Composites Science and Technology 68(2008)3285-3292 Contents lists available at ScienceDirect Composites Science and Technology ELSEVIER journalhomepagewww.elsevier.com/locate/compscitech Measurement and calculation of thermal residual stress in fiber reinforced ceramic matrix composites Hui mei* National Key Laboratory of Thermostructure Composite Materials, Materials Science, Northwestern Polytechnical University, 547 P.O. Box, XIan, Shaanxi 710072, PR China ARTICLE IN F O ABSTRACT Article history: Received 29 January 2008 (C/SiC)and silicon carbide fiber(SiC/SiC) were completely investigated. Thermal residual stress in the C/ Accepted 20 August 2008 Sic was quantified by three different methods of experimental measurement, analytical calculation, and Available online 28 August 2008 heoretical prediction, and then compared with that in the Sic/SiC. Good agreement between these meth- ds was observed and their applicability to the present composite systems was validated. Relationships between the thermal residual stress state and macroscopic mechanical properties of the composites(e.g, A Ceramic matrix composites the first matrix cracking stress)are discusse B Mechanical property e 2008 Elsevier Ltd. All rights reserved. C Residual stress 1 Introduction (not only material surface)during mechanical loading attract more considerable attention, mainly because of its strong influence on Continuous fiber reinforced ceramic matrix composites(CMcs) the macroscopic tensile stress-strain response and of potential re currently considered for applications as structural materials in improvement of mechanical properties of these materials once th aerospace and other industries since they retain the advanta completely understanding the significant TRS. In this regard, Steen ges of ceramics while providing an enhanced damage tolerance [ et al.8-9] pre esents apply method to qu Generally, ceramic matrix composites are fabricated at high tify the residual stress state in continuous fiber ceramic matrix temperature, i.e. typically 900-1100C of the chemical vapor composites. The method consists of a novel interpretation of the infiltration(CVi) processing of Sic or C-matrix composites [2-3 results of tensile tests and offers the advantage that the initial (e.g, C/SiC, SiC/SiC and C/C, etc. ) Thus, thermal residual stresses residual stresses as well as their evolution with temperature and (TRS)are often generated in the composites upon cooling from pro- with applied loading can be determined. Evans et al. [10-11devel cessing to room temperatures due to extensive mismatch of the oped an analytical methodology to correlate the misfit stress with coefficients of thermal expansion( CTEs) between the constituents the unload/reload hysteresis and permanent strain with emphasis (fiber, interphase and matrix) on the interfacial properties. Then the tRS can be estimated as the are misfit stress multiplied by the volume-averaged stiffness coeffi scopic mechanical behavior of CMCs by determining the cient. However, these reported methods have not yet been com- states of the constituents(compressive or tensile stresses) pared systematically when applied to a specified composite, and omposites and forming the damage to the composites in also no description involving tRS comparison of the two composite to release themselves(matrix cracking, fiber-matrix debonding ). systems reinforced with different fibers applied to these methods Accordingly, estimation of TRs is a very important issue for the can be found in the recent literature. development and application of advanced CMCs. X-ray diffraction For this purpose, the present studies focus on investigation on (XRD) is considered as the most traditionally used technique for thermal residual stresses in two Sic-ceramic matrix composite sys- is only suited to the measurement of TRS in very small areas of (Sic/SiC). Three different methods of experimental measurement, the surface of polycrystalline materials in a very fine scale. More- analytical calculation, and theoretical prediction were conducte over, TRS in the fibres can usually not be analysed since they are to quantify thermal residual stress in the C/SiC, and then the ob- only partly crystalline and amorphous to diffraction methods [7]. tained results were compared with that in the SiC/ SiC Agreement Comparatively, axial trs behaviors of as a whole CMc material between and applicability of these methods to the present com- posite systems were concerned. Relationships between the tr TeL:+862988494616;fax:+862988494620. state and macroscopic mechanical properties of the composite (e.g. first matrix cracking stress)are discussed. S-see front matter o 2008 Elsevier Ltd. All rights reserved.Measurement and calculation of thermal residual stress in fiber reinforced ceramic matrix composites Hui Mei * National Key Laboratory of Thermostructure Composite Materials, Materials Science, Northwestern Polytechnical University, 547 P.O. Box, Xi’an, Shaanxi 710072, PR China article info Article history: Received 29 January 2008 Received in revised form 2 July 2008 Accepted 20 August 2008 Available online 28 August 2008 Keywords: A. Ceramic matrix composites B. Mechanical property C. Residual stress abstract In this study, thermal residual stresses in two SiC-ceramic matrix composites reinforced with carbon fiber (C/SiC) and silicon carbide fiber (SiC/SiC) were completely investigated. Thermal residual stress in the C/ SiC was quantified by three different methods of experimental measurement, analytical calculation, and theoretical prediction, and then compared with that in the SiC/SiC. Good agreement between these meth￾ods was observed and their applicability to the present composite systems was validated. Relationships between the thermal residual stress state and macroscopic mechanical properties of the composites (e.g., the first matrix cracking stress) are discussed. 2008 Elsevier Ltd. All rights reserved. 1. Introduction Continuous fiber reinforced ceramic matrix composites (CMCs) are currently considered for applications as structural materials in both aerospace and other industries since they retain the advanta￾ges of ceramics while providing an enhanced damage tolerance [1]. Generally, ceramic matrix composites are fabricated at high temperature, i.e. typically 900–1100 C of the chemical vapor infiltration (CVI) processing of SiC or C-matrix composites [2–3] (e.g., C/SiC, SiC/SiC and C/C, etc.). Thus, thermal residual stresses (TRS) are often generated in the composites upon cooling from pro￾cessing to room temperatures due to extensive mismatch of the coefficients of thermal expansion (CTEs) between the constituents (fiber, interphase and matrix). TRS are known to have a significant influence on the macro￾scopic mechanical behavior of CMCs by determining the stress states of the constituents (compressive or tensile stresses) in the composites and forming the damage to the composites in order to release themselves (matrix cracking, fiber-matrix debonding). Accordingly, estimation of TRS is a very important issue for the development and application of advanced CMCs. X-ray diffraction (XRD) is considered as the most traditionally used technique for characterizing residual stresses in CMC materials [4–6]. However, it is only suited to the measurement of TRS in very small areas of the surface of polycrystalline materials in a very fine scale. More￾over, TRS in the fibres can usually not be analysed since they are only partly crystalline and amorphous to diffraction methods [7]. Comparatively, axial TRS behaviors of as a whole CMC material (not only material surface) during mechanical loading attract more considerable attention, mainly because of its strong influence on the macroscopic tensile stress–strain response and of potential improvement of mechanical properties of these materials once completely understanding the significant TRS. In this regard, Steen et al. [8–9] presents an alternative easy-to-apply method to quan￾tify the residual stress state in continuous fiber ceramic matrix composites. The method consists of a novel interpretation of the results of tensile tests and offers the advantage that the initial residual stresses as well as their evolution with temperature and with applied loading can be determined. Evans et al. [10–11] devel￾oped an analytical methodology to correlate the misfit stress with the unload/reload hysteresis and permanent strain with emphasis on the interfacial properties. Then the TRS can be estimated as the misfit stress multiplied by the volume-averaged stiffness coeffi- cient. However, these reported methods have not yet been com￾pared systematically when applied to a specified composite, and also no description involving TRS comparison of the two composite systems reinforced with different fibers applied to these methods can be found in the recent literature. For this purpose, the present studies focus on investigation on thermal residual stresses in two SiC-ceramic matrix composite sys￾tems reinforced with carbon fiber (C/SiC) and silicon carbide fiber (SiC/SiC). Three different methods of experimental measurement, analytical calculation, and theoretical prediction were conducted to quantify thermal residual stress in the C/SiC, and then the ob￾tained results were compared with that in the SiC/SiC. Agreement between and applicability of these methods to the present com￾posite systems were concerned. Relationships between the TRS state and macroscopic mechanical properties of the composites (e.g. first matrix cracking stress) are discussed. 0266-3538/$ - see front matter 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.compscitech.2008.08.015 * Tel.: +86 29 88494616; fax: +86 29 88494620. E-mail address: phdhuimei@yahoo.com. Composites Science and Technology 68 (2008) 3285–3292 Contents lists available at ScienceDirect Composites Science and Technology journal homepage: www.elsevier.com/locate/compscitech