Influence Of Changes In Thickness Research Articles

Analysis of the effect of antiwear CrN coating thickness on the evolution of thermomechanical interactions in the substrate/PVD coating system

The main goal of this study was to analyze the application possibilities of modulated temperature thermomechanical analysis (MT TMA) for the evaluation of thermomechanical interactions in substrate/PVD coating systems on the example of examination of influence of changes in thickness of a coating on internal stress evolution in these systems. As an indicator of the stress state in the coating at a given measurement temperature, the changes in a value of the equivalent thermal expansion coefficient of the system αAC, which is calculated based on registered changes in temperature and elongation of the sample, were assumed. Independently, numerical simulations of the residual thermal stresses were carried out using finite element method. The objects of research were systems composed of substrates of HS6-5-2 steel and a single layer of chromium nitride CrN with thickness 2, 4, 8 and 10 µm, deposited on the substrate by cathodic arc evaporation method. In order to determine the effect of the CrN coating thickness on evolution of thermomechanical interactions in the system, the samples were annealed according to the assumed curve comprising nine-step isothermal annealing in the range of 150–500 °C. Obtained results have shown that MT TMA is useful to study the thermomechanical interactions in substrate/PVD coating systems. In particularly, obtained values of αAC, calculated on the basis of measured elongation changes for substrate/PVD coating systems, are lower than for the substrate without coatings, and they increase with the thickness of the deposited coating. This means that there is a decrease in compressive stresses in the coatings with increasing coating thickness. It was also found that with increasing temperature there is a local maximum value of αAC, which indicates the temperature of deposition of the coating. This is a key parameter from a technological point of view of the PVD processes.

On the correlation between minimum thickness and central deflection during small punch test

Present paper deals with a detailed study on the correlation between minimum thickness (t/t0) and central deflection (δ/t0). Such data are obtained during the deformation of a small punch test of miniaturized specimen. Finite element studies have been carried out to investigate the effect of various parameters which are expected to influence this correlation. The parameters under consideration are material hardening, material yield stress, coefficient of friction and initial thickness of the specimen. It is shown that the correlation remains unaffected with respect to change in material parameters. Similarly, the coefficient of friction beyond 0.2 also does not affect the correlation. However, change in thickness has significant effect on the correlation. A modification has been suggested in the existing correlation to consider the influence of thickness change. The modified correlation is then used to calculate fracture toughness using the experimental results quoted in the literature. It is shown that the modified correlation improves the fracture toughness prediction considerably.

Chemoresistive conducting polymer-based odour sensors: influence of thickness changes on their sensing properties

Conducting polymer films are widely used in the detection of odours. The change of resistance in the presence of odorants depends on the polymer thickness, and affects the sensitivity properties of the device. Using the vapour phase polymerization technique it is possible to fabricate polymer layers of controllable, uniform thickness. Aiming at the characterization of polymeric sensors as a function of their thickness, we implemented sensors of different thicknesses and carried out sensitivity measurements using toluene as an analyte. Sensitivity in terms of percentage variation of resistance per unitary odour concentration change was found to decrease with increasing thickness. Data on sensitivity as a function of thickness is presented and a possible explanation is proposed to account for the experimentally observed behaviour.

ON THE ABSORPTION‐DISPERSION CHARACTERISTICS OF CHANNEL WAVES PROPAGATING IN COAL SEAMS OF VARYING THICKNESS1

ABSTRACTThe WKB‐method is used for the derivation of both the complex dispersion relation and displacement functions for Love channel‐waves that propagate in a coal seam of varying thickness. The constant Q‐model is used to describe the anelastic friction. With numerical solutions of the absorption‐dispersion relation, the influence of thickness changes on the phase velocity and absorption coefficient of Love seam‐waves is analysed at various frequencies. It is shown that the changes in the seam thickness can be optimally detected around the average Airy‐phase frequency. An equivalence is pointed out between the wave guide structures: homogeneous with varying seam thickness and horizontally inhomogeneous with constant seam thickness.

Quantitative electron probe microanalysis of biological specimens. I, A theoretical analysis of some variables involved

Abstract The mutual effects of several inorganic elements on their X-ray yields were calculated for a theoretical biological sample. These effects were less than 10% for Ca, K, Cl, S, P, Ka radiations. The influence of changes in thickness and density of the specimen on X-ray yields was also calculated. This influence was very large, especially for specimens of thicknesses which were less than half the mean electron range in the material.