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Under cyclic fatigue loading, the stochastic stress occurs and affects the fatigue damage and failure of fiber-reinforced ceramic-matrix composites (CMCs). In this paper, combining the stress and cyclic-dependent fatigue damage mechanisms and models, the damage parameter of fiber’s breakage probability is adopted to characterize fatigue damage and failure in fiber-reinforced CMCs. Two stochastic load spectrums with increasing or decreasing stochastic stress level occurring at different applied cycle number are considered. Relationships between the composite’s fatigue life, stochastic load spectrum, fiber’s breakage probability, and fatigue life degradation rate are established. Experimental fatigue life of 1D unidirectional, 2D cross-ply, 2D plain-woven, 2.5D woven, and 3D braided C/SiC composites subjected to different stochastic load spectrums are predicted. The fatigue damage and failure of CMCs under stochastic load spectrum are affected by the fiber’s volume fraction along the loading direction (i.e., the high fiber’s volume fraction along the loading directional indicating the high resistance of fatigue damage and failure subjected to stochastic loading), the strength degradation caused by fabrication process (i.e., hot pressing, chemical vapor infiltration, etc.), and also the fiber’s preform. Among different fiber’s preforms, the fatigue life degradation rate is the highest for 2D cross-ply C/SiC composite and is the lowest for 2.5D woven C/SiC composite. The fatigue life degradation rate under stochastic load spectrum of increasing stochastic stress level is much higher than that under stochastic load spectrum with decreasing stochastic stress level except for 2D cross-ply C/SiC composite.

In this paper, the 3D needle-punched C/SiC composite was fabricated using the chemical vapor deposition and reactive infiltration method. Four different fiber preforms were formed using the needled...

Ceramic-matrix composites (CMCs) possess high specific strength and modulus at elevated temperature and have already been applied in hot-section components in commercial or military gas turbine engines. Due to low fracture strain in the brittle SiC ceramic, matrix microcracking occurs below the proportional limit stress (PLS). At elevated temperature, the opening of matrix microcracking affects the mechanical properties of CMCs when the oxygen or oxidative gas ingresses the composite through these cracks. To ensure the reliability, safety, and airworthiness level of CMCs components, it is necessary to understand the crack opening behavior of CMCs at elevated temperature. In this paper, a micromechanical approach is developed to predict the time-dependent crack opening behavior in SiC/SiC composite. Micro stress field in the different damage regions are obtained and the cracking opening displacement (COD) are calculated. Experimental CODs in SiC/SiC composite for different matrix crack lengths are predicted. Effects of composite material properties, stress level, and testing temperature on the time-dependent crack opening behavior in SiC/SiC composite are analyzed. Relationships between the cracking opening, composite’s constituent properties, stress level, and testing temperature are established. The analysis results can help the engineering designer better understanding the crack opening behavior in CMCs.

In this paper, the loading rate–dependent tensile damage and fracture behavior of fiber-reinforced ceramic-matrix composites (CMCs) are investigated. A micromechanical tensile constitutive model is developed considering multiple tensile damage mechanisms. A new parameter of the interface debonding rate is proposed to characterize the strain rate–dependent tensile damage evolution in fiber-reinforced CMCs. Experimental tensile stress-strain curves, composite’s tangent modulus, interface debonding ratio, and probability of fiber’s breakage in unidirectional SiC/CAS-II, 2D plain-woven CVI C/SiC and SiC/SiC, 2.5D woven CVI C/SiC, and 3D woven CVI and PIP SiC/SiC composites are predicted for different strain rates at room and elevated temperatures. Effects of fiber’s preforms, testing temperature, and fabrication method on the loading rate–dependent tensile damage and fracture behavior of fiber-reinforced CMCs are analyzed. Relationships between composite’s microstructure, mechanical behavior, and strain rate for different CMCs are established. The rate of interface debonding increased with increasing strain rate and was the highest for unidirectional SiC/CAS-II, and the lowest for 3D woven SiC/SiC, and the rate of interface debonding was independent of testing temperature. For unidirectional SiC/CAS-II and 2D plain-woven CVI SiC/SiC composites, when the loading rate increased, the proportional limit stress, tensile strength, and fracture strain increased; and, for 2.5D woven CVI C/SiC and 3D woven CVI SiC/SiC, when the loading rate increased, the proportional limit stress, composite tensile strength, and fracture strain decreased.

In this paper, a micromechanical fatigue life prediction method for fiber-reinforced ceramic-matrix composites subjected to stochastic overloading at room temperature is developed. Fatigue damage mechanisms in the matrix, interfaces, and fibers are characterized using different damage models. Relationships between the fatigue life and related degradation rate, stochastic overloading stress, and breakage of intact fibers are established. Experimental fatigue life of different C/SiC composites subjected to different stochastic overloading is predicted. For the same stochastic overloading condition, the degradation rate of fatigue life is the highest for cross-ply C/SiC composite, and the lowest for 2.5D C/SiC composite.

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.

In this paper, a micromechanical tension-compression fatigue hysteresis loops model of fiber-reinforced ceramic-matrix composites (CMCs) is developed. Upon unloading or reloading, the stress-strain of tension-compression fatigue hysteresis loops are divided into three different regions. Multiple micromechanical damage parameters of unloading transition stress, closure stress of the matrix cracking, compressive transition stress, complete compressive stress, and reloading transition stress are adopted to characterize the tension-compression stress-strain hysteresis loops. The characteristics of the tension-compression fatigue hysteresis loops of unidirectional SiC/CAS composite are analyzed for different material properties, damage stage, tensile fatigue peak stress, and compression fatigue valley stress. The experimental tension-tension and tension-compression fatigue stress-strain hysteresis loops of unidirectional SiC/CAS composite are predicted using the developed micromechanical models. Under low fatigue valley compressive stress, the tension-compression fatigue hysteresis loop exhibits no closure of matrix cracking; and under high fatigue valley compressive stress, the tension-compression fatigue hysteresis loops exhibit closure of matrix cracking, and complete compressive in the fiber and the matrix. However, the compressive valley stress has no effect on the values of matrix cracking closure stress, compressive transition stress, and complete compressive stress.

In this paper, stress rupture of fiber-reinforced ceramic-matrix composites (CMCs) subjected to different stochastic loading spectrums at intermediate temperatures (600 to 1000 °C) is investigated. Under stress rupture at stress level higher than the first matrix cracking stress, multiple damage mechanisms of matrix cracking, fiber/matrix interface debonding, interphase and fiber oxidation, and fiber fracture are considered to analyze evolution of composite strain. Four different stochastic loading spectrums are considered in the analysis of damage evolution and lifetime of fiber-reinforced CMCs under stress rupture loading. Relationships between stochastic loading stress, frequency, time, interface debonding and oxidation length, fiber failure probability, and stress rupture lifetime are established. Effects of stochastic loading stress and time, fiber volume, matrix crack spacing, interface debonding energy, interface shear stress, and temperature on composite strain, interface debonding and oxidation length, and the fiber failure probability versus time are analyzed. Experimental stress rupture strain and lifetime of SiC/SiC composite under constant stress and stochastic loading spectrums are predicted. When the stochastic loading stress, frequency, and temperature increase, the stress rupture lifetime and the time for the interface complete debonding and oxidation all decrease.

In this paper, a time-dependent vibration damping model of fiber-reinforced ceramic-matrix composites (CMCs) is developed. Considering time and temperature dependent interface damages of oxidation, debonding, and slip, the relationships between composite vibration damping, material properties, internal damages, oxidation duration and temperature are established. The effects of material properties, vibration stress, damage state, and oxidation temperature on time-dependent composite vibration damping and interface damages of C/SiC composite are discussed. The time-dependent composite vibration damping decreases with fiber volume, matrix crack spacing and interface shear stress, and increases with vibration stress. The experimental composite vibration damping and internal damages of 2D C/SiC composite for different oxidation duration t = 2, 5 and 10 h at elevated temperatures T = 700, 1000 and 1300 °C are predicted. When the oxidation duration was short (i.e., t = 2 h), the composite vibration damping decreased with temperature; however, when the oxidation duration was long (i.e., t = 5 and 10 h), the composite vibration damping decreased with temperature below 1000 °C, and increased with temperature to 1300 °C.

Under cyclic fatigue loading, cyclic-dependent damage mechanisms affect the vibration damping of fiber-reinforced ceramic-matrix composites (CMCs). In this paper, a cyclic-dependent vibration damping model of fiber-reinforced CMCs is developed. Combining cyclic-dependent damage mechanisms, damage models and dissipated energy model, relationships between composite vibration damping, cyclic-dependent damage mechanisms, vibration stress and applied cycle number are established. Effects of material properties and damage state on composite vibration damping are analyzed for different applied cycle number and vibration stress. Experimental composite vibration damping of 2D and 3D C/SiC composites without/with coating is predicted for different vibration frequencies and applied cycle number. With increasing applied cycle number, cyclic-dependent composite vibration damping increases due to the increase ratio of interface debonding and slip. When fiber volume and matrix cracking spacing increase, cyclic-dependent composite vibration damping decreases due to the decrease ratio of interface debonding and slip.

A micromechanical vibration damping model of fiber-reinforced ceramic–matrix composites is developed considering interface debonding. The relationship between the stress-dependent composite damping and interface debonding is established. Effects of material properties and damage-related parameters on the vibration damping of fiber-reinforced CMCs are discussed. Experimental vibration damping with interface debonding of C/SiC composites is predicted. When the vibration frequency increases from f = 1–5 Hz, the vibration damping decreases due to the increasing dynamic interfacial shear stress and low frictional dissipated energy in the debonding region. The composite vibration damping decreases with increasing fiber volume, matrix crack spacing and interface shear stress, and increases with fiber radius and fiber elastic modulus. When the interface debonding energy increases, the vibration damping decreases when the interface partial debonding and approaches the same value when the interface complete debonding, and the vibration stress for complete interface debonding increases.

In this paper, the damage accumulation and life prediction in fiber-reinforced ceramic-matrix composites (CMCs) subjected to thermomechanical fatigue (TMF) loading are investigated. The relationships between TMF damage mechanisms, fatigue hysteresis-based damage parameters, fraction of broken fiber, and applied cycles are established. Evolution of fatigue hysteresis dissipated energy, fatigue hysteresis modulus, fatigue peak strain, fatigue broken fiber fraction versus applied cycle curves, and the fatigue life S–N curves is analyzed. Damage accumulation and fatigue life of cross-ply silicon carbide/magnesium aluminosilicate composite under in-phase (IP)- and out-of-phase (OP)-TMF and isothermal fatigue (IF) loading are predicted. Under the same fatigue peak stress, the fatigue lifetime decreases from IF loading at 566°C to IF loading at 1,093°C, IP-TMF and OP-TMF. The TMF loading significantly reduced the fatigue lifetime of CMCs.

In this paper, the effect of pre-fatigue loading on tensile damage and fracture of fiber-reinforced ceramic-matrix composites (CMCs) is investigated using a micromechanical approach. Under cyclic fatigue loading, the fiber/matrix interface shear stress degrades with applied cycles due to the damage mechanism of the interface wear. The micro stress field of the damaged composite including matrix cracking, fiber/matrix interface debonding, and fiber failure is obtained for the fiber and the matrix axial stress and the fiber/matrix interface shear stress in the interface wear region, interface debonding region, and the interface bonding region, respectively. The fracture mechanics approach, stochastic matrix cracking model, and global load sharing (GLS) criterion are used to determine the interface debonding length, matrix cracking density, and fiber failure probability at higher applied stress level considering the damage mechanism of the interface wear. The effects of fiber volume, matrix cracking, fiber/matrix interface shear stress, fiber strength, pre-fatigue peak stress, and number of cycles on pre-fatigue tensile damage and fracture of SiC/SiC composites are analyzed. The experimental tensile damage and fracture of SiC/SiC composites with and without pre-fatigue loading are predicted for different interface properties.

In this paper, the temperature-dependent proportional limit stress (PLS) of SiC/SiC fiber-reinforced ceramic-matrix composites (CMCs) is investigated using the micromechanical approach. The PLS of SiC/SiC is predicted using an energy balance approach considering the effect of environment temperature. The relation between the environment temperature, PLS, and composite damage state is established. The effects of the fiber volume, interface properties, and matrix properties on the temperature-dependent PLS and composite damage state of SiC/SiC composite are analyzed. The experimental PLS and interface debonding length of 2D SiC/SiC composites with the PyC and BN interphase at elevated temperatures are predicted. The temperature-dependent PLS of SiC/SiC composite increases with the fiber volume, interface shear stress and interface debonding energy, and the matrix fracture energy and decreases with the interface frictional coefficient at the same temperature.

In this paper, the temperature-dependent matrix multicracking evolution of carbon-fiber-reinforced silicon carbide ceramic-matrix composites (C/SiC CMCs) is investigated. The temperature-dependent composite microstress field is obtained by combining the shear-lag model and temperature-dependent material properties and damage models. The critical matrix strain energy criterion assumes that the strain energy in the matrix has a critical value. With increasing applied stress, when the matrix strain energy is higher than the critical value, more matrix cracks and interface debonding occur to dissipate the additional energy. Based on the composite damage state, the temperature-dependent matrix strain energy and its critical value are obtained. The relationships among applied stress, matrix cracking state, interface damage state, and environmental temperature are established. The effects of interfacial properties, material properties, and environmental temperature on temperature-dependent matrix multiple fracture evolution of C/SiC composites are analyzed. The experimental evolution of matrix multiple fracture and fraction of the interface debonding of C/SiC composites at elevated temperatures are predicted. When the interface shear stress increases, the debonding resistance at the interface increases, leading to the decrease of the debonding fraction at the interface, and the stress transfer capacity between the fiber and the matrix increases, leading to the higher first matrix cracking stress, saturation matrix cracking stress, and saturation matrix cracking density.

In this paper, a micromechanical constitutive model for prior exposure tensile damage and fracture of fiber-reinforced ceramic-matrix composites is developed considering the multiple damage mechanisms of matrix multicracking, interface debonding and oxidation, and fiber fracture. The relationships between prior exposure temperature, duration time, interface debonding fraction, broken fiber fraction, tensile strength, and fracture strain of C/SiC and SiC/SiC composites are established. The experimental prior exposure tensile damage evolution and final fracture of two-dimensional (2D) C/SiC and SiC/SiC composites are predicted for different temperatures and duration times. The comparison analysis of prior exposure composite tensile strength, fracture strain, interface debonding fraction, and broken fiber fraction between 2D C/SiC and SiC/SiC composites is investigated. The effects of constituent properties and temperature on prior exposure tensile damage and fracture of 2D C/SiC and SiC/SiC composites are discussed. For 2D C/SiC and SiC/SiC composites under prior exposure at 1300℃, the fracture strain decreased with fiber volume, interface shear stress, and prior exposure temperature, and increased with fiber characteristic strength; the tensile strength increased with fiber volume and fiber characteristic strength, and decreased with prior exposure temperature; the interface debonding fraction decreased with fiber volume, and increased with prior exposure temperature; and the fiber broken fraction decreased with fiber volume and fiber characteristic strength, and increased with prior exposure temperature.

In this paper, the stress-dependent matrix multiple fractures of fiber-reinforced ceramic-matrix composites (CMCs) with fiber oxidation and fracture is investigated. The shear-lag model is combined...

The failure of aeroengine rotor will cause a great threat to the flight safety. A new risk assessment model to assess the possibility and severity of failure of aeroengine rotor is presented addressing the problems that its failure samples are not sufficient and that early potential failures are not easy to recognize. The key point of this model is to determine the risk mechanism with diverse failures, failure phase, failure process, historical failure time, and check interval. The risk mechanism is to determine the failure is in the state of relevant failure or not. The failure phases are divided from initial operational state to potential failure and eventually developed to functional failure. The failure process is to confirm possible cascading failure of parts at the same level or of systems. Historical failure time is useful to describe the tendency of failure in the future by Weibull distribution, which is very suitable to depict the rule of mechanical parts failure. Considering check intervals makes the model more complete. These factors to be considered in risk modeling are complete. The relationship has been simulated between failure process and check interval of engine rotor. The risk assessment flowchart of engine rotor has been established after determining failure correlation including nonrelevant failure and relevant failure to another part. The primary failure probability has been predicted through Monte Carlo simulation. In the case of aircraft bursting into flames due to fuel tank breakdown resulted from turbine disk debris, the probability and process model of relevant turbine debris failure have been established through the cartridge receiver, airfoil, fuel tank in sequence. The relevant failure risk of engine part has been evaluated to ensure the safe operation of aeroengine. The aeroengine rotor failure risk model will have great significance in eliminating potential failure and reducing sudden failure.

In this paper, the synergistic effects of interface slip and fiber fracture on stress-dependent mechanical hysteresis of SiC/SiC ceramic-matrix minicomposites (mini-CMCs) are investigated. Upon cyc...