EFFECTS OF AS-RECEIVED DEFECTS ON CERAMIC MATRIX COMPOSITES PROPERTIES USING HIGH- FIDELITY MICROSTRUCTURES WITH PERIODIC BOUNDARY CONDITIONS

2021 ◽  
Author(s):  
KHALED H. KHAFAGY, ◽  
ADITI CHATTOPADHYAY
Keyword(s):  
Boundary Conditions ◽  
Periodic Boundary ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Periodic Boundary Conditions ◽  
Material Behavior ◽  
Recent Effort ◽  
High Fidelity ◽  
Matrix Composites ◽  
Damage Initiation

The presence of microstructural defects in as-received specimens of ceramic matrix composites (CMCs) significantly influences their constitutive response and damage, highlighting the importance of characterization and quantification of these defects for accurate assessment of damage and failure in the service environment. In a recent effort, the authors developed an algorithm to generate stochastic representative volume elements (SRVEs) of Carbon fiber Silicon-Carbide-Nitride matrix (C/SiNC) CMCs based on extensive multiscale material and defect characterization data. This paper implements this algorithm within a commercial finite element solver with periodic boundary conditions (PBCs) for high-fidelity micromechanics analysis and investigation of macroscopic material behavior of C/SiNC composites. Different loading directions are used to predict the global mechanical properties, and the results are in excellent agreement with theoretical (rule of mixture) predictions. Subsequently, the effects of as-received defects on the global and local responses are investigated. The results show that intratow porosity has pronounced degradation effects on the global elastic properties and results in complex stress localization patterns, which can be attributed to potential damage initiation sites.

Effect of Microporosity on Damage Initiation in Ceramic Matrix Composites

2019 ◽  
Author(s):  
Suhasini Gururaja ◽  
Abhilash Nagaraja
Keyword(s):  
Gas Turbines ◽  
Ceramic Matrix Composites ◽  
Local Stress ◽  
Ceramic Matrix ◽  
Matrix Composites ◽  
Damage Initiation ◽  
The Matrix ◽  
Homogenization Approach ◽  
Matrix Porosity ◽  
Monolithic Ceramics

Abstract Ceramic matrix composites (CMC) are a subclass of composite materials consisting of reinforced ceramics. They retain the advantages of ceramics such as lower density and better refractory properties but exhibit better damage tolerance compared to monolithic ceramics. This combination of properties make CMCs an ideal candidate for use in high temperature sections of gas turbines. However, modeling the damage mechanisms in CMCs is complex due to the heterogeneous microstructure and the presence of processing induced defects such as matrix porosity. The effect of matrix pore location and orientation on damage initiation in CMCs is of interest in the present work. CMCs fabricated by various fabrication processes exhibit matrix pores at different length scales. Microporosities exist within fiber bundles in CMCs have a significant effect on microscale damage initiation and forms the focus of the current study. In a previous work by the authors, a two step numerical homogenization approach has been developed to model statistical distribution of matrix pores and to obtain the effective mechanical properties of CMCs in the presence of matrix porosity. A variation of that approach has been adopted to model matrix pores and investigate the severity of pores with respect to their location and orientation. CMC microstructure at the microscale has been modeled as a repeating unit cell (RUC) consisting of fiber, interphase and matrix. Ellipsoidal pores are modeled in the matrix with pore distance from the interphase-matrix interface and pore orientation with respect to the loading direction as parameters. Periodic boundary conditions (PBCs) are specified on the RUC by means of constraint equations. The effect of the pore on the local stress fields and its contribution to matrix damage is studied.

Stochastic microstructural analysis of ceramic matrix composites using a high-fidelity multiscale framework

2021 ◽  
Author(s):  
Khaled H. Khafagy ◽  
Karthik Rajan R. Venkatesan ◽  
Kranthi Balusu ◽  
Siddhant Datta ◽  
Aditi Chattopadhyay
Keyword(s):  
Microstructural Analysis ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
High Fidelity ◽  
Matrix Composites

scholarly journals Prediction of Failure in Ceramic Matrix Composites Using Damage-Based Failure Criterion

2020 ◽  
Vol 4 (4) ◽  
pp. 183
Author(s):  
Neraj Jain ◽  
Dietmar Koch
Keyword(s):  
Failure Criterion ◽  
Damage Mechanics ◽  
Shear Test ◽  
Damage Model ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Filament Winding ◽  
Material Behavior ◽  
Matrix Composites ◽  
Inelastic Behavior

This paper presents a damage-based failure criterion and its implementation in order to predict failure in ceramic matrix composites (CMC) manufactured via filament winding. The material behavior of CMCs is anisotropic and strongly depends on the angle between fiber orientation and loading direction. The inelastic behavior of laminates with different fiber orientations under tension and shear is modeled with the help of continuum damage mechanics. The parameters required for the damage model are obtained from a standard tensile and shear test. An isotropic damage law determines the evolution of damage in thermodynamic space and considers the interaction of damage parameters in different principal material directions. A quadratic damage-based failure criterion inspired by the Tsai-Wu failure criterion is proposed. Failure stress and strain can be predicted with higher accuracy compared to the Tsai-Wu failure criterion in stress- or strain-space. The use of the proposed damage limits allows designing a CMC component based on the microstructural phenomenon of stiffness loss. With the help of results obtained from modeling and experiments, fracture mechanics during the Iosipescu-shear test of CMCs and its capability to determine the shear strength of the material is discussed.

A Damage-Based Fatigue Model of Braided Ceramic Matrix Composites at Elevated Temperature

2020 ◽  
Author(s):  
Changqi Liu ◽  
Duoqi Shi ◽  
Xiaoguang Yang ◽  
Xuefeng Teng
Keyword(s):  
High Temperature ◽  
Cyclic Loading ◽  
Fatigue Damage ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Fatigue Analysis ◽  
Experimental Results ◽  
Fiber Bundles ◽  
Matrix Composites ◽  
Damage Initiation

Abstract Ceramic matrix composites (CMCs) play an increasingly significant role in the modern aerospace industry due to their excellent high-temperature mechanical properties. Fatigue property at elevated temperatures is an essential issue for their application, especially for the turbine blades of aircraft engines subjected to cyclic loading under extreme conditions. A progressive fatigue damage approach was established to predict the damage initiation and evolution of braided SiC/SiC CMCs under tension-tension cyclic loading. The main framework was achieved via a user-material subroutine UMAT in ABAQUS with FORTRAN code. Different damage initiation criteria are introduced for fiber bundles, matrix and interface. Related experimental results reveal that the main reasons for the failure of composites under cyclic loading are the loss of bearing capacity of the matrix, the decrease of fiber strength in high-temperature oxidation environment and the interface wear. Hence, the stiffness and strength degradation of matrix and fiber bundles as well as the interfacial shear stress reduction are used to describe the fatigue damage in this method. And a specific proportion of failure elements on the loading surface is regarded as the symbol of the eventual failure of the composites. Damage evolution of different constituents during the fatigue process can be simulated with this method. Subsequently, the simulation results of static and fatigue analysis were compared with relevant experimental results at 1300°C. It indicates that the predicted static tensile strain-stress curve, and curves of maximum strains vs cycles in the fatigue analysis are in good agreement with that measured during the experiments. Besides, the predicted fatigue life also exhibits an acceptable consistency.

Molecular Dynamics Using Non-Variational Polarizable Force Fields: Theory, Periodic Boundary Conditions Implementation and Application to the Bond Capacity Model

2019 ◽  
Author(s):  
Pier Paolo Poier ◽  
Louis Lagardere ◽  
Jean-Philip Piquemal ◽  
Frank Jensen
Keyword(s):  
Boundary Conditions ◽  
Periodic Boundary ◽  
Force Fields ◽  
Periodic Boundary Conditions ◽  
Computational Effort ◽  
Polarizable Force Fields ◽  
Energy Models ◽  
Capacity Model ◽  
Energy Gradient ◽  
Polarization Models

<div> <div> <div> <p>We extend the framework for polarizable force fields to include the case where the electrostatic multipoles are not determined by a variational minimization of the electrostatic energy. Such models formally require that the polarization response is calculated for all possible geometrical perturbations in order to obtain the energy gradient required for performing molecular dynamics simulations. </p><div> <div> <div> <p>By making use of a Lagrange formalism, however, this computational demanding task can be re- placed by solving a single equation similar to that for determining the electrostatic variables themselves. Using the recently proposed bond capacity model that describes molecular polarization at the charge-only level, we show that the energy gradient for non-variational energy models with periodic boundary conditions can be calculated with a computational effort similar to that for variational polarization models. The possibility of separating the equation for calculating the electrostatic variables from the energy expression depending on these variables without a large computational penalty provides flexibility in the design of new force fields. </p><div><div><div> </div> </div> </div> <p> </p><div> <div> <div> <p>variables themselves. Using the recently proposed bond capacity model that describes molecular polarization at the charge-only level, we show that the energy gradient for non-variational energy models with periodic boundary conditions can be calculated with a computational effort similar to that for variational polarization models. The possibility of separating the equation for calculating the electrostatic variables from the energy expression depending on these variables without a large computational penalty provides flexibility in the design of new force fields. </p> </div> </div> </div> </div> </div> </div> </div> </div> </div>

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