Mechanical properties and multi-objective optimization of random-gradient double-arrow honeycombs under oblique loading

The aim of this study was to investigate the biomechanical behaviour of maxillary premolar teeth regarding root morphology and abfraction depth, submitted to axial and oblique occlusal load. The investigation was conducted using 3D finite element analysis and strain gauge test. Sound maxillary premolar single and double root were selected for 3D model generation. The teeth were scanned for external morphology data acquisition. The 3D geometry was stored in *.STL and exported to Bio-CAD software (Rhinoceros-3D) to model generation. Mesh generation, mechanical properties and boundary conditions were performed in finite element software (Femap, Noran Engineering, USA). Twelve models were generated: sound tooth, 1.25 and 2.5 mm abfraction teeth. 100N compressive static load was applied: axially and 45° angle to the long axis on the palatine surface of the buccal cusp. Two strain gauges were bonded on the teeth mounted in a mechanical testing machine. Von Mises criterion showed that the double-root teeth associated with 2.5 mm abfraction and oblique loading presented higher stress values. Axial loading associated with single-root teeth propitiated the lowest stress rates. Double root sound 1.25 and 2.5 mm abfraction teeth associated with oblique loading showed the highest strain values (μS): 692.6, 1043.31 and 1236.14, respectively. Single root sound 1.25 and 2.5 mm abfraction teeth associated with oblique loading showed 467.10, 401.51 and 420.98 strain values, respectively. Axial loading showed lower strain rates, ranging from 136.12 to 366.91. The association of deep lesions, oblique loading and double-root tooth promoted higher stress and strain concentration.

On design of multi-cell tubes under axial and oblique impact loads

Titanium root form implants are widely accepted because of the advantages of their mechanical properties. This study compared the screw loosening between two types of implant supported crowns (cement retained and screw retained) at the location of left lower first molar, using finite element method in a nonlinear analysis. The Dentis system was used for modeling of the implant, abutment and suprastructure. The amount of preload displacement was almost the same for both types of abutments. Applying force in any direction reduced the amount of downward preload displacement and decreased abutment-implant stability. In the cement retained crown, the amount of inner abutment displacement was always less than the screw head displacement by applying vertical, oblique and vertical-horizontal loads, so the stability of the abutment-implant complex was maintained. In the screw retained crowns under vertical-horizontal load the amount of displacement at the screw head and inner side of abutment was close to each other and this put the screw on the verge of loosening. However, under oblique pressure of 100 N, the inner abutment displacement exceeded the screw head displacement and the screw was loosened. Under vertical loading of 100 and 150 N, the stability of implant abutment was maintained. Screw loosening is less likely to occur under vertical load compared with oblique load. The cemented retained crowns have a higher biomechanical stability than screw retained crowns.

This study aims to assess and compare the impact of Monolithic Zirconia (MZ) and In-Ceram Zirconia (ZP) superstructures on stress distribution within implants and D2/D4 bone densities under 200 N vertical and oblique occlusal loads using three-dimensional finite element analysis via ANSYS WORKBENCH R2. The analysis employed maximum and minimum von Mises stress values. Modeling an implant (4.2 mm diameter, 10 mm length) and abutment (0.47 mm diameter), with an 8 mm diameter and 6 mm length single crown, the research identified lower von Mises stresses in D2 cancellous bone with the MZ model under vertical loading. Conversely, under oblique loading, the ZP model exhibited maximum von Mises stresses in D4 bone around the implant. This underscores the critical need to consider physical and mechanical properties, beyond mere aesthetics, for sustained implant success. The findings highlight the effect of material composition and stress distribution, emphasizing the necessity of durable and effective implant treatments.

PURPOSEZirconia has exceptional biocompatibility and good mechanical properties in clinical situations. However, finite element analysis (FEA) studies on the biomechanical stability of two-piece zirconia implant systems are limited. Therefore, the aim of this study was to compare the biomechanical properties of the two-piece zirconia and titanium implants using FEA.MATERIALS AND METHODSTwo groups of finite element (FE) models, the zirconia (Zircon) and titanium (Titan) models, were generated for the exam. Oblique (175 N) and vertical (175 N) loads were applied to the FE model generated for FEA simulation, and the stress levels and distributions were investigated.RESULTSIn oblique loading, von Mises stress values were the highest in the abutment of the Zircon model. The von Mises stress values of the Titan model for the abutment screw and implant fixture were slightly higher than those of the Zircon model. Minimum principal stress in the cortical bone was higher in the Titan model than Zircon model under oblique and vertical loading. Under both vertical and oblique loads, stress concentrations in the implant components and bone occurred in the same area. Because the material itself has high stiffness and elastic modulus, the Zircon model exhibited a higher von Mises stress value in the abutments than the Titan model, but at a level lower than the fracture strength of the material.CONCLUSIONOwing to the good esthetics and stress controllability of the Zircon model, it can be considered for clinical use.

Multiobjective crashworthiness optimization of hollow and conical tubes for multiple load cases

Crashworthiness analysis and bionic design of multi-cell tubes under axial and oblique impact loads

Crashworthiness optimal design of multi-cell triangular tubes under axial and oblique impact loading

Optimization of foam-filled double circular tubes under axial and oblique impact loading conditions

Thin-walled structures are inevitably subjected to oblique loads which could result in poor crashworthiness. To improve comprehensive crashworthiness, multilayered hexagonal tubes with 2 to 9 layers denoted as L2 to L9 were proposed, and their crash performances were investigated under axial and oblique quasi-static loads. Based on four crashworthiness criteria, complex proportional assessment (COPRAS) and TOPSIS methods were adopted to select out two optimal structures, L2 and L3. Further multiobjective optimizations of L2 were conducted. When selecting the best configuration using the COPRAS method, structures with lower peak crushing force (PCF), higher PCF, specific energy absorption (SEA) and crushing force efficiency (CFE) are preferred. The results are opposite using the TOPSIS method.

In this study, numerical results are conducted to determine the deformation mode of foam filled double circular tubes, namely; half foam filled double circular tube (FD), and full foam filled double circular tube (DD) under oblique loading. To validate the simulation and experimental results, two-parameter Weibull probability distribution was used. The proposed function of the multi-objective optimisation design (MOD) process was based on the Finite Element Analysis results. The metamodels in were constructed to predict the crashworthiness criteria of specific energy absorption and peak crushing force under oblique impact loading. Also examined in the study were the MOD problems of the two structure types under multiple impact angles using the NSGA II algorithm. The findings from the study determined that the optimal full foam filled double circular tube had better crashworthiness under pure axial loading. While the optimal half foam filled, double circular tube had more space to enhance the crashworthiness under an oblique impact.

Statement of problem Dental implants have become the standard of care in the rehabilitation of edentulous areas. However, their long-term success depends on various factors. Titanium, due to its high biocompatibility and favorable mechanical properties, has long been the material of choice, offering superior aesthetic outcomes and inert biological behavior. Additionally, differences in bone density—classified from D1 to D4—can significantly affect stress distribution patterns around implants. Purpose The purpose of the study is to assess the interaction between implant material, bone density, and loading direction to optimize clinical outcomes. Materials and Methods In this analytical study, finite element analysis (FEA) was employed to evaluate the biomechanical behavior of titanium and zirconia implants under different bone densities (D1 to D4). Three-dimensional models were subjected to both vertical loading (200 N) and oblique loading (50 N at 45°). The analysis focused on the maximum von Mises stress values in the cortical and cancellous bone, as well as in key implant components, including the abutment, fixture, and abutment screw. Results The simulation revealed that oblique loading consistently resulted in significantly higher stress values compared to vertical loading. Stress values in abutments were close under vertical loading (titanium: 40.07 MPa, zirconia: 37.67 MPa). However, oblique loading caused a sharp increase in zirconia (44.36 MPa) compared to titanium (27.64 MPa).In lower-density bone types (D3 and D4), stress concentration was predominantly observed in the crestal bone region. Titanium implants demonstrated more uniform stress distribution and lower peak stresses in the surrounding bone, particularly in low-density conditions. Zirconia implants, on the other hand, showed satisfactory performance in denser bone (D1 and D2), but exhibited increased stress accumulation under oblique loading and in softer bone types. Conclusion Titanium implants demonstrated more favorable stress distribution, particularly under oblique loading and in low-density bone (D3—D4). In contrast, zirconia implants performed adequately in denser bone types (D1—D2) with vertical loads. These findings highlight the importance of selecting implant materials based on site-specific biomechanical and esthetic demands to optimize clinical outcomes and long-term stability.

In this study, the plastic deformation mechanism of a fully clamped beam under oblique loading at its free end is analyzed. Supposing the cross sections are variable along the beam length, a characteristic length L∗≡MP/NP, defined as the ratio between fully plastic bending moment MP and fully compression force NP, is employed to estimate the load carrying capacity of each cross section. By finite element (FE) simulations of the conical tubes, it is validated that if the initial failure positon locates in the middle of the beam, it will not change with the total beam length. Then, based on the analytical analysis and FE simulation, a progressive deformation mechanism triggered by bending, notated as progressive bending, is proposed for the first time. From the optimization result of maximizing loading force that the unit mass can withstand, the tubes with constant thickness are found to be better than tubes with graded thickness, when they are used as supporting structures. The multi-objective optimization for tubes with varying cross sections under oblique loading with different angles is also given. Then, two methods to improve the load carrying capacity of tubes are given: (1) to design the cross section of the tube, which is corresponding to let the critical loading force of all the cross sections be equal; (2) to optimize the initial failure point, so as to produce repeated failure modes.

The crashworthiness of Bi-directional corrugated honeycomb aluminum under oblique loading using for nuclear spent fuel transportation casks

Background Dental implants are critical for restoring functionality and aesthetics in patients with missing teeth. The all-on-four treatment concept utilizes four dental implants to support a full-arch prosthesis. Material choice for these implants plays a crucial role in the long-term success of the treatment, affecting everything from biomechanical stability to osseointegration and patient comfort. Aim The purpose of this study is to analyze the biomechanical performance of three different materials used in all-on-four dental implant designs through finite element analysis (FEA). The aim is to determine which material optimally balances stress and deformation under various loading conditions. Objective The main objective of this research is to evaluate the effects of stress, strain, and deformation on all-on-four dental implants made from titanium, zirconia, and polyether ether ketone (PEEK). The study seeks to identify which material demonstrates the best mechanical properties under simulated functional loads. Methods A 3D model simulating the dental implants integrated with cancellous and cortical bone was developed. Finite element analysis was conducted to assess the biomechanical performance of the implants made from titanium, zirconia, and PEEK. A perpendicular load of 100 N was applied to the tips of the implants, followed by an oblique load of 100 N at a 30-degree angle, to simulate different chewing forces. Results The deformation analysis indicated that implants made of zirconia exhibited significantly lower maximum and average deformation compared to those made from titanium and PEEK. Although PEEK implants showed lower maximum and average stress, they did not perform well in stress dissipation compared to zirconia. Similar patterns of stress and deformation were observed under both perpendicular and oblique loading conditions. Conclusion Zirconia implants outperformed titanium and PEEK in terms of deformation and stress distribution under simulated loading conditions. This suggests that zirconia could be a superior material for all-on-four dental implants, offering better mechanical stability and potentially enhancing the longevity and success of dental restorations. Further clinical trials are recommended to validate these findings and assess the long-term outcomes of zirconia-based implants.