Lower Stress Values Research Articles

Finite Element-Based Optimization of Cross-Section Area on 2D Truss Structure with 10-members and 12-members Using Nonlinear Programming Method

Designing a structure requires good planning to obtain optimal results. Some things that need to be considered in designing structures are the materials used, the dimensions of the structure, and others. By optimizing the dimensions of the structure, the use of materials can be minimized so that production costs can be reduced. The experiment requires additional cost and time. Therefore, finite element software can be used to design the structure optimally in compliance with the constraints set according to the requirements. Previous studies have carried out cross-section area optimization of structures with maximum allowable stress limits. In this research, the optimization of 2D truss cross-section area with maximum volume constraint is developed using MATLAB software with fmincon function. The structure is modelled in 2 shapes: a 2D truss with ten members and a 2D truss with twelve members. The optimum area is obtained from the simulation results, which are almost the same in both structures, while the lower stress value is obtained in the ten-member 2D truss structure. The maximum stress (tensile stress) on the 12-member 2D truss occurs on element 12 at 3484.28 psi, and then the minimum stress (compressive stress) occurs on elements 3, 4, 8, and 9 at -3472.10 psi. The maximum stress (tensile stress) on the 10-member 2D truss structure occurs in elements 1 and 9 at 3472.10 psi, and the minimum stress (compressive stress) occurs in element four at -3479.77 psi.

E-cigarette aerosol exposure effect on bone biomechanical properties in murine models

Numerous studies have shown the detrimental health effects of tobacco smoking on bone volume and strength in human and animal models. Little is known regarding the impacts of e-cigarettes, a form of smoke-less nicotine intake, despite their growing population of users. This study uses murine models to evaluate the effects of exposure to e-cigarette aerosols (JUUL) on bone structure and strength through micro-CT imaging and mechanical testing. JUUL mice had more trabecular bone in thickness and volume, yet lower ultimate stress and modulus values in the cortical bone than the control mice. These outcomes suggest that, although vaping can result in a higher bone volume, this bone is weaker than average. E-cigarettes should be examined more closely regarding adolescence and long-term consequences on skeletal health.

Comparing the influence of cuspal angulation, occlusal loading, and connector widths between tooth- and implant-supported zirconia fixed dental prosthesis

BackgroundFew studies have established the relationship between connector widths, cuspal angulation, loading forces, and supporting structures of zirconia fixed dental prosthesis (FDP). The objective of the study was to compare the stress distribution in implant- and tooth-supported zirconia FDP with different connector designs, and cuspal angulations of replaced teeth under diverse angulations of forces. MethodsFinite element (FE) analysis was done by simulating a 3-unit implant- and tooth-supported FDP. FE models with varying cuspal angulations 0°, 20°, and 33° and connector designs 2 mm, 2.5 mm, and 3 mm was generated. The simulated models were loaded with 100 N of forces under different axial and non-axial angulations. The graphical and numerical stresses were observed, recorded, and statistically analyzed. ResultsHigher stress of 245.55 MPa in implant-supported FDP and lower stress value of 28.22 MPa in tooth-supported FDP was observed at 0-cuspal inclination for 3 mm connector width. The data were statistically analyzed with unpaired t test to eliminate the differences. The inter-group, intra-group tests, p and t values for various connector, and tooth angulations of tooth- and implant-supported FDP were statistically insignificant. (p > 0.05) ConclusionThere was no statistically significant difference in stress was observed between tooth- and implant-supported FDP for different connector widths, cuspal inclination, and diverse angulation of forces.

Transient 3D hydrodynamic model of a blast furnace main trough

A transient 3D CFD model is solved to investigate the features of the complex flow in a blast furnace trough. Hot metal, slag, and air are considered as different phases of the flow. The influence of various taphole stream conditions on the hydrodynamics in the trough is examined, such as different slag-hot metal ratios, taphole diameters, and stream velocities. The special case of a dry trough during its first tapping is also addressed. Attention is devoted to the characterization of the wall shear stress, closely related to mechanical erosion, and to the evolution of the interfaces separating the fluid phases. Intricate flow patterns, characterized by large recirculations and return currents of both slag and hot metal, are observed. The simultaneous tapping of slag and hot metal leads to distinct flow features, deviating from the initial stage, when only hot metal is drained, as well as lower shear stress values, up to 31% less with increasing slag content in the taphole stream. Slag and hot metal levels in the trough evolve rapidly to quasi-steady states. Although the influence of the taphole stream velocity and diameter have a modest impact on the free surface dynamics, variations in the taphole slag fraction lead to significant fluctuations in the depth of slag and hot metal pools in the trough. The height of the slag-iron free surface can increase by up to 40% relative to its initial level, while the variation in the slag pool depth approaches 30%. These changes in the interface positions carry potential implications for refractory wear, as they suggest a substantial shift of the slag-hot metal line during each tapping.

Barriers for why pregnant women do not visit a dentist on a regular basis: using group concept mapping methodology

Objectives Periodontitis in pregnancy represents a significant, but often overlooked challenge due to its association to adverse pregnancy (preeclampsia and gestational diabetes) and birth related outcomes (preterm birth and low birth weight). The overall study aim was to identify, organize, and prioritize barriers influencing dental visits among Danish pregnant women not seeing a dentist on a regularly basis. Materials and methods Participants were pregnant women screened at weeks 11–13 of gestation, and were recruited if they were not seeing a dentist regularly. The study was conducted at Holbæk and Nykøbing Falster Hospital in Region Zealand, Denmark. The Group Concept Mapping (GCM) approach was applied. The pregnant women participated in brainstorming (n = 18), sorting (n = 20), and rating (n = 17) the seating question ‘Thinking as broadly as you can, please list all barriers of importance to you for not seeing a dentist on a regular basis’. Results A total of 38 unique barriers were identified, organized, and prioritized online. The multidimensional scaling analysis involved 10 iterations and revealed a low stress value of 0.21. A cluster solution with five clusters including ‘economic reasons’, ‘lack of priority’, ‘lack of time and energy’, ‘no problems with teeth’, and ‘dental fear’, was discussed and interpreted at a validation meeting. Conclusions Five overall clusters explaining barriers for not seeing a dentist regularly were revealed. Of the five clusters, ‘economic reasons’ and ‘lack of priority’ were rated as the most important clusters. Accordingly, such barriers should be considered in the planning of future strategies of dental care during pregnancy.

3D finite element analysis of stress distribution as a result of oblique and horizontal forces after regenerative endodontic treatment part II: comparison of material thickness

AimThis study aimed to evaluate the stress distribution caused by secondary trauma forces after regenerative endodontic treatment (RET) using different thicknesses of coronary barrier material with three-dimensional finite element analysis(FEA).MethodA control model was created using the tomography image of the immature maxillary central tooth with computer software.Study models were created with the modulus of elasticity and Poisson’s ratio of the materials used in RET.Enamel, dentin, cementum, periodontal ligament, cortical, and cancellous bone were modeled. Coronary barrier materials were applied in 3 mm and 5 mm thicknesses (Model 1: control model, model 2:3 mm/Calcium Enriched Mixture(CEM), model 3:3 mm/Mineral Trioxide Aggregate(MTA), model 4:3 mm/Biodentin, model 5:5 mm/CEM, model 6:5 mm/MTA, model 7:5 mm/Biodentin). For the trauma force simulation, 300 N force in the horizontal direction was applied to the buccal surface of the tooth in the first scenario. For the second scenario, maximum bite force simulation, a force of 240 N in the oblique direction was applied to the palatal surface of the tooth. FEA was performed with Algor Fempro. The resulting stresses were recorded as Von Mises, maximum, and minimum principal stresses.ResultsLower stress values were obtained in 5 mm models compared to 3 mm models. However, the difference between them was insignificant. Lower stress values were obtained in all RET models compared to the control model. The lowest stress values in dental tissues and bone tissue were obtained in the CEM models.ConclusionThis is the first study in which the stress caused by different thicknesses of CEM on dental tissues was evaluated with FEA. RET strengthens immature teeth biomechanically. CEM and Biodentin are more successful materials in stress distribution than MTA. Considering the cost of treatment, 3 mm material thickness is ideal for RET since there is no significant difference between the stress values resulting from the use of 5 mm and 3 mm coronary barrier material.

Patient-specific bone material modelling can improve the predicted biomechanical outcomes of sacral fracture fixation techniques: A comparative finite element study

ObjectiveTo evaluate and compare the biomechanical efficacy of six iliosacral screw fixation techniques for treating unilateral AO Type B2 (Denis Type II) sacral fractures using literature-based and QCT-based bone material properties in finite element (FE) models. MethodsTwo FE models of the intact pelvis were constructed: the literature-based model (LBM) with bone material properties taken from the literature, and the patient-specific model (PSM) with QCT-derived bone material properties. Unilateral transforaminal sacral fracture was modelled to assess different fixation techniques: iliosacral screw (ISS) at the first sacral vertebra (S1) (ISS1), ISS at the second sacral vertebra (S2) (ISS2), ISS at S1 and S2 (ISS12), transverse iliosacral screws (TISS) at S1 (TISS1), TISS at S2 (TISS2), and TISS at S1 and S2 (TISS12). A 600 N vertical load with both acetabula fixed was applied. Vertical stiffness (VS), relative interfragmentary displacement (RID), and the von Mises stress values in the screws and fracture interface were analysed. ResultsThe lowest and highest normalised VS was given by ISS1 and TISS12 techniques for LBM and PSM, with 137 % and 149 %, and 375 % and 472 %, respectively. In comparison with the LBM, the patient-specific bone modelling increased the maximum screw stress values by 19.3, 16.3, 27.8, 2.3, 24.4 and 7.8 % for ISS1, ISS2, ISS12, TISS1, TISS2 and TISS12, respectively. The maximum RID values were between 0.10 mm and 0.47 mm for all fixation techniques in both models. The maximum von Mises stress results on the fracture interface show a substantial difference between the two models, as PSM (mean ± SD of 15.76 ± 8.26 MPa) gave lower stress values for all fixation techniques than LBM (mean ± SD of 28.95 ± 6.91 MPa). ConclusionThe differences in stress distribution underline the importance of considering locally defined bone material properties when investigating internal mechanical parameters. Based on the results, all techniques demonstrated clinically sufficient stability, with TISS12 being superior from a biomechanical standpoint. Both LBM and PSM models indicated a consistent trend in ranking the fixation techniques based on stability. However, long-term clinical trials are recommended to confirm the findings of the study.

Switched capacitor based 7-level and 9-level multilevel inverters with single DC source and reduced voltage stress

This paper proposes two different switched capacitor based Multilevel Inverter topologies having single dc voltage source. One of the proposed MLIs is a seven-level structure whereas the other circuit successfully generates a nine-level output voltage. The special features of the seven-level topology consist of reduced number of circuit elements, lower voltage stress on switches, and boosted output voltage. The nine-level MLI having unity gain also possess the reduced switch count along with lower value of switch voltage stress. Fundamental frequency based Nearest Level Control modulation and Level-Shifted Pulse Width Modulation have been used for generating the required voltage levels. Successful implementation of the proposed MLI circuits has been done with the help of a laboratory prototype and its results are presented and explained in the paper to show its practical suitability. Other type of analysis include loss analysis which has been done in PLECS software. From this analysis, the efficiency has been estimated. A comparative analysis of both the proposed structures has been carried out with some other similar topologies on different performance parameters. From the analysis and comparison, it is evident that the proposed MLIs are better than some of the existing topologies and can be used for industrial applications.

Stress Classification Lines for Non-Standard Y-Tee Design in Piping System

All processes fluids in the oil and gas industry are generally transferred from one point to another via complex piping networks. The process temperature and the pressure of the fluids may vary between -21 °C to 816 °C and from atmospheric, 1.013 barg to 431 barg, respectively. Under these conditions, the entire piping networks are exposed to thermal expansion and contraction resulting in mechanical bending, potentially causing mechanical failures. The most common pipe fitting used in piping networks to divide the fluid flow into two different directions would be a standard equal tee which was designed in accordance with ASME B16.9. The equal tee, however, has distinctive flexibility characteristics compared to the pipe, which is well defined in ASME B31.3. These flexibility characteristics generate a stress intensification factor (SIF) through bending moment equations for beam-type element analysis for standard equal tee components. However, due to the limitation of SIF and flexibility characteristics for the non-standard pipe fittings, the stress evaluation could not be done using beam-type element analysis. When using finite element method (FEM) analysis, generally equivalent stresses (Von Mises or Tresca) or principal stresses would be evaluated depending on the stress categorization as explained in ASME codes and standards. In this paper, a stress evaluation method for non-standard Y-tee was developed and demonstrated against ASME VIII Div. 2 Part 5 requirement. The developed SCLs line for the non-standard Y-tee fittings provides the guides for stress assessment against design stress allowable. An optimum design for non-standard Y-tee is proposed at 45° and 60° crotch radii which resulted in lower stress value at SCL lines, hence improving the structural integrity.

Stress distribution of four implant supported overdentures with tilted standard-sized implants and mini implants.

The goal of the current study is to evaluate the stress distribution when tilted implants and mini-implants are used to support a mandibular overdenture. Three-dimensional (3D) finite element models of mandibular overdentures were established using four, axial, standard-sized implants (SA model), four standard-sized implants with the mesial ones axial and the distal ones tilted (ST model) and four mini-implants (MA model) with Locator attachments. On each model, a 100 N load was applied to the overdenture in four different directions; bilateral vertical, unilateral vertical and oblique load on the posterior region, and a vertical load on the incisors. The stresses distributed at the peri-implant bone, implants, the prosthetic components, and the overdentures were evaluated. Non-axial posterior loading caused higher stress values in the implant and the prosthetic component than axial posterior loading. Lower stress values of the implant and the prosthetic component were observed in the ST model than SA model. The stress distribution in the overdenture at posterior loads were mostly observed around the implants. Less prosthetic complications may be expected when the treatment option in the ST model is used. Fatigue fractures may occur around the implants in the overdentures, precautions are advised.

Finite Element Analysis of Fracture Resistance of Mandibular Molars with Different Access Cavity Designs

IntroductionThis study aimed to assess the fracture resistance of mandibular first molars after preparation with 3 different access cavity designs and 2 rotary systems using finite element analysis. MethodsSix 3-dimensionally printed mandibular first molars simulating natural teeth received traditional, conservative, and ultraconservative (truss) access cavity preparations. The root canals in each group were instrumented with either XP-Endo Shaper (FKG Dentaire, La Chaux-de-Fonds, Switzerland) or TruNatomy (Dentsply Sirona, Ballaigues, Switzerland) rotary files. The models were individually digitized, and micro–computed tomographic scans were transferred to Mimics software (Materialise NV, Leuven, Belgium) to create a geometric model of the tooth. The designed model was exported to 3-matic software (Materialise NV), and STL files were transferred to Geomagic Design X (3D Systems, Rock Hill, SC). Point cloud data were used for surfacing and transferred to ANSYS software (Ansys, Canonsburg, PA). A 200-N superficial force was applied vertically to the buccal cusps and central fossa, and the maximum and minimum equivalent von Mises stress values were calculated and reported. ResultsThe traditional and ultraconservative access cavity designs yielded the highest and the lowest von Mises stress values, respectively. In the ultraconservative cavity design, the stress values in pericervical dentin were lower in canal preparation with TruNatomy compared with XP-Endo Shaper. In the traditional and conservative cavity designs, stress was lower in the first 2 mm from the cementoenamel junction in the XP-Endo Shaper group and in the next 3 mm in the TruNatomy group. ConclusionsStress was lower in the ultraconservative and conservative cavity designs compared with the traditional design. Also, root canal preparation with TruNatomy yielded lower stress values in general compared with XP-Endo Shaper.

Oxidation resistance and mechanical properties of AlTiZrHfTa(-N) high entropy films deposited by reactive magnetron sputtering

(AlTiZrHfTa)1−xNx refractory high entropy films (RHEFs) were deposited by direct current magnetron sputtering in various nitrogen ratios (RN2 = N2/(Ar+N2)) on flat glass, silicon and sapphire substrates. The nitrogen-free film is amorphous while the nitrides are single-phased solid solutions with Face-Centered Cubic (FCC) structures. The hardness increases from 6.4 GPa for the nitrogen-free film to 25.3 GPa for the film obtained at RN2 = 20%. A preferred orientation from (111) to (200) occurs when RN2 increases from 5% to 50%. H/E and H3/H2 reports show high values for the film deposited at RN2 = 20% compared to that at 10%. However, this latter has the best compromise in terms of mechanical properties related to a lower residual stress value. The nitrides films obtained with RN2 ≥ 5%, are thermally stable at 800 °C for 3 h under vacuum. Compared to the metallic film they show an improved oxidation resistance. In fact, the Kp constant of the nitride (RN2=20%) is lower (1.22 10−7 g2 cm−4 h−1) than that of the nitrogen-free film (1.77 10−6 g2 cm−4 h−1). The corresponding activation energies (Ea) are respectively calculated at 94.8 KJ. mol−1 and 45.5 KJ.mol−1. After oxidation process, TEM analysis reveal the formation of homogeneous mixed oxide.

Structural Performance of Reinforced Concrete Double Layer Bamboo Bubble Slab Under Uniformly Distributed Load

The architectural use areas in the structure are formed by reinforced concrete (RC) slabs, which transport vertical loads to the beams, columns, load-bearing walls, and shear walls. The slab is an important structural member of reinforced concrete building structures and concrete-intensive parts of structural members. . The slab deflects significantly when the load acting on the slab or the clear span between columns is large. As a result, the slab's thickness increases to accommodate the load received. Since this slab's self-weight increases as the thickness increases, the slabs get heavier and causes the slab unable to withstand the load and to produce cracks on the surface. At the turn of the twentieth and twenty-first centuries, the creation of the bubble deck slab became an innovation to replace conventional slab. This study used bamboo as the bubble material in reinforced concrete bubble slab. This study examined and assessed the mechanical properties and structural behaviour of bamboo as a bubble in supported reinforced concrete double-layer bamboo bubble slab under a uniformly distributed load. In this research, 500 mm x 1250 mm x 175 mm supported reinforced concrete slabs C25 (1 sample) and C30 (1 sample) with double layer (DL) bamboo bubble slabs were constructed. Both samples were compared with the control sample (CS) for each slab type. It was found that the maximum displacement occurred at the centre of the slab, with 6.45 mm for DL25 and 6.89 mm for DL30. According to stress-strain analysis, the double layer bamboo slab produced a lower stress value than the control sample. Since the values were smaller than 2, DL25 and DL30 slab performed better for the ductility factor than CS25 and CS30. As a result, the displacement, ductility and section capacity were improved by employing bamboo as a bubble material in a reinforced concrete slab.

The role of aluminium content on the corrosion initiated mechanical failure of AZ series magnesium alloys

In AZ series magnesium (Mg) alloys, the percentage of aluminium (Al) influences the quantity and the phase distribution within the magnesium matrix. AZ31 and AZ91 are the widely known alloys in the AZ series which contain 3% and 9% of aluminum (Al) by weight, respectively. Due to the presence of more secondary phase and eutectic regions, AZ91 exhibits higher strength and hardness compared with AZ31 Mg alloy. These secondary phases made of Mg and Al also influence the corrosion behavior in AZ series Mg alloys. Mechanical failure of Mg alloys exposed to corroding environment is influenced by several factors in which the time of exposure is one important element. Therefore, in the current work, both the AZ31 and AZ91 Mg alloys were exposed to corroding environment for different intervals of time (1, 3 and 7 days) and then their mechanical performance has been evaluated. Without corrosion attack, AZ91 has shown superior strength compared with AZ31 Mg alloy. Interestingly, when exposed to corroding environment, AZ91 sample has failed at lower stress values compared with AZ31 sample. The results demonstrated the negative role of Al containing secondary phases on the corrosion initiated mechanical failure of AZ series Mg alloys. It is suggested that for environments with moisture or corroding solvents, AZ91 Mg alloy is more susceptible to corrosion compared with AZ31 Mg alloy.

3D finite element analysis of stress distribution on the shape of resected root-end or with/without bone graft of a maxillary premolar during endodontic microsurgery

Background/purposeApical root resection pattern affects the stress distribution behavior in the apical region of the resected tooth. The purpose of the study was to compare the biomechanical responses of resected teeth between endodontic microsurgery (horizontal resection) and targeted endodontic microsurgery (round resection). Materials and methodsFive different models were developed. The basic model without resection (NR) was regarded as the control model, and the others involved: horizontal resection without bone grafting (HN), horizontal resection with bone grafting (HG), round resection without bone grafting (RN), and round resection with bone grafting (RG) models. A static load of 100 N was applied to the buccal and palatal cusps of all the teeth in a 30° oblique direction. The maximum von-Mises stress and tooth displacement values were analyzed and compared. ResultsBoth the HN and RN models exhibited lower stress distribution values on bone compared with the NR (control) model. Regarding maximum stress distribution at the root apex, the stress value of the RN model was slightly higher compared to the HN model, whereas the RG model displayed a slightly lower stress value in comparison with the HG model. For maximum tooth displacement value, there were no significant differences between the HN and RN models, as well as the HG and RG models. ConclusionThe round resection pattern had comparable stress distribution behaviors at the root apex and tooth displacement values with the horizontal resection pattern. Targeted endodontic microsurgery might provide better biomechanical response of the resected tooth after root-end resection.

Mechanical Characterization of Fatigue and Cyclic Plasticity of 304L Stainless Steel at Elevated Temperature

BackgroundThe mechanical characterization of the cyclic elastoplastic response of structural materials at elevated temperatures is crucial for understanding and predicting the fatigue life of components in nuclear reactors.ObjectiveIn this study, a comprehensive mechanical characterization of 304L stainless steel has been performed including metallography, tensile tests, fatigue tests, fatigue crack growth tests and cyclic stress-strain tests.MethodsIsothermal tests were conducted at both room temperature and 300 °C for both the rolling direction and the transverse direction of the hot rolled steel. Mechanical properties were extracted from the uniaxial experiments by fitting relevant material models to the data. The cyclic plasticity behavior has been modelled with a radial return-mapping algorithm that utilizes the Voce nonlinear isotropic hardening model in combination with the Armstrong-Frederick nonlinear kinematic hardening model. The plasticity models are available in commercial FE software and accurately capture the stabilized hysteresis loops, including a substantial Bauschinger effect.ResultsThe material exhibits near isotropic properties, but its mechanical performance is generally reduced at high temperatures. Specifically, in the rolling direction, the Young’s modulus is reduced by 16 % at 300 °C, the yield strength at 0.2 % plastic strain is lower by 23 %, and the ultimate tensile strength is lower by 30 % compared to room temperature. Fatigue life is also decreased, leading to an accelerated fatigue crack growth rate compared to room temperature. A von Mises radial return mapping algorithm proves to be effective in accurately modelling the cyclic plasticity of the material. The algorithm has also been used to establish a clear correlation between energy dissipation per cycle and cycles to failure, leading to the proposal of an energy-based fatigue life prediction model.ConclusionsThe material exhibits reduced mechanical performance at elevated temperatures, with decreased monotonic strength, compared to room temperature. Fatigue life is also compromised, resulting in accelerated fatigue crack growth. The material’s hardening behavior differs at room temperature and elevated temperature, with lower peak stress values observed at higher temperatures. The radial return mapping algorithm can be used to determine the dissipated energy per cycle which together with fatigue testing has been used to propose a low cycle fatigue life prediction model at both temperatures.

Biomechanical effects of different materials for an occlusal device on implant-supported rehabilitation in a tooth clenching situation: A 3D finite element analysis.

The purpose of this 3D finite element analysis was to evaluate the biomechanical effects of different materials used to fabricate occlusal devices to achieve stress distribution in simulated abutment screws, dental implants, and peri-implant bone tissue in individuals who clench their teeth. Eight 3D models simulated a posterior maxillary bone block with three external hexagon implants (Ø4.0×7.0mm) supporting a 3-unit screw-retained metal-ceramic prosthesis with different crown connection (splinting), and the use of an occlusal device (OD). The OD was modeled to be 2-mm thick. ANSYS 19.2 software was used to generate the finite-element models in the pre-and post-processing phases. Simulated abutment screws and dental implants were evaluated by von Mises stress maps, and simulated bone was evaluated by maximum principal stress and microstrain maps by using a finite element software program. The highest stress values in the dental implants and screws were observed in single crowns without OD (M1). Furthermore, the highest stress values and bone tissue strain were found in single crowns without OD (M1). The simulated material for the OD did not cause many discrepancies in terms of the stress magnitude in the simulated dental implant and abutment screw for both single and splinted crowns; however, more rigid materials exhibited lower stress values. The use of OD was effective in reducing stress in the simulated implants and abutment screws and stress and strain in the simulated bone tissue. The material used to simulate the OD influenced the biomechanical behavior of implant-supported fixed prostheses, whereas splints with rigid materials such as PEEK and PMMA exhibited better biomechanical behavior.

Abstract P234: High-fat Diet Reduces Beneficial Effect Of Perivascular Adipose Tissue On Arterial Stiffness

Perivascular adipose tissue (PVAT) is has been shown to significantly contribute to arterial mechanics in health. Our previous results showed that, when including PVAT arterial stiffness is significantly reduced in the thoracic aorta. In this study, we aim to quantify the effect of PVAT on arterial stiffness in an animal model of adiposity driven hypertension. Our model was the thoracic aorta of Dahl Salt-Sensitive rats 8 weeks old on control (CON, n=2) and high-fat (HF, n=2) diets. Uniaxial mechanical tests for aorta + PVAT (+PVAT) and aorta - PVAT (-PVAT) were performed on a custom mechanical stretcher. The data reported is the low-stress stiffness calculated from the Cauchy stress-stretch curve. Blood pressure was also recorded for these animals. As expected, +PVAT samples’ stiffness appear to be lower than -PVAT samples. Including PVAT results in a 61% reduction of stiffness in the animals on CON diet. However, in animals fed a HF diet, the beneficial effect of PVAT is reduced to 21%. Surprisingly, while animals on HF diet had higher blood pressure compered to animals on CON diet, the stiffness recorded for -PVAT samples was lower in animals fed a HF vs CON diet. This could be due to an early remodeling mechanism which increases the cross-sectional area of the vessel, resulting in a lower values of stress for comparable values of stretch. Another possibility is that the collagen fibers in the tissue were not fully engaged during the test, due to the low level of deformation applied. Finally, more tests are required to confirm these initial observations. In conclusion, HF diet appears to decrease the beneficial effect of PVAT on the stiffness of the thoracic aorta.

Comparative analysis of the biomechanical behavior of the maxillary central incisors restored with glass fiber post and cast metal post and core submitted to orthodontic forces: A study with finite elements

Different types of intraradicular restorations and their insertion have an impact on teeth biomechanics. This study aimed to analyze the biomechanical behavior of maxillary central incisors restored with glass fiber post (GFP) and cast metal post and core (CMP) subjected to buccolingual and mesiodistal orthodontic forces using the finite element method. Two models of the maxillary central incisor with periodontal ligament, cortical bone, and trabecular bone were made. One of the models included intraradicular restoration with GFP, whereas, in the other, the incisor was restored with CMP. After creating the tridimensional mesh of finite elements, applying 2 orthodontic forces were simulated: 65 g of buccolingual force and 70 g of mesiodistal force. The forces were applied parallel to the palatal plane in the region of the bracket slot, located 4 mm to the incisal edge. The maximum stresses generated in the GFP-restored root were 3.642 × 10-1 MPa and 4.755 × 10-1 MPa from the buccolingual and mesiodistal forces, respectively. Likewise, the stresses in the CMP restored root were 2.777 × 10-1MPa and 3.826 × 10-1MPa. The radicular area with higher stress on both models was located in the cervical third: on the buccal surface when the buccolingual force was applied and on the mesial surface when the mesiodistal force was applied. The highest stress levels were found on the CMP structure. The incisor restored with cast metal post revealed lower stress values transferred to the root than the one restored with GFP. The stresses on the structure of the GFP were lower and more homogeneous than the ones found on the cast metal post. The difference among the stress values in the materials is within a safe margin for using both materials in relation to orthodontic forces.

A study of the residual stress behavior of rigid and flexible epoxy adhesives during thermal cycle aging for electronics packaging

In the rapidly developing microelectronics industry and technology, epoxy resin based electrically conductive adhesives must be urgently improved in terms of aging resistance, especially residual stress caused by thermal cycle aging. In this study, we investigated the stress behavior of rigid and flexible epoxy systems blended with bisphenol F epoxy (BPF) and fatty acid epoxy. The curing processes, thermal, and thermomechanical properties of the modified epoxy systems were assessed comprehensively. Moreover, the residual stress during the thermal cycle was monitored, and the bond strength was characterized. The results pointed out that by introducing soft molecular segments into a rigid system, the modified epoxy resin system had significantly lower residual stress values and exhibited a higher bond strength over a wider temperature range. Finally, we envision the systematic integration of residual stress testing with material strength testing for quantifying the bond failure of adhesive layers in the near future.