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