The distributed dislocation technique for calculating plasticity-induced crack closure in plates of finite thickness

An analytical method for calculating plasticity-induced fatigue crack closure in plates of finite thickness is presented. The developed method utilizes the distributed dislocation technique (DDT) and Gauss-Chebyshev quadrature. Crack tip plasticity is incorporated by adopting a Dugdale type strip yield model. The finite plate thickness effects are taken into account by using a recently obtained three-dimensional solution for an edge dislocation in an infinite plate. Numerical results for the ratio of the size of the crack tip plasticity zones are presented for the cases of uniform thickness wake and linearly increasing wake for a range of plate thickness to crack length ratios and applied load ratios. The results show a very good agreement with previous analytical solutions in the limiting cases of very thick and very thin plates. Further results for the opening stress to maximum stress ratio are also provided and are compared with known three-dimensional finite element (FE) solutions. A good agreement is observed. The developed method is shown to be an effective and very powerful tool in modeling the crack closure phenomenon.     

Inversion of transmission ellipsometric data for transparent films

Transmission ellipsometry measures the real and imaginary parts of the ratio τ = t(p)/t(s), where t(s), and t(s) are the transmission amplitudes for thep and s polarizations. For a homogeneous layer, the unknowns to be determined are the layer dielectric constant ε = n(2) and the layer thickness Δz. For nonabsorbing films the thickness can be eliminated, and an algebraic equation for e results. This equation is reduced to a quadratic equation. The thickness is then analytically determined also. The effect of measurement errors on the deduced dielectric constant and layer thickness is discussed. Inversion of thin-film data is also considered.     

An analytical model for bending and springback of bimetallic sheets

Springback is an inevitable phenomenon due to elastic redistribution of internal stresses occurring in sheet metal forming operations. Most of the research reported in this area has been concerned with the components formed from single metal. This article deals with the analytical solution for prediction of springback in bending of bimetallic sheets. A mathematical model is derived based on Woo and Marshall's constitutive equation, considering logarithmic strain (nonlinear) distribution across the thickness and thickness change during bending. Analytical modeling, based on logarithmic strain distribution across the thickness, can be used for accurate springback predictions in the case of smaller bend radius to the thickness ratio. The results of the springback and thickness change are validated using experimental results for the aluminum sheet layered with steel. Further, springback variation in bimetallic sheets is studied, with a change in material properties and thickness of each layer.     

Through thickness stress distributions in pultruded GRP materials

This paper describes an experimental methodology for determining the through thickness properties of pultruded GRP materials and their application in finite element analysis (FEA) of adhesively bonded joints. The finite element analysis is validated using an infra-red thermography based experimental mechanics technique known as thermoelastic stress analysis. The obtained results show that the measured through thickness values fall within the assumed bounds of previous work and have highlighted that interactions between the fibres and resin in the through thickness direction are present but not in a particularly intuitive manner. Moreover, the work presented herein highlights that the value of shear modulus used in the numerical model is an important consideration.     

Piezoelectric tantalum pentoxide studied for optical tunable applications

Piezoelectric transparent thin films are of great interest for use in tunable filters. We present experimental results on Ta2O5 single layers coated on fused-silica substrates with an electron-beam deposition process. Above 450 degrees C, coatings change from an amorphous to a polycrystallized structure. When this structure shows a preferred orientation matching the piezoelectric tensor of the Ta2O5 crystal and the external electric field, variation in the piezoelectric layer thickness is expected. We detail experimental results in terms of optical (spectrophotometric and scattering measurements) and nonoptical characterizations (x-ray diffraction and scanning electron microscopy). Then the resultant thickness variation under oscillating applied voltage is measured with an extrinsic Fabry-Perot interferometer setup.     

Increasing biosensor response through hydrogel thin film deposition: Influence of hydrogel thickness

An impedance sensor has been covered with an ultrathin film of the hydrogel poly(hydroxyethyl methacrylate) (pHEMA) by initiated chemical vapor deposition (iCVD) and the influence of the film thickness has been evaluated. The deposited film swells rapidly and reversibly in solution allowing the passage of the analyte. Electrochemical impedance spectroscopy (EIS) shows that the film decreases the electrodes impedance with and without black platinum and the deposited thickness is a parameter to control due to the high influence in the impedance measurement results.     

In-plane P-SV waves from a piezoelectric strip actuator: exact versus effective boundary condition solutions

A piezoelectric strip of finite width and thickness is placed on top of an isotropic elastic half space. It operates in actuator mode, and a time harmonic voltage is thus applied across it. The piezoelectric material is of type 6 mm oriented so that a two-dimensional (2-D) in-plane (P-SV) problem results. By Fourier series expansions, the problem is solved exactly, and this result is compared to the case when the piezoelectric strip is replaced by an effective boundary condition, which is derived by series expansions in the thickness coordinate in the piezoelectric strip. At low frequencies, the results agree very well, and this corresponds to the situation often met in practice. In general, the effective boundary condition should be much easier to apply, for example when a finite element method (FEM) program is used.     

Effects of step slope on thickness measurement by optical interferometry for opaque thin films

Optical interferometry is a simple, quick and cheap method to measure the thickness of opaque thin films. The film edge, being formed as a step on the sample surface, is lighted with monochromatic light in an interference microscope, producing the interferogram that is recorded with a CCD camera. The film thickness (step height) is calculated by measuring offsets of the fringes across the step. However, the morphology of the film edge (step) significantly affects the thickness measurement, in some cases even yields false results. In this work, three kinds of methods were adopted to mask a part of the substrate surface during the deposition for fabrication of the step. The mask used was a thin silicon slice, a straight line of ink imprinted by a pen, or an Aluminum film. The step morphology recorded by a profilometer revealed large variation from one method to another. Accordingly, the accuracy of film thickness (step height) measurement by interferometry varies significantly. Results showed that large error occurs when the slope of the step is small and the step out spans the view field of the microscope. Therefore, the step should be fully visible in the view field of the microscope for reasonable measurement of thickness. A simple equation, in terms of geometrical configuration, is developed for this requirement.     

Fe-Mo/Al_2O_3催化剂催化分解甲烷制备碳纳米管:温度对碳管结构的影响

利用化学气相沉积法,以Fe-Mo/Al_2O_3为催化剂,催化分解甲烷气体制备碳纳米管(CNTs).研究了温度,反应时间和气体流速对碳纳米管结构的影响.结果显示:温度是影响碳纳米管壁厚的关键参数.低温导致壁厚为2 nm～7 nm的多壁碳纳米管(MWCNTs)的生成.相对地,高温有利于双壁碳纳米管(DWCNTs)的生长,而更高的温度促使单壁碳纳米管(SWCNTs)的产生.进一步升高温度,得到了壁厚为3 nm～15 nm的MWCNTs和大的炭颗粒.     

The Impact of Preheating and Postcooling on Critical-to-Quality Characteristics in Hot-Dip Galvanizing

Hot-dip galvanizing (HDG) is a widely used method for protecting steel against corrosion to ensure structure's life expectancy. The HDG process includes surface preparation, galvanizing, and posttreatment operations where multiple stage parameters are controlled to ensure the optimal utilization of zinc to achieve expected results at minimum cost. In this experimental study, we investigated the influence of preheating temperature and the postcooling methods on critical-to-quality (CTQ) characteristics in HDG at various sample thicknesses. Measured CTQ characteristics included the thickness, hardness, roughness, and microstructure of the coated layers. Obtained results showed that coating thickness decreased as preheating temperature increased and as sample thickness decreased. The selection of the postcooling method impacts largely coating hardness and surface roughness both increased as the thickness of the specimen increased and as the preheating temperature increased. Microstructure analysis of coatings illustrated that there was an increase in the variation of readings as the sample thickness increased and as the preheating temperature decreased. Therefore, HDG parameters must be tuned to account for variations in the thicknesses of galvanized structures to better ensure life expectancy.     

Simulation and modeling of self-assembled monolayers of carboxylic acid thiols on flat and nanoparticle gold surfaces

Quantitative analysis of the 16-mercaptohexadecanoic acid self-assembled monolayer (C16 COOH-SAM) layer thickness on gold nanoparticles (AuNPs) was performed using simulation of electron spectra for surface analysis (SESSA) software and X-ray photoelectron spectroscopy (XPS) experimental measurements. XPS measurements of C16 COOH-SAMs on flat gold surfaces were made at nine different photoelectron emission angles (5-85° in 10° increments), corrected using geometric weighting factors and then summed together to approximate spherical AuNPs. The SAM thickness and relative surface roughness (RSA) in SESSA were optimized to determine the best agreement between simulated and experimental surface composition. On the basis of the glancing-angle results, it was found that inclusion of a hydrocarbon-contamination layer on top the C16 COOH-SAM was necessary to improve the agreement between the SESSA and XPS results. For the 16 COOH-SAMs on flat Au surfaces, using a SAM thickness of 1.1 ?/CH(2) group, an RSA of 1.05, and a 1.5 ? CH(2)-contamination overlayer (total film thickness = 21.5 ?) for the SESSA calculations provided the best agreement with the experimental XPS data. After applying the appropriate geometric corrections and summing the SESSA flat-surface compositions, the best fit results for the 16 COOH-SAM thickness and surface roughness on the AuNPs indicated a slightly thinner overlayer with parameters of 0.9 ?/CH(2) group in the SAM, an RSA of 1.06 RSA, and a 1.5 ? CH(2)-contamination overlayer (total film thickness = 18.5 ?). The 3 ? difference in SAM thickness between the flat Au and AuNP surfaces suggests that the alkyl chains of the SAM are slightly more tilted or disordered on the AuNP surfaces.     

Opaque optics thickness measurement using a cyclic path optical configuration setup and polarization phase shifting interferometry

Thickness measurement of an opaque optics using a cyclic path optical configuration (CPOC) setup and polarization phase shifting interferometry (PPSI) is presented. The CPOC setup is used to simultaneously focus two orthogonally polarized counterpropagating converging beams at its hypotenuse arm. The opaque optics is placed at the hypotenuse arm of the CPOC setup such that one of its surfaces reflects back one of the counterpropagating focusing beams. Because of the thickness of the opaque optics, the other focusing beam suffers a longitudinal shift in the beam focus. Applying PPSI, the longitudinal shift in the beam focus which is twice the thickness of the opaque optics is determined. The results obtained for a silicon plate of thickness 0.660 mm with a measurement uncertainty of 0.013 mm are presented.     

Special features of spalling failure of specimens of steel,copper, and lead in loading with sliding detonation waves

The results are presented of experimental examination of the effect of the thickness of the charge of explosive matter (EM) on the characteristics of spalling failure of specimens of steel (St. 3), copper (M1), and lead (S1) in loading with a sliding detonation wave (DW). Two boundary thicknesses of the EM charge below and above which spallation does not take place in the specimens were determined. In the intermediate range of the thickness of EM charges, the thickness of spalling failure increases with an increase of the thickness of the EM charge to the value equal to half the thickness of the specimen. After loading with EM charges whose thickness was smaller than or greater than the boundary thickness these specimens were subjected to metallographic analysis and microhardness measurements. The results show that the metals are hard under the examined pressure range (to 15 GPa). The effect of the processing factor on the strength of the examined metals is noted.Moscow. Translated from Problemy Prochnosti, No. 9, pp. 70–73, September, 1989.     

Free vibration analysis of functionally graded annular plates by state-space based differential quadrature method and comparative modeling by ANN

This paper deals with three-dimensional analysis of functionally graded annular plates through using state-space based differential quadrature method (SSDQM) and comparative behavior modeling by artificial neural network (ANN) for different boundary conditions. The material properties are assumed to have an exponent-law variation along the thickness. A semi-analytical approach which makes use of state-space method in thickness direction and one-dimensional differential quadrature method in radial direction is used to obtain the vibration frequencies. The state variables include a combination of three displacement parameters and three stress parameters. Numerical results are given to demonstrate the convergency and accuracy of the present method. Once the semi-analytical method is validated, an optimal ANN is selected, trained and tested by the obtained numerical results. In addition to the quantitative input parameters, support type is also considered as a qualitative input in NN modeling. Eventually the results of SSDQM and ANN are compared and the influence of thickness of the annular plate, material property graded index and circumferential wave number on the non-dimensional natural frequency of annular functionally graded material (FGM) plates with different boundary conditions are investigated. The results show that ANN can acceptably model the behavior of FG annular plates with different boundary conditions.     

Effect of film thickness on the performance of photopolymers as holographic recording materials

An important issue in developing applications for photopolymers in holography is the effect of film thickness on recording properties. Now it is possible to create these samples with a much wider range of thickness (d = 20-1400 mum) than was previously available. We exploit these recent advances in photopolymer processing to systematically evaluate how the dynamic range of a photopolymer depends on its thickness. The results illustrate that sample performance increases linearly with thickness as predicted by standard models of volume holography. However, above a critical thickness sample performance degrades, and the angular response of recorded plane-wave holograms shows evidence of grating curvature. These distortions are likely the result of photopolymer shrinkage, which in thicker samples occurs in a nonuniform fashion. This problem limits the performance of these photopolymers and is likely to be an issue for any photopolymer that undergoes comparable polymerization shrinkage.     

Hydrocarbon decomposition in alumina membrane: an effective way to produce carbon nanotubes bundles

Carbon nanotubes were synthesised within the pores of an alumina membrane. The membrane had 200 nm diameter pores and 60 microm thickness, and ethylene was used as carbon source. Membrane dissolution by HF results in a bundle of parallel open tubes, aligned without macroscopic defects. The external diameter of the tubes is uniform and there is no evidence of any amorphous carbon. Wall thickness control was obtained by varying the reaction time, length by the thickness of alumina membrane, and external tube diameter by the membrane pore size. Scanning (SEM) and transmission (TEM) electron microscopy, atomic force microscopy (AFM), X-ray diffraction, thermogravimetric analysis (TG) and surface area evaluation by nitrogen adsorption were used for the characterization of membrane and nanotubes.     

直流磁控溅射法制备ZnO∶Zr透明导电薄膜及性能研究

利用直流磁控溅射法在玻璃衬底上制备了ZnO∶Zr(ZZO)透明导电薄膜。研究了厚度对薄膜结构及光电性能的影响。研究结果表明,厚度对薄膜的结构和电学性能有很大的影响。制备的ZZO薄膜为六角纤锌矿结构的多晶薄膜,具有c轴择优取向。在厚度为593nm时,薄膜的电阻率具有最小值1.9×10-3Ω·cm。所制备薄膜样品的可见光平均透过率都超过93%。     

Effects of AlN layer thickness on magnetic anisotropy and transport phenomena of CoPt/AlN layered structure

The magnetic anisotropy was studied as a function of the AlN layer thickness in [AlN(x nm)/CoPt(2 nm)]5/AlN(x nm) layered structure (x is AlN layer thickness, and 5 is the number of multilayer series). The multilayered film was deposited by a sputtering apparatus equipped with two pairs of facing targets. It was found that, in the range of AlN layer thickness below 30 nm, CoPt/AlN multilayers transform from an enhanced in-plane magnetic anisotropy to perpendicular magnetic anisotropy (PMA) through thermal annealing in vacuum, with an optimized AlN thickness of 10 nm for strong PMA. However, beyond this thickness range, the PMA did not occur, and thermal annealing only results in magnetic isotropy in both parallel and perpendicular directions. The related structure analysis revealed that smooth interface and good texture of CoPt (111) make positive contributions to interface anisotropy energy and magnetocrystalline anisotropy energy for producing PMA in CoPt/AlN layered structure. In addition, the transport phenomena were also studied by using a four-probe method.     

Magnetoelectric effect in thick-film heterostructures of PZT and Ni-Zn ferrites

This paper presents an experimental study of the magnetoelectric (ME) properties of layered heterostructures consisting of PZT-46, PZT-19, and Ni-Zn ferrites (1000NN and 2000NN). Their magnetoelectric response is examined as a function of the configuration, shape, and thickness of the layers in the composites. The results demonstrate that increasing the thickness of the magnetostrictive layer from 0.35 to 3.5 mm has an adverse effect on the magnitude of the ME effect. A comparative analysis of the data for rectangular and disk-shaped samples shows that the ME response of the disks is a factor of 2.5 stronger.     

Tuning temperature and size of hot spots and hot-spot arrays

By using scanning thermal microscopy, it is shown that nanoscale constrictions in metallic microwires deposited on an oxidized silicon substrate can be tuned in terms of temperature and confinement size. High-resolution temperature maps indeed show that submicrometer hot spots and hot-spot arrays are obtained when the SiO(2) layer thickness decreases below 100 nm. When the SiO(2) thickness becomes larger, heat is less confined in the vicinity of the constrictions and laterally spreads all along the microwire. These results are in good agreement with numerical simulations, which provide dependences between silica-layer thickness and nanodot shape and temperature.