and G. Ravichandran, ‘‘Experimental Investigation of Damage Evolution in a Ceramic Matrix Composite,’’ J. Eng. Mater. Technol. Trans. ASME, 117, 101–8 (1995). 7 G. Morscher and A. L. Gyekenyesi, ‘‘The Velocity and Attenuation of Acous￾tic Emission Waves in SiC/SiC Composites Loaded in Tension,’’ Compos. Sci. Technol., 62, 1171–80 (2002). 8 G. N. Morscher, ‘‘Modal Acoustic Emission of Damage Accumulation in a Woven SiC/SiC Composite,’’ Compos. Sci. Technol., 59, 687–97 (1999). 9 K. Sato, Y. Kagawa, H. Iba, S. O. Guo, H. Kakisawa, and M. Mizuno, ‘‘Acoustic Emission and Fracture Behavior of SiC Fiber-Reinforced Si–N–C Ma￾trix Composite Fabricated by PIP Process,’’ Ceram. Eng. Sci. Proc., 21 [3] 407–14 (2000). 10D. R. Carroll, L. R. Dharani, J. E. Goethe, S. B. Haug, W. P. Cai, and M. A. Hall, ‘‘Damage Evolution in Hybrid Ceramic Matrix Composites,’’ Ceram. Eng. Sci. Proc., 16 [5] 949–56 (1995). 11J. Lankford, ‘‘Compressive Strength and Damage Mechanisms in a SiC-Fiber Reinforced Glass–Ceramic Matrix Composite,’’ pp. 587–602 in Proceedings of the 5th International Conference on Composite Materials, ICCM-V. Edited by W. C. Harrigan, J. Strife and A. K. Dhingra. Warrendale, PA, 1985. 12J. E. Goethe, L. R. Dharani, and D. R. Carroll, ‘‘Experimental Investigation of the Failure Modes in Hybrid Ceramic Matrix Composites,’’ J. Compos. Tech￾nol. Res., 18 [3] 194–201 (1996). 13M. Enoki, S. Ohtake, and T. Kishi, ‘‘Classification of Microfracture Process Type in Glass Matrix Composites by Quantitative Acoustic Emission Method,’’ Mater. Trans., 42 [1] 108–13 (2001). 14P. M. Kelly, C. A. Leach, and R. D. Rawlings, ‘‘Acoustic Emission Studies of Fatigue-Loaded SiC Platelet-reinforced Y–TZP,’’ J. Mater. Sci. Lett., 13, 211–2 (1994). 15M. Drissi-Habti and D. Rouby, ‘‘Assessment of the Static Fatigue Behaviour of the SiC Fibre-Reinforced Lithium Magnesium Aluminosilicate Glass–Ceramic Matrix Composite Tested Under Uniaxiale Tensile Loading,’’ Key Eng. Mat., 132– 136, 1910–3 (1997). 16A. Haque and M. Rahman, ‘‘Durability and Damage Development in Woven Ceramic Matrix Composites Under Tensile and Fatigue Loading at Room and El￾evated Temperatures,’’ J. Eng. Mater. Technol. Trans. ASME., 122, 394–401 (2000). 17C. Kaya, F. Kaya, and H. Mori, ‘‘Damage Assessment of Alumina Fibre￾Reinforced Mullite Ceramic Matrix Composites Subjected to Cyclic Fatigue at Ambient and Elevated Temperatures,’’ J. Eur. Ceram. Soc., 22, 447–52 (2002). 18V. Kostopoulos, Y. Z. Pappas, and Y. P. Markopoulos, ‘‘Fatigue Damage Accumulation in 3-Dimensional SiC/SiC Composites,’’ J. Euro. Ceram. Soc., 19, 207–15 (1999). 19A. Tiwari, E. G. Henneke, and K. L. Reifsnider, ‘‘Damage Characterization of a Cross-Ply SiC/CAS-II Ceramic Composite Under Fatigue Loading Using a Real-Time Acousto-Ultrasonic NDE Technique,’’ J. Compos. Technol. Res., 17, 221–7 (1995). 20C. Kaya, F. Kaya, and H. Mori, ‘‘Non-Destructive Damage Evaluation of Cyclic-Fatigued Alumina Fiber-Reinforced Mullite Ceramic Matrix Composites Using Forced Resonance and Acoustic Emission Techniques,’’ J. Mater. Sci. Lett., 21, 1333–5 (2002). 21G. N. Morscher and A. Gyekenyesi, ‘‘Room Temperature Creep of SiC/SiC Composites,’’ Ceram. Eng. Sci. Proc., 22, 547–52 (2001). 22G. N. Morscher, J. Hurst, and D. Brewer, ‘‘Intermediate-Temperature Stress Rupture of a Woven Hi-Nicalon, BN-Interphase, SiC-Matrix Composite in Air,’’ J. Am. Ceram. Soc., 83, 1441–9 (2000). 23G. N. Morscher and J. Hurst, ‘‘Stress-Rupture and Stress-Relaxation of SiC/ SiC Composites at Intermediate Temperature,’’ Ceram. Eng. Sci. Proc., 22, 539–46 (2001). 24G. N. Morscher, J. Martinez-Fernandez, and M. J. Purdy, ‘‘Determination of Interfacial Properties Using a Single-Fiber Microcomposite Test,’’ J. Am. Ceram. Soc., 79, 1083–91 (1996). 25J. M. Park, E. M. Chong, D. J. Yoon, and J. H. Lee, ‘‘Interfacial Properties of Two SiC Fiber-Reinforced Polycarbonate Composites Using the Fragmenta￾tion Test and Acoustic Emission,’’ Polym. Compos., 19, 747–58 (1998). 26T. Kishi, M. Enoki, and H. Tsuda, ‘‘Interface and Strength in Ceramic Matrix Composites,’’ Mater. Sci. Eng., A143, 103–10 (1991). 27Y. Yamade, Y. Kawaguchi, N. Takeda, and T. Kishi, ‘‘Interfacial Debonding Behavior of Mullite/SiC Continuous Fiber Composite,’’ J. Am. Ceram. Soc., 78, 3204–16 (1995). 28T. Kishi and M. Enoki, ‘‘Development of Ceramic Matrix Composites and the Meaning of Microcracks,’’ Key Eng. Mater., 127–131, 63–72 (1997). 29Y. H. Yu, J. H. Choi, J. H. Kweon, and D. H. Kim, ‘‘A Study on the Failure Detection of Composite Materials Using an Acoustic Emission,’’ Comp. Struct., 75, 163–9 (2006). 30Y. Z. Pappas, Y. P. Markopoulos, and V. Kostopoulos, ‘‘Failure Mechanisms Analysis of 2D Carbon/Carbon Using Acoustic Emission Monitoring,’’ NDT&E Int., 31 [3] 157–63 (1998). 31Y. Z. Pappas and V. Kostopoulos, ‘‘Toughness Characterization and Acoustic Emission Monitoring of a 2-D Carbon/Carbon Composite,’’ Eng. Fract. Mechan., 14, 1557–73 (2001). 32T. Kishi and J. H. Koo, ‘‘Non-Destructive Evaluation of Engineering Ceramics,’’ Key Eng. Mater., 2, 587–92 (1999). July 2007 Thermal Cycling Damage in Ceramic Matrix Composites Under a Constant Stress 2141