Material Grain Research Articles

Experimental Research on the Compressive Performance of Raw Bamboo Materials along the Grain

This paper carried out a compression test along the grain of the raw bamboo material, analyzed the failure process and failure form of the specimen, studied the relationship between the compression strength along the grain and the elastic modulus and the density, and initially explored the raw bamboo based on the reliability analysis Design value of compressive strength along the grain of the material. The research results show that the compressive load-displacement curve of bamboo along the grain can be divided into elastic, elastoplastic and descending segments, and the specimens show obvious ductile failure characteristics; the compressive strength and elastic modulus along the grain are positively correlated with the density; raw bamboo The standard value of compressive strength along the grain of the material is 48.83MPa, and the design value is 8.71MPa.

Structural formation and evolution mechanisms of fracture plugging zone

A coupled CFD-DEM method is used to simulate the formation process of fracture plugging zone. A photo-elastic system characterizing mesoscale force chain network developed by our own is used to model the pressure evolution in fracture plugging zone to reveal the evolution mechanism of the structure of fracture plugging zone. A theoretical basis is provided for improving the lost circulation control effect in fractured reservoirs and novel methods are proposed for selecting loss control materials and designing loss control formula. CFD-DEM simulation results show that bridging probability is the key factor determining the formation of fracture plugging zone and fracture plugging efficiency. Critical and absolute bridging concentrations are proposed as the key indexes for loss control formula design. With the increase of absolute bridging concentration, the governing factor of bridging is changed from material grain size to the combination of material grain size and friction force. Results of photo-elastic experiments show that mesoscale force chain network is the intrinsic factor affecting the evolution of pressure exerting on the fracture plugging zone and determines the macroscopic strength of fracture plugging zone. Performance parameters of loss control material affect the force chain network structure and the ratio of stronger force chain, and further impact the stability and strength of fracture plugging zone. Based on the study results, the loss control formula is optimized and new-type loss control material is designed. Laboratory experiments results show that the fracture plugging efficiency and strength is effectively improved.

Grain evolution simulation of ceramic tool material in spark plasma sintering process based on an improved cellular automata model

In this paper, a mathematical model for simulating the grain evolution process of ceramic materials was constructed to investigate the effects of the sintering parameters on the microstructure in the spark plasma sintering process. Firstly, a new algorithm of removing the right angle of grain was improved and an improved cell state assignment method was proposed based on the cellular automata model. Then the sintering parameters were coupled into the model, and the simulation method of grain growth and pore evolution were proposed. Finally, a ceramic material grain evolution model with stomata structure for spark plasma sintering was constructed. The simulation results showed that the grain size increased exponentially with the increases of holding time and sintering temperature, while the pores gradually decreased with the increase of the two parameters and the density of the material. Besides, the uniformity of grain growth also decreased with the increase of holding time. These results conformed to the topological characteristics of grain growth and the law of grain boundary migration, and can provide support for the sintering parameters optimization of ceramic tool materials.

Failure behavior of the thermal treated granite under triaxial cyclic loading–unloading compression

Because after being thermal treated, the failure behaviour of granite has an adverse influence on the safety and stability of the HLW disposal repository, its stress–strain curves, elastic modulus, Poisson’s ratio, plastic strain, dissipated energy and failure characteristic were analyzed by conducting and simulating triaxial compression test. According to the results, it was indicated at the initial elastic stage, that indexes above and accumulated AE count slightly increased with cyclic loading processing when T = 25 and 300 °C, suggesting less damage was caused. However, when T = 600 °C, the damage was caused immediately once applying cyclic loading. In the initial stage, under the function of triaxial cyclic loading–unloading, material grains were rearranged. Because of the more complexity of the failure modes of cyclic loading than that of monotonic loading, the rougher shear surface was formed, leading to a higher residual strength. When T = 600 °C, continuous development of micro-crack during uniaxial cyclic loading deteriorates the peak strength. The mechanical behavior of thermal treated granite under triaxial compression was investigated by experiment and numerical simulation. And found that the micro-cracks continuous increases under unloading process, which lead to the reduction of the peak strength

The Effect of Electron Beam Welding on the Microstructure and Microhardness of 3D-Printed Products from Titanium Alloy Ti–6Al–4V

The microstructure of double-sided welded joints of 3D-printed items made of titanium alloy Ti‒6Al–4V by the electron-beam freeform fabrication (EBF3) method has been investigated using the methods of X-ray diffraction analysis, optical metallography, and scanning and transmission electron microscopy. It is found that columnar epitaxial growth of primary β grains with transverse dimensions close to the sizes of primary β grains in the base material occurs in the process of electron-beam welding with a double-sided welded joint. Inside the primary β grains, there are grains of the α-phase with a lamellar shape inherited from the α' martensite, which is formed in the course of transformation β → α'. As in the printed samples, there is a nanocrystalline α"-phase in the metal of the welded joint inside grains of the α-phase and in interlayers of the β-phase. However, the density of particles of this phase in the metal of the welded joint is higher than in the base material. In the metal of the welded joint, tensile macrostresses and elastic residual microstrains also increase. The microhardness of the metal of the welded joint is greater than the microhardness of the base material.

Multiproxy sedimentological and geochemical analyses across the Lower\u2013Middle Pleistocene boundary: chemostratigraphy and paleoenvironment of the Chiba composite section, central Japan

The Chiba composite section (CbCS) in the Kokumoto Formation, Kazusa Group, central Japan is a thick and continuous marine succession that straddles the Lower–Middle Pleistocene boundary and the well-recognized Matuyama–Brunhes paleomagnetic polarity boundary. Although recent studies extensively investigated the CbCS, its chemostratigraphy, particularly around the Lower–Middle Pleistocene boundary, is poorly understood. Therefore, in this study, we performed multiproxy sedimentological and geochemical analyses of the CbCS, including the Chiba section, which is the Global Boundary Stratotype Section and Point for defining the base of the Middle Pleistocene Subseries. The aim of these analyses is to establish the high-resolution chemostratigraphy and to reconstruct the paleoenvironments of its sedimentary basin in detail. We used the K/Ti ratio as a broad proxy for the clastic material grain size of the sediments. Although the K/Ti ratio generally varies throughout the studied interval, the K/Ti ratio especially during Marine Isotope Stage (MIS) 19a shows a variation pattern like those of the foraminiferal oxygen isotope (δ18O) records. The records of the C/N ratio of bulk samples and carbon isotope ratio of the organic carbon (δ13Corg) suggest that the organic matter in the CbCS sediments during MIS 19c mostly originated from marine plankton, whereas the organic matter during MIS 18 and 19a was characterized by a mixture of marine plankton and terrestrial plants. These records are clearly indicative of changes in mixing ratio of marine vs. terrestrial organic matter in association with glacial–interglacial cycles from the late MIS 20 to the early MIS 18. In addition, we calculated the mass accumulation rates (MARs) of organic carbon, biogenic carbonate, and terrigenous material for quantitative interpretations on the paleoenvironmental changes. MAR calculations revealed that the contribution of marine organic carbon relative to terrestrial organic carbon increased during MIS 19c, and that the contribution of the terrigenous material relative to biogenic carbonate decreased during MIS 19c. Furthermore, we observed relatively large variations in the total organic carbon and total nitrogen contents during MIS 19a. These variations were probably caused by the relative decrease in bottom-water oxygen level, which is also supported by our trace-fossil data, although it is not certain whether the increase in organic-carbon flux at ~ 760 ka was due to the synchronous increase in biogenic productivity in surface water. Such a relative decrease in bottom-water oxygen level was partly due to the increased ocean stratification because of the northward displacement of the Kuroshio Extension Front.

Micro-structure evolution-based force model and surface characteristic studies of Inconel 718 during micro-endmilling

An accurate prediction of cutting force is significant, as it plays a critical role on surface quality and tool wear. In micro-endmilling, the machined feature size and feed/tooth are comparable to the material grain size and the edge radius of the endmill. Hence, the effects of scaling issues, material micro-structure and cutting temperature on the machining performance need to be addressed. This article presents a force model for micro-endmilling by incorporating size effect, machining temperature, workpiece spring back effect and micro-structure evolution. The developed force model was validated with experimental results on Inconel 718 and the prediction error was found to be less than 10%. An experimental study to understand the influence of size effect on cutting force, micro-hardness and surface defect during micro-endmilling on Inconel 718 was carried out. Minimum uncut chip thickness was observed adjacent to 0.9 µm. For a feed/tooth less than 0.9 µm, both cutting force and micro-hardness of the endmilled surface shows a nonlinear trend. Higher value of cutting force at feed/tooth less than 0.9 µm was observed due to high strain hardening, and significant plowing effect on the micro-endmilled surfaces.

Progressive failure in elastic–viscoplastic media: from theory to practice

In the risk assessment of soil movement, the comprehension of unexpected collapses involving creeping landslides is crucial. The transition from creeping to fast landslides is very hard to justify theoretically and simulate numerically. In this paper, the authors intend to demonstrate that even the integration of a basic elastic strain softening constitutive relationship under simple shear conditions is sufficient to capture such a transition. With this aim, an infinite slope, a homogeneous cemented/bonded soil and an oscillating water table level are considered. The onset of instability is shown to be anticipated by a local increase in strain rate within the shear band, behaving like a precursory signal. The size of the shear band, evolving with time and not depending only on the material grain size distribution, is governed by both the amplitude of the imposed perturbation and the material constitutive parameters.

Microstructural deformation in the clinching process

Need – There is a need to better understand the shear and plastic deformation that arises during clinch joint formation. Since microstructural texture preserves a history of deformation, grain structure has the potential to reveal the role of the operational parameters. Objective – This study elucidates the grain morphology of clinched joints using electron backscattering diffraction (EBSD) microscopy. Results – The main characteristics of grain morphology are equiaxed grains in the base material, with markedly elongated grain morphology and smaller grains in the necked region. Interpretation – The morphology is attributed to extensive plastic deformation causing the mechanochemical effect of dynamic recrystallization whereby localised recrystallization occurs along with transformation of grain morphology, followed by subsequent solutionizing and precipitation. Originality - An explanation is provided for the microstructural transformations during the clinching process.

CFD modelling of the effect of capillary pressure on retention behaviour of water menisci at inter-particle contacts

This paper presents a Computational Fluid Dynamics (CFD) model on the effect of capillary pressure on the retention behaviour of a granular material. The model proposes an unprecedented CFD insight into the onset of liquid menisci at the inter-particles contact under varying hydraulic conditions. The present work models the material grains as smooth spherical particles that define a porous network filled by two interstitial fluids: air and silicon oil. The numerical model has been subsequently validated against experimental measurements of the degree of saturation at different capillary pressures taken by Dullien et al. [F.A. Dullien, C. Zarcone, I.F. MacDonald, A. Collins, R.D. Bochard. J. Colloid Interface Sci. 127, 2 (1989)] in a system of smooth glass beads flooded with silicon oil. Results from the numerical simulations confirm the good capability of the model to reproduce the experimental retention behaviour of the granular material. Finally, the present paper laid the basis for future CFD studies on the effect of various factors (e.g. hydraulic hysteresis, surface roughness and/or grain shape) on the capillary pressure acting at the interparticle contact.

Improving Properties of Cinder Blended Materials for Construction of Low Volume Roads in Mbeya Region Tanzania

The study to improve engineering properties of cinder blended materials was conducted in Mbeya region Tanzania. The low volume roads (LVRs) comprises of 75% of the whole road network and serves about 80% of population in Tanzania. The abundant materials in Mbeya region are cinders/scoria, pumices and volcanic soils which are originated from volcanic action. The samples from four source materials which are Ituha cinder, Ituha pozzolan, Mlimanyoka clay and Mbalizi gravel were collected for laboratory tests. Characterizations of source materials were conducted and grading coefficients (GC) and shrinkage products (SP) which are the requirements for selection of materials for surface layers of LVRs were computed. The results for GC and SP for all four source materials are out of range of 16 to 34 units and 100 to 365 units respectively. The California bearing ratios (CBR) at 95%MDD (maximum dry density) for four source materials are 17.6% for Ituha cinder, 25% for Ituha pozzolan, 3.2% for Mlimanyoka clay and 5.1% for Mbalizi gravel. The results for GC, SP and CBR for all four source materials indicated that the materials are not suitable for construction of surface layers of LVRs. The four source materials were blended together to get six blended sample materials targeting GC and SP ranges. The results of CBR values at 95%MDD for the six blended samples are 28% for 10MNCl40ITPo50ITCi0MBGr, 43% for 11MNCl40ITPo39ITCi10MBGr, 56% for 12MNCl35ITPo40ITCi13MBGr, 44% for 13MNCl32ITPo35ITCi20MBG, 39% for 14MNCl42ITPo44ITCi0MBGr and 53% for 15MNCl25ITPo35ITCi25MBGr. The improvement of CBR values of the six blended sample is because of enhanced interlocking and friction properties of the mixtures and addition of clay which act as binder to the coarse grain particles. It is important to develop suitable envelopes for surfacing layer materials of LVRs since interlocking and friction resistance are enhanced by gradation characteristics of material grain particles. For easy blending process of materials, an equation have been developed which can be used to blend materials using GC and SP parameters.

Use of the fractal dimension for porosity modification in aluminum foams manufactured using space holder particles

The effect of space holder particles (SHP) fractal distribution on the porosity of aluminum foams manufactured by infiltration is studied in the present work. Physical models were used to estimate aluminum foam porosity, simulating SHP distribution for bimodal mixtures with different particle sizes and relative quantities. Results of these models were compared with mathematical models and the results obtained for experimental aluminum foams manufactured using a 332 Al-alloy base material and NaCl grains as SHP. Experimental foam structural characterization was carried out using image analysis to obtain porosity, density, wall thickness and fractal dimension, while mechanical characterization focused on the compressive Young modulus. Results show that it was possible to manufacture foams with different fractal porosities and a wide variety of unit cells, reaching a maximum of ? 68%. It was also found that pore wall thicknesses significantly decreased with the increase in the fine particles fraction. Besides, all the models presented a peak with a maximum porosity, whose values increased and shifted to low fine particles fraction with the increase in the sizes ratio. This behavior was also observed for the experimental foams with low particle size ratio. Nevertheless, for higher size ratios porosity showed an irregular behavior attributed to the mixing process.

Determination of Critical Dynamic Recrystallization Conditions and Mechanism Analysis of Ti600 High-Temperature Titanium Alloy

The dynamic recrystallization behavior of a high-temperature titanium alloy Ti600 has been investigated by hot compression tests at the strain rates of 0.001-10 s−1 and temperatures of 950-1010 °C. The grain boundary migration during deformation has been analyzed, and a critical DRX dislocation density associated with material essence and grain boundary mobility has been proposed to identify the main softening mechanism of Ti600. Additionally, JMAK model has been employed to describe the dynamic recrystallization behavior, which is essential to concerned dynamic recrystallization with material and deformation parameters to investigate the dynamic recrystallization behavior of Ti600. The activation energy QSRX has been calculated as 91.18 kJ. Finally, processing map has been established, and the optimal process window has been present. And EBSD experiments at different temperatures and strain rates have been conducted to deeply study the grain boundary distribution and crystal orientation.

Effect of severe deformation on the microstructure and properties of Nd-Fe-B powders caused by hydrostatic extrusion

The commercial Nd-Fe-B (Magnequentch MQU-F42) powder was consolidated by hydrostatic extrusion at room temperature in three stages. The values of thru strain obtained after the stages, were 1.38, 2.27, 3.12. A high degree of deformation leads to local changes occurring in the microstructure of the material that negatively affects its magnetic properties. Mossbauer spectroscopy has shown that a new phase appears in the deformed material, most probably as a result of strong local defecting (amorphization) of the Nd2Fe14B phase. Rietveld analysis of the diffraction phase investigation results indicates that deformation leads to a clear fragmentation of the material grain and to the deformation (change of parameters) of the crystal lattice. The heating of deformed materials leads to a series of irreversible transformations that start at a temperature of about 200 °C. As a result, α-Fe is produced from the defected phase in the form of 3 nm crystallites. The release of free Fe changes the chemical composition of the 'defected phase', making it impossible for it to revert to the structure prior to deformation. It can be concluded that the structural changes occurring in Nd-Fe-B powders during severe deformation are irreversible and involve a permanent reduction in the magnetic properties of the material.

Study of Mechanical Properties and Microstructure of Mercedes-Benz and Local Radiator Material

Indonesia has the capability to produced local products such as vehicle radiators. Many studied were carried out to characterize the radiator material. But it still needs to compare local products and imported products. This study carried mechanical properties and microstructure analysis for Marcedes Benz's core radiator and local radiator. The tools used in this study are microhardness tools, optical microscopes, and XRF. The result shows that the Mercedes-Benz radiator binding material before the heat treatment process, using an optical microscope shows the invisible results of a collection of atoms and the matrix and grain boundaries. On local radiator material, Not yet seen the collection of atoms and matrix and grain boundaries. White grains of Mercedes Benz radiator material is more abundant than local radiator materials. Chemical composition test results are; local radiator material content is dominated by three elements Ca (26.3%), Zn (44.4%) and Cu (13.9%) Cu (2.48%), Fe (45.15%), and Mn (44.88%). The German Mercedes-Benz element contents are; Fe (28.7), Mn (27.5), Ca (39.2). The hardness of the Mercedes-Benz radiator before heating is 43.4 HV, after being heated 39.2 HV. The hardness local radiator material before heating 43.5 HV and after heating 38.2 HV.

A Constitutive Material Model Applied to Microforming Processes.

The plastic treatment of products reduced to sizes corresponding to the microscale poses difficulties, due to the occurrence of the so-called size effect, which is responsible for the different behavior of the material during the realization of microforming. In this study, a constitutive equation was elaborated taking into account two types of size effects, with the use of a surface model as well as a composite material model. The influence of the size effect referring to both the material grain size and the geometric scaling of the sample size on the material’s flow stresses was considered. The surface model took into account the different grain shapes present in actual polycrystalline materials. After the application of the presented model for titanium Grade 2, a good agreement of the experimental results with the FEM simulation results was obtained. Thus, the proper FEM modeling of microforming processes should be conducted with the use of a material model, taking into account the occurring size effects.

Observation of grain size limited dynamic failure in a typical granite

Understanding the dynamic fragmentation of geological materials is important to many fields, but is particularly significant for mining. Here, a series of expanding ring experiments are reported, investigating the dynamic fragmentation of a typical granite from a mining environment. In addition to in-situ diagnostics which measure time-resolved loading characteristics, fragments were soft-captured and analysed. Measured fragment size distributions agree well with existing theory, but show unexpected strain rate variation. Specifically, the reduction in fragment size with rate is shown to be limited as the fragments neared the material grain size, a phenomenon not previously observed. Inter-granular failure was confirmed by fractographic analysis of the recovered material. The phenomenon was hypothesised to be caused by the fragmentation being dominated by an intergranular fracture mechanism which becomes inhibited when fragments near the grain size. More generally, the approach provides a new experimental route through which the fragmentation of geological materials can be understood.

Elucidating the Roles of Hole Transport Layers in p‐i‐n Perovskite Solar Cells

AbstractThe hole‐transport layer (HTL) is critical to high performance of perovskite solar cells (PSCs) in terms of hole extraction, transportation, and mediation of the following film formation. Here, the interplay between HTLs and open‐circuit voltage (VOC) in PSCs is directly targeted. The results suggest that there is no evident relation between the obtained VOC and the work function of HTLs and it is directly controlled by the recombination losses inside the perovskite material (grain boundaries and trap states) as well as at the interfacial contacts. Additionally, an insight understanding about the charge transfer behavior in PSCs is provided and it is pointed out that the nature of interfacial contacts is a critical factor in defining charge accumulation and recombination at the interfaces. Analysis of the electroluminescence efficiency and transient absorption spectroscopy confirms the better interfacial contact of HTL/perovskite, and larger grain size of perovskite films mediated by the hydrophobic nature of HTLs can collectively and efficiently eliminate nonradiative recombination, resulting in faster charge transfer and lower resistance at the interfaces. This work provides a profound understanding of how the surface hydrophobicity and the interface contact are correlated in terms of nonradiative losses and J–V characters in real devices.

Optimization of ultrasonic nanocrystal surface modification for surface quality improvement of directed energy deposited stainless steel 316L

Ultrasonic nanocrystal surface modification (UNSM) technology can be used for the surface treatment of specimens produced by additive manufacturing using directed energy deposition. We investigated the change in the surface quality characteristics of the treated specimens with respect to the UNSM process variables. The roughness and waviness of the deposited surface were adopted as the objective functions and the optimal process conditions were determined by the response surface method (RSM). The surface waviness and roughness were determined to be most affected by the static load, with the scanning speed having the least effect. It was observed that a smaller inter-path interval decreased the surface waviness and roughness, and an excessively large or small static load deteriorated the surface modification results. The finally optimized conditions consisted of a static load of 45 N, inter-path interval of 10 μm, and scanning speed of 2600 mm/min. These conditions produced a surface waviness of 1.8097 μm and roughness of 0.3297 μm, which represent improvements of 80% and 72%, respectively, compared with the untreated specimen. It was further observed that UNSM significantly refined the material grains and considerably increased the martensite. This resulted in a surface microhardness increase of up to 71.2%.

Research of high-speed high-performance and small-sized screw conveyors-grain loaders

Currently, agricultural enterprises are offered many conveyors of various typesfor the mechanization of loading and unloading works during cropmovement. The article presents studies of a method of increasing performance of a screw type conveyor allowing to create a small-sized design by increasing its revolutions. It investigates workmechanism, describesoperational technology of conveyors-grain and work disadvantages, namely, problematicgrain transportation over long distances along a spatial route or complication of technological scheme. Loading directly from pile may require manual labor or additional equipment. It is noted that increase in performance with increase in rotor revolutions (from 400 to 1100 rpm) occurs up to a point, after which revolutions increase, and performance decreases. In order to increase screw performance, it is necessary to accelerate material axial advance, i.e. to stretch ascending and, especially, falling material trajectorybranches at high speeds, with bulky material (grain), cast by centrifugal force to inner pipe surface, filling the grooves. Since their locationis close to each other (at 30°), surface braking layer is formed, which decreases circumferential speed component of absolute movement of grain andincreases the axial one. In order to increase screw performance, it is necessary to accelerate material axial advance, i.e. stretch ascending and, especially, falling material trajectorybranches. Further studies will contribute to finding new ways to increase speed coefficient K υ and coefficient ψ and create high-speed, high-performance, and small-sized screw conveyors-grain loaders.