Mechanical Stress Analysis Research Articles

Final Design of the New Grenoble Hybrid Magnet

A CEA-CNRS French collaboration is currently developing a new hybrid magnet; this magnet combines a resistive insert composed of Bitter and polyhelix coils and a new large bore superconductor outsert to create an overall continuous magnetic field of 42+ T in a 34 mm warm aperture. The design of the superconducting coil outsert has been completed after thorough studies and successful experimental validation phases. Based on the novel development of a Nb-Ti/Cu Rutherford Cable On Conduit Conductor (RCOCC) cooled down to 1.8 K by the mean of a bath of superfluid helium at atmospheric pressure, the superconducting coil aims to produce a continuous magnetic field of 8.5 T in a 1.1 m cold bore diameter. The main results of the final design studies of the superconducting coil are presented including the 2D and 3D mechanical stress analysis, the conductor and coil specifications, the coil protection system as well as the required cryogenics infrastructure. The final design of the resistive insert coils is also described.

Dynamic modeling, simulation, and MIMO predictive control of a tubular solid oxide fuel cell

Solid oxide fuel cells are a promising option for distributed energy stationary power generation that offers efficiencies up to 50% in stand-alone applications, 70% in hybrid gas turbine applications and 80% in cogeneration. To advance SOFC technology sufficiently for widespread market penetration, the SOFC must demonstrate improved cell lifetime from the status quo. Much research has been performed to improve SOFC lifetime using advanced geometries and materials, and in this research, we suggest further improving lifetime by designing an advanced control algorithm based upon preexisting mechanical stress analysis [1]. Control algorithms commonly address SOFC lifetime related operability objectives using unconstrained, SISO control algorithms that seek to minimize thermal transients. While thermal fatigue may be one thermal stress driver, these studies often do not consider maximum radial thermal gradients or critical absolute temperatures in the SOFC. In addition, researchers often discuss hot-spots as a critical lifetime reliability issue, but as previous stress work demonstrates, the minimum cell temperature is the primary thermal stress driver in tubular SOFCs modeled after the Siemens Power Generation, Inc. design. In this work, we present a dynamic, quasi-two-dimensional model for a high-temperature tubular SOFC combined with ejector and prereformer models. The model captures dynamics of critical thermal stress drivers and is used as the physical plant for closed-loop simulations with a constrained, MIMO model predictive control algorithm. Closed-loop simulation results demonstrate effective load-following, operability constraint satisfaction, and disturbance rejection.

The Strength Analysis of Aircraft Landing Gear Strut Based on ANSYS

Because the landing gear structure is complicated, it is difficult to draw accurate stress and strain distribution through the theoretical calculation. In this paper, based on the modeling and stress analysis of the buffer mechanism of aircraft landing gear, by converting the stress of a dynamic system into a static stress, the force of the landing gear struts are calculated. This paper analyzes the strength of the aircraft main landing gear by using computer simulation technology and finite element analysis, it provides an effective basis for maintenance and the damage prediction

On the crack propagation modeling of hydraulic fracturing by a hybridized displacement discontinuity/boundary collocation method

Numerical methods such as boundary element and finite element methods are widely used for the stress analysis in solid mechanics. This study presents boundary element method based on the displacement discontinuity formulation to solve general problems of interaction between hydraulic fracturing and discontinuities. The crack tip element and a higher order boundary displacement collocation technique are used to study the hydraulic fracture propagation and its interaction with the pre-existing cracks and discontinuities in an elastic rock mass. The maximum tangential stress criterion (or -criterion) and the strain energy density criterion (SED) are used to obtain the fracture path and the results of both criteria are compared with each other. The comparison of numerical method with the results brought in the literature shows a good performance of the method in the case of interacting cracks.

Mechanical Stress Analysis and Evaluation of Hybrid Land Grid Array Attached Large Form Factor Organic Modules

Recent industry trends to continue enabling increased server system performance and packaging density has driven the need to implement larger form factor hybrid land grid array (LGA) attached organic modules. In addition, given the need to package multiple modules on a single printed circuit board (PCB) assembly, PCB cross-sections and their corresponding physical properties (e.g., flatness, etc.) as well as module bottom surface metallurgy (BSM) co-planarity require a more detailed understanding of impacts to the compliant as well as the soldered connector interfaces. Lastly, the migration to lead (Pb)-free solders has further complicated the issue given both the change in material properties as well as processing temperatures. In this paper we will discuss the mechanical stress analysis and evaluation tests assessment of a recently developed 50 mm square organic processor module, hybrid LGA attached to a multiple site PCB. The analysis presented will highlight the methodology to identify both connector soldered stress and predicted contact load variation across the module's mated interface. Key parameters discuss will include the PCB flatness, Organic substrate BSM co-planarity (both predicted and measured) and the Hybrid LGA as-soldered contact co-planarity. Corroborating predicted analytical results, we will discuss various evaluation tests performed to validate the design's integrity. Key tests include, pressure sensitive film (PSF) studies and environment stress exposures, including thermal shock, mechanical shock and vibration and seismic exposure. Post test electrical integrity and test sample construction analysis, including 3D x-ray and mechanical cross-section, will also be described. The analysis process and testing described will provide a method to evaluate more challenging hybrid LGA applications as both module sizes and/or number applied per PCB assembly increase and Pb-free assembly is introduced in future applications.

In-Situ Analysis of Deformation and Mechanical Stress of Packaged Silicon Dies With an Array of Hall Plates

A technique is presented that allows to simultaneously measure stress and deformation of packaged silicon dies. Required is a test chip with an array of Hall plates assembled in a package made of nonmagnetic materials. Exploiting the highly anisotropic magnetic sensitivity of the integrated Hall plates in an external magnetic field, makes it possible to measure the deformation. Moreover, the piezoresistive and piezo-Hall effect allow for measurements of several stress components without extra sensor elements. An optical measurement verifies the new technique, and a standard plastic package is exemplarily analyzed at different temperatures, under the influence of an external force, and at moisture load. The combined knowledge of stress and deformation allows for deeper insight into the mechanical impact of packaging on integrated circuits.

운전조건을 고려한 전기자동차 구동용 IPMSM의 수치해석 기반의 제 특성 해석

This Paper presents characteristic analysis in terms of interior permanent magnet synchronous motor for electric vehicle propulsion using numerical analysis. Torque ripple analysis, thermal analysis, demagnetization analysis of permanent magnet and mechanical stress analysis with variable operating condition are presented. According to these characteristic analysis, both the performance of motor and possible problems during the operation are examined thoroughly in advance.

Temperature and thickness effects on thermal and mechanical stresses of rotating FG-disks

In the present paper, radial and hoop thermal and mechanical stress analysis of a rotating disk made of functionally graded material (FGM) with variable thickness is carried out by using finite element method (FEM). To model the disk by FEM, one-dimensional two-degree elements with three nodes are used. It is assumed that the material properties, such as elastic modulus, Poisson’s ratio and thermal expansion coefficient, are considered to vary using a power law function in the radial direction. The geometrical and boundary conditions are in the shape of two models including thermal stress (model-A) and mechanical stress (model-B). In model-A there exists no pressure in both external and internal layers, and there is a temperature distribution considered as a second order function in the radial direction of the rotating disk. In this case, the temperature dependency of the material properties is considered and a hyperbolic type is assumed for the geometry of the disk. In model-B, there is a constant pressure only on the internal layer and a pressure on the internal layer of the disk without temperature distribution but with different types of surface profiles. Furthermore, the displacements and stresses for various power law indices (N) and angular velocities are calculated and compared to other results in the literature. The effect of varying thicknesses and dependency of material properties on temperature distribution is investigated.

Multi-physics MRI-based two-layer fluid–structure interaction anisotropic models of human right and left ventricles with different patch materials: Cardiac function assessment and mechanical stress analysis

Multi-physics right and left ventricle (RV/LV) fluid –structure interaction (FSI) models were introduced to perform mechanical stress analysis and evaluate the effect of patch materials on RV function. The FSI models included three different patch materials (Dacron scaffold, treated pericardium, and contracting myocardium), two-layer construction, fiber orientation, and active anisotropic material properties. The models were constructed based on cardiac magnetic resonance (CMR) images acquired from a patient with severe RV dilatation and solved by ADINA. Our results indicate that the patch model with contracting myocardium leads to decreased stress level in the patch area, improved RV function and patch area contractility.

Stress-function variational method for stress analysis of bonded joints under mechanical and thermal loads

High interfacial stresses near the ends of adherends are responsible for debonding failure of bonded joints used extensively in structural engineering and microelectronics packaging. This paper proposes a stress-function variational method for determination of the interfacial stresses in a single-sided strap joint subjected to mechanical and thermal loads. During the process, two interfacial shear and normal (peeling) stress functions are introduced, and the planar stresses of adherends of the joints are expressed in terms of the stress functions according to the static equilibrium equations. Two coupled governing ordinary differential equations (ODEs) of the stress functions are obtained through minimizing the complementary strain energy of the joints and solved explicitly in terms of eigenfunctions. The stress field of the joints based on this method can satisfy all the traction boundary conditions (BCs), especially the shear-free condition near the adherend ends. Compared to results based on finite element method (FEM) and other analytic methods in the literature, the present variational method is capable of predicting highly accurate interfacial stresses. Dependencies of the interfacial stresses upon the adherend geometries, moduli and temperature are examined. Results gained in this study are applicable to scaling analysis of joint strength and examination of solutions given by other methods. The present formalism can be extended conveniently to mechanical and thermomechanical stress analysis of other bonded structures such as adhesively bonded joints, composite joints, and recently developed flexible electronics, among others.

ERROR AND UNCERTAINTY QUANTIFICATION AND SENSITIVITY ANALYSIS IN MECHANICS COMPUTATIONAL MODELS

Multiple sources of errors and uncertainty arise in mechanics computational models and contribute to the uncertainty in the final model prediction. This paper develops a systematic error quantification methodology for computational models. Some types of errors are deterministic, and some are stochastic. Appropriate procedures are developed to either correct the model prediction for deterministic errors or to account for the stochastic errors through sampling. First, input error, discretization error in finite element analysis (FEA), surrogate model error, and output measurement error are considered. Next, uncertainty quantification error, which arises due to the use of sampling-based methods, is also investigated. Model form error is estimated based on the comparison of corrected model prediction against physical observations and after accounting for solution approximation errors, uncertainty quantification errors, and experimental errors (input and output). Both local and global sensitivity measures are investigated to estimate and rank the contribution of each source of error to the uncertainty in the final result. Two numerical examples are used to demonstrate the proposed methodology by considering mechanical stress analysis and fatigue crack growth analysis.

Electro-hydraulic control research of hydraulic support hand-control directional valve with the MR fluid base

By analyzing the driving moment of the hydraulic support hand-control directional valve, this paper presents an electro-hydraulic control method for the directional valve with a magneto-rheological (MR) valve base. Firstly, the theoretical values of the control moment on the feed oil loop and return oil loop of the directional valve are calculated based on the operating principle of the valve and the stress analysis of the control mechanism. Then, the actuator of the directional valve with MR valve base is designed and the mathematical model of its operation moment is established. Simulation and test results show that this method can realize the electro-hydraulic control of the hydraulic support hand-control directional valve, a nd satisfy the regulation of intrinsic safety.

A New Design for the Superconducting Outsert of the GHMFL 42+ T Hybrid Magnet Project

A new superconducting coil outsert has been designed to be integrated within the existing infrastructure of the GHMFL hybrid project. Based on the novel development of a Nb-Ti Rutherford Cable On Conduit Conductor (RCOCC) cooled at 1.8 K by a bath of superfluid helium at atmospheric pressure, the superconducting coil aims to produce a continuous magnetic field of 8.5 T in a 1.1 m bore diameter. Combined with resistive insert coils, an overall continuous magnetic field of 42+ T will be produced in a 34 mm warm aperture. The main results of the conceptual study are reported including the conductor and coil specifications, the mechanical stress analysis, the coil protection scheme as well as the required cryogenics infrastructure. First developments and tests regarding the RCOCC are also presented.

Engineering Design of the Superconducting Outsert for 40 T Hybrid Magnet

A 40 T hybrid magnet system will be built at the Chinese High Magnet Field Laboratory (CHMFL), Chinese Academy of Sciences. It will include a 29 T resistive insert with a clear bore of 32 mm and a 11 T superconducting outsert with a room temperature bore of 580 mm. The superconducting outsert, which will be wound with cable-in-conduit conductors (CICC), is graded in function of the magnetic field. The high field section of the superconducting outsert will use superconductors and the low field section will be made of NbTi superconductors. At present, the preliminary design of the superconducting outsert has almost been completed. This paper describes features, such as conductor design, coil winding, heat treatment, support structure design, mechanical stress analysis.

Rotor-Design Strategy of IPMSM for 42 V Integrated Starter Generator

In this paper, we proposed an optimal design strategy of interior permanent magnet synchronous machine (IPMSM) considering various design constraints in the 42 V integrated starter generator (ISG). Since conventional optimal process needs much calculating time to check many constraints such as high starting torque, the high generating power at the maximum speed, we adopted AT-MGPSO as an optimization algorithm due to its special advantage that it can efficiently search superior peaks in the multimodal problem with short time. In addition, in order to deal with mechanical stress in the rotor by centrifugal force at maximum speed we combined mechanical stress analysis with the optimal design process. The validity of our proposed methods was verified by comparing simulation results with experimental data.

In situ and postradiation analysis of mechanical stress in Al 2O 3:Cr induced by swift heavy-ion irradiation

Optical spectroscopy and TEM techniques have been applied to study the radiation damage and correlated mechanical stresses in Al 2O 3 and Al 2O 3:Cr single crystals induced by (1–3) MeV/amu Kr, Xe and Bi ion irradiation. Mechanical stresses were evaluated in situ using a piezospectroscopic effect through the shift of the respective lines in ionoluminescence spectra. It was found that dose dependence of the stress level for Xe and Bi ions, when ionization energy loss exceeds the threshold of damage formation via electronic excitations, exhibits several alternate stages showing the build-up and relaxation of stresses. The beginning of relaxation stages is observed at fluences associated with beginning of individual ion track regions overlapping. The residual stress profiles through the ion irradiated layers were deduced from depth-resolved photostimulated spectra using laser confocal scanning microscopy set-up. It was determined that stresses are compressive in basal plane and tensile in perpendicular direction in all samples irradiated with high energy ions.

Three-Dimensional Finite Element Analysis of Mechanical Stress in Symphyseal Fractured Human Mandible Reduced With Miniplates During Mastication

In this study we tried to analyze the stress distribution in a symphyseal fractured human mandible reduced by 2 different methods--reduction with 1 miniplate or with 2 miniplates--by using finite element (FE) analysis, and then compared the results with an intact mandible. Three-dimensional FE models of an intact mandible and symphyseal fractured mandibles reduced by 2 fixation methods were developed to analyze mandibular stress distribution and bite forces under 2 basic loading conditions, namely, clenching in the intercuspal position and left unilateral molar clenching. Groups of parallel vectors were used to simulate 9 pairs of masticatory muscles involved in the 2 static biting tasks. Stress distributions in reduced mandible with 1 or 2 miniplates were more or less different from that of the intact mandible. The maximum stress occurred at the biting point. Meanwhile, the subcondylar region was a stress-bearing area. During left unilateral molar clenching, bite forces obviously reduced after fracture. Bite force and the stress distribution pattern in the mandible reduced with 2 miniplates were closer to that in the intact mandible. It is suggested that the effect of the miniplates in stabilizing the continuity-broken mandible influence the restorations of the stress distribution pattern and bite force. Two miniplates have a biomechanical advantage over 1 miniplate on these restorations.

3D finite element modeling of the thermally induced residual stress in the hybrid laser/arc welding of lap joint

In this study, a three-dimensional (3D) finite element model is developed to investigate thermally induced stress field during hybrid laser–gas tungsten arc welding (GTAW) process. In the hybrid welding case, we focus on the GTAW process sharing common molten pool with laser beam and playing an augment role in the hybrid welding system. An experiment-based thermal analysis is performed to obtain the temperature history, which then is applied to the mechanical (stress) analysis. A modified material model is used to consider the influence of face-to-face contact between the top and bottom metal sheets in the thermo-mechanical analysis of welding lap joints. Results show that the normal stress components prevail in the weld zone during hybrid welding process, and maximum thermal stress exceeding the yield point of material exists at the heat affected zone (HAZ) near the weld pool. Increasing the welding speed causes the penetration and width of weld bead to decrease, and the thermal stress concentration at the welded joint is also reduced accordingly. After welding and cooling down, longitudinal tensile stress (SZ) and transverse compressive stress (SX) are retained in the formed weld, and the higher longitudinal compressive stress exists around the weld bead. In addition, a series of experiments are performed to validate the numerical results, and a qualitative agreement is achieved. Compared to the welded joint obtained by GTAW and laser welding alone, the residual stress concentration in the weld joint obtained by hybrid laser–GTAW is the minimal one.

Volume fraction optimization for step-formed functionally graded plates considering stress and critical temperature

Step-formed Functionally Graded Materials (FGMs) flat panels are investigated for volume fraction optimization by considering stress and critical temperature. The structure is composed of numerous layers with homogeneous and different isotropic material properties from ceramic to metal. Material properties are assumed to be temperature dependent, and remain constant in each layer. Further, the properties are assumed to be varied in the thickness direction according to a simple power law distribution in terms of the ceramic and metal volume fractions for the layer. The effective material properties of the plate are obtained by applying linear rule of mixtures for the layers. The 3-D finite element model is adopted to analyze more accurately the variation of material properties and temperature field in the thickness direction. For the various FGM volume fraction distributions and geometric parameters, mechanical stress analysis and thermo-mechanical buckling analysis are performed to get the critical conditions. Based on the results, the volume fraction optimization of the flat panels is performed for stress reduction and improving thermo-mechanical buckling behavior and compared with previous results.

Mechanical Stress Analysis of Microfluidic Environments Designed for Isolated Biological Cell Investigations

Advancements in technologies for assessing biomechanics at the cellular level have led to discoveries in mechanotransduction and the investigation of cell mechanics as a biomarker for disease. With the recent development of an integrated optical tweezer with micron resolution particle image velocimetry, the opportunity to apply controlled multiaxial stresses to suspended single cells is available (Neve, N., Lingwood, J. K., Zimmerman, J., Kohles, S. S., and Tretheway, D. C., 2008, "The muPIVOT: An Integrated Particle Image Velocimetry and Optical Tweezers Instrument for Microenvironment Investigations," Meas. Sci. Technol., 19(9), pp. 095403). A stress analysis was applied to experimental and theoretical flow velocity gradients of suspended cell-sized polystyrene microspheres demonstrating the relevant geometry of nonadhered spherical cells, as observed for osteoblasts, chondrocytes, and fibroblasts. Three flow conditions were assessed: a uniform flow field generated by moving the fluid sample with an automated translation stage, a gravity driven flow through a straight microchannel, and a gravity driven flow through a microchannel cross junction. The analysis showed that fluid-induced stresses on suspended cells (hydrodynamic shear, normal, and principal stresses in the range of 0.02-0.04 Pa) are generally at least an order of magnitude lower than adhered single cell studies for uniform and straight microchannel flows (0.5-1.0 Pa). In addition, hydrostatic pressures dominate (1-100 Pa) over hydrodynamic stresses. However, in a cross junction configuration, orders of magnitude larger hydrodynamic stresses are possible without the influence of physical contact and with minimal laser trapping power.