Synthesis of Single-Phase Anatase TiO2 Nanoparticles by Hydrothermal Treatment

Pure anatase powders of titanium dioxide with a homogeneous nanosized particles distribution were prepared by a facile hydrothermal route using solution of acetic acid and tetraisopropyl orthotitanate as the precursors with a molar ratio of 1:1. The modified hydrolyzed alkoxide was treated at various temperatures under different autogenic pressures. Two different reactors were employed as autoclaves for heating and generation of high pressures during the synthesis and crystallization of TiO2 nanoparticles. The characteristics of TiO2 powders obtained under various synthesis conditions were verified using X-Ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FE-SEM). The results indicated that particles size of the formed TiO2 could be finely tuned by varying the experimental parameters of temperature, pressure and the amount of nitric acid in the peptization step. TiO2 nanoparticles with good dispersion and mean size of about 9 nm could be seen in FE-SEM image of sample synthesized under temperature of 160 °C for 12 h using more nitric acid in the peptization step. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3488

Influence of spark plasma sintering and baghdadite powder on mechanical properties of hydroxyapatite

AbstractSince hydroxyapatite-based materials have similar composition and crystallinity as natural calcified tissues, can be used for bone/tissue engineering. In the present study a novel nanocomposite based on bioceramics such as Natural Hydroxyapatite (NHA) and Baghdadite (BAG), was sintered by spark plasma sintering (SPS) technique. The prepared composite was characterized using scanning electron microscopy (SEM), X-ray diffractometer (XRD) and Brunauer–Emmett–Teller (BET) techniques. The porosity of the samples was measured by Archimedes method. The cold crushing strength (CCS) test was applied to evaluate their mechanical properties. Our results demonstrated that NHA-30wt. %BAG nanocomposite specimens have the lower CCS in comparison with other examined composites. Consequently, NHA/BAG samples exhibited acceptable mechanical properties and could be suitable candidates for bone tissue engineering applications especially orthopaedic fields

Micro-CT-based analysis of fibre-reinforced composites:Applications

The paper presents an overview of cases in which the analysis of the internal structure and mechanical properties of fibre reinforced composites is performed based on the micro-computed X-ray tomography (micro-CT) reconstruction of the composite reinforcement geometry. In all the cases, the analysis relies on structure tensor-based algorithms for quantification of the micro-CT image, implemented in VoxTex software

Detailed experimental validation and benchmarking of six models for longitudinal tensile failure of unidirectional composites

Longitudinal tensile failure of unidirectional fibre-reinforced composites remains difficult to predict accurately. The key underlying mechanism is the tensile failure of individual fibres. This paper objectively measured the relevant input data and performed a detailed experimental validation of blind predictions of six state-of-the-art models using high-resolution in-situ synchrotron radiation computed tomography (SRCT) measurements on two carbon fibre/epoxy composites. Models without major conservative assumptions regarding stress redistributions around fibre breaks significantly overpredicted failure strains and strengths, but predictions of models with at least one such assumption were in better agreement for those properties. Moreover, all models failed to predict fibre break (and cluster) development accurately, suggesting that it is vital to improve experimental methods to characterise accurately the in-situ strength distribution of fibres within the composites. As a result of detailed measurements of all required input parameters and advanced SRCT experiments, this paper establishes a benchmark for future research on longitudinal tensile failure

Effect of Voids on Damage Development in Carbon Fiber-reinforced Polymer Composites

Nothing is perfect, and composite materials are no exceptions. In the micro- and meso-structure of Fiber-Reinforced Composites (FRCs), there are imperfections that are created during their manufacturing. Being called "manufacturing defects", these imperfections can influence the mechanical performance of FRCs. They include fiber waviness and misalignment, broken fibers, initial fiber/matrix debondings, initial delaminations, incomplete matrix cure, and voids. Voids are one of the main types of manufacturing defects. They can cause degradation of matrix- and interface-dominated mechanical properties of FRCs. Though the research on voids has started soon after the emergence of structural composites, accurate and systematic investigation of voids' effect has become possible only in the last decade, exploiting experimental and computational advancements. Still, there are remaining unknowns about how voids can affect the damage development in FRCs, especially about their effect on statistically-controlled properties such as matrix cracking. Matrix cracking is one of the first damage mechanisms occurring in multidirectional composite laminates under mechanical loading. Being sensitive to manufacturing defects, particularly voids, matrix cracks can lead to more dangerous forms of damage such as delamination and fiber breakage. Therefore, understanding of cracking evolution during loading is of high importance in investigation of damage progress and failure, and their sensitivity to voids in FRCs. Real-time analysis of matrix cracking is, however, challenging, in particular in carbon fiber-reinforced polymers due to their opacity. Thus, there is a need for improvement in in-situ detection of cracks. In addition to experimental analysis, simulation of matrix cracking is potentially an efficient and accurate way to evaluate the influence of voids. It can be efficient because it does not need production and testing of real composite specimens, so saving money, time, and energy. It can be accurate since void characteristics, such as shape, size, orientation, and spatial distribution, can be completely controlled, which is not the case in experimental analysis. Nevertheless, modeling of matrix cracking and its sensitivity to voids in composite laminates is not straightforward due to the stochastic nature of cracks and the multi-scale effect of voids. The current dissertation aims to analyze the effect of voids on the damage development, particularly matrix cracking, in carbon fiber-reinforced polymer composites. First, the relevant literature for the last 50 years is extensively reviewed and synthesized. Then, a broad characterization of voids in carbon/epoxy laminates is performed, using X-ray micro-computed tomography. The characteristics of voids, which are shape, size, orientation, and spatial distribution, are measured and their statistics are reported, providing a vast dataset useful for detection and modeling of voids. For analysis of the effect of voids on matrix cracking, two parallel methodologies are developed: one experimental and the other one computational. The experimental approach takes advantage of in-situ image acquisition and digital image correlation. Images are captured from deforming specimens at three different scales: 1) macro-scale images from the front-surface side, 2) meso-scale images from the thickness side, and 3) micro-scale images from the thickness side using electron microscopy. A semi-automatic approach is developed for detection and counting of matrix cracks in the images, processed with digital image correlation. The multi-scale approach allows analysis of the crack initiation along the length and its propagation through the width of the outer ply, the crack density evolution at the edge of the inner and outer plies, and the interactions between cracks and micro-features such as voids. The methodology is applied to a reference and an imperfect material, produced with different cure cycles. It is observed that voids can facilitate the formation of matrix cracks, therefore causing earlier start of cracking. The different cure of the imperfect material brings about higher crack density at saturation and less regular crack propagation paths. The computational methodology is performed also in a multi-scale framework. The effect of voids on certain micro-scale properties are calculated using computational micromechanics. To this end, finite element models with a random distribution of fibers and plasticity and damage for the matrix are created. The micro-scale properties are then transferred to a meso-scale model of a composite laminate, serving as input parameters. Regions with degraded properties, representing voids, are distributed randomly in the laminate. The simulation is carried out for two different void contents and void sizes. The results confirm that the initiation of cracks can be facilitated by voids, and the highest effect is for the model with the highest number of voids. The most noteworthy outcomes of the dissertation are, therefore, 1) a comprehensive review of the literature about voids in FRCs, covering their formation, characterization and effects, which is of great value to the composites society, 2) a full-scale characterization of voids, using X-ray micro-computed tomography, which provides an extensive dataset on voids' characteristics, and 3) approaches for identification of the effect of voids on matrix cracking. The latter, beside revealing results about the influence of voids on damage development in FRCs, help to address the challenges in currently-available approaches for analysis of cracking evolution, which is crucial for understanding of the damage mechanics in composites.status: publishe

In-situ synchrotron computed tomography images of a tensile test on a carbon fiber-epoxy composite for mechanical damage analysis

Using synchrotron computed tomography, we have obtained 3D images of a carbon fiber-epoxy composite laminate loaded under tension. A double-edge notched specimen with a notch section area of ~ 1 mm × 1 mm is cut using waterjet machining from the [904/05]s laminate with 7-µm nominal fiber diameter. It was loaded under continuous tension, with a deformation rate of ~ 1.4 μm/s, and in-situ scanned with a propagation distance of 60 mm, a beam energy of 20 kV, and 1000 projections per scan, each with an exposure time of 9 ms. The magnification was 10×, and the voxel size was 1.1 μm. The test was conducted at the TOMCAT beamline of the Swiss Light Source (SLS) in Villigen, Switzerland. The reconstruction was performed using an absorption-based algorithm provided by SLS. Eight 3D image (out of ~60 images) corresponding to eight loading steps with nearly the same force intervals are selected. These eight steps (Step 0 - 7) are identified on the force-displacement curve that is included in the dataset. The 3D images are overlaid on top of each other (registered), using 3D rigid transform by “Normalized Mutual Information”, and resampled with “Standard” (linear) interpolation, in the commercial software Avizo 2019.1. The empty space around the specimen is cropped out in each image. The eight 3D images are uploaded to this dataset in the folder "Full volumes (no filter)". Moreover, a smaller volume of interest (VOI), with a size of 330 × 580 × 630 μm3, is selected, which is shown with a blue box in the schematics available in the dataset. This volume is copped from the full volume. The eight small VOIs are also uploaded to this dataset in the folder "Cropped VOIs for analysis of damage interaction (non-local means filter)". The image noise in the small VOIs is reduced using a 3D “non-local means” filter with a search window of 10 px and local neighborhood of 3 px, using Avizo 2019.1. These 3D images are used for real-time analysis of mechanical damage in carbon fiber composites. We have performed this using digital image correlation in the reference article "Mehdikhani et al., Digital volume correlation for meso/micro in-situ damage analysis in carbon fiber reinforced composites". Other techniques can be employed to characterize the damage and the evolution of the microstructure in these images

In-situ synchrotron computed tomography images of a tensile test on a carbon fiber-epoxy composite for mechanical damage analysis

Using synchrotron computed tomography, we have obtained 3D images of a carbon fiber-epoxy composite laminate loaded under tension. A double-edge notched specimen with a notch section area of ~ 1 mm × 1 mm is cut using waterjet machining from the [904/05]s laminate with 7-µm nominal fiber diameter. It was loaded under continuous tension, with a deformation rate of ~ 1.4 μm/s, and in-situ scanned with a propagation distance of 60 mm, a beam energy of 20 kV, and 1000 projections per scan, each with an exposure time of 9 ms. The magnification was 10×, and the voxel size was 1.1 μm. The test was conducted at the TOMCAT beamline of the Swiss Light Source (SLS) in Villigen, Switzerland. The reconstruction was performed using an absorption-based algorithm provided by SLS. Eight 3D image (out of ~60 images) corresponding to eight loading steps with nearly the same force intervals are selected. These eight steps (Step 0 - 7) are identified on the force-displacement curve that is included in the dataset. The 3D images are overlaid on top of each other (registered), using 3D rigid transform by “Normalized Mutual Information”, and resampled with “Standard” (linear) interpolation, in the commercial software Avizo 2019.1. The empty space around the specimen is cropped out in each image. The eight 3D images are uploaded to this dataset in the folder "Full volumes (no filter)". Moreover, a smaller volume of interest (VOI), with a size of 330 × 580 × 630 μm3, is selected, which is shown with a blue box in the schematics available in the dataset. This volume is copped from the full volume. The eight small VOIs are also uploaded to this dataset in the folder "Cropped VOIs for analysis of damage interaction (non-local means filter)". The image noise in the small VOIs is reduced using a 3D “non-local means” filter with a search window of 10 px and local neighborhood of 3 px, using Avizo 2019.1. These 3D images are used for real-time analysis of mechanical damage in carbon fiber composites. We have performed this using digital image correlation in the reference article "Mehdikhani et al., Digital volume correlation for meso/micro in-situ damage analysis in carbon fiber reinforced composites". Other techniques can be employed to characterize the damage and the evolution of the microstructure in these images

Preparation, Characterization, Mechanical Properties and Electrical Conductivity Assessment of Novel Polycaprolactone/Multi-Wall Carbon Nanotubes Nanocomposites for Myocardial Tissue Engineering

Cardiac tissue engineering aims to create functional tissue constructs that can reestablish the structure and function of injured myocardium. In this study, nanocomposite scaffolds composed of polycaprolactone and multi-walled carbon nanotubes, containing different amounts of carbon nanotubes, were prepared via solvent casting and vacuum drying technique, for myocardial tissue engineering. Characterization techniques such as Fourier transform infrared spectroscopy and scanning electron microscopy were used. Furthermore, mechanical properties of the prepared polycaprolactone and nanocomposite scaffolds were determined. The results have revealed that the scaffolds contain sufficient porosity with highly interconnected pore morphology. Addition of carbon nanotubes to the polycaprolactone matrix has improved conductivity of the prepared scaffold. The desired distribution of carbon nanotubes with a few agglomerates was observed in the nanocomposite scaffolds by scanning electron microscopy. Polycaprolactone/multi-walled carbon nanotubes nanocomposite scaffold containing 1 wt% of carbon nanotubes has shown the best mechanical behavior and electrical conductivity. In conclusion, the electrically conductive and nanofibrous polycaprolactone/1 wt% multi-wall carbon nanotubes scaffold could be used as an appropriate construct for myocardium regeneration and it deserves further investigations

A dataset of micro-scale tomograms of unidirectional glass fiber/epoxy and carbon fiber/epoxy composites acquired via synchrotron computed tomography during in-situ tensile loading

We have performed synchrotron computed tomography on two different fiber-reinforced composites while they were being continuously in-situ loaded in tension. One material is a glass/epoxy laminate and the other is a carbon/epoxy laminate. The voxel size is 1.1 µm, which allows clear recognition of the glass fibers, but not distinct individual carbon fibers. For each material, four loading steps are selected with approximately 0, 40, 73, and 95% of the failure load, and the 3D images of the four volumes from each material are overlaid. A volume of interest in the middle 0° ply is chosen and located in the 3D image of each loading step. The cropped volumes of interest for each material are presented in this dataset. As examples of two frequently-used type of unidirectional fiber-reinforced composites, the presented data can be used for different microstructural analyses, including investigation of the 3D variability in fiber distribution and orientation, and their evolution during tensile loading. Moreover, real-time formation of fiber breaks with tensile loading can be investigated in the data