Testing and Modeling of Creep Behavior of Different Fiber Content and Type Single-Tow CVI-SiC <sub>f</sub>/SiC Minicomposites

Abstract

The understanding of creep deformation in high-temperature SiCf /SiC composites is essential in order to better predict stress-redistribution and life-limiting scenarios under high temperature and stress conditions. One area that warrants further investigation is the effect of constituent content and type on creep behavior. Therefore, this study evaluated the tensile creep behavior of different fiber volume fraction pristine and precracked Hi-Nicalon, Hi-Nicalon Type S, and Tyranno ZMI SiC fiber reinforced minicomposites with boron nitride (BN) interphase and chemical vapor infiltrated silicon carbide (CVI-SiC) matrix. Creep tests were performed in air at 1200°C for pristine minicomposites and some minicomposites that were pre-cracked. Precracking stresses were determined from room temperature monotonic tensile tests with acoustic emission monitoring. A single fiber tow minicomposite can be considered the basic architectural feature of woven and laminate ceramic matrix composites (CMCs). The minicomposite creep damage behavior represents the creep behavior of 0° fiber tows in the axial loading direction of a macrocomposite or component. A bottom-up creep damage characterization and modeling approach was applied where creep parameters of the different minicomposite constituents were obtained separately at 1200° C. Next, a theoretical model based on the rule of mixtures was derived to model the fibers and matrix creep-time-dependent stress redistribution and fiber volume fraction effect on load transfer. Fiber and matrix creep parameters, load transfer model results, and developed numerical model methodology were used to construct a creep strain model to predict creep damage evolution of the different fiber type and content minicomposites, which was used to model the creep behavior of Hi-Nicalon and Hi-Nicalon Type S SiC fiber-reinforced minicomposites. This study demonstrates a testing methodology and modeling approaches for use in screening, developing, and improving new generation ceramic matrix composites.