7 - Time-dependent nonlinear damage behavior of ceramic–matrix composites

The fatigue hysteresis behavior of unidirectional, 2D cross-ply and woven, and 2.5D woven fiber-reinforced ceramic-matrix composites (CMCs) are analyzed. Based on the fiber/matrix interface debonding and sliding behavior, the fiber/matrix interface debonding and sliding lengths are determined using the fracture mechanics approach. The fiber/matrix interface debonding ratio and interface sliding ratio are determined for different interface slip cases. The effects of fiber volume fraction, peak stress, matrix crack spacing, interface shear stress, interface debonded energy, fibers failure, fiber Poisson contraction, fiber strength, fiber Weibull modulus, matrix cracking mode, applied cycle number and fiber/matrix interface wear on the fatigue stress–strain hysteresis loops and the fiber/matrix interface debonding and sliding are discussed. The experimental cyclic fatigue stress–strain hysteresis loops of unidirectional SiC/CAS, SiC/1723 and C/SiC, 2D cross-ply SiC/CAS and woven SiC/SiC, and 2.5D woven C/SiC composites under cyclic loading/unloading tensile and tension–tension fatigue loading are predicted.

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 with the fiber oxidation and fracture models, and the fiber/matrix interface debonding criterion is adopted to determine the micro-stress field of the damaged fiber-reinforced CMCs. The effects of the fiber volume, interface shear stress, interface debonding energy, oxidation temperature and time on the stress-dependent matrix multiple fractures, interface debonding and oxidation, and fiber fracture are discussed. When the fiber volume fraction and the interface shear stress in the debonding region increased, the matrix first cracking stress and saturation cracking stress increased, the saturation matrix cracking space decreased, and the matrix multiple fracture evolution rate increased. When the interface debonding energy and the interface shear stress in the oxidation region increased, the matrix cracking density increased. When the oxidation temperature and oxidation duration increased, the matrix cracking density decreased. The experimental matrix multiple fractures of unidirectional C/SiC, SiC/SiC, mini-SiC/SiC, SiC/CAS, SiC/CAS-II, and SiC/borosilicate composites are predicted.

6 - Stochastic loading-dependent nonlinear damage behavior of ceramic–matrix composites

In this chapter, the time-dependent first matrix cracking stress of fiber-reinforced ceramic-matrix composites (CMCs) is investigated using the energy balance approach. The shear-lag model combined with the interface oxidation model, fiber oxidation model, and fiber failure model is adopted to analyze the microstress distributions in fiber-reinforced CMCs. The relationships between the first matrix cracking stress, interface debonding and slip, fiber fracture, and oxidation time and temperature are established. The effects of the fiber volume, the interface shear stress, the interface debonding energy, the fiber Weibull modulus, the fiber strength on the first matrix cracking stress, the interface debonding length, and the fiber broken fraction are analyzed. The first matrix cracking stresses of C/SiC with strong and weak interface bonding after unstressed oxidation at 700 °C in air atmosphere are predicted for different oxidation time.

In this paper, the effect of the fiber/matrix interface properties on the tensile and fatigue behavior of 2D woven SiC/SiC ceramic‐matrix composites (CMCs) is investigated. The relationships between the interface parameters of the fiber/matrix interface debonding energy and interface frictional shear stress in the interface debonding region and the composite tensile and fatigue damage parameters of first matrix cracking stress, matrix cracking density, and fatigue hysteresis‐based damage parameters are established. The effects of the fiber/matrix interface properties on the first matrix cracking stress, matrix cracking evolution, first and complete interface debonding stress, fatigue hysteresis dissipated energy, hysteresis modulus, and hysteresis width are analyzed. The experimental first matrix cracking stress, matrix cracking evolution, and fatigue hysteresis loops of SiC/SiC composites are predicted using different interface properties.

In this paper, tensile damage and fracture of 2D SiC/SiC composites are investigated using damage monitoring of acoustic emission (AE) and natural frequency. Nonlinear damage and fracture are mainly attributed to damage mechanisms of matrix cracking, interface debonding, and fibers fracture. Monotonic tensile stress-strain curves are divided into three stages based on the analysis of AE count, amplitude, and energy. Under cyclic loading/unloading, hysteresis loops appear due to internal frictional slip between the fiber and the matrix, and the natural frequency and composite modulus are obtained for different peak stress. A micromechanical tensile and cyclic loading/unloading constitutive model is adopted to predict the tensile curves. Micro damage parameters of interface debonding ratio and broken fibers fraction are used to characterize tensile damage and fracture. Relationships between natural frequency, composite modulus, interface debonding, and fibers fracture are established. Under tensile loading, the AE signal is large and concentrated mainly in the stress range of 50 -100 MPa and 150 -180 MPa, which corresponds to matrix cracking and fiber fracture, respectively. When the degradation rate of natural frequency approaches 0.01, matrix cracking and interface debonding occur, however, fibers failure does not appear; when the degradation rate of natural frequency approaches 0.04, the composite modulus decreases approximately 47 % and the interface debonding ratio approaches 0.8 and the broken fibers fraction is approximately 2.2 %.

In-phase thermomechanical fatigue damage evolution of long fiber-reinforced ceramic-matrix composites using fatigue hysteresis-based damage parameters

9 - Effect of thermal fatigue on nonlinear damage behavior of ceramic–matrix composites

The effect of water on fiber bridging of polymer matrix composites (PMCs) has been studied for stress-corrosion cracking (SCC). The fiber bridging during crack propagation in the PMC was observed directly using a transparent polymer matrix. Specimens were immersed and weighed just before conducting the crack propagation test. The contribution of mechanical degradation caused by the water to the bridging was measured as a function of weight gain due to water absorption. The critical energy release rate of the matrix decreased with increase of the water absorption. The energy release rate of a bridged crack varied with the water absorption. To investigate the variation in the bridging mechanism under the water environment, we calculated the bridging stress the σt and the bridging contribution to crack propagation resistance ΔG based on a single-fiber bridging mechanism with the interfacial debonding length and the interfacial debonding energy. The debonding length was measured directly, and the debonding energy was obtained in a fragmentation test. The calculation showed that the increase in the interfacial debonding length influenced the fiber bridging mechanism.

In the service of composite materials, scenarios involving repeated impacts are frequently encountered. In our study, the time‐frequency characteristics of acoustic emission signals during repeated impact processes were investigated using wavelet packet transform. Principal Component Analysis was utilized to identify the frequency bands containing the most information. Shannon entropy was employed to select the optimal wavelet basis function. The terms DDD3, ADD3, and DAA3 correspond to matrix cracking, delamination, and fiber failure, respectively. The initial impact, due to the presence of numerous internal voids in the specimen, often leads to stress concentration, thus resulting in a prolonged duration of matrix cracking during the initial impact. Delamination becomes more active when matrix cracking initially occurs. Fiber failure typically accompanies unloading when it becomes active. Matrix cracking dissipates the most energy, followed by delamination and then fiber failure. When the final impact penetration occurs, the characteristic frequency band proportions for the quasi‐isotropic matrix cracking, delamination, and fiber failure are 48.99%, 22.39%, and 7.16%, respectively. For the cross‐ply laminate, the corresponding proportions of the characteristic frequency bands are 56.62%, 14.46%, and 6.98%, respectively. Highlights Multiple impact tests were conducted, and acoustic emission signals were recorded. Principal component analysis was performed to select the characteristic frequency bands. The time‐frequency characteristics of the two types of laminated composites during the impact process were analyzed. The trends of the characteristic frequency band proportions under multiple impacts on the composites were investigated.

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.

Continuous SiC fiber‐reinforced titanium matrix (SiC f /Ti) composites are considered promising candidates for low‐pressure compressor blades of aero engines. However, overload failure under coupling conditions of elevated temperature and bending load is the typical failure mode of blade materials, which is important to understand bending damage evolution at service temperature. Herein, three‐point bending interrupted tests of SiC f /Ti composite panel are conducted on parallel specimens at 723 K to capture different damage stages. Combining scanning electron microscopy and micro‐computed tomography, together with finite element analysis, is employed to investigate the failure mechanisms. The composite exhibits a bending strength of 1689 MPa at 723 K. The damage evolution follows a sequential process, interfacial debonding (stage I), tensile‐side fiber fracture (stage II), matrix cracking and multiple fiber breaks (stage III), cladding fracture and limited compressive‐side fiber failure (stage IV), and final catastrophic fracture (stage V). Distinct stress states lead to different fracture morphologies on the tensile and compressive sides, with tensile stress identifies as the primary factor governing failure. These findings establish a coherent understanding of the correlation between stress states and bending damage evolution, providing valuable insights for the structural designs and service reliability of SiC f /Ti composite components in high‐temperature applications.

In this paper, the effect of cyclic fatigue loading on matrix multiple fracture of fiber-reinforced ceramic-matrix composites (CMCs) is investigated using the critical matrix strain energy (CMSE) criterion. The relationships between multiple matrix cracking, cyclic fatigue peak stress, fiber/matrix interface wear, and debonding are established. The effects of fiber volume fraction, fiber/matrix interface shear stress, and applied cycle number on matrix multiple fracture and fiber/matrix interface debonding and interface wear are discussed. Comparisons of multiple matrix cracking with/without cyclic fatigue loading are analyzed. The experimental matrix cracking of unidirectional SiC/CAS, SiC/SiC, SiC/Borosilicate, and mini-SiC/SiC composites with/without cyclic fatigue loading are predicted.

In this chapter, multiple matrix cracking evolution of fiber-reinforced ceramic-matrix composites (CMCs) is investigated using the micromechanical approach. The shear-lag model is adopted to analyze the fiber and matrix stress distributions in the damaged composite. The fracture mechanics approach is used to determine the fiber/matrix interface debonding length. Combining the critical matrix strain energy criterion (CMSE) and fracture mechanics fiber/matrix interface debonding criterion, the stress-dependent multiple matrix cracking evolution is analyzed for different fiber volume fraction, fiber/matrix interface properties, and matrix cracking characteristic stress. Experimental multiple matrix cracking evolution of unidirectional C/Si3N4, SiC/Si3N4, SiC/CAS, SiC/CAS-II, SiC/SiC, SiC/Borosilicate and mini-SiC/SiC composites are predicted.KeywordsCeramic-matrix composites (CMCs)Multiple matrix crackingInterface debonding

A progressive damage model for ceramic matrix mini-composites with thick interphases