Direction Of Grains Research Articles

Grain-Scale Study of SAC305 Oligocrystalline Solder Joints: Anisotropic Elasto-Plastic Constitutive Properties of Single Crystals

Abstract This paper focuses on anisotropic elastic-plastic constitutive modeling of SAC (SnAgCu) solder grains because of their importance in modeling the behavior of oligocrystalline (few-grained) micron-scale solder joints that are increasingly common in heterogeneous integration. Such grain-scale anisotropic modeling approach provides more accurate assessment of the mechanical response of solder interconnects in terms of predicting different failure modes, failure sites, and variability in time-to-failure. Anisotropic plasticity is represented using Hill–Ramberg–Osgood (RO) continuum plasticity model, which utilizes Hill's anisotropic plastic potential along with a RO power-law plastic hardening flow rule. Mechanistically motivated empirical scaling factors are proposed to extrapolate the stress–strain response for different grain sizes/shapes and for different coarseness of microstructures within each grain (generated with different cooling rates). This scaling factor can therefore also capture the effects of microstructural coarsening due to isothermal aging. This goal is achieved by first conducting monotonic tensile and shear tests on monocrystalline and oligocrystalline SAC305 solder joints containing grains of various geometries and also intragranular microscale (dendritic and eutectic) structures of various coarseness. The grain structures are characterized for each tested specimen using electron backscattered diffraction (EBSD). The Hill–RO model constants and the empirical scaling factors are then estimated by matching grain-scale anisotropic elastic-plastic finite element models of each tested specimen to the measured stress–strain behavior, using an inverse-iteration process. Grain shape is seen to influence the sensitivity of the effective stress–strain curves to the applied stress state (i.e., to the orientation of the principal stress directions) relative to (i) the material principal directions and (ii) the geometric principal directions of grains with high aspect ratio. Limitations of the current results and opportunities for future improvements are discussed.

General Spatial Confinement Recrystallization Method for Rapid Preparation of Thickness-Controllable and Uniform Organic Semiconductor Single Crystals.

Organic semiconductor single crystals (OSSCs) are ideal materials for studying the intrinsic properties of organic semiconductors (OSCs) and constructing high-performance organic field-effect transistors (OFETs). However, there is no general method to rapidly prepare thickness-controllable and uniform single crystals for various OSCs. Here, inspired by the recrystallization (a spontaneous morphological instability phenomenon) of polycrystalline films, a spatial confinement recrystallization (SCR) method is developed to rapidly (even at several second timescales) grow thickness-controllable and uniform OSSCs in a well-controlled way by applying longitudinal pressure to tailor the growth direction of grains in OSCs polycrystalline films. The relationship between growth parameters including the growth time, temperature, longitudinal pressure, and thickness is comprehensively investigated. Remarkably, this method is applicable for various OSCs including insoluble and soluble small molecules and polymers, and can realize the high-quality crystal array growth. The corresponding 50 dinaphtho[2,3-b:2″,3″-f]thieno[3,2-b]thiophene (DNTT) single crystals coplanar OFETs prepared by the same batch have the mobility of 4.1 ± 0.4 cm2 V-1 s-1 , showing excellent uniformity. The overall performance of the method is superior to the reported methods in term of growth rate, generality, thickness controllability, and uniformity, indicating its broad application prospects in organic electronic and optoelectronic devices.

Impact of Urbanization on Cropping Structure: Empirical Evidence from China

Food security is a national priority and a cornerstone for maintaining national and regional stability. Focusing on cropping structure directly related to food security, this paper estimates the causal effect of urbanization on cropping restructuring in China. We use provincial panel data between 2000 and 2019 and threshold regression models to identify potential structural mutation characteristics. This study is an attempt to fill the cognitive gap for the nonlinear relationship between urbanization and cropping restructure. Urbanization formed agricultural labor supply constraints that significantly increased the share of sown area of grain crops, but with obvious threshold characteristics, and the effect of urbanization on cropping structure was no longer significant after crossing the threshold. Urbanization in the main grain-producing regions and main grain-selling regions promoted the adjustment of cropping structure in the direction of grain but was not significant in balanced production and marketing regions. Short-distance urbanization did not bring significant effects on cropping restructuring. We propose several suggestions for cultivated land planting structure, urbanization, and food security.

Industry analysis of the competitiveness of Rostselmash as a major manufacturer of agricultural machinery

The article discusses issues related to the industry competitiveness of Rostselmash in the context of agricultural machinery for various purposes and performance classes. As estimated indicators, the total turnover in the direction of grain and forage harvesters, market capacity, total shipments of combines, etc. are highlighted. The analysis of the mutual conditionality of grain prices, effective demand and the world's shifting grain residues is given. A significant part of the article is devoted to assessing the competitive position of Rostselmash in the domestic market and the markets of Belarus, Kazakhstan and Ukraine in the context of grain and forage harvesting equipment and combines of various performance classes. The reasons for the weakening of certain positions and the strengthening of others are analyzed. Conclusions are drawn about the prospects of strengthening positions in the competitive struggle in the designated markets. The illustrative material contains bar charts of the dynamics of the total turnover of Rostselmash grain and forage harvesters for the analyzed period, the Russian market of combine harvesters, the market share of Rostselmash, the fleet of combine harvesters of the Russian Federation, the total shipments of grain and forage harvesters Rostselmash in the Russian Federation and for export, the export of Rostselmash machinery to foreign countries.

Effects of Moisture and Direction of Grain on the Thermal Conductivity and Mechanical Properties of Black Alder and Scots Pine

Aim of study: Relationships between moisture content and thermal conductivity and mechanical properties of wood species were examined. Material and methods: Black Alder (Alnus glutinosa L.) and Scots Pine (Pinus sylvestris L.) specimens were used. Thermal conductivity, modulus of rupture, compression strength and impact bending strength values were determined and analyzed. All specimens were examined at 3 different moisture levels which are oven-dry, fiber saturation point (FSP) and completely wet. Main results: The lowest thermal conductivity value was found in the perpendicular to the grain direction of oven dried Black Alder samples as 0.119 W/mK. The highest thermal conductivity value was found in the parallel direction of Scots pine samples with FSP humidity content as 0.340 W/mK. In addition, the thermal conductivity value parallel to the grain is significantly higher than perpendicular one at all three moisture levels. Highlights: While there is a positive linear relationship between the moisture content of the wood and its dynamic bending resistance and thermal conductivity; It was found that there is a negative linear relationship between bending strength and compressive strength value.

Effect of scan speed on grain and microstructural morphology for laser additive manufacturing of 304 stainless steel

Abstract The laser scanning parameters used in laser additive manufacturing (LAM) can impact the growth direction of the columnar grains produced during rapid solidification. This growth direction affects the mechanical properties of the manufactured parts after cladding. The effective use of a high laser power and a rapid scanning speed for LAM requires an accurate analysis of the relationships between the laser scanning process parameters and the grain growth direction and microstructural morphology of the scanned material. An experimental study was conducted to determine the macromorphology, microstructural morphology, and grain growth direction of 304 stainless steel material obtained during the laser scanning process at different scan speeds. The impact of the scan speed on different regions in the cladding layer (the clad zone (CZ), the heat affected zone (HAZ), and the dilution zone (DZ)) was determined, as well as on the direction of grain growth, the grain morphology and the grain size (which are the microstructures of the cladded materials), the degree of elemental mixing during laser scanning (which are changes in material composition of cladded material), and the microscopic hardness of the CZ (which is one of the mechanical properties of cladded material). With increasing scan speed, the CZ, HAZ, DZ, and dilution rate (DR) of the material gradually decreased, and grain growth gradually oriented towards the building direction of the cladding layer. At a 16 mm·s−1 scan speed, the angle between the grain growth direction and the scan direction was 84°. Changing the scan speed from 4 to 16 mm·s−1 caused the columnar grain size to gradually decrease from 13.3 to 9.2 μm and the corresponding microhardness to gradually increase.

The mechanism of substructure formation and grain growth 316L stainless steel by selective laser melting

This paper aims to investigate the unique substructure and grain growth of 316L stainless steel processed by selective laser melting (SLM) and clarify the mechanism. Results showed that the grain orientation on the x-z plane parallel to the build direction was the same type as the y-z plane, which all grow along the heat flow direction to form elongated columnar grains passing through the multi-layer fusion line. The epitaxial growth direction of grains changed abruptly with the vary of temperature gradient direction. Moreover, to expound the substructure formation based on solidification theory, a finite element model was established to obtain the distribution map of cooling rate G × R and solidified morphology G/R.

Investigation of the use of micro-alloy and As-Cast Microalloy steel in Automotive application

Vehicle industry assume unequivocal role in the financial development of the nation. The significant test before car industry is to deliver light weight parts without diminishing strength parts, for example, connecting rod and driveline segment, this can be accomplished by utilizing high strength low alloy steel. In all metal forming process forged parts posses high yield strength due to the favored direction of grains. Accordingly present exploration work zeroed in on Micro basic and Mechanical Behavior of As-Cast and Hot Forged Microalloy Steel. Impact of thermo-mechanical handling and cooling rate is additionally considered. Characteristic evaluation investigation of As-projected steel and hot fashioned steel is contemplated utilizing optical and SEM technique. Tensile testing performed on Instron testing machine. It is observed that due to the thermomechanical handling of steel there is development of strain instigated precipitate that advantage as far as effect strength and toughness of steel.

Effects of ultrasonic treatment on mechanical properties and microstructure evolution of the Cu/SAC305 solder joints

The effects of different ultrasonic treatment time on microstructure evolution and mechanical property of Cu/Sn-3.0Ag-0.5Cu (SAC305) solder joints were investigated. Experiments were set to obtain Cu/SAC305 solder joints, which were compared with solder joints without ultrasonic treatment. The application of short-term ultrasonic treatment on the solder joints would alter the morphology of interfacial intermetallic compound (IMC) layer, IMC thickness and grains size were reduced. Besides, ultrasonic treatment could significantly improve the shear strength of solder joints. In addition, the liquid solder would further flow along the direction of ultrasound, resulting in the reduction of contact angle. Due to the increase of ultrasonic time, the optimal growth direction of grains was changed after the ultrasonic treatment. However, excessive ultrasonic time would reduce the shear strength of solder joints and increase the IMC thickness, which would reduce the stability of solder joints.

Differences in microstructure and nano-hardness of selective laser melted Inconel 718 single tracks under various melting modes of molten pool

Single tracks of Inconel 718 were manufactured by selective laser melting (SLM) under the same volumetric energy density (VED), but via various scanning speed and laser power, with the aim of discerning the influence of the melting mode of molten pools on their solidification behavior, microstructure and nano-hardness. For this purpose, the geometric appearance of each Inconel 718 single track was firstly investigated. The results indicate that the molten pool geometries are significantly different despite melting under the same VED condition; the typical melting modes of molten pools, including the keyhole and conduction modes, can be obtained. The solidified microstructures of both modes evolve from cellular at the bottom to cellular dendrites at the top; but the dendrites are more developed under the keyhole mode. In addition, the grains of both modes follow the epitaxial columnar crystal growth pattern along the boundary of molten pool. The preferential growth direction of grains under the conduction mode is closer to the <001> direction, but the grains orientation of the keyhole mode tends to be <001> and <101> direction. Moreover, in comparison with the conduction mode, the average nano-hardness for different regions of molten pools corresponding to the keyhole mode is slightly higher.

A review on properties and microstructure of micro-extruded product using SPD and as-cast material

Micromanufacturing has wide application in the development of micro-products, but these methods are limited in developing desired properties such as dimensional tolerance, surface texture and electromechanical properties. Deformation is one of the techniques where such limitations on micro-products can be overcome based on the principle of grain refinement theory. The product developed through subtractive and additive method reveals coarse grain microstructure, whereas ultrafine grains (UFGs) are observed in the severe plastic deformation (SPD) process. Equal-channel angular pressing (ECAP) is one of the best SPD techniques to produce UFG up to a nanometre. As-cast micro-extruded product that contains coarse grains seems to be inhomogeneous, having wide deviation of physical and mechanical properties throughout its volume. ECAP-based micro-extruded product is homogeneous and has uniform physical and mechanical properties. The present review paper discusses about the influence of die geometry, die strength, specimen selection, frictional condition, temperature condition and other boundary conditions on the properties of as-cast and ECAPed extruded material. Similarly, size and direction of grain can alter the mechanical properties based on requirements and type of applications.

Selective laser melting of high strength and toughness stainless steel parts: The roles of laser hatch style and part placement strategy

Laser hatch style and part placement strategy are acknowledged to have a considerable effect on processing quality and mechanical performance of selective laser melting (SLM) products. In an effort to obtain 316L stainless steel products with favorable properties, hatch style integration and part placement optimization were adopted in this study. The tensile property of SLM parts at different placement angle ψ was identified and the corresponding deformation behavior and failure mechanism were investigated. Interestingly, the part prepared by double stagger melt (DSM) style presented a strong <001> texture along the transverse direction (TD) rather than the growth orientation of the columnar grains (building direction, BD). This crystallographic variation imposed an immense effect on yield strength of SLM-processed parts by modifying the orientation relationship between texture and growth direction of grains. As ψ was set to 60°, the DSM-fabricated parts exhibited a lower Schmid factor, hence achieving a higher average yield strength σs of 536.6 MPa. The static fracture toughness UT was closely associated with the normal component force Fn imposed on preferential loading plane. By means of hatch style integration and part placement optimization, the dangerous “opening or tensile” loading mode was effectively avoided and reasonable compromise between the strength and ductility was achieved elaborately, thus obtaining an ultrahigh UT (3.478 × 108 J/m3) of SLM-processed parts. This study scientifically showed the great potentials of the SLM process to prepare 316L stainless steel products demanding challenging high-strength and high-toughness performance.

Microstructural and Texture Evolution of Strip Cast Nd–Fe–B Flake

In this work, the microstructure and texture evolution of the strip cast Nd–Fe–B flake has been systematically investigated by correlating multiple state-of-the-art characterization techniques. We found that (i) besides the existence of random ultrafine equiaxed grains at the wheel side of the flake, elongated (001) textured grains were formed into a V-shape zone between neighboring nucleation sites, which possibly resulted from the in-plane growth of the low energy preferred growth direction of grains (a axis). Both ultrafine random equiaxed grains and elongated (001) textured grains are detrimental to achieving a high-performance Nd–Fe–B magnet, due to the inhomogeneous grain shape and nonuniform distribution of rare earth-rich phase within these grains or along the grain boundaries, which deteriorate the alignment of the Nd–Fe–B powders in the subsequent hydrogen decrepitation process and jet milling procedure. To overcome the issues mentioned above, two potential approaches are proposed, which are inc...

Quantitative analysis of surface roughness evolution in FCC polycrystalline metal during uniaxial tension

The purpose of this work is to present a quantitative description of surface roughness evolution in face-centered cubic (FCC) polycrystalline metal under uniaxial tension. The crystal plasticity model, in which the crystal plasticity constitutive law and the periodic boundary condition are incorporated, is established to analyze the effect of initial surface roughness, grain size and crystallographic orientation distribution on the surface roughness evolution. It is found that the surface topography during plastic straining can be divided into heterogeneous deformation surface and homogeneous deformation surface according to whether considering the heterogeneity of polycrystalline material or not. To quantitatively descript the surface roughness evolution during uniaxial tension, the concepts of equivalent grain size, which represents the comprehensive effect of grain sizes in different directions, and standard deviation of the direction cosines between crystal plane and rolling direction of grains (SD_cHR), which represents the effect of orientation distribution, are proposed. The roughness of the model with flat free surface depends approximately linearly on both the tension strain and the grain size, and exponential on the texture distribution. The uniaxial tensile test is performed to verify the accuracy of the established quantitative description of surface roughness evolution, which shows a favorable agreement with the predicted results.

An Analytical Study of Failure of Transversely Isotropic Rock Discs Subjected to Various Diametrical Loading Configurations

The indirect (Brazilian) tensile strength test is commonly used in rock engineering and rock mechanics. Most of the research on how to interpret Brazilian test is only valid for isotropic rock. The load may be applied to disc shaped samples through flat platens or curved jaws and the different load configurations give rise to subtle but important differences to stress distributions throughout samples during testing and at the onset of failure. To reliably obtain the tensile strength accurate stress distributions, especially at the location of the initial crack, must be determined. However, most real rocks exhibit a certain type of anisotropy known as transverse isotropy due to the presence of preferred directions of grains, beddings, microcracks or pores. This study focuses on the failure modes when transverse isotropy is present. Previous studies for transverse isotropy indicate that the exact location of the initial crack is at the disc centre. These studies, however, ignore the effect of the load contact configuration on the stress distribution. This paper overcomes this limitation and applies Amadei's analytical solution to assess the effects of the load contact area on the stress distribution. The stress distribution is coupled with a transverse isotropy failure criterion in a mechanically consistent way to find the exact location of initial crack. It is shown that the location of the initial crack depends on the transverse isotropy orientation and load configuration.

Influence of vertical temperature gradients on wafer quality and cell efficiency of Seed-assisted high-performance multi-crystalline silicon

The effect of vertical temperature gradients on the performance of Seed-assisted high-performance (HP) multi-crystalline silicon (mc-Si) is investigated by numerical simulations and contrast experiments. The vertical temperature gradients are designed by keeping the temperatures at the top and lowering the temperatures at the bottom. Two Seed-assisted HP mc-Si ingots were grown by means of a larger and a conventional vertical temperature gradient. It is found that the larger vertical temperature gradients result in the more parallel growth direction of grains and the longer crystal growth length, increases the percentages of <112> grain orientation and random grain boundaries, which are benefit for crystal quality. The experimental results also confirm that the wafer of ingot grown with a larger vertical gradient has the better quality, and their cell efficiency can increase.

Mechanical properties and thermal conductivity of Si3N4 ceramics with YF3 and MgO as sintering additives

Si3N4 ceramic was densified by hot pressing sintering at 1750°C for 1h under the uniaxial pressure of 20MPa in N2 atmosphere with YF3 and MgO as sintering additives. The thermal conductivities of SN-YF specimen were both higher than that of Si3N4 ceramic sintered with Y2O3 and MgO before and after annealing treatment. The grain size and aspect ratio in SN-YF specimen were both bigger than those in the SN-YO specimen, which was beneficial for the creation of high thermal conductive path. On the other hand, the improvement of thermal conductivity by the addition of YF3 might be attributed to the reduction of the grain boundary phase due to the evaporation of SiF4, and the resultant reduction of the lattice oxygen due to the reduction of SiO2 in the grain boundary phase. The {0001} direction of grains had the probability of growing along the hot pressing direction in the SN-YF specimen, which was beneficial for the improvement of thermal conductivity while the {0001} direction grew along the X0-Y0 plane in the SN-YO specimen. The mechanical properties of SN-YF specimen were comparable to those of SN-YO specimen.

The New Era of Corn and Soybean Prices Is Still Alive and Kicking

There is no shortage of doom and gloom about grain price prospects at the present time. Prices have indeed fallen to quite low levels compared to the high prices that occurred over much of 2008-2013. For some, this is proof that the high prices of 2008-2013 were a temporary spike, albeit a rather long-lasting one, instead of a shift to a permanent and higher level of prices. This flies in the face of our long-argued position that corn, soybean, and wheat prices moved to a new era of higher average nominal prices beginning in late 2006 (Good and Irwin, 2008; Irwin and Good, 2009; farmdoc daily, March 29, 2011; April 12, 2011; April 19, 2011; February 27, 2013; February 28, 2013; November 7, 2013). The new era replaced the previous era that spanned from January 1973 through November 2006. We argued that the new era of prices was primarily driven by demand shifts associated with rising biofuel production, particularly corn-based ethanol. Our projection of new era average prices and price ranges was based on an extremely simple analysis. This method turned out to be surprisingly accurate but it lacked a strong foundation in more fundamental supply and demand projections. In this article, we use our recently developed models of the relationship between the year-ending stocks-to-use ratio and marketing year average prices for corn and soybeans to provide a more rigorous economic foundation for the original new era grain price projections. These models are particularly useful in helping to frame the ongoing debate about long-term average grain prices. For additional background information on the debate about the long-term direction of grain prices see the farmdoc daily articles by Professor Carl Zulauf on March 11, 2016 and by Professor Paul Peterson on September 3, 2015.

Crack influence on load-bearing capacity of glued laminated timber using extended finite element modelling

Most of the cracks are caused by changes in temperature and relative humidity which lead to shrinkage and swelling of the wood and thereby induce stresses in the structure. How these cracks influence the strength of the wooden structure, especially the shear strength, is not well understood. However, it is reasonable to expect that cracks have an impact on the shear strength as they preferably run along the beams in the direction of grain and bond lines. The purpose of this study was to investigate the load-bearing capacity of cracked glulam beams and to find a model that could predict the failure load of the beams due to the cracks. Three-point bending tests were used on glulam beams of different sizes with pre-manufactured cracks. An orthotropic elastic model and extended finite element method was used to model the behaviour of the cracked beams and to estimate the load-bearing capacity. The conclusions were validated by numerical simulations of the mechanical behaviour of three-point bending of glulam beams with different crack locations. The crack initiation load was recorded as the failure load and compared to the experimental failure load. The results of the compaction simulations agree well with the experimental results.

Design and Analysis of a Novel 3-D Magnetization Structure for Laminated Silicon Steel

A novel 3-D magnetic properties tester for laminated silicon steel specimen has been designed and constructed. The magnetization structure is the critical part of the tester especially for the magnetic properties of the laminated silicon steel in perpendicular direction of grain oriented. To guarantee the experimental precision and accurately analyze the 3-D magnetic properties of the laminated silicon steel, a symmetrical 3-D magnetic flux path in the magnetization structure fit for given dimension of specimen has been calculated and modeled. Magnetic flux in each direction has been homogenized and concentrated on the top of the core poles through finite element analysis. Therefore, magnetic properties in each direction of the laminated specimen can be really concerned and analyzed in practical engineering.