Increasing Thickness Ratio Research Articles

Mechanical properties and microstructure of friction stir welded tailor-made blanks

This paper studies the microstructural features and mechanical properties of friction stir welds with dissimilar alloys and different thicknesses. The welds are produced in five different thickness/material combinations from 2024-T3 and 7075-T6 sheets with different thicknesses. A parametric study is conducted to optimize the welding parameters such that the different configurations can be compared. The paper is divided into two chapters: microstructural features and mechanical properties. In the first chapter, a study of the chemical composition and microstructure of the welds shows that a narrow chemical mixing zone is present in the dissimilar-alloy welds and that the stirring zone embodies the union rings and exhibits heterogeneous texture for most configurations. Study of the hardness, tensile properties and fracture surfaces in the second chapter shows that an asymmetric softened region, which is harder at the advancing side and extends more into the retreating side, is formed in the stirring zone and that the mechanical properties decrease as the thickness ratio increases. The fracture was partially ductile and partially brittle for all configurations.

Experimental and Theoretical Approach for Evaluating the Flexural Properties of a Denture Base Material Relined with Three Soft Lining Materials

The present study attempts to evaluate the flexural properties of a denture base material relined with three different soft lining materials and investigate the effects of the thickness of the soft lining materials on the flexural properties of the relined denture base materials. Three commercially available soft lining materials (GC Reline Soft, S ; GC Reline Extra Soft, ES ; and GC Reline Ultra Soft, US) were evaluated. Acrylic resin (GC Acron) was used as the denture base material. The relined denture base specimens were prepared with four different thickness ratios of the soft lining material (mm)/denture base material (mm) : 0.5/2.5, 1/2, 1.5/1.5, and 2/1. Thus, the thickness ratios were set to 0.2, 0.5, 1, and 2. The flexural strengths and moduli of the relined denture base specimens were obtained from the three-point bending test. As a result, the flexural strengths and moduli of the relined denture base specimens tended to decrease in the order of US, ES, an S. For all relined denture base specimens, flexural strength and modulus decreased with increasing thickness ratio. The predicted values obtained by the Euler-Bernoulli composite beam theory showed that the normalized bending rigidity decreased with increasing thickness and elastic modulus ratio of the soft lining material/denture base material, in agreement with the experimental results of the three-point bending test. It was concluded that the flexural properties of the relined denture bases depend on the soft lining material properties such as the lining thickness and lining material type.

Influences of loading direction and thickness ratio on fatigue properties of tailored welded blanks

Fatigue properties of tailored welded blanks with the same material and different thickness were investigated. Fatigue tests of specimens with angles of 0°, 70° and 90° to the laser weld line were performed in order to clarify the influence of loading direction and thickness ratio. The levels of stress range affected the crack initiation areas of the 0° and 90° specimens, and simple heterogeneous mechanical models roughly expressed the macroscopic fracture behavior. The fatigue strength of the 0° specimens was almost the same as that of the base metal. In the 90° specimens, fatigue strength showed a clear decrease under relatively low stress range. Insufficient grinding of the 70° specimen edge caused crack initiation at the weld toe and low fatigue strength. An increase of thickness ratio induced a decrease of fatigue strength of the 90° specimen, although that of the 0° specimens was independent of thickness ratio. Fatigue crack propagation analyses under cyclic stress distribution revealed a close correlation with the test results. These experimental and analytical results were less sensitive to thickness ratio than estimations by elastic stress concentration factors.

Instability of gravity-driven free-surface flow past a deformable elastic solid

The stability of inertialess gravity-driven free-surface flow of a Newtonian fluid down an inclined plane covered with a deformable elastic solid is examined in this work. Although the inertialess flow of a Newtonian fluid down a rigid inclined plane cannot become unstable, the present system can become unstable if the applied strain, which is proportional to the ratio of gravity forces to elastic forces, becomes larger than a critical value. For linear elastic solids, the critical strain and corresponding wave number asymptote to constant values as the ratio of the solid thickness to the fluid thickness increases. In contrast, the critical strain and wave number for neo-Hookean solids continue to decrease as the thickness ratio increases. Examination of the eigenfunctions for the neo-Hookean solid reveals that the difference in the critical conditions is due to a coupling between base state and perturbation quantities in the neo-Hookean model that remains important even for large values of the thickness ratio. The instability arises due to deformability of the solid-fluid interface, and flow past this interface is found to be more stable than when the free surface is absent. The results of this work reinforce the importance of accounting for large displacement gradients in the solid when modeling elastohydrodynamic instabilities, and suggest that results obtained with linear constitutive models may be misleading when multiple interfaces are present.

Shape Effect on Dielectric and Piezoelectric Properties in Multilayer Actuator

This study presents the piezoelectric and dielectric properties of multilayer actuator, being designed to stack ceramic and electrode layers alternatively, under a consideration of structure geometry, the thickness ratio of the ceramic layer to electrode layer. Increases in polarization and electric field-displacement with increasing thickness ratio of the ceramic/electrode layer were attributed to the change of non-180°/180° domain, ratio of which was affected by the internal stress. The piezoelectricity and actuation behaviors were found to be affected by the volume ratio (or thickness ratio) of ceramic layer relative to ceramic layer as well as the magnitude of external electric field.

Impact of reductive N2∕H2 plasma on porous low-dielectric constant SiCOH thin films

Porous low-dielectric constant (low-κ) SiCOH thin films deposited using a plasma-enhanced chemical-vapor deposition have been comprehensively characterized before and after exposure to a reactive-ion-etch-type plasma of N2 and H2 chemistry. The low-κ film studied in this work is a carbon-doped silicon oxide film with a dielectric constant (κ) of 2.5. Studies show that a top dense layer is formed as a result of significant surface film densification after exposure to N2∕H2 plasma while the underlying bulk layer remains largely unchanged. The top dense layer is found to seal the porous bulk SiCOH film. SiCOH films experienced significant thickness reduction, κ increase, and leakage current degradation after plasma exposure, accompanied by density increase, pore collapse, carbon depletion, and moisture content increase in the top dense layer. Both film densification and removal processes during N2∕H2 plasma treatment were found to play important roles in the thickness reduction and κ increase of this porous low-κ SiCOH film. A model based upon mutually limiting film densification and removal processes is proposed for the continuous thickness reduction during plasma exposure. A combination of surface film densification, thickness ratio increase of top dense layer to bulk layer, and moisture content increase results in the increase in κ value of this SiCOH film.

Dielectric and Piezoelectric Properties in Multilayer Structure Actuator

ABSTRACTThe piezoelectricity and polarization of multilayer structure actuators, being designed to stack ceramic layer and electrode layer alternately, were investigated under a consideration of geometry, the thickness ratio of the ceramic layer to electrode layer. The actuators were fabricated by tape-casting of 0.42PbTiO3-0.38PbZrO3-0.2Pb(Mn1/3Nb2/3)03 followed by laminating, burn-out and co-firing process. The actuators of 5 × 5 mm2 in area were formed in a way that 60–200 μm thick ceramics were stacked 10 times alternately with 5 μm thick electrode. Increase in polarization and electric field-displacement with increasing thickness ratio of the ceramic/electrode layer and thickness/cross section ratio were attributed to the change of non-180°/180° domain ratio which was affected by the interlayer internal stress and Poisson ratio of ceramic layer. The piezoelectricity and actuation behaviors were found to be dependent upon the volume ratio (or thickness ratio) of ceramic layer relative to ceramic layer. Concerning with the existence of internal stress, the field-induced polarization and deformation were described in the multilayer actuator.

Sensitivity evaluation of a multi-layered surface plasmon resonance-based fiber optic sensor: a theoretical study

A multi-layered surface plasmon resonance (SPR)-based fiber optic absorption sensor has been studied theoretically. The sensitivity is evaluated for the p-polarized light launched in the fiber using ray approximation. Four-layers configuration is used to excite the surface plasmon wave. The first layer or the medium considered is the core of the fiber. Second and third layers are metallic (silver and gold). The fourth layer or medium is absorbing medium. The effect of the ratio of the thickness of the metallic layers (silver:gold) on the sensitivity of the sensor has been investigated. The sensitivity increases as the silver to gold thickness ratio increases. The gold should be used only to protect silver layer. In addition, the influences of various parameters like numerical aperture (NA), ratio of sensing region length to fiber core diameter, total bimetallic thickness, maximum absorption wavelength, and half maximum width of the sensing medium on the sensitivity of the sensor have been studied. It has been found that the sensitivity is better for the lower off-resonance excitation frequency. Replacing gold by self-assembled monolayers like thiol does not improve sensitivity much. Further, adding ZrO 2 as the fourth layer does not improve the sensitivity of the four layers configuration.

Coercive force calculation of ferromagnetic bilayer

A domain wall structure of a strongly coupled ferromagnetic bilayer was proposed. Based on the proposed domain wall structure, the interface wall width and coercive force of coupled 10nm thick Co/NiFe and Co/Fe bilayers were calculated by minimizing the Néel wall energy. It was found that the coercive force of the Co/NiFe bilayer linearly decreases with increasing thickness ratio of NiFe to total thickness, followed by a rapid drop when the thickness ratio approaches the unit. A linear relation between coercive force and thickness ratio of Fe to total thickness was found at a given thickness for the Co/Fe bilayer.

Effect of geometry on properties of multilayer structure actuator

The piezoelectricity and polarization of multilayer actuator, being designed to stack ceramic layer and electrode layer alternately, were investigated under a consideration of geometry, the thickness ratio of the ceramic layer to electrode layer. The actuators were fabricated by tape-casting of 0.42PbTiO 3–0.38PbZrO 3–0.2Pb(Mn 1/3Nb 2/3)O 3 followed by laminating, burn-out and co-firing process. The actuators of 5 × 5 mm 2 in cross section size were formed in a way that 50 ∼ 200 μm thick ceramics were stacked 10 times alternately with 5 μm thick electrode. Increase in polarization and electric field-displacement with increasing thickness ratio of the ceramic/electrode layer and thickness/cross section ratio were attributed to the change of non-180/180° domain ratio which was affected by the interlayer internal stress and poisson ratio of ceramic layer. The piezoelectricity and actuation behaviors were found to depend upon the volume ratio (or thickness ratio) of ceramic layer relative to ceramic layer. Comparing with the experimental results and simple calculation based on the existence of the internal stress, the relationship between field-induced deformation and the geometric structure in the actuator was described.

Effect of geometrical factors on the mechanical properties of Si 3N 4/BN multilayer ceramics

The relationships between mechanical properties of Si 3N 4/BN multilayer materials and the geometrical factors, number of layers ( N) and layer thickness ratio ( λ h), have been studied. At a given number of layers, with the increase of layer thickness ratio, the toughness and bending strength both increase, and when it continues to increase, the two curves both level off. Keeping the layer thickness ratio of about 10 and increasing the number of layers, the bending strength decreases slightly, and a maximum toughness was obtained at N≈30. Furthermore, a mechanical model was established and used to analyze the above experimental results. According to the experimental and calculated results, suitable geometrical parameters were advised in the design of Si 3N 4/BN multilayer materials as λ h≈10 and N≈30.

Tailor-welded blanks of different thickness ratios effects on forming limit diagrams

In this paper, the objective is to study the thickness ratio effects of TWBs on forming limit diagrams (FLDs). Tailor-welded blanks (TWBs) of the same material but with different thickness combinations were welded together to form a single part before the formability tests. Thus, SPCC steel sheets of thickness 0.5, 0.6, 0.8 and 1.0 mm were studied and combined to form TWBs of different thickness ratios of 2 (0.5/1.0 mm), 1.67 (0.6/1.0 mm) and 1.25 (0.8/1.0 mm). An Nd:YAG laser was used to weld the tailor-made blanks before the formability tests of the uniaxial tensile test and the Swift test. The experimental findings show that TWBs of different dimensions and radii of cut-off yield different major strain and minor strain values of the FLD. The uniaxial tensile tests show that there are no significant differences between the tensile strengths of TWBs and their relative base metals. In addition, the FLDs of the TWBs indicate that both the level of the forming limit curves and the minimum major strain value decreases as the thickness ratio increases. This implies that the higher is the thickness ratio, the lower is the formability of the TWBs.

Dynamic stability of rotating composite beams with a viscoelastic core

The dynamic stability of a rotating composite beam with a constrained damping layer subjected to axial periodic loads is studied by the finite element method. The unstable regions for simple and combination resonant frequencies are determined by applying Hsu’s procedure to the Mathieu equation. The effects of rotating speed, setting angle and hub radius ratio on the unstable regions are presented. The influences of core thickness ratio and core loss factor on the unstable regions are also studied. The regions of dynamic instability for various parameters are discussed. The rotating composite beam is more stable as the rotating speed, hub radius ratio, core thickness ratio and core loss factor increase. The rotating composite beam is more unstable at the large setting angle.

Solitary waves in a thick walled elastic tube

In the present work, we studied the propagation of solitary waves in a prestressed thick walled elastic tube filled with an incompressible inviscid fluid. The efects of wall inertia and shear deformation are taken into account in determining the inner pressure–inner cross-sectional area relation. Using the reductive perturbation technique, the propagation of weakly nonlinear waves in the long wave approximation is investigated and the Korteweg–de Vries equation is obtained as the evolution equation. Due to dependence of the coefficients of the governing Korteweg–de Vries equation on the initial deformation, the material parameters and the thickness ratio, it is observed that the solution profile changes with these parameters. The numerical calculations indicate that for engineering materials (small α) the wave profile gets steepened with increasing thickness ratio, whereas for soft biological tissues the wave profile is not so sensitive to the thickness ratio but it is quite sensitive to the material nonlinearity characterized by the coefficient α. This shows that for biological tissues the material nonlinearity is more important than the geometrical nonlinearity.

Radiative Heat Transfer through Mold Flux Film during Initial Solidification in Continuous Casting of Steel.

Absorption coefficient and extinction coefficient for various commercial mold fluxes have been determined to quantify the radiative and the total heat transfer through the flux film in continuous casting mold. The absorption coefficient is found to be less than 1000 m-1 for glassy specimens whereas the extinction coefficient is ca. 3000-30000 m-1 for crystalline ones. Comparison of observed with calculated radiative heat flux from the absorption coefficient has shown that gray gas approximation is valid for evaluating the radiative heat flux across the mold flux film. Numerical calculation for both radiative and conductive heat transfer has been carried out for a given total thickness of the flux film. Despite little difference in optical properties among various mold fluxes, the radiative heat flux through molten layer of the flux films for low carbon and ultra low carbon steel is found larger than that for medium carbon steel. This is due to increasing thickness ratio of molten layer to crystalline layer of flux films. Solidifying and crystallizing behavior of mold fluxes is a key factor to control the radiative heat transfer in continuous casting mold, accordingly.

Effects of Shear Deformation and Rotary Inertia on the Free Vibration of a Rotating Annular Plate

This Tech Brief addresses the effects of shear deformation and rotary inertia on the free vibration of a rotating annular plate. Several studies have been done to understand these effects (Irie et al, 1982; Sinha, 1987). In particular, the importance of these terms is well known for disks with a thickness ratio h/a > 0.05 where h is the thickness of the disk and a is its outer radius. However, there is a need to show how they affect the disk vibration as the thickness ratio increases. It is well accepted that shear deformation and rotary inertia should be included in the analysis when h/a > 0.05 (Batoz and Dhatt, 1990). However, this Tech Brief will show that this criterion is not valid for all the modes. It will present the evolution of the number of modes correctly evaluated versus the thickness ratio, and, finally, will give a heuristic criterion to predict when it is necessary to consider shear deformation and rotary inertia.

The effect of shear stress on solitary waves in arteries

In the present work, we study the propagation of solitary waves in a prestressed thick walled elastic tube filled with an incompressible inviscid fluid. In order to include the geometric dispersion in the analysis the wall inertia and shear deformation effects are taken into account for the inner pressure-cross-sectional area relation. Using the reductive perturbation technique, the propagation of weakly non-linear waves in the long-wave approximation is examined. It is shown that, contrary to thin tube theories, the present approach makes it possible to have solitary waves even for a Mooney-Rivlin (M-R) material. Due to dependence of the coefficients of the governing Korteweg-deVries equation on initial deformation, the solution profile changes with inner pressure and the axial stretch. The variation of wave profiles for a class of elastic materials are depicted in graphical forms. As might be seen from these illustrations, with increasing thickness ratio, the profile of solitary wave is steepened for a M-R material but it is broadened for biological tissues.

The effect of shear stress on solitary waves in arteries.

In the present work, we study the propagation of solitary waves in a prestressed thick walled elastic tube filled with an incompressible inviscid fluid. In order to include the geometric dispersion in the analysis the wall inertia and shear deformation effects are taken into account for the inner pressure-cross-sectional area relation. Using the reductive perturbation technique, the propagation of weakly non-linear waves in the long-wave approximation is examined. It is shown that, contrary to thin tube theories, the present approach makes it possible to have solitary waves even for a Mooney-Rivlin (M-R) material. Due to dependence of the coefficients of the governing Korteweg-deVries equation on initial deformation, the solution profile changes with inner pressure and the axial stretch. The variation of wave profiles for a class of elastic materials are depicted in graphic forms. As might be seen from these illustrations, with increasing thickness ratio, the profile of solitary wave is steepened for a M-R material but it is broadened for biological tissue.

Structure and magnetic properties of magnetron-sputtered Fe/Cu multilayered thin films.

The structure and magnetic properties of Fe/Cu multilayered films with a constant total Fe thickness of 1050 \AA{} but varying Fe-layer thickness from 6.3 to 42 \AA{} and varying Cu to Fe thickness ratio from 1 to 3 were investigated using x-ray diffraction (XRD), x-ray absorption fine-structure (XAFS) spectroscopy, and magnetic measurements. Samples were prepared at room temperature on mica, glass, and silicon substrates using the dc-magnetron-sputtering method. For films with the same Fe-layer thickness, it was found that the magnetic moment of Fe decreases with increasing thickness ratio of Cu to Fe. For films with a Cu to Fe thickness ratio of 3, it was found that the magnetic moment of Fe decreases with decreasing thickness of the individual Fe layers. XRD and XAFS results revealed that in the multilayered films, Cu has a well-defined fcc structure with minimal amount of structural disorder independent of the individual layer thickness or thickness ratio. On the other hand, quantitative analysis of EXAFS data revealed that the crystal structure of Fe changes with decreasing thickness of the Fe layers from distorted bcc (for 42- and 21-\AA{}-thick Fe layers) to fcc (for 10.5- and 6.3-\AA{}-thick Fe layers) in films with the Cu layer three times thicker than the Fe layer. The single-phase fcc Fe of the 6.3-\AA{} Fe/19-\AA{} Cu multilayered film was found to have a lattice constant of 3.596 \AA{} and is ferromagnetic with a Curie temperature of 210 K and a spontaneous magnetization of \ensuremath{\sim}690 emu/${\mathrm{cm}}^{3}$.

骨組溶接構造体の変形能に及ぼす鋼材変形特性の影響

Deformability of welded frame-structures in buildings is greatly affected by mechanical properties, especially work-hardening behaviors of steels on deformability of welded frame-structures, bending tests of specimens having a column-beam connection (H-shape beam) were carried out. For these experiments SM41B steel, SM50B steel and two kinds of HT60 steels with the different yield to tensile ratio were used.Main results obtained are summerized as follows.(1) Local buckling occurs and develops first in flange and then in web of the H-shape beams under the bending load. The maximum plateau of load-deflection curve on the H-shape beam is attained after the local buckling in web. The maximum load depends on the geometry of the H-shape beam, and decreases as the width to thickness ratio increases.(2) The maximum load value in H-shape beam is greatly affected by the tensile strength of steels used. Deflection at the load point and the absorbed energy of beam up to the maximum load, which are typical measures of the deformability of frame structures, depend on the yild to tensile ratio and uniform elongation (eT) of steels. Beams made of steels with lower yield to tensile ratio have larger deformability.(3) In order to improve the deformability of beam using steels with small eT, it is effective to enlarge their eT.(4) H-shape beam with scallop has a possibility of fracturing from the corner of the scallop.