Papers by Keyword: Compressive Stress

Abstract: The mechanism of high stress in silicon nitride thin film is studied systematically in this paper. The effects of the various process parameters on the stress in silicon nitride thin film deposited by PECVD are analyzed and discussed. The silicon nitride thin film with high compressive and tensile stress has been deposited on the optimized process parameters and the compressive and tensile stress are up to-1.38GPa and 866MPa, respectively. Finally, the method of further improving the stress in silicon nitride thin film is presented.

Abstract: Uniaxial compressive stress was applied during fatigue process of soft lead zirconate titanate piezoelectric ceramics and their fatigue resistance was improved when the stress was larger than 20MPa. Before fatigue, compressive stress had a strong depolarization effect and restricted domains switching behavior under large electric field and domain walls motion under small electric field. However, in a partially fatigued state, while domains switching behavior was still restricted by compressive stress, domain walls motion was enhanced. Removal of the applied stress after partial fatigue induced the remnant polarization restored significantly.

Abstract: The inverted structure of the 1s ground state of lithium in silicon provides a unique opportunity to study inter-valley spin-orbit interactions of donor electrons. A study of lithium doped silicon enriched in the ²⁸Si isotope with a low oxygen content (N 210¹⁴ cm³) has demonstrated at low temperatures (T = 3.8 K) a family of electron spin resonance (ESR) spectra with anisotropic g factors associated with Li donor centres. The spectra were investigated without and with application of external stress to the sample and their g factors were found to be less then 2.000. The analysis of experimental data and numerical simulation of the spectra and their angular dependencies in the second order perturbation theory assuming the splitting of states due to internal strains in the crystal is larger than the Zeeman and spin-orbit splitting have shown that the spectrum, having g tensor components corresponding to the tetragonal symmetry, consists of two lines belonging to the triplet state T₂, and the other two lines in the spectrum have an angular dependence behaviour of the doublet states E. The ratio of the inter-valley spin-orbit coupling λ and λ' to the Δ parameters, characterizing the splitting of the states under internal strains have been defined. From the dependencies of the triplet ESR lines intensity on the compressive stress of the crystal along the [11 it was obtained the value of the internal strains, which allowed to determine the parameters of the spin-orbit coupling λ and λ'. Their values were found to be three orders of magnitude smaller than were obtained earlier for Li spectra with g > 2. Since experimentally observed Δ value was of the order of the Zeeman splitting parameter the spectra were analyzed using the full matrix of the spin Hamiltonian for the fivefold degenerate ground state. We found that angular dependencies of the spectra observed for the triplet and doublet states with g < 2 are well described by the solutions of the spin Hamiltonian with parameters λ and λ' obtained from our experimental data. At the same time, we are not able to find solutions that satisfy the data obtained for the spectra with g > 2.000 in previous studies.

Abstract: The effect of the surface compressive stress (CS) on the wettability of the chemically strengthened glasses on air side and tin side was investigated. The wettability of the air side of the raw glass is better than the tin side. After chemical strengthening, the surface energy of the air side decrease with the decreasing of the CS while the tin side is just the opposite. These results demonstrated that the wettability of the chemically strengthened aluminosilicate glass could be controlled by the compressive stress.

Abstract: By using the mobile property of silicone oil during deposition, characteristic wedge-shaped chromium (Cr) films have been successfully prepared on glass substrates by direct current magnetron sputtering, and their mechanical instability is investigated. The experiment shows that a disordered network composed of straight-sided buckles, which is due to relief of large compressive stress after deposition, can be widely observed in these films. The size of the buckles increases linearly with the film thickness. In the vicinity of spreading front of the silicone oil, parallel straight-sided buckles perpendicular to the front and bifurcation morphologies can be observed. The influence of the edge effect on the buckle morphologies is also discussed in this paper.

Abstract: In order to find the corrosion cause of petroleum casing premium connection material, the fixture was design to simulate material enduring compressive stress, and the fixture was put in high temperature autoclave, and the corrosion rate of two kind casing material(carbon steel and stainless steel) enduring compressive stress were test in H2S and CO2 and Cl- water solution. The result was that compressive stress accelerated the corrosion of petroleum casing steel, and when compressive stress was greater than the value half as the yield strength the corrosion rate increased quickly.

Abstract: Steel plates connected together are mutually constrained when the member gets elastic buckling failure. A factor χ, embedded coefficient, is used to illustrate the degree of restriction of the flange on the web in GB/T3811-2008’Design Rules for Cranes’. In this standard, the value of the embedded coefficient has been preset in pure bending and pure shearing, while not clearly in compressive stress. In this paper, numerical method is adopted to discuss χ in such load condition.

Abstract: In this paper, three-dimensional(3-D) finite element(FE) method is used to analyze the stresses of face slab of the 300m high concrete face rockfill dam(CFRD) before and after earthquake. Meanwhile, the effect of valley shape on the stress of face slab is considered. The results show that the maximum deflection and axial stress are located near the bottom of face slab in the central valley area before earthquake. And there are compressive stresses in mostly area of face slab. After earthquake, the positions of maximum deflection and axial stress of face slab were changed to the crest of the central valley area. As the valley aspect ratio increases, compressive stress of face slab decreases. For the 300m ultra-high CFRD, the maximum axial stresses exceed the concrete compressive strength before and after earthquake. Therefore, the compression damage of face slab should be considered during the design.

Abstract: Ceramic laminates designed with strong interfaces have shown crack growth resistance (R-curve) behaviour through microstructural design (e.g. grain size, layer composition) and/or due to the presence of compressive residual stresses, acting as a barrier to crack propagation. The goal of the contribution is to model the mechanism of crack bifurcation in laminar ceramics with large compressive stress which still have not been satisfactory explained. Experimental observations of the crack path in the multilayered ceramics tested under several kinds of loading showed crack penetration (i.e. crack propagating normal to the layers followed by crack bifurcation when the crack propagated from the tensile to the compressive layer. Numerical results [1] show that the initiation of crack bifurcation can be explained by the near-tip J-integral, provided that micro-cracks exist near the crack tip. We revisit the problem using the concept of Finite fracture mechanics and the matched asymptotic expansion method in order to evaluate the energy release rate criteria describing the competition of the crack bifurcation and straight crack propagation near behind the bimaterial interface.

Abstract: In order to study the rutting problem of asphalt pavement, this paper sets up a three-dimensional model of asphalt pavement with finite element. By analyzing the mechanical response of high-modulus asphalt concrete at different layers, this paper finds out the layer set of high-modulus asphalt concrete. At the same time, it further analyzes the influence of the modulus’ size and thickness of the high-modulus asphalt concrete on the load-carrying capability of road structure. The results show that high-modulus asphalt concrete can significantly restrain rutting problem and the recommend ideal modulus is between 2000MPa and 2500MPa; the ideal thickness ranges from 5cm to 7cm.