Search

In this paper, the synergistic effects of the stochastic loading stress and time interval on the stress-rupture damage evolution and lifetime of fiber-reinforced ceramic-matrix composites (CMCs) at intermediate temperatures are investigated. The relationships between the stochastic loading stress and stochastic time interval, internal damage evolution, macro strain, broken fiber fraction, and stress-rupture lifetime of fiber-reinforced CMCs are established. The effects of the stochastic loading stress and stochastic time interval, constituent properties, damage condition, and environment temperature on the stress-rupture time, strain evolution, and internal damage of SiC/SiC composite under stress-rupture loading are discussed. The experimental stress-rupture behavior of SiC/SiC composite under constant and stochastic loading condition are predicted. The stress-rupture lifetime decreases with increase of stochastic stress level, stochastic time interval, and environmental temperature, and increases with the fiber volume and interfacial shear stress in the slip region. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a hysteresis energy dissipation based damage model for fiber-reinforced ceramic-matrix composites (CMCs) subjected to multiple loading stress levels is developed. Considering the combination effects of multiple loading sequences and multiple fatigue damage mechanisms, i.e., matrix cracking, fiber/matrix interface debonding and interface wear, the evolution of the fiber/matrix interface debonding and sliding, fatigue hysteresis loops, fatigue hysteresis dissipated energy and fatigue hysteresis modulus changing with increasing applied cycles are analyzed. The effects of fiber volume fraction, matrix crack spacing, fatigue peak stress and fatigue stress range on the damage development inside of CMCs are discussed. The difference of the fiber/matrix interface shear stress existed between the interface wear region and new interface debonded region affects the fiber/matrix interface debonded length and loading carrying ability of intact and broken fibers. The damage evolution for C/SiC and SiC/SiC composites subjected to multiple fatigue loading sequences are predicted using the hysteresis energy dissipation damage model. Under multiple loading stress, the fatigue hysteresis dissipated energy increases when high peak stress and stress range increases due to the increase of fiber/matrix interface sliding range. However, when the low peak stress increases, the evolution of fatigue hysteresis dissipated energy depends on the interface debonding and sliding state. Graphical abstract Image 1 Highlights • Multiple loading fatigue damage of fiber-reinforced ceramic-matrix composites (CMCs) is investigated. • A hysteresis energy dissipation based damage model is developed. • The influences of fiber volume fraction, matrix crack spacing, fatigue peak stress and fatigue stress range are discussed. • The developed hysteresis damage model is validated. [ABSTRACT FROM AUTHOR]

Abstract Under fatigue loading of fiber-reinforced ceramic–matrix composites (CMCs), fiber slipping relative to matrix in the interface debonded region upon unloading/reloading is the mainly fatigue damage mechanism. The shape, location and area of fatigue hysteresis loops would change with degradation of the interface shear stress for interface wear or interface oxidation. Based on the fatigue damage mechanism of interface frictional slip between fiber and matrix, the micromechanics fatigue hysteresis loops models corresponding to four different interface slip cases have been developed, in which the unloading interface counter-slip length and reloading interface new-slip length were determined by fracture mechanics approach. The fatigue hysteresis loss energy, fatigue hysteresis loops and interface slip of unidirectional, cross-ply and woven CMCs are formulated in terms of the interface shear stress. With decrease of the interface shear stress, the fatigue hysteresis loss energy increases to the maximum value first, and then decreases to 0; the fatigue hysteresis loops correspond to different interface slip cases. The effects of the fiber volume fraction, fatigue peak stress, fatigue stress amplitude, matrix crack spacing and matrix cracking mode on the fatigue hysteresis loss energy evolution with decrease of the interface shear stress have been analyzed. The range and extent of the interface frictional slip between fiber and matrix during fatigue loading would be decreased with increase of the fiber volume fraction and matrix crack spacing, increased with increase of the fatigue peak stress and fatigue stress amplitude, and greatly affected by matrix cracking mode in cross-ply CMCs. [ABSTRACT FROM AUTHOR]

Highlights • The synergistic effects of hold time and cyclic loading on fatigue hysteresis loops of fiber-reinforced ceramic-matrix composites at elevated temperature are investigated. • The effects of fiber volume fraction, matrix crack spacing, stress levels, hold time and oxidation temperature on fatigue hysteresis loops and interface slip are investigated. • The experimental damage evolution of cross-ply SiC/MAS and 2D SiC/SiC composites under cyclic loading for different hold times at elevated temperature are predicted. Abstract In this paper, the synergistic effects of the hold time and cyclic loading on the fatigue hysteresis loops of fiber-reinforced ceramic-matrix composites (CMCs) at elevated temperatures in air condition are investigated. Based on the analysis of relative frictional sliding between fibers and the matrix in the fiber/matrix interface oxidation and interface wear region, the interface debonded length, interface counter-slip length and interface new-slip length are determined using the fracture mechanics approach. The fatigue hysteresis loops models are developed considering the synergistic effects of hold time and cyclic loading. The relationships between the fatigue hysteresis loops models and internal multiple fatigue damage mechanisms are established. The effects of fiber volume fraction, matrix crack spacing, fatigue stress levels, hold time and oxidation temperature on the fatigue hysteresis loops shape, location and area, fatigue hysteresis modulus and the fiber/matrix interface slip lengths are investigated. The experimental fatigue hysteresis loops, fatigue hysteresis dissipated energy, fatigue hysteresis modulus and the fiber/matrix interface slip lengths of cross-ply SiC/MAS and 2D SiC/SiC composites under cyclic loading for different hold time at elevated temperatures in air condition are predicted. [ABSTRACT FROM AUTHOR]

In this paper, the damage and fracture of long-fiber-reinforced ceramic-matrix composites (CMCs) subjected to the isothermal cyclic fatigue, dwell-fatigue, and in-phase (IP) and out-of-phase (OP) thermomechanical fatigue (TMF) have been investigated. The fiber/matrix interface shear stress is determined as a function of testing temperature and material properties, which affects matrix multicracking and fiber/matrix interface debonding/sliding upon unloading/reloading. The relationships between the cyclic testing temperature, applied cycle number, fatigue peak stress level, matrix crack spacing, fiber/matrix interface debonding/sliding, and the shape, location and area of thermomechanical fatigue hysteresis loops have been established. The damage evolution of fatigue hysteresis dissipated energy, fatigue peak strain, fatigue hysteresis modulus and fiber/matrix interface debonding/sliding lengths versus applied cycle numbers subjected to isothermal cyclic fatigue, dwell-fatigue, IP/OP TMF cyclic loading have been compared. The damage and fracture of cross-ply SiC/MAS composite subject to different fatigue loading types have been predicted. The comparison analysis among the isothermal cyclic fatigue, dwell-fatigue with different hold-times, and IP/OP TMF loading have been conducted, and the effects of testing temperature and loading frequencies on fatigue damage and fracture of long-fiber-reinforced CMCs have been discussed. [ABSTRACT FROM AUTHOR]

Under in-phase (IP) thermomechanical fatigue (TMF) loading, the thermal cyclic temperature changes with decreasing or increasing applied stress upon unloading or loading, and the fiber/matrix interface shear stress in the long fiber-reinforced ceramic-matrix composites (CMCs) changes with applied cycles. In this paper, the in-phase TMF damage evolution of CMCs has been investigated, considering the coupling effects of TMF loading stress level, thermal cyclic temperature and applied cycles. The interface debonding and sliding lengths are determined based the thermomechanical micromechanical stress field and the fracture mechanics approach. The relationships between the TMF hysteresis parameters, interface damage, thermal cyclic temperature and applied cycles have been developed. The damage accumulation processes subjected to in-phase TMF for different fibers volume fraction, peak stress, matrix crack spacing, interface properties and thermal cyclic temperature range have been analyzed. The distinction of the damage evolution between the in-phase TMF and isothermal fatigue (IF) loading at the same applied stress has been analyzed. The damage evolution of cross-ply CMCs subjected to the in-phase TMF and IF loading have been predicted. [ABSTRACT FROM AUTHOR]

In this paper, the thermomechanical fatigue hysteresis loops of long-fiber-reinforced ceramic-matrix composites (CMCs) subjected to out-of-phase (OP) cyclic loading have been investigated using the micromechanical approach. The fiber/matrix interface shear stress is determined as a function of the testing temperature and material properties, which affects the matrix multicracking and fiber/matrix interface debonding and sliding upon unloading and reloading. The relationships between the cyclic temperature and stress level, matrix multicracking, interface debonding and sliding, and the shape, location and the area of the thermomechanical fatigue hysteresis loops have been established. The effects of the fiber volume fraction, fatigue peak stress, matrix cracking space, fiber/matrix interface debonded energy and cyclic temperature range on the thermomechanical fatigue hysteresis loops subjected to out-of-phase cyclic loading have been analyzed. The differences of the thermomechanical fatigue hysteresis loops, interface debonding and sliding between the out-of-phase (OP) and in-phase (IP) thermomechanical cyclic loading have been analyzed. The thermomechanical fatigue hysteresis loops of cross-ply SiC/MAS composite under out-of-phase tension-tension cyclic loading have been predicted. [ABSTRACT FROM AUTHOR]

In this paper, the damage and failure of fiber-reinforced ceramic-matrix composites (CMCs) subjected to cyclic fatigue, dwell fatigue and thermomechanical fatigue at elevated temperatures have been investigated. The damage and failure models considering multiple fatigue damage mechanisms, including the cracking of matrix, debonding and sliding of the interface, and the oxidation and fracture of the fibers have been established. The effects of material properties, damage mechanisms, fatigue peak stress, hold-times, testing environments and thermomechanical fatigue phase angles on the damage and failure of CMCs at elevated temperatures have been analyzed. The damage and failure of cross-ply SiC/MAS composite under cyclic fatigue, dwell fatigue and thermomechanical fatigue with different phase angles have been predicted. The effects of testing temperature, loading frequency, loading type on the internal damage accumulation and fracture have been discussed. [ABSTRACT FROM AUTHOR]

In this paper, the damage evolution of fiber-reinforced ceramic-matrix composites (CMCs) subjected to stress-rupture and cyclic fatigue loading at elevated temperatures in oxidizing atmospheres has been investigated. The damage parameters of hysteresis dissipated energy, hysteresis modulus, peak strain and hysteresis width have been used to monitor the damage evolution inside of CMCs. The effects of the hold time, stress levels, matrix crack spacing, fiber volume fraction and oxidation temperature on the evolution of damage parameters versus applied cycles have been analyzed. The experimental fatigue hysteresis loops, interface slip lengths, fatigue hysteresis dissipated energy and peak strain of cross-ply SiC/MAS, 2D SiC/SiC and Nextel TM 720/Alumina composites subjected to cyclic fatigue and stress-rupture at elevated temperatures have been predicted. [ABSTRACT FROM AUTHOR]

In this paper, the matrix cracking stress of fiber-reinforced ceramic-matrix composites (CMCs) has been investigated using the energy balance approach considering oxidation at elevated temperature. The shear-lag model cooperated with the interface oxidation model and interface debonding criteria has been adopted to analyze the micro-stress field in the composite. The relationships between matrix cracking stress, interface debonding and slipping, oxidation temperature and time have been established. The effects of fiber volume fraction, interface properties, oxidation temperature on the evolution of matrix cracking stress versus oxidation time have been analyzed. The matrix cracking stresses of C/SiC with strong and weak interface bonding after unstressed oxidation at 700 °C in air have been predicted for different oxidation time. It was found that the strong interface bonding can be used for oxidation resistant of C/SiC at elevated temperature. [ABSTRACT FROM AUTHOR]

The fatigue hysteresis behavior of different fiber-reinforced ceramic-matrix composites (CMCs), i.e., C/SiC, SiC/SiC, SiC/Si‒N‒C, SiC/Si‒B 4 C and Nextel 610™/Aluminosilicate, at room and elevated temperatures has been investigated. Based on the developed hysteresis loops models, the relationships between fatigue hysteresis dissipated energy, interface frictional slip and interface shear stress have been established. The evolution of fatigue hysteresis dissipated energy and interface shear stress versus cycle number curves have been analyzed. For C/SiC, the fatigue hysteresis dissipated energy decreases with increasing cycle number at room temperature, and increases with increasing cycle number at 550 °C in air; for SiC/SiC and SiC/Si‒B 4 C, the fatigue hysteresis dissipated energy increases with increasing cycle number at room temperature, 800 °C and 1200 °C in air; and for SiC/Si‒N‒C and Nextel 610™/Aluminosilicate, the fatigue hysteresis dissipated energy decreases with increasing cycle number at 1000 °C in air. The evolution of fatigue hysteresis dissipated energy versus cycle number can be used to monitor the interface debonding and slipping condition inside of composite. [ABSTRACT FROM AUTHOR]

In this paper, the synergistic effects of fiber debonding and fracture on matrix cracking stress of fiber-reinforced ceramic-matrix composites (CMCs) have been investigated using the energy balance approach. The shear-lag model cooperated with fiber/matrix interface debonding criterion and fiber fracture model has been adopted to analyze stress distribution in CMCs. The relationships between matrix cracking stress, interface debonding and slipping, and fiber fracture have been established. The effects of fiber volume fraction, interface shear stress, interface debonded energy, fiber Weibull modulus, and fiber strength on matrix cracking stress, interface debonded length and fiber broken fraction have been analyzed. The experimental matrix cracking stress of three different CMCs, i.e., SiC/borosilicate, SiC/LAS, and C/borosilicate, with different fiber volume fraction have been predicted. [ABSTRACT FROM AUTHOR]

The effects of loading type, i.e., cyclic loading/unloading tensile, cumulative tensile fatigue loading, and tension-tension fatigue loading, temperature and oxidation on the mechanical hysteresis behavior of carbon fiber-reinforced ceramic-matrix composites (CMCs) have been investigated. Based on the damage mechanism of fiber sliding relative to the matrix in the interface debonded region, the stress-strain relationships upon unloading/reloading when the interface partially and completely debonded have been determined considering fibers fracture. The effects of material properties, damage mode and cycle number on the interface slip and hysteresis loops have been analyzed. The mechanical hysteresis behavior of different loading types of C/SiC at room temperature and 800 °C in air have been predicted. [ABSTRACT FROM AUTHOR]

The hysteresis loops of C/SiC ceramic-matrix composites (CMCs) with different fiber preforms, i.e., unidirectional, cross-ply, 2D and 2.5D woven, 3D braided, and 3D needled at room temperature have been investigated. Based on fiber slipping mechanisms, the hysteresis loops models considering different interface slip cases have been developed. The effects of fiber volume fraction, matrix cracking density, interface shear stress, interface debonded energy, and fibers failure on hysteresis loops, hysteresis dissipated energy, hysteresis width, and hysteresis modulus have been analyzed. An effective coefficient of fiber volume fraction along the loading direction (ECFL) was introduced to describe fiber preforms. The hysteresis loops, hysteresis dissipated energy and hysteresis modulus of unidirectional, cross-ply, 2D and 2.5D woven, 3D braided and 3D needled C/SiC composites have been predicted. [ABSTRACT FROM AUTHOR]

In this paper, the cyclic fatigue hysteresis loops of 2D woven SiC/SiC ceramic-matrix composites (CMCs) at elevated temperatures has been investigated. The interface slip between fibers and the matrix existed in the matrix cracking mode 3 and mode 5, in which matrix cracking and interface debonding occurred in the longitudinal yarns, are considered as the major reason for hysteresis loops of 2D woven CMCs. The hysteresis loops of 2D SiC/SiC composite corresponding to different peak stresses, test conditions and loading frequencies have been predicted using present analysis. The damage parameter, i.e., the proportion of matrix cracking mode 3 in the entire matrix cracking modes of the composite, and the hysteresis dissipated energy increase with increasing fatigue peak stress. With increasing cycle number, the interface shear stress in the longitudinal yarns decreases, leading to transition of interface slip types of matrix cracking mode 3 and mode 5. [ABSTRACT FROM AUTHOR]

In this paper, the interface shear stress in fiber-reinforced ceramic-matrix composites (CMCs) with different fiber preforms, i.e., unidirectional, cross-ply, 2Dwoven, and 3D braided at room and elevated temperatures has been estimated through hysteresis loops. An effective coefficient of the fiber volume fraction along the loading direction (ECFL) was introduced to describe the fiber architecture of preforms. Based on the damage mechanisms of fiber slipping relative to matrix in the interface debonded region, the hysteresis loops models considering different interface slip cases have been developed. The hysteresis dissipated energy for the strain energy lost per volume during corresponding cycle is formulated in terms of the fiber/matrix interface shear stress. By comparing experimental fatigue hysteresis dissipated energy with theoretical computational values, the interface shear stress of unidirectional, cross-ply, 2D woven, and 3D braided CMCs at room temperature, 600 °C, 800 °C, 1000 °C, 1200 °C, and 1300 °C in inert, air and steam conditions, have been estimated. The effects of test temperature, oxidation and fiber preforms on the degradation rate of interface shear stress have been investigated. [ABSTRACT FROM AUTHOR]

The hysteresis loops models of fiber-reinforced ceramic-matrix composites (CMCs) are developed based on the Coulomb friction law instead of a constant frictional shear stress usually assumed in hysteresis analysis. Based on damage mechanism of fiber slipping relative to matrix upon loading/unloading, the interface slip lengths are obtained by fracture mechanics approach. The effects of matrix stochastic cracking, fiber volume fraction, interface debonded energy, interface frictional coefficient and fiber Poisson ratio on hysteresis loops, interface slip lengths and interface slip stresses have been analyzed. [ABSTRACT FROM AUTHOR]

The fatigue behavior of cross-ply C/SiC and 2D woven SiC/SiC composites at elevated temperatures in air or steam condition have been investigated using the hysteresis dissipated energy. The evolution of fatigue hysteresis dissipated energy and hysteresis dissipated energy-based damage parameter of C/SiC and SiC/SiC composites have been analyzed. For SiC/SiC composite at 1000 °C in steam, the experimental fatigue hysteresis dissipated energy lies in the right part of the fatigue hysteresis dissipated energy versus interface shear stress curve, which indicates that the interface partially debonds during cyclic fatigue loading; however, for C/SiC composite at 800 °C in air, the experimental fatigue hysteresis dissipated energy lies in the right and left part of the fatigue hysteresis dissipated energy versus interface shear stress curve, which indicates that the interface completely debonds upon initial cyclic fatigue loading. By comparing the experimental fatigue hysteresis dissipated energy with theoretical computational values, the interface shear stress of C/SiC and SiC/SiC composites have been estimated. The interface shear stress of C/SiC composite at 800 °C in air decreases much more rapidly than that of SiC/SiC composite at higher temperatures in air or steam condition. [ABSTRACT FROM AUTHOR]

An analytical method has been developed to investigate the effect of oxidation on the hysteresis loops of fiber-reinforced ceramic-matrix composites (CMCs) under static fatigue at elevated temperature. The oxidation region propagating model has been adopted to analyze the oxidation effect on the hysteresis loops, which is controlled by interface frictional slip and diffusion of oxygen gas through matrix multicrackings. Based on the damage mechanism of fiber slipping relative to matrix, the hysteresis loops models corresponding to different interface slip cases considering interface oxidation have been established. The relationships between hysteresis loops, hysteresis dissipated energy, interface slip and oxidation time have been established. The effects of stress level, matrix crack spacing, fiber volume content and oxidation temperature on the hysteresis dissipated energy, interface debonding, oxidation and slip lengths versus oxidation time have been analyzed. The experimental hysteresis loops of C/[Si–B–C] composite under static fatigue in air at 1200 °C have been predicted. [ABSTRACT FROM AUTHOR]

In this paper, the tensile fatigue hysteresis behavior of unidirectional C/SiC ceramic-matrix composite under multiple loading stress levels has been investigated. The fatigue hysteresis loops and fatigue hysteresis loss energy corresponding to different number of applied cycles have been analyzed. Based on the fatigue damage mechanism of fiber slipping relative to matrix in the interface debonded region upon unloading/reloading, the unloading interface counter-slip length and reloading interface new-slip length are determined by fracture mechanics method. The fatigue hysteresis loops models corresponding to different interface slip cases under multiple loading stress levels have been developed. The relationships between fatigue hysteresis loops, fatigue hysteresis loss energy and interface slip have been analyzed. The fatigue hysteresis loops of unidirectional C/SiC composite corresponding to different number of applied cycles under multiple loading stress levels have been predicted. [ABSTRACT FROM AUTHOR]

Under fatigue loading, the stress–strain hysteresis loops appear as fiber slipping relative to matrix in the interface debonded region. The area of hysteresis loops, i.e., the hysteresis dissipated energy, changes with the increase of cycle number, and can reveal fatigue damage mechanisms, i.e., matrix multicracking, fiber/matrix interface debonding, interface slipping, interface wear, and fibers fracture. Based on the fatigue hysteresis theories considering fibers failure, the hysteresis dissipated energy and a hysteresis dissipated energy-based damage parameter changing with the increase of cycle number have been investigated. The relationships between the hysteresis dissipated energy, hysteresis dissipated energy-based damage parameter, stress–strain hysteresis loops, and fatigue damage mechanisms have been established. The effects of fatigue peak stress, stress ratio, matrix crack spacing and fiber volume content on the evolution of hysteresis dissipated energy and hysteresis dissipated energy-based damage parameter as a function of cycle number have been analyzed. It was found that the hysteresis dissipated energy-based damage parameter is much more sensitive to interface debonding and interface frictional slipping compared with the hysteresis dissipated energy under fatigue loading, and can be used to reveal the fatigue damage evolution and predict the fatigue life of fiber-reinforced CMCs. The experimental fatigue life S–N curves of unidirectional CMCs have been predicted using the present analysis. [ABSTRACT FROM AUTHOR]

In this paper, the fatigue hysteresis behavior of unidirectional C/SiC ceramic-matrix composite at room and elevated temperatures in air atmosphere has been investigated. The fatigue hysteresis modulus and fatigue hysteresis loss energy corresponding to different cycles have been analyzed. An approach to model fatigue hysteresis loops of unidirectional ceramic composites considering fiber failure has been developed. Based on the damage mechanism of fiber slipping relative to matrix under fatigue loading, the unloading interface counter-slip length and reloading interface new slip length are determined by fracture mechanics approach. The interface shear stress and broken fibers fraction corresponding to different cycles are obtained through comparing the experimental fatigue hysteresis loss energy with theoretical computational value considering fiber failure. The fatigue hysteresis loops of unidirectional C/SiC composite have been predicted for different number of cycles. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the loading/unloading tensile behavior of cross-ply C/SiC ceramic matrix composites at room temperature has been investigated. The loading/unloading stress–strain curve exhibits obvious hysteresis behavior. An approach to model the hysteresis loops of cross-ply ceranic matrix composites including the effect of matrix cracking has been developed. Based on the damage mechanisms of fiber sliding relative to matrix during unloading and subsequent reloading, the unloading interface reverse slip length and reloading interface new slip length of different matrix cracking modes are obtained by the fracture mechanics approach. The hysteresis loops of cross-ply C/SiC ceramic matrix composites corresponding to different peak stresses have been predicted. [Copyright &y& Elsevier]