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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
A finite element based approach for nonlocal stress analysis for multi-phase materials and composites
This study proposes a numerical method for calculating the stress fields in nano-scale multi-phase/composite materials, where the classical continuum theory is inadequate due to the small-scale effects, including intermolecular spaces. The method focuses on weakly nonlocal and inhomogeneous materials and involves post-processing the local stresses obtained using a conventional finite element approach, applying the classical continuum theory to calculate the nonlocal stresses. The capabilities of this method are demonstrated through some numerical examples, namely, a two-dimensional case with a circular inclusion and some commonly used scenarios to model nanocomposites. Representative volume elements of various nanocomposites, including epoxy-based materials reinforced with fumed silica, silica (Nanopox F700), and rubber (Albipox 1000) are subjected to uniaxial tensile deformation combined with periodic boundary conditions. The local and nonlocal stress fields are computed through numerical simulations and after post-processing are compared with each other. The results acquired through the nonlocal theory exhibit a softening effect, resulting in reduced stress concentration and less of a discontinuous behaviour. This research contributes to the literature by proposing an efficient and standardised numerical method for analysing the small-scale stress distribution in small-scale multi-phase materials, providing a method for more accurate design in the nano-scale regime. This proposed method is also easy to implement in standard finite element software that employs classical continuum theory.
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
Synergistic approaches for hexapod mobility: comparative evaluation of structure, navigation, and control strategies on challenging terrains
The study delivers a cohesive system that combines structural stress investigation, navigational planning evaluation, and adaptive joint control to optimize hexapod effectiveness on hills, stairs, and uneven surfaces. The robot was developed through the iterative drafting technique and designed by assigning in PLA material. Structural examination with Finite Element Analysis (FEA) under 10 N and 20 N forces demonstrated a positive stress allocation and a safety factor of 2.8, combining compact development with durability. In the ROS/Gazebo exploration investigations utilizing global planners like A*, Dijkstra, RRT, and Artificial Potential Field (APF) in combination with a PID-driven local planner, A* as well as Dijkstra developed nearly the best pathways with 100% accuracy. This cut down on route variation by about 17% in comparison to RRT. RRT established confident that the exploration was always the same, but it established paths that were more lengthy and less smooth. APF, on the contrary, made paths that were smooth but less reliable due to the local minima. Adaptive synchronization for joint control quantitatively provided an improvement in joint angle stability, reducing oscillatory deviations by 12% and displacement errors by 15% relative to baseline controllers. The core novelty within this approach is the integrative methodology that will inherently synergize finite element structural analysis, comparative path planning, and Adaptive joint synchronization: presenting a comprehensive optimization strategy, new to hexapod robotics. Together, these advances allow for robust and efficient real-world deployment of hexapods. Future work will extend to hybrid learning-based planning, and sensor-driven dynamic adaptation.
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
Finite element analysis of stress in removable lower complete denture under vertical and oblique occlusal forces
Frequent fractures of complete removable dentures during mastication in the anterior zone cannot be explained by bite forces in this area, because occlusal forces on the incisors are small. It appears that the mechanism of fracture must be from lateral mastication forces. The hypothesis of the study was that, under stable support of a complete removable denture on the foundation, its fracture in the anterior segment is possible due to stress generated under masticatory forces typical for denture wearers. This study analyzes stress distribution in removable complete dentures (designed in Exocad), using the finite element method (FEM, Nx Siemens). The denture was loaded on the first molars with bilateral vertical forces of 100 N and oblique forces of 140 N at an angle of 45˚. Under oblique bilateral mastication forces the anterior zone exhibited nominal stresses originating from tension on the lingual side and compression on the labial side. These values were significantly lower than the material’s strength, even under conservative criteria for semi-brittle polymer in tension-dominant zones. The study also showed that the stress in properly manufactured dentures without defects or excessively sharp grooves did not reach the fatigue strength of the denture materials. This negated the hypothesis that denture fracture in the anterior segment is possible under such conditions. Further investigation is required, incorporating factors such as denture foundation resiliency, misfit, occlusal imbalance, and potentially different loading patterns to fully elucidate intraoral failure modes.
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
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
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