Broken Fibers Fraction Research Articles

Stochastic fatigue life prediction in C/SiC composites at elevated temperature by micromechanics-based damage model

In this paper, a micromechanical approach is developed to predict the fatigue life and fracture process in different C/SiC composites subjected to different stochastic fatigue loading spectrums at elevated temperatures. Three types of stochastic fatigue load spectrums are considered in the fatigue life prediction at elevated temperature, that is, constant, increasing, and decreasing stochastic stress with cycles. Stress distribution between intact and broken fibers and the broken fibers fraction under stochastic fatigue loading spectrum are determined using the Global Load Sharing criterion considering multiple fatigue damage mechanisms at elevated temperatures. A new damage parameter of fatigue life degradation rate is developed to characterize the effect of stochastic loading on fatigue damage and fracture in C/SiC composites. Relationships between stochastic fatigue loading spectrum, broken fibers fraction, fatigue life, and fatigue life degradation rate in different C/SiC composite are established. Effects of stochastic fatigue loading spectrum type, stress level, and testing temperature on fatigue life degradation rate are discussed. The fatigue life degradation rate is very sensitive to the fiber preform, loading sequence, and testing temperature.

A micromechanical temperature-dependent vibration damping model of fiber-reinforced ceramic-matrix composites

In this paper, a micromechanical temperature-dependent vibration damping model of fiber-reinforced ceramic-matrix composites (CMCs) is developed. Temperature-dependent damage mechanisms of matrix cracking, interface debonding and slip, and fibers fracture contribute to the vibration damping of damaged CMCs. The temperature-dependent fiber and matrix strain energy and dissipated energy density are formulated of composite constituent properties and damage related micro parameters of matrix crack spacing, interface debonding and slip length, and broken fibers fraction. Theoretical relationships between temperature-dependent composite damping, temperature and temperature-dependent damage mechanisms are established. Effects of composite constituent properties (i.e., fiber volume, interface debonding energy, interface shear stress and interface frictional coefficient) and composite damage state (i.e., matrix crack spacing) on temperature-dependent composite vibration damping of SiC/SiC composite are analyzed. When the fiber volume increases, the composite vibration damping decreases, and the temperature for the peak value of the composite vibration damping increases, mainly due to the decrease of the interface debonding and slip fraction. Experimental temperature-dependent composite vibration damping of 2D SiC/SiC composite at the temperature range of 293–1373 K are predicted using the developed micromechanical vibration damping model. Experimental vibration damping of 2D SiC/SiC composite increases with temperature, and the theoretical predicted composite vibration damping for different vibration stress of σ = 5, 6, and 7 MPa are obtained and agreed with experimental data, and the predicted interface debonding and slip fraction increases with temperature.

Effect of interface damage on tensile behavior of fiber-reinforced ceramic-matrix composites after thermal fatigue loading

ABSTRACT In this paper, the effect of interface damage on the tensile damage and fracture of fiber-reinforced ceramic-matrix composites (CMCs) after thermal fatigue loading is investigated. The damage mechanisms of matrix cracking, fiber/matrix interface debonding and wear, interface and fiber oxidation, and fiber failure after thermal fatigue loading are considered in the tensile stress-strain behavior prediction. The relationships between the thermal fatigue temperature, applied cycle number, composite internal damage, and tensile damage and fracture are established. The effects of thermal fatigue temperature, thermal cycle number, fiber volume, interface shear stress, fiber strength, and fiber Weibull modulus on the tensile damage and fracture of fiber-reinforced CMCs subjected to the thermal fatigue loading are analyzed. The experimental tensile stress-strain curves of different C/SiC composites with and without thermal fatigue loading are predicted. When the thermal fatigue temperature and applied cycle number increase, the composite tensile strength and failure strain decrease, the interface debonding ratio, interface oxidation ratio, and broken fibers fraction increase at low applied stress level.

Damage monitor and life prediction of carbon fiber-reinforced ceramic-matrix composites at room and elevated temperatures using hysteresis dissipated energy-based damage parameter

In this paper, the damage monitor and life prediction of carbon fiber-reinforced ceramic-matrix composites (C/SiC CMCs) have been investigated using the hysteresis dissipated energy-based damage parameter. The evolution of the interface shear stress, hysteresis dissipated energy, hysteresis dissipated energy-based damage parameter and the broken fibers fraction vs. cycle number, the fatigue life S‒N curves of unidirectional, cross-ply and 2.5D C/SiC composites at room temperature and 800 °C in air atmosphere have been analyzed. For unidirectional C/SiC, the hysteresis dissipated energy and hysteresis dissipated energy-based damage parameter first increase and then decrease with cycle number, and the fatigue limit stress decreases from 88% tensile strength at room temperature to 20% of the tensile strength at 800 °C in air atmosphere; for cross-ply C/SiC, the hysteresis dissipated energy and hysteresis dissipated energy-based damage parameter decrease with increasing applied cycles, and the fatigue limit stress decreases from 85% tensile strength at room temperature to 22% tensile strength at 800 °C in air; and for 2.5D C/SiC, the hysteresis dissipated energy and hysteresis dissipated energy-based damage parameter increases with cycle number, and the fatigue limit stress decreases from 70% tensile strength at room temperature to 25% tensile strength at 800 °C in air.

Synergistic Effects of Frequency and Temperature on Damage Evolution and Life Prediction of Cross-Ply Ceramic Matrix Composites under Tension-Tension Fatigue Loading

In this paper, the synergistic effects of loading frequency and testing temperature on the fatigue damage evolution and life prediction of cross-ply SiC/MAS ceramic-matrix composite have been investigated. The damage parameters of the fatigue hysteresis modulus, fatigue hysteresis dissipated energy and the interface shear stress were used to monitor the damage evolution inside of SiC/MAS composite. The evolution of fatigue hysteresis dissipated energy, the interface shear stress and broken fibers fraction versus cycle number, and the fatigue life S–N curves of SiC/MAS composite under the loading frequency of 1 and 10 Hz at 566 °C and 1093 °C in air condition have been predicted. The synergistic effects of the loading frequency and testing temperature on the degradation rate of fatigue hysteresis dissipated energy and the interface shear stress have been analyzed.

Synergistic Effects of Temperature, Oxidation and Multicracking Modes on Damage Evolution and Life Prediction of 2D Woven Ceramic-Matrix Composites under Tension-Tension Fatigue Loading

In this paper, the synergistic effects of temperature, oxidation and multicracking modes on damage evolution and life prediction in 2D woven ceramic-matrix composites (CMCs) have been investigated. The damage parameter of fatigue hysteresis dissipated energy and the interface shear stress were used to monitor the damage evolution inside of CMCs. Under cyclic fatigue loading, the fibers broken fraction was determined by combining the interface/fiber oxidation model, interface wear model and fibers statistical failure model at elevated temperature, based on the assumption that the fiber strength is subjected to two-parameter Weibull distribution and the load carried by broken and intact fibers satisfy the Global Load Sharing (GLS) criterion. When the broken fibers fraction approaches to the critical value, the composite fatigue fractures. The evolution of fatigue hysteresis dissipated energy, the interface shear stress and broken fibers fraction versus cycle number, and the fatigue life S–N curves of SiC/SiC at 1000, 1200 and 1300 °C in air and steam condition have been predicted. The synergistic effects of temperature, oxidation, fatigue peak stress, and multicracking modes on the evolution of interface shear stress and fatigue hysteresis dissipated energy versus cycle numbers curves have been analyzed.

Effects of Temperature, Oxidation and Fiber Preforms on Fatigue Life of Carbon Fiber-Reinforced Ceramic-Matrix Composites

In this paper, the effects of temperature, oxidation and fiber preforms on the fatigue life of carbon fiber-reinforced silicon carbide ceramic-matrix composites (C/SiC CMCs) have been investigated. An effective coefficient of the fiber volume fraction along the loading direction (ECFL) was introduced to describe the fiber architecture of preforms. Under cyclic fatigue loading, the fibers broken fraction was determined by combining the interface wear model and fibers statistical failure model at room temperature, and interface/fibers oxidation model, interface wear model and fibers statistical failure model at elevated temperatures in the oxidative environments. When the broken fibers fraction approaches to the critical value, the composites fatigue fracture. The fatigue life S–N curves and fatigue limits of unidirectional, cross-ply, 2D, 2.5D and 3D C/SiC composites at room temperature, 800 °C in air, 1100, 1300 and 1500 °C in vacuum conditions have been predicted.

Micromechanical Modeling for Tensile Behaviour of Carbon Fiber − Reinforced Ceramic − Matrix Composites

The stress–strain curves of fiber − reinforced ceramic − matrix composites (CMCs) exhibit obvious non-linear behaviour under tensile loading. The occurrence of multiple damage mechanisms, i.e., matrix multicracking, fiber/matrix interface debonding and fibers fracture, is the mainly reason for the non-linear characteristic. The micromechanics approach has been developed to predict the tensile stress–strain curves of unidirectional, cross-ply and woven CMCs. The shear-lag model was used to describe the micro stress field of the damaged composite. The damage models were used to determine the evolution of micro damage parameters, i.e., matrix crack spacing, interface debonded length and broken fibers fraction. By combining the shear-lag model with damage models and considering the effect of transverse multicracking in the 90° plies or transverse yarns in cross-ply or woven CMCs, the tensile stress–strain curves of unidirectional, cross-ply, 2D and 2.5D woven CMCs have been predicted. The results agreed with experimental data.

Modeling fatigue hysteresis behavior of unidirectional C/SiC ceramic–matrix composite

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.