Fatigue Hysteresis Loops Research Articles

Synergistic effects of temperature, oxidation, and stress level on fatigue hysteresis behavior of cross-ply ceramic-matrix composites at room and elevated temperatures under cyclic loading

In this paper, the synergistic effects of temperature, oxidation, and stress level on the fatigue hysteresis behavior of cross-ply SiC/CAS ceramic-matrix composites (CMCs) at room temperature and 700 and 850 °C in air atmosphere has been investigated. The relationships between the fatigue hysteresis loops, fatigue hysteresis-dissipated energy, fatigue hysteresis modulus, and the fiber/matrix interface shear stress have been established using the hysteresis loop models considering different matrix cracking modes. The fatigue damage evolution process of SiC/CAS composite under tension–tension fatigue loading has been analyzed using the hysteresis loops. By comparing the experimental fatigue hysteresis-dissipated energy with theoretical computational values, the interface shear stress of SiC/CAS composite were obtained for different cycle numbers and fatigue peak stress. It was found that at elevated temperature in air, the interface shear stress degradation rate is much more affected by the fatigue peak stress than that at room temperature due to interface oxidation. The comparisons of interface shear stress evolution between unidirectional SiC/MAS and SiC/CAS, 2D SiC/SiC, and cross-ply SiC/CAS composites have been analyzed.

Modeling thermomechanical fatigue hysteresis loops of long-fiber-reinforced ceramic-matrix composites under out-of-phase cyclic loading condition

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 asa 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.

Damage evolution of fiber-reinforced ceramic-matrix composites under stress-rupture and cyclic loading at elevated temperature in oxidizing atmosphere

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 NextelTM 720/Alumina composites subjected to cyclic fatigue and stress-rupture at elevated temperatures have been predicted.

A study of the back stress and the friction stress behaviors of Ti-6Al-4V alloy during low cycle fatigue at room temperature

Low cycle fatigue (LCF) tests were performed on Ti-6Al-4V alloy at room temperature. The fatigue hardening/softening of the Ti-alloy were determined. Both the back stress (X) and the friction stress (σF) were evaluated from analysis of fatigue hysteresis loops and their cycle-dependent behaviors during fatigue tests were obtained experimentally. It is shown that the cyclic stress response or the fatigue hardening/softening of the Ti-alloy actually results from the competition effect of the back and the friction stress behaviors during fatigue cycling. A two-slope behavior in both the εpa-2Nf and the X-2Nf plots was also obtained. The micro-mechanisms associated with the back and friction stress behaviors as well as the two-slope behavior in the εpa-2Nf and X-2Nf plots were further discussed with the help of OM and TEM observations of fatigue failure specimens at representative strain amplitudes. In this study, the DIC technique was also introduced to characterize quantitatively the cyclic deformation heterogeneity of the Ti-alloy at the grain scale.

Tension-tension fatigue behavior of unidirectional SiC/Si 3 N 4 composite with strong and weak interface bonding at room temperature

Abstract In this paper, the tension-tension fatigue behavior of unidirectional SiC/Si 3 N 4 ceramic-matrix composite with strong and weak interface bonding at room temperature has been investigated using a micromechanical approach. The hysteresis loops models considering different interface slip cases have been developed to establish the relationships between fatigue hysteresis loops, hysteresis dissipated energy, hysteresis modulus, and the interface shear stress. The damage evolution process under tension-tension fatigue loading has been analyzed using hysteresis loops. By comparing experimental fatigue hysteresis dissipated energy with theoretical computational values, the interface shear stresses of SiC/Si 3 N 4 composite with weak and strong interface bonding were obtained for different cycle numbers. The fatigue life S‒N curves and broken fibers fraction versus cycle number curves corresponding to different fatigue peak stresses have been predicted. For SiC/Si 3 N 4 with strong interface bonding, the fatigue limit stress approaches to 75% tensile strength, which is much higher than that of composite with weak interface bonding, i.e., 58% tensile strength, due to the higher interface shear stress degradation rate for weak bonding interface.

Simplified Constitutive Model for Fatigue Behavior of Concrete in Compression

AbstractIn the literature, three basic assumptions are used to modify monotonic constitutive models in order to simplify fatigue analysis of concrete. First, the fatigue hysteresis loop at failure ...

Synergistic Effects of Stress-Rupture and Cyclic Loading on Strain Response of Fiber-Reinforced Ceramic-Matrix Composites at Elevated Temperature in Oxidizing Atmosphere.

In this paper, the synergistic effects of stress rupture and cyclic loading on the strain response of fiber-reinforced ceramic-matrix composites (CMCs) at elevated temperature in air have been investigated. The stress-strain relationships considering interface wear and interface oxidation in the interface debonded region under stress rupture and cyclic loading have been developed to establish the relationship between the peak strain, the interface debonded length, the interface oxidation length and the interface slip lengths. The effects of the stress rupture time, stress levels, matrix crack spacing, fiber volume fraction and oxidation temperature on the peak strain and the interface slip lengths have been investigated. The experimental fatigue hysteresis loops, interface slip lengths, peak strain and interface oxidation length of cross-ply SiC/MAS (magnesium alumino-silicate, MAS) composite under cyclic fatigue and stress rupture at 566 and 1093 °C in air have been predicted.

Damage evolution of cross-ply ceramic-matrix composites under stress-rupture and cyclic loading at elevated temperatures in oxidizing atmosphere

In this paper, the damage evolution of cross-ply ceramic-matrix composites (CMCs) under stress-rupture and cyclic loading at elevated temperatures in oxidizing atmosphere has been investigated. The Budiansky-Hutchinson-Evans shear-lag model was used to describe the micro stress field of the damaged composite considering matrix multicracking, interface debonding/wear/oxidation/slip. The damage parameters of fatigue hysteresis dissipated energy, fatigue hysteresis modulus, fatigue peak strain and fatigue hysteresis width have been used to monitor the damage evolution inside of CMCs. The relationship between damage parameters and internal damage of matrix multicracking, interface debonding/slip has been established. The experimental fatigue hysteresis loops, interface slip lengths, fatigue hysteresis dissipated energy and peak strain of cross-ply SiC/MAS composite under cyclic fatigue and stress-rupture at 566°C and 1093°C in air have been predicted.

Fatigue Hysteresis Behavior of Unidirectional SiC/Si3N4 Composite at Elevated Temperature under Tension-Tension Loading

In this paper, the fatigue hysteresis behavior of unidirectional SiC/Si3N4 ceramic-matrix composite at elevated temperature has been investigated. The hysteresis loops models considering interface friction between fibers and the matrix have been developed to establish the relationships between the fatigue hysteresis loops, fatigue hysteresis dissipated energy and the interface frictional coefficient. Using the experimental fatigue hysteresis dissipated energy, the interface frictional coefficient of SiC/Si3N4 composite at 1000 °C were obtained for different cycle numbers and fatigue peak stresses. The effects of fatigue peak stress, test temperature and cycle number on the evolution of fatigue hysteresis dissipated energy and interface frictional coefficient have been analyzed. It was found that the fatigue hysteresis dissipated energy can be used to monitor the interface debonding and damage evolution inside of the composite.

Damage evolution of carbon fiber-reinforced ceramic-matrix composites with different fiber preforms using the fatigue hysteresis loop area

The damage evolution of C/SiC ceramic-matrix composites with different fiber preforms, that is, unidirectional, cross-ply and 2.5D woven, under cyclic fatigue loading at room and elevated temperatures in air and inert atmosphere has been investigated. The experimental fatigue hysteresis modulus and hysteresis loop area versus cycle numbers have been analyzed. The relationships between the fatigue hysteresis loop area, interface slip and interface shear stress have been established. The evolution of the fatigue hysteresis loop area and interface shear stress as a function of applied cycles has been analyzed for different peak stresses, fiber preforms and test conditions. For different fiber preforms and test conditions, the fatigue hysteresis loop area degrades the fastest for unidirectional C/SiC at 800℃ in air, and the slowest for 2.5D C/SiC at 600℃ in an inert atmosphere, due to the different degradation rates of interface shear stress.

Comparisons of Damage Evolution between 2D C/SiC and SiC/SiC Ceramic-Matrix Composites under Tension-Tension Cyclic Fatigue Loading at Room and Elevated Temperatures.

In this paper, comparisons of damage evolution between 2D C/SiC and SiC/SiC ceramic-matrix composites (CMCs) under tension–tension cyclic fatigue loading at room and elevated temperatures have been investigated. Fatigue hysteresis loops models considering multiple matrix cracking modes in 2D CMCs have been developed based on the damage mechanism of fiber sliding relative to the matrix in the interface debonded region. The relationships between the fatigue hysteresis loops, fatigue hysteresis dissipated energy, fatigue peak stress, matrix multiple cracking modes, and interface shear stress have been established. The effects of fiber volume fraction, fatigue peak stress and matrix cracking mode proportion on fatigue hysteresis dissipated energy and interface debonding and sliding have been analyzed. The experimental fatigue hysteresis dissipated energy of 2D C/SiC and SiC/SiC composites at room temperature, 550 °C, 800 °C, and 1100 °C in air, and 1200 °C in vacuum corresponding to different fatigue peak stresses and cycle numbers have been analyzed. The interface shear stress degradation rate has been obtained through comparing the experimental fatigue hysteresis dissipated energy with theoretical values. Fatigue damage evolution in C/SiC and SiC/SiC composites has been compared using damage parameters of fatigue hysteresis dissipated energy and interface shear stress degradation rate. It was found that the interface shear stress degradation rate increases at elevated temperature in air compared with that at room temperature, decreases with increasing loading frequency at room temperature, and increases with increasing fatigue peak stress at room and elevated temperatures.

Interfacial debonding and slipping of carbon fiber-reinforced ceramic-matrix composites under two-stage cyclic loading

In this paper, the interface debonding and frictional slipping of carbon fiber-reinforced ceramic-matrix composites (CMCs) under two-stage cyclic fatigue loading have been investigated using micromechanics approach. Under cyclic fatigue loading, the fiber/matrix interface shear stress degrades with increasing cycle number due to interface wear. The synergistic effect of interface wear and fatigue loading sequence on interface debonding and frictional slipping has been analyzed. Based on the fatigue damage mechanism of fiber slipping relative to matrix, in the interface debonded region, upon unloading and subsequent reloading, the interface debonded length and interface slip lengths, i.e. interface counter-slip length and interface new-slip length, are determined using the fracture mechanics approach. The relationships between interface debonding, interface slipping, interface wear, cycle number, and different loading sequences are determined. There are two types of fatigue loading sequences considered, i.e. (1) cyclic loading under low peak stress for N1 cycles, and then high peak stress; and (2) cyclic loading under high peak stress for N1 cycles, and then low peak stress. The effects of peak stress level, interface wear, cycle number, and loading sequence on interface debonding and frictional slipping of fiber-reinforced CMCs have been analyzed. The fatigue hysteresis loops of cross-ply carbon fiber-reinforced silicon carbide composite corresponding to different cycle number under two-stage cyclic fatigue loading have been predicted.

Modeling of fatigue hysteresis behavior in carbon fiber-reinforced ceramic–matrix composites under multiple loading stress levels

The fatigue hysteresis behavior in fiber-reinforced ceramic–matrix composites under multiple loading stress levels has been investigated. Based on the fatigue damage mechanism of fiber slipping relative to matrix in the interface debonded region upon unloading/reloading, the fatigue hysteresis loops models corresponding to different interface slip cases under multiple loading stress levels have been derived. The fatigue hysteresis loss energy and interface slip corresponding to single/multiple loading stress levels and different loading sequences have been investigated. The fatigue hysteresis loops of unidirectional SiC/CAS−II composite under multiple loading stress levels have been predicted.

Synergistic effect of interface wear and loading sequence on interface debonding and relative slipping of fiber-reinforced ceramic-matrix composites

This study investigates the synergistic effect of interface wear and loading sequence on interface debonding and relative slipping of fiber-reinforced ceramic-matrix composites (CMCs). There are five different fatigue loading sequences considered in the present analysis. Based on the fatigue damage mechanism of fiber slipping relative to the matrix upon unloading/reloading, the interface debonded length and interface slip lengths are determined using the fracture mechanics approach. The relationships between interface debonding, interface slipping, interface wear, cycle number, peak stress and loading sequence have been determined. The fatigue hysteresis loops of C/SiC composite under three-stage cyclic fatigue loading have been predicted using the present analysis.

Modeling Cyclic Fatigue Hysteresis Loops of 2D Woven Ceramic Matrix Composites at Elevated Temperatures in Steam.

In this paper, the cyclic fatigue hysteresis loops of 2D woven SiC/SiC ceramic matrix composites (CMCs) at elevated temperatures in steam have been investigated. The interface slip between fibers and the matrix existing in matrix cracking modes 3 and 5, in which matrix cracking and interface debonding occurred in longitudinal yarns, is considered as the major reason for hysteresis loops of 2D woven CMCs. The hysteresis loops of 2D SiC/SiC composites corresponding to different peak stresses, test conditions, and loading frequencies have been predicted using the 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 modes 3 and 5.

Modeling cyclic fatigue hysteresis loops of 2D woven ceramic-matrix composite at elevated temperatures in air considering multiple matrix cracking modes

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.

Damage development in fiber-reinforced ceramic-matrix composites under cyclic fatigue loading using hysteresis loops at room and elevated temperatures

In this paper, the damage development behavior in fiber-reinforced ceramic-matrix composites (CMCs) with different fiber architectures, i.e., unidirectional, cross-ply and 2D woven, under cyclic fatigue loading at room and elevated temperatures has been investigated using fatigue hysteresis loops, i.e., fatigue hysteresis modulus, fatigue hysteresis dissipated energy, and fatigue hysteresis dissipated energy-based damage parameter. The relationships between fatigue hysteresis loops, fatigue hysteresis modulus, fatigue hysteresis dissipated energy and fatigue hysteresis dissipated energy-based damage parameter have been established. The effects of fiber volume content, fatigue peak stress, fatigue stress ratio, matrix crack spacing, multiple matrix cracking modes, and woven structures on the damage evolution in fiber-reinforced CMCs have been investigated. The experimental fatigue hysteresis modulus, fatigue hysteresis dissipated energy and fatigue hysteresis dissipated energy-based damage parameter versus cycle number have been predicted for unidirectional, cross-ply and 2D woven CMCs at room and elevated temperatures. It was found that the damage parameters derived from the fatigue hysteresis loops can effectively monitor the damage development and predict the fatigue life of fiber-reinforced CMCs.

Damage Evolution and Life Prediction of Cross-Ply C/SiC Ceramic-Matrix Composite under Cyclic Fatigue Loading at Room Temperature and 800 °C in Air.

The damage evolution and life prediction of cross-ply C/SiC ceramic-matrix composite (CMC) under cyclic-fatigue loading at room temperature and 800 °C in air have been investigated using damage parameters derived from fatigue hysteresis loops, i.e., fatigue hysteresis modulus and fatigue hysteresis loss energy. The experimental fatigue hysteresis modulus and fatigue hysteresis loss energy degrade with increasing applied cycles attributed to transverse cracks in the 90° plies, matrix cracks and fiber/matrix interface debonding in the 0° plies, interface wear at room temperature, and interface and carbon fibers oxidation at 800 °C in air. The relationships between fatigue hysteresis loops, fatigue hysteresis modulus and fatigue hysteresis loss energy have been established. Comparing experimental fatigue hysteresis loss energy with theoretical computational values, the fiber/matrix interface shear stress corresponding to different cycle numbers has been estimated. It was found that the degradation rate at 800 °C in air is much faster than that at room temperature due to serious oxidation in the pyrolytic carbon (PyC) interphase and carbon fibers. Combining the fiber fracture model with the interface shear stress degradation model and the fibers strength degradation model, the fraction of broken fibers versus the cycle number can be determined for different fatigue peak stresses. The fatigue life S-N curves of cross-ply C/SiC composite at room temperature and 800 °C in air have been predicted.

Micromechanical Modeling for Fatigue Hysteresis Loops of Fiber-Reinforced Ceramic–Matrix Composites Under Multiple Loading Stress Levels

In this paper, the fatigue hysteresis loops of fiber-reinforced ceramic–matrix composites (CMCs) under multiple loading stress levels considering interface wear have been investigated using micromechanics approach. Under fatigue loading, fiber/matrix interface shear stress decreases with the increase of cycle number due to interface wear. Upon increasing of fatigue peak stress, the interface debonded length would propagate along the fiber/matrix interface. The difference of interface shear stress existing in the new and original debonded region would affect interface debonding and interface frictional slipping between fibers and matrix. Based on the fatigue damage mechanism of fiber slipping relative to matrix in the interface debonded region upon unloading and subsequent reloading, the interface debonded length, unloading interface counter-slip length and reloading interface new-slip length are determined by fracture mechanics approach. The fatigue hysteresis loop models under multiple peak stress levels have been developed. The effects of fiber volume fraction, fatigue peak stress, matrix crack spacing, interface debonding and interface wear on interface slip and fatigue hysteresis loops have been analyzed.

Modeling of fatigue hysteresis loops in C/SiC composite under multiple loading stress levels

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.