Ceramic Matrix Composite Laminates Research Articles

Thermomechanical-induced cracking model for ceramic matrix composite laminates subjected to thermal gradients and transients

Regarding the potential damage and failure issues that may occur in high-temperature transient environments during the service process of ceramic matrix composite laminates, the present work proposes a multi-layer thermomechanical induced crack initiation model for ceramic matrix composite laminates subjected to thermal gradients and transients. This model can determine the history of temperature, deformation, and stress distribution within each layer of the material, as well as the steady-state energy release rate of all possible crack locations. Then the influence of bending constraints on material stress distribution and energy release rate is investigated, finding that maximum stress and energy release rate values are significantly lower without bending constraints compared to those under bending constraints. Furthermore, the study explores the impact of material structural parameters and boundary conditions on the energy release rate of ceramic matrix composite laminates, providing direct insights for designing laboratory tests and evaluating the lifespan of these materials under in-service conditions.

Development of C/PyC/SiC CMCs by CVI Process for Hypersonic Vehicle Application

Hot structures are essentially required for the hypersonic vehicle applications owing to their operation in the dense flight environments. This paper aims at the development and testing of ceramic matrix composite components for air breathing hypersonic vehicle application. In this regard, 2.5D C/PyC/SiC composites were prepared by isothermal Chemical vapour infiltration (CVI) process. X-ray CT analysis was employed to understand the extent of CVI densification in the ceramic matrix composites laminates, and it was under stood that that the intra-bundle infiltration precedes the inter-bundle infiltration with an edge (high) to center (low) gradient. The composite specimens showed an average tensile strength of 206 ± 21 MPa and an average flexural strength of 405 ± 25 MPa, respectively, at room temperature. Thermal conductivity of composite specimens shows an increase in trend with temperature. The composite laminates were successfully tested for use in the air intake ramps of hypersonic air breathing engines.

In-situ observation of damage in unidirectional CMC laminates under tension

We observe microscopic damage progression in un-notched unidirectional SiC–SiC ceramic matrix composite laminates loaded monotonically in tension. In situ tensile testing was conducted in air at room temperature and combined with X-ray tomography imaging. The unidirectional specimens tested were novel double-reduced dogbones designed to develop matrix cracks in the synchrotron field of view. Multiple matrix cracks that rapidly traversed the section of each specimen were observed through the volume until the specimens broke into two pieces. The details of each matrix crack were tracked at each stress increment to better understand how the cracks evolve under load. One of the unidirectional specimens contains a matrix crack that displays a sharp 90° turn along the fiber direction in its final crack path. Fiber breaks were observed and several fibers in the unidirectional specimen showed multiple breaks. Fiber break opening was measured for each fiber break and the average fiber break opening for each stress increment is reported. The location and pullout distance of fiber breaks surrounding a matrix crack, as well as matrix crack spacing, are of modeling interest and are reported.

Combining in-situ synchrotron X-ray microtomography and acoustic emission to characterize damage evolution in ceramic matrix composites

In-situ synchrotron X-ray microtomography and acoustic emission (AE) were combined to study the behavior of ceramic matrix composite laminates subjected to in-plane tensile or flexural loading at room temperature. A detailed characterization of the initiation and progression of two key damage modes (matrix cracking and fiber breaks) is obtained from microtomography, and the relationship between damage and AE is directly observed. A graphical representation of AE data, which has potential for real-time use, is employed to reveal differences in damage progression due to fiber architecture or loading mode. In addition, strong empirical relationships are observed between matrix crack area and AE energy, as well as between fiber breaks and number of AE events.

Experimental assessment of toughness in ceramic matrix composites using the J-integral with digital image correlation part I: methodology and validation

The complex nature of damage in ceramic matrix composites (CMCs) renders conventional methods of measuring quantitative fracture properties impractical. This paper is the first of two-part series that assesses the feasibility of using the J-integral with full-field deformation data from digital image correlation (DIC) to characterize toughness in continuous fiber SiC/SiC CMC laminates. It provides a resource for best practices when incorporating experimentally measured, full-field deformation data into J-integral evaluations of toughness. The techniques discussed are important for researchers attempting to measure fracture properties in advanced materials with damage mechanisms that have yet to be well characterized. Two methods for evaluating potential energy release rates J are presented: (1) numerical integration over a line contour and (2) Gaussian integration over an area contour. Accuracy and path independency for both methods were verified using analytically derived deformation fields for a center-cracked, infinite plate of isotropic material under equi-biaxial tension. Inherent noise in the deformation data and necessary contour truncation at the crack surfaces reduced accuracy and introduced path dependency. However, this was mitigated by careful noise filtering of the deformation data prior to the evaluation of J. Applying the line and area integrals to DIC data from tapered, double-cantilever beam, acrylic compact tension specimens resulted in the findings that (1) both integrals measured fracture toughness within a range of published values; (2) both integrals captured the constant stress intensity factor behavior that is characteristic of the tapered beam geometry; and (3) the area integral measurements were consistently larger than line integral measurements. The area integral is more accurate than the line integral as it samples more data points, reducing its sensitivity to experimental noise. Although variability in experimental data can be minimized, it cannot be eliminated. Measurement error is inevitable; thus, the line and area integrals must be used with caution when characterizing quantitative properties including fracture toughness.

Matrix cracking of fiber-reinforced ceramic composites in shear

The mechanics of cracking in fiber-reinforced ceramic matrix composites (CMCs) under general loadings remains incomplete. The present paper addresses one outstanding aspect of this problem: the development of matrix cracks in unidirectional plies under shear loading. To this end, we develop a model based on potential energy differences upstream and downstream of a fully bridged steady-state matrix crack. Through a combination of analytical solutions and finite element simulations of the constituent stresses before and after cracking, we identify the dominant stress components that drive crack growth. We show that, when the axial slip lengths are much larger than the fiber diameter and when interfacial slip precedes cracking, the shear stresses in the constituents are largely unaffected by the presence of the crack; the changes that do occur are confined to a ‘core’ region within a distance of about one fiber diameter from the crack plane. Instead, the driving force for crack growth derives mainly from the axial stresses—tensile in the fibers and compressive in the matrix—that arise upon cracking. These stresses are well-approximated by solutions based on shear-lag analysis. Combining these solutions with the governing equation for crack growth yields an analytical estimate of the critical shear stress for matrix cracking. An analogous approach is used in deriving the critical stresses needed for matrix cracking under arbitrary in-plane loadings. The applicability of these results to cross-ply CMC laminates is briefly discussed.

A Pre-Stitching Method to Manufacture Z-Pins Reinforced Woven Ceramic Matrix Composite Laminates

Z-pins reinforced 2D ceramic matrix composites (CMCs), integratedly designed new materials, are developed to enhance 2D CMCs through-thickness in the form of Z-pins and to ensure significant increase in interlaminar fracture toughness, delamination resistance and impact resistance, and Z-pins reinforced 2D CMCs have much application. A manual pre-stitching method is developed to make holes in the graphite fixture to control Z-pins row spacings and to introduce yarns of 3000 T300 carbon fibers bundle into a preform. Z-pins reinforced woven CMCs for research were manufactured successfully by repeatedly using chemical vapor infiltration (CVI) to infiltrate SiC matrix into woven preform and carbon fiber sutures. It is shown that this method of manufactured Z-pins reinforced woven CMC is feasible.

Remediation of a constitutive model for ceramic composite laminates

Constitutive models for fiber-reinforced ceramic-matrix composites (CMCs) are needed to enable implementation of these materials in future engineering systems. One such constitutive model, developed by Genin and Hutchinson [1], is based on a phenomenological description of the inelastic response of CMC laminates. Although the model has found some utility in elucidating the role of inelasticity in stress re-distribution around strain concentrating features, we find that, in some instances, finite element analyses based on this model exhibit numerical convergence problems. In the present study, we demonstrate both analytically and by finite element analyses that, for certain anisotropic laminates, these numerical issues stem from the fact that the model formulation is unstable. Additionally, we propose and assess modifications to the formulation that mitigate these problems yet retain the positive features of the original model. The expectation is that the modifications will enable broader utilization of the model within the engineering design community.

An Examination of Failure Criteria for Notched Orthotropic Ceramic Matrix Composite Laminates

The purpose of this paper is to further study the Yeh-Stratton (Y-S) failure criterion when applied to the newly developed ceramic matrix composite (CMC). In this study, the failure analysis of notched CMC laminates is investigated by the Y-S criterion and compared to linear elastic stress models including the average stress criterion (ASC), point stress criterion (PSC), and the D criterion.The materials being examined are fiber-reinforced orthotropic composites, which are a new CMC of interest in the aerospace industry, and a graphite/epoxy AS4/3502. Testing of both fiber-reinforced CMC [0/90] and AS4/3502 [0/902/0] laminates, containing central cracks and under tensile loading conditions, were analytically investigated by the failure criteria and evaluated against the experimental results.The study results indicate that the Y-S criterion and the linear elastic stress models predict the fracture of orthotropic laminated composites containing a center crack under tensile loading to a similar degree of accuracy. The results also indicate that the damage zone size predicted by the Y-S criterion does not represent the actual damage zone size. The linear elastic stress models appear to predict the actual damage zone size within an order of magnitude. It is apparent that further research on this topic of damage zone size prediction is needed.

Nondestructive Evaluation and Mechanical Characterization of a Defect‐Embedded Ceramic Matrix Composite Laminate

A C/SiC composite panel with defects of known size and of familiar nature was manufactured successfully for nondestructive evaluation. A computed tomography (CT) system was used to detect embedded defects. The results show that CT imaging corresponds well with the designed defects. The defect‐embedded composites undergo relatively greater loss in tensile strength and failure strain than the as‐received samples, although their initial Young's moduli are almost identical. It is also observed that the embedded defects make a significant contribution toward the initiation and accumulation of the damage in the composites, which result eventually in the early failure of the composite.

Fracture behaviour of cross-ply Nicalon/CAS-II glass–ceramic matrix composite laminate at room and elevated temperatures

Abstract The fracture behaviour of cross-ply Nicalon/CAS-II glass–ceramic matrix composite laminate has been investigated as a function of temperature, loading rate and environment. Tests were carried out at 20, 600, 800, 1000 °C in air and also at 1000 °C in vacuum. Increased flexural strength was obtained with increased loading rate but it decreased with increasing test temperature. Although the change in flexural strength was not very significant for the loading rates (10−3 and 10−1 mm/min) employed in this study except at 600 °C in air, the influence of environment was dramatic. The flexural strength at 1000 °C in vacuum was comparable to the value obtained at room temperature in air, however, the flexural strength at 1000 °C in air reduced significantly from its room temperature value. Two major damage modes have been identified: fibrous at room temperature and non-fibrous at high temperature.

Probabilistic Modeling of Ceramic Matrix Composite Strength

Uncertainties associated with the primitive random variables such as manufacturing process (processing temperature, fiber volume ratio, void volume ratio), constituent properties (fiber, matrix and interface), and geometric parameters (ply thickness, interphase thickness) have been simulated to quantify the scatter in the first matrix cracking strength (FMCS) and the ultimate tensile strength of SCS-6/RBSN [SiC fiber (SCS-6) reinforced reaction-bonded silicon nitride composite] ceramic matrix composite laminate at room temperature. Cumulative probability distribution function for the FMCS and ultimate tensile strength at room temperature (RT) of [0]8, [02/902] S, and [±452] S laminates have been simulated and the sensitivity of primitive variables to the respective strengths have been quantified. Computationally predicted scatter of the strengths for a uniaxial laminate has been compared with those from limited experimental data. Also the experimental procedure used in the tests has been described briefly. Results show a very good agreement between the computational simulation and the experimental data. Dominating failure modes in [0]8, [0/90] S, and [±45] S laminates have been identified. Results indicate that the first matrix cracking strength for the [0]8 and [0/90] S, laminates is sensitive to the thermal properties, modulus and strengths of both the fiber and matrix whereas the ultimate tensile strength is sensitive to the fiber strength and the fiber volume ratio. In the case of a [±45] S laminate, both the FMCS and the ultimate tensile strengths have a small scatter range and are sensitive to the fiber tensile strength as well as the fiber volume ratio.

Probabilistic Modeling of Ceramic Matrix Composite Strength

Uncertainties associated with the primitive random variables such as manufacturing process (processing temperature, fiber volume ratio, void volume ratio), constituent properties (fiber, matrix and interface), and geometric parameters (ply thickness, interphase thickness) have been simulated to quantify the scatter in the first matrix cracking strength (FMCS) and the ultimate tensile strength of SCS-6/RBSN [SiC fiber (SCS-6) reinforced reaction-bonded silicon nitride composite] ceramic matrix composite laminate at room temperature. Cumulative probability distribution function for the FMCS and ultimate tensile strength at room temperature (RT) of [0]8, [02/902]S, and [±452]S laminates have been simulated and the sensitivity of primitive variables to the respective strengths have been quantified. Computationally predicted scatter of the strengths for a uniaxial laminate has been compared with those from limited experimental data. Also the experimental procedure used in the tests has been described briefly. Results show a very good agreement between the computational simulation and the experimental data. Dominating failure modes in [0]8, [0/90]S, and [±45]S laminates have been identified. Results indicate that the first matrix cracking strength for the [0]8 and [0/90]S, laminates is sensitive to the thermal properties, modulus and strengths of both the fiber and matrix whereas the ultimate tensile strength is sensitive to the fiber strength and the fiber volume ratio. In the case of a [±45]S laminate, both the FMCS and the ultimate tensile strengths have a small scatter range and are sensitive to the fiber tensile strength as well as the fiber volume ratio.

Reliability Analysis of Ceramic Matrix Composite Laminates

At a macroscopic level, a composite lamina may be considered as a homogeneous orthotropic solid whose directional strengths are random variables. Incorporation of these random variable strengths into failure models, either interactive or noninteractive, allows for the evaluation of the lamina reliability under a given stress state. Using a noninteractive criterion for demonstration purposes, laminate reliabilities are calculated assuming previously established load sharing rules for the redistribution of load as the failure of laminae occurs. The matrix cracking predicted by ACK theory is modeled to allow a loss of stiffness in the fiber direction. The subsequent failure in the fiber direction is controlled by a modified bundle theory. Results using this modified bundle model are compared with previous models, which did not permit separate consideration of matrix cracking, as well as to results obtained from experimental data.

A Review of Failure Models for Ceramic Matrix Composite Laminates Under Monotonic Loads

Ceramic matrix composites offer significant potential for improving the performance of turbine engines. In order to achieve their potential, however, improvements in design methodology are needed. In the past most components using structural ceramic matrix composites were designed by “trial and error” since the emphasis on feasibility demonstration minimized the development of mathematical models. To understand the key parameters controlling response and the mechanics of failure, the development of structural failure models is required. A review of short-term failure models with potential for ceramic matrix composite laminates under monotonic loads is presented. Phenomenological, semi-empirical, shear-lag, fracture mechanics, damage mechanics, and statistical models for the fast fracture analysis of continuous fiber unidirectional ceramic matrix composites under monotonic loads are surveyed.

High-Temperature Tensile Properties of Fiber Reinforced Reaction Bonded Silicon Nitride

A testing technique has been developed for measuring the tensile properties of ceramic matrix composite laminates at temperatures up to 1500°C in air. Using this technique, the tensile properties of unidirectional silicon carbide (SiC) fiber reinforced reaction bonded silicon nitride (SiC/RBSN) composite specimens were measured at 25, 1300, and 1500°C. The composite consists of nearly 30 vol % of aligned 142 μm, chemically vapor deposited SiC fibers (Textron SCS-6). The specimens used were straight section flat specimens with bonded end tabs. A specially designed gripping system was used to minimize bending moment and assured that failure always occurred in the gage section. The specimen extension was measured using a high-temperature capacitive extensometer.