Strength Of Grains Research Articles

Micro- and macro-scale strength properties of c-axis aligned hydroxyapatite ceramics

In this study we first investigated the strength of grains, i.e., single crystals, and grain boundaries (micro-scale strength) of hydroxyapatite ceramics in different crystal orientations, using microcantilever bending tests. The specimens were prepared from two types of hydroxyapatite ceramics; one is that with uniaxially aligned c-axes of grains and the other with randomly oriented ones. Both the grain and grain boundary strengths were slightly higher in tensile stress application parallel to c-axis than in the perpendicular in the aligned material. These strengths, however, were substantially higher than those of the randomly oriented one. Then, three-point bending tests were conducted to determine the polycrystalline strength (macro-scale strength) for the above two types of hydroxyapatite ceramics. While the strength values were comparable in tensile stress applications parallel and perpendicular to c-axis in the aligned material, that of the randomly oriented one is again significantly lower than them. In particular, the strength of the grain boundary was higher when the angle between the c-axis of the two hydroxyapatite grains divided by the boundary was close to 0 or 90°. The effects of the grain orientation and alignment on the mechanical properties were discussed on the basis of both the micro-scale and macro-scale results. These results indicate that selective formation of high-strength grain boundaries due to c-axis alignment of hydroxyapatite grains is effective in improving the mechanical properties of bulk ceramics, such as macroscopic strength and fracture toughness.

The use of Preston equation to determine material removal during lap-grinding with electroplated CBN tools

Grinding executed in a lapping configuration is an alternative finishing process benefiting from both grinding and free-abrasive machining, while minimizing the heat effect impact. Electroplated tools can be effectively used in different abrasive processes, including high-speed grinding, however, the assessment of machining performance over time is a key factor in their correct use to achieve satisfactory technological results. In conventional grinding, bigger grain-coverage provides better results due to the higher bonding strength of grains. In lap-grinding, fracturing and crushing of the abrasive particles initially covered by the plating result in a suspension which is typically dosed continuously in free-abrasive machining. Due to this, the process transforms from two-body (grinding) to three-body abrasion (free abrasive machining) which may result in reduced grinding performance approaching asymptotically a specific value while improving surface finish. The main aim of the presented study is the evaluation of electroplated CBN tools used in lap-grinding of 40H alloy steel workpieces whose hardness was 54 HRC. The obtained results and observations of the working surface of CBN wheels and workpieces allowed for the identification of the wear characteristics for three nickel plating thicknesses corresponding to 35%, 50% and 65% of the nominal CBN crystal size and for specific process parameters. The surface roughness Ra parameter decreased gradually from the initial value 1.9 μm to the values below 0.7 μm for bigger B107 grains and for all plating thicknesses. For smaller B64 grains, the surface roughness and waviness parameters reached similar values to those obtained for the larger B107 grains at corresponding processing times. The lowest value of Ra parameter below 0.4 μm was obtained for B64 grains and for the thinnest plating but with a 50% reduction in material removal comparing to B107 grains. The Preston equation was employed to calculate the material removal as a function of time under variable process conditions in the machining zone due to the tool wear. This attempt extended the range of the material removal modeling, despite the fact that the electroplated wheels were subject to wearing down resulting in the gradual reduction in the efficiency, as well as in the change of the working conditions in the workpiece-tool contact zone.

Farmers’ Preference and Willingness to Pay for Climate-Smart Rice Varieties in Uzo-Uwani Local Government Area of Enugu State, Nigeria

Abstract This paper examined farmers’ preference and willingness to pay (WTP) for climate-smart rice varieties in Uzo-Uwani Local Government Area of Enugu State, Nigeria. A total of 80 respondents were purposely selected from 5 major rice growing communities in the study area. Questionnaire was the main tool for data collection. Also, data on climate elements (such as temperature and rainfall volume) for a period of 35 years (1986–2020) were obtained from the Nigerian Meteorological Agency (NIMET). Multinomial logit model, ordinary least square (OLS) regression model, descriptive statistics and trend analysis were employed for data analysis. The results show that FARO 44 was preferred by 95% of the farmers for grain size, 100% of farmers preferred it for days to maturity, 76.2% preferred it for strength of grain to withstand breakage during processing, 98.75% preferred it for potential yield (tons) and plant height (cm) and 87.5% preferred it for its ecological adaptation. Farmers’ preference and willingness to pay for climate-smart rice varieties were influenced by attributes of these varieties and knowledge of such technologies, primary occupation, farm size, extension visits and access to media information and farm size. This study recommends that government should provide extension agents with the adequate resources to enable them carry out their duties more effectively.

Research on the Production of Parchment from Turkey Skin and its Decorative Use

In this study, parchment was made of waste turkey skin and some tests were done. These tests were: Determination of thickness (TS 4117 EN ISO 2589), Determination of tensile strength and elongation (TS EN ISO 3376), Determination of tear load - Part 2: (Double edge tear) (TS 4118-2 EN ISO 3377-2), Leather - of distension and strength of grain (TS 4137 EN ISO 3379), Color fastness to water spotting (TS EN ISO 15700). Due to the low strength properties of turkey skin, a different usage area was tried to be created by making a decorative flower design. In this research, it has been tried to show how a waste material can be transformed into a product with a very high added value.

Mechanical Properties of Wheat Grains at Compression

Abstract Hook’s law for evaluation of the modulus of elasticity of wheat grains and its general behaviour under compressive loads were studied. Whole specimens were subjected to compressive loading between metal parallel plates. The mechanical properties of grains were determined in terms of average failure strengths of grain bran and whole grain; deformation; and modulus of elasticity. The mechanical properties of very dry grains of the winter wheat Triticum aestivum L. with the moisture content of 10.3% were studied. The failure strength of grain bran was 4.43 MPa at the deformation of 10.7%, and the failure strength of whole grains was 4.88 MPa at the deformation of 13.5%. The modulus of elasticity of grains was 43.67 MPa. The apparent energy density at bran failure strength was 0.261 MJ·m−3, and 0.470 MJ·m−3 on the level of grain failure strength of the whole grain. The bran border structure of central inner part of grains was studied using microscope digital sections of longitudinal cuts of the grains using the image computer processing method. The area proportion of starch and pericarp of the border parts of grains was studied to describe the border texture of central sections of grains.

On intergranular mechanical interactions and the theory of deformation crystallography of metals

The equilibrium of intergranular stress and strain can be realized simultaneously, whereas five independent slip systems of the Taylor principle and the criterion of minimal internal work are unnecessary. In fact, the Taylor principle applied in current theories is incorrect both in practice and theory, in which the activation mechanism of plastic deformation systems must violate the Schmid’s law and deviate from the elastic-plastic characteristics of deformed matrix. The intergranular reaction stress (RS) during deformation can be calculated according to Hooke’s law and elastic limit without additional subjective presupposition, therefore the RS theory is established intuitively. Under the combination of the RS (the intergranular elastic effect) and the external loading the slips penetrating grains are activated and produce deformation texture, but certain non-penetrating slips near grain boundaries will become active (the intergranular plastic effect) and produce some random texture when a RS reaches the yield strength of grains. The RS theory is simple, intuitive and reasonable, based on which the texture simulation can well reproduce the texture formation of various metals under different external loadings and under different crystallographic mechanisms.

High Temperature Plasticity of TP347H Stainless Steel Welded Joint Heat Affected Zone

Simulated Heat Affected Zone (HAZ) samples of TP347H stainless steel welded joint with 800-1380°C peak temperature thermal cycles were produced using Gleeble 3180 thermal mechanical simulator. 600°C constant speed tensile tests for simulated HAZ samples were carried out, and the precipitates of the simulated samples were analyzed by EDAX. The results show that the lowest Reduction of Area (RoA) was around 53% - 56% in 900-1150°C, which was about 15% lower than the maximum RoA in 800-1380°C. The reasons for decrease of HAZ high temperature plasticity were related to the precipitation of NbC. The fine NbC precipitated in the crystal and grain boundary enhanced strength of grain at high temperature, which resulted plastic deformation or slip at high temperature were mainly concentrated in the grain boundary, and high temperature plasticity of HAZ were decreased.

Molecular dynamics study on tensile strength of twist grain boundary structures under uniaxial tension in copper

Grain boundaries (GBs) play an important role in deformation responses and mechanical properties of materials. However, the lack of experimental observations of GBs restricts the in-depth understanding on the mechanical behavior of twist GBs and the continuum misorientation effect on the tensile strength of grains. In this paper, the <001>, <101> and <111> twist grain boundary structures for copper are studied by molecular dynamics simulations to obtain the tensile strength and intergranular stress. Over all the twist GB structures, <111> Σ3 GB structure is verified and analyzed to possess the maximum tensile strength, the lowest GBE (grain boundary energy) and the minimum CSL (coincident site lattice) value. The distribution of normal stress on GBs is further investigated to reveal the calculated results that the tensile strength is enhanced with increasing the twist angle for the <001> and <101> twist GB structures, but the misorientation has no significant influence on the tensile strength of almost all <111> twist GB structures, except Σ3. This work provides a fundamental information for understanding the effects of misorientation on interfacial stability and mechanical behaviors of grain boundary structures with different crystal directions.

Preparation, mechanical properties and microstructure of TiB2 based ceramic cutting tool material toughened by TiC whisker

TiC whiskers were synthesized by carbothermal reduction process. By using these whiskers as the toughening phase, a novel TiB2 based ceramic cutting tool material was prepared. Due to that the thermal expansion coefficient of TiC is close to that of TiB2, the addition of no more than 30 vol% TiC whisker not only has little adverse effect on the density and flexure strength of the composite, but also can refine the grains, reduce the defects and improve the grain strength. As a result, both the fracture toughness and flexure strength of the TiB2 based ceramic composite can be significantly improved. Appropriate sintering temperature and holding time can reduce defects, improve the strength of grains and grain boundaries and enhance the toughening effect of TiC whiskers. Experimental results showed that when the whisker content was 30 vol%, the sintering temperature was 1700 °C and the holding time was 30 min, the flexure strength, fracture toughness and Vickers hardness of the TiB2 based ceramic cutting tool material was 860 MPa, 7.9 MPa·m1/2 and 22.6GPa, respectively.

Micro scale fracture strength of grains and grain boundaries in polycrystalline La-doped β-Si3N4 ceramics

Micro scale fracture strength of grains and grain boundaries in polycrystalline La-doped β-Si3N4 ceramics were investigated and compared with theoretically predicted values. The fracture behaviour of SiO2-La2O3 intergranular glassy phase (IGP) between β-Si3N4 grains was modelled by ab initio simulations. Microcantilevers were FIB-milled both from polycrystalline regions and single grains of β-Si3N4 and were tested in bending using a nanoindenter. The fracture strength of β-Si3N4 grains which fractured at fixing was 10.6 ± 0.8 GPa while the strength of the beams that failed at defects was 5.9 ± 2.3 GPa. Polycrystalline β-Si3N4 samples showed intergranular fracture with decreasing strength values in the range of 2.9 ± 0.4 – 2.1 ± 0.5 GPa. The comparison of single grain results with theoretical values in the literature revealed a correlation between theoretical and experimental results, which was used to convert our ab initio simulations from subnano to micro size samples. The converted strength for IGP showed quantitative agreement with micro-bending experiments.

Effect of the Segregation of Embrittling Impurities on the Local Strength of Grain Boundaries in a Martensitic Steel

The finite element method and the results of delayed fracture tests of Charpy specimens are used to determine the local strength of grain boundaries in 18Kh2N4VA steel at various contents of phosphorus, antimony, and tin impurities. The embrittlement of grain boundaries is attributed to the adsorption enrichment of grain boundaries in impurities in initial austenite, which leads to weakening of the intergranular cohesion. Phosphorus is found to have the highest susceptibility to intergranular segregation: during the same heat treatment, its grain-boundary concentration is higher than that in steel with antimony or tin. However, the segregation of antimony is more dangerous than the segregation of phosphorus, since, at its lower intergranular concentration, the local strength of grains of quenched steel decreases as in the case of phosphorus segregation.

Effect of carbon on microstructure and mechanical properties of HR3C type heat resistant steels

The modified HR3C austenitic heat-resistant steels for applications of ultra-supercritical (USC) power plants were developed and investigated. As the C content breaks through the limitation of the HR3C composition range (>0.1 wt%), the evolution of carbides and mechanical properties after isothermal aging at 700 °C have not been understood. In this study, two modified HR3C with different C content were studied by tensile test and Charpy impact test at room temperature after long-term aging up to 10,000 h. The M23C6 carbide is rapidly precipitated at the interface (GBs, TBs or NbC/γ), and these carbides at grain boundaries (GBs) are gradually changed from a continuous distribution to a semi-continuous distribution, then finally agglomerate and coarsen near the GBs. Moreover, a new morphology type lamellar M23C6 carbide forms in the grain. The effect of lamellar carbides on mechanical properties at room temperature (RT) is not obvious because the strength of GB is rapidly weakened. Besides, the Larson-Miller parameter was obtained and the creep strength of the modified HR3C was extrapolated, by conducting creep rupture experiments on un-aged sample. The creep tests reveal that the rupture lives decrease with increasing C content. Lamellar carbides are precipitated and weaken the strength of grain during high temperature creep.

Innovation an Eco Friendly Technology: Tanning System using Semi Chrome and Improved Indigenous Tannins (Acacia Nilotica Pods)

Semi-chrome tanned leathers were obtained using spray dried powder which were carried out using leaching of 70% crushed ‘Garad’ and 30% ‘Neem’ barks mixture to develop the fulfillment of ‘Garad’ tanning power. Tanning system was conducted in industrial research consultancies center, Sudan. Mechanical and physio-chemical analyses of the leather were executed using SLTC. Mechanical properties of the produced leather were compared with traditional tanned leather and the strengths, of tensile, one edge tear and two edges tear, of semi chrome tanned leather were: (200 kg/cm2, 52 and 100 kg/cm) respectively where the distension and strength of grain was (10 mm) and the thermal stability (100°C). The experimental explain that the blending ’Garad - Neem’ significantly enhanced the quality of tannins powder and tanned leather.

Remobilisation of phosphorus fractions in rice flag leaves during grain filling: Implications for photosynthesis and grain yields.

Phosphorus (P) is translocated from vegetative tissues to developing seeds during senescence in annual crop plants, but the impact of this P mobilisation on photosynthesis and plant performance is poorly understood. This study investigated rice (Oryza sativa L.) flag leaf photosynthesis and P remobilisation in a hydroponic study where P was either supplied until maturity or withdrawn permanently from the nutrient solution at anthesis, 8 days after anthesis (DAA) or 16 DAA. Prior to anthesis, plants received either the minimum level of P in nutrient solution required to achieve maximum grain yield (‘adequate P treatment’), or received luxury levels of P in the nutrient solution (‘luxury P treatment’). Flag leaf photosynthesis was impaired at 16 DAA when P was withdrawn at anthesis or 8 DAA under adequate P supply but only when P was withdrawn at anthesis under luxury P supply. Ultimately, reduced photosynthesis did not translate into grain yield reductions. There was some evidence plants remobilised less essential P pools (e.g. Pi) or replaceable P pools (e.g. phospholipid-P) prior to remobilisation of P in pools critical to leaf function such as nucleic acid-P and cytosolic Pi. Competition for P between vegetative tissues and developing grains can impair photosynthesis when P supply is withdrawn during early grain filling. A reduction in the P sink strength of grains by genetic manipulation may enable leaves to sustain high rates of photosynthesis until the later stages of grain filling.

Degradation of the Strength of Grains and Grain Boundaries of Ni-Base Superalloy under Creep and Creep-Fatigue Loadings

The degradation process of the micro texture of Ni-base superalloys was observed under fatigue and creep-fatigue loading conditions at elevated temperatures higher than 700oC by applying electron back-scatter diffraction (EBSD) analyses. The local distribution of the crystallinity of a grain and a grain boundary was defined quantitatively by analyzing the Kikuchi pattern obtained from each electron-beam-irradiated area with a diameter of 50 nm. The calculated image quality value was used for the analysis. It was found that the crystallinity of grain boundaries degraded seriously under creep-fatigue loading conditions due to the acceleration of anisotropic strain-induced diffusion of component elements. Since the initial finely-controlled strengthened micro texture disappeared due to the anisotropic diffusion of component elements, this degradation was found to cause the drastic decrease of the strength of grains and grain boundaries and thus, lifetime of the material. The decrease of the strength of both grains and grain boundaries was measured by micro tensile test system in a scanning electron microscope by making a small sample from bulk specimen using focused ion beam. The strength of a grain and a grain boundary varied drastically depending on their crystallinity, in other words, the image quality value.

An experimental investigation of the micromechanics of Eglin sand

The mechanical behaviour of Eglin sand at the micro-scale was studied in this work. Laboratory experiments using unconventional apparatuses were carried out in order to study the contact behaviour of pairs of particles in both compression (normal loading) and shearing (tangential loading) and the strength of grains. Particle fractions were identified according to their colour by visual observation and both their chemical composition and surface morphologies were obtained. The tangential stiffnesses and inter-particle coefficients of frictions for the different fractions found in the sand sample were determined under the range of normal loadings applied (1–9N). The results show some discrepancies between the theoretical models commonly found in literature to describe either the normal or the tangential loading response, which are able to predict the trend of the force-displacement curves but using elastic moduli that are lower than those found in literature, especially in the case of tangential loading. Also, the results of particle crushing tests show quite consistent results (excluding one particle group), probably related to the similar mineralogy of all fractions, which are mainly constituted by silica.

Improved mechanical properties of a twinning-induced plasticity steel prepared by directional solidification

Two kinds of twinning induced plasticity (TWIP) steels with coarse columnar grains and equiaxed grains were fabricated by directional solidification technique and traditional induction melting process, respectively. The mechanical behavior of them was studied by interrupted tensile tests and correlated with the microstructures evolution. The directional solidified (DS) sample showed much more improved mechanical properties along the longitudinal direction of columnar grains, especially with the extremely high ultimate elongation (106.8%). Furthermore, unique strain hardening behavior was also found in DS sample, which can be roughly divided into five stages. Where, in stage C, the strain hardening rate increases from a plateau of 1.0GPa to 1.5GPa. Dislocation substructure was taken into account for the strain hardening behavior besides deformation twins and dynamic recovery of dislocation glide. Microstructural evolution revealed that deformation twinning in normal TWIP steel with equiaxed grains (EG) activated earlier but fewer slip systems at a low strain level. Within subsequent strain, DS sample appeared to have a higher twinning rate with a more uniform distribution of deformation twins and fragments occurred in part of grains. Crack first activated along the twin boundary (TB) and grain boundary (GB), then in the matrix of EG. In case of DS sample, it preferentially formed along the primary slip bands, then along GB and matrix. These differences are heavily affected by the initial microstructure, strength of grains and grain boundaries. The improved mechanical properties of DS sample were attributed to four factors: 1. Scarcity of transverse grain boundaries; 2. Simplified orientation ([2 2 0]) of columnar grain; 3. Reduction of impurities and inclusions caused by directional solidification; 4. More prevalent deformation twins and unique dislocation substructures.

Statistical analysis of compression strength of single grains of SHM powders and improvement of the strength assessment procedure

A new approach to strength assessment of diamond powders has been proposed. It is based on the statistical theory of extremes and provides the small-sampling prediction of strength properties. A comparative statistical analysis of several powder batches has been performed. The strength of grains is shown to be satisfactorily approximated by a Weibull distribution rule over the entire range of grain sizes and grades considered. The relation between the Weibull parameters and the average strength has been studied. The convergence of empirical statistics is investigated and the criterion of sufficiency of a sample size for the assessment of average compression strength of diamond grains is stated. The authors have found the possibility to reduce the number of tests, thus significantly shortening the testing duration and minimizing the anvil wear, which results in lower investigations costs. These findings provide a theoretical basis for improving the existing methods of quality inspection of SHM powders and elaborating new methods.

Aluminum-calcium based three-component systems with addition of zinc and magnesium compounds for absorption of the hydrochloric acid vapor

To prepare granulated sorbents for absorption of the hydrochloric acid vapor, the formulations ZnO-CaO-Al(OH)3, Zn4CO3(OH)6-CaO-Al(OH)3, and MgO-CaO-Al(OH)3 with a 1: 1: 1 molar ratio of the oxides were studied. Mechanical processing of the mixtures leads to amorphization of compounds of the bivalent metals and to an increase in the size of gibbsite crystallites, accompanied by deformation of its crystal lattice. The composition of the chemisorbent has no effect on the number of basic surface centers, but determines the mechanical strength of grains and their absorbing capacity. The most promising formulation for preparing the chemisorbent is the Zn4(CO3(OH)6-CaO-Al(OH)3 system possessing the highest absorbing capacity for HCl vapor and retains its mechanical strength in tests.

Influence of the particle size on the microstructure and mechanical properties of grains containing mixtures of nanoparticles and microparticles: Levitator tests and pilot-scaled validation

Abstract The spray drying process is used in many industrial applications. However, different grain properties can be desirable depending on the later use of the powders produced. In this work the influence of the particle size on the particle packing fraction and the mechanical strength of grains containing silica nanoparticles, microparticles and their mixtures, was analyzed. Single droplet tests were carried out in an acoustic levitator at 120 °C. The shell thickness was calculated using the fluidity limits obtained from the modelling of the viscosity data. Results obtained showed good agreement with the experimentally measured ones. The addition of nanoparticles and high pH values produce an increase in the mechanical strength of the grains. Finally, different suspensions were dried in a pilot-scaled spray dryer. The results obtained for the mechanical strength of the spray died powders confirm the results obtained in the levitator test.