Showing papers on "von Mises yield criterion published in 2022"

Influence of Framework Material and Posterior Implant Angulation in Full-Arch All-on-4 Implant-Supported Prosthesis Stress Concentration

Abstract: This study evaluated the influence of distal implants angulation and framework material in the stress concentration of an All-on-4 full-arch prosthesis. A full-arch implant-supported prosthesis 3D model was created with different distal implant angulations and cantilever arms (30° with 10-millimeter cantilever; 45° with 10-millimeter cantilever and 45° with 6-millimeter cantilever) and framework materials (Cobalt–chrome [CoCr alloy], Yttria-stabilized tetragonal zirconia polycrystal [Y-TZP] and polyetheretherketone [PEEK]). Each solid was imported to computer-aided engineering software, and tetrahedral elements formed the mesh. Material properties were assigned to each solid with isotropic and homogeneous behavior. The contacts were considered bonded. A vertical load of 200 N was applied in the distal region of the cantilever arm, and stress was evaluated in Von Misses (σVM) for prosthesis components and the Maximum (σMAX) and Minimum (σMIN) Principal Stresses for the bone. Distal implants angled in 45° with a 10-millimeter cantilever arm showed the highest stress concentration for all structures with higher stress magnitudes when the PEEK framework was considered. However, distal implants angled in 45° with a 6-millimeter cantilever arm showed promising mechanical responses with the lowest stress peaks. For the All-on-4 concept, a 45° distal implants angulation is only beneficial if it is possible to reduce the cantilever’s length; otherwise, the use of 30° should be considered. Comparing with PEEK, the YTZP and CoCr concentrated stress in the framework structure, reducing the stress in the prosthetic screw.

Numerical study on the effect of residual stress on mechanical properties of laser welds of aluminum alloy 2024

Abstract: The fusion zone is the weak area of weld joint which will experience complex thermal mechanical process during laser welding aluminum alloy 2024-T4. The resulting residual stress in the weld joint may exceed the yield stress, which will significantly affect the hardness and tensile strength. The purpose of this study is to predict the residual stress, and analyze its relationship with hardness and yield stress of the aluminum alloy 2024-T4 weld joint. Herein, three sequential models are established: (i) a thermal finite element model using double cone combined heat source that allows the prediction of time-dependent temperature distribution during laser welding of aluminum alloy 2024; (ii) a mechanical model using sequential coupling method and loading temperature in each increment to predict strain and residual stress; (iii) a theoretical empirical model to link the residual stress, hardness and yield stress. The simulated temperature field from the thermal model is in good agreement with the experimental result. The predicted stress field shows that the average von Mises stress at the center of the Al 2024-T4 and Al 2024-O weld joints are 303.60 MPa and 62.85 MPa, respectively, which are close to their yield stress. Moreover, it is found that the hardness decreases by 6 HV0.1 under the influence of residual stress in Al 2024-T4 fusion zone. The results indicate that the yield stress of 2024-T4 weld joint decreases by 16.5 MPa as a result of the residual stress. Above results indicate that residual stress has non-negligible influences on the mechanical properties of laser weld joint.

Influence of margin design and restorative material on the stress distribution of endocrowns: a 3D finite element analysis

Abstract: This study aimed to evaluate the stress distributions in endocrown restorations as applied to endodontically treated teeth (ETT), according to the factors of "margin design" (four levels) and "restorative material" (six levels).Four 3D-finite elements models were constructed for endocrown restored molars considering different margin designs. Model A was prepared with a flat butt joint margin and received an endocrown with a 2.0-mm occlusal thickness. Model B was prepared with a 20° bevel margin and received an endocrown with a 2.0-mm occlusal thickness. Model C was prepared with an axial reduction and 1-mm shoulder margin and received an endocrown with a 2.0-mm occlusal thickness. Model D was prepared with an anatomic margin and received an endocrown with a 2.0-mm occlusal thickness. The following endocrown materials were used: In-Ceram Zirconia (Zr), Vita Suprinity (VS), IPS Empress (IE), Grandio blocs (GR), VisCalor bulk (VS), and CopraPeek Light (CP). The Load application (600 N) was performed at the food bolus and tooth surface during the closing phase of the chewing cycle. The results for the endocrown and tooth remnants were determined according to the von Mises stress. The failure risk of the cement layer was also calculated based on the normal stress criterion.Model D (with an anatomic margin) showed the greatest stress concentrations, especially in the irregular and sharp angles of the restoration and tooth remnants. The stress concentrated on the dentin was significantly lower in Model B with a 20° bevel margin (20.86 MPa), i.e., 1.3 times lower than the other three margin designs (27.80 MPa). Restorative materials with higher elastic moduli present higher stress concentrations inside the endocrown and transmit less stress to the cement layer, resulting in lower bonding failure risks. In contrast, materials with an elastic modulus similar to that of dentin presented with a more homogeneous stress distribution on the whole structure.An endocrown with a 20° bevel margin design could be a favorable preparation option for ETT. Composite resins (GR and VC) exhibit a more even stress distribution, and seem to be more promising materials for endocrown molars.

Influence of margin design and restorative material on the stress distribution of endocrowns: a 3D finite element analysis

Abstract: This study aimed to evaluate the stress distributions in endocrown restorations as applied to endodontically treated teeth (ETT), according to the factors of "margin design" (four levels) and "restorative material" (six levels).Four 3D-finite elements models were constructed for endocrown restored molars considering different margin designs. Model A was prepared with a flat butt joint margin and received an endocrown with a 2.0-mm occlusal thickness. Model B was prepared with a 20° bevel margin and received an endocrown with a 2.0-mm occlusal thickness. Model C was prepared with an axial reduction and 1-mm shoulder margin and received an endocrown with a 2.0-mm occlusal thickness. Model D was prepared with an anatomic margin and received an endocrown with a 2.0-mm occlusal thickness. The following endocrown materials were used: In-Ceram Zirconia (Zr), Vita Suprinity (VS), IPS Empress (IE), Grandio blocs (GR), VisCalor bulk (VS), and CopraPeek Light (CP). The Load application (600 N) was performed at the food bolus and tooth surface during the closing phase of the chewing cycle. The results for the endocrown and tooth remnants were determined according to the von Mises stress. The failure risk of the cement layer was also calculated based on the normal stress criterion.Model D (with an anatomic margin) showed the greatest stress concentrations, especially in the irregular and sharp angles of the restoration and tooth remnants. The stress concentrated on the dentin was significantly lower in Model B with a 20° bevel margin (20.86 MPa), i.e., 1.3 times lower than the other three margin designs (27.80 MPa). Restorative materials with higher elastic moduli present higher stress concentrations inside the endocrown and transmit less stress to the cement layer, resulting in lower bonding failure risks. In contrast, materials with an elastic modulus similar to that of dentin presented with a more homogeneous stress distribution on the whole structure.An endocrown with a 20° bevel margin design could be a favorable preparation option for ETT. Composite resins (GR and VC) exhibit a more even stress distribution, and seem to be more promising materials for endocrown molars.

Stress state sensitivity for plastic flow and ductile fracture of L907A low-alloy marine steel: From tension to shear

Abstract: High-performance marine steel is essential for the marine industry worldwide. L907A low-alloy marine steel was developed by China independently and is now widely used in ship construction. In this study, the plasticity and ductile fracture behavior of L907A steel under various stress states are systematically investigated by experiments, mechanical modeling, and numerical simulations. Through the use of different microscopic methods, the initial microstructure of the material is well characterized. The constituent phases and grain morphologies of L907A introduce a good combination of strength and ductility and exhibit isotropic in-plane features. Specimens with various geometries are designed and tested to characterize the mechanical response of the L907A steel under various stress states ranging from tension to shear. The isotropic von Mises yield function with mixed Swift-Voce hardening law is used to characterize large deformation, while fracture initiation under various stress states is described by the Hosford-Coulomb model. A new parameter identification method, which combines hybrid numerical-experimental approach with simulated annealing optimization algorithm, is proposed to obtain the globally optimal model parameters. It is demonstrated that the calibrated model can predict the plasticity and fracture behavior of L907A with great accuracy. Finally, the mechanical performance of L907A is compared with competing marine steels (e.g., DH36 steel and EH36 steel). Results indicate that the yield stress of L907A is close to DH36 and higher than EH36, but its average strain hardening rate is lower than DH36 and close to EH36; the ductility of L907A is close to DH36 but worse than EH36. The fracture locus of L907A exhibits minimal stress state dependence compared to both DH36 and EH36.

Transient operation effects on the thermal and mechanical response of a large-scale rotary kiln

Abstract: Rotary kilns are central equipment in material processing operations such as oxide ore reduction, clinker manufacturing, and hazardous waste incineration. This work focuses on an industrial-scale rotary kiln for Ferronickel production via the Rotary Kiln-Electric Furnace (RKEF) process. Rotary kilns are prone to mechanical failure exacerbated by thermal effects, mainly during transient operation, such as preheating and cooling. However, few studies have tackled the impact of the transient operation on the stress state in the rotary kiln wall. Therefore, we evaluate the thermal and mechanical behavior of the rotary kiln wall during preheating. Actual operation data and a thermal model enable to obtain the temperature distribution along the kiln length. This temperature distribution is the starting point for calculating the stress state of the shell and refractory. The maximal thermal gradient occurs at 10 m from the hot end, with temperatures at the outer and inner surfaces of 200 °C and 820 °C, respectively. The von Mises stress shows a maximum of 121 MPa at the wheel position in the hot region of the refractory and a range of 30–60 MPa in the shell. In addition, the compressive stress is higher than the ultimate compressive strength of the refractory. However, it does not necessarily represent refractory detachment due to the plastic deformation undergone by the refractory under high temperatures. This work paves the way towards developing a tool for accurately predicting rotary kiln mechanical failure, which can help optimize operating conditions and assist in programming maintenance.

Stress distribution optimization in dished ends of cylindrical pressure vessels

Abstract: The standard geometries of dished ends of cylindrical pressure vessels were developed at the beginning of the last century. Among them, there are ellipsoidal and torispherical geometries characterized by disadvantageous stress distribution, which is the primary determinant when designing shell structures. This paper focuses on shape optimization of dished ends with the depth equivalent to the standard ones, with the intent to minimize the maximum von Mises stress in a cylindrical pressure vessel. Referring to the Bézier curve (BC), a unique geometry of arbitrary order is developed to describe the parametric shape of the dished end. The optimization is implemented using two approaches. Initially, the fitness function is obtained analytically through the membrane theory (MT). A deterministic optimization algorithm is adopted to complete the procedure. Further, the optimization method is modified to obtain the fitness function using the finite element method (FEM). To process the solution, a genetic algorithm (GA) is employed. The obtained improvement of stress distribution is compelling while maintaining the manufacturability of the shell structure.

Comparative Analysis of Mine Shaft Hoisting Systems’ Brake Temperature Using Finite Element Analysis (FEA)

Abstract: This paper studies both the thermal and mechanical behavior of brake system models in the case of the emergency braking of a mine hoist model. Using a step-by-step approach inspired by studies conducted on small brake systems with high rotation speeds specific to road and rail vehicles, a comparative analysis using a computer simulation was performed for the two types of brakes of a mine hoist system. A Solidworks model was built for two configurations: the drum-and-shoe and the disc-and-pads, and it was imported to COMSOL Multiphysics, where the material properties and simulation parameters were defined. Simulations were performed for each configuration, first using a Heat transfer module in the solids to investigate the frictional heat. The results showed the locations of the hot points on the disc and on the drum, with the surface temperature reaching 97 °C on the disc and 115 to 159 °C on the drum. Next, simulations using a Structural Mechanics module were run to obtain the stress and deformation induced by the heat generated during braking. The von Mises stress of the drum-and-shoe brake occurred on the external surface of the drum and had a value of 2 × 108 N/m2. For the disc-and-pad brake, the stress occurred towards the edges of the brake pad contact and was 4 × 108 N/m2. Both values were under the yield stress of the passive brake element material. Regarding the deformations, for the drum-and-shoe brake, it appeared towards the outer boundary of the drum, being 0.45 mm, and for the disc-and-pad brake, it was situated at the external edge of the disc, being 0.25 mm. COMSOL Multiphysics allowed the evaluation of the thermo-mechanical behavior using noninvasive techniques since actual emergency braking testing on a working mine hoisting installation is not possible because of safety and logistic concerns.

Coupling effects of strain rate and fatigue damage on wheel-rail rolling contact behaviour: a dynamic finite element simulation

Abstract: ABSTRACT A comprehensive 3-D explicit finite element (FE) model was established to investigate the frictional wheel-rail rolling contact responses in this study, in which the strain rate effect and initial fatigue damage of wheel/rail materials were taken into account via inputting relevant stress-strain response curves. Four friction exploitation levels were included to examine the dynamic contact responses in terms of contact load, contact patch area, creep characteristic, and stress/strain state. It is found that the nodal velocities on the rail surface at the trailing and leading edges of the contact patch are in opposite directions once the slip occurs. The strain rate hardening effect will significantly increase the Mises stress and suppress the plastic deformation of the wheel and rail at high creep levels, while the Mises stress will decrease with the increase of fatigue damage but the plastic strain will increase correspondingly.

On estimating plastic zones and propagation angles for mixed mode i/ii cracks considering fractal effect

Abstract: This paper mainly investigated the influence of the fractal dimension of mixed mode I/II crack on its near-tip plastic zones and propagation angles. The near-tip distortional strain energy density for mixed mode I/II crack is modified by considering its fractal dimension. Using the Von Mises yield condition, the plastic zones at the fractal crack tip are evaluated. The effects of the fractal dimension of crack on the near-tip plastic zones are analyzed qualitatively. A modified criterion minimizes the fractal distortional strain energy density to predict the propagation direction of mixed mode I/II crack. Based on this, the effects of fractal dimension on the mixed mode I/II crack propagation direction at different inclination angles are discussed quantitatively. In addition, the modified criterion is compared to the experimental data in the literature, as well as the classical maximum tangential stress criterion and minimum strain energy density criterion. The results indicate that the fractal dimension of crack is an important factor in evaluating the crack-tip plastic zones and predicting the crack propagation angle, and the modified fractal criterion is more accurate and effective in predicting the crack propagation angles.

Mechanism of microweld formation and breakage during Cu–Cu wire bonding investigated by molecular dynamics simulation

Abstract: Currently, wire bonding is the most popular first-level interconnection technology used between the die and package terminals, but even with its long-term and excessive usage, the mechanism of wire bonding has not been completely evaluated. Therefore, fundamental research is still needed. In this study, the mechanism of microweld formation and breakage during Cu–Cu wire bonding was investigated by using molecular dynamics simulation. The contact model for the nanoindentation process between the wire and substrate was developed to simulate the contact process of the Cu wire and Cu substrate. Elastic contact and plastic instability were investigated through the loading and unloading processes. Moreover,the evolution of the indentation morphology and distributions of the atomic stress were also investigated. It was shown that the loading and unloading curves do not coincide, and the unloading curve exhibited hysteresis. For the substrate, in the loading process, the main force changed from attractive to repulsive. The maximum von Mises stress increased and shifted from the center toward the edge of the contact area. During the unloading process, the main force changed from repulsive to attractive. The Mises stress reduced first and then increased. Stress concentration occurs around dislocations inthe middle area of the Cu wire.

Evaluation of Zirconia and High Performance Polymer Abutment Surface Roughness and Stress Concentration for Implant-Supported Fixed Dental Prostheses

Abstract: Background: The High Performance Polymer is a based polymer biomaterial that was introduced as dental material to manufacture dentures superstructure and dental implants abutments. However, its surface characteristics and stress state still need to be properly described. The aim of this study was to compare the surface characteristics of a High Performance Polymer (Bio-HPP, Bredent, Senden, Germany) for computer-aided design and computer-aided manufacturing (CAD/CAM) milling and a Zirconia (Zirkonzahn, Steger, Ahrntal, Italy). Methods: The abutments surface roughness (Ra) was evaluated for each abutment material (N = 12) using a confocal laser microscope. Data were evaluated using One-Way ANOVA and Tukey tests (p < 0.05). In addition, a finite element analysis software was used to present stress measurement data as stress maps with 100 N loading. Results were generated according to Von-mises stress criteria and stress peaks were recorded from each structure. Results: Results showed a mean Ra of 0.221 ± 0.09 μm for Bio-HPP and 1.075 ± 0.24 μm for Zirconia. Both surface profiles presented a smooth characteristic regardless the measurement axis. The stress peaks from implant fixture and screw were not affected by the abutment material, however the high performance polymer showed the highest stress magnitude for the abutment region. Conclusions: Comparing the present results with the literature it is suggested that the CAD/CAM High Performance Polymer abutments present an adequate surface roughness with acceptable values of stress.

Rehabilitation of severely-destructed endodontically treated premolar teeth with novel endocrown system: Biomechanical behavior assessment through 3D finite element and in vitro analyses

Abstract: Rehabilitation of endodontically treated premolars with extensive coronal destruction through endocrown approach remains a controversial topic in reconstructive dentistry. There is no clear consensus in the literature which endocrown design with which material is the most effective restoration option for severely-destructed endodontically treated premolars. The aim of this study was to assess the biomechanical behavior of endodontically treated maxillary first premolars restored with a novel endocrown system compared to the conventional one varying the applied load type through finite element and in vitro analyses.For finite element analysis, two models representing two endocrown systems used for restoration of severely-destructed endodontically treated maxillary first premolar tooth were generated: Model C for the conventional monolithic IPS e.max CAD endocrown and Model P for the novel bi-layered endocrown (PEKKTON ivory coping veneered with cemented IPS e.max CAD). Modified von Mises stress values on the remaining tooth structure, cement lines and restorative materials were evaluated separately under axial and oblique loading of 450 N. For in vitro analysis, forty sound human bifurcated maxillary first premolars were collected, endodontically-treated, and divided into 2 main groups (n = 20) according to the system used for endocrown fabrication; Group C: the conventional monolithic endocrowns and Group P: the novel bi-layered endocrowns. All specimens were subjected to an artificial thermomechanical aging protocol. Each main group was subdivided into two subgroups (n = 10) according to the loading type (axial and oblique) applied during the fracture resistance test. Qualitative analysis using Stereomicroscopy and Scanning Electron Microscopy was performed. Data were statistically analyzed at p-value ≤ 0.05.Regarding stress distribution pattern of remaining tooth structure (enamel and dentin), both endocrown systems and cement lines under both axial and oblique load application, Model P resulted in lower stresses than Model C. The oblique stress values of all analyzed structures were higher than corresponding values resulted axially. Considering failure load, a significantly higher load was recorded for Group P when axial or oblique loading was applied (p = 0.00). A significantly higher failure load was recorded with axial loading for both main groups. With regard to failure mode, a statistically significant difference was observed between main groups (p = 0.033), with more favorable failures detected for Group P axially.Compared to the conventional endocrown system, the studied novel system improved the biomechanical behavior within tooth/restoration complex of the restored severely-destructed endodontically treated maxillary first premolar teeth, whatever the applied load type.The novel endocrown system using a PEKK coping veneered with cemented IPS e.max CAD can be considered a favorable promising option for restoration of severely-destructed endodontically treated premolar teeth, with more protection for residual tooth structure. It can be considered as a conservative alternative option to the conventional treatment modalities not only for normal clinical conditions, but also for parafunctional cases.

An artificial neural network for surrogate modeling of stress fields in viscoplastic polycrystalline materials

Abstract: Abstract The purpose of this work is the development of a trained artificial neural network for surrogate modeling of the mechanical response of elasto-viscoplastic grain microstructures. To this end, a U-Net-based convolutional neural network (CNN) is trained using results for the von Mises stress field from the numerical solution of initial-boundary-value problems (IBVPs) for mechanical equilibrium in such microstructures subject to quasi-static uniaxial extension. The resulting trained CNN (tCNN) accurately reproduces the von Mises stress field about 500 times faster than numerical solutions of the corresponding IBVP based on spectral methods. Application of the tCNN to test cases based on microstructure morphologies and boundary conditions not contained in the training dataset is also investigated and discussed.

Effect of local texture and residual stress on the bendability of extruded 6000-series Al alloy profiles

Abstract: In this study, X-ray cosα measurement was optimized with 3-axis oscillation to perform highly accurate measurements of residual stress in extruded Al alloy (A6061 and A6005C) profiles having preferred orientations and large grain sizes. In A6005C, a grain-growth region was observed just below the surface–bulk boundary and visualized via texture differences. The regions of preferred orientations corresponded well with the major changes in the residual stress as a function of depth from the surface. The boundary of the (110) and (100) textures corresponded well with the first local maximum in the von Mises stress (σvM) for both the alloys. The grain-growth region of A6005C corresponded to the region between the first and second local maxima of σvM. The principal stress (σ1) direction was almost parallel to the extrusion direction in the grain-growth region of A6005C. The changes in the σ1 direction with depth resulted in the observed anisotropic bending behavior.

Assessment of the Best FEA Failure Criteria (Part I): Investigation of the Biomechanical Behavior of PDL in Intact and Reduced Periodontium

Abstract: The accuracy of five failure criterions employed in the study of periodontal ligaments (PDL) during periodontal breakdown under orthodontic movements was assessed. Based on cone-beam computed tomography (CBCT) examinations, nine 3D models of the second lower premolar with intact periodontium were created and individually subjected to various levels of horizontal bone loss. 0.5 N of intrusion, extrusion, rotation, tipping, and translation was applied. A finite Elements Analysis (FEA) was performed, and stresses were quantitatively and qualitatively analyzed. In intact periodontium, Tresca and Von Mises (VM) stresses were lower than maximum physiological hydrostatic pressure (MHP), while maximum principal stress S1, minimum principal stress S3, and pressure were higher. In reduced periodontium, Tresca and VM stresses were lower than MHP for intrusion, extrusion, and the apical third of the periodontal ligament for the other movements. 0.5 N of rotation, translation and tipping induced cervical third stress exceeding MHP. Only Tresca (quantitatively more accurate) and VM are adequate for the study of PDL (resemblance to ductile), being qualitatively similar. A 0.5 N force seems safe in the intact periodontium, and for intrusion and extrusion up to 8 mm bone loss. The amount of force should be reduced to 0.1–0.2 N for rotation, 0.15–0.3 N for translation and 0.2–0.4 N for tipping in 4–8 mm periodontal breakdown. S1, S3, and pressure criteria provided only qualitative results.