Degradation of Continuous Fiber Ceramic Matrix Composites under Constant Load Conditions

Abstract

Ten different ceramic matrix composite (CMC) materials were subjected to a constant load and temperature in an air environment. Tests conducted under these conditions are often referred to as stressed oxidation or creep rupture tests. The stressed oxidation tests were conducted at a temperature of 1454°C at stresses of 69 MPa, 172 MPa and 50% of each material's ultimate tensile strength. The ten materials included such CMCs as C/SiC, SiC/C, SiC/SiC, SiC/SiNC and C/C. The time to failure results of the stressed oxidation tests will be presented. Much of the discussion regarding material degradation under stressed oxidation conditions will focus on C/SiC composites. Thermogravimetric analysis of the oxidation of fully exposed carbon fiber (T300) and of C/SiC coupons will be presented as well as a model that predicts the oxidation patterns and kinetics of carbon fiber tows oxidizing in a nonreactive matrix.

Mechanical and environmental models for ceramic matrix composites

“…In the interest of simplicity but without losing generality, in contrast to the experimental observations, the oxidation-assisted stressrupture prediction illustrated in Figure 5 exhibits an intrinsic nature of the typical creep strain response of the CMCs in stressed and oxidizing environments (e.g. see Halbig et al [8]). …”

Transient Creep Behavior of a Plain Woven SiC Fiber/SiC Matrix Composite

“…Furthermore a contribution of creep deformation to nonlinear behavior is significant at elevated temperature (6) - (9) . The present work investigates the transient creep behavior of a plain woven NUSK-CMC at elevated temperature.…”

Modeling the Environmental Effects on Carbon Fibers in a Ceramic Matrix at Oxidizing Conditions

“…When all factors relating to the material and environment are held constant and only temperature is changed in the range of 600°C to 1500°C, the effect of temperature on the reaction rate constant and diffusion coefficient in an oxygen environment can be realized. The reaction rate constant has a strong temperature dependence and can change by approximately three orders of magnitude while the diffusion coefficient only changes by three times across this temperature range [5]. Depending on the value of these two variables, the Sherwood number will have either a relatively high or relatively low value.…”