《复合材料 Composites》课程教学资源（学习资料）第五章陶瓷基复合材料_SiC-SiC-2.pdf_大学文库

opposites Science and Technology 70(2010)435-441 Contents lists available at ScienceDirect Composites Science and technology ELSEVIER journalhomepagewww.elsevier.com/locate/compscitech Correlation of elastic properties of melt infiltrated SiC/Sic composites to in situ properties of constituent phases Y. Gowayed,, G. Ojard R Miller U Santhosh, ]. Ahmad,R. John ersity, 311 W Magnolia Ave, AL 36849-5327, United States Pratt S Whitney, 400 Main Street, M/S 114-43, East Hartford, CT 06108, United States d Research Applications, Inc, 11772 Sorrento valley Rd, Suite 260, San Diego, CA 92121-1085, United States ARTICLE INFO ABSTRACT Article history: The ability to correlate the elastic properties of melt infiltrated Sic Sic composites to properties of con- eceived 14 July 2009 stituent phases using a hybrid Finite Element approach is examined and the influence of material internal Accepted 19 November 2009 vailable online 26 November 2009 esting was carried out in air at room temperature and 1204oC. Through-thickness compres odulus utilizing the stacked disk method was measured at room temperature. In situ moduli uent materials were experimentally evaluated using nano-indentation techniques at room temperature A Ceramic matrix composites A consistent relationship is observed between constituent properties and composite properties for in- A MI SiC/Sic blane normal and shear moduli and Poissons ratio at room temperature. However, experimental data or through-thickness compressive elastic modulus is lower than the calculated value. It is hypothesized B. In situ properties that the existence of voids inside the fiber tows and their collapse under compressive loads is the cause of Elastic properties such discrepancy. Estimates for the change in elastic moduli of constituent phases with temperature were obtained from literature and used to calculate the elastic properties of the composites at 1204C A reasonable correlation between the in-plane elastic moduli of the composite and the in situ elastic properties of constituent phases is observed. 2009 Elsevier Ltd. All rights reserved. 1 Introduction of each of these constituent phases are dependent on the composite manufacturing process limiting the ability to obtain properties of Ceramic matrix composites(CMC) are currently considered for distinctive"stand-alone"phases. Although each stand-alone phase applications in gas turbine engines as well as other high tempera- can be considered isotropic, the composite, as a whole, is aniso- ture applications. Barriers to their successful application include tropic due to the geometry and structure of its constituent phases the lack of knowledge of in situ properties of their constituent The alignment of fibers inside the fabric architecture initiates such phases and the correlation of these properties to as-manufactured anisotropy. The Bn and the Sic-CVI are deposited over the fibers/ omposite properties. The effect of voids and fabric architecture, as fabric further stressing the directional nature of the material prop material internal structure variables, add to complexity of such erties. This deposition leaves closed porosity inside the yarns. The correlation. Overcoming these barriers will provide confidence in composite is then infiltrated with SiC-SC and Si into the open inter- material design tools and help develop design procedures utilizing stices filling most of the remaining space and leaving some voids as the full range of 2D and 3D fabric architectures. open porosity. The large number of constituent phases, combined One of the most promising CMC materials is melt infiltrated ( Mi) with the internal structural features of the composite, outlines a SiC/SiC composites. During their manufacture, woven or braided compound relationship between the properties of constituent fabrics are coated with one or more layers of boron nitride to in- phases and the properties of the composite. rease the composite toughness and provide environmental prote To allow for the development of robust and efficient desig tion to the fibers [1, 2]. The matrix is introduced to the fabric in three tools, a systematic methodology is needed to elucidate the unde consecutive densification steps: (i)chemical vapor infiltration(Cvi) lying mechanisms of contribution of different phases to the com- of Sic, (ii)slurry cast(SC)of SiC, and (iii) melt infiltration( Mi)of a posite properties and consequently aid model development and silicon metal leaving some entrapped voids. Mechanical properties verification. Furthermore, since CMC materials will be primarily used in high temperature applications, the effect of temperature 4 Corres g author.Tel:+13348445496:ax:+13348444068 on each constituent phase needs to be isolated and investigated to understand its contribution to the overall composite behavior. 538/s- see front matter o 2009 Elsevier Ltd. All rights reserved. 0.1016 compscitech200911.016

Correlation of elastic properties of melt infiltrated SiC/SiC composites to in situ properties of constituent phases Y. Gowayed b,*, G. Ojard c , R. Miller c , U. Santhosh d , J. Ahmad d , R. John a a Air Force Research Laboratory, AFRL/RXLM, Wright-Patterson AFB, OH 45433, United States bDepartment of Polymer and Fiber Engineering, Auburn University, 311 W Magnolia Ave., AL 36849-5327, United States c Pratt & Whitney, 400 Main Street, M/S 114-43, East Hartford, CT 06108, United States d Research Applications, Inc., 11772 Sorrento Valley Rd, Suite 260, San Diego, CA 92121-1085, United States article info Article history: Received 14 July 2009 Received in revised form 4 November 2009 Accepted 19 November 2009 Available online 26 November 2009 Keywords: A. Ceramic matrix composites A. MI SiC/SiC C. Numerical modeling B. In situ properties C. Elastic properties C. Modeling abstract The ability to correlate the elastic properties of melt infiltrated SiC/SiC composites to properties of constituent phases using a hybrid Finite Element approach is examined and the influence of material internal features, such as the fabric architecture and intra-tow voids, on such correlation is elucidated. Tensile testing was carried out in air at room temperature and 1204 C. Through-thickness compressive elastic modulus utilizing the stacked disk method was measured at room temperature. In situ moduli of constituent materials were experimentally evaluated using nano-indentation techniques at room temperature. A consistent relationship is observed between constituent properties and composite properties for inplane normal and shear moduli and Poisson’s ratio at room temperature. However, experimental data for through-thickness compressive elastic modulus is lower than the calculated value. It is hypothesized that the existence of voids inside the fiber tows and their collapse under compressive loads is the cause of such discrepancy. Estimates for the change in elastic moduli of constituent phases with temperature were obtained from literature and used to calculate the elastic properties of the composites at 1204 C. A reasonable correlation between the in-plane elastic moduli of the composite and the in situ elastic properties of constituent phases is observed. 2009 Elsevier Ltd. All rights reserved. 1. Introduction Ceramic matrix composites (CMC) are currently considered for applications in gas turbine engines as well as other high temperature applications. Barriers to their successful application include the lack of knowledge of in situ properties of their constituent phases and the correlation of these properties to as-manufactured composite properties. The effect of voids and fabric architecture, as material internal structure variables, add to complexity of such correlation. Overcoming these barriers will provide confidence in material design tools and help develop design procedures utilizing the full range of 2D and 3D fabric architectures. One of the most promising CMC materials is melt infiltrated (MI) SiC/SiC composites. During their manufacture, woven or braided fabrics are coated with one or more layers of boron nitride to increase the composite toughness and provide environmental protection to the fibers [1,2]. The matrix is introduced to the fabric in three consecutive densification steps: (i) chemical vapor infiltration (CVI) of SiC, (ii) slurry cast (SC) of SiC, and (iii) melt infiltration (MI) of a silicon metal leaving some entrapped voids. Mechanical properties of each of these constituent phases are dependent on the composite manufacturing process limiting the ability to obtain properties of distinctive ‘‘stand-alone” phases. Although each stand-alone phase can be considered isotropic, the composite, as a whole, is anisotropic due to the geometry and structure of its constituent phases. The alignment of fibers inside the fabric architecture initiates such anisotropy. The BN and the SiC-CVI are deposited over the fibers/ fabric further stressing the directional nature of the material properties. This deposition leaves closed porosity inside the yarns. The composite is then infiltrated with SiC-SC and Si into the open interstices filling most of the remaining space and leaving some voids as open porosity. The large number of constituent phases, combined with the internal structural features of the composite, outlines a compound relationship between the properties of constituent phases and the properties of the composite. To allow for the development of robust and efficient design tools, a systematic methodology is needed to elucidate the underlying mechanisms of contribution of different phases to the composite properties and consequently aid model development and verification. Furthermore, since CMC materials will be primarily used in high temperature applications, the effect of temperature on each constituent phase needs to be isolated and investigated to understand its contribution to the overall composite behavior. 0266-3538/$ - see front matter 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.compscitech.2009.11.016 * Corresponding author. Tel.: +1 334 844 5496; fax: +1 334 844 4068. E-mail address: gowayya@auburn.edu (Y. Gowayed). Composites Science and Technology 70 (2010) 435–441 Contents lists available at ScienceDirect Composites Science and Technology journal homepage: www.elsevier.com/locate/compscitech

2. Experimental program 2.1. Materials, manufacturing and testing The material chosen for this study is the melt infiltrated SiC/SiC CMC system, which was initially developed under the Enabling Propulsion Materials Program (EPM) and is still under further refinement at NASA-Glenn Research Center (GRC). The Sylramic fiber used in this study was a stochiometric SiC fiber fabricated by DuPont with an average diameter of 10 lm bundled into tows of 800 fibers and sized with polyvinyl alcohol (PVA). Fibers were wound on spools and then woven into a balanced 5 harness satin (5-HS) weave at 20 ends per inch. An in situ Boron Nitride (iBN) treatment was performed on the weave (at NASA-GRC) to create a fine layer of BN on every fiber producing what is referred to as an iBN-Sylramic fiber. Eight layers of fabric were laid in a graphite tool with perforated holes and a BN layer doped with Si was introduced via a CVI process to provide a weak interface coatings on the fibers (the thickness of the Si-doped BN layer was 0.5 ± 0.2 lm). This step was followed by the introduction of a layer of SiC via CVI until the open porosity of the composite reached about 30%. SiC particulates were then slurry casted into the plate followed by melt infiltration of a Si alloy to arrive at a nearly full density plate. The composite plate at this time had around 2% open porosity. By measuring the weight gain after each process and using the density of each material, the volume fractions of the constituents were calculated as: fiber volume fraction of 36%, BN coat of 7.2%, SiC-CVI of 23%, SiC-SC of 17.7%, Si of 13.5% and a 2.6% total porosity. Fig. 1 shows micrographs of the manufactured SiC/SiC composite plates and their constituent phases. After fabrication, panels were interrogated by pulse echo ultrasound (10 MHz) and film X-ray. As shown in Fig. 2, there was no Fig. 1. Micrographic images of MI SiC/SiC. 436 Y. Gowayed et al. / Composites Science and Technology 70 (2010) 435–441

Y. Gowayed et aL/ Composites Science and Technology 70(2010)435-441 分AA Fig. 2(a) Film X-ray image of panel and(b) through transmitted ultrasound image of typical panel The white circle and the red dot are a tungsten marker placed on the anel. For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article. indication of any delamination and no large scale porosity was the stress-strain curve was reached, stress-strain data are fitted noted in the panels. In addition, each panel had two tensile bars ex to determine the modulus. validation of the stacked disks experi- tracted and tested at room temperature. All samples tested failed mental approach was carried out by using a rod of machineable above a 0.3% strain to failure requirement set to screen for process- monolithic glass ceramic MACOR [4]. A 28 mm long piece of the ing induced embrittlement. Since no anomalies were noted, these rod was tested in compression at room temperature to obtain panels were accepted into the experimental effort. the compressive elastic modulus which was determined to be Tensile tests were performed per EPM testing standards(equiv- 68.9 GPa. A series of disks were machined out of the rod with the alent to ASTM C1359)at room temperature and 1204C as a pos- same dimensions to be used in the testing of the CMC materiaL. sible operating temperature. Typical stress-strain curves are Testing was conducted at room temperature and the modulus of shown in Fig. 3. The elastic modulus was calculated as the slope the stacked disks was determined to be 66.0 GPa. This agreement of the stress-strain curve in the linear region between 13.79 and between the compressive elastic modulus of the rod and the 55. 16 MPa(2-8 Ksi) Strain gages were fitted to evaluate the Pois- stacked disks shows that the stacked disk method can be accepted sons ratio at room temperature. The shear modulus was deter- as a sound testing method ine/ s g biaxial extensometry on samples machined out of Nano-indentation experiments were carried out on the cross- nels at 45 and shear analysis was done consistent with section of samples to measure the in situ elastic moduli of the dis- D3518. The curves were fitted between 6.90 and crete phases of the composite [5]. This work was performed at 27.58 MPa(1-4 Ksi)in the linear shear region to be consistent with room temperature using a Nano-Indenter Il at Oak Ridge National the tensile modulus calculation Laboratory. The modulus was determined by analysis of the load A compressive test was performed on a series of stacked disks displacement recorded during nano-indentation as well as the va- to determine the through-thickness modulus at room temperature lue of the elastic modulus of the indentor [ 6]. The value of the elas in conformance with a recently developed technique [3. In this tic modulus of the iBN-Sylramic fiber measured using nano- experiment, each individual disk is ground flat to remove asperities indentation was found to be similar to that evaluated using a and enough disks are machined for a 2.54 cm extensometer to be tow testing techniques 5. A Hysitron's Tribo-lndenter was used flagged onto the sample. Through the center of each disk a hole to evaluate the elastic properties of the relatively compliant BN is machined so that a graphite rod could be inserted to hold the phase due to its ability to apply ultra-low load levels(a 400 HN stack in place and eliminate disk movement during initial loading. load was used in this case). Additionally, the Tribo-Indenter al- The rod is machined short so that it would not see any load that lowed in situ imaging by scanning probe microscopy as shown in could affect the measured modulus. Even though the disks are ma- Fig. 4. Up to the authors'knowledge this is the first time that chined flat, there is a typical initial compliance to the stack that the Young,s Modulus of the boron Nitride is measured within a had to be overcome by sufficient load. Once the linear region of systematic procedure to evaluate the in situ elastic moduli of con- stituent phases. The result of this nano-indentation work is listed aperature 3. Analysis of experimental data Nano-indentation experiments for constituent phases the in situ elastic modulus of the fiber as 394.9 GPa. the as 20.27 GPa. the sic-CVI as 438. 8 GPa. the sic-Sc as 405.6 GPa and the mi si metal as 164. 9 gPa as listed in table 1. results for the in situ modulus for the fiber, the Sic phases and the Si metal did not change much from their values for stand-alone phases. Up to the authors'knowledge, the value for the in situ modulus of the bn coat has not been previously reported in literature. Typical stress-strain curves at room temperature and 1204C for the Sic/SiC composite material are shown in Fig 3. It strain o0o 0s 0, seen for both temperatures, that at low load levels there is a linear Fig 3. Tensile stress-strain curves at room temperature and 1204 is followed by a knee in the curve and another linear region

indication of any delamination and no large scale porosity was noted in the panels. In addition, each panel had two tensile bars extracted and tested at room temperature. All samples tested failed above a 0.3% strain to failure requirement set to screen for processing induced embrittlement. Since no anomalies were noted, these panels were accepted into the experimental effort. Tensile tests were performed per EPM testing standards (equivalent to ASTM C1359) at room temperature and 1204 C as a possible operating temperature. Typical stress–strain curves are shown in Fig. 3. The elastic modulus was calculated as the slope of the stress–strain curve in the linear region between 13.79 and 55.16 MPa (2–8 Ksi). Strain gages were fitted to evaluate the Poisson’s ratio at room temperature. The shear modulus was determined using biaxial extensometry on samples machined out of the panels at 45 and shear analysis was done consistent with ASTM D3518. The curves were fitted between 6.90 and 27.58 MPa (1–4 Ksi) in the linear shear region to be consistent with the tensile modulus calculation. A compressive test was performed on a series of stacked disks to determine the through-thickness modulus at room temperature in conformance with a recently developed technique [3]. In this experiment, each individual disk is ground flat to remove asperities and enough disks are machined for a 2.54 cm extensometer to be flagged onto the sample. Through the center of each disk a hole is machined so that a graphite rod could be inserted to hold the stack in place and eliminate disk movement during initial loading. The rod is machined short so that it would not see any load that could affect the measured modulus. Even though the disks are machined flat, there is a typical initial compliance to the stack that had to be overcome by sufficient load. Once the linear region of the stress–strain curve was reached, stress–strain data are fitted to determine the modulus. Validation of the stacked disks experimental approach was carried out by using a rod of machineable monolithic glass ceramic MACOR [4]. A 28 mm long piece of the rod was tested in compression at room temperature to obtain the compressive elastic modulus which was determined to be 68.9 GPa. A series of disks were machined out of the rod with the same dimensions to be used in the testing of the CMC material. Testing was conducted at room temperature and the modulus of the stacked disks was determined to be 66.0 GPa. This agreement between the compressive elastic modulus of the rod and the stacked disks shows that the stacked disk method can be accepted as a sound testing method. Nano-indentation experiments were carried out on the crosssection of samples to measure the in situ elastic moduli of the discrete phases of the composite [5]. This work was performed at room temperature using a Nano-Indenter II at Oak Ridge National Laboratory. The modulus was determined by analysis of the load– displacement recorded during nano-indentation as well as the value of the elastic modulus of the indentor [6]. The value of the elastic modulus of the iBN-Sylramic fiber measured using nanoindentation was found to be similar to that evaluated using a tow testing techniques [5]. A Hysitron’s Tribo-Indenter was used to evaluate the elastic properties of the relatively compliant BN phase due to its ability to apply ultra-low load levels (a 400 lN load was used in this case). Additionally, the Tribo-Indenter allowed in situ imaging by scanning probe microscopy as shown in Fig. 4. Up to the authors’ knowledge, this is the first time that the Young’s Modulus of the Boron Nitride is measured within a systematic procedure to evaluate the in situ elastic moduli of constituent phases. The result of this nano-indentation work is listed in Table 1. 3. Analysis of experimental data Nano-indentation experiments for constituent phases reported the in situ elastic modulus of the fiber as 394.9 GPa, the BN coat as 20.27 GPa, the SiC-CVI as 438.8 GPa, the SiC-SC as 405.6 GPa and the MI Si metal as 164.9 GPa as listed in Table 1. Results for the in situ modulus for the fiber, the SiC phases and the Si metal did not change much from their values for stand-alone phases. Up to the authors’ knowledge, the value for the in situ modulus of the BN coat has not been previously reported in literature. Typical stress–strain curves at room temperature and 1204 C for the SiC/SiC composite material are shown in Fig. 3. It can be seen for both temperatures, that at low load levels there is a linear relationship between stress and strain until around 170 MPa. This is followed by a knee in the curve and another linear region. Fig. 2. (a) Film X-ray image of panel and (b) through transmitted ultrasound image of typical panel. The white circle and the red dot are a Tungsten marker placed on the panel. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) 0 100 200 300 400 500 600 0 0.001 0.002 0.003 0.004 0.005 0.006 Stress (MPa) Strain Room Temperature 1204ºC Fig. 3. Tensile stress–strain curves at room temperature and 1204 C. Y. Gowayed et al. / Composites Science and Technology 70 (2010) 435–441 437

Y. Gowayed et aL/ Composites Science and Technology 70(2010)435-441 numerical solutions. Most of these models lack the detailed geom- stability study was conducted and a mesh of three hexahedra brick etry that can represent the composites internal fabric architecture elements per yarn in each direction was chosen. This resulted in a hich may have a strong impact on the mechanical behavior of the 225 eight-noded hexahedra brick elements per unit cell of the fab- textile composites. Quantification of elastic properties requires an ric architecture as shown in Fig. 6. Results of the calculations are understanding of the spatial location of yarns and the contribution listed in Table 2 for composites with and without voids. Since no of each composite constituent to the composite overall respon information is available on the exact location of the voids the To this end, a geometric model previously developed was used to upper bound values are for the case when all the voids exist in a evaluate the spatial location of yarns [10 for the composite under spherical form in the matrix away from the fibers, while the lower consideration. The knowledge of yarn location and matrix distribu- bound values are when all the voids are within yarns and at yarn tion provide basis for application of numerical mechanical models, cross-over points [15]. It can be seen from the table that estimates such as traditional finite element analysis(FEA), to evaluate the for in-plane tensile moduli (Ex and Ey), shear modulus( Gxy) and omposite properties. Nevertheless, the use of traditional FEA is Poissons ratio(vxy)using properties of constituent materials are limited by the complexity of the fabric geometry and associated very close to the experimental data hing problems, and requires a large number of elements. a typ- The value for the through-thickness modulus calculated by the ical plain weave fabric would require a few thousands elements to numerical model is approximately 50% higher than the experimen- model [7]. It is expected that other complex fabrics, such as 3D fab- tal value as shown in Table 2. But it can also be observed that the rics, would require hundreds of thousands of elements. To solve experimental value of the compressive modulus is lower than the this problem a hybrid FEa was used [11 where a unit cell of the uli of major composite constituents listed in Table 1 which is fabric architecture is identified and divided into hexahedra brick not a typical result. The effect of the compressive stress on the elements with fiber and matrix around each integration point. modulus value, in the stacked disks experiment, is evident from Material homogenization was carried out around each integration Fig. 5. The modulus showed a linear increase with the increase in oint to define the anisotropic material response 12. The bound compressive stress until it reached a plateau at a stresses higher ary conditions of the unit cell, dictated by the assumptions of than 300 MPa. This can be due to the existence of asperities be- repeatability and continuity, helped reduce the size of the stiffness tween the disks being flattened by the stress or the existence of latrix. A virtual work technique was used to calculate the elastic voids inside the yarns, or both. Micrographic images of yarns properties of the unit cell. Both geometric and mechanical FEa cross-sections showed intra-yarn voids between fibers of approxi- odels were combined and integrated using a visual C++ computer algorithm 5. Correlation of in situ properties of constituent phases to mposite properties Properties of constituent materials obtained from nano-inden- tation and information on fabric architecture. obtained from the weaver, were used as input in the numerical model presented above to calculate the elastic properties of the composites Calcu lated values of elastic properties of the composite were compared to experimental data to examine the consistency of the relation- ship between constituent properties and the composite properties. Such comparison would also present, if any, the impact of internal features like voids on the relationship. Material properties of ents are listed in Table 1 along with their relative volume fractions. the poisson 's ratios of constit uents were obtained from[13 and the shear moduli were calcu- lated using the elasticity equation E=2G(1+v), assuming all constituent phases are locally isotropic; where e is the elastic mod ulus. g is the shear modulus and y is the poisson's ratio To reduce the complexity of the problem imposed by the large number of constituents, an initial step was carried out by dividing the composite into two parts - coated fibers comprised of iBN-Syl- ramic fibers coated with Si-doped BN, and a matrix formed from Fig. 6. Geometric model and FE mesh of 5-hamess satin woven MI SIC/SiC SiC-CVI, SiC-SC and Si Properties of the coated fibers were calcu lated using the micromechanics model developed in [14 The micrographic images shown in Fig. 1 reveal a shiny material (Si) mixed with another grayish color material Sic-SC)in the place be- Table 2 ween the yarns with some dark areas that are most probably Experimental data and results of numerical model for elastic properties at room voids. Based on this micrograph, an in-series model was used to temperature (GPal calculate the combined properties of Sic-SC and si(iso-stress mod Property Without voids With 2.6% void el)and an in-parallel model (iso-strain model)was used to com- Upper bound bine these properties with the properties of Sic-CVl. Utilizing this approach the matrix properties were calculated as Em=329.3 GPa. Ex Ey 2748±1034 2138 1300±3.39 Gm=139.1 GPa, and Vm=0. 182: where the subscript m denotes the 9584±0 m temperature elastic properties of the composite were cal- 0.14 0.127±0003 0.188 using the numerical model described above. A numerical

numerical solutions. Most of these models lack the detailed geometry that can represent the composites internal fabric architecture which may have a strong impact on the mechanical behavior of the textile composites. Quantification of elastic properties requires an understanding of the spatial location of yarns and the contribution of each composite constituent to the composite overall response. To this end, a geometric model previously developed was used to evaluate the spatial location of yarns [10] for the composite under consideration. The knowledge of yarn location and matrix distribution provide basis for application of numerical mechanical models, such as traditional finite element analysis (FEA), to evaluate the composite properties. Nevertheless, the use of traditional FEA is limited by the complexity of the fabric geometry and associated meshing problems, and requires a large number of elements. A typical plain weave fabric would require a few thousands elements to model [7]. It is expected that other complex fabrics, such as 3D fabrics, would require hundreds of thousands of elements. To solve this problem a hybrid FEA was used [11] where a unit cell of the fabric architecture is identified and divided into hexahedra brick elements with fiber and matrix around each integration point. Material homogenization was carried out around each integration point to define the anisotropic material response [12]. The boundary conditions of the unit cell, dictated by the assumptions of repeatability and continuity, helped reduce the size of the stiffness matrix. A virtual work technique was used to calculate the elastic properties of the unit cell. Both geometric and mechanical FEA models were combined and integrated using a visual C++ computer algorithm. 5. Correlation of in situ properties of constituent phases to composite properties Properties of constituent materials obtained from nano-indentation and information on fabric architecture, obtained from the weaver, were used as input in the numerical model presented above to calculate the elastic properties of the composites. Calculated values of elastic properties of the composite were compared to experimental data to examine the consistency of the relationship between constituent properties and the composite properties. Such comparison would also present, if any, the impact of internal features like voids on the relationship. Material properties of constituents are listed in Table 1 along with their relative volume fractions. The Poisson’s ratios of constituents were obtained from [13] and the shear moduli were calculated using the elasticity equation {E = 2G (1 + m)}, assuming all constituent phases are locally isotropic; where E is the elastic modulus, G is the shear modulus and m is the Poisson’s ratio. To reduce the complexity of the problem imposed by the large number of constituents, an initial step was carried out by dividing the composite into two parts – coated fibers comprised of iBN-Sylramic fibers coated with Si-doped BN, and a matrix formed from SiC-CVI, SiC-SC and Si. Properties of the coated fibers were calculated using the micromechanics model developed in [14]. The micrographic images shown in Fig. 1 reveal a shiny material (Si) mixed with another grayish color material (SiC-SC) in the place between the yarns with some dark areas that are most probably voids. Based on this micrograph, an in-series model was used to calculate the combined properties of SiC-SC and Si (iso-stress model) and an in-parallel model (iso-strain model) was used to combine these properties with the properties of SiC-CVI. Utilizing this approach the matrix properties were calculated as Em = 329.3 GPa, Gm = 139.1 GPa, and mm = 0.182; where the subscript m denotes the matrix. Room temperature elastic properties of the composite were calculated using the numerical model described above. A numerical stability study was conducted and a mesh of three hexahedra brick elements per yarn in each direction was chosen. This resulted in a 225 eight-noded hexahedra brick elements per unit cell of the fabric architecture as shown in Fig. 6. Results of the calculations are listed in Table 2 for composites with and without voids. Since no information is available on the exact location of the voids, the upper bound values are for the case when all the voids exist in a spherical form in the matrix away from the fibers, while the lower bound values are when all the voids are within yarns and at yarn cross-over points [15]. It can be seen from the table that estimates for in-plane tensile moduli (Ex and Ey), shear modulus (Gxy) and Poisson’s ratio (mxy) using properties of constituent materials are very close to the experimental data. The value for the through-thickness modulus calculated by the numerical model is approximately 50% higher than the experimental value as shown in Table 2. But it can also be observed that the experimental value of the compressive modulus is lower than the moduli of major composite constituents listed in Table 1 which is not a typical result. The effect of the compressive stress on the modulus value, in the stacked disks experiment, is evident from Fig. 5. The modulus showed a linear increase with the increase in compressive stress until it reached a plateau at a stresses higher than 300 MPa. This can be due to the existence of asperities between the disks being flattened by the stress or the existence of voids inside the yarns, or both. Micrographic images of yarns cross-sections showed intra-yarn voids between fibers of approxiFig. 6. Geometric model and FE mesh of 5-harness satin woven MI SiC/SiC composite. Table 2 Experimental data and results of numerical model for elastic properties at room temperature (GPa). Property Without voids With 2.6% voids Experiment Lower bound Upper bound Ex, Ey 269.5 224.3 263.0 274.8 ± 10.34 Ez 213.8 203.0 209.0 130.0 ± 3.39 Gxy 92.39 88.46 90.39 95.84 ± 0.6 Gxz, Gyz 90.12 86.46 87.77 – mxy 0.14 0.161 0.146 0.127 ± 0.003 mxz, myz 0.195 0.188 0.204 – Y. Gowayed et al. / Composites Science and Technology 70 (2010) 435–441 439

40 Y. Gowayed et aL/Composites Science and Technology 70(2010)435-441 Fig. 7. ohic images showing voids(in red)between fibers inside the yarnYarn edges are identified in green. (For interpretation of the references to color in this the reader is referred to the web version of this article 6. Conclusions mental data and results of numerical model for elastic properties at 1204C The ability to consistently correlate the elastic properties of melt infiltrated Sic/SiC 5-HS composite panels from information Property Without voids With 2.6% voids Experiment on their constituent properties and the effect of internal features, Lower bound Upper bound like voids and fabric architecture, on the accuracy of such correla 233.7±19.51 tion were examined. Composite panels were manufactured their in-plane elastic moduli, through-thickness compressive mod- 8288 86.53 84.12±28 ulus and in-plane Poissons ratio at room temperature and 1204C were evaluated. Nano-indentation experiments were conducted to 0.186 0.193 evaluate the in situ moduli of constituent materials at room tem perature. Properties of constituents at 1204C were estimated from literature. A micromechanics numerical model using hybrid FEA of a repeat unit cell was used to correlate in situ constituent mately 10% of the yarn cross-section area as shown in Fig. 7. Voids properties to composite properties at room temperature and nay have been an important player in the reduction of modulus. a 1204C possible scenario would be that as the compressive stress in A reasonable correlation was found for the in-plane tensile and eased, the voids collapsed exhibiting an apparent decrease in shear moduli and Poissons ratio at room temperature and 1204C the value of the through-thickness modulus. If this is true, then Experimental values for the through-thickness modulus utilizing the phenomenon of voids collapse was not captured by the voids the stacked disks testing approach was lower than the calculated model [15] leading to a discrepancy between model calculations value. The testing method showed a dependence of the value of and experimental data. The model was not able to capture the the through-thickness modulus on the level of compressive stress change in the internal structure of the composite and micrographic images showed voids between fibers inside Data available in literature on the effect of temperature on var- yarns. There is a possibility that the voids played a role in reducing ious composite constituents was used to evaluate the change of the value of the through-thickness modulus as compared to the elastic properties of the composite from room temperature to calculated value 1204C. Elastic constants of silicon were reported to depreciate It can be concluded that it is possible to find a consistent corre- with temperature in a linear fashion up to around 1220c lation between properties of constituent phases and properties of a [16, 17]. The elastic moduli of covalent carbides were reported in complex composite system like MI SiC/Sic composite, especially [18 to also follow a linear depreciation pattern Using room tem- for in-plane properties. The model used in this study was effec- perature data and depreciation rates obtained from these sources, tively able to model the yarn undulation of the fabric architecture the properties of the matrix at 1204C were calculated as and calculate the value of the in-plane moduli with a reasonable Em=302.9 GPa, Gm=127. 9 GPa, and vm=0. 182. Data for the change accuracy. On the other hand, correlation for the compressive of properties of Si-doped BN with temperature was not available in through-thickness modulus, as an out of plane property, was not literature, and was assumed to be constant. The reduction of as successful possibly due to the collapse of intra-yarn voids. The mechanical properties of iBN-Sylramic fibers with temperature model was not able to capture the change in the internal structure as also not available according to personal communications with of the material the manufacturer. Change of properties of other Sic fibers such as Hi-Nicalon and CG Nicalon are available [19) and was similar Acknowledgments values of covalent Sic [18]. This data was used in the current anal- ysis for the iBN-Sylramic fiber. Table 3 shows a comparison be- The authors are grateful to Laura Riester and Dr. Edgar Lara- tween experimental data and modeling values. It can be seen Curzio of ORNL for the help and discussions about nano- indenta- that results of the numerical model show reasonable estimates tion. The authors would also like to acknowledge discussions with for the value of the composite in-plane tensile and shear moduli Terry Barnett of Southern research Institute in regards to various test methods

mately 10% of the yarn cross-section area as shown in Fig. 7. Voids may have been an important player in the reduction of modulus. A possible scenario would be that as the compressive stress increased, the voids collapsed exhibiting an apparent decrease in the value of the through-thickness modulus. If this is true, then the phenomenon of voids collapse was not captured by the voids model [15] leading to a discrepancy between model calculations and experimental data. The model was not able to capture the change in the internal structure of the composite. Data available in literature on the effect of temperature on various composite constituents was used to evaluate the change of elastic properties of the composite from room temperature to 1204 C. Elastic constants of silicon were reported to depreciate with temperature in a linear fashion up to around 1220 C [16,17]. The elastic moduli of covalent carbides were reported in [18] to also follow a linear depreciation pattern. Using room temperature data and depreciation rates obtained from these sources, the properties of the matrix at 1204 C were calculated as Em = 302.9 GPa, Gm = 127.9 GPa, and mm = 0.182. Data for the change of properties of Si-doped BN with temperature was not available in literature, and was assumed to be constant. The reduction of mechanical properties of iBN-Sylramic fibers with temperature was also not available according to personal communications with the manufacturer. Change of properties of other SiC fibers such as Hi-Nicalon and CG Nicalon are available [19] and was similar to values of covalent SiC [18]. This data was used in the current analysis for the iBN-Sylramic fiber. Table 3 shows a comparison between experimental data and modeling values. It can be seen that results of the numerical model show reasonable estimates for the value of the composite in-plane tensile and shear moduli depreciation with temperature. 6. Conclusions The ability to consistently correlate the elastic properties of melt infiltrated SiC/SiC 5-HS composite panels from information on their constituent properties and the effect of internal features, like voids and fabric architecture, on the accuracy of such correlation were examined. Composite panels were manufactured and their in-plane elastic moduli, through-thickness compressive modulus and in-plane Poisson’s ratio at room temperature and 1204 C were evaluated. Nano-indentation experiments were conducted to evaluate the in situ moduli of constituent materials at room temperature. Properties of constituents at 1204 C were estimated from literature. A micromechanics numerical model using hybrid FEA of a repeat unit cell was used to correlate in situ constituent properties to composite properties at room temperature and 1204 C. A reasonable correlation was found for the in-plane tensile and shear moduli and Poisson’s ratio at room temperature and 1204 C. Experimental values for the through-thickness modulus utilizing the stacked disks testing approach was lower than the calculated value. The testing method showed a dependence of the value of the through-thickness modulus on the level of compressive stress and micrographic images showed voids between fibers inside yarns. There is a possibility that the voids played a role in reducing the value of the through-thickness modulus as compared to the calculated value. It can be concluded that it is possible to find a consistent correlation between properties of constituent phases and properties of a complex composite system like MI SiC/SiC composite, especially for in-plane properties. The model used in this study was effectively able to model the yarn undulation of the fabric architecture and calculate the value of the in-plane moduli with a reasonable accuracy. On the other hand, correlation for the compressive through-thickness modulus, as an out of plane property, was not as successful possibly due to the collapse of intra-yarn voids. The model was not able to capture the change in the internal structure of the material. Acknowledgments The authors are grateful to Laura Riester and Dr. Edgar LaraCurzio of ORNL for the help and discussions about nano-indentation. The authors would also like to acknowledge discussions with Terry Barnett of Southern Research Institute in regards to various test methods. Fig. 7. Micrographic images showing voids (in red) between fibers inside the yarn. Yarn edges are identified in green. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) Table 3 Experimental data and results of numerical model for elastic properties at 1204 C (GPa). Property Without voids With 2.6% voids Experiment Lower bound Upper bound Ex, Ey 246.6 204.4 246.2 233.7 ± 19.51 Ez 200.7 190.6 200.4 – Gxy 86.60 82.88 86.53 84.12 ± 2.8 Gxz, Gyz 84.67 81.22 84.60 – mxy 0.144 0.166 0.144 – mxz, myz 0.193 0.186 0.193 – 440 Y. Gowayed et al. / Composites Science and Technology 70 (2010) 435–441

Y. Gowayed et aL/ Composites Science and Technology 70(2010)435-441 The Materials Manufacturing Directorate, Air Force Research [7 Woo K, Whitcomb jGlobal/local finite element analysis for textile composites. retary for Energy Efficiency and Renewable Energy, Office of Free lomCAR and Vehicle Technology Program, as part of the High [10 Pastore G, Gowayed y, Cai y. Application of computer aided geometric Temperature Materials Laboratory User Program, Oak Ridge Na ional Laboratory managed by UT-Battelle, LLC for the US Depart-[ C Modification and application of a unit cell ment of Energy under Contract No DE-AC05-00OR22725. try model: modification Reference textile composites. J Compos Technol R [13]Mur d Hi-Nicalon, BN-interphase, Sic-matrix composite in air. J Am Ceram Soc conference on composite materials an restricted 00:83(6):1441-9 ocoa Beach Florida: 1999 [2 Linus U, Ogbuji T. A pervasi de of oxidative degradation in a Sic-Sic [14] Van Fo Fy GA. On the equation connecting the stresses and strains in glass omposite. J Am Ceram Soc 1998: 81(11): 2777-84 [3] Ojard G. Barnett T. Calomino A, Gowayed Y, Santhosh U. Ahmad J. et al. [15] Goway he effect of voids on the elastic properties of textile composites. Compos Technol Res 1997: 18(2): 168-73 Bornstien numerical data and functional [4] Ojard G, Barnett T, Calomino A, Gowayed Y, Santhosh U. Ahmad J. et al. relationships in science and technology. New series, vols. 17 and 22. Through thickness modulus(E33) of ceramic matrix composites: mechanical [17] Burenkov YuA, Nikanorov SP Sow Phys Solid State(USA)1974: 16: 963 [51 Ojard G. Rugg K, Riester L Gowayed Y, Colby M. Constituent properties [18] Graves GA Hecht NL Effects of environment on the mechanical behavior of determination and model verification for a ceramic matrix composite systems. Ceram Eng Sci Proc 2005: 26(2): 343-50. Ims Int& Li X Nanomechanical characterization of solid surfaces and thin [19] BodetR, Bourrat X, Lamon]. Naslain R. Tensile creep behaviour of a silicon later Rev 2003: 4s low oxygen content. J Mater Sci 1995: 30(3): 661-7

The Materials & Manufacturing Directorate, Air Force Research Laboratory under Contract F33615-01-C-5234 sponsored this work. Research work at ORNL was sponsored by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of FreedomCAR and Vehicle Technology Program, as part of the High Temperature Materials Laboratory User Program, Oak Ridge National Laboratory managed by UT-Battelle, LLC for the US Department of Energy under Contract No. DE-AC05-00OR22725. References [1] Morscher G, Hurst J, Brewer D. Intermediate-temperature stress rupture of a woven Hi-Nicalon, BN-interphase, SiC-matrix composite in air. J Am Ceram Soc 2000;83(6):1441–9. [2] Linus U, Ogbuji T. A pervasive mode of oxidative degradation in a SiC–SiC composite. J Am Ceram Soc 1998;81(11):2777–84. [3] Ojard G, Barnett T, Calomino A, Gowayed Y, Santhosh U, Ahmad J, et al. Through thickness modulus (E33) of ceramic matrix composites: mechanical test method development. Ceram Eng Sci Proc 2007;27(2):331–8. [4] Ojard G, Barnett T, Calomino A, Gowayed Y, Santhosh U, Ahmad J, et al. Through thickness modulus (E33) of ceramic matrix composites: mechanical test method confirmation. Ceram Eng Sci Proc 2008;28:109–13. [5] Ojard G, Rugg K, Riester L, Gowayed Y, Colby M. Constituent properties determination and model verification for a ceramic matrix composite systems. Ceram Eng Sci Proc 2005;26(2):343–50. [6] Bhushan B, Li X. Nanomechanical characterization of solid surfaces and thin films. Int Mater Rev 2003;48(3):125. [7] Woo K, Whitcomb J. Global/local finite element analysis for textile composites. J Compos Mater 1997;28(14):1305–21. [8] Chou TW, Wang JM, Ma CL. Fiber inclination model of three-dimensional textile structural composites. J Compos Mater 1986;20:472–84. [9] Tarnopolski YM, Polyakov VA, Zhigun IG. Polym Mech 1973(5):853. [10] Pastore G, Gowayed Y, Cai YJ. Application of computer aided geometric modeling for textile structural composites. In: CADCOM 1989, vol. 45. Southampton (UK): Computational Mechanics Publications. [11] Gowayed Y, Pastore C, Howarth C. Modification and application of a unit cell continuum model to predict the elastic properties of textile composites. Composites: Part A 1996;27a(2):149. [12] Pastore C, Gowayed Y. A self-consistent fabric geometry model: modification and application of a fabric geometry model to predict the elastic properties of textile composites. J Compos Technol Res 1994;16(1):32–6. [13] Murthy P, DiCarlo J, Mital S. Characterizing the properties of a 5-H woven SiC/ SiC composite using CEMCAN/WCMC computer code. In: 23rd Annual conference on composite materials and structures (restricted sessions), Cocoa Beach, Florida; 1999. [14] Van Fo Fy GA. On the equation connecting the stresses and strains in glass reinforced plastics. Polym Mech 1965;1(2):110. [15] Gowayed Y. The effect of voids on the elastic properties of textile composites. Compos Technol Res 1997;18(2):168–73. [16] Hellwidge KH, editor. Landolt–Bornstien numerical data and functional relationships in science and technology. New series, vols. 17 and 22. Germany: Springer Verlag; 1979. [17] Burenkov YuA, Nikanorov SP. Sov Phys Solid State (USA) 1974;16:963. [18] Graves GA, Hecht NL. Effects of environment on the mechanical behavior of high-performance ceramics. Report No. UDR-TR-94-136. University of Dayton Research Institute; 1995. [19] Bodet R, Bourrat X, Lamon J, Naslain R. Tensile creep behaviour of a silicon carbide-based fibre with a low oxygen content. J Mater Sci 1995;30(3):661–7. Y. Gowayed et al. / Composites Science and Technology 70 (2010) 435–441 441

《复合材料 Composites》课程教学资源（学习资料）第五章 陶瓷基复合材料_SiC-SiC-2

《复合材料 Composites》课程教学资源（学习资料）第五章陶瓷基复合材料_SiC-SiC-2