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Under cyclic fatigue loading, hysteresis loops appear in fiber-reinforced ceramic-matrix composites (CMCs) due to composite's internal damage mechanisms. Loading/unloading inverse tangent modulus (ITMs) of the hysteresis loops reflect the composite's internal damage state and can be used an effective tool to monitor composite's fatigue damage evolution and fracture. In this paper, characterization of cyclic fatigue hysteresis loops of CMCs using ITMs are investigated. Loading/unloading ITMs are derived using a micromechanical hysteresis constitutive model considering fatigue damage mechanisms of matrix cracking, interface debonding, wear and slip, and fiber's failure. Relationships between composite's fatigue hysteresis loops, ITMs and interface slip state (i.e., interface reverse slip ratio (IRSR) and interface new slip ratio (INSR)) are established. Experimental fatigue hysteresis loops, ITMs, and IRSR/INSR of cross-ply SiC/CAS and SiC/MAS composites from the literature are predicted, and the effects of fiber's volume fraction, matrix crack spacing, and interface debonding energy on composite's fatigue hysteresis loops, ITMs, and IRSR/INSR are analyzed. [ABSTRACT FROM AUTHOR]

To ensure the reliability and safety of ceramic-matrix composites (CMCs) hot-section components used in the aero engines, it is necessary to perform the strain response of CMCs at intermediate temperatures (600 to 1000 °C) under stress-rupture with stochastic loading. In this paper, the strain response of SiC/SiC composite under stress-rupture with stochastic load at intermediate temperatures is investigated. Multiple damage mechanisms of matrix cracking, interface debonding and oxidation, and fiber's oxidation and fracture are considered. Matrix crack spacing, interface oxidation and debonding length, fiber's broken probability, and intact fiber's stress are determined using micromechanical damage models. Experimental strain response and internal damage evolution of SiC/SiC composite under constant and stochastic stress are predicted. Effects of stochastic stress level and stochastic time, material properties, damage state and environment temperature on composite's strain response and stress-rupture life are discussed. When stochastic stress level and environment temperature increase, the composite's strain at the stochastic stress increases, the time for the interface complete debonding and oxidation decreases, and the stress-rupture life decreases. [ABSTRACT FROM AUTHOR]

In this paper, the cyclic fatigue hysteresis of carbon fiber reinforced silicon carbide (C/SiC) and SiC/SiC ceramic–matrix composites with different fiber preforms at room and elevated temperatures is investigated. The evolution of fatigue hysteresis dissipated energy versus applied cycle number for unidirectional C/SiC (σ max = 240 MPa at room temperature and σ max = 250 MPa at 800℃ in air atmosphere), cross-ply C/SiC (σ max = 105 MPa at room temperature and 800℃ in air atmosphere), 2D C/SiC (σ max = 387 and 425 MPa at room temperature), 2.5D C/SiC (σ max = 180 MPa at room temperature, σ max = 140 MPa at 800℃ in air atmosphere, and σ max = 230 MPa at 600℃ in inert atmosphere), 2D SiC/SiC (σ max = 130 MPa at 600℃, 800℃, and 1000℃ in inert atmosphere, σ max = 80 MPa at 1000℃ in air atmosphere, σ max = 100 MPa at 1000℃ in steam atmosphere, σ max = 140 MPa at 1200℃ in air and in steam atmospheres, σ max = 90, 120 MPa at 1300℃ in air atmosphere), and 3D SiC/SiC (σ max = 100 MPa at 1300℃ in air atmosphere) is analyzed. The change rate of the fatigue hysteresis dissipated energy between C/SiC and SiC/SiC composites is compared. The fatigue hysteresis dissipated energy decreases with applied cycle number for unidirectional, and cross-ply C/SiC composite at 800℃ in air, and 2.5D C/SiC composite at 600℃ in inert; and the fatigue hysteresis dissipated energy increases with applied cycle number for 2.5D C/SiC composite at 800℃ in air, 2D SiC/SiC composite at 600℃, and 800℃ in inert. [ABSTRACT FROM AUTHOR]

A theoretical model is developed to study the fiber debonding and pull-out in hybrid-fiber-reinforced brittle-matrix composites. By adopting the shear-lag model which includes the matrix shear deformation in the bonding region and friction in the debonding region, the relationship between the pull-out length and the debonding length of fiber is obtained by treating the interface debonding as a particular crack propagation problem along the interface. The interface debonding criterion for the hybrid-fiber-reinforced composites is obtained by applying the energy release rate relation in an interface debonding process. The analysis is applied to hybrid carbon/glass fiber-reinforced epoxy composites, and the theoretical results have a reasonable agreement with the experimental data. The hybrid effect is studied and the effect of material parameters is discussed. [ABSTRACT FROM AUTHOR]

The effect of matrix cracking on hysteresis behavior of cross-ply ceramic matrix composites is investigated in the present analysis. The cracking of cross-ply ceramic composites was classified into five modes, where cracking mode 3 and mode 5 involve matrix cracking and fiber/matrix interface debonding in 0° ply. The matrix crack space and interface debonded length are obtained by matrix statistical cracking model and fracture mechanics interface debonding criterion. Based on the damage mechanisms of fiber sliding relative to matrix in the interface debonded region, the unloading interface reverse slip length and reloading interface new slip length of cracking mode 3 and mode 5 are determined by the fracture mechanics approach. The hysteresis loops of four different cases for cracking mode 3 and mode 5 are derived respectively. The hysteresis loss energy as a function of interface shear stress of mode 3 and mode 5 are analyzed. The theoretical results have been compared with experimental data of two different cross-ply ceramic composites. [ABSTRACT FROM PUBLISHER]

ABSTRACT: By the secondary development of a commercial finite element package, the present study simulates the simultaneous growth of interfacial debonding and matrix annular crack surrounding fiber of fiber reinforced composites under tension-tension cyclic load. Energy release rates are utilized in the Paris law to avoid concerning the singularity of crack tips. With the combination of finite element method and difference approximation, the authors program the degradation model of coefficient of friction, debond criterion, propagation law and loop of load process, and then the relationships between the parameters (such as the crack length and debond length) and number of cyclic load are obtained and discussed. The numerical results show that interaction of growth of two cracks plays an important role in fatigue damage of fiber reinforced composites. [ABSTRACT FROM AUTHOR]

Finite element micromechanical modelling of SCS-6 SiC fibre reinforced Ti-6A1-4V has been performed. The fibres have a relatively thick coating consisting of pyrolytic carbon and SiC. The mechanical and thermal properties are estimated by considering both components, among which the properties of pyrolytic carbon are highly anisotropic. The effects of the low stiffness and highly anisotropic coating have been ignored in most other studies on the same material. However, it is shown that the coating has a significant effect on the composite thermal residual stresses, elastic transverse tensile properties and interface debonding. Methods of estimating the interface tensile strength are proposed. The transverse loading-unloading-reloading behaviour of this material is modelled and compared with experimental results. Possible ways of improving the transverse properties of SCS-6/Ti-6-4 unidirectional composite are suggested. [ABSTRACT FROM PUBLISHER]