O b j e c t i v e s: The aim of study was to investigate the association between anxiety, depression, stress and determinants of quality of life among Iranian students. M e t h o d s: The questionnaires were completed by 275 students. The random sampling was conducted in two phases, the stratified sampling which some classes were selected among different classes of faculty of health and at the second phase, in each class the number of students who had the requirements to enter in the study were selected randomly. the logistic regression to find out the association between demographic characteristics with the quality of life was run and according to the normality status of the distribution of data the parametric or non-parametric tests were used. R e s u l t s: In the univariable model, the students that were living in their own homes had the odds of 2.18 times more than the others to have a higher quality of life level (95% CI: 1.07–4.45). In the multi variable model the anxiety and stress were significantly related to the quality of life and for increasing each 1 unit in the amount of anxiety and stress the odds of a better quality of life decreases 0.19 and 0.03 respectively. Even after adjusting for other covariates – in the multivariable model – both anxiety and stress were associated with the quality of life. C o n c l u s i o n: It is useful for the universities to understand different aspects of the students’ lives which are under the influence of stress, anxiety and depression, and also determining the resources from which they are originated.
An algorithm of determination of mechanical stresses and deformations of the magnetic circuit shape, caused by forces of magnetic origin, is presented in this paper. The mechanical stresses cause changes of magnetizing characteristics of the magnetic circuit. The mutual coupling of magnetic and mechanical fields was taken into account in the algorithm worked out. A computational experiment showed that it was possible to include the interaction of both fields into one numerical model. The elaborated algorithm, taking into account the impact of mechanical stresses on magnetic parameters of construction materials, can be used in both the 2D and the 3D type field-model.
The numerical algorithm of thermal phenomena is based on the solution of the heat conduction equations in Petrov-Galerkin’s formula using the finite element method. In the modeling of phase transformation in the solid state, the models based on the diagrams of continuous heating and continuous cooling (CHT and CCT). In the modeling of mechanical phenomena, equations of equilibrium and constitutive relationships were adopted in the rate form. It was assumed that the hardened material is elastic-plastic, and the plasticizing can be characterized by isotropic, kinematic or mixed strengthening. In the model of mechanical phenomena besides thermal, plastic and structural strains, the transformations plasticity was taken into account. Thermo-physical size occurring in the constitutive relationship, such as Young’s modulus and tangential modulus, while yield point depend on temperature and phase composition of the material. The modified Leblond model was used to determine transformation plasticity. This model was supplemented by an algorithm of modified plane strain state, advantageous in application to the modeling of mechanical phenomena in slender objects. The problem of thermoelasticity and plasticity was solved by the FEM. In order to evaluate the quality and usefulness of the presented numerical models, numerical analysis of temperature fields, phase fractions, stresses and strains was performed, i.e. the basic phenomena accompanying surface layer of progressive-hardening with a movable heat source of slender elements made of tool steel for cold work.
Mechanical properties and residual stresses of friction stir welded and autogenous tungsten inert gas welded structural steel butt welds have been studied. Friction stir welding (FSW) of structural steel butt joints has been carried out by in-house prepared tungsten carbide tool with 20 mm/ min welding speed and 931 rpm tool rotation. Tungsten inert gas (TIG) welding of the butt joints was carried out with welding current, arc voltage and the welding speed of 140 amp, 12 V and 90 mm/min respectively. Residual stress measurement in the butt welds has been carried out in weld fusion zone and heat affected zone (HAZ) by using blind hole drilling method. The magnitude of longitudinal residual stress along the weld line of TIG welded joints were observed to be higher than friction stir welded joint. In both TIG and FSW joints, the nature of longitudinal stress in the base metal was observed to be compressive whereas in HAZ was observed to be tensile. It can be stated that butt welds produced with FSW process had residual stress much lower than the autogenous TIG welds.
Metallographic investigations and a computer simulation of stresses in a gravity die-casting bushing were performed. Simulation of the casting process, solidification of the thick-walled bushing and calculations of the stress was performed using MAGMA5.3 software. The size variability of phases κIIaffecting the formation of phase stresses σf, depending on the location of the metallographic test area, was identified. The distribution of thermal σtand shrinkage stresses σs, depending on the location of the control point SC in the bushing's volume, was estimated. Probably the nature of these stresses will change slightly even after machining. This can cause variations in operating characteristics (friction coefficient, wear). Due to the strong inhomogeneity of the stress distribution in the bushing's casting, it is necessary to perform further tests of the possibility to conduct thermal treatment guaranteeing homogenization of the internal stresses in the casting, as well as to introduce changes in the bushing's construction and the casting technology. The paper presents the continuation of the results of research aimed at identifying the causes of defects in the thick-walled bushing, die-casting made of CuAl10Fe5Ni5Cr aluminium bronze.
A thermoelastic boundary value problem of a hollow circular disc made of functionally graded materials with arbitrary gradient is analysed. The steady-state temperature distribution is assumed to be the function of the radial coordinate with prescribed temperature at the inner and outer cylindrical boundary surfaces. The material properties are assumed to be arbitrary smooth functions of the radial coordinate. A coupled system of ordinary differential equations containing the radial displacement and stress function is derived and used to get the distribution of thermal stresses and radial displacements caused by axisymmetric mechanical and thermal loads. General analytical solutions of functionally graded disc with thermal loads are not available. The results obtained by the presented numerical method are verified by an analytical solution. The considered analytical solution is valid if the material properties, except the Poisson ratio, are expressed as power functions of the radial coordinate.
Twist extrusion is a processing method involving the extrusion of a sample with a prismatic cross-section using a tool composed of four prismatic parts bisected by a screw component. A beneficial change in mechanical durability is one of the main factors enabling the use of highly durable Al-Mg-Mn-Sc-Zr alloys to construct functional components of non-stationary robots. As part of the present research, ANSYS® software was used to simulate a twist extrusion process. An analysis of a sample entering and passing through the entire twisting area was performed, up to the point of full twisting of the base of the sample. The stress conditions in the sample were analysed as it passed through the twisting area. The highest stress values (reaching up to 600 MPa) were detected at the tips of the sample face as the sample exited the twisting area. The lowest stress values, at around 170 MPa, were detected at the side edges of the sample.
The volume changes caused by coupled temperature and moisture variations in early-age concrete elements lead to formation of stresses. If a restraint exists along the contact surface of mature concrete against which a new concrete element has been cast, generated stresses are mostly of a restraint origin. In engineering practice a wide range of externally restrained concrete elements can be distinguished such as tank walls or bridge abutments cast against an old set foundation, in which early-age cracking may endanger their durability or functionality. Therefore, for years methods were being developed to predict early-age stresses and cracking risk of externally restrained concrete elements subjected to early-age thermal-moisture effects. The paper presents the comparative study of the most recognised analytical approaches: the method proposed in EC2, the method proposed by ACI Committee 207 and the method developed at the Luleå University of Technology.
The results of research on the effect of the type of cooling agent used during heat treatment and thermal-chemical treatment on the formation of temperature gradient and stress-deformation distribution in cast pallets, which are part of furnace accessories used in this treatment, are disclosed. During operation, pallets are exposed to the effect of the same conditions as the charge they are carrying. Cyclic thermal loads are the main cause of excessive deformations or cracks, which after some time of the cast pallet operation result in its withdrawal due to damage. One of the major causes of this damage are stresses formed under the effect of temperature gradient in the unevenly cooled pallet construction. Studies focused on the analysis of heat flow in a charge-loaded pallet, cooled by various cooling agents characterized by different heat transfer coefficients and temperature. Based on the obtained temperature distribution, the stress distribution and the resulting deformation were examined. The results enabled drawing relevant conclusions about the effect of cooling conditions on stresses formed in the direction of the largest temperature gradient.
The purpose of this study was to establish a relationship between the type of wall connection used in the cast grates, which are part of the equipment operating in furnaces for heat treatment and thermal-chemical treatment, and stresses generated in these grates during the process of rapid cooling. The places where the grate walls are connected to each other are usually characterized by the thickness larger than the remaining parts of walls. Temperature variations in those places are responsible for the formation of hot spots, and in the hot spots temperature changes much more slowly. The type of wall connection shapes the temperature gradient in the joint cross-section, and hence also the value of thermal stresses generated during cooling. In this study, five different designs of the grates were compared; the difference in them was the type of the designed wall connection. The following design variants were adopted in the studies: X connections with and without holes, T connections with and without technological recesses, and R (ring) connection. Numerical analysis was performed to examine how the distribution of temperature changes in the initial phases of the cooling process. The obtained results served next as a tool in studies of the stress distribution in individual structures. The analysis were carried out by FEM in Midas NFX 2014 software. Based on the results obtained, the conclusions were drawn about the impact of different types of wall connections on the formation of thermal stresses in cast grates.
By the very nature of their work, castings used in furnaces for heat treatment and thermo-chemical treatment are exposed to the effect of many unfavorable factors causing their deformation and cracking, significantly shortening the lifetime. The main source of damage are the micro- and macro-thermal stresses appearing in each cycle. As the cost of furnace instrumentation forms a significant part of the total furnace cost, in designing this type of tooling it is important to develop solutions that delay the damage formation process and thus extend the casting operation time. In this article, two structural modifications introduced to pallets castings to reduce thermal stresses arising at various stages of the cooling process are proposed. The essence of the first modification consists in making technological recesses in the wall connections, while the aim of the second one is to reduce the stiffness of the pallet by placing expanders in the external walls. Using the results of simulation analyses carried out by the finite element method, the impact of both proposed solutions on the level of thermal stresses was evaluated.
Depending on the course of the processes of heat treatment and thermo-chemical treatment, the technological equipment of heat treatment furnaces is exposed to different operating conditions, as the said processes differ among themselves in the temperature of annealing and atmosphere prevailing in the furnace chamber, in the duration of a single work cycle and in the type and temperature of the coolant. These differences affect the magnitude of stresses occurring in each cycle of the operation of furnace accessories, and thus play an important role in fatigue processes leading to the destruction of these accessories. The kinetics of temperature changes during each cooling process plays an important role in the formation of thermal stresses on the cross-section of the cooled parts. It depends on many factors, including the initial cooling temperature, the type and temperature of the cooling medium, or the dimensions and shape of the object. This article presents a numerical analysis of the effect of the initial temperature on the distribution of stresses on the cross-section of the grate ribs, generated in the first few seconds of the cooling process carried out in two cooling media, i.e. hardening oil and water. The analysis was carried out by the finite element method, based on the results of experimental testes of temperature changes in the rib during its cooling.