Mechanical Stress Distribution Research Articles

Investigation of the magnetostriction coefficient of amorphous ferromagnetic glass coated microwires

We measured the magnetostriction coefficient using small angle magnetization rotation method in amorphous ferromagnetic glass-coated Fe, Co, FeCo, and FeCoNi-based microwires. It was found that when the metallic nucleus of the microwire has a high magnetostriction—of the order (10–30) × 10−6 for FeCo-based microwires, the changing of diameters ratio, and hence, the magnitude and distribution of mechanical stresses have no significant effect on the value of the magnetostriction coefficient. In the case of nearly zero magnetostrictive FeCoNi-based microwires, increasing of the ρ−ratio leads to decreasing in the absolute value of the magnetostriction coefficient.

Effect of an inhomogeneous initial stress on Love wave propagation in 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 single crystal layered structure poled along [011

The propagation behavior of Love wave in 0.67Pb(Mg1/3Nb2/3)O–0.33PbTiO3 (PMN–0.33PT) single crystal layered structure with the inhomogeneous initial stress varying along thickness is studied in this paper. The interface between PMN–PT layer and elastic substrate is perfectly bonded. The surface of the layered system is free of traction and electrically shorted or open. PMN–0.33PT single crystal is considered [011]c polarized, and has macroscopic symmetry of orthogonal mm2. The Frobenius method is employed to solve governing equation with variable coefficient. The analytical dispersion equations are derived for different boundary conditions. The numerical results show that the Frobenius method can provide a good asymptotic approximation when the retained number of items in Frobenius series is sufficient. It is found that the inhomogeneous initial stress has strong effect on the dispersion characteristics comparing with constant initial stress, whereas has less effect on the cut-off frequency for the first two modes of Love wave. The gradient coefficients of inhomogeneous initial stress can obviously affect the phase velocity and corresponding electromechanical coupling factor, and can also change the distributions of mechanical displacement, electrical potential and stress. The obtained results can provide a predictable and theoretical basis for design and manufacture of high performance surface acoustic wave devices.

Analysis of a Bow-Free Prestressed Test Specimen

Broadening the temperature range in accelerated testing of electronic products is a typical measure to assure that the product of interest is sufficiently robust. At the same time, a too broad temperature range can lead to the shift in the modes and mechanisms of failure, i.e., result in failures that will not occur in actual operation conditions. Application of mechanical prestressing of the test specimen could be an effective means for narrowing the temperature range during accelerated testing and thereby achieving trustworthy and failure-mode-shift-free accelerated test information. Accordingly, simple engineering predictive models are developed for the evaluation of the magnitude and the distribution of thermal and mechanical stresses in a prestressed bow-free test specimen. A design, in which an electronic or a photonic package is bonded between two identical substrates, is considered. Such a design is often employed in some today's packaging systems, in which the “inner,” functional, component containing active and/or passive devices and interconnects is placed between two identical “outer” components (substrates). The addressed stresses include normal stresses acting in the component cross sections and the interfacial shearing and peeling stresses. Although the specimen as a whole remains bow-free, the peeling stresses might be nevertheless appreciable, since the outer components, if thin enough, deflect to a greater or lesser extent with respect to the inner component. The numerical example has indicated that the maxima of the interfacial thermal shearing and peeling stresses are indeed comparable and that these maxima are on the same order of magnitude as the normal thermal stresses acting in the components' cross sections. It is shown that since the thermal and the prestressing mechanical loads are of different physical nature, the stresses caused by these two load categories are distributed differently over the specimen's length. It is shown also that although it is possible and even advisable to apply mechanical prestressing for a lower temperature range, it is impossible to reproduce the same stress distribution as in the case of thermal loading. The obtained results enable one to shed light on the physics of the state of stress in prestressed bow-free test specimens in electronics and photonics engineering.

Finite element method model of the mechanical behaviour of Jatropha curcas L. bulk seeds under compression loading: Study and 2D modelling of the damage to seeds

This article is focused on comprehensive research of a pressing process of Jatropha curcas L. bulk seeds during linear compression. Compression experiments were performed and the strain and brittle fracturing of the seeds visualised. The mechanical behaviour and stress distribution at the volumetric strain of bulk seeds in pressing cylinders and semi-cylinders with diameters of 60, 80 and 100 mm were described by 2D FEM models. It has been determined that the study of nonlinear visco-elastic and plastic strain seed interactions and the damage and crack growth in such seeds can be significantly improved through computer simulations using an explicit FEM algorithm. In this study, the compressibility of ripe J. curcas L. bulk seeds was analysed and compared depending on the volume strain and energy performance of the linear pressing process. Empirical equations and differential deformation theory describing the seeds interacting beyond the oil point were reported. In addition, the issue of contact theory in numerical modelling of the point contact of interacting seeds was also described. Statistical results showed that the 2D FEM model can be used to study the volumetric strain, stress and damage of J. curcas L. bulk seeds. These studies suggest that FEM models may be considered an important tool to assess the energy performance of the pressing process of J. curcas bulk seeds and can provide valuable information for the design and optimisation of pressing equipment.

Influence of microscale heterogeneity and microstructure on the tensile behavior of crystalline rocks

AbstractThis study investigates the influence of microscale heterogeneity and microcracks on the failure behavior and mechanical response of a crystalline rock. The thin section analysis for obtaining the microcrack density is presented. Using micro X‐ray computed tomography (μCT) scanning of failed laboratory specimens, the influence of heterogeneity and, in particular, biotite grains on the brittle fracture of the specimens is discussed and various failure patterns are characterized. Three groups of numerical simulations are presented, which demonstrate the role of microcracks and the influence of μCT‐based and stochastically generated phase distributions. The mechanical response, stress distribution, and fracturing process obtained by the numerical simulations are also discussed. The simulation results illustrate that heterogeneity and microcracks should be considered to accurately predict the tensile strength and failure behavior of the sample.

Analysis of Transient Thermal Stress of IGBT Module Based on Electrical-Thermal-Mechanical Coupling Model

Reliability of IGBT power module is one of the biggest concerns regarding wind power system, which generates the non-uniform distribution of temperature and thermal stress. The effects of non-uniform distribution will cause failure of IGBT module. Therefore, analysis of thermal mechanical stress distribution is crucially important for investigation of IGBT failure mechanism. This paper uses FEM method to establish an electrical-thermal mechanical coupling model of IGBT power module. Firstly, thermal stress distribution of solder layer is studied under power cycling. Then, the effects of initial failure of solder layer on the characteristic of IGBT module is investigated. Experimental results indicate that the strain energy density and inelastic strain are higher which will reduce reliability and lifetime of power modules.

The effects of misalignment during in vivo loading of bone: Techniques to detect the proximity of objects in three-dimensional models

Theories of mechanical adaptation of bone suggest that mechanical loading causes bone formation at discrete locations within bone microstructure experiencing the greatest mechanical stress/strain. Experimental testing of such theories requires in vivo loading experiments and high-resolution finite element models to determine the distribution of mechanical stresses. Finite element models of in vivo loading experiments typically assume idealized boundary conditions with applied load perfectly oriented on the bone, however small misalignments in load orientation during an in vivo experiment are unavoidable, and potentially confound the ability of finite element models to predict locations of bone formation at the scale of micrometers. Here we demonstrate two different three-dimensional spatial correlation methods to determine the effects of misalignment in load orientation on the locations of high mechanical stress/strain in the rodent tail loading model. We find that, in cancellous bone, the locations of tissue with high stress are maintained under reasonable misalignments in load orientation (p<0.01). In cortical bone, however, angular misalignments in the dorsal direction can alter the locations of high mechanical stress, but the locations of tissue with high stress are maintained under other misalignments (p<0.01). We conclude that, when using finite element models of the rodent tail loading model, small misalignments in loading orientation do not affect the predicted locations of high mechanical stress within cancellous bone.

Fluid–structure interaction analysis of the left coronary artery with variable angulation

The aim of this study is to elucidate the correlation between coronary artery branch angulation, local mechanical and haemodynamic forces at the vicinity of bifurcation. Using a coupled fluid–structure interaction (FSI) modelling approach, five idealized left coronary artery models with various angles ranging from 70° to 110° were developed to investigate the influence of branch angulations. In addition, one CT image-based model was reconstructed to further demonstrate the medical application potential of the proposed FSI coupling method. The results show that the angulation strongly alters its mechanical stress distribution, and the instantaneous wall shear stress distributions are substantially moderated by the arterial wall compliance. As high tensile stress is hypothesized to cause stenosis, the left circumflex side bifurcation shoulder is indicated to induce atherosclerotic changes with a high tendency for wide-angled models.

Numerical analysis of stress distribution in Cu-stabilized GdBCO CC tapes during anvil tests for the evaluation of transverse delamination strength

Rare-earth–Ba–Cu–O (REBCO) based coated conductors (CCs) are now being used for electric device applications. For coil-based applications such as motors, generators and magnets, the CC tape needs to have robust mechanical strength along both the longitudinal and transverse directions. The CC tape in these coils is subjected to transverse tensile stresses during cool-down and operation, which results in delamination within and between constituent layers. In this study, in order to explain the behaviour observed in the evaluation of c-axis delamination strength in Cu-stabilized GdBCO CC tapes by anvil tests, numerical analysis of the mechanical stress distribution within the CC tape has been performed. The upper anvil size was varied in the analysis to understand the effect of anvil size on stress distribution within the multilayered CC tape, which is closely related to the delamination strength, delamination mode and delamination sites that were experimentally observed. The numerical simulation results showed that, when an anvil size covering the whole tape width was used, the REBCO coating film was subjected to the largest stress, which could result in low mechanical delamination and electromechanical delamination strengths. Meanwhile, when smaller-sized anvils were used, the copper stabilizer layer would experience the largest stress among all the constituent layers of the CC tape, which could result in higher mechanical and electromechanical delamination strengths, as well as high scattering of both of these delamination strengths. As a whole, the numerical simulation results could explain the damage evolution observed in CC tapes tested under transverse tensile stress, as well as the transverse tensile stress response of the critical current, Ic.

Tensile and compressive stress in the metal around a corrosive nonmetallic inclusion, in the presence of an aqueous medium

The formation of a region where corrosive inclusions interact with metal in an aqueous medium is investigated. The inclusion expands as a result of hydration, and corresponding tensile and compressive zones are formed. On the basis of the results, the mechanical-stress distribution around hydrating inclusions is simulated.

Numerical analysis of the thermal and mechanical effects of laser windows of a high-power all-solid-state 2-μm laser system

The output window of a high-power laser system is vulnerable to damage, and this is the main limiting factor on the power scaling and structure integrity of the laser system. In endeavoring to obtain higher output powers from the laser system, the impact of the thermal and mechanical effects and the damage mechanism of the output window must be considered. In order to study these issues, a thermal model of the laser window is established based on the heat transfer and thermoelastic theories, and the expressions for the transient thermal and mechanical stress distributions of the output window are deduced in terms of the integral-transform method. Taking the infrared quartz window material as an example, the temperature and mechanical field distributions of a high-power all-solid-state 2-μm laser system window are simulated, and the laser-induced damage mechanism is deeply analyzed. The calculation results show that the laser window-induced damage is mainly caused by melting damage when the temperature exceeds the melting point of the material. The presented theoretical analysis and numerical simulation results are significant for the design and optimization of high-power laser windows. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this

Research on Elimination of Electric Power System Fault Based on Electrical Engineering Automatic Control Technology

In this paper we introduce the computer software fault analysis system to the power fault detection system, and design power fault elimination system of electrical engineering automatic control, and do simulation and experimental study on the performance. When using the turbine blade of electric machinery to detect fault, we can get the automated troubleshooting displacement curve, and using computer simulation to get the electric mechanical stress distribution nephogram. To further verify the effectiveness of the algorithm, we test the frequencies for eight different units, and obtain eight different sets of five order fault diagnosis frequency, and draw the frequency spectrum distribution of frequency response. It provides the theory reference for the automation of power system fault exclusion.

Thermal shock resistance and failure probability analysis on solid oxide electrolyte direct flame fuel cells

A detailed two-dimensional model of direct flame fuel cell (DFFC) was developed by considering the coupling effects of heterogeneous chemical and electrochemical reactions, electrode microstructure, transport processes of mass, charge and energy, as well as the thermal mechanical stress. The stress distribution was simulated at different heat-up rates which represent the typical DFFC and the common solid oxide fuel cell (SOFC) operation. Transient temperature field and associated thermal stress distributions are determined and analyzed for two different cell structures. The failure probability of the fuel cell is defined and estimated by employing the Weibull statistic. The model is demonstrated to be a useful tool for understanding the mechanical stress distribution within a DFFC cell and for the cell structure design and optimization. The results reveal that the failure probability of an SOFC cell plate working in flame conditions may be 6 orders higher than that in the common SOFC operation conditions. The anode-supported SOFC shows better thermal shock resistance compared with the electrolyte-supported SOFC. The uniformity of the flame temperature is vital in the DFFC system since the non-uniform distribution of the flame temperature greatly increases the failure probability.

Effects of mechanical properties and atherosclerotic artery size on biomechanical plaque disruption – Mouse vs. human

Mouse models of atherosclerosis are extensively being used to study the mechanisms of atherosclerotic plaque development and the results are frequently extrapolated to humans. However, major differences have been described between murine and human atherosclerotic lesions and the determination of similarities and differences between these species has been largely addressed recently. This study takes over and extends previous studies performed by our group and related to the biomechanical characterization of both mouse and human atherosclerotic lesions. Its main objective was to determine the distribution and amplitude of mechanical stresses including peak cap stress (PCS) in aortic vessels from atherosclerotic apoE-/- mice, in order to evaluate whether such biomechanical data would be in accordance with the previously suggested lack of plaque rupture in this model. Successful finite element analysis was performed from the zero-stress configuration of aortic arch sections and mainly indicated (1) the modest role of atherosclerotic lesions in the observed increase in residual parietal stresses in apoE-/- mouse vessels and (2) the low amplitude of murine PCS as compared to humans. Overall, the results from the present study support the hypothesis that murine biomechanical properties and artery size confer less propensity to rupture for mouse lesions in comparison with those of humans.

Determination of the dislocation structure in paratellurite single crystals using the piezo-optic effect

It is shown theoretically and experimentally that dislocations in paratellurite single crystals can be revealed using the piezo-optic effect. The mechanical-stress distribution near dislocations is calculated. Dislocations in the samples are observed using the photoelastic method and chemical etching. Data on the spatial distribution of dislocations in Czochralski-grown paratellurite crystals are reported.

Mechanical Stress Analyses of Packaged Pressure Sensors for Very High Temperatures

Methods for investigations of stresses specialized for devices operating up to 500°C are presented in this study. Resistive pressure sensors and test chips with microstrain (μ-strain) gauges are processed in thin film technology. The sensor structure was a Wheatstone bridge on a silicon membrane with platinum resistors. The μ-strain gauges were characterized with tensile tests in combination with optical strain measurements. A gauge factor of 3.6 was measured at room temperature. After characterization as bare dice, the chips were mounted with a borosilicate glass solder on two ceramic substrates, AlN and Si3N4. We generated a FE model of the sensor assemblies including temperature-dependent material properties. The distribution of mechanical strains and stresses in the sensor was analyzed. The chip warpage dependent on temperature up to 500°C was obtained from FE simulations and compared with high-precision 3D deformation measurements. Deformation results from digital image correlation (DIC) verified the utilized FE model. The correlation of experimental results for the chip warpage exhibited good agreement with the numerical results obtained from FEM. The chip deflection from the center to the edges in the out-of-plane direction on AlN was 4.5 μm; on Si3N4 a concave warpage of 3 μm at 25°C was found. Temperature-induced deformations of the sensor chip in the range of micrometers were recorded up to 500°C. The output signal of the pressure sensors is strongly affected by superimposed strains based on the sensor assembly. The bridge voltage increased by 40% after the glass solder process on AlN and by 34% for devices on Si3N4. The analysis of the μ-strain gauges showed compressive strains in the sensor membrane of −1.39% on average for assemblies on AlN and of −0.168% for glass soldered chips on Si3N4. The FEM simulations revealed an average in-plane stress in the sensor membrane of −45 MPa for chips on AlN and −20 MPa for Si3N4 substrates. The compressive strains in the membrane obtained by FEM were verified by the μ-strain gauge measurements. A higher strain and stress gradient in the membrane of devices on AlN was found with FEM, which is consistent with the higher signal offset of assembled pressure sensors that was measured in this study.

Finite Element Modeling of Shear Strain in Asymmetric and Symmetric Rolling in Multi Roll Calibers

Methods of severe plastic deformation are used in the production of profiles for automobile, aircraft and chemical industry, medical implants, etc. However these methods have some shortcomings (low manufacturability, small size of produced bars, uneven distribution of deformations and mechanical stresses throughout cross sections and length of bars, significant heterogeneity of a deformable material structure, low ratio of material utilization, irregularity and anisotropy of deformed bars characteristics etc.). It significantly limits possibilities of their wide commercial use. New methods and apparatus of asymmetric rolling of metal profiles in multi roll passes are developed at Magnitogorsk State Technical University named after Nosov. Numerical comparison of values of shear strain in case of symmetric and asymmetric rolling is made in the paper. Adequacy of the developed models is demonstrated.

Characterization of local residual stress inhomogeneities in combined wire drawing processes of AISI 1045 steel bars

Cold formed semi-finished products face an increasing demand from industry as they can be manufactured to dimensional precision and high surface quality. Products from cold formed bar, on the other hand, may contain inhomogeneous distributions of mechanical properties and residual stresses which arise from the elastic response of the material to an inhomogeneous distribution of elastic–plastic strains. These material properties may cause distortion in further manufacturing operations, and consequently, precision of components then could be reestablished at higher costs only. X-ray diffraction residual stress analysis, for example, is misleading if only slices or cross sections of a bar or a component are considered and residual stress fields and their variations are neglected. Automotive products generally are cut from drawn bars, and local differences in microstructure, mechanical properties and residual stress states are increasing the danger of dimensional changes out of a specified range. Cold-drawn bars were manufactured with different drawing angles and uncoated and TiCN-coated dies. Surface and subsurface properties were investigated along the length and around the periphery of drawn bars. Differences in material states, those affected by the contact zone and those related to the elastic–plastic deformation of the drawing process, were observed. The variation of surface residual stresses of up to a factor of 2 can be correlated with locally different friction coefficients and slip stick effects. As subsurface material states (residual stresses and strain hardening) do not show a significant variation around the periphery and along the length of bars, the effects of geometry variations of hot rolled bar, the effect of a not perfectly concentric bar at the die entrance and/or the level of pre-straightening ahead of drawing are assumed to be of minor importance, compared to the high level of plastic strain involved in cold drawing. The local properties identified here will lead to a higher degree of dimensional scatter of individual automotive components cut from these long cold-drawn bars.

Frequency characteristics of elastically fastened cantilevered laminated beams

We consider the application of a new method aimed at the analysis of the stress state to the evaluation of the influence of the conditions of fastening of laminated beams on their dynamic properties. We study the stress state in the zone of fastening in detail. The proposed theoretical model includes the analysis of strains in layers with regard for the transverse shear strains and normal strains and stresses. We carry out the numerical analysis of the dependence of the frequency spectrum on the anisotropy of the mechanical properties and stress distribution in the region of elastic fastening.

Finite Element Analysis and Design of Thermal–Mechanical Stresses in Multilayer Ceramic Capacitors

A three‐dimensional finite element model describing the thermal–mechanical stress distribution in multilayer ceramic capacitors (MLCCs) during termination firing, soldering, and bending tests is presented. Numerical results indicate that the thermal residual stresses originating from the soldering process are approximately one‐fifth to half of the magnitude of the flexural stresses at the crack occurrence during the board flex test. The peak tensile stress from numerical simulations correlates with the crack initiation site observed in situ in board flex tests. The effects of inner electrode number, solder wicking height, lateral margin length, and the thickness of nickel in the termination component on mechanical failure during the board flex test are also investigated. Numerical results demonstrate that the maximum tensile stress could be effectively relieved by increasing the length of the lateral margin. In addition, a judicious combination of the solder wicking height and nickel termination thickness can further diminish the peak tensile stress during the board flex test. Finally, better design criteria are also developed by modifying the geometric parameters of MLCCs using Taguchi orthogonal arrays to decrease the peak tensile stresses that occur during board flex tests.