Estimation Of Mechanical Stress Research Articles

An estimation of mechanical stresses in the stator of the NB-514 motor of an electric locomotive

The aim of the research is to determine the causes of cracks in stators of traction electric motors of the NB-514 series. The application of mathematical modeling using the finite element method, which allows one to evaluate the mechanical stresses arising in the stator under the influence of thermal and vibration loads, is considered. The results of thermal modeling are presented for uneven heating of the electric motor frame to temperatures typical for the hourly operation of a traction motor. The results of vibration modeling, including the study of natural vibration modes and frequencies, are also presented. Based on the results of the studies, it was concluded that the cause of the formation of cracks in the area of ventilation hatches is a complex of cyclically repeating temperature and vibration effects, creating points of mechanical stress with a large value in the area of crack formation. Vulnerabilities in the design of the electric motor frame have been identified. Options have been proposed for improving the design of the ventilation hatches of the frame, allowing reducing mechanical stresses with a constant area of the ventilation and inspection hatches.

Possibility of estimation of mechanical stresses in nickel by the magnetic ponderomotive method

The paper considers a technique for assessing mechanical stresses in coatings by the magnetic ponderomotive method, based on the use of the magnitude of the magnet breakaway force and its relation to the magnetic characteristics of nickel (magnetic susceptibility), which change under the action of internal stresses. It is shown that the existing mechanical stress measuring equipment using X-ray, magnetic or ultrasonic methods have specimen size limitations or have low measurement locality. At the same time, a magnetic ponderomotive method for controlling mechanical stresses is presented, which does not have the indicated disadvantages. The change in the magnetic breakaway force on the thickness, applied and residual stresses caused by elastic and plastic deformations in the sample is theoretically substantiated. It is shown that the presence of residual stresses in the sample changes the nature of the dependence of the magnet breakaway force on the applied stresses. A calculation algorithm has been developed that allows measuring the magnet breakaway force to obtain the ratio between the applied and residual stresses. It is shown that the ratio between residual and applied stresses can be used to assess the degree of proximity to the critical stresses levels that lead to failure. Calibration surfaces are constructed for the dependence of applied stresses on magnetic separation force and thickness, corresponding to elastic-plastic deformation, as well as leveled calibration surfaces, corresponding to elastic deformation in the presence of residual stresses in the material. Experiments have been carried out on real samples and coatings, that determine the degree of approximation of internal stresses in the material to critical levels that may lead to destruction. It is shown that when comparing the readings of calibrated gauges with a certified tool, the largest deviation occurs at low stress values due to the inverse dependence of the breakaway force on the stress level.

Transient hydrodynamic stresses on reciprocating hollow fibers using Hydro-Rattle algorithm: A constraint dissipative hydrodynamics simulation

Hollow fiber membranes are widely used for unit processes in wastewater treatment, including (submerged) membrane bioreactors. Interfacial fouling on the fiber surfaces, often caused by small fiber diameters, is controlled, using energy-intensive bubble blowers. A new cost-effective paradigm is to reciprocate submerged cassettes that carry hollow fibers undergoing hydrodynamic shear stresses. Oscillation dynamics of flexible fibers seems to be a challenging investigation because fluid–fiber hydrodynamic interactions need to be rigorously formulated while applying the wave equation is precluded. As the order-of-magnitude estimation of mechanical stresses on moving fibers is of great interest, we assumed that a hollow fiber can be mathematically modeled as a chain of many connected spheres of an order of O103, having the chain length and sphere diameter set equal to those of identical fibers. Holonomic and non-holonomic constraints are implemented to keep spheres from dispersing and the dissipative hydrodynamics, and to satisfy the position–velocity orthogonality. Hydrodynamic interactions were calculated using the grand-mobility matrix of poly-dispersed spheres, and the constraint forces are implemented using an updated algorithm of Hydro-Rattle [Kim (2012)]. Dynamic locations of the highest mechanical stresses are identified, and practical suggestions for the optimal, long-term operations of the cassette-reciprocating process are included.

Self-Sensing Estimation of Mechanical Stress in Magnetostrictive Actuators

Magnetostrictive actuators show interesting performances related to high-precision actuation with high-energy density, which focused the interest of research in the past years. Nevertheless, the output deformation is related to the current and the applied stress, through a complex multi-input multi-output (MIMO) hysteresis process. As a consequence, a reliable and accurate control task cannot neglect the stress monitoring. Such task, if performed by an ad hoc stress sensor, e.g., a load cell, will face with the sensor’s placement in the device, resulting in an increase in cost, complexity, and bulkiness of the system. This issue can be circumvent if the current and magnetic flux measurements, available in the control chain, are exploited. To this aim, a novel self-sensing approach to deliver real-time estimation of the stress is presented in this paper, involving some recent results of a thermodynamic compatible MIMO model of hysteresis for magnetostrictive materials.

An estimation of mechanical stress on alveolar walls during repetitive alveolar reopening and closure

Alveolar overdistension and mechanical stresses generated by repetitive opening and closing of small airways and alveoli have been widely recognized as two primary mechanistic factors that may contribute to the development of ventilator-induced lung injury. A long-duration exposure of alveolar epithelial cells to even small, shear stresses could lead to the changes in cytoskeleton and the production of inflammatory mediators. In this paper, we have made an attempt to estimate in situ the magnitudes of mechanical stresses exerted on the alveolar walls during repetitive alveolar reopening by using a tape-peeling model of McEwan and Taylor (35). To this end, we first speculate the possible ranges of capillary number (Ca) ≡ μU/γ (a dimensionless combination of surface tension γ, fluid viscosity μ, and alveolar opening velocity U) during in vivo alveolar opening. Subsequent calculations show that increasing respiratory rate or inflation rate serves to increase the values of mechanical stresses. For a normal lung, the predicted maximum shear stresses are <15 dyn/cm(2) at all respiratory rates, whereas for a lung with elevated surface tension or viscosity, the maximum shear stress will notably increase, even at a slow respiratory rate. Similarly, the increased pressure gradients in the case of elevated surface or viscosity may lead to a pressure drop >300 dyn/cm(2) across a cell, possibly inducing epithelial hydraulic cracks. In addition, we have conceived of a geometrical model of alveolar opening to make a prediction of the positive end-expiratory pressure (PEEP) required to splint open a collapsed alveolus, which as shown by our results, covers a wide range of pressures, from several centimeters to dozens of centimeters of water, strongly depending on the underlying pulmonary conditions. The establishment of adequate regional ventilation-to-perfusion ratios may prevent recruited alveoli from reabsorption atelectasis and accordingly, reduce the required levels of PEEP. The present study and several recent animal experiments likewise suggest that a lung-protective ventilation strategy should not only include small tidal volume and plateau pressure limitations but also consider such cofactors as ventilation frequency and inflation rate.

Mechanical Stresses Estimation in Silicon and Glass Bonded at Elevated Temperature

During electrostatic bonding, also known as anodic bonding, silicon is bonded to glass by applying an external voltage and simultaneous heating to temperatures of 200...450 $\deg$C. While cooling to working temperature after bonding happened pieces are mutually deformed. Due to linear thermal expansion coefficients mismatch of anodically bonded glass and silicon samples an internal stress state is generated. Such stresses are called thermal mismatch stresses. The aim of this paper is a determination of technological and design solutions to achieve minimal thermal mismatch stresses in resulting bond. The nonlinear dependence of linear thermal expansion coefficients of bonded samples' materials on temperature makes it difficult to minimize thermal mismatch stresses by chosing materials with close average thermal expansion coefficients in particular temperature range. To assess means of lowering thermal mismatch stress in this paper two different ways to describe assembly are used: two thin bonded layers and multilayered composite material. Based on properties of two brands of glass (LK5, Borofloat 33) and silicon used with described mathematical models thermal mismatch stresses at temperature $T_w$ in samples bonded at several different temperatures $T_b$ are evaluated. Bonded silicon surface stress dependence of glass to silicon wafer thickness ratio is evaluated. Based on such evaluations one can say that by varying thickness of glass bonded to silicon one can obtain zero thermal mismatch stress at a particular depth of material or obtain stress of some defined value at this depth. Models of assembly description used in this paper can be used to optimize anodic bonding process parameters. Such usage aimed to minimize thermal mismatch stresses at device working temperatures is presented in this paper.

Near Infrared Spectroscopy as a Tool for Estimation of Mechanical Stresses in Wood

Significant scientific work has been dedicated for exploration of the infrared applications within wood science and technology, not much has been done linking it to the mechanical testing. It is expected that due to mechanical stresses (and related deformations) the interaction between constitutive elements of wood changes, proportionally to the stresses applied. The response of the material to mechanical stresses (such as tensile loading) on the molecular level should be therefore detectable by means of infrared spectroscopy. Dedicated tests have been devoted for proving this hypothesis. Self-developed testing machine has been integrated with infrared spectrometer in order to conduct a series fully controlled mechanical tests. It was possible to predict stress level of wood during tension by applying proper chemometric analysis (partial least square (PLS) models). Implementation of infrared spectroscopy in to timber engineering and mechanical testing of wood provides very essential supplement to the typical information collected during standard tests. More additional tests and reference data is necessary in order to create more reliable and universal model suitable for routine assessments. Nevertheless, it was demonstrated that prediction of the stress on the basis of the infrared spectra is possible.

Nature and forecast of regional zoning of dynamic phenomena in mines of Donbass

Principal propositions of the method and results of prediction of regional zones development of dynamic phenomena in the mines of Donets Basin are considered on the basis of geological environment mechanical stresses estimation caused by disturbance of the equilibrium state according to gravimetric data.

Sensitivity Tests of Simulation Models Used in Chosen Calculation Codes on Uncertainty of Thermo-Mechanical Parameters during Virtual Mechanical Stress Estimation for Ferrous Alloy Castings

Simulation systems used for many years in foundry industry such as MAGMASOFT, NovaFlow&amp;Solid and ProCAST, contain thermo-mechanical modules permitting the estimation of mechanical stresses and hot tears appearing in casting during its cooling. It is also known that these modules are rarely used because of the very limited thermo-mechanical database especially for ceramic materials such as foundry sand moulds. These technologies – castings pouring in non-permanent sand moulds, particularly iron alloys are most often applied in foundry. In our study the method of evaluating the algorithms quality applied in thermo-mechanical phenomena models based on parameters sensitivity testing from the proper database of the simulation system was used [1]. The comparative analyses of both experimental and virtual results were realized (by stress estimation). The methodology of experimental research was similar to that described where gray cast iron castings of stress bars (grid) were casted in sand mould bonded by organic resins.

A Microscopic and Analytic Study of Aluminum Particles Agglomeration

Aluminum powders added to solid propellants burn either as single particles or agglomerates. Combustion efficiency is very dependent on the final aluminum particle size injected into the chamber flowfield. This work has investigated experimentally the microscopic behavior of powdered aluminum particles during gradual heating in inert and oxidative atmospheres. Effects of surrounding gas composition, particle size, initial oxide layer thickness, and dilution by refractory compound on the particles behavior during heating have been studied. A novel model of a crucial stage in aluminum particles agglomeration based on estimation of mechanical stresses appearing in the oxide layer during particle heating has been suggested. Results of estimation confirm that disruption of oxide layer takes place during aluminum melting. This disruption results in the flow of a molten metal through cracks formed in the oxide layer and in the formation of large liquid drops. Results of theoretical calculations are in a good agreement with experimental data.

Respiratory mechanics in acute respiratory distress syndrome: relevance to monitoring and therapy of ventilator-induced lung injury

In a nonhomogeneous lung with acute respiratory distress syndrome and at a transpulmonary pressure of 30 cm H2O, the forces acting on an atelectatic region surrounded by fully expanded lung could be subject to a pressure of 140 cm H2O. Stress caused by the repeated opening and closing of such alveolar units because of recruitment/derecruitment that may be exacerbated with ventilation at low positive end-expiratory pressure levels may also occur. Recent findings seem to confirm that only ventilatory strategies tailored to the estimation of mechanical stress in terms of respiratory mechanics (lower inflection and upper inflection points on the volume–pressure [V–P] curve, respectively) may prevent ventilator-induced lung injury. These data address the key role of the assessment of respiratory mechanics to identify, prevent, and treat ventilator-induced lung injury. The optimum method to clinically obtain the V–P curve has not been established as yet. Another caveat is the fact that the V–P curve takes into account both the lung and chest wall as opposed to measuring the V–P properties of the lung itself. In the case of a stiff chest wall (eg, in a patient with ascites), limiting the plateau pressure to less than 35 cm H2O would mean that the clinician is unnecessarily limiting tidal volumes. Clearly, extensive experience with the measurement of the inspiratory V–P curve should be obtained.

Estimation of mechanical stresses on closed cusps of porcine bioprosthetic valves: Effects of stiffening, focal calcium and focal thinning

The magnitude and distribution of mechanical stresses acting on the closed cusps of porcine bioprosthetic valves (PBVs) were estimated using a finite element model. The effects of leaflet stiffening, focal calcium and focal thinning on leaflet stresses were determined. In a normal closed PBV leaflet, stresses increased as pressure was increased. At a pressure of 80 mm Hg, the maximal normal principal stresses were 11 g/mm 2 near the center of the leaflet and increased to 19 g/mm 2 at a pressure of 160 mm Hg. These observations suggest that the closed valve in the mitral position would experience higher mechanical stresses than the closed valve in the aortic position. Tissue stiffening increased stresses throughout the leaflet and introduced a site of stress concentration near the center of the leaflet. At a pressure of 80 mm Hg, the maximal principal normal stress increased 55% when the leaflet was stiff in comparison to the normal leaflet. Focal calcium and focal thinning caused marked gradients of stress between the sites of calcium or thinning and the immediate surrounding tissue. The magnitude of these stress gradients increased with increasing pressure. These sites of mechanical stress concentration or stress gradients appear to be compatible with sites of leaflet calcification or disruption. Such stresses may contribute to spontaneous degeneration of PBVs.