Structures Of Variable Thickness Research Articles

Microscopic and X-Ray Analysis of the Surface Changes in Aluminum Alloys during Friction

The effect of the introduction of additives of low-melting alloying elements in antifriction aluminum alloys on a change in the surface after tribological tests is estimated. Compositions are described and sample preparation is performed. For the study, a combination of electron microscopy methods (with elemental analysis) and probe microscopy (with the modes of spreading current and thermal-conductivity analysis) are used. It is shown that after heat treatment, the phase components acquire a globular shape in both alloys. Grain deformation, soft phase release to the surface, and mass transfer take place during the friction process. The hard phase components of the shoe material act as an abrasive, while mass transfer forms a film of secondary structures of variable thickness on the roller (under certain conditions, the film becomes thicker, which can lead to scuffing). The analysis of sections allows the presence of a near-surface layer (50–100 µm thick) with a modified structure to be established. The SPM method is used to establish that the thermal conductivity map at the micro level correlates with the electrical conductivity map. X-ray structural analysis of the surfaces carried out before and after tribological tests showed that the lattice spacing decreased, lattice deformation increased, and texture appeared.

A contribution to understanding the origin of platy structure in silty soils under no tillage

In silty soils under no tillage (NT), platy (P) soil structure is widespread and constrains water infiltration. Our objectives were (i) to evaluate how traffic and the presence of crop residues influence P structure development in the field and (ii) to characterize changes in soil structure caused by alternation of wetting and drying (w-d) periods for two topsoil layers of a silty soil and two compaction levels in the laboratory. The five-year field experiment was carried out on a Typic Argiudoll under NT and the structure of the A horizon was analyzed using visual soil evaluation (VSE) both before and five years after two traffic levels were applied to four crop sequences. The laboratory experiment of w-d cycles was carried out with two disturbed layers of a Typic Argiudoll, which was repacked to achieve two different bulk densities, and the columns were subjected to 5, 10, or 15 w-d cycles. In the field experiment, the P structure was clearly identified by VSE and corroborated by shear strength and bulk density measurements. The proportion of P structure increased until about 50% of the A horizon after 5 years, irrespective of the traffic or presence of crop residues at the expense of the Φ structure proportion. In the laboratory, consecutive w-d cycles caused changes in soil volume, cracking of the soil surface, and formation of P structure of variable thickness up to 20mm, confirming that alternation of w-d periods can cause structural modification of the silty soil, in particular horizontally oriented cracks. The number of w-d cycles increased the thickness of the P structure in the upper layer (R2=0.55) and in the compacted treatment (R2=0.81). The results obtained constitute important progress in the understanding of the evolution of P structure of silty soils under NT.

Computer modeling of tasks in dynamics of viscoelastic thin-walled elements in structures of variable thickness

Computer modeling of tasks in dynamics of viscoelastic thin-walled elements in structures of variable thickness

Determination of individual layer composition and thickness in multilayer HgCdTe structures

The reproducible molecular-beam epitaxy (MBE) growth of dual-band Hg1−xCdxTe (MCT) heterostructures requires routine post-growth wafer analysis for constituent layer thickness and alloy composition, therefore, demanding nondestructive characterization techniques that offer quick data feedback. This paper reports a multilayer structure model, which can be least-square fit directly to either Fourier transform infrared (FTIR) transmission or reflection spectra to provide individual layer thickness, alloy composition, and grading information for various complex structures. The model, we developed, is based on an accurate representation of both the real and imaginary parts of the MCT dielectric function across and above Eg as a function of alloy composition. The parametric, MCT optical-dielectric function for compositions varying between x=0.17 to x=0.5 was developed in the range from 400 cm−1 to 4,000 cm−1, based on a semi-empirical model for the absorption coefficient and extrapolation of the refractive index across Eg. The model parameters were refined through simultaneous fits to multiple reflection and transmission data sets from as-grown, double-layer planar heterostructure (DLPH) structures of variable thickness. The multilayer model was tested on a variety of simple DLPH structures with thick absorber layers (>8 µm) and was compared against traditional FTIR analysis and cross-section optical microscopy and showed good agreement in both composition and thickness. Model fits to dual-color MCT data and subsequent analysis of the internal parameter correlation have demonstrated that error bars on absorber layer composition and thickness could be as low as ∼0.0005 and ∼0.02 µm, correspondingly.