Cyclic‐Fatigue Behavior of SiC/SiC Composites at Room and High Temperatures

Abstract

Tension‐tension cyclic‐fatigue tests of a two‐dimensional‐woven‐SiC‐fiber‐SiC‐matrix composite (SiC/SiC) prepared by chemical vapor infiltration (CVI) were conducted in air at room temperature and in argon at 1000°C. The cyclic‐fatigue limit (107 cycles) at room temperature was ∼160 MPa, which was ∼80% of the monotonic tensile strength of the composite. However, the fatigue limit at 1000°C was only 75 MPa, which was 30% of the tensile strength of the composite. No difference was observed in cyclic‐fatigue life at room temperature and at 1000°C at stresses >180 MPa; however, cyclic‐fatigue life decreased at 1000°C at stresses < 180 MPa. The fracture mode changed from fracture in 0° and 90° bundles at high stresses to fracture mainly in 0° bundles at low stresses. Fiber‐pullout length at 1000°C was longer than that at room temperature, and, in cyclic fatigue, it was longer than that in monotonic tension. The decrease in the fatigue limit at 1000°C was concluded to be possibly attributed to creep of fibers and the reduction of the sliding resistance of the interface between the matrix and the fibers.

Strength enhancement of 2D-SiCf/SiC composites after static fatigue at room temperature

“…Low τ values make the composite less sensitive to the nucleation of defects by decreasing both the stress concentrations and the load transfer from matrix to fibers. 2 Similar strength enhancements have been observed in C f /SiC and Hi-Nicalon-SiC f /Si,B,C composites. 3,4 This work is focused on the influence of the static fatigue during long periods of time (about 120 h) on the residual strength of Nicalon-SiC f /SiC composites and to determine if residual strength of the composites is linked to the previous fatigue damage.…”

“…2 The origin of this enhancement is not yet well understood, but the authors suggest that it could be related to a decrease of the fiber/matrix shear stress, τ. Low τ values make the composite less sensitive to the nucleation of defects by decreasing both the stress concentrations and the load transfer from matrix to fibers.…”

Temperature Dependence of Tensile Strength for a Woven Boron‐Nitride‐Coated Hi‐Nicalon™ SiC Fiber‐Reinforced Silicon‐Carbide‐Matrix Composite

“…This condition appears when the composite cools from the processing temperature to room temperature, as a result of the thermal expansion mismatch between the matrix and the fiber, which occurs because the CTE of the matrix is larger than that of the fiber. 23, 25 In the present study, the decrease in the interfacial shear stress is attributed to the relaxation of the clamping stress at the interface with an increase in test temperature.…”

Strength evolution of cyclic loaded LSI-based C/C-SiC composites

“…1. Most importantly, the initiation and propagation of cracks in the transverse fiber bundle can effectively relieve the thermal residual stress in the composites, which enable more fiber bundles to carry the applied load uniformly and simultaneously [17]. Fig.…”