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"Stress analysis"
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A Bayesian multiscale CNN framework to predict local stress fields in structures with microscale features
Multiscale computational modelling is challenging due to the high computational cost of direct numerical simulation by finite elements. To address this issue, concurrent multiscale methods use the solution of cheaper macroscale surrogates as boundary conditions to microscale sliding windows. The microscale problems remain a numerically challenging operation both in terms of implementation and cost. In this work we propose to replace the local microscale solution by an Encoder-Decoder Convolutional Neural Network that will generate fine-scale stress corrections to coarse predictions around unresolved microscale features, without prior parametrisation of local microscale problems. We deploy a Bayesian approach providing credible intervals to evaluate the uncertainty of the predictions, which is then used to investigate the merits of a selective learning framework. We will demonstrate the capability of the approach to predict equivalent stress fields in porous structures using linearised and finite strain elasticity theories.
Journal Article
Effect of porosity distribution on flexural and free vibrational behaviors of laminated composite shell using a novel sinusoidal HSDT
This work analyzes the impact of porosity on the static and dynamic behaviors of laminated composite shells using a novel high-order shear deformation theory. The employed model considers five unknown variables with a new sinusoidal shear function which provides precise distribution of transversal shear stresses through the thickness direction of the shell. The porosity can occur in the structure and can reduce their mechanical properties. For this purpose, three different porosity distributions in the thickness direction are considered in this investigation, the first model has the same percentage of the micro-void in the all thickness, the second one the percentage of the porosity is higher in the upper and lower surfaces contrary the third model the porosity percentage is maximum at the means axis. The governing differentials equations are derived using Hamilton’s principle and solved by Navier’s method. In the numerical results, transversal deflection, natural frequencies and axial and shear stresses are determined for laminated composite plates and shells with porosity, to verify the exactness and effectiveness of the new shell theory and to compare the results with those of the other solutions previously published.
Journal Article
Using the appropriate modulus of elasticity of periodontal ligament matters in stress analysis of human first premolar tooth and periodontium structures
Although the modulus of elasticity of the human periodontal ligament (E
PDL
) values used in dentistry widely ranged from 0.01 to 175 MPa, the exact E
PDL
value has not been determined. This study aimed to verify whether and how E
PDL
values affect the stress distribution over the tooth and periodontium structures, and to determine the appropriate E
PDL
range. A 3D multi-component human first premolar model was created based on a cone-beam computed tomography dataset. Finite element analysis was performed to analyze stress distribution and deformation of the structures under an average Asian occlusal force with different E
PDL
values (0.0689–68.9 MPa). The low E
PDL
caused excessive PDL deformation, contributing to a non-uniform stress distribution and localized stress concentration, especially in the cementum, enamel, and dentin. With the low E
PDL
value, the stress magnitude was overestimated by 1,195%, potentially leading to erroneous conclusions regarding material failure and tooth movement. The E
PDL
value significantly affects the stress magnitude and distribution over the tooth and periodontium. The appropriate E
PDL
range of 0.964 ± 0.276 MPa is suggested for human first premolars to ensure accurate and reliable FEA simulations and help avoid misinterpretation of the stress results, which could compromise orthodontic planning and restoration design.
Journal Article
A yield design approach to the stability analysis of A seabed subjected to wave loading and pseudo-static seismic forces
The stability analysis of a seabed under the combined action of wave and seismic loading is investigated in the light of limit analysis theory and related static and kinematic approaches. Effects of cyclic wave loading are addressed in the context of the first-order Stokes theory, whereas the pseudo-static method is adopted to account for inertial forces induced in the seabed soil mass by earthquake events. Compared to existing works, the key contribution of the paper is two-fold: (i) incorporation of the destabilizing effects induced by the passage of seismic waves, and (ii) poromechanics-based evaluation of the pore pressure generated by the cyclic wave in the finite thickness seabed layer. Resorting to a total stress analysis, the stability condition of a purely cohesive seabed is formulated based on lower bound static and upper bound kinematic approaches, leading to closed-form expressions for seabed stability in terms of loading parameters or in terms of wave characteristics. For granular seabed soil, the stability analysis is handled within the framework of effective stress limit analysis reasoning in which the seepage flow related to pore pressure gradient can be accounted for by means of driven body forces. In that respect, particular emphasis is given to the decisive role of seepage forces that are derived from the pore pressure distribution associated with soil densification under the cyclic wave loading. Formulation of a seabed stability condition is then achieved by implementing the kinematic approach through a class of failure mechanisms, thus providing preliminary elements for assessing the influence of each loading component. Numerical simulations notably emphasized the destabilizing effects induced by seismic loading.
Journal Article
Evaluatıon of stress dıstrıbutıon by applıed dıfferent forces on ımmature maxıllary central teeth wıth dıfferent treatment optıons: a laboratory fınıte element stress analysıs
Background
Immature maxillary central teeth can be managed by using several treatment options. The aim of this finite element stress analysis study was to evaluate the effect of different treatment procedures on the stresses on immature maxillary incisor teeth models that generated on cone beam computed tomography, by trauma and bite forces.
Methods
A total of 11 different models consisting of revascularization treatment using MTA and biodentine and the state of the root apex formed with cement after treatment, apexification, modified apexification, traditional root canal treatment and two different control groups have been created. 300N traumatic force and 240N bite force was applied with 90 and 130 angles. The stress values were examined in apical, middle and coronal sections using the finite element stress analysis method.
Results
The highest stress density was observed in the coronal root section in all models except for modified apexification treatment. While the highest vonMises stress value in coronal root dentin was found in the traditional root canal treatment group, the lowest value was found in the mature control group. In the modified apexification treatment groups, the stress was intensified in the middle and apical root section. It has been observed that in the models in which MTA is used, less stress occurs in all root parts compared to the models in which biodentine is used.
Conclusions
The use of MTA in immature teeth makes it more resistant to fracture compared to biodentine. Modified apexification method can reduce stress in the cervical area. More studies are needed on this subject.
Journal Article
Design and Interlaminar Stress Analysis of Composite Fan Blade Shank
The fan blade shank serves as a critical transition structure connecting the airfoil and dovetail, with its geometric design significantly influencing the blade’s structural integrity. This study investigates the geometric configuration and static strength of the laminated composite fan blade shank, with emphasis on design methodology and analytical approaches. Utilizing Bézier spline curve techniques, two shank configurations—thickened and thinned—were developed for the laminated composite fan blade shank, followed by ply design and static strength analysis. The results demonstrate that high-stress regions in the laminated composite fan blade are predominantly located at the junction between the shank section and the leading edge of the dovetail. Furthermore, the thickened shank configuration effectively reduces the peak σ33 by approximately 15% and simultaneously alleviates the interlaminar shear stress σ13, without introducing adverse ply drop angles, which exhibits superior interlaminar stress resistance under tensile loading conditions.
Journal Article
Influence of a new abutment design concept on the biomechanics of peri-implant bone, implant components, and microgap formation: a finite element analysis
Background
A new two-piece abutment design consisting of an upper prosthetic component and tissue-level base has been introduced; however, the biomechanical behavior of such a design has not been documented. This study aimed to investigate the effect of a two-piece abutment design on the stress in the implant components and surrounding bone, as well as its influence on microgap formation.
Methods
To simulate the implant models in the mandibular left first molar area, we established nine experimental groups that included three bone qualities (type II, III, and IV) and three implant–abutment designs (internal bone level, tissue level, and a two-piece design). After the screw was preloaded, the maximum occlusal (600 N) and masticatory (225 N) forces were established. Finite element analysis was performed to analyze the maximum and minimum principal stresses on the peri-implant bone; the von Mises stresses in the implants, abutments, bases, and screws, and the microgaps at the implant–abutment, implant–base, and base–abutment interfaces.
Results
For all three loading methods, the two-piece abutment design and bone-level connection exhibited similarities in the maximum and minimum principal stresses in the peri-implant bone. The von Mises stresses in both screws and bases were greater for the two-piece design than for the other connection types. The smallest microgap was detected in the tissue-level connection; the largest was observed at the implant–base interface in the two-piece design.
Conclusions
The present study found no evidence that the abutment design exerts a significant effect on peri-implant bone stress. However, the mechanical effects associated with the base and screws should be noted when using a two-piece abutment design. The two-piece abutment design also had no advantage in eliminating the microgap.
Journal Article
Biomechanical behavior of implant retained prostheses in the posterior maxilla using different materials: a finite element study
Background
The aim of this study is to evaluate the biomechanical behavior of the mesial and distal off-axial extensions of implant-retained prostheses in the posterior maxilla with different prosthetic materials using finite element analysis (FEA).
Methods
Three dimensional (3D) finite element models with three implant configurations and prosthetic designs (fixed-fixed, mesial cantilever, and distal cantilever) were designed and modelled depending upon cone beam computed tomography (CBCT) images of an intact maxilla of an anonymous patient. Implant prostheses with two materials; Monolithic zirconia (Zr) and polyetherketoneketone (PEKK) were also modeled .The 3D modeling software Mimics Innovation Suite (Mimics 14.0 / 3-matic 7.01; Materialise, Leuven, Belgium) was used. All the models were imported into the FE package Marc/Mentat (ver. 2015; MSC Software, Los Angeles, Calif). Then, individual models were subjected to separate axial loads of 300 N. Von mises stress values were computed for the prostheses, implants, and bone under axial loading.
Results
The highest von Mises stresses in implant (111.6 MPa) and bone (100.0 MPa) were recorded in distal cantilever model with PEKK material, while the lowest values in implant (48.9 MPa) and bone (19.6 MPa) were displayed in fixed fixed model with zirconia material. The distal cantilever model with zirconia material yielded the most elevated levels of von Mises stresses within the prosthesis (105 MPa), while the least stresses in prosthesis (35.4 MPa) were recorded in fixed fixed models with PEKK material.
Conclusions
In the light of this study, the combination of fixed fixed implant prosthesis without cantilever using a rigid zirconia material exhibits better biomechanical behavior and stress distribution around bone and implants. As a prosthetic material, low elastic modulus PEKK transmitted more stress to implants and surrounding bone especially with distal cantilever.
Journal Article
Residual Stress Engineering for Wire Drawing of Austenitic Stainless Steel X5CrNi18-10 by Variation in Die Geometries—Effect of Drawing Speed and Process Temperature
As a result of conventional wire-forming processes, the residual stress distribution in wires is frequently unfavorable for subsequent forming processes such as bending operations. High tensile residual stresses typically occur in the near-surface region of the wires and can limit further application and processability of the semi-finished products. This paper presents an approach for tailoring the residual stress distribution by modifying the forming process, especially with regard to the die geometry and the influence of the drawing velocity as well as the wire temperature. The aim is to mitigate the near-surface tensile residual stresses induced by the drawing process. Preliminary studies have shown that modifications in the forming zone of the dies have a significant impact on the plastic strain and deformation direction, and the approach can be applied to effectively reduce the process-induced near-surface residual stress distributions without affecting the diameter of the product geometry. In this first approach, the process variant using three different drawing die geometries was established for the metastable austenitic stainless steel X5CrNi18-10 (1.4301) using slow (20 mm/s) and fast (2000 mm/s) drawing velocities. The residual stress depth distributions were determined by means of incremental hole drilling. Complementary X-ray stress analysis was carried out to analyze the phase-specific residual stresses since strain-induced martensitic transformations occurred close to the surface as a consequence of the shear deformation and the frictional loading. This paper describes the setup of the drawing tools as well as the results of the experimental tests.
Journal Article