Mechanical Properties of Two Plain‐Woven Chemical Vapor Infiltrated Silicon Carbide‐Matrix Composites

Abstract

The elastic and inelastic properties of a chemical vapor infiltrated (CVI) SiC matrix reinforced with either plainwoven carbon fibers (C/SiC) or SiC fibers (SiC/SiC) have been investigated. It has been investigated whether the mechanics of a plain weave can be described using the theory of a cross-ply laminate, because it enables a simple mechanics approach to the nonlinear mechanical behavior. The influences of interphase, fiber anisotropy, and porosity are included. The approach results in a reduction of the composite system to a fiber/matrix system with an interface. The tensile behavior is described by five damage stages. C/SiC can be modeled using one damage stage and a constant damage parameter. The tensile behavior of SiC/SiC undergoes four damage stages. Stiffness reduction due to transverse cracks in the transverse bundles is very different from cross-ply behavior. Compressive failure is initiated by interlaminar cracks between the fiber bundles. The crack path is dictated by the bundle waviness.For SiC/SiC, the compressive behavior is mostly linear to failure. C/SiC exhibits initial nonlinear behavior because of residual crack openings. Above the point where the cracks close, the compressive behavior is linear. Global compressive failure is characterized by a major crack oriented at a certain angle to the axial loading. In shear, the matrix cracks orientate in the principal tensile stress direction (i.e., 45°to the fiber direction) with very high crack densities before failure, but only SiC/SiC shows significant degradation in shear modulus. Hysteresis is observed during unloading/reloading sequences and increasing permanent strain.

Multiscale Modeling of Advanced Materials for Damage Prediction and Structural Health Monitoring

“…Following cool-down, loading the specimen in tension caused the damage to progress further, contributing to the nonlinear tensile behavior of the C/SiC composite. The results from the simulation were plotted with the experimental results from Jacobsen and Brøndsted (2001), as seen in Figure 2.11. To determine if the as-produced mechanical state of the composite was accurately predicted, the initial tensile modulus was compared to experimental data from Jacobsen and Brøndsted (2001) and Shuler et al (1993).…”

“…The initial tensile modulus obtained from the thermoelastic simulation was ~107.5 GPa. Experimental moduli of ~113.5 and ~100.0 GPa were obtained by Jacobsen and Brøndsted (2001) and Shuler et al (1993), respectively. A subsequent simulation was performed to determine the error that would result if the damage induced during the thermal cool-down of the plain weave CMC was ignored.…”

“…In this figure, the through-thickness discretization utilized by MSGMC to represent the woven tow architecture is evident; the four cells in the thickness direction are composed of either matrix subcells (red) or tow subcells (white with black lines representing tow fiber direction). The specific CMC under investigation is manufactured through densification of the carbon fiber preform via a chemical vapor infiltration (CVI) process, which follows the coating of the carbon fibers with a pyrolytic carbon (PyC) interphase, also performed via CVI (Jacobsen and Brøndsted, 2001). Since the carbon fibers are susceptible to corrosion at elevated temperatures, the PyC interphase offers increased corrosion resistance while also serving as a toughening mechanism through crack deflection, fiber/matrix debonding, and fiber pullout (Lamouroux et al, 1993).…”

“…The extreme stiffness, strength, and toughness, as well as nonbrittle failure of advanced CMCs make them an ideal choice over traditional materials for many aerospace applications, such as for components used in the hot section of turbine engines, rocket nozzles, and thermal protection systems (Inghels and Lamon, 1991;Camus, Guillaumat, and Baste, 1996;El Bouazzaoui, Baste, and Camus, 1996;Jacobsen and Brøndsted, 2001;Murthy, Gyekenyesi, and Mital, 2004;Aboudi, 2011;Goldberg, 2012;Goldsmith et al, 2014). Additionally, CMCs offer oxidation and creep resistance and thermal shock stability at elevated temperatures.…”

Improvement in the Specific Strength by Arranging Closed Pores in Fully Densified Zirconia Ceramics

“…Consequently, many nonlinear strengthening or toughening mechanisms have been proposed. [1][2][3][4][5][6] One of the most extreme examples is a SiC-SiC composite, [7][8][9][10][11] for which the strength or toughness is improved substantially, although the dispersoid is the same as the matrix (D ¼ M).…”