Static mechanics analyses of different laser weld bonding structures in joining AZ61 Mg alloy

This paper presents the results of recent investigations on laser seam weld bonding (LWB) of magnesium alloy AZ61 sheets. There are two types of LWB structures: perpendicular weld seam (LWB-PE) and parallel weld seam (LWB-PA). In this paper the differences between the two structures are compared and discussed. In tensile shear tests, both LWB-PE and LWB-PA joints can offer higher failure force than that of laser welding or adhesive bonding alone, and LWB-PA joint offers better performance than LWB-PE joint. This is because the weld seam can increase the peel resistance at the free end of the adhesive bonded part, where a stress concentration exists. Maximum T-Peel strengths of LWB joints depend on the laser seam weld. The LWB-PA joint has both the advantages of maximum failure force caused by laser weld and the peel displacement caused by adhesive, so a synergistic effect is obtained in energy absorption.     

The role of the hydrogen bonding network for the shear modulus of PIPD

Ab initio total energy calculations at the DFT-GGA level for PIPD are reported. Both the monoclinic crystal with a bi-directional hydrogen-bond network and the triclinic crystal with a sheet-like network are studied. It is concluded that the latter is the more plausible microstructure for the fibre based on the following: (i) After optimisation of the lattice parameters and atomic positions it has a lower energy. (ii) The calculated internal shear modulus agrees better with experiment. (iii) The minimal shear stiffness constant, which is interpreted as the upper limit on the compressive strength, compares favourably with the experimental compressive strength.The hydrogen bonding network plays a crucial—but indirect—role in explaining the high compressive strength. It replaces the weak components of the lateral bonding, such as present in many high performance polymer materials with low compressive strength, e.g. PBO and PBZT, with much stronger hydrogen bonds. This makes that in PIPD the relatively strong π-π interaction has the weakest resistance against shear.     

Young's modulus of isotropic porous materials with spheroidal pores

Based on the Eshelby solution for the single-inclusion problem and Wu's specification of this solution to spheroidal pores, we show that the Eshelby–Wu coefficients for Young's modulus, in contrast to their counterparts for the bulk and shear moduli, are quite insensitive to changes of the Poisson ratio. Therefore the Eshelby–Wu coefficients of Young's modulus can be described (to a very good approximation) by a unique function of the aspect ratio, which is calculated in this paper and for which a master curve is obtained by segment-wise fitting. Also the implementation of the Eshelby–Wu coefficients into the well-known effective medium approximations (Maxwell, self-consistent, differential) and our exponential relation is discussed. Irrespective of the model into which the Eshelby–Wu coefficients are implemented, prolate pore shape affects the porosity dependence of Young's modulus only very weakly, whereas oblate pore shape can lead to an arbitrary reduction of Young's modulus.     

A re-examination of the elastic modulus dependence on crystallinity in semi-crystalline polymers

The elastic modulus versus crystallinity linear relationship in Polyethylene (PE) is re-examined via meticulous measurements over a wide set of PE. First, large discrepancies to linearity are observed; moreover, Raman spectroscopy revealed that the content of the so-called interphase exhibits considerable variations over the set of PE. Therefore a novel strategy based on DMA is developed for a better identification of the modulus of each phase along the temperature.On the one hand, below the α and β relaxations, the young modulus proved to be linearly dependant on the sum of the crystal and interphase content. On the other hand, between the α and β relaxations, the interphase appears surprisingly as stiff as the crystal. In addition, the quenched samples exhibit a particular behavior. A simple model has lead to the conclusion that their mechanical coupling and/or amorphous modulus are significantly different as compared with all others materials.     

YM-1非硫化型点焊密封剂的研制与应用

概述了ＹＭ－１非硫化型点焊密封剂的组份、性能与应用,为ＹＭ－１非硫化型点焊密封剂的应用提供了使用依据。     

Separation of the effects of pH and polymer concentration on the swelling pressure and elastic modulus of a pH-responsive hydrogel

The elastic shear modulus G and swelling pressure ω are studied for a basic, pH-responsive hydrogel synthesized by crosslinking copolymerization of co-monomers hydroxypropyl methacrylate and N,N-dimethylaminoethyl methacrylate with crosslinker tetraethylene glycol dimethacrylate. Under normal conditions of use as a “smart” material, hydrogel swelling ratio Q and pH vary simultaneously, but here G and ω values are presented as a function of pH with Q held constant and vice versa. At fixed pH, G decreases with increase in Q in a power law dependence, as predicted by the Flory-Rehner model. However, at fixed Q, G increases with decrease in pH (i.e., increase in degree of ionization). The pH effect is more pronounced than the volume effect, thus the hydrogel stiffens as it swells in response to pH change. At high pH, ω values of the uncharged hydrogel obey the Flory-Rehner model, whereas explicit ionic contributions can be identified at lower pH values.     

Microstructure and interface-adhesion of thermally sprayed continuous gradient elastic modulus FeCrAl-ceramic coatings

The bond strength between thermally sprayed metal bond-coats and ceramic top-coats is a key factor in determining their service life. However, most studies focus on interface modifications. In this research, based on FeCrAl bond-coats prepared by arc spraying, top-coats (Al₂O₃-40 wt% TiO₂) were prepared by plasma spraying, and heat treatment was carried out in a hypoxic atmosphere. Continuous gradient elastic modulus FeCrAl-ceramic coatings were successfully prepared, and the microstructural and mechanical properties from the substrate to the top-coats were systematically investigated. The Al₂O₃ content gradually decreased from the top-coats to the substrate, forming continuous gradient elastic modulus FeCrAl-ceramic coatings. The oxide formed during the heat treatment filled the defects in the bond-coats and greatly improved the mechanical properties of the coating. The bonding strength of the continuous gradient elastic modulus coating was 21.7% greater than that of the as-received coating.     

Influence of plasma ionization on the elastic modulus and tribology behavior of carbon films deposited by the HiPIMS technique

This work reveals the influence of discharge current on carbon-ion energies of plasma, elastic modulus, and friction coefficient at the nano- and macroscale of carbon films deposited via high-power impulse magnetron sputtering. Three applied discharge current conditions in deposition processes were employed to obtain three-carbon films of interest. The number of carbon ions with their energies was obtained via mimic tests of the deposition process using three similar discharge currents through a quadrupole mass spectrometer detector based on the time-averaged ion energy distribution function. The bonding structure of the films was evaluated using Raman spectroscopy, fitting the Diamond and Graphite peaks to obtain a semiquantitative analysis. The elastic modulus of the carbon films was determined from atomic force acoustic microscopy measurements avoiding the influence of the substrates. The friction coefficient was analyzed at the nanoscale via atomic force microscopy and at the macroscale via tribometry. Significant alterations were observed in the number and energy level of the carbon ions with the variation of discharge current. These alterations significantly influenced the bonding properties, elastic modulus, and tribology behavior. A higher elastic modulus and higher sp³ bond content were observed for the film with a lower number of carbon ions and less energy.     

Influence of side branch on the elastic modulus of ethylene–tetrafluoroethylene terpolymers

Influence of side branches on the storage modulus of ethylene–tetrafluoroethylene (ETFE) terpolymers has been investigated on the basis of dynamic mechanical analysis. The terpolymer containing short branches (CF₃) has been found to behave in a different manner from the case of long branches (C₄F₉). The storage modulus was found to depend sensitively on the content of branches and also the degree of crystallinity in the case of terpolymer with long branches, while the modulus did not change very much for the sample with short branches even when the crystallinity was changed remarkably. The storage modulus of the terpolymer with long branches was found to behave similarly to that of ETFE copolymer without any branch. These differences were successfully interpreted on the basis of mechanical series model of crystalline and amorphous phases, where the modulus of the bulk sample is dependent sensitively on Young's modulus of the crystalline region. The short branches (CF₃) are included in the crystal lattice and the crystal lattice is expanded with an increment of branch content, resulting in the remarkable decrease in Young's modulus of the crystal lattice. The long branches (C₄F₉) are on the other hand, excluded out of the crystal lattice and Young's modulus of the crystal region is not affected very much. This difference in Young's modulus of the crystal lattice reflects on the different behavior of the modulus of the bulk sample as mentioned above.     

Comparison of experimental and theoretical transverse elastic modulus of carbon fibers

The transverse elastic modulus of PAN-based carbon fibers as measured by experimental methods, calculated from theoretical equations and analyzed by the finite element method (FEM) is discussed. Raman spectroscopy was the primary method utilized to measure the transverse elastic modulus of carbon fibers in carbon-fiber reinforced plastics (CFRP). A lead oxide (PbO) thin film was deposited on the surface of a CFRP specimen using physical vapor deposition as the pretreatment in order to measure the strains of the carbon fibers and epoxy matrix phases by Raman spectroscopy. Since the relation between the Raman peak wave number of PbO thin films and tensile strain has already been developed, the transverse strain of the carbon fibers could be measured. The transverse strain of the carbon fibers was analyzed using a 2-D FEM model. The transverse modulus of the carbon fibers was determined by fitting the experimental result from Raman spectroscopy to the FEM model. The determined transverse modulus (10.4 GPa) is compared with those experimentally measured by nanoindentation (13.4 GPa), numerically analyzed using 2-D and 3-D FEM models (5.25 GPa and 28.7 GPa, respectively), and theoretically calculated from the Mori-Tanaka, Halpin-Tsai, and Uemura equations (24.8 GPa, 17.4 GPa, and 28.4 GPa, respectively).     

Effect of focusing flow on stationary spot machining properties in elastic emission machining

Ultraprecise optical elements are applied in advanced optical apparatus. Elastic emission machining (EEM) is one of the ultraprecision machining methods used to fabricate shapes with 0.1-nm accuracy. In this study, we proposed and experimentally tested the control of the shape of a stationary spot profile by introducing a focusing-flow state between the nozzle outlet and the workpiece surface in EEM. The simulation results indicate that the focusing-flow nozzle sharpens the distribution of the velocity on the workpiece surface. The results of machining experiments verified those of the simulation. The obtained stationary spot conditions will be useful for surface processing with a high spatial resolution.     

Prediction of macroscopic effective elastic modulus of micro-nano-composite ceramic tool materials based on microstructure model

In order to investigate the effect of microstructure parameters on the elastic modulus, based on the microstructure model represented by Voronoi tessellation, the reasonable macro-micro connection and boundary conditions were proved through the Hill’s lemma, and the uniaxial tensile process of composite ceramic tool materials was simulated. The influences of grain size, second phase volume fraction and nanoparticle volume fraction on elastic properties were studied through numerical simulation, and the elastic modulus of composite ceramic tool materials was predicted. The results showed the elastic modulus of Al₂O₃-based ceramic tool materials could be increased effectively with the contents of the second phase TiB₂ and nano-particle TiC being 20% and 10%, respectively. The numerical simulation results were in good agreement with the experimental results.     

The influence of hydrogen bonding on mechanical anisotropy in oriented nylon-12

The anisotropy of dynamic tensile modulus in uniaxially and uniplanar-axially oriented nylon-12 sheets has been measured over the temperature range encompassing the α′-relaxation process. The influence of hydrogen bonding on the mechanical behaviour has been demonstrated by comparing these anisotropy measurements for specimens which have been subjected to different thermal treatments.     

Studies on delayed ettringite formation in early-age, heat-cured mortars: I. Expansion measurements, changes in dynamic modulus of elasticity, and weight gains

Mortars were prepared from laboratory cements blended from a set of six representative ground clinkers and Terra Alba gypsum. The addition of gypsum was such that cements containing 1% SO₃ less than the optimum SO₃ content, the optimum SO₃ content, and 1% greater than the optimum SO₃ content were produced. Mortar bars and mortar cubes containing each of these cements were exposed to continuous room temperature (23 °C) curing, or to early-age curing cycles involving maximum temperatures of 55 and 85 °C, followed by long-term exposure at 100% RH over water, but not immersed in water. Measurements of expansion, dynamic elastic modulus, and weight gain were recorded at intervals of up to 900 days. Severe cracking and prominent delayed ettringite formation (DEF)-induced expansions were observed in 85 °C cured mortar bars derived from four of the six “oversulfated” cements. Much smaller expansions were observed in mortar bars from two cements with optimum SO₃ content cements also cured at 85 °C. No expansion or other visible indication of distress was observed for any of the 55 °C or continuously room-temperature-cured mortars. The dynamic elastic modulus increased progressively on prolonged exposure for the unaffected mortar bars, but it decreased precipitously after the onset of expansion in affected mortar bars. Significant weight increases also accompanied the processes of expansion. Mortars that showed severe cracking and deterioration when exposed as mortar bars suffered almost no visible damage when exposed as cubes.     

胶层尺寸对单搭胶接接头性能的影响研究

针对汽车车身中应用日益广泛的钢板胶接结构,通过试验得到了不同胶层尺寸对胶接接头承载能力的影响规律,建立了钢板单搭接头的三维弹塑性有限元模型,分析了胶层尺寸对胶接接头应力分布的影响.研究结果表明:随着胶层厚度的增加,胶接件的承载能力呈先升后降的趋势,合理的胶层厚度应为0.3-0.5 mm;无论胶层厚度为多少,增加搭接区域胶层的长度或宽度.均会提高胶接件的承载能力.     

Isothermal and adiabatic Young's moduli of alumina and zirconia ceramics at elevated temperatures

The elastic moduli (Young's moduli) of alumina and zirconia ceramics with porosities ranging from almost dense (2–3%) to highly porous (46–52%), the latter prepared with starch as a pore-forming agent, have been measured via impulse excitation and four-point bending tests from room temperature up to more than 1200 °C. It is shown that, independent of the temperature and the material, the porosity dependence of the Young's modulus is well predicted by our exponential relation and that, irrespective of porosity, the temperature dependence follows a master curve that is characteristic of the material (for alumina exhibiting a decrease with a gradually growing tangent slope and for zirconia exhibiting a steep decrease with an inflection point at moderately elevated temperatures below 400 °C). Differences between isothermal (static) and adiabatic (dynamic) values are negligible as long as the materials are purely elastic (i.e. at temperatures below approximately 1000 °C).     

The effect of coal properties on the viscosity of coal-water slurries

Studies on coal-water slurries (CWSs) have been conducted for many years to replace fuel oil. In this research project, the effect of coal properties on CWSs have been investigated using two Turkish coals of different ranks and a Siberian bituminous coal. Physical, chemical and surface properties of coal samples were determined. Furthermore, adsorption tests were carried out in order to put forward the effect of additive adsorption on the viscosity of CWSs. Viscosity measurements were realized for CWSs of various solid ratios by weight that were prepared using coal samples having mean particle sizes of 19, 35 and 50 μm.     

Effect of plasma sprayed and laser re-melted Al2O3 coatings on hardness and wear properties of stainless steel

Commercially available austenic stainless steel substrate was coated with commercially available, raw Al₂O₃ powder applied by means of plasma spraying method and then re-melted with CO₂ laser beam of various parameters. Tribological and mechanical properties of the 120 J/mm and 160 J/mm laser re-melted coatings were compared with the tribological and mechanical properties of the “as-sprayed” coating. The influence of the laser beam of various parameters on the microstructure, phase constituents, and mechanical and tribological properties of the ceramic coating was investigated by means of scanning electron microscopy, light microscopy, computer tomography, X-ray diffraction technique and nanoindentation tests. The micro sliding wear performance of the coatings was tested using a nanoindenter. The study showed an improvement of the mechanical and tribological properties caused by the laser treatment. The best results were achieved for coating re-melted with 120 J/mm laser beam.     

Effect of microstructure on the viscosity of hard sphere dispersions and modulus of composites

Results from theory and experiment in the literature for the viscosity of dispersions of monodisperse hard spheres are contrasted to highlight the effects of particle microstructure, such as ordered spatial distributions versus random or partially aggregated dispersions. Hard spheres, comprising a simple ideal limit with no interparticle forces other than infinite repulsion at contact, are achieved experimentally by either minimizing van der Waals attractions or negating them with short range repulsions. For dispersions, the balance between viscous forces and Brownian motion, as gauged by the Peclet number Pe, determines the microstructure and, hence, the viscosity. This results in a progression from isotropic equilibrium at Pe = 0, a small perturbation oriented in the principle direction of strain for Pe 1, two-dimensional anisotropy for Pe 1, and a return to isotropy, albeit hydrodynamicaUy dominated, at Pe = ∞. The viscosities for hard spheres vary in the order η_hyd(Pe = ∞) η₀(Pe1) η_∞(Pe 1)η'_∞'(Pe = 0). The first three represent steady shear viscosities, while the last results from high frequency, small amplitude oscillations. At low Peclet numbers, both aggregation owing to short range attractions and long range repulsions increase the steady shear viscosity. With permanent aggregates the effect persists to Pe = ∞, with the data available for η_hyd indicating a monotonic increase with degree of aggregation. Hence, these results for hard spheres generally represent limiting cases. A fundamental connection also exists between composites of hard particles in an incompressible, elastic continuous phase and dispersions of spheres with a corresponding microstructure. The analogy between Hookean elasticity and Stokes flow means that the static shear modulus of the former, normalized by the modulus of the continuous phase, equals the high frequency limiting relative viscosity of the latter. A combination of data and rigorous theory demonstrates that the modulus of a composite decreases in the order: simple cubic> random> body centered cubic> face centered cubic, that is, in order of increasing distance between nearest neighbors at the same volume fraction.