Effect Of Microstructural Parameters Research Articles

Predicting the effective properties of 3D needled carbon/carbon composites by a hierarchical scheme with a fiber-based representative unit cell

This paper presents a fiber-based representative unit cell (fRUC) on the mesoscale to estimate the elastic constants of a three-dimensional (3D) needled carbon/carbon (C/C) composite through a hierarchical modeling scheme. The material variations due to needle-punching, including fiber dislocations, fiber distributions and matrix pockets, are precisely considered in the proposed fRUC model. A quarter-size mathematical model with a periodic boundary condition of a general mesh is established to perform the fRUC analysis by using interpolation functions. The predictive results from the fRUC are transitioned to a ply representative unit cell (pRUC) based on the developed analytical homogenization method. The proposed model agrees well with the experimental results, and the effects of microstructural parameters on the overall composite properties are discussed. The results allow great confidence in the reliable predictions of the effective properties and the damage and strength of 3D needled C/C composites.

Influence of microstructural parameters on the mechanical properties of oxide dispersion strengthened Fe-14Cr steels

The effect of microstructural parameters on the microstructure, tensile properties from room temperature to 800 °C and creep properties at 650 °C has been investigated in a 14%Cr oxide dispersion strengthened (ODS) steel. Combining a control of oxide addition, consolidation route and thermo-mechanical processing, the different parameters of the microstructure have been varied systematically, namely the size and volume fraction of oxide nano-precipitates, the grain size and the dislocation density.The volume fraction of nano-precipitates is shown to influence the tensile strength throughout the temperature range, whereas a change in precipitate size influences only the low temperature behavior. The effect of grain size is shown to be similar to that of precipitation strengthening. A recrystallized microstructure is shown to improve the ductility of the ODS steel while not degrading the strength or creep resistance. The material processed by hot extrusion presents improved strength and reduced creep rate as compared to that consolidated by hot isostatic pressing. This difference is attributed to the long-range internal stress resulting from the high dislocation density, stabilized by the oxide nano-precipitates.A strength model is presented, and validated on every material using the quantitative microstructural parameters obtained by combination of electron back-scattered diffraction, transmission electron microscopy and small-angle X-ray scattering.

과공석 강선에서 미세조직 인자들이 단면감소율에 미치는 영향

과공석 강선에서 미세조직 인자들이 단면감소율에 미치는 영향

Micro-effects of surface polishing treatment on microscopic field enhancement and long vacuum gap breakdown

In this paper, three surface polishing treatments were employed to treat plate titanium electrodes, and microscopic surfaces of the electrodes after polishing were presented. Through comparing the breakdown strength of the 2.5 cm vacuum gap formed by plate titanium electrodes after the three treatments, experimental results showed that the breakdown strength was enhanced by 35% while the micro-surface roughness dropped from 3.5μm to 0.35μm. In view of that, effects of microstructural parameters after polishing on the microscopic field enhancement factor were investigated. The field-uniformity mechanism and the shield effect between micro-protrusions on the rough electrode surface were put forward and demonstrated. Based on the idea that electric field can be shield in a pit, a theoretical model was established to evaluate the maximum field enhancement factor βEmax on the micro-surface. It revealed that 1 ≤ βEmax ≤ 3.96, and βEmax had the maximum decrements of 1.96 and 2.1 both from 3.96 after the mirror polishing and the chemical polishing, respectively. When the surface roughness decreased to the scale from nm to μm, the effort on βEmax reduction through surface polishing was not effective to enhance the vacuum gap breakdown strength any more.

3D micromechanical analysis of thermo-mechanical behavior of Al2O3/Al metal matrix composites

In this paper an elastoplastic finite element model for studying the thermomechanical behavior of Al/Al2O3 particulate composites is proposed. 3D representative volume elements (RVEs) are created to model the microstructures of Al/Al2O3 composites and the finite element models generated from RVEs are used to study the mechanical and thermal expansion properties. In order to study the effect of thermal residual stresses, first the RVEs are simulated for cooling process from sintering temperature to room temperature and thermal residual stress are estimated for different mechanical behaviors of Al matrix. Next, the thermomechanical properties are examined with existing residual stresses. The predicted effective elastic moduli and the coefficient of thermal expansion are compared with the experimental results reported in literature. The FE results have good correlation with the experimental data and the effects of microstructural parameters, voids and properties of the constituents are further discussed. In order to study the influence of voids on the elasto-plastic behavior of composites, the Gurson–Tvergaard–Needleman (GTN) model is applied. The nucleation and growth of voids in composites, under uniaxial tension, is studied.

Elastic Property Simulation of Nano-particle Reinforced Composites

A series of numerical micro-mechanical models for two kinds of particle (cylindrical and discal particle) reinforced composites are developed to investigate the effect of microstructural parameters on the elastic properties of composites. The effects of both the degree of particle clustering and particle’s shape on the elastic mechanical properties of composites are investigated. In addition, single particle unit cell approximation is good enough for the analysis of the effect of averaged parameters when only linear elastic response is considered without considering the particle clustering in particle-reinforced composites.

Prediction of contact angle for hydrophobic surface fabricated with micro-machining based on minimum Gibbs free energy

When an interface exists between a liquid and a solid, the angle between the surface of the liquid and the outline of the contact surface is described as the contact angle. The size of the contact angle is the metrics of the hydrophobicity of the surface. The prediction of the contact angle has significant effect on the design of hydrophobic surface and improvement of hydrophobicity. In this paper, a prediction model for contact angle has been proposed based on minimum Gibbs free energy. It considers the effects of unilateral force and area constraints of the droplets. The effect of micro-structural parameters on contact angle has also been investigated. Micro-milling experiments have been conducted to fabricate the hydrophobic surface in order to validate the predictive capability of the contact angle model. Results revealed that the established prediction model could estimate the contact angle of hydrophobic surface. The contact angle could be increased by increasing concave width or reducing convex. The outcome of this research will lead to new methodologies for preparing hydrophobic surfaces with micro-machining technology.

Effect of Microstructure Parameters on Hardness of SnCu4Pb3 produced by Horizontal Centrifugal Casting

Horizontal centrifugal casting is an effective method for the production of hollow metal with good mechanical properties, low defect, cast to size and relatively cheap. The ability of a metal to satisfy the above requirements highly depends on its microstructure. In this study, the relationship between microstructural parameters such as grain size and the amount of phases with bulk hardness of SnCu4Pb3 is concerned in three areas of the product. Consequently, to achieve the desired hardness of the product in a particular area, the interaction of two factors of the microstructure including, grain size and particles amount of the hard intermetallic compositions (Cu6Sn5) should be noted.

Combined Strengthening-Toughening Technology of High Property Titanium Alloys for Aviation Uses in China

Combined strengthening-toughening technologies of several high property titanium alloys, such as TC4-DT, TC6, TC18, TC21 for aviation uses, have been studied via purification, quasi-b heat treatment, quasi-b forging and grain refinement. The effects of microstructure parameters of lamellar structure, basket-weave structure, refined grain structure etc. on the comprehensive mechanical properties of titanium alloys have been analyzed. The results have shown that, to acquire highly comprehensive static mechanical properties and excellent damage tolerance properties, quasi-b treatment and purification processing should be used for medium strength titanium alloys to get high ductility lamellar structure, while quasi-b forging processing be utilized for high strength titanium alloys to obtain high ductility basket-weave structure. Grain refinement processing is very necessary for both the strength levels of titanium alloys.

Relationships between Microstructure and Mechanical Properties of Polycristalline Alumina

Some low purity alumina ceramics with an alumina content ranging from 86% to 93% were investigated, in order to explore the effects of microstructural parameters (grain size, intergranular phase) on mechanical (wear) and dielectrical parameters. The microstructure and worn surfaces were analysed using scaning electron microscopy. The correlation between microstructural, dielectrical properties and wear is discussed. It has been proposed that mechanical and electrical properties are two aspects of the same fundamental mechanism. Key words: Al2O3, Microstructure final, Wear resistance, Breakdown.

PREDICTION OF EFFECTIVE THERMAL CONDUCTIVITY OF POROUS MEDIA WITH FRACTAL-MONTE CARLO SIMULATIONS

On the basis of the fractal scaling laws of pore distribution in natural porous media, a probability model is developed for thermal conductivity in porous media by combining fractal theory and Monte Carlo technique. The current numerical model, which was validated by comparison with the existing experimental data, shows that the thermal conductivity of porous media is a function of the thermal conductivities of volume fraction, pore area fractal dimension, tortuosity fractal dimension and random number. The effect of microstructure parameters on the effective thermal conductivity of porous media is studied. The proposed fractal Monte Carlo simulation technique has advantages compared with conventional numerical methods and may have the potential in analyzing other transport properties of porous media.

Effect of microstructural parameters, microtexture and matrix strain on the Charpy impact properties of low carbon HSLA steel containing MnS inclusions

Low-carbon micro-alloyed steel containing coarse MnS inclusions was subjected to different thermo-mechanical processing routes to evaluate the effect of microstructure on its Charpy impact properties over a range of temperatures. MnS inclusions were found to deteriorate the upper shelf energy (USE) of the steel but its effect on the impact transition temperature was not as detrimental as that due to the presence of TiN particles. MnS inclusions were responsible for the initiation of micro-voids; however, the propagation of the cracks from these depends on the effective grain size and the strength of the matrix. An increase in the density of dislocations and low-angle boundaries enhances the strength and the strain-hardening ability of the ferrite matrix. This helps in retarding the growth of micro-voids, thereby reducing USE and promoting cleavage crack propagation resulting in an increase in its impact transition temperature. Refinement of effective grain size, on the other hand, increases the crack propagation resistance and therefore, improves the low-temperature toughness of the steel. Finish rolling of the steel just above the Ar3 temperature (austenite to ferrite transformation start temperature) or a simple normalizing treatment of the as-rolled plates at a low austenitization temperature is recommended from the point of view of higher impact toughness and lower impact transition temperature.

Investigation of the effect of microstructural parameters on the initial yield surface of non-isothermal composites

AbstractIn this paper, the effects of microstructural parameters on the initial yield surface of non-isothermal composites were investigated. The fiber phase was assumed to be a linear elastic material, and the matrix was assumed to be a non-linear material. Incorporating the Bodner-Partom viscoplastic constitutive model into a high-fidelity generalized method of cells allowed the initial yield surfaces of non-isothermal composites with different microscopic arrays and fiber cross-section shapes to be studied. Moreover, working temperature effects on initial yield surface are also discussed. The results show that the initial yield stress in the σxx–σyyplane of unidirectional fiber-reinforced composites tends to decrease with increasing working temperature. Furthermore, the effects of fiber arrays and fiber off-axis angles on initial yield stress show similar variation at different working temperature conditions.

Effect of microstructure parameters on tensile toughness of tool steel after deep cryogenic treatment

Microstructure of an alloy has a significant effect on mechanical properties. Deep cryogenic treatment extends life of tool steels because of microstructure changes. In this research, effects of microstructural parameters were studied on tensile toughness of a medium carbon-low alloy tool steel. The results showed that the maximum population density of sub-micron sized secondary carbide was obtained after 36 h of soaking time. Also, amount of secondary carbides increased with soaking or tempering times from 2.18 vol% to 12.87 vol%. In addition, high population density and high content of secondary carbides were responsible for tensile toughness enhancement. Therefore, the best results (12–35% improvement in tensile toughness) were obtained for a specimen, which underwent a full treatment cycle consisting of heating, water quenching, soaking at −196°C for 36 or 48 h and tempering at 200°C for 1 or 2 h, respectively.

Microstructure and Tensile Toughness Correlation of 1.2542 Tool Steel after Deep Cryogenic Treatment

Microstructure of an alloy has a significant effect on mechanical properties. Deep cryogenic treatment extends life of tool steels because of microstructure changes. In this research, effects of microstructure parameters were studied on tensile toughness of 1.2542 tool steel. The results showed that high population density and high volume fraction of secondary carbides were responsible for tensile toughness enhancement.

Fennel-like nanoaggregates based on polysaccharide derivatives and their application in drug delivery

Biodegradable polymeric nanoparticles, which hold hierarchical morphologies, are of importance for controlled drug delivery. In this work, nanoparticles with fennel-like morphology were prepared from graft copolymers of hydroxyethylcellulose and poly(p-dioxane). The effect of microstructure parameters on the morphological transition of the nano-aggregates was studied and the nanoparticles were investigated as a carrier of hydrophobic drug. The morphology and drug release property of the nanoparticles were found to be related with the degree of substitution and molecular weight of graft chain of the copolymer.

Particulars of the In-Reactor Behavior of VVER and PWR Uranium Dioxide Fuel with Pellets of Different Geometry

The results of experiments performed in the research reactors HBWR (Norway) and MIR (Dimitrovgrad, Russia) with different variants of pelleted uranium dioxide fuel used in VVER and manufactured by Elektrostal MSZ and PWR using a standard method are analyzed. The analysis of the experiments made possible to study the effect of microstructural parameters on the thermomechanical behavior of the experimental fuel elements with this type of fuel. The experimental data on the temperature, length of a fuel kernel, and gas pressure beneath the fuel-element cladding can be used to verify models and thermomechanical codes describing the behavior of VVER fuel elements.

Study on Optimum Structure and Residual Stress of Ti/TiAl Micro-Laminated Sheet

The residual stress and the effect of microstructure parameters on failure performance of Ti/TiAl micro-laminated sheet were studied by Correlative theory and FE method. The results showed that the fracture work increases gradually with the increasing of layer number or thickness ratio. However, the rising extent reduced gradually and when the two parameters exceeded a certain value, the fracture work would not be changed. The value of residual stress reached its maximum at the centre and reached its minimum at the edge of micro-laminated sheet. Residual stress in Ti layers and Ti-Al layers was compressive stress and tension stress respectively. With increasing of layer number or thickness ratio, compressive stress would rise gradually and compressive stress would reduce gradually.

3D Finite Element Modeling for Particle-Reinforced Polymer Composites for Wind Energy Application

A series of numerical meso-mechanical models for different kinds of particle (include spherical, cylindrical and discal) reinforced composites are developed to investigate the effect of microstructural parameters on the elastic properties of composites. In these models, an effective interface concept is adopted. Finite element models with prescribed and random parameters are automatically generated in ABAQUS PDE (Python Development Environment). In the simulative investigations, it is observed that the degree of particle clustering and particle’s shape have strong effects on the elastic mechanical properties of composites.

Predicting the elastoplastic response of fiber-reinforced metal matrix composites

This paper aims to investigate the effect of microstructure parameters (such as the cross-sectional shape of fibers and fiber volume fraction) on the stress–strain behavior of unidirectional composites subjected to off-axis loadings. A micromechanical model with a periodic microstructure is used to analyze a representative volume element. The fiber is linearly elastic, but the matrix is nonlinear. The Bodner–Partom model is used to characterize the nonlinear response of the fiber-reinforced composites. The analytical results obtained show that the flow stress of composites with square fibers is higher than with circular or elliptic ones. The difference in the elastoplastic response, which is affected by the fiber shape, can be disregarded if the fiber volume fraction is smaller than 0.15. Furthermore, the effect of fiber shape on the stress–strain behavior of the composite can be ignored if the off-axis loading angle is smaller than 30°.