An analysis of the tensile elongation to failure of laminated metal composites in the presence of strain-rate hardening

We extend the analysis of Hutchinson and Neale (Hutchinson JW, Neale KW. Acta Metall 1977;25:839) and Ghosh (Ghosh AK. Acta Metall 1977;25:1413) predicting the tensile elongation to failure of strain-rate-dependent plastic materials to two-phase composites deforming quasistatically according to the equistrain rule of mixtures. The analysis incorporates the influence of work hardening and strain-rate hardening in both composite constituent phases. It is shown that the problem can be formulated in a manner that condenses the seven underlying material parameters into four dimensionless numbers for composites of power-law hardening phases, the number of parameters falling to two for linear hardening. It then emerges that the stabilizing influence of both work hardening and strain-rate hardening is, within assumptions of the model, always predominantly exerted by the phase that carries the greater share of the composite stress. It is also shown that the prediction can be simplified so as to enable an approximate but convenient direct graphical deduction of the tensile elongation of ductile laminated metal composites (LMCs), knowing the work hardening and strain-rate hardening characteristics of the two phases making the composite. The utility of this graphical scheme is illustrated with two examples, namely LMCs containing one phase of (moderately ductile) aluminium alloy or of a (low-ductility) nanocrystalline metal.     

SAXS study on the crystallization of PET under physical confinement in PET/PC multilayered films

The present work is concerned with the study of the development of the crystalline structure of poly(ethylene terephthalate) in multilayered films of poly(ethylene terephthalate)/polycarbonate (PET/PC) prepared by means of layer multiplying coextrusion. Small angle X-ray scattering patterns were recorded during isothermal crystallization experiments and evaluated by means of Ruland's interface distribution function. Thus, structural parameters describing the thickness distribution of crystalline and amorphous layers were determinated. It is shown that the crystallization of PET is delayed with increasing confinement. However when the crystallization process comes to an end, the values of the nanostructural parameters of the lamellar system are nearly the same for the confined and non-confined PET.     

Evidence for quantum confinement effects in CdSe/ZnSe multilayer thin films prepared by the physical vapor deposition method

CdSe/ZnSe heterostructure multilayer thin films were prepared with different sublayer thicknesses of CdSe using the physical vapor deposition method. X-ray diffraction studies were used to calculate the average size of the particles and confirmed the (1 1 1) plane of ZnSe. Due to the stacking of alternate CdSe and ZnSe layers, stress was created in the multilayer systems. This results in quantum size effects. Experimentally measured energy values from (hν) vs. (αhν)² dependence confirm the presence of spin–orbit split in the valence band of CdSe. The calculated band gap energies are greater than that of bulk CdSe. Crystallite sizes (12–4 nm) were calculated based on the predictions of the effective mass approximation model (i.e. Brus model). Results show that the diameters of crystallites are smaller than the Bohr exciton diameter (11.2 nm) of CdSe. Upon particle size decrease, the photoluminescence peak is shifted from the green region to the blue region. Analysis shows that the sublayer thickness of CdSe material changes the properties of CdSe/ZnSe multilayer systems.     

Elastoplastic buckling as source of misinterpretation of micropillar tests

Microscopic compression tests (micropillar tests) are typically used to obtain stiffness and strength properties of materials at small length scales. In this work it is shown that structural effects, in particular instabilities, have implications on the resulting load–displacement diagram. Care has to be taken when the measured load–displacement path of a micropillar is interpreted as a stress–strain path of the material. Several structural effects are discussed by means of computational analysis.     

Fabrication of evacuated glazing at low temperature

An indium-based seal augmented with an adhesive, developed to maintain a vacuum between two sheets of glass, avoids the high temperatures required to produce a seal in evacuated glazings to date. An experimentally-validated three-dimensional transient model has been used to predict heat transfer for an indium/adhesive sealed 1 m² area evacuated window with a highly insulating frame. An overall heat loss coefficient of 0.9 W m⁻² K⁻¹, with a midplane value of 0.36 W m⁻² K⁻¹, can be achieved with 0.72 visible transmittance for two 6 mm panes separated by 0.2 mm diameter pillars 40 mm apart. The conduction through a 3 mm edge-seal was 1.14 W m⁻² K⁻¹. Detailed three-dimensional isothermal contour plots through the system are presented.     

Interfacial reactions in Mo-Zr multilayer structure: an X-ray reflectivity study

The effect of elevated temperature on the structural stability and alloy formation in Mo-Zr multilayers is investigated. Mo-Zr multilayers deposited by the electron beam evaporation technique under ultra-high vacuum conditions are annealed up to 650 °C. The changes induced due to thermal treatment are observed using X-ray reflectivity (both specular and off-specular) and X-ray diffraction techniques. The Mo-Zr multilayers remained as an insoluble layered structure even after annealing as revealed from X-ray reflectivity measurements. The interfacial roughness is found to be very similar at all interfaces and decreases on annealing. The multilayer structure remains intact on annealing with expansion of the multilayer period and a marginal increase in X-ray reflectivity.     

CO and methanol electrooxidation on Pt/Ir/Pt multilayers electrodes

This work describes the CO and methanol electrooxidation over an Ir/Pt bilayer electrodeposited on a platinum polycrystalline substrate. In the blank acidic solution it was observed that the electrochemical behavior of both the polycrystalline Pt and Pt/Ir/Pt nanostructured electrodes were very similar. The electroactive area, calculated using the hydrogen desorption method, are the same for both materials. In order to investigate the effect of the thickness change of Ir interlayer, two different samples were prepared. One with 1 Ir monolayer and the second with 3 monolayers thick. CO stripping voltammograms showed a shift in the anodic peak potential towards the negative direction of 160 and 180 mV for Pt/Ir/Pt 3:1 and 1:1 ML, respectively, compared to polycrystalline Pt. Besides, for methanol electrooxidation, the Pt/Ir/Pt electrodes presented an increase of 170% in the peak current density compared to polycrystalline Pt. These results are in agreement with the calculated activation energies which were 31.5, 39.0 and 43.5 kJ mol⁻¹ for Pt/Ir/Pt 1:1, 3:1 ML and polycrystalline Pt electrodes, respectively. Using the electrochemical impedance spectroscopy, surprisingly, the Pt/Ir/Pt electrodes, did not exhibit the inductive arc which means that the poisoning of the electrode surface is not important in this case.     

Fitting of RBS data including roughness: Application to Co/Re multilayers

In this work automated fitting of Rutherford backscattering (RBS) data including the effect of roughness is performed, by calculating the effect of roughness on the apparent energy resolution as a function of depth. This depends on the exact type of roughness, and three different models have been implemented: inhomogeneous layer thickness, corrugated sample, and rough substrate surface. Full automated fitting can be performed including one, or more, of the models, with the roughness parameters (e.g. standard deviation of the thickness of any number of layers), as well as the sample structure, as fitting parameters. The code is applied to the system substrate/Re 50 Å/(Co 20 Å/Re 5 Å)₁₆, which had been studied before by other methods. The results are excellent, providing a new tool for RBS data analysis.     

Hybrid self-assembled multilayer film formed by alternating layers of H4SiW12O40 and 1,10-diaminodecane (DAD)

A hybrid self-assembled multilayer film was prepared by alternating adsorption of H₄SiW₁₂O₄₀ and 1,10-diaminodecane. The film was uniformly deposited and was found to be photochromic, as monitored by the UV spectroscopy. The film was also studied by X-ray photoelectron spectroscopy.