Samples Of Different Geometries Research Articles

The impact of crystal grain size on the behavior of disordered ferromagnetic systems: from thin to bulk geometry

We report the findings of an extensive and systematic study on the effect of crystal grain size on the response of field-driven disordered ferromagnetic systems with thin, intermediate, and bulk geometry. For numerical modeling we used the athermal nonequilibrium variant of the random field Ising model simulating the systems with tightly packed and uniformly cubic-shaped, magnetically exchange-coupled crystal grains, conducted over a wide range of grain sizes. Together with the standard hysteresis loop characterizations, we offer an in-depth examination of the avalanching response of the system, estimating the effective grain-size-related exponents by analyses of the distributions of various avalanche parameters, average avalanche shape and size, and power spectra. Our results demonstrate that grain size plays an important role in the behavior of the system, outweighing the effect of its geometry. For sufficiently small grains, the characteristics of the system response are largely unaffected by grain size; however, for larger grains, the effects become more noticeable and show up as distinct asymmetry in the magnetization susceptibilities and average avalanche shapes, as well as characteristic kinks in the distributions of avalanche parameters, susceptibilities, and magnetizations for the largest grain sizes. Our insights, unveiling the sensitivity of the system’s response to the underlying structure in terms of crystal grain size, may prove beneficial in interpreting and analyzing experimental results obtained from driven disordered ferromagnetic samples of different geometries, as well as in extending the range of possible applications.

Potential of digital autoradiography for characterization of uranium materials

This study evaluates the capabilities of a commercial digital autoradiography set-up in characterizing the spatial distribution of radioactivity in U-bearing materials. Two different imaging plates (IPs) from various manufacturers, as well as three read-out granularities (25 µm, 50 µm, and 100 µm) of a high-resolution IP scanner, were tested. A custom software, developed using Python, was used for processing of the image raw data obtained from the IP scanner. The software extracted 25 intensity profiles from each autoradiographic image, allowing for a detailed analysis of the data. By applying various mathematical fitting functions, important metrics such as edge width, amplitude of the flat top, and central core width of the intensity profiles were determined. This provided valuable insights into the interaction between the U samples and IPs, particularly for samples of different geometry and thickness. Comparisons were made between samples embedded in epoxy resin or modelling clay and non-embedded U specimens. The results highlighted the superior performance of epoxy embedding in the characterization of U-bearing materials. The variation in signal intensity between runs for individual samples reached up to 20 %, showing consistent behavior across all samples in each measurement. This suggests that the inconsistency in signal response during repetitive analysis is likely due to the IP scanner rather than the IP itself. By using the analytical method of global spatial autocorrelation (Moran’s I), we were able to effectively detect enrichment inhomogeneity within low enriched UO2 pellets. The Moran’s I value quantified the levels of inhomogeneity, providing a numerical measure that was not visually apparent from the digital autoradiographic image.

Numerical analyses of brittle crack growth experiments in compression using a modified phase-field theory

There has been a huge interest in recent years in using phase-field theories for numerical analyses of fracture phenomena. However, in phase-field fracture theories, a critical aspect often involves a decomposition of the strain energy density to select physically trustworthy crack paths and to prevent interpenetration of crack surfaces. This aspect becomes even more critical in the case of mixed-mode loading under compression. To overcome these challenges, a hydrostatic-spectral-deviatoric decomposition, enhanced by separate critical energy release rates for different fracture modes, is employed in this study. In order to evaluate the enhanced decomposition strategy, a set of biaxially loaded crack experiments in global compression is designed. Samples of different geometries contain multiple flaws and holes. The experiments are numerically simulated using a unified set of material parameters and three different strain energy decomposition methods (i.e., hydrostatic-spectral-deviatoric, spectral and hydrostatic–deviatoric). Simulations using the hydrostatic-spectral-deviatoric decomposition scheme capture both intricate crack paths and critical loads in the experiments. The enhanced decomposition strategy seems capable of simulating the experiments with reasonable precision, in sharp contrast to the two commonly used decomposition strategies (spectral and hydrostatic–deviatoric).

A Comprehensive, Multidimensional First‐Principles Model for Free‐Radical Photopolymerizations in Bulk and Thin Films

AbstractDecades of advances in understanding and simulating the polymerization kinetics and structural evolution that arises in free‐radical photopolymerizations of multifunctional monomers are combined into a single, first‐principles 3D model. The model explicitly accounts for polymerization features including diffusion‐controlled kinetics, oxygen inhibition, light attenuation, chain‐length dependent termination, reaction‐diffusion termination, heat transfer, composition and conversion‐dependent material properties, crosslinking effects, and species diffusion. Using the homopolymerization of 1,6‐hexanediol diacrylate as a model system, a minimum of two kinetics experiments performed at different initiation rates are required to fit model parameters. The model accurately predicts known relationships regarding oxygen inhibition, light intensity, and curing temperature for samples of different geometries and boundary conditions. The emphasis of the results herein is placed on the interactions between polymerization features, motivating the importance of a model that accommodates these features all in one simulation. The model is shown to be robust in its handling of thermal boundary conditions, alternative polymerization techniques or mechanisms, and characteristics of 3D voxel formation. The model in this work provides a useful tool for property prediction in a wide variety of applications, most notably coatings, dental materials, industrial photocuring processes, additive manufacturing, and holography, where complex interactions of the various features of polymerization play a substantial role.

A Heating and Cooling Stage With Fast Temporal Control for Biological Applications.

The study of biological processes involving live microscopy techniques requires adequate temperature control to respect the physiology of the organism under study. We present here a design strategy for a microscope temperature stage based on thermoelectric elements. The design allows the user to access a range of temperatures below and above room temperature and can accommodate samples of different geometries. In addition, by cooling simultaneously the sample insert and the objective, we minimize the temperature gradients along the sample for large magnification objectives requiring immersion oil. We illustrate how this design can be used to study the physiology of the zebrafish embryo over the temperature tolerance of this species. We envision that this device could benefit the communities using model and non-model organisms with physiological temperatures different from typical mammalian cell culture incubation in biomedical research.

Freeform injection molding of functional ceramics by hybrid additive manufacturing

Freeform Injection Molding (FIM) is a hybrid manufacturing approach where 3D-printed sacrificial polymeric molds are used for Ceramic Injection Molding (CIM). This technique offers great additive manufacturing capabilities with shape complexity and material versatility. In this paper, we present a thorough analysis of the ability of FIM to process a variety of ceramic feedstocks and evaluate samples of different geometries with increasing geometrical complexity. The materials selected are zirconia, alumina and Pb-free piezoelectrics (BaTiO 3 and (Bi, Na)TiO 3 – BaTiO 3 ). Injection molding simulations are used to optimize the processing parameters. The quality of the fabricated ceramic parts is assessed by the microstructure, macro-defects, the geometrical features of the structural ceramics and the piezoelectric performance of BaTiO 3 and (Bi, Na)TiO 3 – BaTiO 3 . The effect of green- and sintered-density, linear shrinkage (associated with sintering), and shape distortion are also discussed. • Hybrid additive manufacturing and injection molding produce 3D complex shapes • 3D-printed sacrificial molds allow molding the ceramics in freeform geometries • Photopolymer formulation results in robust printing and injection performance • Strategy to reduce defects by simulations and to adjust injection molding parameters • Sintered parts show isotropic shrinkage, no delaminations and limited shape distortion • 3D Pb-free piezoceramics preserve their piezoelectric properties

Multiple resonances in lossy acoustic black holes - theory and experiment

Acoustic properties of the metamaterial graded absorber, also known as ``acoustic black hole'', are studied in the linear regime. The absorber consists of thin metallic circular plates, each with a central perforation, separated by annular air cavities. Radius of the perforation in each plate is gradually decreasing with the distance from the plate to the front surface, forming a central channel with a staircase radius profile. A semi-analytical equivalent fluid model accounting for the variations of both the effective density and compressibility of air inside this channel is developed, which incorporates the staircase variations of the perforation radius with distance and assumes motionless plates. The viscous and thermal losses inside the side cavities and the central channel are accounted for using a well-established Johnson-Champoux-Allard-Lafarge model. It is demonstrated that high absorption coefficient values are achieved in a wide range of frequencies starting from a few hundred Hz or less. At low frequencies, the resonances along the length of the structure, i.e. global resonances, are responsible for sound attenuation. At higher frequencies, the resonances of the lateral cavities, i.e. local resonances, play a major role. The upper boundary of the frequency range of high sound absorption is determined by the resonance frequency of the front annular plate. The model is validated against impedance tube measurements on five samples of different geometry and FEM models. FEM model predicts that the elasticity of the plates affects the absorption coefficient behaviour in the frequency range of plate resonances and at frequencies well below the plate resonances.

Computational modelling of magnesium degradation in simulated body fluid under physiological conditions

Magnesium alloys are highly attractive for the use as temporary implant materials, due to their high biocompatibility and biodegradability. However, the prediction of the degradation rate of the implants is difficult, therefore, a large number of experiments are required. Computational modelling can aid in enabling the predictability, if sufficiently accurate models can be established. This work presents a generalized model of the degradation of pure magnesium in simulated body fluid over the course of 28 days considering uncertainty aspects. The model includes the computation of the metallic material thinning and is calibrated using the mean degradation depth of several experimental datasets simultaneously. Additionally, the formation and precipitation of relevant degradation products on the sample surface is modelled, based on the ionic composition of simulated body fluid. The computed mean degradation depth is in good agreement with the experimental data (NRMSE=0.07). However, the quality of the depth profile curves of the determined elemental weight percentage of the degradation products differs between elements (such as NRMSE=0.40 for phosphorus vs. NRMSE=1.03 for magnesium). This indicates that the implementation of precipitate formation may need further developments. The sensitivity analysis showed that the model parameters are correlated and which is related to the complexity and the high computational costs of the model. Overall, the model provides a correlating fit to the experimental data of pure Mg samples of different geometries degrading in simulated body fluid with reliable error estimation.

Efficiency calibration of high-purity germanium detector using Monte Carlo simulations including coincidence-summing corrections: volume source case

The gamma-ray spectrometry by the instrumentality of Ge detectors is used for the detection of low activity environmental samples of different geometry (soil samples, air filters with aerosols, milk powder, etc.). Such measurements require separate calibration of the detector. The high purity germanium (HPGe) gamma-ray spectrometer of GC2520 series was used for experiments. For the efficiency calibration, three cylindrical containers filled with different 60Co water solution levels were used, and the gamma-ray coincidence summing was modelled using MCNP6. The dimensions of the pure germanium crystal, provided by Canberra, were used for the simulations. The true coincidence summing takes place when two or more gamma quanta, which are emitted in a cascade from an excited nucleus, are detected within the resolving time of the detector. However, there is often a mismatch between the simulated and experimental efficiencies. The experimentally obtained and modelled spectra were compared: a good consistency of experimental and modelled results allows investigating the volume sources. During the simulation it was found that the factors affecting the accuracy of modelling are the thickness of the dead layer, crystal dimensions and the thickness of the Al detector cap. The analysis allows measuring the radionuclides activity concentration of samples placed in the containers with different filling heights having only standard shape calibration sources. The obtained accuracy is sufficient to fulfil criteria of 5–10% for such type of simulation to be applied for measurements of real samples in standard BURK-60 containers of various sample filling heights.

Studies about the design of magnetic bionanocomposite

AbstractMagnetic nanocomposites are a class of smart materials that have attracted recent interest as drug delivery systems or as medical implants. A new approach toward the biocompatible nanocomposites suitable for remote melting is presented. It is shown that magnetite nanoparticles (MNPs) can be embedded into a matrix of biocompatible thermoplastic dextran esters. For that purpose, fatty acid esters of dextran with adjustable melting points in the range of 30–140 °C were synthesized. Esterification of the polysaccharide by activation of the acid as iminium chlorides guaranteed mild reaction conditions leading to high-quality products as confirmed by Fourier-transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy as well as by gel permeation chromatography (GPC). A method for the preparation of magnetically responsive bionanocomposites (BNCs) was developed consisting of combined dissolution/suspension of the dextran ester and hydrophobized MNPs in an organic solvent followed by homogenization with ultrasonication, casting of the solution, drying and melting of the composite for a defined shaping. This process leads to a uniform distribution of MNPs in BNC as revealed by scanning electron microscope (SEM). Samples of different geometries were exposed to high-frequency alternating magnetic field (AMF). It could be shown that defined remote melting of such biocompatible nanocomposites is possible for the first time. This may lead to a new class of magnetic remote-control systems, which are suitable for controlled release applications or self-healing materials. BNCs containing biocompatible dextran fatty acid ester melting close to human body temperature were prepared and loaded with Rhodamine B (RhB) or green fluorescent protein (GFP) as model drugs to evaluate their potential use as drug delivery system. The release of the model drugs from the magnetic BNC investigated under the influence of a high-frequency AMF (20 kA/m at 400 kHz) showed that on-demand release is realized by applying the external AMF. The BNC possessed a long-term stability (28 d) of the incorporated iron oxide particles after incubation in artificial body fluids. Temperature-dependent mobility investigations of MNP in the molten BNC were carried out by optical microscopy, magnetometry, alternating current (AC) susceptibility, and Mössbauer spectroscopy measurements. Optical microscopy shows a movement of agglomerates and texturing in the micrometer scale, whereas AC susceptometry and Mössbauer spectroscopy investigations reveal that the particles perform diffusive Brownian motion in the liquid polymer melt as separated particles rather than as large agglomerates. Furthermore, a texturing of MNP in the polymer matrix by a static magnetic field gradient was investigated. First results on the preparation of cross-linkable dextran esters are shown. Cross-linking after irradiation of the BNC prevents melting that can be used to influence texturing procedures.

Microstructural And Mechanical Properties Of Selective Laser Melted Inconel 718 For Different Specimen Sizes

Abstract Selective laser melting (SLM) falls into the category of additive manufacturing technologies that are being increasingly used in the aerospace industry. This study presents the results of the examination of the microstructure and mechanical properties of selective laser melted Inconel 718. The tests were carried out for samples of different geometry (thickness, shape). The investigation showed the effect of the specimen’s size and the printing direction on the microstructure and mechanical properties. In the microstructural investigation, light and scanning electron microscopes were used. The microstructure investigation included measurements of the grain size and the carbides’ content. In order to estimate porosity computer tomography was used. Tensile tests were carried out at room temperature. The results showed differences in mechanical and microstructural properties of different size specimens.

Oxidation/corrosion of BN-based coatings as prospective interphases for SiC/SiC composites

The ceramic matrix composites envisaged as structural parts in the hot section of aircraft engines consist of SiC-based fibres and matrices with a BN interphase coating between them. To control their service life, the oxidation/corrosion behaviour of these materials must be determined. For this purpose, samples of different geometries were prepared by chemical vapour deposition and thermally subjected to wet air. The behaviour of BN alone depends on its crystallization degree, structural homogeneity and the considered direction in the coating. In the case of a thin layer of pure BN of interphase type, recession is significantly reduced at 800 °C by the formation of a sealing borosilicate phase in the confined space surrounded by SiC. At 1000 °C, the protection is no longer sufficient and a steady recession remains. The presence of aluminium added to BN improves protection at 1000 °C due to the formation of alumina combined with borosilicate.

Mechanical behavior of coarse- and fine-grained Al-6101 samples of different geometry under tension

The paper presents the experimental data obtained during static tension of cylindrical samples of two structural states and two types of geometry from Al-6101 alloy at room temperature.

Accurate characterization of complete set constants of single domain 0.72Pb(Mg1/3Nb2/3)O3–0.28PbTiO3 single crystal by resonant ultrasound spectroscopy using only one sample

In order to find out the origin of the giant piezoelectric effects of relaxor-PbTiO3 single crystals when poled along nonpolar directions, it is necessary to obtain the complete physical property data of a single domain state. Conventional characterization methods using multiple samples of different geometries often produce inconsistent data set because the domain patterns produced during poling are strongly dependent on the sample geometry. Here, we used the resonant ultrasound spectroscopy (RUS) technique to determine the material constants of a single domain 0.72Pb(Mg1/3Nb2/3)O3–0.28PbTiO3 single crystal, which has a high mechanical quality factor (QM). Errors caused by sample-to-sample variation are avoided because all constants were measured from the same sample. The data set obtained is highly self-consistent, which provides a base for theoretical analysis as well as the input for simulation designs of piezoelectric devices. Comparison with data measured by other methods shows the advantage and higher accuracy of this characterization strategy.

Field of first magnetic flux entry and pinning strength of superconductors for rf application measured with muon spin rotation

The performance of superconducting radiofrequency (SRF) cavities used for particle accelerators depends on two characteristic material parameters: field of first flux entry $H_{entry}$ and pinning strength. The former sets the limit for the maximum achievable accelerating gradient, while the latter determines how efficiently flux can be expelled related to the maximum achievable quality factor. In this paper, a method based on muon spin rotation ($\mu$SR) is developed to probe these parameters on samples. It combines measurements from two different spectrometers, one being specifically built for these studies and samples of different geometries. It is found that annealing at 1400{\deg}C virtually eliminates all pinning. Such an annealed substrate is ideally suited to measure $H_{entry}$ of layered superconductors, which might enable accelerating gradients beyond bulk niobium technology.

Characterization of Full Set Material Constants and Their Temperature Dependence for Piezoelectric Materials Using Resonant Ultrasound Spectroscopy

During the operation of high power electromechanical devices, a temperature rise is unavoidable due to mechanical and electrical losses, causing the degradation of device performance. In order to evaluate such degradations using computer simulations, full matrix material properties at elevated temperatures are needed as inputs. It is extremely difficult to measure such data for ferroelectric materials due to their strong anisotropic nature and property variation among samples of different geometries. Because the degree of depolarization is boundary condition dependent, data obtained by the IEEE (Institute of Electrical and Electronics Engineers) impedance resonance technique, which requires several samples with drastically different geometries, usually lack self-consistency. The resonant ultrasound spectroscopy (RUS) technique allows the full set material constants to be measured using only one sample, which can eliminate errors caused by sample to sample variation. A detailed RUS procedure is demonstrated here using a lead zirconate titanate (PZT-4) piezoceramic sample. In the example, the complete set of material constants was measured from room temperature to 120 °C. Measured free dielectric constants and were compared with calculated ones based on the measured full set data, and piezoelectric constants d15 and d33 were also calculated using different formulas. Excellent agreement was found in the entire range of temperatures, which confirmed the self-consistency of the data set obtained by the RUS.

Characterization of Full Set Material Constants and Their Temperature Dependence for Piezoelectric Materials Using Resonant Ultrasound Spectroscopy.

During the operation of high power electromechanical devices, a temperature rise is unavoidable due to mechanical and electrical losses, causing the degradation of device performance. In order to evaluate such degradations using computer simulations, full matrix material properties at elevated temperatures are needed as inputs. It is extremely difficult to measure such data for ferroelectric materials due to their strong anisotropic nature and property variation among samples of different geometries. Because the degree of depolarization is boundary condition dependent, data obtained by the IEEE (Institute of Electrical and Electronics Engineers) impedance resonance technique, which requires several samples with drastically different geometries, usually lack self-consistency. The resonant ultrasound spectroscopy (RUS) technique allows the full set material constants to be measured using only one sample, which can eliminate errors caused by sample to sample variation. A detailed RUS procedure is demonstrated here using a lead zirconate titanate (PZT-4) piezoceramic sample. In the example, the complete set of material constants was measured from room temperature to 120 °C. Measured free dielectric constants and were compared with calculated ones based on the measured full set data, and piezoelectric constants d15 and d33 were also calculated using different formulas. Excellent agreement was found in the entire range of temperatures, which confirmed the self-consistency of the data set obtained by the RUS.

Aspects of varying crosslinker and catalyst concentrations on tear strength of silicone polymer networks: Comparison of tear strengths using samples of different geometries

ABSTRACTCrosslinker and catalyst concentrations have been varied to prepare different hydroxyfunctional poly(dimethylsiloxane) (HOPDMS) polymer network compositions. The tear strengths of these silicone polymer networks have been measured using different geometries, as trouser, crescent, and Graves (angled) specimens. It has been observed that the results of tear strength of Graves and crescent‐shaped specimens do not show a constant ratio with the concentration of crosslinker used for curing of HOPDMS networks. Instead, it has been observed and reported for the first time that the tear strengths of Graves and crescent‐shaped samples show a crossover at about 1.2% crosslinker. The observation of this crossover pattern for different compositions of silicone networks show that it is difficult to compare the results of the tear test of the same polymer performed on samples of different geometries with one another. The crossover pattern of the tear energy results for the test specimens of two different geometries has been explained in the light of essential work facture theory based on the geometry of the testing sample, crosslinking, and testing that alters the distribution of force over the width of the specimen. It was shown that the change in composition of the HOPDMS networks changes the order of ranking of Graves and crescent tear tests. With varying catalyst concentration in the silicone network composition, the tear property differences between the Graves and crescent‐shaped specimens are not significant. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43115.

Modified foundation modelling of dowel embedment in glulam connections

This paper examines the embedment behaviour of single-dowel connections in Scandinavian Spruce Glulam by means of experimental and numerical investigations. First, the experimental results of a series of single-dowel tests on samples of different geometry and grain directions are presented. The evolution of local strain concentrations around the fastener at increasing levels of bearing deformation, is reported in detail by means of non-contact field strain measurements and its implications are discussed. Detailed Finite Element simulations are also carried out and subsequently employed to highlight the main features of the response of doweled connections in glulam. A foundation model, initially developed for Douglas-fir (Pseudotsuga menziesii) timber, is upgraded and adapted for Scandinavian Spruce Glulam (Picea abies) elements subjected to loads acting perpendicular and parallel to the grain direction. The proposed model is based on the definition of equivalent material parameters for the crushing region around the dowel hole. To this end, relationships for the estimation of material characteristics as a function of the crushing volume are suggested. The validity and accuracy of the proposed modified foundation models are examined against the experimental results. It is shown the improved foundation model is able to simulate the embedment stiffness, capacity and inelastic behaviour of single-dowel connections on glulam with reasonable accuracy for strains of up to 8%, and can therefore be used for design and assessment purposes.

Magnetic Biocomposites for Remote Melting

A new approach toward the fabrication of biocompatible composites suitable for remote melting is presented. It is shown that magnetite nanoparticles (MNP) can be embedded into a matrix of biocompatible thermoplastic dextran esters. For that purpose, fatty acid esters of dextran with adjustable melting points in the range of 30-140 °C were synthesized. Esterification of the polysaccharide by activation of the acid as iminium chlorides guaranteed mild reaction conditions leading to high quality products as confirmed by FTIR- and NMR spectroscopy as well as by gel permeation chromatography (GPC). A method for the preparation of magnetically responsive bionanocomposites was developed consisting of combined dissolution/suspension of the dextran ester and hydrophobized MNPs in an organic solvent followed by homogenization with ultrasonication, casting of the solution, drying and melting of the composite for a defined shaping. This process leads to a uniform distribution of MNPs in nanocomposite as revealed by scanning electron microscope. Samples of different geometries were exposed to high frequency alternating magnetic field. It could be shown that defined remote melting of such biocompatible nanocomposites is possible for the first time. This may lead to a new class of magnetic remote control systems, which are suitable for controlled release applications or self-healing materials.