Calculation Of Stress Distribution Research Articles

Generation mechanism of dislocations during directional solidification of multicrystalline silicon using artificially designed seed

We investigated the generation mechanism of dislocations by comparing dislocation occurrence in multicrystalline silicon with calculated results of the shear stress on the slip plane by finite element analysis. To mimic the multicrystalline Si and to observe structural modification around grain boundaries a model crystal growth set-up was applied using artificially designed seed. We found that the dislocations occur at grain boundary and propagate as crystal growth proceeds. The generation of dislocations was not spatially uniform but often localized in one of the grains. The calculated stress distribution, which depends on crystallographic orientation, implies that the shear stress on the slip plane around the grain boundary is likely to cause occurrence of dislocations.

J0206-3-4 フェーズフィールド法を応用した肺微細構造の3次元モデリング([J0206-3]生命体統合シミュレーション(3))

The lung has a very complicated porous structure composed of millions of alveoli. Modeling of the lung microstructure is important for various numerical analyses such as computation of stress distribution in the lung with mechanical ventilation. In this paper we have developed a new technique to model the lung microstructure using phase-field method. This method allows us to model varied structures by changing the numbers or shape of nuclei, which are the origins of alveoli. In addition, we have modeled the realistic structures of lung microstructure (alveolar duct and alveolar sac) by using columnar shaped nucleus. Moreover, we analyzed the local stress distribution in the lung microstructure model that is assumed to be inflated by ventilator. We found that the 3^<rd> principal stress is high near the connection of alveolar walls, the 1^<st> principal stress has no feature, and the 3^<rd> principal stress at the connection increases with the increase of the region volume or with the decrease of alveolar pressure.

Prediction of fretting fatigue behavior under elastic-plastic conditions

Fretting fatigue generally leads to the degradation of the fatigue strength of a material due to cyclic micro-slip between two contacting materials. Fretting fatigue is regarded as an important issue in designing aerospace structures. While many studies have evaluated fretting fatigue behavior under elastic deformation conditions, few have focused on fretting fatigue behavior under elastic-plastic deformation conditions, especially the crack orientation and fatigue life prediction for Ti-6Al-4V. The primary goal of this study was to characterize the fretting fatigue crack initiation behavior in the presence of plasticity. Experimental tests were performed using pad configurations involving elastic-plastic deformations. To calculate stress distributions under elastic-plastic fretting fatigue conditions, FEA was also performed. Several parametric approaches were used to predict fretting fatigue life along with stress distribution resulting from FEA. However, those parameters using surface stresses were unable to establish an equivalence between elastic fretting fatigue data and elastic-plastic fretting fatigue data. Based on this observation, the critical distance methods, which are commonly used in notch analysis, were applied to the fretting fatigue problem. In conclusion, the effective strain range method when used in conjunction with the SMSSR parameter showed a good correlation of data points between the pad configurations involving elastic and elastic plastic deformations.

Progressive failure mechanism in one-dimensional stability analysis of shallow slope failures

In many slopes, overstressed zones can develop where the shear stress is larger than the available shear strength. Along a shear surface within a soil exhibiting a strain-softening behavior, the shear displacement increases while the available shear strength decreases. The excess shear stress is transferred from the overstressed zone to the adjacent zones, providing more shear strength. This stress-transferring mechanism induces stress redistribution within the slope and could enlarge the overstress zone. A one-dimensional model that satisfies the strain compatibility and force equilibrium is proposed for the stability analysis of a slope of strain-softening behavior. This paper’s objective is to facilitate the application of this model to estimate stress distribution along the failure surface of a strain-softening slope and thereafter the stability status. The study presents a set of specific solutions to this model by describing and demonstrating procedures to identify the pattern of a stress state and to calculate stress distribution within a one-dimensional, strain-softening slope. The progressive failure mechanism is also investigated by using the proposed approach. As the magnitude of released stress gets large enough, it induces an overstressed zone adjacent to the initial unstable zone and progressive failure develops. The proposed approach is also applied to study the pattern of stress redistribution. It is found that the pattern of stress redistribution is affected by the magnitude of released stress. It is too complex to be reasonably expressed by simple models. Though some limitations exist, the proposed approach serves as a simple tool for a better understanding of the progressive failure mechanism.

The relationship between Shore hardness of elastomeric dental materials and Young's modulus

Objectives Hardness of elastomers can be directly related to Young's modulus, a relationship that was investigated in detail by Gent in a paper in 1958. The aim of this study was to test this relationship for 13 dental elastomers (12 silicone and 1 polyether) using the equation derived by Gent and one from BS 903 (1950) that accounts for departures at low values. Methods The dental elastomers were subjected to tensile testing and Shore A scale hardness measurements. Young's moduli were calculated from the hardness values using the Gent equation and the BS 903 equation. These calculated values were then compared with values derived experimentally from the tensile tests. Results Hardness values were in the range 30.2 (±0.5)–62.9 (±0.8) with the corresponding calculated modulus values in the range 1.1–4.1 MPa and 0.9–4.3 MPa for the Gent and modified equations, respectively. Young's modulus values derived from the tensile data were in the range 0.8 (±0.3)–4.1 (±0.3) MPa, showing good agreement with those calculated from the hardness values. Providing viscoelastic creep is minimal during the duration of the test, there is a reasonably well-defined relationship between Shore hardness and Young's modulus in the hardness range studied. Significance Simple, non-destructive hardness measurements can be used to determine Young's modulus values. Such values are needed in any calculations of stress distributions in soft lining materials, e.g. by FEA.

311 ハブベアリングの異なる接触状態がハブに及ぼす影響(OS4-(1) 材料強度と構造設計,オーガナイズドセッション)

Transport machine is developed by new material. Above all, it is important that transport design with safety, environmental compatibility and productivity in mind. Serious accident occurs frequently by transport capacity reinforced. So, in this research, it paid notice to automobile hub that occurs frequently since 1990's. Experiment analysis is used the stress freezing method in static load. And theoretical analysis is used finite element method. From both parties, it is calculated stress distribution in automobile hub model and stress concentration factor. In the result, it aims to optimization of design element, improvement of enhanced safety and base redefining research of automobile hub.

Estimating the Effects of Microscopic Stress Concentrations on the Fatigue Endurance of Thin-walled High Strength Steel

The effects of microscopic surface stress concentrations on the fatigue endurance of thin-walled high strength steel were systematically estimated by numerical analysis and plane-bending fatigue tests with Schenck-type specimens, using the commercially available static implicit method FEA software I-DEAS ver. 11 for the stress distribution calculations. The microscopic stress concentration factor αi, from notch depth t=50 μm and notch root radius ρ=6 μm microscopic surface ridges, monotonously increased with increases in the roughness ridge direction, θ, from 1 to 7 in the bending mode. A fitted curve was developed for deriving the calculated stress concentration, αθ, from the superposition of the principal stresses. In the twisting mode, αi varied from about 4 to 7. The θ dependency of αi was smaller than that in bending mode. The empirical rule that the specimen collection direction has a lesser effect in twisting mode fatigue was supported by the αi value. It is reported that the fatigue notch factor β increased linearly with increases in the macroscopic stress concentration factor αa of up to 3. On the other hand, β slowly increased with increases in αi until it exceeded about 2. This marked difference might be due to differences between their respective stress gradients, which was well described by Nisitani and Endo by using a parameter ρ. A plane-bending fatigue test was performed with an artificial surface micro-groove of θ=0, 90° using 590 MPa class strength circumferentially flattened electric resistance welded tube. The θ=0° micro-groove had little effect on the fatigue endurance in bending. On the other hand, the fatigue cracks of all the θ=90° specimens initiated at the basilar part of the micro-groove without any nonpropagating cracks. The fatigue notch factor β seems to be determined by only αi independent of ρ in the microscopic stress concentration field.

Relation between subject-specific hip joint loading, stress distribution in the proximal femur and bone mineral density changes after total hip replacement

In the prediction of bone remodelling processes after total hip replacement (THR), modelling of the subject-specific geometry is now state-of-the-art. In this study, we demonstrate that inclusion of subject-specific loading conditions drastically influences the calculated stress distribution, and hence influences the correlation between calculated stress distributions and changes in bone mineral density (BMD) after THR. For two patients who received cementless THR, personalized finite element (FE) models of the proximal femur were generated representing the pre- and post-operative geometry. FE analyses were performed by imposing subject-specific three-dimensional hip joint contact forces as well as muscle forces calculated based on gait analysis data. Average values of the von Mises stress were calculated for relevant zones of the proximal femur. Subsequently, the load cases were interchanged and the effect on the stress distribution was evaluated. Finally, the subject-specific stress distribution was correlated to the changes in BMD at 3 and 6 months after THR. We found subject-specific differences in the stress distribution induced by specific loading conditions, as interchanging of the loading also interchanged the patterns of the stress distribution. The correlation between the calculated stress distribution and the changes in BMD were affected by the two-dimensional nature of the BMD measurement. Our results confirm the hypothesis that inclusion of subject-specific hip contact forces and muscle forces drastically influences the stress distribution in the proximal femur. In addition to patient-specific geometry, inclusion of patient-specific loading is, therefore, essential to obtain accurate input for the analysis of stress distribution after THR.

Numerical studies of the influence of textural gradients on the local stress concentrations around fibers in carbon/carbon composites

AbstractCarbon/carbon composites produced by chemical vapor infiltration consist of carbon fibers embedded in a matrix of pyrolytic carbon with anisotropic mechanical properties. The matrix around fibers consists of cylindrically shaped pyrolytic carbon layers of coating, which may have different textures with different mechanical properties in the axial, radial and circumferential directions. The goal of the present numerical study is to investigate the influence of the coating microstructure on stress concentrations and possible modes of failure in the carbon composite.Numerical modeling was performed on two length scales. First, the material properties of the differently textured pyrolytic carbon layers were determined on the nanometer scale using methodology based on the Eshelby theory for continuously distributed inclusions. Then, the obtained material parameters for each layer were used as input for the finite element models on the micrometer scale. The numerical simulations were conducted for three basic loading scenarios: uniaxial tension, shear loading and hydrostatic compression. The calculated stress distributions show zones of maximum stress concentrations and provide information on the possible failure regions for each material under all considered loading cases. The numerical results demonstrate good correspondence with experimentally identified failure regions. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Determining strength of the modified wood

The article presents results of investigations of the effect of pinewood modification with methyl polymethacrylate on the anisotropy of its strength in complex stress conditions. The investigations aimed at determining the resistance of the examined wood to stretching, compression, stretching with shear, and compression with shear. For the investigations oriented on shear, shear with stretching, and shear with compression, a special specimen was prepared which differs by notch geometry from a typical Iosipescu specimen. A new test machine is described in the article, which is equipped with special specimen holders to perform investigations in complex stress conditions. Crack patterns recorded for the natural and modified wood are presented. For all tests, numerical FEM simulations were performed to obtain stress distributions inside the specimens. The calculated stress distributions were visualised as contour line projections for the natural and modified wood.

Finite Element Method Analysis of Nanoscratch Test for the Evaluation of Interface Adhesion Strength in Cu Thin Films on Si Substrate

Mechanical processes of the nanoscratch test are investigated using a finite element analysis of Cu/Ta/SiO2/Si multilayer films. The calculated stress distribution at the moment of delamination suggests that delamination occurs in a small region of approximately 100 nm. The driving force for delamination is the stress concentration due to strain-incompatibility at the Cu/Ta interface resulting from the large plastic deformation in Cu. The degree of stress concentration is found to depend on internal variables, such as plastic deformation, residual stress, and the elastic modulus, and on the magnitude of lateral force.

Theoretical Analysis of Voltage-Driven MOSLM with 1-D Magneto Photonic Crystal

The magneto-optic spatial light modulator (MOSLM) can modulate amplitude, phase, and polarization of optical wave front at high speed. However, past MOSLM requires large driving current. To overcome the disadvantage, we have developed the MOSLM with PZT layer driven by electric field and external magnetic field. The effective structure of the voltage-driven MOSLM was also investigated using finite element simulation. A magneto photonic crystal(MPC), which consists of dielectric mirror and magnetic defect layer, can largely enhance MO effect. The stress distribution calculation of MPC structure with good stress distribution and a large Faraday rotation was done based on a structure of a thin MO film.

Whisker Initiation Behavior from Electrodeposited Sn/Cu Coating on Cu Leadframe

Tin/copper (Sn/Cu) coatings on Cu leadframes (CUFE), in which Fe atoms are doped as a minor element, showed whisker initiation at room temperature over a long period of 47 months. By means of the planar slice method and electron back scattering pattern (EBSP) measurement, the whisker roots were consistently found to be located at the intersections of grain boundaries in the coating. Whisker roots were also located above the peaks and ridge lines of intermetallic compound (IMC) Cu6Sn5, which was formed with a pyramid-shaped configuration between the Sn/Cu coating and Cu leadframe. Using finite element analysis (FEA), we calculated stress distribution in the coating. The results indicated that compressive stress normal to the grain boundary was induced with a gradient toward the surface in the coating. Therefore, the compressive stress gradient induced by the pyramid-shaped IMC is thought to be the root cause of whisker initiation in Sn/Cu coatings on Cu leadframes. When the Cu leadframe with a minor doped element of Cr atoms (CUCR) was used as the substrate with the same Sn/Cu coating, no whisker initiation was observed even after a longer storage time of 65 months. Through field-emission scanning transmission electron microscopy (FE-STEM) and field-emission transmission electron microscopy (FE-TEM) microstructural observations of vertical sections of each sample, the shape of the IMCs formed between the coating and the leadframe in the Sn/Cu-CUFE sample was found to be different from that in the Sn/Cu-CUCR sample. The difference in whisker initiation tendency can therefore be explained by the difference in compressive stress depending on the shape of the Cu-Sn IMCs, because stress distribution in the coating of the Sn/Cu-CUCR sample calculated using FEA revealed a smaller stress gradient than that in the Sn/Cu-CUFE sample.

Fatigue Analysis and Life Prediction of Dumpers with Cumulative Fatigue Damage Approach and Finite Element Model

A fatigue damage model is developed for evaluating accumulative fatigue damage of dumpers. The loading spectrums acted on dumpers are created according to measured strain data in field. The finite element model is meshed for assessing and calculating stress distribution and strength characteristics of dumpers. The stress distribution and stress concentration factors of main components of dumper at different loading cases are numerically simulated. A fatigue damage model is developed for evaluating accumulative fatigue damage of dumpers. Fatigue damage indexes and service life are calculated by a modified Palmgren-Miner rule. The investigation shows that fatigue notch factor has a significant influence on the calculation of fatigue damage of dumpers.

Analyses of layer-thickness effects in bilayered dental ceramics subjected to thermal stresses and ring-on-ring tests

Objectives The purpose of this study was to analyze the stress distribution through the thickness of bilayered dental ceramics subjected to both thermal stresses and ring-on-ring tests and to systematically examine how the individual layer thickness influences this stress distribution and the failure origin. Methods Ring-on-ring tests were performed on In-Ceram Alumina/Vitadur Alpha porcelain bilayered disks with porcelain in the tensile side, and In-Ceram Alumina to porcelain layer thickness ratios of 1:2, 1:1, and 2:1 were used to characterize whether failure originated at the surface or the interface. Based on (1) the thermomechanical properties and thickness of each layer, (2) the difference between the test temperature and the glass transition temperature, and (3) the ring-on-ring loading configuration, the stress distribution through the thickness of the bilayer was calculated using closed-form solutions. Finite element analyses were also performed to verify the analytical results. Results The calculated stress distributions showed that the location of maximum tension during testing shifted from the porcelain surface to the In-Ceram Alumina/porcelain interface when the relative layer thickness ratio changed from 1:2 to 1:1 and to 2:1. This trend is in agreement with the experimental observations of the failure origins. Significance For bilayered dental ceramics subjected to ring-on-ring tests, the location of maximum tension can shift from the surface to the interface depending upon the layer thickness ratio. The closed-form solutions for bilayers subjected to both thermal stresses and ring-on-ring tests allow the biaxial strength of the bilayer to be evaluated.

Microstructure of nitrogen implanted stainless steel after wear experiment

Outstanding wear resistance of austenitic stainless steel after nitrogen insertion and formation of expanded austenite in the temperature range below 420 °C is a well established phenomena. However, detailed information on the wear mechanism for the modified surfaces is still missing. This paper presents the results of wear experiments performed in a dry oscillating geometry against a WC ball (diameter 3 mm, load 3 N), together with metallographic investigations of the resulting cross-sections, both with and without nitriding. Comparisons with calculated stress distributions indicate that those nitrided samples showing a specific wear reduction by a factor of about 100 were subjected to a combination of stress maxima within the surface layer and below the layer in the bulk material.

The accuracy of thin-shell theory in estimation of aneurysm rupture

If the mechanical stress in the aneurysm wall exceeds the strength of the wall tissue, aneurysm rupture occurs. Therefore, the mechanical stress distribution should be calculated to evaluate the need for surgical intervention to avoid aneurysm rupture. To find the stress distribution in the wall, several methods such as thick-wall and thin-shell theories can be used. The thick-wall theory, using full equilibrium equations, gives the most accurate results. However, because the thick-wall theory is more complicated and takes longer CPU time, usually simpler theories like the thin-shell theory are preferred. In this study, the results of the thick-wall theory are compared with those of the thin-shell theory to evaluate the accuracy of the thin-shell theory in calculating stress distribution. The results show that for many cases the thin-shell theory is not sufficiently accurate, and, thus, the use of the thin-shell theory may be misleading in evaluating the need for surgical intervention.

Evaluation of Rolling Contact Fatigue Properties of White Layer in Railway Wheel Steel

Spalling is one of the typical rolling contact fatigue (RCF) failure of railway wheels, initiating at white layers, as the result of unexpected wheel slides. As for spalling, evaluation methods of fatigue strength have not been tried and tested. The purpose of this study is to propose a prediction method of RCF strength for crack initiation at white layers. In this study, 1) RCF tests in order to evaluate spalling behavior of wheel steels, 2) axial fatigue tests to obtain fatigue strength of white layer itself, and 3) elastic-plastic FEM analyses simulating the RCF tests to calculate stress distribution in/around white layers were conducted. As the results, the following facts were clarified. 1) In RCF tests, cracks were initiated at the leading edge of white layers particularly under slip condition. 2) Fatigue strength of the white layer can be evaluated accurately using the endurance limit diagram estimated by a straight line passing the true fracture strength and fully reversed fatigue strength. 3) According to FEM analysis results, the maximum stress at the leading edge of white layer is larger than at the trailing edge, and the maximum stress of the white layer increases by taking into consideration of small surface profile change during RCF test. Moreover, Dang Van model, which is one of the multiaxial fatigue strength evaluation methods, was applied to predict the white layer's fatigue strength in RCF tests. It can be concluded that the present prediction method is reasonably acceptable for crack initiation assessment of spalling and that in case of the existence of relatively apparent surface profile change, stress evaluation has to be done by taking it into consideration.

Microstructure-induced thermal stresses in pyrolytic carbon matrices at temperatures up to 2900 °C

Carbon/carbon composites produced by chemical vapor infiltration consist of carbon fibers embedded in a pyrolytic carbon matrix with a cylindrically layered structure at the microscale. Each coating layer has a different texture and different mechanical properties that depend on temperature. Stress distributions in such carbon matrices subjected to thermal loading and their possible failure scenarios are analyzed. A two-scale numerical model is developed. At the nanoscale, material properties of each layer are determined using a methodology based on the Eshelby's theory for continuously distributed inclusions. The resulting material parameters for each layer are then used in the finite element modeling at the microscale. Calculations are conducted for composites with different matrix structures for several cases of thermal loading. Calculated stress distributions show zones of maximal stress concentration and provide information on possible failure regions which correspond well with experimentally identified failure regions.

Methods for modelling the ultimate strength of orthotropic plate with a central hole under uniaxial tension

The stress state in plates with circular holes made of orthotropic homogeneous material has no singularities and it can be exactly determined. The numerical stress distribution calculation by the finite element method will be compared with those obtained by the analytical equations developed by several authors. The goal of this work is to validate the finite element method, in conjunction with in-plane and out of plane failure criteria, in order to calculate not only the stress distribution for orthotropic plates with circular holes but also to determine their ultimate strength.The tool used has been a user subroutine (UMAT) specially developed for this work that implements the features of the commercial FE program (ABAQUS). The code performs an implicit analysis of the stress-state with progressive damage modelling.Finally, both of them, numerical and analytical method, will be checked with experimental tests by means of strain gauges.