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Material extrusion‐based additive manufacturing becomes interesting to fabricate oxide ceramic matrix composites. Herein, 0–30 vol% alumina fibers are added to zirconia‐toughened alumina powder mixture and extruded into filaments. Shrinkage and mechanical properties of filaments and 3D‐printed samples are investigated. Thermomechanical analysis is conducted on filaments with and without fiber content indicating lower shrinkage in the direction of fiber alignment during the sintering process. The flexural strength of the extruded filaments and printed bars is measured through a 4‐point bending test. Filaments containing 15 vol% fiber exhibit the highest flexural strength of 110 MPa, with additional fiber content leading to a reduction in flexural strength. Using Weibull calculation, it is observed that printed bars without fibers result in significantly lower bending strength in comparison to the filaments because of the presence of printing failures. Bars with 10 vol% fibers, printed with 0° infill orientation achieve the same mechanical properties as the filaments, even though in microcomputed tomography gaps between printed lines and voids between raster lines can be observed. These results demonstrate that fiber reinforcement of ceramics offers a great potential to avoid the reduction of mechanical properties by printing defects. [ABSTRACT FROM AUTHOR]

In the present work, the microstructure and chemical behavior of TiC ceramic reinforced steel matrix composite material after stabilizing heat treatments have been studied. The composition of the naturally formed oxide layer on the surface of the composite and the potential natural oxidation mechanisms are also elucidated. The results showed that the naturally formed oxide layer contained mainly O, C, Fe and Ti, with small amounts of Cr and Mo. In the multi-metallic oxide layer, Fe3+, Mo6+, and Ti4+ species are enriched on the free external surface of the composite, the protective Fe2+ oxides were distributed in the relative inner part of the oxide layer, and Mo4+ was more uniformly distributed throughout the natural oxide film. The Cr oxides formed near the substrate acted as a diffusion barrier for iron and chromium ions, and the preferential oxidation of chromium formed a passivation film, which effectively improved the corrosion resistance of the material. Due to the interfacial evolution and complex stress changes in the composite during the stabilizing heat treatments, the XPS spectral peaks were shifted towards lower binding energies than in the annealed sample. The core level spectra of Mo 3d, Ti 2p, and Fe 2p were all shifted to lower binding energies due to the combination of ligand and strain effects after quenching, and there was no significant difference in the spectra of the tempered and thermal cooling cycling (TCC) treated composites, which suggested that the chemical state was relatively stable during the subsequent stabilizing heat treatments. [Display omitted] [ABSTRACT FROM AUTHOR]

This study is aimed to develop an artificial neural network (ANN)-based method for predicting the elastic modulus of Continuous SiC fiber-reinforced SiC ceramic matrix (SiC/SiC) mini-composites. The mesomechanical model with pores is established based on the microstructure of ceramic matrix mini-composites. The main factors affecting the tensile elastic modulus of mini-composites were obtained using a fidelity mesomechanical model combined with finite element analysis (FEA). Secondly, based on the main factors and the finite element simulation data, the backpropagation (BP) neural network is established to map the complex relationship between the elastic modulus and the structural parameters of the mini composite material. Finally, FEA is used to verify the rationality of the neural network. The results show that the ANN algorithm is robust in the prediction of tensile modulus of mini composite materials, and the prediction error of the neural network model using only one hidden layer and 2300 groups of data samples is less than 0.7% in the input of fiber elastic modulus, fiber volume ratio, and porosity. Therefore, the ANN model proposed in this study helps to evaluate the performance of SiC/SiC mini-composites during the design phase, shortening the design and manufacturing time. [ABSTRACT FROM AUTHOR]

Copyright of Science of Sintering is the property of National Library of Serbia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The grinding force is an important index during the grinding process, which affects the surface quality and other aspects after machining. However, the research on the grinding force of ceramic matrix composites assisted by two-dimensional ultrasonic vibration-assisted grinding is very weak. In this paper, the impact of the relationship between the critical cutting depth and the maximum undeformed chip thickness on the removal mode of ceramic matrix composites was analyzed. On this basis, the grinding force model of two-dimensional ultrasonic vibration-assisted grinding were developed for ductile removal and brittle removal, respectively. Finally, the correctness of the model was verified, and the impact of grinding parameters on the grinding force was analyzed. The experimental results show that compared with the conventional grinding force, the two-dimensional ultrasonic vibration assisted grinding force decreases obviously. When the feed rate and grinding depth increase, the grinding force increases. When the grinding velocity and ultrasonic amplitude increase, the grinding force decreases. Compared with the experimental value, the average relative error of normal grinding force is 8.49%, and the average relative error of tangential grinding force is 13.59%. The experimental and theoretical values of the grinding force have a good fitting relationship. [ABSTRACT FROM AUTHOR]

A comparative analysis of typical stress-strain diagrams obtained for in-plain shear of 25 unidirectional and cross-ply reinforced polymer matrix composites under quasistatic loading was carried out. Three of them were tested within the framework of this study, and the experimental data on other materials were taken from the literature. The analysis of the generalized shear-strength curves showed that most of the tested materials exhibit a similar deformation pattern depending on their initial shear modulus: a linear section is observed at the beginning of loading, whereas further increase in the load decreases the slope of the curve, reaching the minimum at the failure point. For three parameters (end point of the linear part, maximum reduced deviation of the diagram, tangent shear modulus at the failure point) characterizing the individual features of the presented stress-strain diagrams, approximating dependences on the values of the reduced initial shear modulus are obtained. At the characteristic points of the deformation diagrams, boundary conditions are determined that can be used to find the parameters of the approximating functions. A condition is proposed for determination of the end point of the linear section on the experimental stress-strain curve, according to which the maximum deviation between the experimental and calculated (according to Hooke's law) values of the shear stress in this section is no more than 1%, thus ensuring rather high accuracy of approximation in the linear section of the diagram. It is recommended to use the results of this study when developing universal and approximating functions relatively simple in structure that take into account the characteristic properties of the experimental curves of deformation of polymer composite materials under in-plane shear of the sheet. The minimum set of experimental data is required to determine the parameters of these functions. [ABSTRACT FROM AUTHOR]

Composite materials comprised of a ceramic matrix with metal-containing nanoparticles were prepared by sintering iron (II) oxalate and polycarbosilane. The chemical composition of the material can be controlled by a sintering process. Sintering in inert atmosphere leads to reduction of the sample and metal iron formation (a-Fe, carbide). Formation of iron oxides requires calcination procedure in series (argon and air) for removing by products. The air-sintering materials consist mainly of oxide phases, but also contain metal iron. The prepared samples were characterized by the: SEM, TEM, XRD and EMR techniques and the Mössbauer spectroscopy. It was shown unique behavior that iron containing particles after calcination in air decreased from 5-30 nm to 2–5 nm due to interaction with matrix under air atmosphere. [ABSTRACT FROM AUTHOR]

This paper proposes a method for manufacturing a metallic composite material made of Ti64 titanium alloy reinforced with SiC ceramic fibers using surface laser cladding technology. The influence of the laser action parameters on the shape of a single track is studied. The stability of the formed composite material under a high-velocity impact is considered. It is shown that, for a sample reinforced with ceramic fibers, the depth of a crater in a substrate is 37% smaller than for a sample made of Ti64 alloy. [ABSTRACT FROM AUTHOR]

C f /C–SiC composites were fabricated via liquid silicon infiltration with 2.5D needle-punched carbon fiber reinforced C f /C composites. The effect of surface topography and carbon content of the C f /C–SiC composites on the tribological properties was researched by the ball-on-disk reciprocating tribometer. The results indicate that different fiber layers and cross-section of the composites have various surface topography and show significant differences in the friction and wear properties. By the wear morphology and model analyses, the reason for the tribological anisotropy of the composites is that the distribution of carbon and SiC phases in the composites are inhomogeneous caused by the difference of the carbon fiber orientation and the relative content in each layer. Moreover, the wear rate of the short-cut fiber web layer was the lowest and there is an obvious linear decrease in coefficient of friction with increase of carbon content. The present work explains why the tribological properties of the composites are inconsistent and provides a way to adjust the friction properties of composite materials by optimizing the friction surface. [ABSTRACT FROM AUTHOR]

WC/Y–TZP–Al2O3 hybrid ceramic–matrix composites (CMCs) with dispersed Hadfield steel particles were sintered and then tested at sliding speeds in the range of 7–37 m/s and contact pressure 5 MPa. Fast and low-temperature sinter-forging allowed obtaining micron-sized WC grains, submicron-sized alumina-reinforced yttria partially stabilized polycrystalline tetragonal zirconia (Y–TZP–Al2O3), and evenly distributed Hadfield steel grains. Such a microstructure provided new hybrid characteristics combining high hardness with high fracture toughness and tribological adaptation. The CMCs demonstrated low friction and high wear resistance that were better than those demonstrated by other composite materials such as, for example, MAX-phase composites, zirconia-base ceramics, ZrB2-SiC ceramics, and metal matrix WC–(Fe–Mn–C) composites. These good tribological characteristics were obtained due to the in situ mechanochemical formation of iron tungstates FeWO4 and Fe2WO6 on the worn surfaces of composite samples. These mixed oxides were included in multilayer subsurface structures that provided the self-lubricating and self-healing effects in high-speed sliding because of their easy shear and quasi-viscous behavior. [ABSTRACT FROM AUTHOR]

In order to solve the problem of the surface damage coupling mechanism of ceramic matrix composites, a method oriented to the damage coupling mechanism of the plain weave art ceramic matrix is proposed by the author. First, the author uses the composite material prepared by a chemical vapor infiltration process as the research object, and the damage mechanical behavior of materials under simple and complex plane stress states is studied. Second, the calculation of the mechanical property parameters of the material components and the research on the mechanical behavior of the material in-plane shear mesodamage are studied; Finally, the research on the damage coupling effect of materials under complex stress state is conducted, as well as the decoupling test research of the damage coupling effect. It is demonstrated that based on 0 and 45° off-axis tensile stress-strain behavior, a prediction model of off-axis tensile stress-strain behavior of the material was established, and the prediction results were in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Cotton Textile Technology is the property of Cotton Textile Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of China Sciencepaper is the property of China Sciencepaper and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper deals with solving the problem of constructing two-level computational models relating the stress-strain state at the microscale to the stress-strain state of the structural component at the macroscale for layered polymer composite materials with unidirectional fiber stacking in a monolayer. The paper presents a two-level computational mechanical model of a ten-layer cross-ply fiberglass-reinforced polymer composite with (0/90) laying patterns. The model is based on microindentation data. The model is constructed using the finite element method. The constructed model has allowed us to predict the elastic properties of the composite and to calculate stresses at the microscale and macroscale levels of a specimen prior to fracture under tensile conditions. The elastic properties of the polymer composite material predicted by the computational model are compared with the properties obtained from real experiments. Calculated for fiberglass, the elasticity modulus and Poisson's ratio are 31 GPa and 0.11, respectively. Similar elastic properties obtained from real experiments are 28 GPa and 0.10. The technique used in the paper can be applied to computational experiments with an actual structural component made of a multilayer polymer composite in order to determine the stress-strain state at the micro- and macroscale under external mechanical impact on the structure. [ABSTRACT FROM AUTHOR]

ZrB 2 /SiC ceramic granules with uniform a size and spherical shape were prepared by spray drying technology. ZrB 2 /SiC ceramic granules were added into ceramic matrix, and ZrB 2 /SiC/Si 3 N 4 ceramic tool materials with double composite architectures were prepared by spark plasma sintering technology. The mechanical properties from room temperature to 1100°C were measured. The hardness, flexural strength and fracture toughness at room temperature are 18.0 GPa, 589.0 MPa and 5.93 MPa m1/2, respectively. While the fracture toughness at 1100°C reach 6.1 MPa m1/2 increase by 74.3% compared with the ceramic tool material without double composite architectures. At high temperature, the improvement of fracture toughness is due to the addition of ZrB 2 /SiC ceramic granules that deflect the cracks and propagates along the boundary between the granules and the matrix, which greatly increase the path during the crack propagation process, thereby improving the fracture toughness of the ceramic tool material. [ABSTRACT FROM AUTHOR]

SiC fiber-reinforced SiC ceramic matrix (SiC f /SiC) is an advanced high-temperature material widely used in the heat-resistant componets of the aerospace engine and nuclear reactor, which are generally precisely ground to achieve the designed dimensional and geometrical tolerances. This research investigates the scribing force and material removal mechanism of 2.5D woven SiC f /SiC with the flat and sharp diamond grits, which present the new dressed and worn grinding wheel. The results show that the sharp grit has larger wear on the cutting edge and generates lower force than that of the flat grit at the same scribing depth and groove cross-section area. In both sharp and flat grits, the SiC matrix is mainly removed by the fracture cracks, peeling off, fiber exposure and powdering. In transverse diamond scribing of the SiC f , the fiber debonding and shear breakage are dominant removal feature for the flat grit scribing. Two additional removal patterns, the ductile scratch and fiber cracking, are observed for the sharp grit. In parallel diamond scribing of the SiC f , the shear and bending fractures in the cut-in and cut-out points are two key material removal modes, respectively, especially in the fiber woven structure. This research provides a fundamental understanding of interaction force and the material removal process of SiC f /SiC in grinding. [ABSTRACT FROM AUTHOR]

This review deals with the potential of combining self-propagating high-temperature synthesis (SHS) and spark plasma sintering (SPS) for obtaining single-phase ceramic materials and ceramic and metal matrix composites. The materials discussed in this review contain compounds produced by the SHS process: carbides, borides, and silicides of metals and intermetallics. Factors in the structure formation of materials obtained by sintering of SHS products and the influence of SPS conditions on the characteristics of the materials (relative density and grain size) are analyzed. Advantages of combining the SHS and SPS techniques, including the possibility of additional processing of SHS products (grinding and adding components) to modify the composition and properties of materials are discussed. [ABSTRACT FROM AUTHOR]

Use of soldering methods for preparing high-temperature permanent joints of silicon carbide ceramic matrix composites (CMC) with metals is analyzed. The main problems in joining CMC with metals are considered associated with poor wettability of CMC with molten metals, a significant difference in the LTEC of CMC and metals, and formation of substances with high hardness and brittleness within a connecting layer. Analysis of practical experience of using traditional and diffusion soldering methods for joining CMC of the Cf/SiC type with metal alloys based on Ni, Nb, Ti, Mo, and stainless steel is provided. The most typical solder compositions and soldering process production methods are considered. It is shown that these technologies make it possible to create reliable and strong joints for CMC components and various metals. [ABSTRACT FROM AUTHOR]

• Temperature dependence of contact mechanical properties is characterized by theory. • The theoretical models are expressed in terms of some basic material properties. • Nature and underlying physical control mechanisms at high temperatures are revealed. • Excellent agreements are obtained between model calculations and measurements. The novel theoretical models for the temperature dependence of the contact mechanical properties of the particulate composites in Hertzian contact are proposed in this paper, based on an assumption of the temperature-independent constant energy storage capacity for a specific brittle particulate composite, associating with the material yielding, and the theory of Hertzian contact. The yield stress, critical loads for the onset of the brittle and quasi-plastic damage modes, indentation strength, and the more commonly used fracture strength of the composites are expressed in terms of the basic material properties—the temperature-dependent Young's modulus and specific heat capacity, and the critical flaw size. The models enable the priori and quantitative predictions of the contact damage behavior of the composites during the whole process of the Hertzian contact. The models are validated by comparing against the experimental measurements of the temperature-dependent contact mechanical properties of the particulate-reinforced ultra-high temperature ceramic matrix composites in the temperature range of 25 ∼ 800 °C, which were found probably to be the only reported experimental studies of the particulate composites. The temperature dependence of the contact damage behavior of the composites is revealed to be mainly governed by the temperature-dependent Young's modulus and specific heat capacity, and the change of the flaw size above a certain temperature point. The models provide additional adequate methods for the determination of the nature and the underlying physical control mechanisms of the damage behavior of the composites at high temperatures. [ABSTRACT FROM AUTHOR]

The laser energy absorption and melting behavior of ceramic reinforced metal matrix composites during selective laser melting (SLM) additive manufacturing are vital for the subsequent metallurgical behavior. In this study, the mesoscopic simulation was proposed to investigate the influence of ceramic addition on the laser energy absorption and powder melting behaviors during SLM of TiC/Ti6Al4V composites. As the addition of TiC particles increased from 0 wt.% to 5 wt.%, the packing density of composite powder increased from 2.357 g cm−3 to 2.588 g cm−3, while the hall velocity decreased from 36.00 s to 73.14 s, indicating the powder flowability decreased with the ceramic addition. Meanwhile, the number of laser-powder interactions increased from 1.267 × 106 to 1.626 × 106, thereby enhancing the laser multiple reflection phenomenon in the powder bed. The concentrated irradiance distribution on the metal powder was dispersed into the surrounding powder. The average irradiance intensity on TiC particles was continuously improved, which increased the overall laser absorptivity from 0.655 to 0.72, yielding an elevated maximum operating temperature within the molten pool from 3501 K to 3668 K. However, with the excessive addition of ceramics (5 wt.%), balls and trapped unmelted particles deteriorated the surface morphology of the melted track. It can be attributed to the high required energy for complete melted TiC and the elevated difficulty of completely wetting unmelted particles. These results provided the physical understanding of high-quality and defect-free components of SLM processed composite materials. [ABSTRACT FROM AUTHOR]

Modern composite materials are normally composed of at least two components. The fibres in ceramic matrix composites are often coated with a "weak" material that is the interphase arresting a macrocrack and providing the composite with fracture toughness. In many biological materials of a ceramic type an organic weak material of a tiny quantity plays actually two roles those being the matrix and interphase. Oxide fibres produced by the internal crystallization method have two plane and two concave surfaces. It is shown in the present work that the composite microstructure composed only of sapphire fibres contacting one another by plane surfaces is characterized by the non-brittle behaviour. [ABSTRACT FROM AUTHOR]

Ceramic particles-reinforced casted aluminium matrix composites are extensively used in aircraft and in the manufacturing of automobile components due to its excellent properties such as light weight, high strength and increased hardness. In this present research work, conventional liquid metallurgy method has been adopted to fabricate the AA7075/BN-reinforced metal matrix composites. The boron nitride ceramic powder is added with different wt% such as (0, 4 & 8). The distribution of reinforcement particles in the matrix material is identified through scanning electron microscopy. Drilling experiments are performed on fabricated composites through vertical CNC drilling machine using fully carbide drill bit and by modifying the process parameters such as spindle speed, feed and point of angle. Subsequently by varying the cutting tool angle (118°, 108° & 98°), drilling experiment is conducted. Mill tool dynamometer is used to find out the thrust force while drilling. Response surface methodology is used to optimize the output responses of thrust force and surface roughness effects from drilled metal matrix composites. The setting of experimental parameters is made with L27 Box–Behnken design factors and is performed with four factor three level. This investigation has shown that feed and point of angle are major influencing factors affecting the thrust force and surface roughness. Also, the tool wear, chip morphology and hardness of the fabricated composite material were examined. [ABSTRACT FROM AUTHOR]

Numerical homogenization of multiphase brittle materials, such as ceramic matrix composites is obviously a computationally intensive task. Common approach involving multiscale finite element models remains quite limited to scientific applications instead of being a reasonable alternative for analytical constitutive models. Despite the exponential growth of computational resources (known as Moore's law) numerical complexity of the underlying algorithms is simply too high to ensure proper scaling to millions of elements. One of the approaches in-between continuous and discrete mechanics is the use of fast Fourier transform (FFT). The aim of this paper is to extend FFT-based methodology beyond its usual elastic regime, using mathematical formalism developed earlier for FE by means of variational principles. Governing equations are formulated in the frequency domain and solved iteratively on a parallel system. Well-known computational specifics of the discrete FFT algorithm itself provide uncompromised efficiency and a first, promising step towards truly multiscale mechanical analysis of random microstructures. [ABSTRACT FROM AUTHOR]

HfB2-ZrB2 based ultra-high temperature ceramics (UHTCs) are used as protective tiles for leading edges and nose cones of the hypersonic vehicles that face harsh re-entry conditions. In the present work, the effect of SiC (20 vol.%) and carbon nanotube (CNT, 6 vol.%) incorporation on the room temperature damage initiation and wear damage tolerance of HfB2-ZrB2-based ceramics, consolidated via spark plasma sintering (SPS), is assessed. The wear rate decreased by almost > 90% in CNT-reinforced HfB2-ZrB2–SiC composites (for both scratch and fretting tests), and a significant increase in the Hertzian contact pressure (from ~ 15 GPa, in case of fretting to ~ 21 GPa, in case of scratch wear) and scratch hardness (from ~ 27 GPa to ~ 46 GPa, respectively) was observed with synergistic reinforcements of SiC and CNT. The study examines synergistic interfacial strengthening by SiC and CNT reinforcement in HfB2-ZrB2 ceramic composites as potential materials for aerospace applications where damage initiation and tolerance are issues. [ABSTRACT FROM AUTHOR]

In the current research, the production of composites, characterization, mechanical and wear behavior of 5 and 10 wt.% of nano composites have been investigated by reinforcing the nano B4C ceramic particulates into Al2024 alloy. The composites were prepared by using two stage stir casting technique containing Al2024 alloy as a matrix phase and nano B4C particulates as reinforcement. After the composite preparation, the prepared composite material was examined by using various techniques such as SEM, EDS and XRD for characterizing the chemical elements and microstructures of reinforced and unreinforced material. Later, the mechanical properties and wear behavior of as cast Al2024 alloy and Al2024 −5 and 10 wt.% nano B4C composites were studied. Different mechanical properties such as hardness, percentage elongation, ultimate and yield strength were evaluated as per the ASTM standards. The dry sliding wear tests were conducted by using pin on disc equipment. The experiments were conducted for the sliding distance of 3000 m by varying the sliding speed and load. It was found that due to the addition of nano B4C ceramic particles in the Al2024 alloy matrix, the hardness, ultimate tensile strength and yield strength of the prepared composites were increased and the percentage elongation was decreased. Furthermore, there was an improvement in the volumetric wear loss with respect to the speed, load, and sliding distance for all the prepared composite materials. However, with the addition of nano B4C ceramic particulates in the base Al2024 matrix, the volumetric wear loss was decreased. The scanning electron microscope was used to study and analyze the fractography and different wear mechanisms for various test conditions of different compositions, tensile fractured surfaces and worn surfaces. [ABSTRACT FROM AUTHOR]

One of the main challenges of using laser ultrasonic techniques for non-destructive testing applications is the typically low signal-to-noise ratio of the laser ultrasonic signals. In the case of thick composite structures, this is even more problematic since composite materials have very strong sound attenuation. This article investigates the effects of laser beam size and profile to the amplitude of pulse-echo laser ultrasonic signals with the constraint that the peak energy density (fluence) must be kept constant under the thermal damage threshold of material like polymer matrix composites. Such constraint is very important for the non-destructive feature of non-destructive testing, yet in a number of the existing parameter studies of laser ultrasonics, it was not fully investigated. In this article, a series of A-scan and C-scan experiments on thick composite specimens shows that the amplitude of the direct waves and the reflected waves increases with the increase in laser beam size with constant peak energy density. This amplitude enhancement significantly improves the propagation depth, thereby optimizing the system for inspection of thick composite structures. The validity of experimental results is verified theoretically by solving the thermoelastic model of epicenter displacement using Laplace–Hankel transformation. [ABSTRACT FROM AUTHOR]

Most modern matrix composite materials employ a variety of carbon nanofillers to improve their mechanical, electrical, and functional properties. Nanofillers are separately implanted into the initial ceramic matrix, which complicates the composite manufacturing technology and increases the final cost. In this work, the synthesis of nanocarbon fillers was carried out using high-temperature (1200°C) pyrolysis of phenolic resin directly inside the silicon carbide matrix. This results in the formation of a continuous 3D nanocarbon mesh uniformly binding and reinforcing the final product throughout the volume. The nanocarbon filler synthesized in the SiC matrix contains two allotropic carbon forms: nanographite and nanofibers. The study of the features of the carbon structure and morphology showed that during the pyrolysis the multilayered nanographite structures had been formed on the surface of SiC grains of average crystallite size equal to 20–35 nm. In the matrix pores, carbon nanofibers a few micrometers in length and 20–40 nanometers in diameter are synthesized. The reiteration of the phenolic resin impregnation–pyrolysis cycle increased the free carbon content from 4 to 7 wt.% for once and twice impregnated and pyrolyzed samples, respectively, and the Young's modulus, from 50.7 to 94.3 GPa. The obtained carbon content and structure are appropriate to produce C/SiC composite for application of ceramics and electrodes. [ABSTRACT FROM AUTHOR]

Highlights • Deformation and fracture of coated aluminum is numerically studied across spatial scales. • In hard matrices, particle cracking is accompanied by interface debonding. • Interface strength lower than the particle strength provides the best composite strength. • Stress concentration depends non-monotonically on the volume fraction of particles. • Distances between the cracks in coatings increase with the coating thickness. Abstract The mechanisms of stress concentration and plastic strain localization operating in an aluminum substrate with an aluminum-matrix composite coating subjected to uniaxial loading are investigated. The plane strain deformation of the coated material across micro-, meso- and macroscales is simulated numerically by the finite-difference method. The constitutive models used in the study include the elastic-brittle and isotropic elastic-plastic responses of ceramic particles and metal matrixes/substrates, respectively. The experimentally observed microstructure of the coated material is explicitly taken into account in the calculations. The formation of local regions experiencing bulk tension under compression of the composite material is simulated in order to control crack initiation and growth in ceramic particles, with the irregular geometry of matrix-particle and coating-substrate interfaces being a major factor of stress concentration. The influence of the coating thickness, distance between ceramic particles, mechanical properties of the constituents, and matrix-particle interfacial strength on the macroscopic strength of the composite and coated materials are studied. [ABSTRACT FROM AUTHOR]

• A micro-mechanical model for failure of unidirectional fiber reinforced epoxy. • The matrix follows a multi-mechanism nonlocal damage viscoelastic–viscoplastic model. • This accounts for size effects of epoxy behavior as matrix phase incomposites. • Localization behavior characterizes the post-failure of composite materials. • Peak stress and critical energy release rate define the homogenized cohesive law. We propose a micro-mechanical numerical model able to predict the nonlinear behavior and failure of unidirectional fiber reinforced high-crosslinked epoxy subjected to transverse loading conditions. Statistical microstructural volume elements (SMVE) of a realistic composite material are generated from the statistical characterization of the fibers distribution and fiber radius estimated from SEM images of a similar material system. The fibers are assumed to be transversely hyperelastic isotropic and the matrix obeys a hyperelastic viscoelastic–viscoplastic constitutive model enhanced by a multi-mechanism nonlocal damage model. This polymer model captures the pressure dependency and strain rate effects. Besides, it also accounts for size effects through its internal length scales, allowing capturing, with the same unique set of parameters, the behaviors of the epoxy as pure material as well as matrix phase in composites, which are experimentally observed to be different. Additionally, since fiber/matrix interfaces of the considered composite material are categorized as strong ones, the true underlying failure mechanism is located in the matrix close to the fibers, and the interface does not need to be explicitly introduced in the model. The model prediction is found to be in good agreement with experimental results in terms of the global nonlinear stress–strain curves over various strain rates and pressure conditions, on the one hand for pure matrix samples, and on the other hand for the composite coupons, making the proposed framework a predictive virtual testing facility for material design. Finally, using this model, we study the localization behavior in order to characterize the post-failure behavior of the composite material: the cohesive strength is given by the stress–strain curve peak stress while the critical energy release rate is estimated by evaluating the dissipated energy accumulated during the post-peak localization stage. Finally, different SMVE realizations are considered allowing assessing the discrepancy in the failure characteristics of composites. [ABSTRACT FROM AUTHOR]

The process of forming, by means of a proposed technology, the transitional layer between a dispersed medium and a dispersed phase of a ceramic matrix composite is investigated and a method of fabricating multilayer samples modeling at the macro level the interface between phases in the direction matrix–core of the composite material is presented. A qualitative and semiquantitative analysis is presented of new phases which are products of an interaction, occuring during firing, of a core made from sludgy iron-ore wastes and a matrix made from clayey raw material. [ABSTRACT FROM AUTHOR]

Tensile stress‐strain and tensile creep behaviors of an oxide‐oxide composite containing an array of small circular holes were evaluated at 1200°C. The composite consists of Nextel™720 alumina‐mullite fibers in a porous alumina matrix. Test specimens contained an array of 17 holes with 0.5‐mm diameter drilled using a CO2 laser. The presence of holes caused reduction in tensile strength and modulus. Tensile creep tests were conducted at 1200°C in air and in steam at creep stresses ranging from 38 to 140 MPa. Primary, secondary, and tertiary creep regimes were noted in air and in steam. The presence of the laser‐drilled holes accelerates the steady‐state creep rates. Creep run‐out, defined as 100 hours at creep stress, was attained for stress levels <60 MPa in air and for stresses <40 MPa in steam. The presence of the laser‐drilled holes significantly degrades creep resistance of the composite. The retained tensile properties of all specimens that attained run‐out were determined. Composite microstructure was examined; the damage and failure mechanisms were considered. The degradation of tensile properties and creep resistance are attributed to damage caused to composite microstructure by laser drilling. [ABSTRACT FROM AUTHOR]

This paper reports unprecedentedly capacitance-based nondestructive detection of aggregate proportion variation in cement-based materials. It uses the fringing electric field of a capacitor comprising a cement-based slab and two relatively small copper electrodes. The aggregate volume fraction increases from cement paste to mortar and to concrete, thus causing the apparent permittivity (high due to the fringing field) to decrease in the same order. Each slab consists of two regions with different aggregate proportions. The through-thickness and in-plane capacitances are measured using sandwiching and coplanar electrodes, respectively. To locate the interface, the capacitance is innovatively measured using a series of electrodes. [ABSTRACT FROM AUTHOR]

We investigate the structural, dielectric, ferroelectric and magnetic properties of a ferroelectric-ferrite material: praseodymium doped lead zirconium titanate (PZT) and cobalt ferrite (CFO) composite. The praseodymium doped PZT and CFO powders were synthesized separately by sol-gel auto combustion technique. The ferroelectric-ferrite composites were then synthesized by mixing the appropriate amount of individual phases using conventional sintering method. The morphological studies revealed a uniform distribution of grains of parent phases in the composite. Powder X-ray diffraction studies showed that the Pr doped PZT possess tetragonal perovskite structure while as Pr doped CFO possesses cubic spinel structure. The parent phases retain their crystal structures in the composite, without formation of any new secondary phase. The dielectric studies of composite, in the temperature range 100–750 K at a selected frequency of 100 kHz, revealed a diffused ferroelectric phase transition. Variation of dielectric constant with frequency in the range of 20 Hz- 3 MHz was carried out at room temperature. The reduction in the leakage current due to Pr doping leads to typical saturated P-E hysteresis loops for the composite, confirming their ferroelectric nature. The low temperature ac conductivity follows Motts law, confirming the hopping conduction mechanism in the composites. At room temperature, the composite exhibit typical magnetic hysteresis loop, indicating the presence of a long range magnetic order. The calculated values of squareness ratio for the composites confirmed the presence of multi-domain structure. [ABSTRACT FROM AUTHOR]

Nanolayered metal-ceramic composite systems provide the possibility to produce new materials with exceptional strength, toughness, and radiation resistance not exhibited by their individual constituents. The unusual behaviors are frequently attributed to the high density of internal interfaces. Most layered structures studied to date contain sharp interfaces and the synthesis of more diffuse interfacial structures, where the interface is graded out of the interface plane, has not been deeply explored. Here we show how neutron reflectometry was used to study the structure of magnetron sputter deposited titanium and titanium nitride (Ti/TiN) layers as a function of deposition parameters: temperature, rate of N 2 flow or pressure, electrical bias applied to the sample, and orientation of the ion source relative to the sample. These different deposition and post-processing strategies resulted in profound changes in the structure of the interfacial region between the two components in Ti/TiN x bilayers. The results show that temperature and low step-wise N 2 flow rates, but not electrical bias, can form graded interfaces in a controlled manner. [ABSTRACT FROM AUTHOR]

In this paper, based on a temperature-dependent fracture strength model and the theory of composite materials, two temperature-dependent fracture strength models for unidirectional and short random fiber reinforced ceramic matrix composites are developed. The effects of temperature, fiber content, fiber distribution, and matrix strength on the strength of fiber-reinforced ceramic matrix composites are included in the models. Furthermore, considering the effects of oxidation reaction for some kinds of fiber and size effect of unidirectional fiber on the strength of composites, a new temperature-dependent fracture strength model considering size effect and oxidation of reinforcing fiber is established. And good agreement between model predictions and experimental data indicates the applicability and rationality of our models. So the models can be used to predict the temperature-dependent fracture strength of fiber-reinforced ceramic matrix composites. [ABSTRACT FROM AUTHOR]

Ferroelectric PZT-PVDF composites (0–3 connectivity) of specific dimensions were made utilizing a hot press technique. Linear variation in the experimental density of the pellets made from 0.1 to 0.8 PZT volume fraction was observed. The surface morphology of the composite has been micro-graphed using SEM. The variation of the dielectric properties of the composites on PZT volume fractions is reported and analyzed. It is observed that there was an increment in dielectric constant (ϵr) with an increase in temperature and volume fractions. The piezoelectric strain coefficient (d33) increases with an increase in the volume fraction and voltage coefficient (g33) were calculated. Comparisons were made with the Furukawa model to ϵrand d33. The remnant polarization and coercive field were analyzed from the hysteresis plots. [ABSTRACT FROM AUTHOR]

This paper applies estimation and control techniques to achieve the desired bondline temperature for out-of-autoclave, adhesive bonding of carbon-fiber composite components. Rather than heating the entire system to cure the adhesive, e.g., in an autoclave, this research uses controlled heating targeted at the bondline with an embedded heater. The main contribution o f this work is control using estimates o f the bondline temperature without embedded sensors and wiring (of materials not intrinsic to the system) that can lead to reduced bond strength. Sensors placed outside the bond region are used to accurately estimate the bondline temperature to within 2% of the temperature range over which the bondline temperature is changed. Experimental results show that the estimated temperature can be used with feedback to achieve the desired, bondline, time-temperature profile that is needed to cure the adhesive. Additionally, shear lap joint tensile tests show that the resulting joint strength is comparable to specimens bonded using an external heat blanket. [ABSTRACT FROM AUTHOR]

SiC/C–SiC composites were fabricated via a chemical vapor infiltration (CVI) method using porous SiC/C composites as preform. The influences of the SiC/C preform densities on the mechanical, microstructure and electromagnetic interference shielding properties (EMI) of the SiC/C–SiC composites have been studied. Results show that the SiC/C–SiC composites densities increase with increasing the SiC/C preform densities. When the SiC/C preform density is 1.21 g/cm 3 , the flexural strength, shear strength and toughness of the corresponding SiC/C–SiC composite can reach 220 MPa, 20.98 MPa and 10.21 MPa m 1/2 , respectively. The surface reflection (SE R ) and the internal absorption (SE A ) both increase with increasing the SiC/C preform densities. The enhancement of the EMI is mainly attributed to the formation of conductive networks by the continuous pyrolytic carbon (PyC) matrix and the surface reflection is the dominant shielding mechanism. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to prevent their recession caused through chemical reaction with high-temperature water vapor, SiC-fiber/SiC-matrix ceramic-matrix composite (CMC) components used in gas-turbine engines are commonly protected with so-called environmental barrier coatings (EBCs). EBCs typically consist of three layers: a top thermal and mechanical protection coat; an intermediate layer which provides environmental protection; and a bond coat which assures good EBC/CMC adhesion. The materials used in different layers and their thicknesses are selected in such a way that the coating performance is optimized for the gas-turbine component in question. Design/methodology/approach – Gas-turbine engines, while in service, often tend to ingest various foreign objects of different sizes. Such objects, entrained within the gas flow, can be accelerated to velocities as high as 600 m/s and, on impact, cause substantial damage to the EBC and SiC/SiC CMC substrate, compromising the component integrity and service life. The problem of foreign object damage (FOD) is addressed in the present work computationally using a series of transient non-linear dynamics finite-element analyses. Before such analyses could be conducted, a major effort had to be invested toward developing, parameterizing and validating the constitutive models for all attendant materials. Findings – The computed FOD results are compared with their experimental counterparts in order to validate the numerical methodology employed. Originality/value – To the authors’ knowledge, the present work is the first reported study dealing with the computational analysis of the FOD sustained by CMCs protected with EBCs. [ABSTRACT FROM AUTHOR]

Fiber orientations play the decisive role in grinding process of woven ceramic matrix composites, but the influence of woven fibers in grinding process is not clear. This paper studies the surface quality and grinding force by comparing different woven surfaces. Through a series of experiments in optimized sampling conditions, we analyze characteristics of the material surface topography height, wave distribution and surface support properties in details. And we find some outstanding characteristics of the surface microstructure. We also study the influence of grinding processing parameters on surface microstructure. The results show that machining surface which contains more parallel fibers is rougher and more keenness than gauss surface. Grinding wheel speed and depth of cut have great influence on surface topography and surface support properties. And it is discovered that grinding forces are also highly dependent on fiber orientations. The mechanism of the grinding phenomena is also analyzed in this paper according to knowledge of fracture mechanics and mechanical damage phenomenology. The research obtained will be an important technical support on improving the processing quality of woven ceramic matrix composites. [ABSTRACT FROM AUTHOR]

Picosecond laser is an important machining technology for high hardness materials. In this paper, high power picosecond laser was utilized to drill micro-holes in C/SiC composites, and the effects of different processing parameters including the helical line width and spacing, machining time and scanning speed were discussed. To characterize the qualities of machined holes, scanning electron microscope (SEM) was used to analyze the surface morphology, energy dispersive spectroscopy (EDS) and X-ray photoelectric spectroscopy (XPS) were employed to describe the element composition change between the untreated and laser-treated area. The experimental results indicated that all parameters mentioned above had remarkable effects on the qualities of micro-holes such as shape and depth. Additionally, the debris consisted of C, Si and O was observed on the machined surface. The Si C bonds of the SiC matrix transformed into Si O bonds after machined. Furthermore, the physical process responsible for the mechanism of debris formation was discussed as well. [ABSTRACT FROM AUTHOR]

The objectives of this paper include identifying important architectural parameters that describe the SiC/SiC five-harness satin weave composite and characterizing the statistical distributions and correlations of those parameters from photomicrographs of various cross sections. In addition, realistic artificial cross sections of a 2D representative volume element (RVE) are generated reflecting the variability found in the photomicrographs and include explicitly modeled voids (something not routinely done for woven CMCs). These models are used to make preliminary observation of the effects of architectural variability on the thermo-mechanical properties (material constants). Lastly, information is obtained on the sensitivity of linear thermo-mechanical properties to architectural variations. Two-dimensional finite element analysis is used in combination with a response surface and it is shown that the present method is effective in determining the effects of architectural variability on thermo-mechanical properties and their variability. [ABSTRACT FROM AUTHOR]

Highly filled polymer composites based on bisphenol-A/aniline based polybenzoxazine (PBA-a) and alumina particles were investigated. A very low A-stage viscosity of benzoxazine monomer gives it excellent processability exhibiting maximum alumina content as high as 83% by weight (60% by volume) which is one of the highest maximum packing values with negligible void contents. The storage modulus ( E′) at room temperature was increased from 5.93 GPa of the polybenzoxazine to 45.27 GPa of the composites. The significant high microhardness of the composites up to 1124 MPa was obtained and the behavior can be well predicted by the Halpin-Tsai model. Moreover, the modulus dependence of the composites on the alumina contents is well fitted by Lewis-Nielsen equation. Glass transition temperatures, degradation temperature, and solid residue of the composites also significantly increased with increasing the alumina contents. Finally, the scanning electron microscope of the composite fracture surface indicated a good distribution of the alumina particles in the PBA-a matrix. The resulting PBA-a/alumina composites are a highly attractive for an application that requires high modulus and hardness as well as high thermal stability. POLYM. COMPOS., 35:2269-2279, 2014. © 2014 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]