Push‐Out Tests on a New Silicon Carbide/Reaction‐Bonded Silicon Carbide Ceramic Matrix Composite

Abstract

Fiber push-out tests have been performed on a ceramic matrix composite consisting of Carborundum sintered SIC fibers, with a BN coating, embedded in a reaction-bonded SIC matrix. Analysis of the push-out data, utilizing the most complete theory presently available, shows that one of the fiber/coating/matrix interfaces has a low fracture energy (one-tenth that of the fiber) and a moderate sliding resistance T = 8 MPa. The debonded sliding interface shows some continuous but minor abrasion, which appears to increase the sliding resistance, but overall the system exhibits very clean smooth sliding. The tensile response of a fullscale composite is then modeled, using data obtained here and known fiber strengths, to demonstrate the good composite behavior predicted for this material.

Transformation Plasticity in (GdxDy1−x)PO4 Fiber Coatings During Fiber Push Out

“…40,41 Higher resolution TEM images show extensive microcracking and plastic deformation in individual grains (Figs. [10][11][12]. Regions with fine-grained, <200 nm grain size microstructure between larger particles with less deformation were prevalent.…”

“…A major concern is their high fiber push‐out/pull‐out stresses, typically ~70–200 MPa . These stresses contrast with 5–80 MPa typically measured or inferred for carbon and BN interphases . High pull‐out stress biases fiber failure toward shorter pull‐out lengths, which may slightly increase CMC strength, but at the expense of lower strain to failure and flaw tolerance, the most desirable CMC attributes .…”

“…[6][7][8] These stresses contrast with 5-80 MPa typically measured or inferred for carbon and BN interphases. [9][10][11] High pull-out stress biases fiber failure toward shorter pull-out lengths, which may slightly increase CMC strength, but at the expense of lower strain to failure and flaw tolerance, the most desirable CMC attributes. 12,13 Optimal pull-out stresses are not well-defined and will depend on the CMC application.…”

Determining the shear properties of the PyC/SiC interface for a model TRISO fuel

“…b Coefficient of thermal expansion. an interfacial crack, i.e., interfacial debonding [10][11][12]. Fig.…”

“…Additionally, it would be difficult to determine an actual crack path of multi-layered interface material, which may propagate at both the BPyC/ IPyC and the IPyC/SiC interfaces. Currently, the only viable relevant tests for measuring the interfacial shear properties are the single fiber push-in and push-out tests, most widely used in the mechanical characterization of the fiber/matrix interface for the composite system [8][9][10][11][12][13][14][15].…”