Abstract
Fatigue limit stress is a key design parameter for the structure fatigue design of composite materials. In this paper, a micromechanical fatigue limit stress model of fiber-reinforced ceramic-matrix composites (CMCs) subjected to stochastic overloading stress is developed. The fatigue limit stress of different carbon fiber-reinforced silicon carbide (C/SiC) composites (i.e., unidirectional (UD), cross-ply (CP), 2D, 2.5D, and 3D C/SiC) is predicted based on the micromechanical fatigue damage models and fatigue failure criterion. Under cyclic fatigue loading, the fatigue damage and fracture under stochastic overloading stress at different applied cycle numbers are characterized using two parameters of fatigue life decreasing rate and broken fiber fraction. The relationships between the fatigue life decreasing rate, stochastic overloading stress level and corresponding occurrence applied cycle number, and broken fiber fraction are analyzed. Under the same stochastic overloading stress level, the fatigue life decreasing rate increases with the occurrence applied cycle of stochastic overloading, and thus, is the highest for the cross-ply C/SiC composite and lowest for the 2.5D C/SiC composite. Among the UD, 2D, and 3D C/SiC composites, at the initial stage of cyclic fatigue loading, under the same stochastic overloading stress, the fatigue life decreasing rate of the 3D C/SiC is the highest; however, with the increasing applied cycle number, the fatigue life decreasing rate of the UD C/SiC composite is the highest. The broken fiber fraction increases when stochastic overloading stress occurs, and the difference of the broken fiber fraction between the fatigue limit stress and stochastic overloading stress level increases with the occurrence applied cycle.
Highlights
Ceramic-matrix composites (CMCs) possess high specific strength and specific modulus, high temperature resistance, and have already been applied on hot section components of commercial aero engines [1,2,3]
Matrix cracking, interface debonding, interface wear, and fiber fracture occur with the applied cycle, and these fatigue damage mechanisms degrade the mechanical performance of fiber-reinforced ceramic-matrix composites (CMCs) [5,6,7]
At applied cycles Ns = 10, 102, 103, 104, and 105, the broken fiber fraction increases from Pf = 0.03153, 0.04397, 0.11358, 0.1795, and 0.22527 under σlimit = 348 MPa to Pf = 0.03261, 0.04547, 0.11731, 0.18516, and 0.23215; when stochastic overloading stress σs = 355 MPa occurs at applied cycles Ns = 10, 102, 103, 104, and 105, the broken fiber fraction increases to Pf = 0.03546, 0.04941, 0.12704, 0.19983, and 0.24996; 4, Materials
Summary
Ceramic-matrix composites (CMCs) possess high specific strength and specific modulus, high temperature resistance, and have already been applied on hot section components of commercial aero engines [1,2,3]. Matrix cracking, interface debonding, interface wear, and fiber fracture occur with the applied cycle, and these fatigue damage mechanisms degrade the mechanical performance of fiber-reinforced CMCs [5,6,7]. Stochastic overloading stress may occur due to a special operation condition of the aero engine, which can affect the internal fatigue damage evolution and Materials 2020, 13, 3304; doi:10.3390/ma13153304 www.mdpi.com/journal/materials. In the developed micromechanical model, the effect of stochastic of stochastic overloading stress on fatigue limit stress has not been considered. A micromechanical fatigue limit stress model of fiber-reinforced CMCs subjected a micromechanical fatigue limitThe stress model of fiber-reinforced. The fatigue limit stress for different carbon fiber-reinforced reinforced silicon carbide (C/SiC) composites is predicted based on the micromechanical fatigue silicon carbide (C/SiC).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
