Equivalent Stress Values Research Articles

Finite Element Stress Analysis of Cast Metal Inlays Restored Posterior Teeth

ABSTRACTCast metal inlays have overall characteristics unavailable in any other restorative procedure, including low restoration wear, low wear of opposing teeth, lack of breakage, burnishability, malleability, and proven long term service. They replace missing teeth structures, without doing anything to reinforce the remaining structures. Stress concentrations can manifest themselves in various forms of failures. The aim of the study was to investigate the effect of preparation design on stress distribution in molars with different class II preparations and restored with cast metal inlays.3D models of premolars and molars were created: intact teeth, unrestored teeth with class II preparations with different tapers (between 0 and 10 degree); the same teeth restored with metalic inlays. The geometries of the intact teeth were obtained by 3D scanning using a manufactured device. With Rhinoceros modeling program the preparations and the appropriately inlays were designed. These were exported in Ansys finite element analysis software for structural simulations. Stresses were registred around the occlusal contact areas. For the studied cases, the stress values were not significant influenced by the taper of the preparation. In the teeth restored with cast metal inlays, the von Mises equivalent stress values were similar to those in the intact tooth.From biomechanical point of view, it was demonstrated that class II cast metal inlays on posterior teeth restore the original strength of the teeth. Taking into account the other characteristics of these restorations, they remain the standard of care for long-term rehabilitations. A taper between 0 and 10 degree of the preparation is not decisive for the stress values.

A new distortion energy-based equivalent stress for multiaxial fatigue life prediction

A new equivalent stress amplitude expression has been developed for the assessment of fatigue life in components under multiaxial loading. The expression was generated by incorporating non-linear/plastic stress–strain relation into a mechanical energy calculation, and then applying the calculation to the distortion energy theory for a cyclic loading case. Therefore, the new uniaxial equivalent stress expression determines an appropriate stress amplitude value for multiaxial cyclic loading. The purpose of the equivalent stress value is to determine multiaxial fatigue failure using an energy-based fatigue life prediction criterion. The governing understanding behind the criterion states that the physical damage quantity for failure is equal to the accumulated strain energy in a monotonic fracture, which is also equal to the accumulated strain energy during fatigue failure. Using the new equivalent stress amplitude expression and the energy-based life prediction method, a comparison is made between prediction results and multiaxial empirical data. The multiaxial data was acquired by a vibration-based biaxial bending fatigue test and a torsion fatigue test with an assumed axial misalignment. The results of the comparison provide encouragement regarding the capability of the newly developed equivalent stress amplitude expression for fatigue life prediction.

Reliability Analysis of the Diamond Saw Blades Based on ANSYS

The structure reliability of the diamond saw blade in milling process is studied. With probability design features of ANSYS, take the flange diameter ,thickness, diameter of the diamond saw blade and load suffered in the milling process as input variables, and take the maximum equivalent stress of dangerous parts of the diamond saw blades stress as output variable. The diamond saw blade structure reliability is analysed using Monte Carlo method and the maximum equivalent stress value cumulative distribution and dangerous parts of various parameters on the distribution of the maximum equivalent stress sensitivity under the impact of the load are got. The result provides a theoretical basis for improving the parameters of diamond saw blade and has the significant practical and theoretical value for the stone processing theory and diamond saw blade study.

Three-dimensional finite element analysis of torsion extrusion (TE) as an SPD process

► Finite element analysis was successfully performed on the TE and FE processes. ► Lower values of equivalent stresses have been found for the TE samples. ► Smoother strain gradient can be considered on the TE samples. ► TE samples show superior tensile strength and lower ductility in the tensile test. In the present study, torsion extrusion (TE) process was compared with conventional forward extrusion (FE) process as a severe plastic deformation (SPD) method. To simulate the above-mentioned processes, finite element analysis (FEA) was carried out using three-dimensional finite element analysis ABAQUS/Explicit simulation. It was shown that the load requirement for the TE is lower than that for the FE. Calculation of the equivalent stress also showed that a lower stress magnitude was imposed during the TE. The maximum principal stresses on the surface of the specimen indicate that more compressive stresses can be expected during plastic deformation using the TE. Calculation of the equivalent plastic strains by the FEA proved that higher strain values can be obtained by the TE. The strain distribution of the TE sample at the final stage of the extrusion showed a smoother strain gradient in comparison with the sample produced by the FE. Higher values of ultimate tensile strength and lower values of ductility were also obtained for the TE samples. To evaluate the results of the tensile tests, the Kocks and Mecking model was utilized.

Effects of rigid and nonrigid extracoronal attachments on supporting tissues in extension base partial removable dental prostheses: A nonlinear finite element study

Resilient (nonrigid) and non-resilient (rigid) attachments are used in extension base partial removable dental prostheses for retention. However, the biomechanical effects of these 2 types of retainers on the terminal abutment and supporting tissues, which may influence clinical treatment planning, have not been compared. The purpose of this study was to compare the mechanical effects of 2 types of extracoronal attachments (rigid and nonrigid) in distal extension removable partial prostheses on the alveolar ridge and abutment tooth periodontal ligament. A finite element model of a human left mandible edentulous arch distal to the second premolar was fabricated. The second premolar was the terminal abutment for an attachment-retained denture. Two types of attachments (rigid and nonrigid) were modeled in the study. For the nonrigid attachment, there was movement between the patrix and matrix component of the attachment, but there was no movement between the 2 component parts for the rigid attachment. Six levels of loading (100, 150, 200, 250, 300, and 350 N) were applied from 3 directions (axial, buccolingual, and mesiodistal) on the central fossa of the first and second molars. Denture motion and stress distributions of denture supporting tissues were observed. Maximum equivalent stress values (SEQV) were recorded for 6 regions (cervical bone, cervical and apical periodontal ligaments, mesial and distal ridges, and mucosa). The data were divided into 2 groups according to the attachment type. Paired t tests were used to compare the values of the 2 groups. Factorial ANOVA was used to test the difference between the loading directions (α=.05). Multiple linear regression was used to analyze the interactions among the factors of region, direction, and level (α=.05). Stress distributions in the rigid and nonrigid attachment models were similar but the magnitudes were different. For all 3 loading directions, significantly different stresses in the alveolar ridge and periodontal tissue of the terminal abutment were found between the rigid and nonrigid groups (P<.05). There were significant differences among the 3 loading directions (P<.05). In the nonrigid group, the stress ratio of the mesial to the distal area was higher than that of the rigid group from axial and mesiodistal loading (P<.05). Linear interactions were found between the direction and level and region and level combinations (P<.05). Movement between the patrix and matrix components increased as loading increased. The most obvious movement of attachment occurred when loading was in the buccolingual direction. Stress on the terminal abutment can be reduced by the use of an extracoronal resilient attachment that allocates more loads onto the distal edentulous ridge. The level of loading influenced the extent of reduction. A resilient attachment with a universal hinge had the most movement when loading was in the buccolingual direction. Interactions were found between direction and level, as well as region and level combinations (P<.05).

Reduction of Stress Concentration at the Corner Bends of the Anti-Roll Bar by Using Parametric Optimisation

Stress concentration at the corner bends of an anti-roll bar that is designed for an intercity passenger bus is reduced by optimising the shape of the critical regions. In order to do this, parameters which constitute the geometry of the stress concentrated regions are determined. The effect of these parameters on stress concentration is evaluated by using Design of Experiments (DoE) approach. Possible design options and their corresponding mass and maximum equivalent stress values are obtained by using finite element analysis. The results are assessed by means of response surfaces generated by FEA software. Transition form that gives optimum stress concentration is determined.

English

In the present work, 3D finite element analyses (FEA) of a low pressure (LP) steam turbine bladed disk assembly are carried out at constant speed loading condition. The prime objective of this work is to optimize the geometry of the bladed disk root with the aid of the Peterson’s stress concentration factor (SCF) charts available in the literature. Secondly, design rules are developed for the structural integrity of the blades and disk considering a safety factor for material, manufacturing and temperature uncertainties. These design rules are in turn used as design checks with the aid of finite element analysis results. Special investigations were performed based on Neuber formulae for reducing the local peak stresses at the blade and disk root fillet using linear analysis to identify the equivalent non linear stress values by the strain energy distribution method for estimating the minimum number of cycles required for the onset of crack initiation.

Bucket wheel failure caused by residual stresses in welded joints

Cracks in the welded joints on the bucket wheel (BW) body of the bucket wheel excavator (BWE) SRs 1300 were discovered after merely 1800 h of operation. Investigations are carried out in order to detect the causes of cracks occurrence and thus prevent possible heavy damages to the machine. Working stresses in the BW body are defined by using FEM. Methods of strain gauges are used for the experimental stress analysis in real working conditions. Measurements of welding residual stresses are carried out by applying the centre hole drilling method. Additionally, experimental investigations defined the chemical composition, tensile properties, hardness, impact toughness, as well as the susceptibility to cracking (measurement of residual hydrogen, FISCO, Tekken and CTS methods). External loads induced by the resistance-to-excavation are determined by following a model that encompasses all relevant structural parameters and also the BWE duty cycle parameters. By using FEM, it was identified that the maximum values of equivalent stress in the zones of cracks occurrence are lower than the allowable values. This conclusion is confirmed by measurements. The measured values of welding residual stresses reach the value of yield strength in critical zones. Non-compliances during grooving (clearance in the root is substantially larger than the prescribed one) caused large filler material deposition and heat input. Such welded joints are susceptible to cold cracking. Based on the results of the numerical–experimental analysis, findings show that in critical zones the combination of working (dynamic) and residual (static) stress can be above the limit lines of modified Goodman’s diagrams i.e. that the fatigue safety of the BW body structure was insufficient.

Contact Stress Analysis of NCD Coating on Roll Ball of Ball Bearing

Chemical vapor deposition nanocrystalline diamond (NCD) film has numerous unsurpassed properties, among them, bulk modulus, hardness; abrasion resistance and thermal conductivity are notable ones like polycrystalline CVD diamond film. The super mechanical properties have made NCD film to be an effective way to improve the resistance performance of the ceramic bearing and extended its life. The contact stress of bearing ball with NCD coating in elastic contact was analyzed. Factors such as substrate material, thickness of NCD coating, load and interlayer material which affect the shear stress distribution of NCD coating on bearing ball were investigated. The results show that substrate with low elastic modulus and heavy load will enlarge the difference of equivalent stress value at NCD/substrate interface. Thick film will make the stress distribution at the interface uniform. Soft interlayer should be inhibited to avoid extra stress in contact status.

Structural optimization with CADO method for a three-dimensional sheet-metal vehicle body

The aim of this study is to increase power/weight ratio of a steel-alloyed vehicle body without any structural weakness and to use an integrated engineering solution of “computer-aided design, engineering and optimization (CADO)”. In this optimization study, primarily the body's “computer-aided design (CAD)” parametric model has been prepared for some static analyses are essential for the design study. In the following step, some critical dimensions of the structure's parts have been defined as design parameters. The goal of the optimization study is a minimization of critical equivalent stress value is under the yield limit. In addition, a sensitivity study has been made on the body model with stress measures for an in-depth analysis. In various steps, Pro/Engineer CAD and Pro/MECHANICA computer-aided engineering (CAE) software has been used. Finally, the obtained results have been presented as both visually and in diagrams or tables. In other words, this study can be defined as a computer-aided design and optimization application of a sophisticated three-dimensional (3D) sheet-metal structural model. Consequently, for the solution of a sophisticated structural design problem, it has been seen that integrated CAD/CAE programs supported optimization techniques are vital much more proper to provide the time, error and cost reduction compared to classical design processes, can be given as contributes of this study to previous literature.

T-root blades in a steam turbine rotor: A case study

The present work illustrates, 3D finite element analysis (FEA) of low-pressure (LP) steam turbine bladed disk assembly are carried out at a constant speed loading condition. The prime objective is to study structural integrity of bladed disk root with aid of design considerations at design stage. Secondly, design rules are developed for structural integrity of blades and disk considering a factor of safety for material, manufacturing and temperature uncertainties. These design rules are in turn used as design checks with aid of finite element analysis results. Investigations are performed based on Neuber formulae for solving a highly non-linear problem employing linear analysis tool ANSYS 12.0. Local peak stresses at blade and disk root fillet of linear analysis is used to identify the equivalent non-linear stress value by strain energy distribution method for estimating the minimum number of cycles required for crack initiation for low cycle fatigue (LCF) calculations. Design methodology is developed to address the structural integrity of blades at design point and for off-design conditions.

CRITICAL ISSUES IN STRENGTH EVALUATION OF TURBO MACHINERY BLADE DISK ASSEMBLY AT CONSTANT RPM

In this present work, 3D Finite Element Analyses (FEA) of Low Pressure (LP) steam turbine bladed disk assembly are carried out at a constant speed loading condition. The prime objective of this work was to optimize the geometry of bladed disk root with the aid of Peterson’s Stress Concentration Factor (SCF) charts available in literature. Secondly design rules are developed for structural integrity of blades and disc considering a common factor for material, manufacturing and temperature uncertainties.These design rules are in turn used as design checks with aid of finite element analysis results. Special investigations were been performed based on Neuber formulae for reducing the local peak stresses at blade and disc root fillet using linear Analysis to identify the equivalent non linear stress value by strain energy distribution method for estimating the minimum no of cycles required for crack initiation by Low Cycle Fatigue (LCF) calculations

Deformation behaviour and microstructure development of a high-carbon steel during its hot and cold processing

The heritability of structural properties of the high-carbon steel 1 CS67 during laboratory casting, hot and cold strip rolling, soft annealing, as well as the impact of processing conditions on the final mechanical properties of the strip were studied. Ferrite grain size seems to be more intensively affected by the casting's cooling rate and subsequent heating time than by the phase transformations before conventional rolling. Owing to higher ferrite content resulting from finer austenite grain size, samples obtained after laboratory remelting and casting are characterised by lower yield stress and strength, in combination with higher ductility. A simple model of mean equivalent stress values dependent on temperature, strain and strain rate was developed using the results of hot flat-rolling tests.

Longitudinal Structural Determinants of Atherosclerotic Plaque Vulnerability: A Computational Analysis of Stress Distribution Using Vessel Models and Three-Dimensional Intravascular Ultrasound Imaging

This study theoretically examined the longitudinal structural determinants of plaque vulnerability using a color-coded stress mapping technique for several hypothetical vessel models as well as three-dimensional intravascular ultrasound (IVUS) images with use of a finite element analysis. It has been shown that an excessive concentration of stress is related to atherosclerotic plaque rupture. However, the local determinants of in-plaque longitudinal stress distribution along the coronary arterial wall remain unclear. Using a finite element analysis, we performed a color mapping of equivalent stress distribution within plaques for three-dimensional vessel models as well as longitudinal IVUS plaque images (n = 15). Then, the effects of plaque size, shape, expansive remodeling, calcification, and lipid core on the equivalent stress distribution were examined. The color mapping of vessel models revealed a concentration of equivalent stress at the top of the hills and the shoulders of homogeneous fibrous plaques. Expansive remodeling and the lipid core augmented the surface equivalent stress, whereas luminal stenosis and superficial calcification attenuated the equivalent stress. The location of excessive stress concentration was modified by the distribution of the lipid core and calcification. The thickness of the fibrous cap was inversely related to the equivalent stress within the fibrous cap. However, the color mapping of IVUS plaque images showed that the equivalent stress value at the fibrous cap varied with changes in plaque shape and superficial calcification, even when the thickness of the fibrous cap remained constant. A distribution analysis of longitudinal stress revealed specific effects of plaque shape, size, and remodeling, as well as effects of the interior distribution of tissue components, on the concentration of stress at the plaque surface. Moreover, fibrous caps of the same thickness did not consistently represent the same vulnerability to rupture.

Influence of tooth preparation design on the stress distribution in maxillary central incisors restored by means of alumina porcelain veneers: A 3D-finite element analysis

The present study aimed at providing 3D-FEA engineering tools for the understanding of the influence of tooth preparation design on the stress distribution and localization of critical sites in maxillary central incisors restored by means of alumina porcelain veneers under functional loading. A 3D-FEM model of a maxillary central incisor is presented. An arbitrary chewing static force of 10 N was applied with an angulation of 60 and 125 degrees to the tooth longitudinal axis at the palatal surface of the crown. The model was considered to be restored by means of alumina porcelain veneers with different tooth preparation designs. The differences in occlusal load transfer ability of the two restorative systems are discussed. The maximum Von Mises equivalent stress values were observed in the window restorative system for both 125 and 60 degrees load angulations. When the chamfer with palatal overlap preparation was simulated, the stress distributed uniformly in the cement layer, whereas in the window preparation the stress mainly occurred in the incisal area of the cement layer. When restoring a tooth by means of porcelain veneers, the chamfer with palatal overlap preparation better restores the natural stress distribution under load than the window technique.

Approximate Prediction Methods For Multiaxial Notch Stresses and Strains Under Elastic-Plastic and Creep Conditions

This paper describes general techniques for predicting multiaxial notch stresses and strains under elastic-plastic and creep conditions. The Neuber method, which is often used in elastic-plastic analysis, has been adapted and extended for predicting creep equivalent notch stresses and strains, based on a time-stepping integration scheme. A linear interpolation method, often used in creep analysis, is adapted and extended for predicting elastic-plastic equivalent stresses and strains. Then notch principal stresses and strains are obtained by applying plasticity theory in combination with assumptions concerning the ratios of the stress or strain components. The accuracy of the predicted equivalent and principal stress and strain values are assessed by comparing predictions based on them with results obtained from finite element analyses.

Non-Linear Analysis of the Modular Coil Windings for the National Compact Stellarator Experiment

A non linear FEA study has been performed on the modular coils of the National Compact Stellarator Experiment (NCSX). The modular coils provide the primary magnetic field within NCSX and consist of flexible cable conductor wound on a cast and machined winding form and vacuum impregnated with epoxy. Eighteen coils and associated winding forms are connected at assembly into a toroidal shell structure. The purpose of this study was to evaluate the structural response of the windings and shell structure during cooldown and normal operation. Two separate software packages were used for the study, and two independent analyses were undertaken. The first analysis performed with Pro/Mechanica®, examined both the response of the modular coils to magnetic pressure and thermal effects during a 2 Tesla pulse. Modeled items included a portion of the shell structure the winding packs, and a set of 48”pseudo clamps”. The so called ”pseudo clamps” are represented simply by blocks of material that are restrained in their respective normal directions and have properties which mimic the stiffness of the spring washers of the actual preload clamps. The winding pack is free to slide on the shell structure and is restrained only by the clamps. A second model, including the complete shell structure of all three coils, was studied with the FEA program ANSYS®. Contact regions defined in both Pro/Mechanica and Ansys allow the winding to slide and detach form the shell structure. The two analyses are compared for parameters such as winding/structure gap, overall displacement, equivalent stress and principle strain values.

3D FEA of cemented steel, glass and carbon posts in a maxillary incisor

A comparative study on the stress distribution in the dentine and cement layer of an endodontically treated maxillary incisor has been carried out by using Finite Element Analysis (FEA). The role of post and cement rigidity on reliability of endodontic restorations is discussed. A 3D FEM model (13,272 elements and 15,152 nodes) of a central maxillary incisor is presented. A chewing static force of 10 N was applied at 125 degree angle with the tooth longitudinal axis at the palatal surface of the crown. Steel, carbon and glass fiber posts have been considered. The differences in occlusal load transfer ability when steel, carbon and glass posts, fixed to root canal using luting cements of different elastic moduli (7.0 and 18.7 GPa) are discussed. The more stiff systems (steel and carbon posts) have been evaluated to work against the natural function of the tooth. Maximum Von Mises equivalent stress values ranging from 7.5 (steel) to 5.4 and 3.6 MPa (respectively, for carbon posts fixed with high and low cement moduli) and to 2.2 MPa (either for glass posts fixed with high and low cement moduli) have been observed under a static masticatory load of 10 N. A very stiff post works against the natural function of the tooth creating zones of tension and shear both in the dentine and at the interfaces of the luting cement and the post. Stresses in static loading do not reach material (dentine and cement) failure limits, however, they significantly differ leading to different abilities of the restored systems to sustain fatigue loading. The influence of the cement layer elasticity in redistributing the stresses has been observed to be less relevant as the post flexibility is increased.

Influence of implant length and diameter on stress distribution: A finite element analysis

Statement of problem Masticatory forces acting on dental implants can result in undesirable stress in adjacent bone, which in turn can cause bone defects and the eventual failure of implants. Purpose A mathematical simulation of stress distribution around implants was used to determine which length and diameter of implants would be best to dissipate stress. Material and methods Computations of stress arising in the implant bed were made with finite element analysis, using 3-dimensional computer models. The models simulated implants placed in vertical positions in the molar region of the mandible. A model simulating an implant with a diameter of 3.6 mm and lengths of 8 mm, 10 mm, 12 mm, 14 mm, 16 mm, 17 mm, and 18 mm was developed to investigate the influence of the length factor. The influence of different diameters was modeled using implants with a length of 12 mm and diameters of 2.9 mm, 3.6 mm, 4.2 mm, 5.0 mm, 5.5 mm, 6.0 mm, and 6.5 mm. The masticatory load was simulated using an average masticatory force in a natural direction, oblique to the occlusal plane. Values of von Mises equivalent stress at the implant-bone interface were computed using the finite element analysis for all variations. Values for the 3 most stressed elements of each variation were averaged and expressed in percent of values computed for reference (100%), which was the stress magnitude for the implant with a length of 12 mm and diameter of 3.6 mm. Results Maximum stress areas were located around the implant neck. The decrease in stress was the greatest (31.5%) for implants with a diameter ranging from of 3.6 mm to 4.2 mm. Further stress reduction for the 5.0-mm implant was only 16.4%. An increase in the implant length also led to a decrease in the maximum von Mises equivalent stress values; the influence of implant length, however, was not as pronounced as that of implant diameter. Conclusions Within the limitations of this study, an increase in the implant diameter decreased the maximum von Mises equivalent stress around the implant neck more than an increase in the implant length, as a result of a more favorable distribution of the simulated masticatory forces applied in this study.

Effect of in-plane constraint on mechanical behaviour of a metallic composite in biaxial stress states

This investigation focuses on the effect of in-plane constraint, which is a measure of the hydrostatic tension at the plane stress condition, on the yielding, fracture and fatigue of thin-walled tubes of an alumina particle-reinforced 6061 aluminium alloy composite. The results are compared with that of the unreinforced alloy. The yield surface radius of the particulate reinforced metal matrix composite (PMMC) is larger than that of the alloy in all loading paths. The fracture strength of the PMMC in terms of equivalent stress value is less sensitive to the change of the in-plane constraint of biaxial loading than that of the unreinforced alloy. The fatigue lives of the composite under the same equivalent strain decrease with the increase of the in-plane constraint factor, but by a lesser amount in comparison to that of the alloy.