Showing papers on "von Mises yield criterion published in 2021"

Thermal and mechanical design of tangential hybrid microchannel and high-conductivity inserts for cooling of disk-shaped electronic components

Abstract: The efficiency of electronic equipment is the cornerstone of technology development. Thermal conditions significantly affect the performance of electronic components. Moreover, mechanical strength, size, and mass are the parameters that impose some limitations. Thus, they should be considered in the high tech industry. Therefore, it is needed to examine both mechanical and thermal behaviors simultaneously. Microchannel and inserted high-conductivity materials are two usual cooling approaches. To improve cooling efficiency and mechanical strength, a new method named Hybrid is introduced here. This method is a combination of microchannel and high-conductivity methods. In this study, the consumed energy, the conductivity ratio of the material with high conductivity, peak temperature, and maximum Von Mises stress have been investigated and analyzed. For the hybrid method, the peak temperature and stress were minimized regarding the volume of high-conductivity change in the tangential direction of the duct. The results showed that the tangential hybrid method could decrease the peak temperature and peak Von Mises stress, up to 40% and 34% in comparison to the microchannel and high-conductivity inserts method.

A thermomechanical model for the analysis of disc brake using the finite element method in frictional contact

Abstract: In this work, we presented a numerical modeling using the ANSYS software adapted in finite element method in which, the transient thermal analysis and the static structural one is performed here sequentially with the coupled thermo-structural method. A numerical procedure of calculation relies on important steps such that the CFD thermal analysis is well illustrated in 3D, showing the effects of heat distribution over the brake disc. This CFD analysis will help us in the calculation of the values of the thermal coefficients (h) that will be exploited in 3D transient evolution of the brake disc temperatures. Three different brake disc materials were tested and a comparative analysis of the results was conducted in order to derive the one with the best thermal behavior. Finally, the resolution of the coupled thermomechanical model allows us to visualize other important results of this research such as; the deformations, and the equivalent Von Mises stress of the disc, as well as the contact pressure of the brake pads. Following our analysis and the results we draw from it, we derive several conclusions. The choice will allow us to deliver the rotor design excellence to ensure and guarantee the good braking performance of vehicles.

Controlling the maximum first principal stress in topology optimization

Abstract: Previous studies on topology optimization subject to stress constraints usually considered von Mises or Drucker–Prager criterion. In some engineering applications, e.g., the design of concrete structures, the maximum first principal stress (FPS) must be controlled in order to prevent concrete from cracking under tensile stress. This paper presents an effective approach to dealing with this issue. The approach is integrated with the bi-directional evolutionary structural optimization (BESO) technique. The p-norm function is adopted to relax the local stress constraint into a global one. Numerical examples of compliance minimization problems are used to demonstrate the effectiveness of the proposed algorithm. The results show that the optimized design obtained by the method has slightly higher compliance but significantly lower stress level than the solution without considering the FPS constraint. The present methodology will be useful for designing concrete structures.

Practically Examining the Effect of Thermal Loads on Curved Tubes Made of Different Natural Composite Materials

Abstract: This paper examines the effect of changing temperature on the curved natural composite material pipe (Walnut husks powder with polyester) and curvature angle θ= 34° practically. This work involves the design and fabricates of curved pipe samples with an angle of curvature θ=34° at 50 % weight fraction. Also, tensile and thermo-mechanical test were performing to find the mechanical properties of the specimens. Experimental work included design and manufacturing test rig to simulate thermal stress. The experimental results revealed that a maximum hoop strain and longitudinal strain increased with increasing the temperature. The hoop stresses at crown and intrados positions were more than the hoop stress at extrados position by 150.762% and 138.363% respectively, and the von mises stresses at crown and intrados positions were more than the von mises stress at extrados position by 218.259% and 178.193% respectively. In the curved pipe, the hoop strains at intrados and crown positions were more than the hoop strain at extrados position by 114.583% and 60.416% respectively.

3D Finite Element Analysis of Rotary Instruments in Root Canal Dentine with Different Elastic Moduli

Abstract: The aim of the present investigation was to calculate the stress distribution generated in the root dentine canal during mechanical rotation of five different NiTi endodontic instruments by means of a finite element analysis (FEA). Two conventional alloy NiTi instruments F360 25/04 and F6 Skytaper 25/06, in comparison to three heat treated alloys NiTI Hyflex CM 25/04, Protaper Next 25/06 and One Curve 25/06 were considered and analyzed. The instruments’ flexibility (reaction force) and geometrical features (cross section, conicity) were previously investigated. For each instrument, dentine root canals with two different elastic moduli(18 and 42 GPa) were simulated with defined apical ratios. Ten different CAD instrument models were created and their mechanical behaviors were analyzed by a 3D-FEA. Static structural analyses were performed with a non-failure condition, since a linear elastic behavior was assumed for all components. All the instruments generated a stress area concentration in correspondence to the root canal curvature at approx. 7 mm from the apex. The maximum values were found when instruments were analyzed in the highest elastic modulus dentine canal. Strain and von Mises stress patterns showed a higher concentration in the first part of curved radius of all the instruments. Conventional Ni-Ti endodontic instruments demonstrated higher stress magnitudes, regardless of the conicity of 4% and 6%, and they showed the highest von Mises stress values in sound, as well as in mineralized dentine canals. Heat-treated endodontic instruments with higher flexibility values showed a reduced stress concentration map. Hyflex CM 25/04 displayed the lowest von Mises stress values of, respectively, 35.73 and 44.30 GPa for sound and mineralized dentine. The mechanical behavior of all rotary endodontic instruments was influenced by the different elastic moduli and by the dentine canal rigidity.

Improvement of DDA with a New Unified Tensile Fracture Model for Rock Fragmentation and its Application on Dynamic Seismic Landslides

Abstract: Discontinuous deformation analysis (DDA) method is a discrete element method, presenting a great advantage in modelling deformation and rigid body movements, and it is also an alternative approach for problems involving the fracturing process from continuity to discontinuity if the failure mechanism in DDA is well constituted. This paper presents a new united tensile fracture model (UTFM) for the two-dimensional DDA method to simulate the fracture behaviors of various brittle materials (e.g., rock, soil, and concrete). The new fracture model unifies four classical failure modes, including the maximum normal stress criterion, Tresca criterion, Mohr–Coulomb criterion, and the von Mises criterion, for tensile fracture. By incorporating UTFM into the original DDA frame, the improved DDA (I-DDA) can predict the crack initiation and propagation paths in Brazil disc and simulate rock fracture of various brittle materials. Numerical examples of the direct tensile test and the Brazil disc split tests are investigated to verify the accuracy and validity of the I-DDA method. The simulated results agree well with those obtained from physical tests and other numerical analyses, suggesting that the I-DDA has obvious advantage in simulating the fracture behaviors of the Brazil disc split test. Further, the I-DDA is applied to analyze the failure process of a practical earthquake-induced landslide with consideration of the tensile strength of the rock mass. The results indicate that the I-DDA is more feasible to analyze the slope failure, which can consider both the tensile and shear characteristics simultaneously compared with the original DDA.

On the effect of anisotropy on the performance and simulation of shrinking tubes used as energy absorbers for railway vehicles

Abstract: The standard BS EN 15227 requires accurate numerical modelling of railway vehicle energy absorbers that must be correlated against experimental data. Although thin-walled tubes can exhibit anisotropy, such numerical models have traditionally included isotropic material properties. Thus, this work investigates whether anisotropic material models may increase the accuracy of numerical models of shrinking tube energy absorbers. Tensile testing of extruded AW-6082 aluminium alloy shrinking tubes showed the yield strength of the tubes was 10% lower in the hoop direction than in the longitudinal direction. Further, to assess the effect of incorporating anisotropic material behaviour in the numerical model, the tubes were compressed under quasi-static conditions. Numerical models of the shrinking tubes, including isotropic (von Mises yield function) and anisotropic (Hill’s quadratic yield function) material properties, were compared to the experimental data. The isotropic numerical models overestimated the steady-state reaction force, even without the inclusion of friction, indicating that such models do not fulfil the requirements of the standard. Conversely, incorporating anisotropic material models predicted a lower reaction force and enabled the inclusion of energy dissipation by friction, by means of a coefficient of friction μ ​= ​0.03. Although these results demonstrate the need to include anisotropy in the numerical simulation, the friction value was lower than expected due to the methodology of the material characterization and the accuracy of the anisotropic model implemented.

Nickel-Titanium peripheral stents: Which is the best criterion for the multi-axial fatigue strength assessment?

Abstract: Ni-Ti stents fatigue strength assessment requires a multi-factorial complex integration of applied loads, material and design and is of increasing interest. In this work, a coupled experimental-numerical method for the multi-axial fatigue strength assessment is proposed and verified for two different stent geometries that resemble commercial products. Particular attention was paid to the identification of the material fatigue limit curve. The common approach for the Ni-Ti stents fatigue assessment based on the von Mises yield criterion was proven unsuitable for a realistic fatigue strength assessment. On the other hand, critical plane-based criteria were more representative of the experimental outcomes regardless of stent design.

Stress-constrained optimization using graded lattice microstructures

Abstract: In this work, we propose a novel method for predicting stress within a multiscale lattice optimization framework. On the microscale, a scalable stress is captured for each microstructure within a large, full factorial design of experiments. A multivariate polynomial response surface model is used to represent the microstructure material properties. Unlike the traditional solid isotropic material with a penalization-based stress approach or using the homogenized stress, we propose the use of real microscale stress components with macroscale strains through linear superposition. To examine the accuracy of the multiscale stress method, full-scale finite element simulations with non-periodic boundary conditions were performed. Using a range of microstructure gradings, it was determined that 6 layers of microstructures were required to achieve periodicity within the full-scale model. The effectiveness of the multiscale stress model was then examined. Using various graded structures and two load cases, our methodology was shown to replicate the von Mises stress in the center of the unit lattice cells to within 10% in the majority of the test cases. Finally, three stress-constrained optimization problems were solved to demonstrate the effectiveness of the method. Two stress-constrained weight minimization problems were demonstrated, alongside a stress-constrained target deformation problem. In all cases, the optimizer was able to sufficiently reduce the objective while respecting the imposed stress constraint.

Snap-through and Eulerian buckling of the bi-stable von Mises truss in nonlinear elasticity: A theoretical, numerical and experimental investigation

Abstract: In this paper, equilibrium and stability of the von Mises truss subjected to a vertical load are analyzed from theoretical, numerical and experimental points of view. The bars of the truss are composed of a rubber material, so that large deformations can be observed. The analytical model of the truss is developed in the fully nonlinear context of finite elasticity and the constitutive behavior of the rubber is modeled using the Mooney–Rivlin law. The constitutive parameters are identified by means of a genetic algorithm that fits experimental data from uniaxial tests on rubber specimens. The numerical analysis is performed through a finite element (FE) model. Differently from the analytical and FE simulations that can be found in the literature, the models presented in this work are entirely developed in three-dimensional finite elasticity. Experiments are conducted with a device that allows the rubber specimens to undergo large axial deformations. For the first time, snap-through is observed experimentally on rubber materials, showing good agreement with both theoretical and numerical results. Further insights on Eulerian buckling of the rubber specimens and its interaction with the snap-through are given. A simple formulation to determine the critical load of the truss is presented and its accuracy is validated through experimental observation. Comparisons with a linear elasticity based approach demonstrate that an accurate prediction of snap-through and Eulerian buckling requires nonlinear formulations, such as the ones proposed in this work.

Comparison finite element analysis on duralium strength against multistage artificial aging process

Abstract: Purpose: To analyze and estimate the strength of duralium rivets which had been treated by using multistage artificial aging compared with duralium that had not been treated. This processwas necessary to be conducted in riveting process effectively. Duralium has been widely used in aerospace industry, one of duralium usage in aerospace industry is aircraft fittings such as rivet. Riveting is one of method that used for joining airframe structural components. During riveting process, the load transfer causing stress that led to the fatigue. Riveting process also causes deformation on the rivet and sheet metal. Deformation that occurs on the rivet will affect the performance of rivet structure. Thus, duralium rivet was analyzed its total deformation, shear stress, and its equivalent stress Von Misses. Design/methodology/approach: that used in this study was finite element analysis. Geometry of rivet that used in this study was drawn by using Autodesk Inventor Professional 2018. While total deformation, shear stress and equivalent stress Von Mises on duralium rivets were found out by using ANSYS Workbench 18.1. Findings: Comparison result was obtained between duralium rivet with and without treatment of multistage artificial aging. The result shown that total deformation, shear stress and equivalent stress Von Mises which obtained by duralium rivet with multistage artificial aging had the lower value than duralium rivet without multistage artificial aging. Duralium rivet with multistage artificial aging could be used as aircraft fitting which had the higher strength. Research limitations/implications: Direct experiment on duralium rivet had not been done yet, this study only did simulation based on data that obtained form previous research that had been conducted by the researcher. Practical implications: Duralium rivet with multistage artificial aging had lower value on total deformation, shear stress, and equivalent stress Von Misses, thus duralium rivet with multistage aritificial aging had a higher strength. Originality/value: Application of duralium as a rivet with treatment of multistage artificial aging.

A numerical solution to thermo‐mechanical behavior of temperature dependent rotating functionally graded annulus disks

Abstract: The purpose of this study is to investigate Thermo-mechanical limit elastic speed analysis of functionally graded (FG) rotating disks with the temperature-dependent material properties. Three different material models i.e. power law, sigmoid law and exponential law, along with varying disk profiles, namely, uniform thickness, tapered and exponential disk was considered.,The methodology adopted was variational principle wherein the solution was obtained by Galerkin’s error minimization principle. The Young’s modulus, coefficient of thermal expansion and yield stress variation were considered temperature-dependent.,The study shows a substantial increase in limit speed as disk profiles change from uniform thickness to exponentially varying thickness. At any radius in a disk, the difference in von Mises stress and yield strength shows the remaining stress-bearing capacity of material at that location.,Rotating disks are irreplaceable components in machinery and are used widely from power transmission assemblies (for example, gas turbine disks in an aircraft) to energy storage devices. During operations, these structures are mainly subjected to a combination of mechanical and thermal loadings.,The findings of the present study illustrate the best material models and their grading index, desired for the fabrication of uniform, as well as varying FG disks. Finite element analysis has been performed to validate the present study and good agreement between both the methods is seen.

Comparative Analysis of Stress and Deformation between One-Fenced and Three-Fenced Dental Implants Using Finite Element Analysis.

Abstract: Finite element analysis (FEA) has always been an important tool in studying the influences of stress and deformation due to various loads on implants to the surrounding jaws. This study assessed the influence of two different types of dental implant model on stress dissipation in adjoining jaws and on the implant itself by utilizing FEA. This analysis aimed to examine the effects of increasing the number of fences along the implant and to compare the resulting stress distribution and deformation with surrounding bones. When a vertical force of 100 N was applied, the largest displacements found in the three-fenced and single-fenced models were 1.7469 and 2.5267, respectively, showing a drop of 30.8623%. The maximum stress found in the three-fenced and one-fenced models was 13.518 and 22.365 MPa, respectively, showing a drop of 39.557%. Moreover, when an oblique force at 35° was applied, a significant increase in deformation and stress was observed. However, the three-fenced model still had less stress and deformation compared with the single-fenced model. The FEA results suggested that as the number of fences increases, the stress dissipation increases, whereas deformation decreases considerably.