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Typical stress/strain curves in the GCS of the off-axis specimens with different off-axis angles (θ) under monotonic and incremental cyclic compression loadings.
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This paper reports an experimental investigation on the macroscopic mechanical behaviors and damage mechanisms of the plain-woven (2D) C/SiC composite under in-plane on- and off-axis loading conditions. Specimens with 15°, 30°, and 45° off-axis angles were prepared and tested under monotonic and incremental cyclic tension and compression loads. The...
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... Extensive characterization of multiple classes of CMCs has been performed at ambient temperature using the standard tensile test. 6,16,20,[22][23][24][25][26][27][28][29][30][31] Such tests create a low-effort baseline to compare properties, evaluate processing techniques, understand materials architectures, and evaluate setups. However, when a material is intended to be used in a hightemperature environment, it is critical to know how its properties will change with temperature, which is not a simple extrapolation from room temperature tests. ...
Careful material selection is paramount to meet the significant challenges posed by harsh environments in advanced applications. Ceramic matrix composites (CMCs) have come to the forefront of consideration for many of these applications where environmental resistance needs to be combined with structural stability at high temperatures (1200°C+). Many gaps exist in understanding how material variations pose unique material and design challenges that affect the final performance in a particular application. Thorough materials testing at relevant temperatures is required for various candidate materials to realize an analytical approach to materials selection. This review will discuss mechanical and environmental tests and their use at high temperatures including tensile tests, flexure tests, lifetime testing methods, interlaminar tests, and environmentally relevant tests. Challenges for performing these tests at high temperatures and on CMCs will be discussed. A literature review will provide examples of state‐of‐the‐art testing, and the test results from historical work and improvement opportunities will be addressed. This review aims to provide an overview of the current capabilities and practices for high‐temperature testing and recommend best practices for performing high‐temperature tests and interpreting and sharing the results and metadata with the larger community to expand the CMC material property database.
... Due to the anisotropic physical characteristics of carbon fibers and the directional woven structure of preforms, C/SiC composites have anisotropy in both mechanical and thermal properties. [10][11][12][13][14] According to the woven method of fibers, the woven types of C/SiC composites include 2D plain woven, 3D orthogonal woven, and 3D needled structure types. [1,15] The heat transfer along the carbon fiber is several times greater than that perpendicular to it, [16][17][18] while the SiC matrix is isotropic. ...
Due to the anisotropic fibers and structure distribution, fiber-reinforced composites possess anisotropic mechanical and heat transfer properties. For C/SiC composites, the out-of-plane thermal conductivity was mainly studied whereas the in-plane thermal conductivity received less attentions due to its limited thickness. In this study, the slab module of transient plane source method is adopted to measure the in-plane thermal conductivity of 2D plain woven C/SiC composite slab and the test uncertainty is analyzed numerically for the first time. The numerical investigation proves that the slab module is reliable for measuring the isotropic and anisotropic slabs with in-plane thermal conductivity greater than 10 W·m ⁻¹ ·K ⁻¹ . The anisotropic thermal conductivity of 2D plain woven C/SiC composite slab is obtained within the temperature range of 20℃-900℃ by combining with the laser flash analysis method to measure the out-of-plane thermal conductivity. The results demonstrate that the out-of-plane thermal conductivity of C/SiC composite decreases with temperature while its in-plane thermal conductivity increases with temperature first and then decreases, and the ratio of in-plane thermal conductivity to out-of-plane thermal conductivity is within 2.2-3.1.
... A similar phenomenon has been later discovered from the in-plane shear experiment of 2D C/SiC composite. 5 Li et al. 6 have systematically discussed the failure modes and failure mechanisms of 2D C/SiC composite. The damage modes of 0 • tensile specimen include transverse matrix cracking, interface debonding, fiber breakage, and pullout. ...
... To verify the proposed model, it needs the experimental results at different temperatures. The experimental stress-strain curves at RT are referred to in the work of Li et al. 6 In this paper, we will supplement ultra-high-temperature experiments for 2D C/SiC composites. ...
... In-plane off-axis tensile, off-axis compressive, and shear stress-strain curves of 2D C/SiC composite referred to Li et al. 6 at RT are shown in Figure 2A-C. It is observed that all of the off-axis tensile and in-plane shear stress-strain responses of the material are dramatically nonlinear. ...
Complex microstructure and multiple internal microcrack propagation of braided silicon carbide ceramic matrix composites (CMCs‐SiC) make their mechanical behavior remarkably nonlinear. Still, few models have been developed at ultra‐high temperature due to the challenge to incorporate detailed micromechanisms of nonlinearity into the formulation. Based on the observations of fracture morphologies of previous experiments of CMCs‐SiC under different stress states and current on‐axis tensile experiments of 2D C/SiC composites at ultra‐high temperature, some assumptions are proposed. Then, a physically based constitutive model at ultra‐high temperature is established within the thermo‐elastoplastic framework. The novelty of this model is that we proposed a thermal yield criterion, which considers the material orthotropy, tension‐compression asymmetry, unilateral crack closure effect, and temperature effect. The thermal hardening effect is a distinctive phenomenon for CMCs‐SiC in vacuum and is described using an improved Johnson–Cook model. The proposed model is implemented using a return mapping algorithm. The results show that the model predictions of stress–strain relationships agree well with experimental data at different stress states and different temperatures.
... A similar phenomenon has been later discovered from the in-plane shear experiment of 2D C/SiC composite. 5 Li et al. 6 have systematically discussed the failure modes and failure mechanisms of 2D C/SiC composite. The damage modes of 0 • tensile specimen include transverse matrix cracking, interface debonding, fiber breakage, and pullout. ...
... To verify the proposed model, it needs the experimental results at different temperatures. The experimental stress-strain curves at RT are referred to in the work of Li et al. 6 In this paper, we will supplement ultra-high-temperature experiments for 2D C/SiC composites. ...
... In-plane off-axis tensile, off-axis compressive, and shear stress-strain curves of 2D C/SiC composite referred to Li et al. 6 at RT are shown in Figure 2A-C. It is observed that all of the off-axis tensile and in-plane shear stress-strain responses of the material are dramatically nonlinear. ...
With the improvement on materials performance gradually reaching its bottleneck, more and more works focus on optimizing the device structures to seek further performance enhancement of thermoelectric (TE) devices. This paper proposed an analytical model to calculate the performance of thermoelectric generators (TEGs) with varied leg cross-sections considering temperature-dependent material properties. The explicit expressions of output power and efficiency are derived and the model is verified by finite element method (FEM). Furthermore, the optimization of leg geometry for higher device performance is performed based on the presented model, the results show that the key to maximum output power is to minimize the leg resistance; and increasing the leg volume may simultaneously raise the output power and efficiency. In addition, we apply the presented model to optimize the leg shape of a commercial TEG module and find that the optimized geometry can simultaneously achieve an enhancement up to 43.1% for output power and 9.67% for efficiency. The presented model thus may be useful in designing high-performance TEGs and shed considerable light on the principles of TEG design.
... An accurate evaluation of the mechanical behavior of woven fiberreinforced ceramic matrix composite (CMC) becomes essential for structural design and application, therefore the preparation methods, the subsequent mechanical properties, and failure responses of the composite material have been extensively studied in past few years [7][8][9][10][11][12][13]. Some important results have been reported accordingly. ...
... An interesting damage coupling effect of a 2D woven carbon fiberreinforced silicon carbide composite under proportional loading conditions was reported by HB Guo et al. [12,24]. It was demonstrated that the axial tensile and compressive strength of the 2D-C/SiC composite decreases by 52% and 25% with increasing off-axis angle from 0°to 45°. ...
... It has been reported that the shear contribution coefficient α is a crucial parameter for the macroscopic stress-strain behavior of woven composite material under a planar tension-shear stress state due to the interaction of stress components on the damage initiation and evolution. The coupling effect on the acceleration of the damage has been observed and proposed for 2D woven ceramic matrix composite [12,13]. Three monotonic increasing functions g 12 ; g 16 , and g 61 were proposed to characterize the damage coupling effect in the global constitutive model, which depends on the thermodynamic forces. ...
The focus of this work is to characterize the progressive damage and failure behavior of 2.5D woven alumina fiber reinforced silica ceramic matrix thin composite specimen under a planar tension-shear stress state. The tensile and shear stress-strain diagrams in the principal material coordinate system were obtained using the off-axis tension test with the digital image correlation technique. A mesoscale finite element model of the composite material was developed within the framework of continuum damage mechanics. The thickness effect on the macroscopic mechanical response was considered by removing the periodic boundary conditions along the thickness direction. The macroscopic stress-strain response given by the numerical model was validated by the experimental results. The interaction of the planar biaxial tension and shear stresses was taken into account in the model, quantified using a shear contribution coefficient in the modified 3D Hashin failure criterion. The results from the damage evolution analysis indicate that the linear tensile stress-strain response with a brittle fracture characteristic for the on-axis tension specimen is governed by the axial fiber bundle. The nonlinear tensile stress-strain response with the significantly reduced ultimate stress under biaxial tension and shear stress state results from multiple damages with evolution in both axial and transverse fiber bundles. Both the effective tensile modulus and the ultimate tensile strength increase with increasing the thickness of the specimen due to the increase of the fiber volume fraction. The strengthening induced by the size effect is less significant for the specimen under biaxial tension and shear stress state than that for the on-axis tension specimen owing to the involvement of shear response dominated by the matrix of the material. The results of this study provide new insight into the failure of 2.5D woven ceramic-based composite material, which contributes to the optimal design of the reusable thermal protection system structure.
... A number of experimental works reported so far have demonstrated such damage coupling effects. [21][22][23] However, for CMCs under multiaxial loadings, the influence of coupled damage evolution upon the ultimate rupture strength has not been extensively and deeply investigated. Recently, Yang et al proposed a failure criterion in terms of damage variables to predict strength envelop of damageable CMCs, and the damage evolutions were characterized by a decoupling method. ...
... The worse the internal damage presents, the smaller the unloading modulus becomes and the larger the residual strain remains. [23][24] Such correlations are meaningful for the establishment of damage constitutive model. ...
... Parameters appeared in Eqs. (23) and (24) are assumed to be constants which can be identified by a set of single loading tests. According to the maximum DERR criterion, if external load is imposed along either 1-or 2-axis of the material, the failure condition is ...
To predict the nonlinear stress‐strain behavior and the rupture strength of orthotropic ceramic matrix composites (CMCs) under macroscopic plane stress, a concise damage‐based mechanical theory including a new constitutive model and two kinds of failure criteria was developed in the framework of continuum damage mechanics (CDM). The damage constitutive model was established using strain partitioning and damage decoupling methods. Meanwhile, the failure criteria were formulated in terms of damage energy release rate (DERR) in order to correlate the failure property of CMCs with damage driving forces, and the maximum DERR criterion and the interactive DERR criterion were suggested simultaneously. For the sake of model evaluation, the theory was applied to a typical CMC with damageable and nonlinear behavior, that is, 2D‐C/SiC. The damage evolution law, strain response and rupture strength under incremental cyclic tension along both on‐axis and off‐axis directions were completely investigated. Comparison between theoretical predictions and experimental data illustrates that the newly developed mechanical theory is potential to give reasonable and accurate results of both stress‐strain response and failure property for orthotropic CMCs.
... For the ceramic matrix composite sub-components, the maximum stress failure criterion has been adopted [25][26][27][28][29]. The failure index is evaluated according to the following equation taking into account the orthotropy of the material system: ...
... (1) 0.647537 0.659381 (2) 0.656857 0.669227 (3) 0.647964 0.659764 (4) 0.657707 0.670065 (24) 0.644913 0.65589 (25) 0.657207 0.668989 (26) 0.643905 0.654769 (27) 0.623415 0.635386 (28) 0.580365 0.59134 ...
... The temperature distribution, evaluated by means of the thermal analysis, shows that the results of the local models, illustrated in the previous paragraphs, are very accurate (see Figure 13). The maximum temperature value at 1200 s in the area of interest is 1097 • C which is very close to the one predicted with the local models (1095 • C and 1115 • C). (24) 0.644913 0.65589 (25) 0.657207 0.668989 (26) 0.643905 0.654769 (27) 0.623415 0.635386 (28) 0.580365 0.59134 Finally, the authors have investigated the influence of the local models size on the structural analyses results. Considerations obtained for the thermal analyses can be repeated showing that local model B and C are the best choices. ...
The thermo-structural design of the wing leading edge of hypersonic vehicles is a very challenging task as high gradients in thermal field, and hence high thermal stresses, are expected. Indeed, when employing passive hot structures based thermal protection systems, very high temperatures (e.g., 1400 °C) are expected on the external surface of the wing leading edge, while the internal structural components are required to not exceed a few hundred degrees Celsius (e.g., 400 °C) at the interface with the internal cold structure. Hence, ceramic matrix composites (CMC) are usually adopted for the manufacturing of the external surface of the wing leading edge since they are characterized by good mechanical properties at very high temperatures (up to 1900 °C) together with an excellent thermal shock resistance. Furthermore, the orthotropic behavior of these materials together with the possibility to tailor their lamination sequence to minimize the heat transferred to internal components, make them very attractive for hot structure based thermal protection systems applications. However, the numerical predictions of the thermo-mechanical behavior of such materials, taking into account the influence of each ply (whose thickness generally ranges between 0.2 and 0.3 mm), can be very expensive from a computational point of view. To overcome this limitation, usually, sub-models are adopted, able to focus on specific and critical areas of the structure where very detailed thermo-mechanical analyses can be performed without significantly affecting the computational efficiency of the global model. In the present work, sub-modeling numerical approaches have been adopted for the analysis of the thermo-mechanical behavior of a ceramic matrix composite wing leading edge of a hypersonic vehicle. The main aim is to investigate the feasibility, in terms of computational efficiency and accuracy of results, in using sub-models for dimensioning complex ceramic matrix components. Hence, a comprehensive study on the size of sub-models and on the choice of their boundaries has been carried out in order to assess the advantages and the limitations in approximating the thermo-mechanical behavior of the investigated global ceramic matrix composite component.
... In general, ceramic materials are characterized by a very brittle behavior, then a fiber reinforcement is needed to increase the strength and damage tolerance characteristics towards a more ductile behavior. Several works have demonstrated that C/SiC components can be largely adopted in aerospace applications since they can guarantee lightness, high damage tolerance, crack/fracture resistance, high tensile, bending and compression strength aside from high temperature stability (1900°C) and excellent thermal shock resistance [2][3][4][5]. Concerning the connections between hot and cold structures, the presence of major thermal gradients associated to significant thermal expansion coefficients variations suggests to allow relative displacements of the joining components, as much as possible. Typically, in order to fulfill this requirement, very thin structures and joining elements are adopted to minimize the interfacial stresses [6][7][8][9][10][11]. ...
The design of the wing leading edge of re-entry vehicles is a very challenging task since severe aerothermal loads are encountered during the re-entry trajectory. Hence, advanced materials and structural concepts need to be adopted to withstand the elevated thermal gradients and stresses. Furthermore, particular attention must be paid to the design of hot areas and connections between hot and cold areas of the structure, where the presence of major thermal gradients associated to significant thermal expansion coefficients variations, can lead to damage onset and failure. In order to face this issues, Ceramic Matrix Composites are generally employed as passive hot structures due of their capability to operate at elevated temperatures retaining acceptable mechanical properties. In the present work a novel thermo-structural concept of an hypersonic wing leading edge is introduced and verified by means of an advanced finite element thermo-structural model.
... Due to their superior mechanical properties under elevated temperature, woven Ceramic Matrix Composites (CMCs) such as C/SiC are competitive materials for thermal structural applications [1][2][3]. CMCs typically begin to exhibit nonlinear behaviors in stress-strain curves under relatively low stress states (less than 20% compared to ultimate strength [4,5]). The nonlinear behavior is mainly induced by the growth of micro-cracks and the corresponding material damage as discussed in [6]. ...
... For off-axis tension and compression, four SGs were used: one along and one transverse to the loading direction, and two along the material's orthogonal axis. Three strain components under planar stress state can be derived [4]. ...
Due to damage coupling and anisotropic evolution, constitutive models of Ceramic Matrix Composites are generally deficient in the description of material behavior under complex load conditions. This paper studied the mechanical behavior of a PIP prepared 3k carbon fabric plain woven C/SiC material under complex stress states. The phenomenon and mechanism of the anisotropy damage were analyzed. A constitutive model was proposed considering the anisotropy damage effect by load ratio functions, and only scalar damage variables were used to maintain a simple formulation. The constitutive model was validated against tensile tests of hat-shaped CMC components, and a FEM model of the experiments was established. The comparisons of strain results between the experiments and the FEM simulation showed good agreement under different loads. The model can be employed to facilitate structural analysis and design where material non-linearity is important.
... Blackketter et al. [4] firstly proposed an instantaneous stiffness reduction scheme (i.e., termed as "birth and death" element method ) to simulate the damage in a plane weave composite, where the material fails instantaneously once damage initiates, which could overestimate the material damage [5][6][7]. In addition, the damage evolvement law on the basis of the thermodynamics of irreversible process [8] was developed [9][10][11][12][13]. However, the potential of dissipation required to establish the damage evolvement law is difficult to be determined, since many internal state variables like the thermodynamic potentials must be calibrated through the experimental data. ...
... For the yarn, 11 ...
