Local Stress Analysis Research Articles

Experimental and numerical analysis of quasi-static bubble size and shape characteristics at detachment

When investigating the physical mechanisms responsible for pool boiling heat transfer, individual bubbles are commonly assumed to be spherical. This is done in order to ease the computational expense when solving the Navier–Stokes equations. However, bubbles are observed to deviate from spherical depending on fluid properties, cavity sizes and gravitational field strengths. Since it is bubble detachment volume that dictates ebullition frequency, improvements in detachment size and shape predictions would improve nucleate pool boiling heat and mass transfer models.Recent studies have shown that a numerical treatment of the capillary equation’s detachment criterion – which is a result of an interfacial pressure balance analysis – generates profiles corresponding to axis-symmetric quasi-static bubbles for adiabatic conditions. In the present work, this criterion is validated for heat induced bubbles providing the basis for a full analysis of size and shape characteristics of a detaching vapour bubble. A volume detachment correlation is validated for heat induced vapour bubbles and detachment correlations for other size and shape characteristics such as bubble height, width, apex principal radius of curvature, contact angle, and degree of sphericity are developed. Furthermore, a local stress analysis reveals detachment regimes and bubble profile regions.

Ab initio study of symmetrical tilt grain boundaries in bcc Fe: structural units, magnetic moments, interfacial bonding, local energy and local stress

We present first-principle calculations on symmetric tilt grain boundaries (GBs) in bcc Fe. Using density functional theory (DFT), we studied the structural, electronic and magnetic properties of Σ3(111) and Σ11(332) GBs formed by rotation around the [110] axis. The optimized structures, GB energies and GB excess free volumes are consistent with previous DFT and classical simulation studies. The GB configurations can be interpreted by the structural unit model as given by Nakashima and Takeuchi (2000 ISIJ 86 357). Both the GBs are composed of similar structural units of three- and five-membered rings with different densities at the interface according to the rotation angle. The interface atoms with larger atomic volumes reveal higher magnetic moments than the bulk value, while the interface atoms with shorter bond lengths have reduced magnetic moments in each GB. The charge density and local density of states reveal that the interface bonds with short bond lengths have more covalent nature, where minority-spin electrons play a dominant role as the typical nature of ferromagnetic Fe. In order to understand the structural stability of these GBs, we calculated the local energy and local stress for each atomic region using the scheme of Shiihara et al (2010 Phys. Rev. B 81 075441). In each GB, the interface atoms with larger atomic volumes and enhanced magnetic moments reveal larger local energy increase and tensile stress. The interface atoms constituting more covalent-like bonds with reduced magnetic moments have lower local energy increase, contributing to the stabilization, while compressive stress is generated at these atoms. The relative stability between the two GBs can be understood by the local energies at the structural units. The local energy and local stress analysis is a powerful tool to investigate the structural properties of GBs based on the behavior of valence electrons.

FEA Structural Stress of Modalohr System for Semi-trailer Rail Transportation: Weld Root Fatigue Focus

In order to fulfill green requirement (reduction of CO2 emissions given by French “Grenelle”), a great need appears concerning roll-on roll-off efficient technology. Heavy seam welded structures manufacturer has to present an optimized product to fulfill this requirement. In this purpose, the Modalohr system overcomes several challenges: transport 4m height and 38 tons semi- trailer in UIC kinematic gauging with a low floor rail vehicle, use of conventional large wheel bogie with maximum axle load, 9 million kilometers running over 30 years service life. For cost effectiveness, the compact vehicle design uses welded assembly and avoids systematic full penetration welds which may require costly preparation machining. The idea is to develop a one shot FEA which provides both global structural bending and torsional vehicle behaviors and also the fatigue focus on each joint for both weld toe and weld root. The local stress analysis requires too much effort and the structural stress using appropriate inclined shell element in a global system model complies such requirement. A home made tool implements these techniques. LOHR “Seam Sim” development deals with the partial automation of the FEA model generation based on the following key points: solid weld feature are generated in CAD, FEA model automation idealization is achieved without additional manual operation. Postal2 post processing tool has been developed to allows standard FEA code results processing for both static and fatigue assessment. The final display is a scalar stress safety margin map associated for each element to the appropriate criterion over the system depending on the area type; plain metal, sheet metal edges, weld toe, weld root, bolt connection … “Seam Sim” theory [2,3] and Verification & Validation (V&V) has been presented during last fatigue Design conference in 2011 [4], today's aim is to present a highly fatigue demanding industrial application. Loads are applied at a system level to fulfill EN12663-2 standard and additional manufacturer load cases (including longitudinal dynamic fatigue load for 1050m long train and lifting, boarding kinematic load cases). The fatigue results are focused on each detail.

Analysis of micro-Raman spectra combined with electromagnetic simulation and stress simulation for local stress distribution in Si devices

We have developed a Raman simulation method using a finite-difference time-domain electromagnetic simulation and a finite element method stress simulation for precise local stress analysis of Si devices. This method accounts for the modification of light distribution by the sample structure, which significantly affects the Raman spectra near a metal gate structure with high refractive index and extinction coefficient. The precise stress estimation by this method is verified by analyzing polarized UV Raman measurements of a metal-oxide semiconductor field-effect transistor structure with a metal gate.

Analysis of Local Stress and Vertical Deflection of Down Chord of Inverted Triangle Cargo Boom of Tower Crane

Based on the inverted triangle cargo boom of ST80238 tower crane as the research object, the author took its local down chord as calculation model. ANSYS software is applied to impose the constraints and loads on the model, and the stress and deflection are analyzed. The results show that the top flange of the down chord and the web will be influenced by the axial force of the oblique truss, and larger local stress in the joint position and the surrounding of the oblique truss and the down chord are produced, as well as the largest local stress will be produced in the centre of the connective position, and reducing gradually to the surrounding. In the condition of the box section center line of the down chord is constant, moreover the size of the down flange and the web is increased, and the local stress and vertical deflection nearby the joint of the oblique truss and the down chord will be reduced. Though the research, the local instability of down chord of ST80238 tower crane can be prevented,and a direct reference and basis for box beam of down chord can be provided.

Fluid‐driven multiple fracture growth from a permeable bedding plane intersected by an ascending hydraulic fracture

In bedded sedimentary rocks, the energy for spontaneous growth of multiple vertical fractures from a bedding plane may be provided by an overpressurized sublayer fracture that connects a fluid source to the bedding plane. In this paper, using our coupled deformation and flow model, we study the processes and mechanisms involved in the formation and interaction of closely space fractures from preexisting flaws or starter fractures located along the bedding plane. Fracture growth from multiple flaws can be convergent, parallel or divergent, depending on the factors like contrasts in moduli and far‐field stresses, flaw sizes and locations, and initial bed conductivity, fluid viscosity, and injection rate, as well as time. The results presented here have been obtained for conditions where fluid viscous dissipation is dominant, in contrast to other results available in literature based on uniform pressure assumption equivalent to use of an inviscid fluid. It is demonstrated that the earlier a hydraulic fracture starts to extend, the more likely it is to become the primary fracture in a system of closely spaced fractures. The fracture closest to the fluid source typically grows faster as a result of a higher pressure level because viscous dissipation results in a decrease in pressure with distance from the fluid source. But its development does not completely inhibit the growth of other hydraulic fractures. Simultaneous growth of closely spaced fractures is supported by the local stress and energetic analyses, and the fracture distance can be very small. Their length to spacing ratio is accordingly much larger than that predicted previously. Under certain circumstances, a longer and more permeable fracture may grow to a greater extent than a shorter fracture closer to the fluid source, which may grow toward and merge with the longer fracture to create fracture clusters adjacent to a bedding plane.

Method for processing of the results of low-cycle fatigue tests

We propose a method for processing the data of low-cycle fatigue testing metals. This method enables us to determine the characteristics of the materials in various periods of the fatigue life. The results ob- tained by using the proposed method make it possible to take into account all visible changes in the cy- clic properties of the material in the course of fatigue-life calculations. This is of especial importance for materials characterized by the absence of stabilization period. In the method of fatigue-life calculations based on the local strain and stress analyses (1), it is customary to use the data on materials determined in the course of fatigue tests in the area of low-cycle fatigue. The proce- dures of realization of the tests and processing of their results correspond to the ASTM E 606-04: Standard Prac- tice for Strain-Controlled Fatigue Testing. According to the directions specified in this document, the low-cycle properties of metals are determined on the basis of constant-amplitude tests for several (minimum five) levels of controlled stresses or strains (2). For each level of strains or stresses, at least three fatigue tests are performed. In each fatigue test, instantaneous values of the loading force and strains formed in the specimen are recorded for the selected loading cycles. The recorded values of stresses and strains enable to carry out the analysis of the basic parameters of the hysteresis loop and deduce relations between these parameters. One of the two characteristics evaluated on the basis of the performed fatigue tests is the diagram of cyclic strains describing the relationship between the plastic strain amplitude eap and the stress amplitude σ a . It is assumed that these parameters obey an exponential relationship from the stabilization period. In the bilogarith- mic coordinate system, this relationship is described by the Morrow equation (3):

Fatigue damage assessment of corroded oil tanker details based on global and local stress approaches

Fatigue damage assessment of double hull oil tanker structural details is performed, based on global and local structural finite element models. The wave-induced vertical and horizontal bending moments, as well as local pressure loads are accounted for in the fatigue damage calculations. Local stress analyses are considered based on the notch stress approach. Time-dependent stresses as a function of corrosion deterioration are analyzed based on nonlinear corrosion wastage during the design life of ship. The effective notch stress approach is applied for analyzing the stress distributions and the fatigue damage of the welded joint at two hotspots. The hotspots are located between the flat bar stiffener of a transverse web frame and the flange of a longitudinal stiffener at the side shell of a tanker ship hull. The details under consideration are modeled separately in a fine mesh employing the sub model techniques. Finally the fatigue damage assessment accounting for corrosion deterioration of the considered hotspots is analyzed.

Identification of local stress parameters influencing the optimum design of box girders

Research into the effect of local stress on the carrying capacity and optimum design of box girders was performed in this paper. A mathematical model of the girder was created for the purpose of defining the stress–strain state of local character. Mathematical dependence which defines the length of the influential zone in box girders was established. The segment length relevant for the analysis of local stress is functionally dependent on geometrical parameters of the girder cross section, area of action and size of load. The methodology carried out in this paper showed that the identification of local stress can be performed only on a segment of the girder. The procedure of calculation and experimental determination of the local stress state in carrying structures was thus considerably simplified, without reducing accuracy. The influential parameters were identified and the guidelines for optimum design of quadrilateral shape of the girder cross section were given from the aspect of local stress. The comparative analysis was used to establish, under the same conditions of global carrying capacity, a more favourable stress state in trapezoidal shape in comparison with the traditional rectangular cross section of the girder. Application of the results of this paper is a contribution to the process of optimal design of supporting structures, especially those that are used for construction of transport equipment and rack structures in storage systems, where the effect of reducing the weight affects on the efficiency of transport in supply chains.

Influence of Attachment Rigidity on Stress Analysis

In pressure vessels design, WRC107 provides a typical method of local stress analysis to supports and attachments. But influence of the rigidity of attachments on calculation is not considered. For fatigue analysis of round hollow attachment on cylindrical shell, equivalent stresses calculated by WRC107 were compared with those by finite element method. Three attachment thickness configurations, that half, equal, double of the shell thickness were tested. Results show that, in key point Au defined by WRC107 equivalent stress decreases while attachment rigidity increases, and in key point Cu, equivalent stress increases while attachment rigidity increases. When the thickness of attachment equals to that of shell, equivalent stress of WRC107 in Cu comes closest to FEM.

Global and Local Elastic-Plastic Stress Analysis of Coke Drum Under Thermal-Mechanical Loadings

Coke drums are critical equipment in the petroleum industry. The failure modes of coke drums include excessive bulging deformation and fatigue cracking. The elastic-plastic behavior of a coke drum, subjected to both thermal and mechanical loadings, is analyzed for a complete cycle of operation. The effects of multiple operational cycles and localized hot/cold spots are also investigated. It is found that yielding of the clad layer starts at the very early stage in an operating cycle and permanent deformation is caused in the first operating cycle. Plastic shakedown occurs in the clad layer under combined operating thermal and mechanical loadings. It is also found that both hot and cold spots will cause bulging of the shell and the cold spot can cause more severe deformation than the hot spot.

Local stress analysis in granular materials at a mesoscale

SUMMARYThe purpose of this paper is to contribute to the change of scale techniques developed for granular materials. The proposed approach consists in considering an intermediate scale between the macroscales and microscales, called the mesoscale, using the classical homogenization scheme. In this approach, the mesoscale for 2D granular materials was defined at the level of local volumes, called mesodomains, which are local closed structures composed of particles in contact. In this paper, we focused on defining a local stress field at this scale. Two different methods are proposed, both based on the equivalent continuum mean stress but using different approximations of the mean stress tensor for each mesodomain. The two proposed methods were then compared to each other. Analyses performed on the stress field at the mesoscale show that this local field is heterogeneous and, in particular, that its heterogeneity is significantly structured at this scale. The distribution of the local mean stress (first invariant of the local stress tensor) is uniform in any mesodomain, whereas the distribution of the stress deviator (second invariant of the deviatoric part of the local stress tensor) is significantly dependent on the elongation direction and on the elongation degree of the mesodomains. The local stress ratio (ratio of the stress deviator to the mean stress) is higher within the mesodomains that are elongated in the global compression direction than that within the ones elongated in the global extension direction. Copyright © 2011 John Wiley & Sons, Ltd.

Local Stress Analysis of Orthotropic Steel Bridge Decks in High-Speed Railway

Orthotropic decks are commonly used in high-speed railway bridges. Finite-element model is established by ANSYS for orthotropic steel bridge deck in this paper. Taking the standard PDL ZK live load as the train load, the local stress of the rib-to-deck joint, the rib-to-crossbeam joint, and the cut-outs of the crossbeam are analyzed respectively. Analysis results show that the stress concentration of bridge deck mainly appears at the intersecting part of the U-shaped rib, crossbeam, and bridge deck. In the whole bridge deck, the local stress level of the cut-outs in crossbeam is almost the highest, and the cut-outs is distorted seriously; the maximum stress of crossbeam cut-outs is mainly concentrated at the lower arc of the cut-outs, which is one of the positions prone to fatigue failure.

The 3D Stress Analysis of Arch Foot for a Through Tied Arch Bridge

Due to computer performance, nowadays only parts of the structure can be executed the simulation analysis of 3D. For the prestressed structure, after took out the target segment from the original structure, the accuracy of the result is mainly depended on the boundary conditions and the accurate simulation of the tendons. This article took the 3D simulation analysis of the arch foot for an 80m tied arch bridge for example which introduced a method that could simulate the tendons precisely when performed local stress analysis and compared the results of the common method to this method. Via the contrast the rationality and advantages of the method are clear. A certain accuracy method was presented in this article when came across the similar analysis of local structure.

Local stress analysis on semiconductor devices by combined experimental–numerical procedure

Intrinsic stresses in bondpads may lead to early failure of IC’s. In order to determine the intrinsic stresses in semiconductor structures, a new procedure is set up. This procedure is a combined experimental/numerical approach which consists of the following steps: First, a conductive gold layer (20 nm thickness) is deposited on the power line surface; subsequently markers (small holes) for Digital Image Correlation (DIC) purposes are added using a Focused Ion Beam (FIB). Next, a scanning electron microscope (SEM) is used to image the original (‘before’) surface. The FIB is then used to mill a slot into the surface to release the intrinsic stresses, which results in contraction of the surface. Finally, a SEM image is made of the contracted (‘after’) surface. DIC is used to determine in-plane displacements due to FIB milling. DIC performance was verified by the traditional strain gauge approach. An inverse Finite Element (FE) modelling approach is used to determine the before mentioned stresses. The slot displacements found with DIC are inserted into an FE model of the product. Stresses which now emerge from closing the (virtual) FIB slot correspond to the intrinsic stresses which were originally present in the product. Favorable positions for FIB milling are near the edge of the structure and displacements are determined to be in the nanometer range. This indicates a presence of substantial (50–250 MPa) compressive stresses. Displacements near the center of the structure appear to be smaller than DIC resolution.

Conductive atomic force microscopy studies on dielectric breakdown behavior of ultrathin Al2O3 films

Ultrathin films of Al2O3 prepared by atomic layer deposition have been subjected to local electrical stress analysis using conducting atomic force microscopy. The loss of local dielectric integrity through current leakage in these extremely thin films is studied using scanning spreading resistance imaging. Our experimental results shows that repeated voltage stress progressively increases number of leakage spots. While the density of leakage spots increase with higher applied bias for thin oxide films, initial increase and reduction in leakage spots are observed for thick films.

Measuring and Analysis of Local Stress under Anchorage of Continuous Rigid Frame Bridge

Under the Large Tonnage Pre-Stress, the stress of concrete which is under the anchor plate is complicated. To ensure the safety of construction and structure, the condition of local stress of the bridge structure should be investigated. When the pre-stress steel of Segment 1# of Pier 1# of Hongwuwo Bridge is tensioned, the strain situation of concrete near the anchor plate of the box girder is measured. The measured value is compared with the analytical value which is obtained through space finite element method.

Automated Local Texture and Stress Analysis in Cu Interconnects Using D-STEM and Precession Microscopy

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Local Stress Analysis of the Fatigue Behaviour of Adhesively Bonded Thick Composite Laminates

Results of fatigue tests on adhesive lap joints of thick (9.9 mm) composite laminates are presented and discussed. Specimens of different overlap length (from 25 to 110 mm), different shape, (with and without taper), and different materials (composite on composite, composite on steel) were fatigue tested and distinct fatigue curves were obtained in terms of maximum applied force and number of cycles to failure. In order to investigate the relationship between peak elastic stresses in the adhesive layer and fatigue life, a 2-D structural analysis of the joints by the finite element method was performed. The analysis evidenced a close relationship between the peak elastic stresses and the number of cycles to failure in the all-composite joints, as all experimental points in terms of peak shear (or Tresca) stress and number of cycles to failure collapsed within a band of relatively low scatter, irrespective of the shape of the joint and the overlap length. This behaviour suggested that peak elastic stresses in the adhesive layer could be adopted as a design criterion, at least as an engineering tool for industrial applications. In order for this method to be applied to the design of real components made of thick composite laminates, the sensitivity of the model results to the number and type of elements used to model the adhesive layer (solid or cohesive) was investigated and results compared. The limitations of the proposed approach with reference to the role of crack propagation are also discussed.

Microelectronic packaging reliability using the RSM technique

Purpose The purpose of this paper is to identify the critical parameters that influence ball grid array and chip size package fatigue life in a random vibration environment by using a design of experimental (DOE) approach using simulation results. Design/methodology/approach The use of DOE and analysis of variation to identify the critical parameters and a response surface to generate a functional form for global modeling would be determined. Once the global modeling’s functional form was known, it can be used as boundary condition, which would be input to a local model. Knowing the critical stress, one would estimate the fatigue life from a damage model. It is the curvature of the printed wiring board in the region of the component of interest that is driving the component’s solder joint damage. The approach in this present work involves global-local modeling approaches. In the global model approach, the vibration response of the printed circuit board (PCB) will be determined. Findings This global model will give the response of the PCB at specific component locations of interest. This response is then fed into a local stress analysis for accurate assessment of the critical stresses in the solder joints of interest. The stresses are then fed into a fatigue damage model to predict the life. Originality/value The analysis proposed in this paper uses a failure type approach to damage analysis and involves global and local model approaches.