Papers by Keyword: Stress

Abstract: In this work, we report the impact of combined surge current stress and bipolar gate switching stress (GSS) on the threshold voltage (V_th) shift of planar SiC MOSFETs. The V_th shift exhibits a strong dependence on the sequence of these two applied stresses. It is found that both the surge current stress and GSS can separately result in a positive shift in V_th, and the V_th shift is cumulatively aggravated in the combined stresses only if the bipolar GSS is applied first. This is attributed to the generation of new defects during the bipolar gate switching, which act as trap centers for subsequent surge stress. This finding reveals the cumulative damage characteristics of SiC MOSFETs under complex operating conditions.

Abstract: An exact analytical solution is presented for the problem of plane transverse bending of a segment of a narrow multilayer circular arch subjected to a normal uniformly distributed load on its longitudinal surfaces. The solution is constructed using the superposition principle based on the general solutions obtained by the authors for the bending problems of multilayer cantilevers with a circular axis under the action of loads on the free end and a uniformly distributed normal load on the longitudinal surfaces. Methods for modelling different types of end restraints for multilayer arches are considered: rigid, hinged, and combined. Using the example of a five-layer arch with varying restraints at the end, the influence of transverse shear deformations on the deflection and normal stresses is analyzed. The obtained relations allow determining the stress-strain state of multilayer arches with an arbitrary number of homogeneous (orthotropic, isotropic) layers, taking into account transverse shear and compression deformations, and can be used to construct other important solutions to arch deformation problems and develop more universal methods for calculating such structural elements.

Abstract: The impact of air pollution on public and environmental remains huge burden in Nigeria that has not been properly addressed. Poverty energy supply has further exacerbated the current situations making business to rely on generators for energy power supply. This study aims to assess the impact of generators-induced air pollution on stress levels among printing press workers in a specific setting Abuja. This cross-sectional designed was adopted to conduct this study among printing press workers who use generators in Abuja. A total of 508 workers were selected using simple random sampling. Data on stress levels were collected using a validated perceive stress scale (PSS) 10 item scale, while exposure to air pollution from generators was assessed through on-site air quality monitoring device. A Generalized Linear Model (GLM) was employed to analyze the relationship between generator-related air pollution and stress levels, adjusting for potential confounders. Statistical analysis was performed using SPSS version 27, with significance set at p < 0.05. Results, shows that the mean PSS 10 scale was: >25.90 (SD 4.35), a bivariate correlation analysis indicates statistically significant positive correlation between the air pollutant variables and perceive stress, p-value 0.001. A GzLM analysis show that; In model 1, the air pollutant variable was found to have a significant positive effect on stress scale (PM2.5: β = 1.029 (95% CI; 1.024-1.034)). In model 2, both the two air pollutants PM2.5 and PM10 were found to be significantly associated with increase in stress levels (PM2.5: β = 1.568 (95% CI: 1.397 – 1.759)) and (PM10: β = 1.336 (95% CI: 1.202 – 1.486)) separately. Contrary to model 1 and 2, most of the variables model 3 were not statistically significantly associated with increase in log odds higher perceive stress, except for PM2.5 which was adjusted. Inconclusion, this study demonstrates statistically significant association between air pollutants and stress scale. The findings highlighted the importance of addressing energy policy issues and air quality concerns as potential factors affecting stress and mental health.

Abstract: The assessment of bridge structures is not only relevant, but also an integral part of effective infrastructure management aimed at ensuring safety, convenience and comfort for citizens. Many bridges have been destroyed due to imperfect design, the use of low-quality materials, and inappropriate construction methods. Consideration of natural and human factors in the design, construction and operation of bridge structures is key to ensuring their safety, durability and long-term performance. Any defects require careful monitoring, assessment and timely repair to ensure the safety and reliability of bridges. Various methods are used to inspect bridge structures. Inspection methods can be used individually or in combination to obtain comprehensive information on the condition of bridge structures and take the necessary measures for their maintenance and repair. In work to determine the stresses in a bridge, we use the finite element method (LIRA 9.4 R3). The inspection of the bridge's structures revealed a number of defects resulting from corrosion processes, operational factors and certain structural deficiencies. To ensure the durability of the bridge structures, it is necessary to reconstruct the bridge.

Abstract: An exact analytical solution to the problem of plane transverse bending of a section of a narrow multilayer beam under the action of a normal load on the longitudinal faces, distributed according to the law of the trapezoid, is presented. The solution is constructed using the principle of superposition on the basis of the authors’ general solutions to the problems of bending multilayer consoles under the action of loads at the free end, uniformly and linearly distributed load on longitudinal faces. On its basis, separate interchanges for multilayer beams with different methods of fixing the ends were obtained: hinged, rigid and combined. The obtained relations make it possible to determine the stress-strain state of multilayer beams with an arbitrary number of homogeneous (orthotropic, isotropic) and functional-gradient layers, taking into account transverse shear and compression deformations.

Abstract: The purpose of research is to determine the influence character of the way the composite rope is connected to the permanent structure elements on its stress-strain state and to develop a determination method for such a state. Research methodology involves constructing the models of interaction between rigid fibers in a rope of composite design, using the methods of mechanics of layered composite materials, with complex consideration of its design and mechanical properties, and the condition of connecting rope ends to the permanent structure. The model is solved analytically using Fourier series on a discrete axis of layer numbers of a finite length while defining the distribution patterns of internal forces and displacements in rope layers. The algorithm for determining a stress-strain state of a rope with rigid fibers while considering a rope connection scheme to the permanent structure is established. The scientific novelty of research is in determination of the character and influence mechanism of a connection scheme of a composite rope with rigid fibers to the permanent structure on its stress-strain state. Practical value of the research is in that the obtained results make it possible to consider the influence character of the rope connection scheme to the permanent structure on a rope stress state and this allows justified determination of its safe operation conditions.

Abstract: The purpose of research is to construct an algorithm for calculating a stress-strain state of a multilayer orthotropic composite rope. Research methodology involves constructing and solving the interaction model of parallel reinforcing rigid fiber elements regularly placed in layers connected through an elastic material. A method for calculating a stress-strain state of a multilayer orthotropic composite rope is developed. The scientific novelty of research is in the establishment of a dependency for distribution of internal loading forces in reinforcing rigid fibers on stay rope parameters. The distribution of internal loading forces in reinforcing fibers depends on the amount and relative location of fibers in a stay rope. Along the length, the stress-strain state of a rope depends on a square root of the ratio of shear modulus of elastic matrix and tensile rigidity of fibers. The practical value of the research is in that the presented method allows determining the rope stress-strain state during the designing stage of a permanent structure. This is based on structural parameters and mechanical properties of components of a composite rope and conditions of its interaction with the structure, thereby increasing reliability and operation efficiency of the structure, in particular, the cable-stayed bridge.

Abstract: In this paper the stress field distribution in 3C-SiC (111) resonators has been studied by micro-Raman measurements and COMSOL simulations. The measurements show that the asymmetry of the anchor points configuration produce an asymmetry in the stress filed distribution. This behavior has been confirmed also by the simulations. Furthermore, from the simulations the importance of the reduction of the under etching of the anchor points of the resonators has also been observed. In fact the reduction of this under etch produces a decrease of the stress in the double clamped beams, a small reduction of the resonance frequency, and a large reduction of the Q-factor and then of the oscillation frequency stability of the resonators in closed-loop operation.

Abstract: The paper deals with the problem of stress in the connection detail of vertical supporting structures with a flat slab and possible methods for its analysis. It mainly focuses on the problem of non-axial connection of columns and walls, which is typical for today's architectural designs. The parametric study compares the effect of the distance of the connected vertical support structures on reinforcement in the discontinuity region. Three different computational methods are used to stress analysis of this region - linear Finite Elements Method in SCIA Engineer software, 2D Strut-and-Tie Model and 2D non-linear Finite Elements Method in IDEA StatiCa software. The conclusion of the study is a comparison of the accuracy of different calculation methods and also a comparison of the solved design variants in terms of shear and bending stress and specific form of reinforcement.

Abstract: Alloy steel is known to be different from carbon steel due to the presence of the alloying element in varying compositions which is usually done for the purpose of modifying and improving the performance of the steel. However, a major problem with the alloy steel is that it usually exhibits different behavior in terms of the microstructures and the mechanical properties, especially, in sulphide environment. Thus, this study focused on the different microstructure of alloy steel and their performance in different environment with strong emphasis in sulphide environment. It was established in the study that a major problem of alloy steel in hydrogen sulphide environment is the sulphide stress cracking which is attributed to the presence of hydrogen and its absorption by the alloy steel. Hence, this study provides a potential guide and information on the capacity of the grades of alloy steel that can thrive in sulphide environment.