《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_j.1744-7402.2008.02331.x[1]

./. Appl. Ceram. Technol, 612/151-163(2009) DO:10.J11.1747402.2008.02331.x Applied Ceramic Technolog ceramic Product Development and Commercialization Design Guidelines for In-Plane Mechanical Properties of SiC Fiber-Reinforced Melt-Infiltrated SiC Composites Ohio Aerospace Institute, Cleveland, Ohio 44142 Vijay V.Pt Materials and Simulation Technical Center, Goodrich Corporation, Brecksville, Ohio 44141 In-plane tensile stress-strain, tensile creep, and after-creep retained tensile properties of melt- infiltrated SiC-SiC com- posites reinforced with different fiber types were evaluated with an emphasis on obtaining simple or first-order microstructural design guidelines for these in-plane mechanical properties. Using the minimatrix approach to model stress-strain behavior and he results of this study, three basic general design criteria for stress and strain limits are formulated, namely a design stress limit, a design total strain limit, and an after-creep design retained strength limit. It is shown that these criteria can be useful for Introduction for composite designers and fabricators who often have to weigh the benefits of cost savings, for example, a less Woven silicon carbide fiber-reinforced melt- infil- expensive fiber, with performance targets demanded by rated(MD)silicon carbide matrix composites are an application. Constituent-based and fiber-architec- considered to be important enabling materials for ture-based design models need to be developed to as- composites(CMC); however, even within that subset, given application. To validate these models, composite onsiderable variations in thermomechanical properties property data are needed over wide variations in con- are possible depending on the composite constituent stituent compositions, geometries, and content. A con- materials, geometries, and content. This is important siderable amount of data has been generated on composites with a wide variation in fber fraction and fiber architectures for the Sylramic-iBn (Syl-iBN)fiber- ork was financially supported by both internal Goodrich and NASA Supers reinforced MI composite system. 4 ./- These results .grams as well as a partially reimbursable Space Act Agreement between Goodrich and have enabled the development of simple constituent based and fiber-architecture- based relationships that can an Ceramic guide designers, fabricators, and end users in predicting

Design Guidelines for In-Plane Mechanical Properties of SiC Fiber-Reinforced Melt-Infiltrated SiC Composites Gregory N. Morscher* Ohio Aerospace Institute, Cleveland, Ohio 44142 Vijay V. Pujar Materials and Simulation Technical Center, Goodrich Corporation, Brecksville, Ohio 44141 In-plane tensile stress–strain, tensile creep, and after-creep retained tensile properties of melt-infiltrated SiC–SiC com￾posites reinforced with different fiber types were evaluated with an emphasis on obtaining simple or first-order microstructural design guidelines for these in-plane mechanical properties. Using the minimatrix approach to model stress–strain behavior and the results of this study, three basic general design criteria for stress and strain limits are formulated, namely a design stress limit, a design total strain limit, and an after-creep design retained strength limit. It is shown that these criteria can be useful for designing components for high-temperature applications. Introduction Woven silicon carbide fiber-reinforced melt-infil￾trated (MI) silicon carbide matrix composites are considered to be important enabling materials for high-temperature turbine1,2 applications. MI matrix SiC composites are a subset of SiC/SiC ceramic matrix composites (CMC); however, even within that subset, considerable variations in thermomechanical properties are possible depending on the composite constituent materials, geometries, and content.3–6 This is important for composite designers and fabricators who often have to weigh the benefits of cost savings, for example, a less expensive fiber, with performance targets demanded by an application. Constituent-based and fiber-architec￾ture-based design models need to be developed to as￾sess whether a given fiber type can meet the property requirements or the cost/performance objectives for a given application. To validate these models, composite property data are needed over wide variations in con￾stituent compositions, geometries, and content. A con￾siderable amount of data has been generated on composites with a wide variation in fiber fraction and fiber architectures for the Sylramic-iBN (Syl-iBN) fiber￾reinforced MI composite system.4,7–11 These results have enabled the development of simple constituent￾based and fiber-architecture-based relationships that can guide designers, fabricators, and end users in predicting Int. J. Appl. Ceram. Technol., 6 [2] 151–163 (2009) DOI:10.1111/j.1744-7402.2008.02331.x Ceramic Product Development and Commercialization This work was financially supported by both internal Goodrich and NASA Supersonic programs as well as a partially reimbursable Space Act Agreement between Goodrich and NASA. *gregory.n.morscher@nasa.gov r 2008 The American Ceramic Society

International Journal of Applied Ceramic Technolog-Morscher and pujar Vol.6,No.2,2009 properties such as matrix cracking stresses, ultimate ten- dustries, Tokyo, Japan). In addition, Table I also in- ile properties, and elevated temperature creep and cludes data from two panels with Hi-Nicalon Type- atigue properties Compared with other commercially (Nippon Carbon) fber that came from the earli far available fibers, the Syl-iBN fber evaluated in these study, 'which is included in this paper for property studies is very stable against high-temperature degrade stud comparison. For convenience, the composite panels are tion both during processing and service, and as a result referred to as xxx-Y where xxx is the reinforcing fiber is expected to be less prone to mechanical performance type(Syl-iBN, SA, HN, ZMI, HNS)and Y is the panel variation arising from process and/or application varia- number with that particular fiber tions. However, the Syl-iBN fiber is not commercially For in-plane mechanical property evaluation ailable readily, and the other fiber types may be more tensile specimens, 150 mm long and 12.6 mm wide attractive as they offer an overall cost advantage over the at the ends, were machined from the panels into a Syl-iBN fiber in meeting the necessary property require- dog-bone shape where the gauge section length and ments for some applications. width were approximately 25 and 10 mm, respectively The purpose of this study was to assess the in-plane The length of each specimen was aligned as close as mechanical performance of 2D 0/90 MI composites possible with one of the two orthogonal fiber directions, (oriented in one of the orthogonal fiber directions) commonly referred to as the 0 direction. The ends of forced with different commercially available polycrys- the tensile bars were encased in a wire mesh to alleviate line SiC-based fibers. The fber types evaluated in this grip stresses and bending moments at and near the udy included (1) the Tyranno ZMI fiber,(2)the Nicalon fiber, (3)the Tyranno SA-3 fiber, and(4) performed along one of the two orthogonal fiber direc the Syl-iBN fiber. In this order, the fiber types typically tions. Room-temperature tensile tests were performed increase in modulus ance. high-tempe using a universal testing machine (Model 8562, capability, and acquisition cost. In addition, MI com- Instron, Canton, MA). Specimens were loaded at a con- posite data reported previously for the Hi-Nicalon stant rate of 4 kN/min. Two clip-on strain gauges(2.5% ype-S fiber, another commercially available high-mod- max strain) were attached, one on each face, and the lus SiC fiber type, are also included in this paper for average of the two strain gauges was used for determin- ing the strain values for the tests. Unload-reload inter ruptions were also performed, usually at least two, in order to determine the residual stress in the composite Experimental Procedure matrIX Modal acoustic emission(AE) was monitored dur- fiber types were produced by 0o ting of four different ing the room-temperature tensile tests. A fracture wave Several fiber preforms consi symmetric lay-up of detector was used with wide- band pass frequency sen- eight plies of 2D-woven five-harness satin fabric with sors(50-2000 kHz), both from Digital Wave Corpo fiber content balanced in the two orthogonal directions. tion(Model B1025, Englewood, CO). Two AE sensors The preforms were then interphase coated with a thin were placed on the face of the specimen, one on each layer of boron nitride by chemical vapor infiltration side of the gauge section, and approximately 50-60 mm CVD), followed by CVI SiC, slurry-cast SiC, and silicon from one another. The two AE sensors were synchro- MI, producing what is commonly referred to 4.5 from the same event at the same time if either sensor was nized, that is, both sensors would record the waveform the slurry-cast melt- infiltration matrix composite Table I lists the panels evaluated in this study, and the triggered. Events that occurred in the gauge section key constituent properties based on in-process panel(25 mm region of the extensometers)were sorted out data and measurements on different specimens from using a threshold voltage crossing technique.and each panel. The panels included (1)three panels rein- used for analysis according to the location of each event forced with Syl-iBN (NASA-treated Syl fiber produced based on the speed of sound of the extensional wave, by Dow Corning, Midland, Mr);(2)three panels with which was determined posttest from events that oc- the Tyranno SA(Ube Industries, Japan);(3)one panel curred between the sensors. .1 Typically, 70% of the with a Hi-Nicalon(Nippon Carbon, Tokyo, Japan); AE activity events occurred outside the gauge section and(4)two panels with the Tyranno ZMI (UBE In- and were not used in the aE analysis

properties such as matrix cracking stresses, ultimate ten￾sile properties, and elevated temperature creep and fatigue properties. Compared with other commercially available fibers, the Syl-iBN fiber evaluated in these studies is very stable against high-temperature degrada￾tion both during processing and service, and as a result is expected to be less prone to mechanical performance variation arising from process and/or application varia￾tions.6 However, the Syl-iBN fiber is not commercially available readily, and the other fiber types may be more attractive as they offer an overall cost advantage over the Syl-iBN fiber in meeting the necessary property require￾ments for some applications. The purpose of this study was to assess the in-plane mechanical performance of 2D 0/90 MI composites (oriented in one of the orthogonal fiber directions) re￾inforced with different commercially available polycrys￾talline SiC-based fibers. The fiber types evaluated in this study included (1) the Tyranno ZMI fiber, (2) the Hi-Nicalon fiber, (3) the Tyranno SA-3 fiber, and (4) the Syl-iBN fiber. In this order, the fiber types typically increase in modulus, creep resistance, high-temperature capability, and acquisition cost. In addition, MI com￾posite data reported previously5 for the Hi-Nicalon Type-S fiber, another commercially available high-mod￾ulus SiC fiber type, are also included in this paper for comparison. Experimental Procedure Several fiber preforms consisting of four different fiber types were produced by 0/90 symmetric lay-up of eight plies of 2D-woven five-harness satin fabric with fiber content balanced in the two orthogonal directions. The preforms were then interphase coated with a thin layer of boron nitride by chemical vapor infiltration (CVI), followed by CVI SiC, slurry-cast SiC, and silicon MI, producing what is commonly referred to as the slurry-cast melt-infiltration matrix composite.1,4,5 Table I lists the panels evaluated in this study, and the key constituent properties based on in-process panel data and measurements on different specimens from each panel. The panels included (1) three panels rein￾forced with Syl-iBN (NASA-treated Syl fiber produced by Dow Corning, Midland, MI6 ); (2) three panels with the Tyranno SA (Ube Industries, Japan); (3) one panel with a Hi-Nicalon (Nippon Carbon, Tokyo, Japan); and (4) two panels with the Tyranno ZMI (UBE In￾dustries, Tokyo, Japan). In addition, Table I also in￾cludes data from two panels with Hi-Nicalon Type-S (Nippon Carbon) fiber that came from the earlier study,5 which is included in this paper for property comparison. For convenience, the composite panels are referred to as xxx-Y where xxx is the reinforcing fiber type (Syl-iBN, SA, HN, ZMI, HNS) and Y is the panel number with that particular fiber. For in-plane mechanical property evaluation, tensile specimens, B150 mm long and 12.6 mm wide at the ends, were machined from the panels into a dog-bone shape where the gauge section length and width were approximately 25 and 10 mm, respectively. The length of each specimen was aligned as close as possible with one of the two orthogonal fiber directions, commonly referred to as the 01 direction. The ends of the tensile bars were encased in a wire mesh to alleviate grip stresses and bending moments at and near the pneumatic pressure grips. All tensile tests were performed along one of the two orthogonal fiber direc￾tions. Room-temperature tensile tests were performed using a universal testing machine (Model 8562, Instron, Canton, MA). Specimens were loaded at a con￾stant rate of 4 kN/min. Two clip-on strain gauges (2.5% max strain) were attached, one on each face, and the average of the two strain gauges was used for determin￾ing the strain values for the tests. Unload–reload inter￾ruptions were also performed, usually at least two, in order to determine the residual stress in the composite matrix.12 Modal acoustic emission (AE) was monitored dur￾ing the room-temperature tensile tests. A fracture wave detector was used with wide-band pass frequency sen￾sors (50–2000 kHz), both from Digital Wave Corpora￾tion (Model B1025, Englewood, CO). Two AE sensors were placed on the face of the specimen, one on each side of the gauge section, and approximately 50–60 mm from one another. The two AE sensors were synchro￾nized, that is, both sensors would record the waveform from the same event at the same time if either sensor was triggered. Events that occurred in the gauge section (25 mm region of the extensometers) were sorted out using a threshold voltage crossing technique7,13 and used for analysis according to the location of each event based on the speed of sound of the extensional wave, which was determined posttest from events that oc￾curred between the sensors.7,13 Typically, 70% of the AE activity events occurred outside the gauge section and were not used in the AE analysis. 152 International Journal of Applied Ceramic Technology—Morscher and Pujar Vol. 6, No. 2, 2009

wwceramics. org/ACT SiC Fiber-Reinforced MI SiC Composites 153 Table I. Composite Phy fber specimen Average f radius [ specimens] Average Average (um)per tow epcm (mm) (scatter) SYLiBN-1 Sylramic-iBN 5 226[1 0.352[11 0.1140.286 (+0.07/-0.19)(+0.014/-0.004) SYLiBN-2 Sylramic-iBN 5 0.386[10] 0.1570.287 (+0.14/-0.12)(+0.026/-0.022) SYLiBN-3 Sylramic-iB 5 800 1.93[10] 0.410[10 0.130.270 0.09 (+0.02/-0.018) SA-1 Tyranno SA3 5 8007.12.057 0.348[7] 0.1200.281 (+0.06/-0.12)(+0.02/-0.01) Tyranno SA3 5 5] 0.3625] 0.281 (+0.04/-0.05)( SA-3 yranno SA3 5 800 215[10 0.332[10 0.098 0.274 (+0.05/-0.08)(+0.006/-0.004) Hi-Nicalon 500 7.1 0.0390.227 (+0.1l/-0.13)(+0.012/-0.01) Tyranno ZMI 5.5 800 3.759 0.227 (+0.004/-0.006 Z-2 Tyranno ZMI 5.5 8.7 362{4] 0.292[4] 0.072 0.198 (+0.12/-0.14)(+0.01/-0.01) HNS-1 Hi-Nicalon S 6.5 5007.12.49团7] 0.3029 (+0.04/-0.09)(+0.012/-0.004) Hi-Nicalon S 6.5 50 217[9 0.3489] 0.040.21 (+0.08/-0.12)(+0.020/-0.018) The preforms were detooled after CVI SiC infiltration. Therefore, the volume of BN could not be measured volume of BN was estimated from average BN thickness measurements of polished specimens. The volume of Sic after CVI infiltration after subtracting the estimated weight of Bn and the known weights of the fibers for the p: i diret d rom lined from the weight gain The fiber. BN, and Cy SiC densities used were 3.05, 1.5, and 3.2 g/cm,, respectively Elevated temperature tensile -rupture tests Results were performed at 1200.C and 1315.C in ambient air on a different machine(Instron Model 5569), which had a resistance-heated MoSiz element furnace inserted into the center of the dog-bone section. The ends of the Table i lists the nominal and calculated values for tensile bars in these tests were also encased in a wire key properties of the constituents in each composite mesh, but the pneumatic grips were water cooled. A panel, based on in-process data and data measured contact extensometer with SiC contacting pins 25 mm on the final processed panels and test specimens apart from one another was used to measure strain at the Because the woven architectures for all panels were bal- edge of the specimen in the gauge section Displacement anced in fiber content in the two orthogonal directions, was measured with an LVDT that featured a maximum the fiber volume fraction in the tensile loading direc- strain capability of 1%. Before the elevated temperature tion, f o, was half of the total fiber volume. For this creep test, a tensile modulus measurement was made on study, fo was determined from the estimated total fiber each specimen over the stress range 5-50 MPa at room area in the loading direction divided by the measured physical area of the composite specimen in the

Elevated temperature tensile creep-rupture tests were performed at 12001C and 13151C in ambient air on a different machine (Instron Model 5569), which had a resistance-heated MoSi2 element furnace inserted into the center of the dog-bone section. The ends of the tensile bars in these tests were also encased in a wire mesh, but the pneumatic grips were water cooled. A contact extensometer with SiC contacting pins 25 mm apart from one another was used to measure strain at the edge of the specimen in the gauge section. Displacement was measured with an LVDT that featured a maximum strain capability of 1%. Before the elevated temperature creep test, a tensile modulus measurement was made on each specimen over the stress range 5–50 MPa at room temperature. Results Constituent Analyses Table I lists the nominal and calculated values for key properties of the constituents in each composite panel, based on in-process data and data measured on the final processed panels and test specimens. Because the woven architectures for all panels were bal￾anced in fiber content in the two orthogonal directions, the fiber volume fraction in the tensile loading direc￾tion, fo, was half of the total fiber volume. For this study, fo was determined from the estimated total fiber area in the loading direction divided by the measured physical area of the composite specimen in the gauge Table I. Composite Physical Properties Panel Fiber type Average fiber radius (lm) # of fibers per tow epcm Average specimen thickness (mm) Average f [# specimens] (scatter) Average fBN Average fCVI SiC SYLiBN-1 Sylramic-iBN 5 800 7.9 2.26 [11] 0.352 [11] 0.114 0.286 (10.07/0.19) (10.014/0.004) SYLiBN-2 Sylramic-iBN 5 800 7.9 2.05 [10] 0.386 [10] 0.157 0.287 (10.14/0.12) (10.026/0.022) SYLiBN-3 Sylramic-iBN 5 800 7.9 1.93 [10] 0.410 [10] 0.134 0.270 70.09 (10.02/0.018) SA-1 Tyranno SA3 5 800 7.1 2.05 [7] 0.348 [7] 0.120 0.281 (10.06/0.12) (10.02/0.01) SA-2 Tyranno SA3 5 800 7.1 1.97 [5] 0.362 [5] 0.126 0.281 (10.04/0.05) (70.008) SA-3 Tyranno SA3 5 800 7.1 2.15 [10] 0.332 [10] 0.098 0.274 (10.05/0.08) (10.006/0.004) HN Hi-Nicalon 6.85 500 7.1 3.05 [7] 0.274 [7] 0.039 0.227 (10.11/0.13) (10.012/0.01) Z-1 Tyranno ZMI 5.5 800 8.7 3.75 [9] 0.281 [9] 0.082 0.227 10.06 (10.004/0.006) Z-2 Tyranno ZMI 5.5 800 8.7 3.62 [4] 0.292 [4] 0.072 0.198 (10.12/0.14) (10.01/0.01) HNS-1 Hi-Nicalon S 6.5 500 7.1 2.49 [7] 0.302 [9] 0.04 0.25 (10.04/0.09) (10.012/0.004) HNS-2 Hi-Nicalon S 6.5 500 7.1 2.17 [9] 0.348 [9] 0.04 0.21 (10.08/0.12) (10.020/0.018) The preforms were detooled after CVI SiC infiltration. Therefore, the volume of BN could not be measured directly from weight gain. Instead, the volume of BN was estimated from average BN thickness measurements of polished specimens. The volume of SiC was determined from the weight gain after CVI infiltration after subtracting the estimated weight of BN and the known weights of the fibers for the panel preform. The fiber, BN, and CVI SiC densities used were 3.05, 1.5, and 3.2 g/cm3 , respectively. DiCarlo et al. 6 www.ceramics.org/ACT SiC Fiber-Reinforced MI SiC Composites 153

154 International Journal of Applied Ceramic Technolog-Morscher and pujar Vol.6,No.2,2009 section; that is, is shown for comparison. In Fig. 1, the hysteresis loops f o=(Nply N )(epcm/10)(R)/t(1) were removed for clarity, while Fig. 2 shows represen- tative stress-strain curves with the initial loops and the where Noly is the known number of plies in the lay-up attendant residual stress for the different com- (eight for all the tested in this study); N posite specimens. From these figures and Tables I and the nominal number of fibers per tow: epcm/10 is the II, there are some general fiber-related observations that known tow ends per centimeter of the 2D weave(i.e can be made concerning the as-fabricated number of fiber tows per centimeter) converted to mil specimens. First, as expected from composite theory, limeter; R is the nominal fiber radius in millimeter; and increasing the fiber volume fraction increased the com- t is the measured specimen thickness in millimeter. Ta- posite secondary modulus as well as the ultimate ble l lists the calculated values for the total fiber volume. strength and strain. Second, for the higher modulus fi- bers(Er 380 GPa), increasing the fibe er volume fraction Table I are the nominal N and R values for each iber also increased the composite initial elastic modulus type, as well as the specimen t values and lulus for the Mi matrix in the loading direction is lower than that of the fiber. Third, composite specimen Room-Temperature Stress-Strain Bebavior witb AE with the higher modulus fibers showed that the matrix was under a mild compressive stress(ig. 2 and Table The average room-temperature mechanical proper- ID); in contrast, specimens with approximately the same ties from the stress-strain tests are listed in Table I l, and fraction of the lower modulus fiber showed the matrix some representative stress-strain curves are shown in essentially under zero to a very mild tensile residual stress Fig. 1 for individual specimens from each composite Fourth, for approximately the same fiber fraction, the system. In addition, the stress-strain behavior of an lower modulus fibers exhibited higher composite ultimat HNS-2 composite specimen from Morscher and pujar strain,with the HNS panels being an exception Table Il. Composite Room Temperature Mechanical Properties Average A A UTS (MPa) 8(%) on fibers(GPa) 0.005% AE onset Residual [#RT spec] [ specimens] [ specimens] [#RT spec] offset stress stress stress catter (scatter (s catter (scatter) (MPa) (MPa) (MPa) SYLiBN-1 247 3 0.35{3] 1997[2] 194[3 (+0.007/-0.006)(+36/-32)(+0.04/-0.06(+79-143)(+6/-9) SYLiBN-2 271 2 465[2 0.47[2] 18l[2 189[2]-60[2 (±12) ±0.03 +16 +10 SYLiBN-3 238 1 4[ 0.45[ 176[]155[1]-45[1] SA-1254[ 358[1] 0.33[1] 2000[ 152[ 145[1-20[1 SA-2 236[1] 372[1] 0.34[ 2047[ 178[]138[1 15[ SA-3 230[1 334[l 978[ 178[] 135[1 -30[1] HN 244[7 3l1[ 0.79[7 2272[7] 1266]114团6-46 43/-31)(+17/-10)(+0.12/-0.04)(+208/-141)(+4/-5)(+12/-8)(+7/-8) 213[4] 279[3 0.95[3] 973[4] 111(485[4]+12[4] (+5/-3) 9-6(+0.04/-0.03)(+66/-35)(+7/-6(+10/-15)(+5/-9) 0.83[4] 179[4] 12/-6)(+0.02/-0.03)(+49-53)(+5/-4)(+11/-14)(+8/-7) 1*262[ [ 0.63[1] 2278[1 154[1]150 412[1 147[1 135

section; that is, fo ¼ ðNplyNfÞðepcm=10ÞðpR2 f Þ=t ð1Þ where Nply is the known number of plies in the lay-up (eight for all the composites tested in this study); Nf is the nominal number of fibers per tow; epcm/10 is the known tow ends per centimeter of the 2D weave (i.e., number of fiber tows per centimeter) converted to mil￾limeter; Rf is the nominal fiber radius in millimeter; and t is the measured specimen thickness in millimeter. Ta￾ble I lists the calculated values for the total fiber volume, f 5 2fo, for all specimens from each panel. Also listed in Table I are the nominal Nf and Rf values for each fiber type, as well as the specimen t values and specimen-to￾specimen scatter in these t values. Room-Temperature Stress–Strain Behavior with AE The average room-temperature mechanical proper￾ties from the stress–strain tests are listed in Table II, and some representative stress–strain curves are shown in Fig. 1 for individual specimens from each composite system. In addition, the stress–strain behavior of an HNS-2 composite specimen from Morscher and Pujar5 is shown for comparison. In Fig. 1, the hysteresis loops were removed for clarity, while Fig. 2 shows represen￾tative stress–strain curves with the initial loops and the attendant residual stress for the different com￾posite specimens. From these figures and Tables I and II, there are some general fiber-related observations that can be made concerning the as-fabricated composite specimens. First, as expected from composite theory,14 increasing the fiber volume fraction increased the com￾posite secondary modulus as well as the ultimate strength and strain. Second, for the higher modulus fi- bers (EfB380 GPa), increasing the fiber volume fraction also increased the composite initial elastic modulus. This is consistent with the hypothesis that the effective modulus for the MI matrix in the loading direction is lower than that of the fiber. Third, composite specimens with the higher modulus fibers showed that the matrix was under a mild compressive stress (Fig. 2 and Table II); in contrast, specimens with approximately the same fraction of the lower modulus fiber showed the matrix essentially under zero to a very mild tensile residual stress. Fourth, for approximately the same fiber fraction, the lower modulus fibers exhibited higher composite ultimate strain, with the HNS panels being an exception. Table II. Composite Room Temperature Mechanical Properties Panel Average E (GPa) [#RT spec] (scatter) Average UTS (MPa) [# specimens] (scatter) Average e (%) [# specimens] (scatter) Average stress on fibers (GPa) [#RT spec] (scatter) 0.005% offset stress (MPa) AE onset stress (MPa) Residual stress (MPa) SYLiBN-1 247 [3] 361 [3] 0.35 [3] 1997 [2] 194 [3] 192 [2] 60 [3] (10.007/0.006) (136/32) (10.04/0.06) (179/143) (16/ 9) 72 77 SYLiBN-2 271 [2] 465 [2] 0.47 [2] 2368 [2] 181 [2] 189 [2] 60 [2] (712) 737 70.03 775 74 716 710 SYLiBN-3 238 [1] 444 [1] 0.45 [1] 2210 [1] 176 [1] 155 [1] 45 [1] SA-1 254 [1] 358 [1] 0.33 [1] 2000 [1] 152 [1] 145 [1] 20 [1] SA-2 236 [1] 372 [1] 0.34 [1] 2047 [1] 178 [1] 138 [1] 15 [1] SA-3 230 [1] 334 [1] 0.30 [1] 1978 [1] 178 [1] 135 [1] 30 [1] HN 244 [7] 311 [7] 0.79 [7] 2272 [7] 126 [6] 114 [6] 4 [6] (143/31) (117/10) (10.12/0.04) (1208/141) (14/5) (112/8) (17/8) Z-1 213 [4] 279 [3] 0.95 [3] 1973 [4] 111 [4] 85 [4] 112 [4] (15/3) (19/ 6) (10.04/0.03) (166/35) (17/6) (110/15) (15/9) Z-2 202 [4] 261 [4] 0.83 [4] 1794 [4] 107 [4] 83 [4] 112 [4] (15/3) (112/6) (10.02/0.03) (149/53) (15/4) (111/14) (18/7) HNS-1 262 [1] 341 [1] 0.63 [1] 2278 [1] 154 [1] 150 20 HNS-2 232 [1] 412 [1] 0.60 [1] 2245 [1] 147 [1] 135 20 DiCarlo et al. 6 154 International Journal of Applied Ceramic Technology—Morscher and Pujar Vol. 6, No. 2, 2009

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