Free Surface Side Research Articles

The evolution of the compaction process and the deformed state of porous blanks during their hot forging in the open die

The article presents the results of the study of the evolution of the deformed state of the workpieces, the energetic parameters of the process and the distribution of porosity over the volume of the forging at all stages of hot forging of porous powder forgings in an open die. Modeling of the process was carried out using the finite element method using the DEFORM 2D/3D software complex. As a result of the simulation, it was found that at the initial stage of the process, the blank is mainly compacted with minimal radial flow of the material. Noticeable flow of metal into the groove groove area begins only when the forging material reaches an average relative density exceeding 90%. A significantly different nature of the distribution of axial er and radial ez deformations over the volume of the forging was noted. A zone with increased levels of values of axial deformations is formed in the central layer of the forging, equidistant from the upper and lower surfaces of the die cavity, and the values of radial deformations decrease with distance from the zone bordering the free side surface of the workpiece in the radial (to-center) direction. The minimum values of ez and er appear in the upper and lower angular stagnant zones of the forging. It is shown that the graph of the dependence of the deformation force on the displacement of the punch is marked by the presence of at least three characteristic sections due to the relationship between the processes of compaction and forging shape change at each stage of the process.

Solution of the Dynamic Lame Problem

The well-known Lame problem, posed in 1852, involves solving the static equilibrium of a parallelepiped with free side surfaces subjected to action of opposite end forces. In this article, the same problem for a more complicated case of impacts of end forces is considered. An exact analytical solution of this problem is found. Emphasizing the particular difficulty of solving this problem, Lamé, in his book “Leçons sur la thorie mathematique de Ielasticite des corps solides” (Paris, 1852), wrote: “C’est une sorte d’engine aussi digne d’exercer la sagasite des analystes que le fameux problem des trios corps de la Mécanique celeste”,—“This is a kind of drive, as worthy of training the clairvoyance of analysts as the famous three-body problem of celestial mechanics.” At that time, this problem was the subject of a prize from the Paris Academy of Sciences, that was intended for the one who solved the Lamé problem. Despite this, to date, no solution has been found even for a static case of this problem, not to mention the complicated version of the problem.

EVALUATION OF DEFORMABILITY OF MATERIAL OF PREPARATIONS DURING ROLLING

The article presents the results of development and research of the technological process of cold forming rolling of aluminum billets. The main obstacle to the implementation of such processes is the danger of destruction of materials, which necessitated the study of the stress-strain state, plasticity and assessment of the deformability of the workpiece material. To experimentally determine the ductility of metals, a rolling method was developed, according to which the deformation of the free side surface of the cylindrical sample occurs under uniaxial tension. Increasing the degree of deformation and bringing the material to fracture is provided due to the increase in the radii of the rolls during rolling and deformation of the sample on the wedge. Analysis of the stress-strain state of the free side surface of the cylindrical workpiece was performed by the finite element method, which used a specialized engineering software package DEFORM 3D. As a result, a significant inhomogeneity of the stress-strain state in the deformation zone is established. The most severe stress state is observed on the free side surfaces of the workpiece, which causes the danger of its destruction in this area. The dependence between the relative compression of the workpiece during rolling and the intensity of deformation on its side surface is obtained, which allows to determine the limiting thickness of the workpiece before destruction. As a result of the assessment of the deformability of aluminum alloys during cold rolling, using the curves of limit deformations and the scalar criterion of deformation, the limits to the destruction of the intensity of deformation and the limit value of the relative compression of the workpiece. The use of constructed models makes it possible to determine the value of the used plasticity resource at intermediate stages of rolling.

Crystallization behavior and soft magnetic properties of Fe–B–P–C–Cu ribbons with amorphous/α-Fe hierarchic structure

In this work, Fe83+x(B4P8C4)16-xCu1 (x = 0, 1, 1.5 and 2 at. %) alloy system with amorphous/α-Fe hierarchic structures in as-cast state were artificially designed. The microstructure, crystallization kinetics, nanocrystalline structure, and magnetic properties of the alloys were systematically investigated. And the structural mechanism for the magnetic properties of these alloys was discussed. It is shown that the structure is evolved from full amorphous to amorphous/α-Fe dual-phase microstructure in the free surface side, and/or roller side layer with Fe content increasing. The formation of hierarchic structure decreases the activation energies of onset and peak crystallization of α-Fe phase, and increases the size of nanocrystalline grains, and subsequently is beneficial to improve the Bs of alloys. The Hc of alloys increases due to the formation of hierarchic structure, whereas this effect is gradually eliminated by the annealing process at the suitable crystallization annealing temperature (Ta). Typically, Fe85B3.5P7C3.5Cu1 nanocrystalline alloy exhibit the Bs of 1.86T and Hc of 5.7 A/m after annealing at 723 K. High Fe bearing alloys have lath domain structure with stronger orientation preference in as-cast state, and transformed into labyrinth packing with thinner spacing after structural relaxation annealing, demonstrating that hierarchic structure leads to the high magnetic anisotropy in the alloys.

Grain-size gradient NiTi ribbons with multiple-step shape transition prepared by melt-spinning

A grain-size gradient NiTi ribbon with multiple-step shape transition was papered by means of melt-spinning. The ribbons contain coarse and fine grains in the free surface side and copper roller surface side, respectively. The grain-size gradient microstructure induces a two-stage phase transformation behavior in the ribbons during heating or cooling. After tensile deformation pre-treatment, the ribbons exhibit a back-and-forth shape change (shape A→B→A) upon a single heating or cooling process, resulting from the sequential phase transformation through the thickness of the ribbon as dictated by gradient grain size. The activating performance of the ribbons, i.e. shape transition amplitude and speed, can be customized by controlling the pre-deformation strain. This work offers a new opportunity for innovative designs to reach a novel shape memory behavior in NiTi alloys conveniently and efficiently.

Development of Ti–Zr–Hf–Y–La high-entropy alloys with dual hexagonal-close-packed structure

TiZrHfYLa0.2 high-entropy alloys (HEAs) with dual hexagonal-closed-packed (HCP) structures were designed based on the concept of liquid phase separation (LPS) and segregation for enhancing the immiscibility of the constituent elements. The LPS leads to a particular solidification microstructure on the free surface side and Cu-hearth contacted area in the ingots. The dual HCP structures with equi-axis Ti–Zr–Hf dendrite and Y-La-rich interdendrite were observed at most regions of the arc-melted ingots. The mixing enthalpy among the constituent elements and predicted phase diagrams constructed by the Materials Project were effective for the alloy design of the HEAs with dual HCP structures.

Fracture mechanism of steel plate loaded by explosive-induced shock waves

The fracture mechanism of in-plane notched steel plate were experimentally investigated under the loading of the triangle shock waves. A series of 20 mm thick steel plates were loaded by explosive charges with different weights and the steel plates were notched in the load surface and free surface. The explosives cut the central part of the plate along the notches and the recovered specimens were processed and analyzed by the scanning electron microscope (SEM). It was found that the explosive charges and the notch properties had a significant effect on the notch fracture and the spall observed in the experiments. Thick explosive charge plate generated deeper, smaller and more dimples on the spall fracture surface which means the ductile of the fracture was increased and the crack extension resistibility was strengthened. This led to a step-like morphology on the spall surface. Moreover, the fractures of two sides of the notch were different. The shear fracture emerged on the loading side and the tensile fracture appeared to the free surface side. However, when there was no notch in the loading surface, the shear fracture appeared to the free surface side and extended to the loading surface. At the same time, the spall and notch fractures interrelated near the notch. Based on the experimental results, a new damage level function was proposed considering the statistic of crack length instead of the void volume. The theoretical analyses of spalls under all six loadings were performed and compared with the experimental results. The comparison showed a good agreement and the reliability of the proposed model was verified. The fracture behavior and mechanism obtained from the experiments provided a good foundation for the further theoretical investigations and the improved damage model was applicable in engineering analysis.

Longitudinal wave speed in cylindrical auxetic rods with elastic constraint in radial direction

The combined influence of material auxeticity, strain and lateral boundary condition on the longitudinal wave speed in a prismatic rod of circular cross-section is developed herein. The lateral surface of the rod is elastically restrained in the radial direction such that twisting and bending are prevented while the axial displacement is fully permitted. As such, the imposition of zero and infinite radial spring stiffness reduces this model into longitudinal wave motion in a prismatic rod with free side surface and a plane wave of dilatation, respectively. The wave speed was made dimensionless by two ways, i.e. by normalizing against the elementary wave speed in prismatic rods and against the speed of plane waves of dilatation. Both approaches demonstrate the manner by which the wave speed transits between the two extreme lateral boundary conditions: from being a purely rod (1D stress with 3D strain) to a purely bulk (3D stress with 1D strain) wave motion, with the strain and material properties taken into consideration. Results indicate that the wave speed is increased by (a) greater radial elastic restraint stiffness, (b) more positive longitudinal strain, and (c) the higher Poisson's ratio magnitude of the rod material. These results also suggest that the adjustment of wave speed is more easily controlled in the auxetic region than in the conventional region.

Cutting force measurement and analyses of shell cutters on a mixshield tunnelling machine

In this study, a real-time measurement method for cutting forces of a mixshield tunnelling machine is proposed. The strain of the cutter saddle is monitored and used to back-calculate the forces acting on the cutter. The normal cutting forces are primarily analyzed in this study. Four resistance strain gauges are placed on the two free side surfaces of the saddle with effective protection, two strain gauges among which are installed in the vertical direction on one free side surface, and individual strain gauge is installed in the vertical and horizontal directions on the other free side surface. Then strain gauges are punched out from the cutter casing and sealed to connect with the data acquisition system. DataTaker DT80G intelligent data logger is employed as the core of the data acquisition system. The data logger is powered by a chargeable battery, and equipped on the back of the cutter-head and rotates with the cutter-head synchronously, which ensures continuous monitoring. The feasibility, durability, and stability of the monitoring system are calibrated and demonstrated. Subsequently, this measurement method has been implemented on the Herrenknecht mixshield machine at the Sanyanglu Tunnel in China. Monitoring was performed from chainage at No. 416 to No. 432 ring segmental lining, which lasted more than 20 days. A complete data set and corresponding tunnelling parameters of the mixshield were acquired. Statistical and trend analyses are carried out, the distribution along the installation radius, as well as the correlations between the cutting force and tunnelling parameters are analyzed. Results show that: (1) the cutting force decreases with increasing installation radius, center cutters experience maximum loading, panel cutters experience relatively equal moderate loads, and edge cutters experience the smallest loads; (2) the cutting force increases with penetration rate following a linear increasing function in general, where the cutting force mainly ranges from 20 to 70 kN; (3) after new cutter replacement, the increasing cutting force is in accordance with the increasing cutter-head thrust forces, however with continuous excavation, the increase in cutting force is slightly lower than the cutter-head thrust force, which may be due to cutter wear and mud cake wrapping; (4) the consistency between the cutting force and the cutter-head thrust force is better than the consistency between the cutting force and the cutter-head torque.

Influence of Cooling Condition of Casted Strips on Magnetic Properties of Nd–Fe–B Sintered Magnets

We investigated the additional (secondary) cooling effect of casted strips on the magnetic properties of Nd–Fe–B sintered magnets. The Nd–Fe–B sintered magnets were fabricated with the casted strips prepared without and with additional cooling. Additional cooling was achieved by blowing Ar gas at various pressures (0.1, 0.3, and 0.6 MPa) on the free-side surface of the strips during the strip-casting process. The higher magnetic properties of Hc, Br, and (BH)max of the final Nd–Fe–B sintered magnets were obtained for 0.1 MPa rather than for 0.0 MPa. The best microstructure of the columnar grains in the casted strips was produced with the aid of a lower pressure of gas on the free-side surface. It was found that the microstructure of the strips affects the distribution of grains grown in the sintered magnets. This report demonstrates that the improved magnetic performance of Nd–Fe–B sintered magnets was achieved via additional gas cooling.

Magnetic and Mechanical Properties of the Amorphous Alloys

It is clearly seen that the magnetic induction of the amorphous ribbon produced by conventional technology implying heating up to 1490 °С increases as the thickness of specimens increases, with this growth being especially intensive at the 100 А/m magnetic field strength. At the same time, the melt preparation supplemented by overheating contributes to the magnetic induction stabilization, i.e. magnetic induction is essentially independent of the ribbon’s thickness. It is only at high values of h that a slight increase in magnetic induction becomes evident. The fracture diameter of the free side surface is linearly increasing as the annealing temperature increases. The structure has been shown to influence magnetic and mechanical properties of the material in preparing the melt before casting.

Experimental and numerical investigation of the interfacial strength of bi-material joints

An integrated experimental and numerical investigation is employed to examine the interfacial strength of bi-material bonded joints with the aim to quantify the influence of three-dimensional (3-D) stress singularity. The stress singularities at 3-D interface corners and edges have been investigated numerically using finite element methods (FEM). It is found that the effect of the vertex angle on the order of stress singularity at interface corner can be eliminated by smoothing the intersection of interface edges, which can be achieved simply by generating a circular-arc fillet at the intersection of the two free side surfaces. Motivated by this, four-point flexure experiments of bi-material bonded joints, both with and without circular-arc fillet, are conducted. The experimental results suggested that, with a circular-arc fillet design, the strength of the joints may be increased due to the disappearance of 3-D stress singularity at interface corner. Finally, based on an analysis of the intensity of the singularity, an empirical equation that describes the relationship between the failure stress and the largest value of tress singularity order −λ at 3-D interface was determined to predict the interfacial strength of brittle bonded joints.

Microstructure of the NiMnGa Heusler Alloys Prepared by Suction Casting and Melt-Spinning

The microstructure of the Ni50Mn25Ga25 Heusler alloy (HA) rod cast to a copper mould and melt-spun ribbon was studied. According to X-ray diffraction analyses in both cases, the solidified alloy is a single-phase. In suction casting, the radial columnar crystals grow by cellular or dendritic growth, which leads to chemical inhomogeneity of the whole cast rod on the microscopic scale. The melt-spun ribbon exhibits a homogeneous alloy at the wheel side and an inhomogeneous alloy on the free surface side of the ribbon formed by cellular and dendritic growth. At both types of casting, the columnar crystals growth along the <100> crystal direction. According to texture analyses by EBSD, the fine grain structure at the wheel side of the ribbon exhibits no texture, while the columnar grain structure on the free surface side exhibits the <100> fibre texture with a declination by about 10 degrees in the spinning direction. Melt-spinning leads to significant refinement of the HA microstructure.

Photoconductivity in Magnetic Field of р-Type Cadmium – Mercury – Tellurium Films Grown by Liquid Phase Epitaxy

Photoconductivity in a magnetic field is studied for Faraday geometry on the p-type cadmium – mercury –tellurium films grown by liquid-phase epitaxy on cadmium – zinc – tellurium substrates. From the magnetic-field dependence of the photoconductivity signal under the film illumination from the side of the substrate or from the side of free surface, different values of mobility of minority carriers (electrons) are obtained. It is shown that for the mathematical description of the photoconductivity signal in a magnetic field, two types of electrons – “fast” and “slow” electrons, as well as “heavy” holes can be used.

Three-Dimensional in Bonded Joints: A Short Review

Distributions of stress 3D in the vicinity of the overlapping corners of joints with a single lap were investigated with accuracy at present the man. A (Fe), model accurately Finite Element 3D has been carried out in order to investigate the intensity of the stress of adjustments in the plan and outside of stress by the width of the plate. The influences of the thickness of the adhesive and the Poisson distribution have been taken into account. Numerical results showed the presence of modes engaged has been detected with precision a sudden rise in the way the out-of-plan is very close to the free surface side of the fitting.

Histological and morphological observations on tongue of Scincella tsinlingensis (Reptilia, Squamata, Scincidae)

The histology and morphology characteristics of the tongue in Scincella tsinlingensis were studied by light and electronic microscopy. Under light microscopy, the tongue consists of tip, lingual body and radix in sequence. Numerous lingual papillae widely distribute on the surface of the dorsal and ventral flanks in the tongue, in addition to some regions of the tip. The papillae’s surface is covered with the epithelial layer. The lamina propria and dense connective tissue are distinct existing under the epithelial layer. There are many lingual glands spread over the lamina propria. Tongue muscle is developed and composed of distinct intrinsic muscle, hyoglossus and genioglossus. By scanning electron microscopy, at higher magnification, the epithelial cells of the dorsal surface in the divaricate tongue tips show numerous microvilli, micro-ridges and micro-pores. The surface of dorsal side of the papillae in lingual body is covered with abundant of micro-ridges and taste bud lacuna. On the surface of the papillae in radix, micro-facets and micro-ridges are compactly distributed, as well as scattered mucilage-pores. The lingual epithelium is divided into four layers observed by the transmission electron microscope. Cells of basal layer are irregularly elliptical in shape, with sparse organelles in the cytoplasm. The deep intermediate layer is not always distinct. Small numbers of organelles are scattered into the cytoplasm. The cells of the superficial intermediate layer gradually flatten, as do their nuclei. The cytoplasm contains many keratohyalin granules. Cell membranes are formed processes around cells and joined by abundant desmosomes to the cell membranes of adjacent cells. The cells located on the extreme free-surface side of the keratinized layer have fallen off. The basal lamina is intercalated between the basal layer and the lamina propria. The lamina propria of lingual body contains lingual gland. A large part of the cytoplasm is occupied by mucus granules which located in the distal part of the cell. The connective tissue contains myelinated nerve fibers, vessel and muscle cells.

Formation mechanisms of NaZn13-type phase in giant magnetocaloric La–Fe–Si compounds during rapid solidification and annealing

The promise of the La–Fe–Si alloys for energy efficient magnetic refrigeration devices stems from a strong magneto-structural transition in the La(Fe,Si)13 (1:13) phase near room temperature. The formation of the 1:13 phase during rapid solidification was compared in detailed microstructural studies of the wheel-side and free-side surfaces of melt-spun ribbons. On the free-side, clusters of similarly-oriented crystallites are observed; chemical segregation of La, Fe, and Si leads to a nanoscale texturing of α-Fe and LaFeSi. In contrast, equiaxed 1:13 grains ∼100–400 nm form the microstructure of the wheel-side surface, with a minor α-Fe phase precipitated in the matrix. Upon annealing, the 1:13 phase grows via dissolution of the α-Fe phase on the wheel side and a peritectoid reaction from the free side. For longer annealing times, the completion of the peritectoid reaction improves the magnetic entropy change under a magnetic field change of 1.5 T from 12 J/kg K (2 min) to 17 J/kg K (2 h), and increases the Curie temperature of the ribbons from 189 K to 201 K.

Free-surface molecular command systems for photoalignment of liquid crystalline materials

The orientation of liquid crystal molecules is very sensitive towards contacting surfaces, and this phenomenon is critical during the fabrication of liquid crystal display panels, as well as optical and memory devices. To date, research has focused on designing and modifying solid surfaces. Here we report an approach to control the orientation of liquid crystals from the free (air) surface side: a skin layer at the free surface was prepared using a non-photoresponsive liquid crystalline polymer film by surface segregation or inkjet printing an azobenzene-containing liquid crystalline block copolymer. Both planar-planar and homoeotropic-planar mode patterns were readily generated. This strategy is applicable to various substrate systems, including inorganic substrates and flexible polymer films. These versatile processes require no modification of the substrate surface and are therefore expected to provide new opportunities for the fabrication of optical and mechanical devices based on liquid crystal alignment.

Photovoltaic Properties of Fungal Melanin

The films of fungal melanin (FM) were fabricated from solution, and also optical and photovoltaic properties of the films and heterostructures with other semiconductors were studied. Color and absorption spectra of studied FM were like in eumelanin. Photovoltage of ITO/FM structures under illumination of the free surface side is 2–3 orders of magnitude lower than in the films of phthalocyanines and polyacenes. The photovoltage of double layer heterostructures of FM with C60, SnCl2 phthalocyanine, sulfonamide zinc phthalocyanine, lead phthalocyanine, pentacene is lower than one in the ITO/FM structures under illumination through the free surface and in organic semiconductor films.

Fabrication and Magnetic Properties of \(\text{Nd}_2\text{Fe}_{14}\text{B/Fe}_{65}\text{Co}_{35}\) Hard Magnetic Ribbons

Nd\(_2\)Fe\(_{14}\)B/Fe\(_{65}\)Co\(_{35}\) hard magnetic ribbons were fabricated by melt-spinning technique using Nd\(_{16}\)Fe\(_{76}\)B\(_{8 }\) and Fe\(_{65}\)Co\(_{35}\) pre-alloys as starting materials. The results showed that the formation of the interactive hard/soft nanocomposite with the homogeneous distribution of the Fe-Co phase throughout the Nd\(_{2}\)Fe\(_{14}\)B matrix provided the Curie temperature (\(T_{c})\) as high as 747 K, the magnetic remanence (B\(_{r}\)) of 8.88 kG and the maximum energy product, (BH)\(_{\max}\), of 16.75 MG.Oe for the fabricated Nd\(_{2}\)Fe\(_{14}\)B/Fe\(_{65}\)Co\(_{35}\) ribbons at the optimal speed of 25 m/s. In addition, the intrinsic coercivity (\(_{i}\)H\(_{c}\)) of 9.27 kOe and remanence coercivity (\(_{b}\)H\(_{c}\)) of 6.94 kOe were found for these ribbons. The roles of the soft Fe\(_{65}\)Co\(_{35}\) phase in the increasing of \(T_{c}\), \(B_{r}\) as well as in the (00l) preferred crystallographic orientation of hard magnetic grains on the free surface side of the fabricated ribbons were also discussed.