Principal Stress Values Research Articles

Reliability evaluation of secondary support structure in hypothetical drop of reactor core barrel assembly

Dynamic responses of the secondary support structure are investigated to evaluate its structural reliability in a hypothetical drop impact accident of the reactor core barrel assembly in this work. Impact analyses both in still water situation (20 °C) and dynamic water situation (289 °C) are carried out by LS-DYNA. Tensile tests in both temperature cases are conducted for the secondary support structure material (Inconel 690) in order to make the simulation results more accurate with real material properties. Various aspects of structural dynamic responses during impact are analyzed, including distributions of equivalent stress, equivalent plastic strain, and maximum principal stress as well as time histories of impact force, vertical displacement, vertical velocity, and energy. In still water situation, equivalent stress of the secondary support structure exceeds the yield strength due to the higher initial impact velocity and downward base acceleration. But in dynamic water situation, there is no plastic deformation due to the lower initial impact velocity and upward base acceleration. Peak values of the maximum principal stress distributed in the secondary support structure are less than the corresponding ultimate tensile strengths respectively in both analysis cases. Results reveal that both of the secondary support structure and the reactor pressure vessel meet the design criteria of RCC-M Code with respect to stress limits, thus the structural reliability can be ensured in this drop accident.

Comparative Assessment of Three Microimplant Assisted Biomechanical Strategies for the Simultaneous Intrusion and Retraction of Anterior Teeth in Relation to Alveolar Bone Stress and Change in Incisor Inclinations – A 3D Finite Element Analysis Study

Microimplants are widely used to provide absolute anchorage in cases with bimaxillary dentoalveolar protrusion especially in those that require simultaneous retraction and intrusion of anterior teeth. The position of the microimplant significantly affects the build up of stress in the alveolar bone as well as the incisor inclinations, and is therefore a critical factor in treatment plannning. Keeping this in mind, this finite element method(FEM) study was taken up to identify the most suitable combination of implant placement sites for cases in which en-masse anterior retraction is done along with intrusion. The geometric model was constructed from a CBCT scan of the maxilla of an adult patient with full permanent dentition.The images were saved as DICOM files and were later exported to the 3D image processing software (Mimics,version 17). The center of resistance for the 6 anterior teeth was 9 mm superiorly and 13.5 mm posteriorly from the midpoint of crown tip of central incisors. The working archwires were assumed to be 0.019 / 0.025-in stainless steel. The three mini-implant placement sites compared were – S1- Midline micro implant between the maxillary central incisors with two placed posteriorly between maxillary 2nd premolar 1st molar roots. S2 – Micro implant placed between the lateral incisor and canine along with posterior mini implants as above. S3- Micro implant placed high up between the maxillary second premolar and first molar roots. The amount of tooth displacement after finite element analysis was compared with central and lateral incisor and canine axis graphs. For the system S1, intrusive components were seen on the archwire mainly in the anterior region with maximum displacement between central incisors and gradually decreasing away from point of force application. In S2, the intrusive component of force was more evenly distributed. In S3, pattern of intrusive component was similar to S2 but the maximum displacement was slightly lower. Greatest value of minimal principal stress was seen on cervical and apical third of central incisors as well as apical third of lateral incisors in S1; and cervical third of lateral incisors and apical and cervical third of canines in S2. Maximum retraction of anterior teeth was seen in S3. In all of the three systems of force application, tooth inclinations were maintained. Maxillary anterior teeth showed more tendency towards retraction in the case where two micro implants were placed posteriorly high up above the roots of maxillary premolars and molars such that the force is directed diagonally having both horizontal and vertical components, and hence eliminating the need for anterior implants. Greater intrusion tendency was seen when implants were placed between the roots of maxillary central incisors.

The Effect Of Tapered And Cylindrical Implants On Stress Distribution In Different Bone Qualities: A Finite Element Analysis.

To examine the stress values of different bone densities and to compare the tapered and the cylindrical implant designs. Finite element analysis was used to apply a force of 100 N vertically and at an angle of 30 degrees to implants with a cylindrical or tapered design in D1and D4 bones in eight separate models. The von Mises and principal stress values obtained from the models were compared, and the optimal stress values were determined and compared with the physiologic stress limit of the bone. Von Mises stress was found to be lower in D1 bone densities, in vertical loading, and in implants with a tapered design. In the case of both implant designs, the von Mises and principal stress values were lower for D1 bone densities. The tapered implant was found to have higher principal stress than the cylindrical implant in both bone densities, while von Mises stress was higher in the cylindrical implant than in the tapered implant. Vertical loading was found to induce less stress than loading at a 30-degree angle. D4 bone density and loading at a 30-degree angle increases von Mises and principal stress more than selection of different implant designs.

Experimental and numerical evaluation of mortar specimens shape and size influence on compression tests

Abstract The axial compressive strength of cementitious compounds is an important parameter for classification, quality assessment and material design. The values obtained in tests are influenced due intrinsic properties of the compounds and external factors such specimen size and shape. The present work aims to evaluate experimentally and numerically using finite element method, the specimen shape and dimension influence over results of the mortar axial compressive strength test. The specimen geometry aspects are cubic, (4x4x4) cm, column with height/thickness ratio equals two prismatic, (4x4x8) cm, beam with height/thickness ratio equals one prismatic also with dimensions (4x4x8) cm however tested with horizontal 8 cm dimension and 5 cm diameter cylindrical with 5 cm and 10 cm of height. Specimen material are strong and weak mortar. We tested five specimen of every mortar strength one for each geometry therefore ten specimen total at 28 days of age. The cylindrical specimen resulted in lower mechanical strength among all geometry. Between cylindrical ones the results exibited equivalent strength however, among prismatic and cubic ones the strength results diverged. Ones with height/thickness ratio equals one, i.e., cubic and beam, resulted in higher strength then one with height/thickness ratio equals two, named column. Numerical simulations verify these results indicating equally height/thickness ratio equals one geometry with higher strength. This could be happening because in height/thickness ratio equals one geometry the maximum principal stress values (tractions) are lower.

Fully-coupled simulations of thermally-induced cracking in pegmatite due to microwave irradiation

Fully-coupled thermo-mechanical simulations are implemented in COMSOL Multiphysics to investigate micro-scale stress-strain variability in pegmatite specimens subjected to thermal loading using microwaves. Thermally-induced compressive and tensile stresses increase as the microwave irradiation duration increases. The dielectric constant, coefficient of expansion, and type and size of mineralogical boundary have significant impacts on the responses of the rock to microwave irradiation. The maximum principal stress of the chlorite is the smallest, indicating that the chlorite experiences the most damage under microwave irradiation, followed by the quartz. The maximum principal stress values of plagioclase and orthoclase are larger, indicating that they are likely to incur the least damage. Where quartz or chlorite is dominant, the resulting von Mises stresses are consistently higher after 120 s of microwave irradiation. The rate of generation of von Mises stresses increases most rapidly along the interface between quartz and plagioclase, and the interface between quartz and orthoclase, followed by the interface between quartz and chlorite, and finally the interface between plagioclase and orthoclase. The presented modeling approach provides a practical method to investigate stress-strain relationships within mineralogical boundaries inside a rock thin section.

Simulation-based Prediction of Structural Design Failure in Fishing Deck Machinery a Hydraulic Type with Finite Element Method

The fishing deck machinery is the tools used to collect fish in fishing activities. Fishing deck machinery is intended to improve the effectiveness of fishing operations. The mission of the Ministry of Marine Affairs and Fishery Year 2015-2019 in the Regulation of the Minister of Marine and Fisheries No. 45/PERMEN-KP/2015 which is a priority is to provide assistance for fishing facilities for fishermen; it is necessary to develop and optimize fishing deck machinery. To assure the safety and dependability of these fishing deck machinery, calculations, simulation and functional tests are needed. This paper discusses the prediction of structural failure in the design of fishing deck machinery a hydraulic type with finite element method simulation approach. The results of the FEM simulation analysis are (i) the maximum value of von-Mises stress is greater than the ultimate tensile strength of the material; (ii) 1st principal stress value minimum is smaller than the ultimate tensile strength of material; (iii). the Poisson ratio value higher than the Poisson ratio value of the material. Base on the simulation result, the structural design of fishing deck machinery is safety.

Stress analysis of the TMSR graphite component under irradiation conditions

TMSR uses nuclear graphite as a neutron moderator, a reflector, and the structural material, and utilizes molten salt as a coolant. When running normally, the graphite components are immersed in the molten salt. Thus, the nuclear graphite comes into direct contact with the molten salt, which infiltrates the open pores of the nuclear graphite. This infiltration may influence the stress analysis of the graphite component. In this study, a User Material subroutine was used to analyze the stress distribution of the graphite component, both with and without molten salt infiltration. Many influence factors were taken into consideration, such as the dose gradient, the shape of the permeation zone, and the permeation area. The results show that the dose gradient, shape, and area of the permeation zone all significantly influence the stress distribution. Furthermore, the results of the stress analysis indicate that for a regular graphite component with a square cross section, the peak maximum principal stress value occurs at the center of the cross section, and the symmetry of the maximum principal stress distributions was modified by quarter circle and half ellipse permeation zones.

Estimation of the CTOD-crack growth curves in SENT specimens using the eXtended finite element method

The single edge notched tension (SENT) test is commonly used to evaluate the less-conservative fracture toughness of pipeline steels. The R-curve (crack tip opening displacement (CTOD)-crack growth) behavior measured by SENT tests is similar to that measured during full-scale tests. This paper compares the ductile fracture mechanism of X42 grade steel, including crack initiation and propagation, using the extended finite element method (XFEM) with experimental data obtained from SENT tests. Two major parameters in XFEM (maximum principal stress and fracture energy) were calibrated in numerical models using experimental results obtained from SENT tests performed on six X42 grade steel samples to provide a CTOD-crack growth curve. With appropriate values of maximum principal stress and fracture energy, the numerical models can reasonably reproduce the experimental results. This method could be used to anticipate full-scale test behavior and simulate crack propagation in pipelines under operational loading conditions.

Simulation of stress fields and quantitative prediction of fractures distribution in upper Ordovician biological limestone formation within Hetianhe field, Tarim Basin, NW China

The carbonate is the main gas producing system in the Hetian River gas field of Tarim Basin, within which structural fractures serve as the main seepage channel and accumulation spaces. The development process of carbonate gas field in the Hetianhe area shows that the enrichment of gas is closely related to the development of fracture parameters. On the basis of core data and imaging logging data, the characteristics of tectonic fractures parameters were determined. Combining three dimensional finite element numerical simulation method, we simulated paleo tectonic stress field of two key fracture periods(late Hercynian and Himalayan period) and current stress field in Hetian river gas field. The fracture linear density and aperture formulas were established to calculate the distribution of tectonic fractures in different periods. Then the impacts of faulting and folding on the development of fractures could be analyzed. The simulation results showed that the value of maximum principal stress during the Late Hercynian period in the Hetianhe area is 300–320 MPa with a direction of NW-SE(310-130°), and the direction of maximum principal stress is NE-SW(40–220°), with a 500–520 MPa value. The folding play the primary role, and the faults paly the secondary control in the generation of fractures during the late Hercynian and Himalayan periods. The 3-D finite element geo-mechanical numerical modelling and fracture density, aperture calculation methods are not only for carbonate fractures in the Hetianhe area, but also for the development of other reservoir fractures.

Real time high cycle fatigue estimation algorithm and load history monitoring for vehicles by the use of frequency domain methods

Abstract Real time high cycle fatigue estimation problem for vehicles is examined by the use of frequency domain methods. The purpose was twofold: monitoring of fatigue damage and tracking of load history in real time. Firstly, power spectral density functions (PSDs) of acceleration measurement at a selected location are calculated in a piecewise manner by dividing the acceleration-time history into pieces. Following, Frequency Response Functions (FRF’s), whose outputs are the absolute maximum principal stress values at selected components, are calculated by finite element methods to account for multi-axial stress state in fatigue life estimations. Then, fatigue damage intensity at selected output locations is estimated using the FRF results. To this end, the following frequency domain fatigue estimation methods (FDFEMs) proposed for Gaussian and stationary data sets are applied to the selected components of a heavy duty truck: narrow-band approximation, Tovo and Benasciutti, Zhao and Baker, Dirlik and Tovo’s α 0.75 methods. Gaussianity and stationarity of acceleration-time data set used to estimate fatigue life of a component is checked to ensure the validity of FDFEMs. Numerical results are compared with experimental fatigue lives and damage calculations in time domain made by the combination of rainflow counting and Miner-Palmgren rules. There are two difficulties in implementing this approach using on-board equipment in real time such as overcoming the limited memory to store data sets and completing the computations sufficiently fast. To overcome them, the proposed approach is implemented in a piecewise manner and associated normalized PSDs are updated accordingly. Then, spectral moments and damage intensities are calculated in frequency domain. Implementation of the proposed approach is described in detail and numerical results are presented. It is shown that the proposed approach is able to predict the fatigue damage accurately and can keep track of loading conditions in real time.

Development of New Three-Dimensional Rock Mass Strength Criteria

Two new three-dimensional rock mass strength criteria are developed in this paper by extending an existing rock mass strength criterion. These criteria incorporate the effects of the intermediate principal stress, minimum principal stress and the anisotropy resulting from these stresses acting on the fracture system. In addition, these criteria have the capability of capturing the anisotropic and scale dependent behavior of the jointed rock mass strength by incorporating the effect of fracture geometry through the fracture tensor components. The new criteria are proposed after analyzing 284 numerical modeling results of the polyaxial, triaxial and biaxial compression tests conducted on the jointed rock blocks having one or two joint sets by the PFC3D software. Some of these simulation results were compared with experimental results to validate the developed PFC3D model that was used for numerical modeling of jointed blocks. In this research to have several samples with the same properties a synthetic rock material that is made out of a mixture of gypsum, sand and water was used. Altogether, 12 joint systems were chosen; some of them had one joint set and the rest had two joint sets. Joint sets have different dip angles varying from 15° to 45° at an interval of 15° with dip directions of 30° and 75° for the two joint sets. Each joint set also has three persistent joints with the joint spacing of 42 mm in a cubic sample of size 160 mm. The minimum and intermediate principal stress combination values were chosen based on the uniaxial compressive strength (UCS) value of the modeled intact synthetic rock. The minimum principal stress values were chosen as 0, 0.2, 0.4 and 0.6 of the UCS. For each minimum principal stress value, the intermediate principal stress value varies starting at the minimum principal stress value and increasing at an interval of 0.2 of the UCS until it is slightly lower than the strength of the sample under the biaxial loading condition with the same minimum principal stress value. To express the new rock mass strength criteria, it was also necessary to determine the intact rock strengths under the same confining stress combinations mentioned earlier. Therefore, the intact rock was also modeled for all three compression tests and the intact rock strengths were found for 33 different minimum and intermediate principal stress combinations.

Effects of Prosthetic Material and Framework Design on Stress Distribution in Dental Implants and Peripheral Bone: A Three-Dimensional Finite Element Analysis.

BackgroundThe purpose of this study was to evaluate the effects of prosthetic material and framework design on the stress within dental implants and peripheral bone using finite element analysis (FEA).Material/MethodsA mandibular implant-supported fixed dental prosthesis with different prosthetic materials [cobalt-chromium-supported ceramic (C), zirconia-supported ceramic (Z), and zirconia-reinforced polymethyl methacrylate (ZRPMMA)-supported resin (ZP)] and different connector widths (2, 3, and 4 mm) within the framework were used to evaluate stress via FEA under oblique loading conditions. Maximum principal (σmax), minimum principal (σmin), and von Mises (σvM) stress values were obtained.ResultsMinimum stress values were observed in the model with a 2-mm connector width for C and ZP. The models with 3-mm and 4-mm connector widths showed higher stress values than the model with a 2-mm connector width for C (48–50%) and ZP (50–52%). Similar stress values were observed in the 3- and 4-mm models. There was no significant difference in the amount of stress with Z regardless of connector width. The Z and ZP models showed similar stress values in the 3- and 4-mm models and higher stress values than in the C model. Z, ZP, and C showed the highest stress values for the model with a 2-mm connector width.ConclusionsChanges in the material and width of connectors may influence stress on cortical bone, cancellous bone, and implants. C was associated with the lowest stress values. Higher maximum and minimum principal stress values were seen in cortical bone compared to cancellous bone.

Implant-Supported Fixed Partial Prostheses With Different Prosthetic Materials: A Three-Dimensional Finite Element Stress Analysis.

To evaluate the effects of prosthetic material on the degree of stress to the cortical bone, trabecular bone, framework, and implants using finite element analysis (FEA). A mandibular implant-supported fixed prosthesis was designed. Different prosthetic materials [cobalt-chromium-supported ceramic, zirconia-supported ceramic, and zirconia-reinforced polymethyl methacrylate (ZRPMMA)-supported resin] were used. FEA was used to evaluate stress under different loading conditions. Maximum principal (σmax), minimum principal (σmin), and von Mises (σvM) stress values were obtained. Similar σmax, σmin, and σvM values were observed in the cortical and trabecular bones and in implants under both loading conditions, with the exception of the ZRPMMA model, which showed the highest σmax, σmin, and σvM values in oblique loading. The ZRPMMA model had the lowest σvM value in the framework under both loading conditions. ZRPMMA had the lowest stress values in the framework, with increased stress values in the implants and bone tissue. Framework and veneering materials may influence stress values under different loading conditions.

Global shape optimization of fixtures to suppress wrinkles in large-displacement membrane structures

Membrane fixtures provide external tensile forces and boundary conditions for thin membranes; thus, they play an important role in the minor principal stress distribution and wrinkling patterns. Here, we propose a global optimization approach for designing the shape of membrane fixtures to suppress stress-related wrinkles under large membrane deformations. The objective of the optimization model is to maximize the minimal value of the in-plane minor principal stress over the entire membrane. This model incorporates the Kriging surrogate method, which is a robust optimization technique, to make the membrane in a taut state and to find out the global optimal solution. Several examples with different stretching displacements are presented to demonstrate the effectiveness of this proposed optimization method. Moreover, the method provides an efficient way to obtain wrinkle-free membrane structures without reducing the membrane area.

Biomechanical analysis of different implant-abutments interfaces in different bone types: An in silico analysis

The purpose of this study was to analyze the stress distribution of bone tissue around implants with different implant-abutment interfaces: platform switching (PSW); external hexagon (EH) and Morse taper (MT) with different diameters (regular: Ø 4 mm and wide: Ø 5 mm), bone types (I–IV) and subjected to axial and oblique load conditions using three-dimensional finite element analysis (3D-FEA). Sixteen 3D models of various configurations were simulated using InVesalius, Rhinoceros 3D 4.0, and SolidWorks 2011 software, and processed using Femap 11.2 and NeiNastran 11.0 programs. Axial and oblique forces of 200 N and 100 N, respectively, applied at the occlusal surface of prostheses. Maximum principal stress values were obtained from the peri-implant cortical bone of each model. Statistical analyses were performed using ANOVA and Tukey's test for maximum principal stress values. Oblique loading showed higher tensile stress than axial loading (P < 0.001). Wide-diameter implants showed lower stress concentration rather than regular-diameter implants, regardless of both connection and bone type (P < 0.001). Under axial loading, wide-diameter EH implants with regular platforms showed more favorable stress distribution than PSW implants for axial loading (P < 0.001); however, under oblique loading, PSW implants exhibited lower stress concentrations (P < 0.001). Regular-diameter MT implants showed lower stress than EH implants (P < 0.001). Bone type IV showed higher stress in the cortical region than bone types I and II (P < 0.001), but no significant difference when compared with bone type III (P > 0.05). The conclusion drawn from this in silico is that MT implants should be considered for use in situations that preclude the placement of wide-diameter implants, particularly where bone types III and IV are concerned.

Numerical fatigue analysis of premolars restored by CAD/CAM ceramic crowns

ObjectivesThe purpose of this study was to estimate the fatigue life of premolars restored with two dental ceramics, lithium disilicate (LD) and polymer infiltrated ceramic (PIC) using the numerical method and compare it with the published in vitro data. MethodsA premolar restored with full-coverage crown was digitized. The volumetric shape of tooth tissues and crowns were created in Mimics®. They were transferred to IA-FEMesh for mesh generation and the model was analyzed with Abaqus. By combining the stress distribution results with fatigue stress–life (S–N) approach, the lifetime of restored premolars was predicted. ResultsThe predicted lifetime was 1,231,318 cycles for LD with fatigue load of 1400N, while the one for PIC was 475,063 cycles with the load of 870N. The peak value of maximum principal stress occurred at the contact area (LD: 172MPa and PIC: 96MPa) and central fossa (LD: 100MPa and PIC: 64MPa) for both ceramics which were the most seen failure areas in the experiment. In the adhesive layer, the maximum shear stress was observed at the shoulder area (LD: 53.6MPa and PIC: 29MPa). SignificanceThe fatigue life and failure modes of all-ceramic crown determined by the numerical method seem to correlate well with the previous experimental study.

Bearing capacity and slope stability assessment of rock masses at the Subasi viaduct site, NE, Turkey

This study investigates the bearing capacity of rock masses and stability of slopes at the Subasi viaduct site which is a part of the improvement project of the Artvin–Hopa government highway between KM 6 + 500 and 13 + 787 in NE Turkey. The geotechnical studies were performed in three stages. Firstly, the bearing capacity of moderately weathered andesitic tuff was evaluated using the empirical equations. Secondly, the major principal stress and vertical displacement due to the viaduct and traffic loadings at the level of foundations were determined by the finite element method (FEM). The vertical displacement value and comparison of bearing capacity and major principal stress show that any problem is not expected at the viaduct site in terms of the bearing capacity. Finally, the stability of slopes at the viaduct site was investigated using kinematic, limit equilibrium, and finite element method-based shear strength reduction analyses methods. It was concluded that no discontinuity controlled failures at the slopes are expected. However, a circular failure is possible to occur at the face slope excavated in highly weathered andesitic tuff. After support application, the long-term stabilization of face slope has been achieved. Consequently, it is suggested that the empirical, analytical, and numerical methods should be combined for a more reliable construction design.

Establishment of a three-dimensional finite element model of pelvic anteroposterior compression for analysis of related ligamentous damages

Objective To establish a three-dimensional finite element model of pelvic anteroposterior compression (APC) for analysis of mechanisms for related ligamentous damages. Methods A finite element model and a laboratory mechanical model of APC were established using the same pelvic specimens. In a finite element model of normal pelvic bones and ligaments, after the right pelvis was fixated the pubic symphysis (PS) was sectioned. Next, a manual external mobile force was gradually applied to the left hemipelvis to make the PS diastasis 10, 20, 30, 40, 60, 80 and 100 mm apart. The mechanical experiment revealed the anterior sacroiliac ligament (ASIL) was ruptured when the PS diastasis reached 28 mm. After the strain value of ASIL was calculated through the finite element model, it was applied to the other pelvic ligaments. The displacement in front of the sacroiliac joint (SIJ), stress, strain and extent of injury and disruption of sacrotuberous/sacrospinous ligaments (STL/SSL) with a corresponding PS diastasis were observed and recorded. Results ASIL failed at the point when the PS diastasis was 28 mm and the displacement in front of SIJ was 7.41±1.14 mm. The strain and maximum principal stress of ASIL calculated in the finite element model were 259.5% and 543.24 MPa respectively. The maximum principal stress value of SSL was 35.00 MPa at the point of failure when the PS diastasis and the displacement in front of SIJ were 51 mm and 15.23±2.88 mm, respectively. When the PS diastasis and the displacement in front of SIJ were 100 mm and 7.5 mm respectively, the maximum principal stress value of STL was 16.17 MPa but the strained ligament was not ruptured. When the pelvis was rotated externally step by step, the ASIL failure was followed by the rupture of SSL but not necessarily by the STL failure. Conclusion As the finite element pelvic bone-ligament model established in this study can effectively simulate the mechanisms for APC injury, it can be used to evaluate different extents of pelvic ligamentous injury, providing a basis for the biomechanical study of pelvic bones and ligaments. Key words: Pelvis; Ligaments; Wound and injuries; Biomechanics; Finite element analysis

The stress state around an elliptical borehole in anisotropy medium

Under the assumption of generalized plane strain condition, this paper presents an analytical solution for stresses near an inclined elliptical wellbore drilled in anisotropic formation based on the linear theory of anisotropic elasticity and complex variable method. The solution is suitable for calculating the stresses around an elliptical borehole drilled with any inclination and orientation angles in a linear elastic, continuous, homogeneous and general anisotropic medium. The solution for the stresses can also show the effects of the liquid pressure exerted by drilling mud, the ratio and the direction of the in-situ stresses. For engineering utilization the transformation of compliance matrix for the transversely isotropic medium is formulated. An example is calculated and shown by contours of stress components around an inclined elliptical wellbore in a transversely isotropic formation. The stress contours can be utilized to some extent to predict the location, the range, the depth and even the outlines of fractured or collapsed well wall. Then a range of parametric analysis is carried out on the impacts of borehole inclination, orientation and ellipticity on the first principal stress and maximum shearing stress. The results indicate that for various boreholes with different degree of formation anisotropy the algebraic values of the first principal stress and maximum shearing stress go down gradually with the increase of borehole inclination, and these two stresses vary in the pattern of half a sinusoidal wave with the variation of orientation angles. Furthermore, the stresses go up with the increase of ellipticity. The solution presented in this paper might supply a more realistic technique for assessing the stability of borehole and optimizing the well path in anisotropic medium.

Effect of finish line design on stress distribution in bilayer and monolithic zirconia crowns: a three-dimensional finite element analysis study.

This study evaluated the influence of different finish line designs and abutment materials on the stress distribution of bilayer and monolithic zirconia crowns using three-dimensional finite element analysis (FEA). Three-dimensional models of two types of zirconia premolars - a yttria-stabilized zirconia framework with veneering ceramic and a monolithic zirconia ceramic - were used in the analysis. Cylindrical models with the finish line design of the crown abutments were prepared with three types of margin curvature radius (CR): CR=0 (CR0; shoulder margin), CR=0.5 (CR0.5; rounded shoulder margin), and CR=1.0 (CR1.0; deep chamfer margin). Two abutment materials (dentin and brass) were analyzed. In the FEA model, 1N was loaded perpendicular to the occlusal surface at the center of the crown, and linear static analysis was performed. For all crowns, stress was localized to the occlusal loading area as well as to the axial walls of the proximal region. The lowest maximum principal stress values were observed when the dentin abutment with CR0.5 was used under a monolithic zirconia crown. These results suggest that the rounded shoulder margin and deep chamfer margin, in combination with a monolithic zirconia crown, potentially have optimal geometry to minimize occlusal stress.