J.A. DiCarlo et al. Appl Math. Comput. 152(2004)473-481 fiber-reinforced SiC matrix composites [1, 2]. Since these SiC/SiC composites are still in their infancy in terms of selecting and demonstrating the optimum fiber, interphase, and matrix constituents, there currently exists a strong need for studies that mechanistically analyze and predict the fracture- limited enve lope of thermostructual capability provided by currently available constituents Thus the objective of this paper is to present mechanistic models concerning the high-temperature stress-rupture behavior of SiC fibers and Sic/Sic com posites of current technical interest. Since the time-dependent fracture of these materials is controlled by creep-induced flaw growth, these models are based on key experimental observations made on the creep-rupture behavior for various SiC fiber types. These observations are important not only because the fibers are the primary structural constituents controlling ultimate composite rupture, but also because SiC fibers display microstructures and fracture be- havior representative of SiC matrices, which can also carry structural loads Sic/SiC composites 2. SiC fiber creep-rupture In terms of providing good thermomechanical reinforcement capability for SiC/SiC composites, small-diameter SiC fiber types with low oxygen content, such as the non-stoichiometric (C/Si>)Hi-Nicalon fiber from Nippon Car- bon and the stoichiometric(C/SiN I)Sylramic fiber from Dow Corning, have many desirable physical and chemical properties [3, 4]. For this reason, con- siderable creep-rupture property data exist for these two fiber types not only as single fibers [3-8], multifilament tows[9, 10], and woven fabric pieces [ll],but so as reinforcement for Sic/Sic composites with various types of Sic ma trices [12-15]. For example, Fig. I shows typical creep strain versus time curves ④F140c cREEPsTRAIN TIME. HRS Fig. 1. Typical creep curves for Sic fibers tested under high-temperature stress-rupture conditionsfiber-reinforced SiC matrix composites [1,2]. Since these SiC/SiC composites are still in their infancy in terms of selecting and demonstrating the optimum fiber, interphase, and matrix constituents, there currently exists a strong need for studies that mechanistically analyze and predict the fracture-limited enve￾lope of thermostructual capability provided by currently available constituents. Thus the objective of this paper is to present mechanistic models concerning the high-temperature stress-rupture behavior of SiC fibers and SiC/SiC com￾posites of current technical interest. Since the time-dependent fracture of these materials is controlled by creep-induced flaw growth, these models are based on key experimental observations made on the creep-rupture behavior for various SiC fiber types. These observations are important not only because the fibers are the primary structural constituents controlling ultimate composite rupture, but also because SiC fibers display microstructures and fracture be￾havior representative of SiC matrices, which can also carry structural loads in SiC/SiC composites. 2. SiC fiber creep-rupture In terms of providing good thermomechanical reinforcement capability for SiC/SiC composites, small-diameter SiC fiber types with low oxygen content, such as the non-stoichiometric (C/Si >1) Hi-Nicalon fiber from Nippon Car￾bon and the stoichiometric (C/Si
1) Sylramic fiber from Dow Corning, have many desirable physical and chemical properties [3,4]. For this reason, con￾siderable creep-rupture property data exist for these two fiber types not only as single fibers [3–8], multifilament tows [9,10], and woven fabric pieces [11], but also as reinforcement for SiC/SiC composites with various types of SiC ma￾trices [12–15]. For example, Fig. 1 shows typical creep strain versus time curves 0 10 20 30 40 50 0.0 0.5 1.0 1.5 2.0 2.5 TIME, HRS 1400C 270 MPa AIR : Sylramic : Hi-Nicalon. : Ultra SCS : Nicalon : SCS-6 C R E E P S T R A I N, % Fr R. Fr A D D B B E C A C E Fig. 1. Typical creep curves for SiC fibers tested under high-temperature stress-rupture conditions. 474 J.A. DiCarlo et al. / Appl. Math. Comput. 152 (2004) 473–481