Compacted Samples Research Articles

Modelling and simulation of a compact sample of composite materials

Additive manufacturing of composite materials has a high degree of structural strength, which aids in the production of geometrically more complex shapes of components. This paper aims to investigate the crack propagation in the case of eccentric tension, to compare the Von - Mises stresses for the different materials, and to evaluate the stress intensity factor, which will provide a basis for further experimental measurements. In solving the simulations, three different materials were compared with each other, with emphasis on the comparison of carbon fiber reinforced Onyx and aluminum alloy materials. Crack propagation was monitored by simulations in Ansys using the Smart command.

Features for obtaining of RuAl-based powder alloys

Refractory heat-resistant ruthenium monoaluminide β-RuAl is a promising material for operation in high-velocity gas oxidizing flows at temperatures above work temperatures and melt temperatures of nickel superalloys and refractory nickel and titanium aluminides. The possibilities of preparing high-quality powder materials from RuAl for the manufacture of compact samples are considered. Compact materials with minimum porosity and practically equilibrium phase composition can be obtained under conditions of high-temperature reaction alloying during three-stage hot isostatic pressing with intermediate homogenizing annealing. Preliminary treatment of mixtures of Ru and Al powders in an attritor for 15 h reduces the exothermic effect of RuAl formation and lowers the temperature at which the contact interaction begins.

О ПРОБЛЕМЕ ИДЕНТИФИКАЦИИ СТРУКТУР АУСФЕРИТНОГО ВЫСОКОПРОЧНОГО ЧУГУНА ПРОИЗВОДСТВЕННЫМИ МЕТОДАМИ КОНТРОЛЯ

The paper presents results of analysis of literature data and own researches in the field of the austempered high-strength cast irons with spherical and vermicular graphite. Difficulty of control and identification of needle (bainite and martensite) and non-needle (troostite) quenching structures is noted. The basic methods of control of quenching structures are considered. 12austempered compacted graphite iron samples have been investigated to find reliable criteria for identification of quenched structures by methods available to production metallographic laboratories. The results of microstructural analysis (using light microscope) of several hundred fields of view and several hundred measurements of microhardness by Vickers method have been analyzed. It is found that the use of light microscopy and microhardness determination of the austempered compacted graphite iron matrix separately does not give reliable identification of hardened structures. It is established that combination of these methods is the best solution of the problem of qualitative control of the hardening structures of cast irons under production conditions. On the basis of the conducted research a method of checking and identifying the hardening structures of the austempered high-strength cast irons is proposed, which consists in comparing the results of microhardness measurement with microstructure areas that can be used using the equipment available in the production laboratory.

Investigation of Metal Matrix Composites Aluminium Reinforced Graphite Particles Produced Using Powder Metallurgy

Many industries have been in demand for metal matrix composites (MMC), especially in the aerospace and automotive sectors. The advancement of MMC is being investigated to improve the material's mechanical properties. MMC is a composite material consisting of at least two materials. One of them would act as a matrix, and the other materials would serve as reinforcement. MMC allows for overcoming the specific limitations of metallic and ceramic materials by blending their mutually exclusive property profiles. The main objective of this research is to successfully fabricate aluminium and graphite metal matrix composites using powder metallurgy. In this research, powder metallurgy was used, where aluminium and graphite were blended according to the sample volume ratio. Both graphite and aluminium were in the form of metal powder. Graphite powder with each ratio of volume percentages of 0%, 1.5%, 3%, 4.5%, and 6% was mixed with aluminium powder. The blended material is produced by powder metallurgy via the compaction process using the hydraulic press brake machine. Subsequently, the compacted sample was sintered using a laboratory furnace at 600°C for 4 hours. The mechanical tests show that the highest tensile strength and Young's modulus were obtained by MMC aluminium – 1.5 % volume graphite. While for the highest hardness was achieved by aluminium – 4 % volume graphite.

Structural, Thermal and Magnetic Analysis of Two Fe-X-B (X = Nb, NiZr) Nanocrystalline Alloy.

High-energy ball milling was used to produce two Fe-X-B (X = Nb, NiZr) nanocrystalline alloys. X-ray diffraction (XRD), differential scanning calorimetry (DSC), and vibrating sample magnetometry (VSM) were used to analyze the microstructure, thermal, and magnetic characteristics of the milled powders, the agglomerated particles (also generated during the milling process), and the compacted specimens of both alloys. The main crystallographic phase is always a bcc Fe-rich solid solution; whereas a minor Nb(B) phase is detected on powders and agglomerated particles in the Fe80Nb8B12 alloy. The crystalline size of the Fe80(NiZr)8B12 alloy is between 11 and 14 nm, whereas in the Fe80Nb8B12 alloy, it ranges between 8 and 12 nm. Microstrain and dislocation density are higher in agglomerated samples for both alloys than in milled powders. Thermal analysis detects structural relaxation and crystal growth exothermic processes with high dispersion in the temperature intervals and in the calculated apparent activation energy of the main crystallization process. Regarding magnetic behavior, the coercivity values of all powdered-agglomerated specimens were around 800 A/m. The coercivity is higher in compacted sample, but controlled annealing favors enhanced soft behavior.

Effect of Heat Treatment on Elastic Properties and Fracture Toughness of Fused Filament Fabricated PEEK for Biomedical Applications.

This work presents the results of an experimental investigation of the mechanical properties of polyetheretherketone (PEEK) specimens additively manufactured (AM) by using fused filament fabrication with different printing parameters and subjected to postprocessing heat treatment. Standard and compact tension samples were manufactured with a different infill angle using 0.4 mm and 0.6 mm nozzle diameters. Some of the samples were subjected to heat treatment at 220 °C after manufacturing. Tensile tests were conducted to determine the values of elastic modulus, tensile strength, as well as mode-I fracture toughness and critical strain energy release rate. Tensile properties of single-thread and as-delivered filaments were also studied. It was concluded that heat treatment significantly improved the elastic properties, tensile strength and fracture toughness of the AM PEEK samples: the fracture resistance increased by 33 to 45% depending on the stacking order, while the tensile strength increased by some 45-65%, with the elasticity modulus grown by up to 20%. Strain fields induced in specimens by crack propagation were captured with a digital image correlation technique and compared with results of numerical simulations implemented with the extended finite-element method (XFEM). Conclusions on the optimal parameters of 3D printing of PEEK were made.

Evaluating reclaimed asphalt mixture homogeneity using force chain transferring stress efficiency

Numerous studies have demonstrated a direct link between the homogeneity of asphalt mixture and the rutting performance, water stability, tensile strength, and service life of the asphalt pavement. Due to the existence of RAP clusters, poor homogeneity of the recycled asphalt mixtures is more severe than natural ones. However, previous studies have mainly focused on analyzing the distribution of aggregates, ignoring the transfer of the internal stress in the mixture. This paper proposed a novel approach for the analysis of the homogeneity of recycled asphalt mixture using the efficiency of force chain transferring stress. Therefore, to prepare gyratory compacted samples, diabase in green color was used as the virgin aggregate and marble in white color as the RAP aggregate. Moreover, to obtain the vertical section images, the samples were cut and processed by digital image processing (DIP). This included distinguishing the virgin and RAP aggregates by global gray threshold segmentation, adding asphalt film around the aggregates, and constructing a force chain network relied on the aggregate contact information. Also, the intensity of the force chain was determined using the finite element method (FEM). In addition, the efficiency of force chain transferring vertical stress (ETVS) was introduced and the homogeneity index D of the recycled asphalt mixture was proposed based on the variation coefficient of ETVS. Furthermore, uniaxial compression tests were carried out to mathematically analyze the homogeneity index D proposed in this paper and the homogeneity index D′ proposed based on the aggregate area ratio in previous studies. The obtained result showed that the homogeneity index D increased first and then decreased with the increase of RAP content. Moreover, the correlation analysis demonstrated the compressive performance of the mixture to be mainly reflected by the homogeneity index D. The correlation coefficients of the compressive strength and the compressive resilient modulus were found to be 0.9010 and 0.8464, respectively. Finally, the homogeneity index D′ was observed to mainly reflect the stability of the compressive performance of the mixture, with the correlation coefficients of the variation coefficient of the compressive strength and the compressive resilient modulus of 0.8745 and 0.8869, respectively.

Prevalence of Trachoma in Pre-validation Surveillance Surveys in 11 Evaluation Units (Covering 12 Districts) in Oromia Regional State, Ethiopia: Results from 2018−2020

ABSTRACT Purpose Interventions to reduce the prevalence of trachoma and transmission of ocular Chlamydia trachomatis have been implemented in Oromia Region, Ethiopia. Following an impact survey in which the trachomatous inflammation—follicular (TF) prevalence in 1–9-year-olds is <5%, a surveillance survey is recommended 2 years later, without additional antibiotic treatment. We report results of surveillance surveys in 11 evaluation units (EUs) covering 12 districts in Oromia Region, to plan whether future interventions are needed. Method We use a two-stage cluster-sampling cross-sectional survey design. In each EU, 26 clusters (villages) were systematically selected with probability proportional to size; from each cluster, 30 households were selected using compact segment sampling. Water, sanitation and hygiene (WASH) access was assessed in all selected households. All residents of selected households aged ≥1 year were examined for TF and trachomatous trichiasis (TT) by certified graders. Result Of 31,991 individuals enumerated, 29,230 (91% of) individuals were examined. Eight EUs had an age-adjusted TF prevalence in 1−9-year-olds of ≥5% and seven had a TT prevalence unknown to the health system among adults aged ≥15 years of ≥0.2%. About one-third of visited households had access to an improved water source for drinking, and 5% had access to an improved latrine. Conclusion Despite TF reductions to <5% at impact survey, prevalence recrudesced to ≥5% in all but three of the 11 EUs. Operational research is needed to understand transmission dynamics and epidemiology, in order to optimise elimination strategies in high-transmission settings like these.

Experimental study of particle lift initiation on roller-compacted sand–clay mixtures

Civil engineering works are sources of dust emissions, which can cause severe security, health and environmental damages to workers and neighbourhoods. This is particularly significant for implementation of earthwork sites. The present paper reports a study conducted to characterise the soil–atmosphere interaction above compacted soils where particle lift is initiated. Mixtures of kaolin clay and sand have been compacted using a laboratory roller compactor that reproduces near-field compaction conditions. Shear testing conducted at the interface confirms that the sand content affects the friction angle between the soil and the compaction roller. The experimental velocity profiles above the compacted samples have been obtained in a wind tunnel using a non-intrusive measurement technique (laser Doppler velocimetry). Results show that the sand fraction affects velocity profiles. Compaction, therefore, may not fully reduce the roughness of the soil surface. The airflow friction velocities at the sample surfaces have been determined from the boundary layer profiles. The results achieved demonstrate that all tested soils reach the threshold friction velocity required to initiate particle lift, and the higher the sand content of the soil, the more likely it is that particle lift occurs.

Analysis of pore geometry in the compacted fine aggregate matrix by x-ray microtomography

This study employs the advanced X-ray microtomography technique to evaluate the open and closed porosity geometry within fine aggregate matrix specimens extracted from different locations of SGC samples compacted with distinct densities. The adoption of advanced techniques such as the X-ray microtomography facilitate the fabrication of FAMs that are more representative of those that comprise asphalt concretes, as well as allow the use of similar replicates in mechanical tests. In addition, the traditional porosity assessment methods are well documented, but provide only global average results for the entire sample. In this context, X-ray microtomography stands out because, besides porosity information, pore distribution and a series of other parameters related to the internal structure of the object can be evaluated. This study evaluated the geometry of open and closed pores of FAM specimens extracted from different locations of SGC compacted samples. From the results and analyses, it can be concluded that the shape of the closed pores is spherical and the shape of the open pores is cylindrical for the SGC samples compressed with 2.26 g/cm3, 2.34 g/cm3 and 2.44 g/cm3.

Engineering Properties Investigation of Soft Clay as Potential Subgrade Material

Highway pavement design using soft clay soil as a subgrade is always a great challenge and can cause problems such as roadbed instability and soil settlement. To overcome this problem, the knowledge of the subgrade soil characteristic should be studied first because it needs to be considered during the design phase of pavement. This study was conducted to investigate the engineering properties of soft clay that can be used as potential subgrade material. Some soil laboratory tests were performed to establish the engineering properties of the soft clay. From the standard proctor compaction test, the results revealed that the maximum dry density and optimum moisture content are 1.58 Mg/m³ and 20.15 %, respectively. The finding from the soil-water characteristic curve (SWCC) test indicates that the SWCC did not present a residual suction. The compression modulus and pre-consolidation pressure obtained from the compacted soil sample for the consolidation test are higher than the undisturbed soil sample. Based on triaxial test results, the effective cohesion acquired from the compacted soil sample is greater than the undisturbed sample. This research provides a reference for the study of soft clay engineering characteristics.

On a quantum martingale convergence theorem

It is well known in quantum information theory that a positive operator-valued measure (POVM) is the most general kind of quantum measurement. Mathematically, a quantum probability is a normalized POVM, namely, a function on certain subsets of a (locally compact and Hausdorff) sample space that satisfies the formal requirements for a probability measure and whose values are positive operators acting on a complex Hilbert space. A quantum random variable is an operator-valued function which is measurable with respect to a quantum probability. In this work, we study quantum random variables and generalize several classical limit results to the quantum setting. We prove a quantum analogue of the Lebesgue-dominated convergence theorem and use it to prove a quantum martingale convergence theorem. This quantum martingale convergence theorem is of particular interest since it exhibits nonclassical behavior; even though the limit of the martingale exists and is unique, it is not explicitly identifiable. However, we provide a partial classification of the limit through a study of the space of all quantum random variables having quantum expectation zero.

Characterizing asphalt emissions under in-service conditions

Recent studies have suggested that asphalt related emissions at environmentally pertinent conditions are a major contributor of volatile organic compounds ubiquitous to the environment. Many variables such as temperature/viscosity of asphalt binder, solar irradiance of the asphalt binder, and geometric constraints including film thickness, the act of coating aggregate to produce Hot Mix Asphalt, and compaction into pavements influence the magnitude and composition of measured emissions. Continuous films of asphalt binder were used to determine how temperature/viscosity and film thicknesses can influence measured emissions. The magnitude of emissions scaled with the inverse of viscosity, whereas the composition of emissions varied with film thickness and age of the asphalt binder sample. Asphalt binder exposed to solar irradiance showed short term impacts on emissions in the first hours of exposure. Compacted asphalt pavements were used to simulate real world new in-service conditions. The emissions from a freshly compacted asphalt pavement were compared to a 17-year-old pavement sample collected from the field to determine how the act of compacting asphalt binder coated in aggregate influenced emissions over a 17-year period. An increase in the complexity of the system caused slowing in the total emissions profile. While lower than what was observed in the freshly compacted samples, emissions were still observed in the 17-year-old pavement. The composition of emissions indicated that smaller and more volatile compounds are capable of being released from deeper within the compacted pavement, whereas the larger and less volatile compounds tend to remain trapped. • Asphalt emission generator used to measure emissions under in-service conditions. • The effects of solar irradiation on asphalt pavement emission. • Solar irradiation of asphalt binders generates short term increases in emissions. • Effects of asphalt pavement compaction on released emissions.

Locality preserving triplet discriminative projections for dimensionality reduction

The graph embedding framework is widely used for developing dimensionality-reduction algorithms. Many such supervised algorithms construct an intrinsic graph to compact intra-class samples or describe their local structures and build a penalty graph to increase the separability of inter-class samples. However, in the available intrinsic graph construction, manually selecting a set of appropriate neighbors associated with each sample is challenging. In addition, the construction of a penalty graph may seriously impair the intrinsic structures of the samples. Thus, in an attempt to address these issues, this study proposes an algorithm referred to as locality-preserving triplet discriminative projections. The proposed algorithm comprises locality-preserving and discriminative graphs. First, a weighted least-square function is used to calculate the edge weights of the locality-preserving graph. An improvement of the locality-preserving graph constructed in this study is that suitable neighbors are soft-selected. Meanwhile, the triplets of the samples are exploited for discriminative graph construction. Through the separation of the marginal samples and using less focus on samples with good discriminability, this graph enhances the discriminability with less damage to the intrinsic structure. In addition, to further improve the performance of the discriminative graph, a class-relevant margin is added to separate similar classes. The experimental results on four public datasets show that the proposed algorithm outperforms several other dimensionality reduction methods.

Simplified protocol for fatigue cracking characterization of asphalt mixtures using the direct tension cyclic fatigue test

Several test methods exist to characterize asphalt mixtures with respect to their fatigue cracking resistance, but only a few can be used in mechanistic models for pavement performance predictions. The direct tension cyclic fatigue test is one such test method because it measures fundamental properties of asphalt mixtures. However, the amount of material and time required for specimen fabrication and preparation are substantial, which impairs the implementation of this test method. Thus, this paper proposes a simplified protocol to characterize asphalt mixtures with respect to fatigue cracking using the direct tension cyclic fatigue test. First, the method to estimate the appropriate Superpave gyratory compacted samples’ mass was evaluated and recalibrated, reducing the amount of material needed to obtain test specimens with acceptable air void content. Second, a statistical analysis showed that reusing specimens tested via AASHTO TP 132 for the direct tension cyclic fatigue test does not yield significant differences at either material or pavement levels. Finally, a practical example indicated that the recalibrated mass estimate equation and the reuse of specimens for the direct tension cyclic fatigue test result in substantial savings of material and time. The simplified protocol proposed in this paper has several advantages when either partially or fully implemented including testing mixtures with limited amount of material (e.g., field cores), replacing problematic specimen data, and expediting performance testing.

Synthesis, processing and phase analysis of quasi crystal particle reinforced aluminium matrix composite

ABSTRACT The main goal of the present study involves synthesis of Al-Cu-Fe based icosahedral quasi-crystal (QC) particles reinforced Al matrix composite and analyze its microstructure, phase and hardness property. The icosahedral quasi-crystal phase nominal composition was taken to Al63Cu25Fe12 (%). Mechanical alloying as a viable powder metallurgy route was used to synthesize the quasi-crystal phase with various milling parameters. The X-Ray diffraction analysis immediately after milling revealed that there was no formation of quasi-crystal phase exclusively by milling. However, after annealing the 100 hours milled powders at 600°C for 4 hours, the quasi-crystal phase was observed to form. The quasi-crystal phase was identified to be the 1/1 cubic approximant (α-Al85.5Cu36.95Fe15.5) of the icosahedral phase. The quasi-crystal particles reinforced aluminum composites were prepared with different concentrations (10–50 weight %) of the quasi-crystal phase by cold compaction. The compacted samples were then sintered for 4 hours at different temperatures such as 400°C, 500°C, and 600°C. The icosahedral Al64.3Cu23.5Fe12.2 phase formation was observed in the 600°C sintered composite, whose composition is approximately similar to the nominal composition used. The results uncovered that, while increasing the concentration of the reinforcement quasi-crystal phase, the hardness of the composite increased.

Effect of activating additives on the cold sintering process of (MnFeCoNiCu)&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; high-entropy ceramics

Objectives. To obtain experimental data on the effect of activating additive type on the cold sintering process of (MnFeCoNiCu)3O4 high-entropy ceramic. The following substances were used as activating additives: ammonium acetate (CH3COONH4), acetic acid (CH3COOH), ammonium chloride (NH4Cl), potassium fluoride dihydrate (КF·2H2O), lithium fluoride (LiF), sodium fluoride (NaF), and sodium hydroxide (NaOH).Methods. Synthesis of the initial powder by low-temperature self-propagating method; investigation of the powder particles size distribution by laser diffraction method; analysis of the particle shape and compacted sample microstructure by scanning electron microscopy; investigation of the phase composition by X-ray phase analysis; high-entropy ceramic sample consolidation by cold sintering process. The density of the initial powder and the relative density of cold sintered samples were determined by the Archimedes method.Results. Samples with a relative density of over 0.70 were obtained using distilled water, CH3COONH4 and NaOH during cold sintering at 300 °C, with a holding time of 30 min and pressure 315 MPa.Conclusions. For the first time, the effect of the type of activating additive on the relative density of high-entropy ceramics (MnFeCoNiCu)3O4 samples obtained by cold sintering process has been experimentally demonstrated. The samples microstructures have pronounced differences: 20 wt % distilled water does not lead to grain growth, with only their compaction to 0.71 relative density observed; however, the addition of 0.1 wt % CH3COONH4 and NaOH increases the average grain size when reaching similar relative densities (0.70 and 0.71, respectively). X-ray diffraction analysis showed that the cold sintering process does not lead to a change in the phase composition of the initial (MnFeCoNiCu)3O4 powder, confirming the preservation of the high-entropy structure.

Assessing the Tensile Properties of Asphalt Concrete

The tensile strength of asphalt concrete is essential to control the rutting behavior of the pavement. In the present work, asphalt concrete mixtures were compacted at optimum binder content to a target density using roller compaction. Extra mixtures with 0.5 % binder content above and below the optimum were also prepared. Core specimens were extruded from the compacted slab samples for testing. The tensile strength of asphalt concrete was assessed using the indirect tensile strength test and the semi-circular bending test. It was detected that the tensile strength as obtained by SCB is five and half fold and five-fold higher than that obtained by ITS when the specimens are tested at (20 and 0) °C respectively. The SCB tensile strength increase by 72.1 % when the specimens are tested at 0°C as compared with the testing at 20°C. However, it was observed that the tensile strength obtained from the Semi-Circular Bend test (SCB) increases as the binder content increase when compared with that obtained from Indirect tensile strength test (ITS). The slope of the SCB – Binder content at both testing temperature relationship increases while the intercept declines as the binder content increase. This can refer to the sensitivity of the SCB test to the binder and temperature variation. The ITS declines when the testing temperature changes from (0 to 20 and 40) ° C by (48.3, and 80.1) %, (48.5, and 78.1) %, and (48.3, and 81.3) % for mixtures with (4.4, 4.9, and 5.4) % binder respectively.

Enhancing Barite Carbothermal Reduction with Brown Coal by Compaction of the Charge

Barium sulfide is an important intermediate in the manufacture of ceramics, glass, plastics, and pharmaceutical products. This substance is traditionally obtained by carbothermal reduction of barite (barium sulfate) in the presence of a carbon-containing reducing agent, mainly coal. Herein, it is demonstrated that compaction of the charge before the carbothermal reduction significantly enhances the conversion of barium sulfate to sulfide due to an increase in the contact time of carbon monoxide with barite in a compact sample in comparison with a powder sample. In the presence of NaOH as a catalyst, the degree of conversion of barium sulfate in a compact sample was 0.95–0.97 upon roasting at 1150 °C for 65 min, while in a powder sample this value did not exceed 0.6. Furthermore, charge compaction reduced the conversion activation energy (136 vs. 264 kJ mol−1), which could be a tool for reducing the energy intensity of obtaining barium sulfide from its sulfate.

Tip-scan high-speed atomic force microscopy with a uniaxial substrate stretching device for studying dynamics of biomolecules under mechanical stress.

High-speed atomic force microscopy (HS-AFM) is a powerful tool for studying the dynamics of biomolecules in vitro because of its high temporal and spatial resolution. However, multi-functionalization, such as combination with complementary measurement methods, environment control, and large-scale mechanical manipulation of samples, is still a complex endeavor due to the inherent design and the compact sample scanning stage. Emerging tip-scan HS-AFM overcame this design hindrance and opened a door for additional functionalities. In this study, we designed a motor-driven stretching device to manipulate elastic substrates for HS-AFM imaging of biomolecules under controllable mechanical stimulation. To demonstrate the applicability of the substrate stretching device, we observed a microtubule buckling by straining the substrate and actin filaments linked by α-actinin on a curved surface. In addition, a BAR domain protein BIN1 that senses substrate curvature was observed while dynamically controlling the surface curvature. Our results clearly prove that large-scale mechanical manipulation can be coupled with nanometer-scale imaging to observe biophysical effects otherwise obscured.