Mechanical Properties Of Bulk Material Research Articles

Determining the relationship between the simulation duration by the discrete element method and the computer system technical characteristics

The object of this study is the relationship between the technical characteristics of a computing system and the duration of modeling the motion of particles of granular materials by the discrete element method. The scheme of the calculation algorithm is presented; its main stages are analyzed. A 3D model of a belt feeder and a mathematical model of particle motion were developed for calculations by the discrete element method in the EDEM 2017 environment. The physical and mechanical properties of bulk material are defined; the structural and technological parameters of equipment are determined. The parameters of the algorithm and computing system are analyzed. Those parameters are defined, the change of which does not affect the accuracy of calculations but can change the volume of computing resources used. These include the number of particles of loose material, the «grid» step, and the number of processor cores. The influence of these parameters on the duration of simulation was determined using a complete factor experiment. Experimental studies have shown that for the duration of the simulation, the determining parameters are the number of particles and the number of processor cores. It was established that there is a linear relationship between the duration of the simulation and the number of particles. The regression equation is built, which makes it possible to predict the simulation time. It was also established that the software does not fully use all available computing resources; the maximum load on the processor when utilizing all available cores is 57 %. The use of RAM and disk subsystem almost did not change during simulation. The results reported here make it possible to plan the use of computing resources for research using the discrete element method and to predict the simulation time

Analytical solution of indentation response of an elliptical cylindrical indenter on elastic microbeam with surface tension

<p indent="0mm">In addition to the measurement of mechanical properties of bulk materials, the indentation technology is widely used to measure the mechanical properties of soft films and microscale materials. As the material scale decreases, surface effects play an important role in the force and deformation in the indentation contact problem. In this paper, the two-dimensional indentation problem of an elastic microbeam under an elliptical cylinder indenter is studied theoretically. For the microbeam with the surface tension, the differential governing equation satisfied by the surface pressure distribution and the normal deflection is solved. The analytical solutions of the surface pressure and surface displacement inside and outside the contact area are obtained, where the undetermined coefficients are determined by the contact zone half-width and the indentation depth. The deformation solution of the microbeam under uniform load and Betty’s reciprocal theorem of the indentation problem are given. Then, the contact zone half-width and indentation depth under different measurement forces are solved, and the analytical solution of the indentation problem of an elliptical cylindrical indenter on elastic microbeam is obtained. The effect of surface tension, elliptical indenter parameters and microbeam size parameters on surface pressure and deformation in the indentation problem is analyzed theoretically. This study helps to understand the surface effect on the indentation behavior of microscale materials, and provides some reference for related indentation testing techniques.

On the micromechanism of superior strength and ductility synergy in a heterostructured Mg-2.77Y alloy

Heterostructured metals and alloys are a new class of materials in which mechanical behaviors between the heterogeneous regions are significantly different, and the mechanical properties of bulk materials are superior to the superposition of individual regions. In this paper, three distinct types of heterostructures were constructed in Mg-2.77Y (wt.%) alloy by applying simple thermomechanical processing. Namely, Type I: the non-recrystallized grains of several tens of microns were embedded in the micron-scaled recrystallized grains that were distributed along shear bands and dispersed near grain boundaries; Type II: the aggregations of micron-scaled recrystallized grains were surrounded by the non-recrystallized grains; Type II: the micron-scaled recrystallized grains dominated the microstructure, and the non-recrystallized regions with diameters of tens of micrometers were surrounded by those fine recrystallized grains. Mechanical tests showed that the material with type III heterostructure had the optimal combination of yield strength and uniform elongation. This is attributed to its remarkable hetero-deformation induced (HDI) strengthening and dislocation strengthening. At the initial stage of plastic deformation (engineering strain below 4%), the rapid accumulation of geometrically necessary dislocations (GNDs) at the interfaces between recrystallized and non-recrystallized regions and between neighboring recrystallized grains lead to the significant HDI strengthening. As deformation proceeded, the HDI strengthening effect gradually decreased, and the traditional dislocation strengthening that was caused by GNDs accumulation at grain boundaries became significant. In-situ electron back-scattered diffraction (EBSD) testing revealed that the non-basal slip in the non-recrystallized regions became more remarkable in the late stage of deformation, which improved ductility and strain hardening of the alloy. These findings provide new insight into the design of high-performance hexagonal close-packed structural materials by using the concept of HDI strengthening.

Invisible assassin coated on dental appliances for on-demand capturing and killing of cariogenic bacteria

The accumulation of microbes on long-wear artificial dental materials creates a great risk for oral diseases and causes deterioration of material properties. Therefore, smart antibacterial materials capable of resisting the colonization of microorganisms and simultaneously eliminating pathogenic bacteria as needed show outstanding superiority for the recovery of dental health, which are scarcely reported until now. Here, we present a responsive hydrogel coating as invisible assassin on clear overlay appliances target for dental caries. Taking advantage of pH-responsive carboxybetaine methacrylate-dimethylaminoethyl methacrylate copolymer P(CBMA-co-DMAEMA) and antibacterial peptides, the surface potential of hydrogel shifts positively, accompanied with the release of antibacterial peptides when pH gets lower. The hybrid hydrogel layer hence exerts antifouling property and resists bacterial adhesion in normal physiological, while captures and kills cariogenic bacteria in acidic condition. This biocompatible, transparent and stable hydrogel coating has little influence for the aesthetics and mechanical properties of bulk materials. The strategy developed here can provide reference for the design of biomedical devices in other areas.

Thermodynamic stability and mechanical properties of (V, M)C (M = W, Mo and Cr) multicomponent carbides: A combined theoretical and experimental study

Vanadium carbides (VCs) usually function as reinforced phases of metallic materials, and their elastic and ductile-brittle properties are essential for mechanical properties of bulk materials. In this work, a multi-alloying method is adopted to modify physical properties of VCs. The stability, mechanical and electronic properties of multi-component (V, M)C (M = W, Mo and Cr) carbides were investigated by both first-principles calculations and nano-indentation experiments. The results show that W stabilizes (V, W)C while Cr destabilizes (V, Cr)C as demonstrated by the calculated formation energy. Doping with an appropriate amount of W, Mo and Cr may produce larger ratios of bulk modulus to shear modulus (B/G) and thereby enhance the ductility of (V, M)C carbides according to the Pugh’s criteria while retaining high hardness. The nano-indentation measurements confirm the W doping effect on mechanical properties and agree well with the calculations. The physical properties of doped (V, M)C carbides can be rationalized by the evolution of intrinsic chemical bonding as suggested by the electronic structures.

Beyond surface nanoindentation: Combining static and dynamic nanoindentation to assess intrinsic mechanical properties of chemical vapor deposition amorphous silicon oxide (SiOx) and silicon oxycarbide (SiOxCy) thin films

Nanoindentation is a well-known technique to assess the mechanical properties of bulk materials and films. Despite that, nanoindentation of thin films is not straightforward, given that the measured properties are composite information from a film/substrate system and depend on the indentation depth. By using dynamic indentation experiments and analytical or empirical models, we assessed the intrinsic film properties of chemical vapor deposited silicon oxide (SiOx) and silicon oxycarbide (SiOxCy) thin films with thicknesses ranging from 60 to 700 nm. In this work, the Bec rheological model and several mixing laws were reviewed. Measured Young modulus appeared to be affected by the substrate properties more than hardness: for the thinnest films, moduli were measured at ca. 90 GPa whereas intrinsic moduli were calculated at ca. 50 GPa. Using calculated intrinsic film modulus and hardness, it was possible to establish correlations between these properties, the chemical composition and the structural organization of the films.

A novel method for determination of surface treatment effect on mechanical properties of titanium bulk material

Improving the mechanical properties of the material surface has been the main aim of the researchers for a long time. Utilizing of mechanical treatment procedures, such as direct impact, has been widely used for the bulk materials, but determination of the change in the mechanical properties of impacted material has not been exactly investigated. The main novelty of this paper is the determination of the effect of mechanical treatments on the mechanical properties of bulk materials. For this purpose, the new developed combined algorithm of modified dimensional analysis and minimum resultant error methods were emerged with FEA and experimental data. The finite element analysis (FEA) included the analysis of the impact with nanoindentation in a continued procedure to allow the investigation of the impact on the results of the nanoindentation. Previously, this trend had not been applied to analyze such phenomenon. The challenges of preparing a perfect analysis model to suit the nanoscale process (nanoindentation) and macro process (ball impact) were another investigation field of this research work. The result of this research was a complete calculation of the parameters of Johnson–Cook constants for titanium (Ti) bulk material including the most important strain rate coefficient (C). Comparison of Ti mechanical characteristics shows high improvement in yield stress (24%) against lower change in the elastic modulus (1.2%).

The Effect of Ultrasonic Cleaning Upon Mechanical Properties of Metal Matrix Composites

The aim of this study is to produce composite materials by recycling metallic chips, which are found in industry as a large amount of waste. In addition, it is aimed to investigate the effect of ultrasonic cleaning process as the consolidation behavior and mechanical properties of bulk material directly depend on the cleaning of waste metallic chips. In the present investigation, spheroidal graphite cast iron (GGG-40) was employed as reinforcement material in tin bronze (CuSn10) matrix system. GGG-40 and CuSn10 chips were cleaned by ultrasonic agitation in water for 20 and 40 min. Consolidation of the cleaned metallic chips was achieved with a hot press by applying 820 MPa pressure under 450 °C, and the cylindrical and prismatic metal matrix composite materials with different reinforcement ratios were successfully produced. Energy-dispersive X-ray and scanning electron microscopy analyses were carried out to determine the amount of the oxide removed from the surfaces of chips. The mechanical properties of the samples were determined by hardness, porosity, compression and three-point bending tests. According to the results of the analyses, it was found that CuSn10 surfaces were cleaned from 20%, 50% and GGG-40 surfaces from 35%, 39% oxides during 20- and 40-min cleaning time, respectively. In addition, the results of the mechanical tests revealed that increased ultrasonic cleaning time improves the consolidation quality of metallic chips and it provides successful covering of GGG-40 chips by the CuSn10 chips as a result of a better structural integrity. New machinery parts with high mechanical properties can be produced as a result of recycling of the metallic chips which are available as waste in industry by appropriate cleaning process and this situation makes this study more innovative, economical and environmentally friendly research.

ДОСЛІДЖЕННЯ РУХУ ЧАСТИНКИ СИПКОГО МАТЕРІАЛУ РЕШЕТОМ СЕПАРАТОРА НОЖИЧНОГО ТИПУ

У статті запропонована конструкція гравітаційного сепаратора сипких матеріалів ножичного типу і представлені результати теоретичних досліджень руху частинки сипкого матеріалу решетом сепаратора. У результаті дослідження одержані залежності та умови для обґрунтування раціональних параметрів сепаратора з урахуванням фізико-механічних властивостей сипкого матеріалу.

Quantitative assessment of surface wave in kidney using optical coherence elastography

Patients with chronic kidney disease (CKD) and renal transplant rejection are at high risk to develop advanced pathology including glomerular sclerosis and renal interstitial fibrosis. The elasticity of kidney tissues is associated with the disease progression and can be evaluated with ultrasound elastography. Understanding how tissue pathology changes the renal mechanical properties is crucial. Optical coherence elastography (OCE) might be a promising tool for evaluating renal tissues due to higher resolution. A phantom with 8% gelatin and 2% cellulose (50 mm) was fabricated to validate the ability of OCE to bulk materials and the results were confirmed by comparing the dataset obtained with an ultrasound-based Verasonics system as the ground truth. Excitation signals, composed with 4 cycles of a 400 Hz harmonic wave repeated at a rate of 38 Hz, were directly applied to the surface area with two directions and cortical regions of ex vivo porcine kidneys that had been cut open. Preliminary results showed that the velocity of surface wave on the cortical regions was near 1 m/s and corresponded with the result of shear waves from Verasonics system (1.2 m/s). Our study demonstrated that OCE has an ability to assess the mechanical properties of bulk materials and is a promising tool to evaluate mechanical properties of renal tissue with high resolution and sensitivity.Patients with chronic kidney disease (CKD) and renal transplant rejection are at high risk to develop advanced pathology including glomerular sclerosis and renal interstitial fibrosis. The elasticity of kidney tissues is associated with the disease progression and can be evaluated with ultrasound elastography. Understanding how tissue pathology changes the renal mechanical properties is crucial. Optical coherence elastography (OCE) might be a promising tool for evaluating renal tissues due to higher resolution. A phantom with 8% gelatin and 2% cellulose (50 mm) was fabricated to validate the ability of OCE to bulk materials and the results were confirmed by comparing the dataset obtained with an ultrasound-based Verasonics system as the ground truth. Excitation signals, composed with 4 cycles of a 400 Hz harmonic wave repeated at a rate of 38 Hz, were directly applied to the surface area with two directions and cortical regions of ex vivo porcine kidneys that had been cut open. Preliminary results showed ...

Lattice Defects and Their Influence on the Mechanical Properties of Bulk Materials Processed by Severe Plastic Deformation

Lattice Defects and Their Influence on the Mechanical Properties of Bulk Materials Processed by Severe Plastic Deformation

Investigation of the mechanical properties of steel using instrumented indentation test with simulated annealing particle swarm optimization

A methodology is proposed to obtain mechanical properties of bulk materials from multiple loading-unloading curves of an instrumented indentation test (IIT). The mechanical properties, including strain-hardening exponent (n) and strain-hardening rate (K), were extracted from IIT data using iterative finite element simulation coupled with a simulated annealing swarm particle optimization. A systematical study was carried out to discuss the uniqueness of the identified properties. Results showed that the mechanical properties obtained in this way are unique and accurate adequately. It was found that the maximum errors of K and n generated from the macro indentation tests are 8.2% and 6.3% respectively. The identified mechanical properties from ten loading-unloading curves was compared with those obtained from a single loading-unloading curve. We found that ten loading-unloading cycles of an indentation test will result in more precise mechanical properties.

Nanomechanics to 1000 °C for high temperature mechanical properties of bulk materials and hard coatings

It is important to measure nanomechanical properties of materials for extreme environments at temperatures that match their operating conditions so that the data are more relevant than those obtained from room temperature measurements. Reliable high temperature mechanical property data improves our understanding of the linkage between the small-scale mechanical behaviour and the performance and design of advanced materials systems for increasingly extreme environments. Accurate high temperature nanomechanical measurements require significantly more careful instrumental and experimental design than at room temperature. It is important to consider (i) instrumental stability and thermal drift (ii) the test environment and its influence on the stability of the indenter and sample (iii) modifications to the experimental load history and analysis procedures to minimise the effect of greater time-dependency. In this review of best practice and published studies effective strategies for mitigating these effects and achieving reliable, validated data are discussed with illustrative examples on thin films and bulk materials operating in extreme environments in applications in the nuclear, aerospace, fuel cell and cutting tool industries to 1000 °C.

Influence of hierarchical porous structures on the mechanical properties of cellulose aerogels

Aerogels of cellulose exhibit remarkable mechanical properties as a function of density. Modifying the pore volume in classical cellulose aerogels using sacrificial template methods provide scaffold like microstructure. In the present study, we have developed aerogels of cellulose scaffolds having almost same density values but differ in microstructure and analysed the influence on the mechanical properties of bulk materials. This study can give an insight into the materials design for advanced engineering materials. Employing four surfactants having difference in hydrophilic-lipophilic balance (HLB), namely polyoxyethylene tert-octylphenyl ether (PT), polyoxyethylene (20) oleyl ether (PO), polyoxyethylene (40) nonylphenyl ether (PN) and polyoxyethylene (100) stearyl ether (PS), the cellulose scaffolds with hierarchical porous structures were developed. The mechanical properties of cellulose scaffolds were compared with classical pure cellulose aerogels. The results indicate that the solid fraction of cellulose nanofibers per unit volume of cell walls of scaffolds plays an important role in determining the elastic properties and strength. As the nanofibrils support the cell walls of scaffolds, Young’s modulus can be improved if the concentration of cellulose nanofibers is high at the cell walls or cell wall thickness is larger. The scaffold materials of this kind could be used as supporting materials with desired properties for filter, catalysis and biomedicine.

Effect of addition of SiC and Al2O3 refractories on Kapitza resistance of antimonide-telluride

Invoking Effective Media Percolation theory (EMPT), Hasselaman-Johnson effective media theory (EMT), and Nan and Birringer EMT, the effect of addition of SiC and Al2O3 nanoparticles on Kapitza resistance (RBd) of Ni0.05Mo3Sb5.4Te1.6 was investigated. Pore size and their volume distribution, and surface area were characterized using BET technique to correlate pore effect and surface area on RBd. Bounds for effective thermal conductivity were determined using Lipton–Vernescu model. Variation of thermal conductance with respect to temperature was studied and compared with the results of other materials. According to EMPT, RBd in Ni0.05Mo3Sb5.4Te1.6/SiC composites ranged from 3.84 × 10-7 to 5.42 × 10-7 m2KW–1 and 3.36 × 10-7 to 3.86 × 10-7 m2KW–1 for Ni0.05Mo3Sb5.4Te1.6/Al2O3 composites. Kapitza radius (aK) for SiC samples was ranged between 2.01 – 2.84 μm; for Al2O3 samples it was 1.86 μm. Hasselman-Johnson model gave RBd values 55%, 51%, and 8% more than what EMPT is predicting, but of the same order and aK values 3.5 μm, 4 μm, 3 μm for SiC samples and 1.2 μm, 0.6 μm, 0.55 μm for Al2O3 samples. Nan-Birringer model yielded large aK of 7.25 μm and RBd ∼ 1.4 × 10–6 m2KW–1 for Ni0.05Mo3Sb5.4Te1.6/SiC. So obtained parameters are reasonable estimates. Variation of effective thermal conductivity in Al2O3 samples is more sensitive to particle size compared to SiC samples. Mechanical properties were studied using micro–indentation technique and their effect on effective thermal properties was ascertained. Addition of Al2O3 nanoparticles have aided in enhancing mechanical properties of bulk material.

Technical vision system for analysing the mechanical characteristics of bulk materials

In this article actual topics concerned with mechanical properties of bulk materials, usage of computer vision and artificial neural networks in this research are discussed. The main principles of the system for analysis of bulk materials mechanical characteristics are described. Bulk material outflow behaviour with predefined parameters (particles shapes and radius, coefficients of friction, etc.) was modelled. The outflow was modelled from the calibrated conical funnel. Obtained dependencies between mechanical characteristics and pile geometrical properties are represented as diagrams and graphs.

Dynamics of Entangled Polymers Confined between Graphene Oxide Sheets as Studied by Neutron Reflectivity

For graphene-based composites, the dynamics of polymers confined between graphene sheets are a key parameter governing the overall mechanical properties of bulk materials. Here, we used neutron reflectivity (NR) to measure the diffusion dynamics of polymer melts confined between graphene oxide (GO) surfaces. From the NR results, we found that the diffusion coefficients of poly(methyl methacrylate) (PMMA) between the GO sheets were dramatically reduced by more than 1 order of magnitude when the film thickness was less than ∼3 times the gyration radius of the bulk polymer (Rg), whereas the diffusion of the polystyrene (PS) films sandwiched between GO sheets was only three times slower as the PS thickness decreased from ∼8 Rg to 1 Rg. This difference was due to the fact that the polymer-GO interaction significantly influences the dynamics of confined polymer melts.

Investigation of high concentration of benzotriazole on corrosion behaviour of titania–benzotriazole hybrid nanostructured coating applied on Al 7075 by the sol–gel method

ABSTRACTNowadays, surface modification with self-healing ability is a valuable technique to improve chemical stability, oxidation behaviour and corrosion resistance of materials without interference with its physical, chemical or mechanical properties of bulk material underneath. In this paper, hybrid organic amorphous titania coatings are deposited on 7075 aluminium alloy substrates by using the sol–gel method. A titania–benzotriazole (BTA) nanostructured hybrid sol–gel coating is impregnated with three different high concentrations of BTA, 1.4, 2.8 and 4.2%. The bonds existing in the hybrid coating, structure and morphology and coating corrosion behaviour have been studied using the FTIR, GIXRD, field emission scanning electron microscopy and electrochemical impedance spectroscopy (EIS) test in a 3.5 wt-% NaCl solution during different immersion times, 24, 48, 72, 96 and 120 h. EIS studies indicated that a higher coating resistance value was gained for titania–4.2% BTA even after 120 h of immersion and BTA acted mainly on the amorphous titania coating as a corrosion inhibitor and a healing agent that acts by two mechanisms: first, release of a healing agent to the formation of corrosion products, then finally blocking surface defects; second, release of a healing agent during 48 h of immersion and its adsorption to produce an insulating layer on the surface of the coating in contact with the solution.

Estimating the unconfined yield strength of coal in the case of longwall coal mining with hanging wall top caving

Abstract This study presents an innovative approach for determining the unconfined yield strength σc during the excavation of coal from the earth’s crust by using an equipment that was developed for measuring the mechanical properties of bulk materials stored in silos. Highly productive excavation of coal with a hanging wall top caving leads to intensive deformations in the hanging wall and the broken coal can be considered as bulk material. In this research, the shear tester Johanson Hang-Up Indicizer was used to measure the unconfined yield strength of the tested samples, even though such a tester cannot produce stress-strain conditions similar to those occurring during the excavation. An attempt was made to estimate the real unconfined yield strength of broken coal deep under the surface through a combination of measured data and extrapolation.

Is the second harmonic method applicable for thin films mechanical properties characterization by nanoindentation?

The second harmonic method is a dynamic indentation technique independent of the direct indentation depth measurement. It can be used to determine near-surface mechanical properties of bulk materials more precisely than classical dynamic nanoindentation. In this paper, the second harmonic method is extended to the measurement of the mechanical properties of thin poly(methyl methacrylate) (PMMA) layers deposited onto silicon wafers. It is shown that this new technique gives precise results at small depths (less than 100 nm), even for films with a thickness lower than 500 nm, which was not possible to achieve with the classical continuous stiffness measurement method. However, experimental and numerical results obtained both with classical nanoindentation and second harmonic methods differ at high indentation depth. Using finite element (FE) simulations and AFM measurements, it is shown that the contact depth calculation with classical models can explain this difference.