Lower Stress Values Research Articles

Stress analysis and factor of safety in three dental implant systems by finite element analysis

ObjectiveThe purpose of this study was to compare the stress distribution and the factor of safety of three dental implant systems using the finite element method. Materials and methodsThree commercial dental implant systems were designed using Solid Works 2020 software: Model A with an internal octagonal connection and matching platform, Model B with an internal hexagon connection and switching platform, and Model C with an internal 15° conical-cylindrical connection and switching platform. A 200 N load was applied to each design in both axial and 30° oblique directions using the finite element method. ResultsIn the three dental implant systems, the maximum von Mises stress was concentrated at the cervical level of the bone-implant interface in all models. Model C showed lower maximum stress values in both axial and 30° oblique loads. The highest maximum stress value was observed with the application of the oblique load in all the study models, and the factor of safety was less than one in Model A when subjected to a 200 N oblique load. ConclusionThe switching platform models generated lower maximum stress values and a factor of safety higher than one which is considered an acceptable value.Clinical relevance: A dental implant system with an internal hexagon or conical connection and a switching platform generates lower maximum von Mises stress values both on the implant components and on the peri-implant tissues.

The undrained behaviour of over-consolidated clay subjected to pure rotation of principal stress directions

Foundation soil of offshore structures may be subjected to various non-proportional cyclic loadings, such as wave loading, tide loading and earthquake loading. The consolidation state may affect the undrained behaviour of clay under pure rotation of principal stress directions. A series of cyclic undrained torsional tests were performed on normally and over consolidated clay subjected to pure rotation of principal stress directions at constant deviatoric stress conditions. The effects of over consolidation ratio (OCR) on the excess pore water pressure, stress-strain loop, stiffness and non-coaxial behaviour of the clay were analyzed under different deviatoric stresses and intermediate principal stress coefficients (b values). The results indicate that owing to the pure principal stress rotation alone, strain and excess pore water pressure accumulated in samples and the accumulation is affected by OCRs, deviatoric stress amplitudes and b values. Negative excess pore water pressure and stress dilatancy can be observed in over consolidated clay. Compared with shear stiffness, the normal differential stiffness experiences greater degradation under the pure rotation of principal stress. The shear stiffness of over consolidated clay may show an increase with loading cycles, while the normal differential stiffness degrades at low deviatoric stress value. Over consolidated clay shows non-coaxial behaviour and the greater the OCR values or the smaller the deviatoric stress, the larger the non-coaxial angle. The effects of b values on the non-coaxial behaviour of over consolidated clay are also observed. HIGHLIGHTS Over-consolidated clay subjected to pure rotation of principal stress. The effects of OCR, deviatoric stress and b value were analyzed. Negative EPWP and stress dilatancy were observed in over consolidated clay. The greater the OCR, the larger the non-coaxial angle.

MOOD STATES AND QUALITY OF LIFE IN PARALYMPIC BOCCIA ATHLETES IN THE COVID-19 PANDEMIC

ABSTRACT Introduction: Although studies have been conducted in the athlete population during the pandemic, its impacts on Paralympic athletes are still unknown. Objective: To evaluate the mood and quality of life of Paralympic boccia players during the COVID-19 pandemic period. Method: Questionnaires assessing mood, quality of life, and demographic data were sent electronically via social media. The study included 43 athletes from all functional classes (BC1 = 8, BC2 = 12, BC3 = 11, and BC4 = 11) and four regions of Brazil (Northeast = 12, Southeast = 12, Central-West = 3, and South = 17). ANOVA, t test, and similar non-parametric tests were used, with the respective effect sizes (ES). Results: Regarding mood states, BC4 athletes differed from BC1 athletes in the depression subscale score (25.5 vs. 14.5, p = 0.026, ES=1.47). The fatigue subscale score differed between BC4 and BC1 athletes (17.8 vs. 10.4, p = 0.023, ES=1.38) and between BC4 and BC2 athletes (17.8 vs 10.3, p = 0.008, ES=1.32). BC4 athletes had higher total mood disturbance (TMD) values than BC1 (175 vs. 141, p = 0.025, ES=1.35) and BC2 (175 vs.141, p = 0.025, ES=0.97) athletes. Lower stress (18.5 vs.21.8, p = 0.027, ES=0.64) and TMD (148.0 vs 162.0; p = 0.044; ES= 0.53) values were observed among the national level athletes. In terms of quality of life, differences were found between BC4 and BC2 athletes in the psychological health domain (3.73 vs. 4.49, p = 0.024, ES=0.89) and between athletes from the Northeast and South in the environment domain (3.39 vs. 4.18, p=0.030, ES=0.44). Conclusion: BC4 athletes are more susceptible to negative mood and quality-of-life perceptions. Additionally, athletes from the Northeast region may have poorer perceptions of quality of life related to the environment in which they live. Level of evidence III; Retrospective study.

Possibility of estimation of mechanical stresses in nickel by the magnetic ponderomotive method

The paper considers a technique for assessing mechanical stresses in coatings by the magnetic ponderomotive method, based on the use of the magnitude of the magnet breakaway force and its relation to the magnetic characteristics of nickel (magnetic susceptibility), which change under the action of internal stresses. It is shown that the existing mechanical stress measuring equipment using X-ray, magnetic or ultrasonic methods have specimen size limitations or have low measurement locality. At the same time, a magnetic ponderomotive method for controlling mechanical stresses is presented, which does not have the indicated disadvantages. The change in the magnetic breakaway force on the thickness, applied and residual stresses caused by elastic and plastic deformations in the sample is theoretically substantiated. It is shown that the presence of residual stresses in the sample changes the nature of the dependence of the magnet breakaway force on the applied stresses. A calculation algorithm has been developed that allows measuring the magnet breakaway force to obtain the ratio between the applied and residual stresses. It is shown that the ratio between residual and applied stresses can be used to assess the degree of proximity to the critical stresses levels that lead to failure. Calibration surfaces are constructed for the dependence of applied stresses on magnetic separation force and thickness, corresponding to elastic-plastic deformation, as well as leveled calibration surfaces, corresponding to elastic deformation in the presence of residual stresses in the material. Experiments have been carried out on real samples and coatings, that determine the degree of approximation of internal stresses in the material to critical levels that may lead to destruction. It is shown that when comparing the readings of calibrated gauges with a certified tool, the largest deviation occurs at low stress values due to the inverse dependence of the breakaway force on the stress level.

Power Module Using Ceramic Heat Sink and Multilayers Silver Sintering

A new packaging technology allowing the development of high-performance power modules for harsh environments and the optimization of the manufacturing process is presented. The assembly is achieved using an aluminum nitride ceramic heat sink and multilayer silver sintering to make both current track and die attach layers. In order to control the properties of silver sintered layers, a focus on the pressureless sintering process parameters at conventional and unusually high temperatures was performed. Depending on the sintering temperature and the dwell time, the relative density of the sintered layers was evaluated in the range of 56%–88%. The electrical resistivity was measured in a large temperature range for various densities, and the latter can only be 30% higher than the one of bulk silver once the paste is sintered at 500 °C for 1 h. Finally, the mechanical and microstructure properties of assemblies using several metal adhesion layers on the ceramic heat sink and silver sintered multilayers were investigated. Assemblies using Ti/Ni/Ag sputtered layers and silver ink sintered layer as adhesion layers on the AlN ceramic show acceptable shear stress values of about 20 MPa, while the values less than 10 MPa are obtained for W/Ni/Au and W/Ni/Ag adhesion layers. For W/Ni/Au adhesion layers, Ag–Au solid solution was formed at the interface between the sintered silver and the Au finish, leading to a depletion zone at the sintered silver interface and, hence, low shear stress. For W/Ni/Ag adhesion layers, the low shear stress value is mainly due to the oxidation of the Ni layer.

Finite Element Analysis of the Stresses Induced by One-Piece and Two-Piece Dental Implants Supporting All-on-4 Implant-Supported Prostheses.

To find out the difference in the stresses induced by one-piece monophasic and two-piece dental implants supporting All-on-4 implant-supported prostheses using finite element analysis. Two finite element maxillary models were designed: In the two-piece model, two-piece dental implants were used, and in the one-piece model, one-piece dental implants were used. The dental implants were placed according to the All-on-4 treatment concept. The anterior implants were axially placed; however, the posterior implants were placed with a distal inclination of 15 degrees. In each model, the prosthetic superstructure was designed to be a titanium implant prosthesis with zirconia crowns. Three loading scenarios were applied in this study. The first scenario simulated biting function with a total load of 250 N. The second scenario simulated incision function in which 90-N horizontal static load was applied to the palatal surface of central incisors. The third scenario simulated biting in the presence of a cantilever. In the three loading scenarios, the stresses were higher in the two-piece model. Higher stress values were recorded posteriorly rather than anteriorly in both models. One-piece dental implants induce lower stress values compared with two-piece dental implants when used in All-on-4 implant-supported prostheses.

Stresses induced by one piece and two piece dental implants in All-on-4® implant supported prosthesis under simulated lateral occlusal loading: non linear finite element analysis study

BackgroundCorrect choice of the implant design and the occlusal scheme is important for the success of implant supported restorations. So, the aim of the current study was to find out the difference in the stresses induced by the one piece dental implants designed to be used in the All-on-4® concept and the conventional two piece ones under simulated lateral occlusal schemes using nonlinear finite element analysis.MethodsTwo finite element models of the maxilla, implants, and prostheses were designed according to the All-on-4® concept. In the model TP, two piece dental implants were placed while in the model OP one piece dental implants were used. Two loading scenarios were applied to each model; the first one simulated a group function occlusal scheme while the second scenario simulated a canine guided one.ResultsThe highest stress value was recorded in the model TP with the group function occlusion and the lowest stress value was in the model OP with the canine guidance occlusion.ConclusionThe one-piece dental implants can be concluded to induce less stress compared to the two piece dental implants when used in the All-on-4® implant supported prosthesis in the different lateral occlusal schemes. Canine guided occlusion can be concluded to cause lower stress values in comparison to the group function occlusal scheme.

Comprehensive Evaluation of Rock Mechanical Properties and in-situ Stress in Tight Sandstone Oil Reservoirs

Comprehensive research on reservoir rock mechanics and in-situ stress properties combined with petrophysical experiments, logging models and numerical simulation is an important means to achieve efficient development of tight sandstone oil reservoirs. In this study, a large number of rock mechanics and acoustic experiments, full-wave train array acoustic wave tests, hydraulic fracturing data and three-dimensional finite element simulations were used to study the rock mechanical properties and in-situ stress characteristics of continental tight oil reservoirs in the Yanchang Formation. The results show that under uniaxial conditions, the tight sandstone samples mainly suffer from tensional ruptures. With the increase of confining pressure, the tight sandstone samples undergo obvious shear ruptures. When the confining pressure is loaded to 35 MPa, a typical vertical shear fracture will be formed. The hydraulic fracturing calculation results show that the in-situ stress state of the target layer satisfies σv (vertical principal stress)>σH (maximum horizontal principal stress)>σh (minimum horizontal principal stress). Based on the results of rock mechanics and acoustic tests, we have constructed the dynamic and static mechanical parameter conversion models of tight oil reservoirs and the logging interpretation model of current in-situ stress. Furthermore, the finite element method is used to simulate the three-dimensional structural stress field of the target layer. The simulations show that the horizontal principal stress distribution in the work area is consistent with the applied environmental stress. The σH of the target layer is mainly distributed in 32–50 MPa, and the σh is mainly distributed in 20–34 MPa. Both σH and σh are relatively high in the southern uplift of the work area; among them, σH is usually greater than 44 MPa, and σh is usually greater than 24 MPa. The northern part of the study area developed several grooved areas with relatively low stress values. The regions with high stress values are often distributed in bands, which may be related to the compression caused by the deformation of the strata. For shear stress, left-handed and right-handed regions usually alternate with each other. However, the extent of the left-handed area in the southern uplift area is larger than that of the right-handed area, indicating that the tight oil reservoirs in the study area are mainly affected by left-handed activities.

On the effect of irregular uterine activity during a vaginal delivery using an electro-chemo-mechanical constitutive model

During a normal vaginal delivery, the muscle cells propagate electrical signals throughout the uterine wall, resulting in uterine contractions. However, uncoordinated uterine activity may disturb the uterine contractions pattern and negatively impact fetal and maternal health. Some of the abnormalities identified by the specialists are excessively short resting intervals and tachysystole. This work aims to investigate the influence of abnormal uterine activity in terms of maximum principal stress distribution and collagen fibers stretch in the uterine tissue during vaginal delivery with (i) excessively short resting intervals without changing the contraction time, and (ii) tachysystole (contraction and reduced resting times). These patterns are compared with a normal uterine contraction pattern. To achieve our aims, a biomechanical model was developed, including finite element models of the uterus and the fetus, and an electro-chemo-mechanical constitutive model. Generally, the excessively short resting intervals exhibit higher average maximum principal stresses during the contraction and resting stages, lower average fibers stretch values in the longitudinal direction and higher stretch in the circumferential direction. On the other hand, the tachysystole exhibit generally lower stress values during the uterine contraction and higher stress values during the resting stages, higher stretch in the longitudinal direction, and lower stretch in the circumferential direction.

Evaluation of a Uniaxial Powder Tester and Comparison with an Annular Shear Tester

Bulk flowability measurement of particulate systems for quality control and product development purposes requires a fast, repeatable, accurate and affordable characterization approach. In the present study, two versions of the recently developed Freeman Technology Uniaxial Powder Tester (UPT) are compared to the Schulze Ring Shear Tester and the Johanson Hang-Up Indicizer. The UPT instruments were found to have excellent repeatability in measurements of uniaxial unconfined yield stress and compressed bulk density across a broad range of materials. Amongst the testing devices investigated in this study, the computer-controlled Advanced UPT (AUPT) instrument showed higher repeatability than the Manual UPT (MUPT) and the Johanson Indicizer. The Schulze Ring Shear Tester (RST) had slightly better repeatability than the AUPT, but there were a few situations in which its automated software did not produce a value of unconfined yield stress, resulting in a need to manually process the data. For most of the test cases, the AUPT measured a higher value of uniaxial unconfined yield stress than the MUPT. This was attributed to the stress relaxation that the powder bed experiences in the MUPT, where the consolidation stress is not automatically maintained on the sample. The AUPT measured lower values of unconfined yield stress compared to the Schulze RST for all the cases in this study. This is a well-recognized occurrence as the Schulze RST and other biaxial testers, in contrast to the AUPT, brings the sample to the critical consolidation state before measuring the shear strength. The AUPT produced its flow function data in about half the time as the Schulze RST.

Hot Deformation Behavior of an As-Extruded Mg-2.5Zn-4Y Alloy Containing LPSO Phases

The hot deformation and dynamic recrystallization (DRX) characteristics of an as-extruded Mg-2.5Zn-4Y alloy containing long-period stacking ordered (LPSO) phases were investigated using a Gleeble 3500 thermal simulator at temperatures (300–400 °C) and strain rates (0.001–1 s−1). The results revealed that low flow stress corresponded to a high temperature and a low strain rate. An increase in the temperature of deformation caused an increase in the amount of dynamic recrystallization. Additionally, as the strain rate decreased at a given deformation temperature, dislocations were less likely to cause pile-up and dynamic recrystallization was more appropriate, resulting in a lower stress value. Kink deformation was clearly minimized as the number of dynamic recrystallizations increased. The test alloy’s activation energy value was determined as 212.144 kJ/mol.

Effect of Temperature and Strain Rate Variation on Tensile Properties of a Defective Nanocrystalline Copper-Tantalum Alloy

Nanocrystalline alloys of immiscible in nature are emerging topics of interest for researchers due to better mechanical stability at high temperatures. Nanocrystalline Copper-Tantalum alloy is of particular interest for research exploration due to its high strength, limited solubility and high-temperature stability. In the present work, the mechanical properties of nanocrystalline 90/10 copper-tantalum (9Cu-Ta) alloy have been investigated using the molecular dynamics approach. Embedded atom method (EAM) of potential has been used to analyze the mechanical properties at high temperatures due to the high stability of EAM in molecular dynamic simulation. At high-temperature defects plays a very important role therefore a specific 9Cu-Ta nanostructure having 3% vacancies has been selected to explore its performance under a particular type of point defect. This study has been conducted under uniaxial tensile loading. The tensile properties of this defective nanocrystalline alloy have been compared at specific temperatures i.e. 300 K, 600 K, 800 K, 1000 K and 1200 K. The study revealed that the variation in temperature from 300 K to 1200 K results in the shifting of the stress-strain graph to lower stress values. It has also been noticed that the variation in ultimate tensile strength is the least in comparison to yield strength and elastic constant for the same variation in temperature. These results indicate the importance of avoiding thermal agitations during the synthesis and surface modification of nanocrystalline copper-tantalum alloy.

Investigation of postero-anterior mobilization in the lumbar spine: A finite element analysis study

Background/Aim: Postero-anterior (PA) mobilization is a non-invasive treatment method traditionally used to treat low back pain (LBP) in many countries. However, the effects of PA mobilization on lumbar spine biomechanics are still unknown. The aim of this study is to determine the maximum von Mises stresses on the lumbar vertebra (L5), with force applied at different angles during PA mobilization therapy using finite element analysis (FEA). Methods: L5 vertebra CT images of a 30-year-old male patient were modeled in three dimensions (3D) with MIMICS software to examine the PA mobilization biomechanics. The resulting L5 spine model was submitted to the finite element software ANSYS (version 19) to evaluate the effects of PA mobilization. To simulate PA mobilization on the L5 vertebra, a static force of 100 N was applied over the spinal process in three different directions. The distribution of von Mises stresses occurring in the L5 spine was determined in the analyses. Results: During PA mobilization, the stress distributions on the vertebrae caused by the static force applied in three different directions in the L5 vertebra spinal process was determined. As a result of the analysis, higher stress values were found in the posterior elements of the vertebrae in all directions compared to the vertebral corpus. However, when compared according to the direction of application, the lowest stress values were detected in the pedicles and laminas in PA mobilization applied toward the spine center. Conclusion: Vertebral pedicles, laminae, and spinous process are critical areas prone to fracture. It was argued that the change in the direction of PA mobilization applied in the L5 vertebral spinal process affects the von Mises stress distributions occurring in the pedicles and laminae.

Comparison of zygoma plates and infrazygomatic crest miniscrews used open bite treatment: A 3-dimensional finite element study

This study aimed to evaluate infrazygomatic crest (IZC) miniscrews, which represent a new approach to maxillary posterior tooth intrusion and extra-alveolar skeletal anchorage, using 3-dimensional finite element stress analysis to predict the clinical usability instead of zygoma plates. Six different models were developed. The direction of the intrusion force was generated parallel to the maxillary first molar, and the posterior bite-block intrusion appliance was connected with 2 steel arches. A zygoma plate, stainless steel (SS)-IZC miniscrew, and a titanium alloy (TiA)-IZC miniscrew were used as anchorage units, and 200 g and 400 g of intrusion forces were applied. The cortical bone, spongious bone, stress values, and displacements in the anchorage unit were examined. The anchored materials were considered nonosseointegrated. Zygoma plates formed low-stress values under 200 g and 400 g of force. The greatest stress and displacement occurred in the first miniscrew that fixed the plate. SS-IZC miniscrews gave lower stress and displacement values than TiA-IZC miniscrews. The most stress was detected inferior to the screw-to-bone contact in IZC miniscrews. Considering the initial value of resorption in cortical bone, it is predicted that SS-IZC and TiA-IZC miniscrews can be used in the clinic under 200 g of intrusion force, although there is not as little stress and displacement as for zygoma plates. Under 400 g of intrusion force, clinical use cannot be recommended because of the critical stress value they generate in the cortical bone.

Slip activity during low-stress cold creep deformation in a near-α titanium alloy

Near-α titanium alloys are known to be susceptible to cold dwell fatigue (CDF) debit, which has been linked to the occurrence of cold creep during high-load dwell times superimposed onto low cycle fatigue loading. In order to shed new light on the deformation mechanisms during cold dwell and to understand better the role of the microstructure, two different bimodal microstructures (fine and coarse transformation product) of TIMETAL®834 were investigated at stress levels below the 0.2% proof stress using a combination of grain orientation mapping and in-situ electron microscopy imaging. This enabled in-depth analysis of 2D slip patterns and slip system activity using High-Resolution Digital Image Correlation (HRDIC), showing that in both microstructures basal slip is initially the dominant slip mode before prismatic slip activity increases approaching the 0.2% proof stress. Comparing the two constituents in the bimodal microstructure, first slip bands are localised predominantly in primary α grains, indicating higher strength of secondary α colonies, particularly for finer transformation products. During 10 min load holds at stresses below 0.2% proof stress, more plastic strain and longer connected slip traces across several grains were observed in the sample with coarse transformation product, indicating higher susceptibility to cold creep deformation.Full-field crystal deformation modelling was used to determine local stresses in individual grains at the onset of plasticity and test the hypothesis that the dominance of basal slip at low-stress levels can be explained by the elastic anisotropy in Ti alloys. While consideration of elastic anisotropy increased resolved shear stress (RSS) values for basal slip relative to prismatic slip, it did not unambiguously explain the early activation of basal slip. Furthermore, thermal residual stresses at the crystal level, due to the anisotropy of coefficients of thermal expansion (CTE), were included in the simulation, which created a wider spread of the RSS data but did not preferentially promote high RSS values for grains well aligned for basal slip. In the absence of an unambiguous conclusion, it is hypothesised that basal slip might display lower critical resolved shear stress values than typically reported but high work hardening rates compared to prismatic slip.

Relationship Among Blastocystis, the Firmicutes/Bacteroidetes Ratio and Chronic Stress in Mexican University Students

The role played by Blastocystis in humans has been a subject of discussion due to its intestinal effects and modifications in the intestinal microbiota. We aimed to analyze the relationship between Blastocystis subtypes ST1-4 and 7, the Firmicutes to Bacteroidetes ratio (F/B ratio) of fecal microbiota, and chronic stress in university students. This study had a cross-sectional design with a sample of 202 students. We analyzed fecal and hair samples, and stress inventories were applied to the students. The results showed a frequency of Blastocystis-colonized students of 52.97%. Regarding fecal microbiota, a median RAU of 0.801 for Firmicutes and 0.82 of Bacteroidetes were obtained, with an F/B ratio of 0.83. A low F/B ratio (66.04%) was more frequent in Blastocystis-colonized students, whereas a high F/B ratio (68.09%) (p = < 0.0001) was found in the Blastocystis-non-colonized. Only Blastocystis ST3 did not significantly correlate with a low F/B ratio (p = 0.290). The ST4 was associated with lower values of cortisol (p = 0.030), psychological stress (p = 0.040), and lower frequency of constipation (p = 0.010). Only two students with the ST1 had abdominal pain (p = 0.007). Our results suggest that colonization by Blastocystis subtypes can modify the intestinal microbiota due to a decreased ratio between the two most representative phyla (F/B). Also, the results of this study show that ST4 colonization is related to a lower level of chronic stress.Graphical abstract

Geosynthetic Interface Friction at Low Normal Stress: Two Approaches with Increasing Shear Loading

The evaluation of geosynthetic interface friction is a key parameter for the stability of coupled geosynthetics, as in landfill capping liner. At the present time, few types of tests are suitable for measuring the interface friction at low normal stress: one of these is the inclined plane, usually carried out under a vertical stress of 5 kPa. This type of test is not without critical aspects, mainly due to the nonuniform normal stress state induced by the inclination of the plane, but, on the other hand, the most widespread direct shear test generally cannot be performed at such low values of normal stress. After a short discussion on the pros and cons of these two types of test, the paper presents a comparison of the interface friction angles obtained, for three interfaces, by means of an inclined plane and an unconventional direct shear apparatus, under the same low normal stress. The peculiarity of this latter device is of ensuring a gradual increase of the mobilized strength, in a way similar to what occurs during the inclined plane test. The good correspondence of the results of the two types of tests confirmed the validity of both the test approaches.

EVALUATION OF BIOMECHANICAL EFFECTS OF PROSTHETIC COMPONENTS WITH DIFFERENT MATERIALS ON THE ABUTMENT SCREW

Objectives: The purpose of this study was to evaluate the effects of different resin-based and ceramic superstructure materials and two different abutment types on the stress distribution of the abutment screw using the three-dimensional finite element stress analysis method. Materials and Methods: A three dimensional implant, abutment (zirconia and titanium), abutment screw, crown (zirconia reinforced lithium silicate, lithium disilicate, polymer-infiltrated resin ceramic, and PEEK), and alveolar bone were designed using Rhinoceros 3D modeling software and VRMesh Studio software and combined to form 8 simulations. On the models prepared, loading was made on the lingual tubercule of the maxillary right first premolar crown at an angle of 30° with 150 N force obliquely in the buccolingual direction. The von Mises values obtained from the abutment screw were compared according to the types of abutment and crown materials. Results: The von Mises stress values in the abutment screw were higher in the models using a titanium abutment abutment (on average 1336.24 MPa), and the lower stress values were obtained in the models using a zirconia abutment (on average 964.26 MPa). When the prosthetic material used was changed, no apparent difference was observed in the stress values on the abutment screw. Conclusions: Considering that the abutment screw is the weakest link of the implant system, zirconia abutments can be used reliably in the maxillary first premolar region where aesthetic expectations are high.

Predicting peak stresses in microstructured materials using convolutional encoder–decoder learning

This work presents a machine-learning approach to predict peak-stress clusters in heterogeneous polycrystalline materials. Prior work on using machine learning in the context of mechanics has largely focused on predicting the effective response and overall structure of stress fields. However, their ability to predict peak – which are of critical importance to failure – is unexplored, because the peak-stress clusters occupy a small spatial volume relative to the entire domain, and hence require computationally expensive training. This work develops a deep-learning-based convolutional encoder–decoder method that focuses on predicting peak-stress clusters, specifically on the size and other characteristics of the clusters in the framework of heterogeneous linear elasticity. This method is based on convolutional filters that model local spatial relations between microstructures and stress fields using spatially weighted averaging operations. The model is first trained against linear elastic calculations of stress under applied macroscopic strain in synthetically generated microstructures, which serves as the ground truth. The trained model is then applied to predict the stress field given a (synthetically generated) microstructure and then to detect peak-stress clusters within the predicted stress field. The accuracy of the peak-stress predictions is analyzed using the cosine similarity metric and by comparing the geometric characteristics of the peak-stress clusters against the ground-truth calculations. It is observed that the model is able to learn and predict the geometric details of the peak-stress clusters and, in particular, performed better for higher (normalized) values of the peak stress as compared to lower values of the peak stress. These comparisons showed that the proposed method is well-suited to predict the characteristics of peak-stress clusters.

Macroeconomic Stress Test on the Probability of Default Banking in Indonesia (Study on Conventional Banks 2007-2021)

The role of the Bank in mobilizing is a necessity, especially related to the provision of financing facilities to economic actors in the form of loans or credit. Usually, when an economy expands, it will be followed by a procyclical trend of credit growth, which will cause banking vigilance. And cause banks to have more expectations and are too optimistic about the ability to pay customers, thus making banks less careful. Furthermore, this condition will result in excessive delays which will eventually become a nightmare during the boom or expansion of the economy. This situation will lead to the failure of the debtor in dealing with his credit, causing a nonperforming ratio, and eventually becoming a probability of default. Meanwhile, to measure the risk of a bank failure, it can use the macroeconomic stress testing method and sensitivity analysis. This study aims to measure how big the impact of macroeconomic shocks on the probability of default that will be borne by banks, as well as to see the sensitivity of the probability of default of banking to macroeconomic variable shocks. To measure the impact of macroeconomic shocks on the probability of default, the study uses regression analysis. And to determine the sensitivity of macroeconomic variables to the probability of default using the stress test method by calculating macroeconomic variable shocks. The results showed that there was a significant effect of macroeconomic variables (Real GDP, exchange rates, inflation, interest rates, and world oil prices) on the probability of bank failure. Furthermore, after calculating the stress test, the result is that of the three bank samples, only BCA Bank has the lowest stress value. Meanwhile, to see how big the Probability of Default is, when there is a shock or session on macroeconomic variables, it shows that Mandiri Bank is very sensitive to macroeconomic variable shocks compared to others.