Maximum Principal Stress Values Research Articles

Design, analysis and topology optimization of connecting rod

This paper focuses on the design, analysis, and topology optimization of the connecting rod. All the Internal Combustion (IC) Engines require a number of connecting rod depending on the number of cylinders that have been used. The Creo Parametric software has been used for designing the connecting rod 3D model and then the designed connecting rod model is imported into the ANSYS software in which the design is meshed and analyzed by using the Finite Element Method (FEM) and the result is manipulated. From the results obtained from the ANSYS by doing static stress analysis, the topology optimization of the connecting rod has been done by using the Autodesk Fusion 360 software. Topology optimization is an efficient mathematical technique that is used to optimize the layout of the design for the given loads and boundary conditions within the given design space and the objective of the technique is to increase the desired performance characteristics of the given design. The optimized design is fine-tuned for manufacturability and it is imported into ANSYS for meshing and analyzing. Then, the values of maximum principal stress, equivalent stress, maximum principal strain, and total deformation of the connecting rod before and after the topology optimization are manipulated and also compared. It is found that the optimized model is efficient in design as the stresses are lesser then the existing model and the weight reduction of about 3.5% is achieved in the optimized design for the material of steel.

Computer-aided simulation of a vertical-axis wind turbine

In many studies, computer-aided simulation methods are used to design vertical-axis wind turbines. Compared with conventional optimization methods, computer-aided optimization methods, which show continuous improvement in parallel with technology, provide important advantages, particularly in terms of time and cost. On the one hand, a wind turbine is designed to obtain maximum power; on the other hand, this design must be able to operate safely under extreme conditions. When considered from this point of view, computational fluid dynamic analysis is the first step that provides input to structural analysis, and the accuracy of the structural analysis is directly related to the accuracy of the computational fluid dynamic analysis. In this study, the fluid–structure interaction method of the H-type Darrieus wind turbine was carried out. The computational fluid dynamic model was confirmed by experimental data in the literature. The results showed that the six-degrees-of-freedom solver deviates on average 5.0% less than experimental data. Using the fluid–structure interaction method, the maximum principal stress, equivalent stress and deformation values on the blade were obtained depending on the pressure load distribution on the turbine blade, and it was determined that the turbine can operate safely under operating conditions.

Quantitative evaluation of geological conditions for shale gas preservation based on vertical and lateral constraints in the Songkan area, Northern Guizhou, southern China

Organic rich Wufeng-Longmaxi shales (WLS) occur widely in the Upper Ordovician–Lower Silurian strata in southeastern Sichuan Basin, SW China. However, complex structural deformation and faulting activity in this area since the Mesozoic time has had significant impact on shale gas preservation. Thus, difference in the structural deformation strength is an important constraint for differential shale enrichment in a shale reservoir. Fracture analysis and bedding surface normal stress data obtained from the outcrop, core and fluid inclusion samples were used to determine the vertical and lateral constraints on shale gas preservation conditions. Using the finite element method, 2D mechanical models were established in the Songkan area, based on seismic inversion, rock mechanics and acoustic emission tests. Paleotectonic stress fields were estimated for the Middle Yanshanian (K11/K12), Late Yanshanian (K22/K23) and Himalayan （E-N）times. Fracture type distribution was determined from the rock failure criterion, and the shale bedding surface normal stress calculated by dip angle and burial depth. The results indicate that optimal conditions for shale gas preservation occur where the maximum principal stress values reach the fracture development stage (around 63.96–73.8 MPa). When the value increases to over 65 MPa, shale bedding surface closure favors the shale gas preservation. Based the vertical and lateral constraints, the best preservation area occurs where fracture development coincides with the shale bedding closure.

In situ Stress Measurement in Kilometer-Deep Mine and Its Relationship with Minefield Fault Structure

In view of the complicated geological stress structure and fuzzy distribution characteristics of a kilometer-deep mine, the KX-81 hollow inclusion stress relief method was used to test in situ stress in Shuanghe Coal Mine at the level of –1100. On the basis of the field test data, the 3D grid diagram of the principal stress distribution in the deep mining area of Shuanghe Coal Mine was drawn, and the relationship between the in situ stress distribution characteristics and the fault structure in wellfield was studied. Results showed that 1) the directions of σ1 and σ3 at each measurement point were horizontal, and the other principal stress σ2 was vertical. 2) The maximum principal stress value was 1.26–1.48 times of the self-weight stress value, indicating that the horizontal tectonic stress plays a leading role in the in situ stress of the mine. 3) The horizontal and vertical stresses at a depth of about 1090 m were estimated according to the theory. A comparison revealed that the theoretical values were lower than the field measured values. The area was found to be dominated by horizontal tectonic forces belonging to the dynamic stress field. 4) The direction of σ1 at each measurement point was 114.70°–124.72°, with an average of 120°. The direction was NWW-SEE. In accordance with the distribution law of the fault structure in the wellfield, the consistency between the wellfield geological structure and the measured direction of the maximum principal stress was analyzed and verified. The research results provide technical basis for deep well roadway layout and stability control and improve the scientific nature and reliability of surrounding rock control of high stress roadway in deep wells under complex geological structures.

The effect of the design of a mandibular implant-supported zirconia prosthesis on stress distribution

Statement of problemProsthetic complications have been frequently reported in implant-supported complete-arch prosthesis. Prosthetic restorations designed with an all-on-four treatment concept and fabricated from zirconia ceramic may be used to overcome these problems. PurposeThe purpose of this biomechanical study was to evaluate the effects of cantilever length and inclination of implant on the stress distribution in bone tissue, implant, and a monolithic zirconia ceramic-lithium disilicate glass-ceramic superstructure for all-on-four prosthesis. Material and methodsAll-on-four mandibular prosthesis fabricated from a zirconia and lithium disilicate glass-ceramic (LDGC) superstructure was designed with cantilever lengths of either 5 mm or 9 mm and posterior implants with a distal tilt of either 15 or 30 degrees. Stresses were evaluated with a simulated application of a static load of 600 N. ResultsIncreasing implant inclination from 15 to 30 degrees led to a decrease in maximum principal stress (MaxPS) values of approximately 4 to 7 MPa in cortical bone around all implants except the right anterior implant in the designs with short cantilevers and an increase in MaxPS values (approximately 3 to 19 MPa) in the same places in the designs with the long cantilevers. Increasing cantilever length from 5 to 9 mm resulted in an increase in minimum principal stress (MinPS) values of approximately 3 to 13 MPa in the cortical bone surrounding all posterior implants. In the designs with the long cantilever, MaxPS values increased approximately 3 to 4 MPa in spongy bone adjacent to the right posterior implant. An increase in cantilever length also led to higher vMS values at the first and second implant grooves in the right posterior implant in the design with the 15-degree implant tilt. An increase in implant inclination in the design with the short cantilever resulted in lower vMS values at the apex and all grooves of the left posterior implant, whereas in the design with the long cantilever, an increase in implant inclination resulted in lower stress values in the first and second grooves of the same implant. An increase in implant inclination led to in an increase in vMS values in the core structure. ConclusionsIn zirconia ceramic restorations by using an all-on-four design with an LDGC superstructure, short cantilevers may be preferable because they result in a more favorable distribution of stress than long cantilevers. An increase in implant angulation from 15 to 30 degrees decreased MaxPS values in cortical bone.

Effect of Principal Stress Field on the Development of Plastic Zone ahead of the Gateroad

The distribution of a plastic zone ahead of a gateroad plays a significant role in maintaining the long-term stability of mining spaces. For a long time, the principal stress field such as the values, the direction, etc. have been observed to have impacts on plastic zone development, but has not been looked into deeply and systematically. To this end, the influence of principal stress field including the maximum principal stress (P1), the angle between the P1 direction and the Z-axis (α), the minimum principal stress (P3), and the ratio of maximum principal stress to minimum principal stress (P1/P3) on the expansion of the plastic zone ahead of the gateroad is investigated by the (Fast Lagrangian Analysis of Continua) FLAC3D models. The results show that: (1) The plastic zone volume increases first and then decreases with the increase of α, and the direction of butterfly-shaped plastic zone ahead of gateroad is rotating with the evolution of α. (2) The plastic zone volume ahead of excavation face increases gradually with the increase of P1/P3. Mutagenicity of butterfly-shaped plastic zone occurs ahead of the gateroad under a certain value of P1/P3. (3) With the increase of P1 and decrease of P3, the plastic zone volume is of exponential growth. The plastic zone volume approaches infinity when the critical value of maximum principal stress ([P1]) and the minimum principal stress ([P1]) is obtained. (4) The study of the effect of principal stress field on the expansion of plastic zone ahead of the gateroad is helpful for revealing the mechanisms of coal and gas outbursts. The critical stress state of butterfly-shaped plastic zone mutagenicity ahead of the gateroad can be used as an important indicator for assessing the risk of coal and gas outburst. The research can also guide the prevention of coal and gas outburst ahead of the gateroad.

The Effect of Shear Sliding of Vertical Contraction Joints on Seismic Response of High Arch Dams with Fine Finite Element Model

The contraction joints of arch dams with and without shear keys are simplified to be with no-slip condition and with relative sliding condition, respectively. Based on the Lagrange multiplier method, a contact model considering the manner of independent cantilever dead load type with no-slip condition and relative sliding condition is proposed to model the nonlinearities of vertical contraction joins, which is special to the nonlinear analysis of arch dams considering the manner of dead load type. Different from the conventional Gauss iterative method, the strategy of the alternating iterative solution of normal force and tangential force is employed. The parallelization based on overlapping domain decomposition method (ODDM) and explicit message passing using distributed memory parallel computers is employed to improve the computational efficiency. An existing high arch dam with fine finite element model is analyzed to investigate the effect of shear sliding of vertical joints on seismic response of the arch dam. The result shows that the values of maximum principal tensile stress under relative sliding condition are significantly greater than those under no-slip condition.

Numerical investigation of a novel pattern for reducing residual stress in metal additive manufacturing

Deposition patterns can significantly affect residual stress distribution in additive manufacturing processes. In this paper, a novel pattern, the S-pattern, is proposed for the metal additive manufacturing process. The finite element method is used to study the temperature field and the stress field of a cuboid structure under the S-pattern and five other representative patterns: zig-zag, raster, alternate-line, in-out spiral, and out-in spiral. The results show that the S-pattern achieves the lowest values of both equivalent residual stress and maximum principal residual stress, and the warpage of the S-pattern is close to that of counterparts. By analyzing the temperature and stress fields under all patterns, it is found that the residual stress distribution is determined by the uniformity of temperature distribution which is correlated with the peak temperatures of corners. The equivalent residual stress and the maximum principal residual stress are inversely correlated with the average peak temperature and the minimum peak temperature of corners, respectively. These correlations between temperature and residual stress provide an effective approach to evaluate the residual stress of different patterns and guide the deposition process in practice.

Biomechanical comparison of the All-on-4, M-4, and V-4 techniques in an atrophic maxilla: A 3D finite element analysis

BackgroundPatients with severely atrophied jaws can be challenging in implantology. The All-on-4 treatment concept eliminates advanced augmentation procedures in highly resorbed ridges by preserving the relevant anatomic structures. In addition, the inclination of the distal implants enables the placement of longer implants. Hence, tilting the anterior implants allows longer implant placement, in line with the distal implants of the All-on-4 concept. This study compared the biomechanical aspects of the standard All-on-4 treatment concept with the M-4 and V-4 techniques. MethodsA three-dimensional model of an edentulous maxilla was created to perform three-dimensional finite element analysis. Three different configurations (All-on-4, M-4, and V-4) were modeled by changing the tilt angle of the anterior implants. In each model, to simulate a foodstuff, a solid spherical material was placed on the midline of the incisors and the right first molar region, separately applying an occlusal load of 100 Newtons. The maximum principal stress and minimum principal stress values were acquired for cortical bone, and von Mises stress values were obtained for ductile materials. ResultsAccording to the present study's findings, although there were no considerable differences among the models, in general, the All-on-4 group demonstrated slightly higher stresses and the M-4 and V-4 group showed lower stresses. ConclusionM-4 or V-4 configurations may be used in cases of severely atrophied anterior maxillae to achieve better primary stabilization.

Comparative Finite Element Analysis of Short Implants with Different Treatment Approaches in the Atrophic Mandible.

This three-dimensional finite element analysis study aimed to compare the stresses transmitted to short, tilted, and vertical implants used in different configurations and to the surrounding peri-implant bone in the atrophic mandible. A three-dimensional model of an atrophic mandible was made using customized computer software. Four models including short, tilted, and vertical implants were constructed with and without cantilever extension. Four or six implants in different configurations were placed into the models and mounted with the same fixed prosthesis. An oblique force of 200 N was bilaterally applied to the most distal part of the fixed denture. Von Mises stress values on implants and minimum and maximum principal stress values transmitted to peri-implant bone were analyzed. The highest stress values recorded in the tilted implants (von Mises: 129 MPa), in the peri-implant bone around the tilted implants (minimum principal stress: -40 MPa), and overall stress values were found to be higher in the model including tilted implants with cantilever extensions. Distally placed short implants, with consequent elimination of the cantilevers, resulted in decreased stress values for all of the treatment variabilities of an atrophic mandible. Von Mises stress values were found as 129 MPa in tilted (model I), 48 MPa in short (model II), 47 MPa in short (model III), and 57 MPa in vertical (model IV) at the most distal implant location. Lower compressive stress values were noted in the bone around straight and short implants compared with the tilted implants in all models (model I, tilted: -40 MPa; model II, short: -34 MPa; model III, short: -33 MPa; model IV, vertical: -25 MPa). Distally placed short implants contributed to the reduction of stress values of the implants and the surrounding bone. The combination of two short and four straight implants without cantilevers may be a beneficial design in the rehabilitation of posteriorly atrophic mandibles.

Three-dimensional finite element analysis of extra short implants focusing on implant designs and materials

AimWhen using short implants, fracture of the implant body and bone resorption are a concern because stress concentrates on and around a short implant. The purpose of this research is to investigate the differences in stress distribution between tissue level (TL) and bone level (BL) implant body designs, and between commercially pure titanium (cpTi) and the newer titanium–zirconium (TiZr) alloy in using short implants.Materials and methodsModels of TL and BL implants were prepared for three-dimensional finite element analysis. The implants were produced in 10 mm, 8 mm, and 6 mm lengths, and the TL was also produced in a 4-mm length. A static load of 100 N inclined at 30° to the long axis was applied to the buccal side of the model. The largest maximum principal stress value in the cortical bone and the largest von Mises stress value in the implant body were evaluated.ResultsStress concentration was observed at the connection part of the implant, especially above the bone in TL and within the bone in BL. In the TL design, tensile stress occurred on the buccal side and compressive stress on the lingual side of the cortical bone. Conversely, in the BL design, tensile stress occurred on the lingual side of the cortical bone. CpTi and TiZr showed a similar stress distribution pattern. The maximum stress values were lower in the TL design than the BL design, and they were lower with TiZr than cpTi for both the cortical bone and implant body. The maximum value tended to increase as the length of the implant body decreased. In addition, the implant body design was more influential than its length, with the TL design showing a stress value similar to the longer BL design.ConclusionUsing TiZr and a TL design may be more useful mechanically than cpTi and a BL design when the length of the implant body must be shorter because of insufficient vertical bone mass in the mandible.

Clinical Contrast-Enhanced Computed Tomography With Semi-Automatic Segmentation Provides Feasible Input for Computational Models of the Knee Joint.

Computational models can provide information on joint function and risk of tissue failure related to progression of osteoarthritis (OA). Currently, the joint geometries utilized in modeling are primarily obtained via manual segmentation, which is time-consuming and hence impractical for direct clinical application. The aim of this study was to evaluate the applicability of a previously developed semi-automatic method for segmenting tibial and femoral cartilage to serve as input geometry for finite element (FE) models. Knee joints from seven volunteers were first imaged using a clinical computed tomography (CT) with contrast enhancement and then segmented with semi-automatic and manual methods. In both segmentations, knee joint models with fibril-reinforced poroviscoelastic (FRPVE) properties were generated and the mechanical responses of articular cartilage were computed during physiologically relevant loading. The mean differences in the absolute values of maximum principal stress, maximum principal strain, and fibril strain between the models generated from semi-automatic and manual segmentations were <1 MPa, <0.72% and <0.40%, respectively. Furthermore, contact areas, contact forces, average pore pressures, and average maximum principal strains were not statistically different between the models (p >0.05). This semi-automatic method speeded up the segmentation process by over 90% and there were only negligible differences in the results provided by the models utilizing either manual or semi-automatic segmentations. Thus, the presented CT imaging-based segmentation method represents a novel tool for application in FE modeling in the clinic when a physician needs to evaluate knee joint function.

Effect of Framework Type on the Biomechanical Behavior of Provisional Crowns: Strain Gauge and Finite Element Analyses.

The aim of this study was to evaluate the effects of different frameworks on the biomechanical behavior of implant-supported provisional single crowns to indicate or not the use of plastic framework as infrastructure. For finite element analysis, a hemi-jaw stone model was scanned and modeled with an external hexagon implant. A framework was screwed onto the implant and a crown was constructed over it. The set was made in triplicate according to framework type: plastic, cobalt-chromium (CoCr), and titanium. Models were exported in volumetric format to analysis software where structures were considered isotropic, linear, elastic, and homogeneous. Axial loads (100, 200, and 300 N) were applied to the fossa bottom, and the system's fixation occurred on the bone base. For strain-gauge analysis, the same hemi-jaw model was built in polyurethane and an implant was placed on it. Three crowns were made, each one with a different framework. Four strain gauges were glued around the implant to obtain microstrain values. The data were analyzed by three-way analysis of variance (ANOVA) and Tukey tests (P < .05). Finite element analysis exhibited microstrain results for bone, von Mises stress values for the implant and screw, and maximum principal stress values for the crown. For computational method, as the applied load increased, so did the stress generated. Titanium frameworks concentrated more stress in the crown and bone, while plastic ones concentrated more in the implant and screw. ANOVA showed that the higher the load value and the framework elastic modulus, the higher the generated microstrain in bone. It can be concluded that all evaluated framework types can be used in the manufacturing of provisional crowns.

Three-dimensional finite element analysis of cuspal-coverage thickness influence on the stress distribution of all-ceramic onlay-restored premolars

To investigate the influence of cuspal-coverage thickness on the stress distribution of all-ceramic onlay-restored premolars by using 3D finite element (FE) analysis and to provide references for the design of all-ceramic onlays for clinical application. 3D FE models of all-ceramic onlays with three cuspal-coverage thicknesses (2, 3, and 4 mm) of endodontically treated maxillary premolar were constructed based on micro-CT images. Stress distributions in the onlay, adhesive resin cement layer, and dentin of models were analyzed under vertical load (600 N) and oblique load (200 N). When the cuspal-coverage thickness increased, the peak maximum principal stress value decreased inside the onlay but increased in the margin of the adhesive resin cement layer. In addition, stress concentration areas increased in the coronal residual dentin on the palatal side under oblique load. An increase in the cuspal-coverage thickness of all-ceramic onlays may reduce the risk of rupture of the restoration but may deteriorate the restoration and cause palatal dentin fracture.

Determination of stress distribution on active fault by means of Casagrande method; an innovative approach

The investigation deals with the stress distributions of undisturbed soil samples taken by preconsolidation press method from paleoseismological studies in the Gerede (Bolu) segment of the North Anatolian Fault System (NAFS), which is one of the most important intra-continental active transform faults in the world. Taking into consideration of the theoretical principal stress directions causing the faulting in the soil samples, consolidation experiments were carried out in different directions and the preconsolidation pressure values (PPV) of the samples were found by Casagrande method. Relations between the prime stress directions which are effective in the mechanism of fault formation and the values of PPV found by the Casagrande method were revealed. With all these calculations, the principal directions and magnitudes of the principal stresses causing faulting in the near-surface depths on the Gerede segment of the NAFS have been determined by a new method. The Gerede segment of the maximum principal stress (σ1) value at N 55.50 W and N 600 W was found 554.08 kPa and 327.54 kPa respectively. The maximum principal stress (σ1) direction of the fault was found to be N 55.50 W and the angle value was 44.50.

Evaluation of Stress in Tilted Implant Concept With Variable Diameters in the Atrophic Mandible: Three-Dimensional Finite Element Analysis.

The beneficial mechanical properties provided by greater diameter or short implants increases their usage in the tilted implant concept. The aim of the present study is to compare the stress distribution of 4 different treatment models including variable implant numbers and diameters under a static loading protocol in the atrophic mandible using 3-dimensional finite element analysis. Three models included 2 tilted and 2 vertically positioned implants with different diameters, whereas 2 distally placed short implants were added to the fourth model. The von Mises stress as well as the maximum and minimum principal stress values were evaluated after applying 200 N bilateral oblique loads to the first molar teeth with the inclination of 45° to the longitudinal axis. Tilted implants were associated with higher stress values when compared with vertical implants in all models. The lowest stress values were obtained in the fourth model, including short implants. Although all stress values showed slight increases by descending implant diameters, the stress values of the model including implants with 3.3-mm diameter were within physiologic limits. All in all, an increasing number or diameter of implants may have a positive effect on implant survival. In addition, when narrow-diameter implants need to be inserted in the tilted implant concept, combination with short implants may be recommended for long-term success.

Effects of abutment screw preload in two implant connection systems: A 3D finite element study

Statement of problemFinite element analysis (FEA) has been used to evaluate the biomechanical behaviors of dental implants. However, in some FEA studies, the influence of the preload condition has been omitted to simplify the analysis. This might affect the results of biomechanical analysis significantly. The preload condition requires analysis. PurposeThe purpose of this FEA study was to evaluate and verify the effects of the presence of the preload condition on abutment screws under the occlusal load for external and internal hexagonal connection systems. Material and methodsThe finite element models consisting of bone blocks, 2 different implant systems (Osstem US and GS system; Osstem Implant Co), and crowns were created. With these components, a total of 6 models with different conditions were constructed for FEA: external hexagonal connection system only with preload (EO), external hexagonal connection system with no preload but occlusal load (EN), external hexagonal system with both preload and occlusal load (EP), internal hexagonal system only with preload (IO), internal hexagonal system with no preload but occlusal load (IN), and internal hexagonal system with both preload and occlusal load (IP). An 11.3-degree oblique load (100 N) to the axis of the implant was applied on the occlusal surface of the crown for the models with occlusal load. A preload of 825 N was applied in the abutment screw of the models EO, EP, IO, and IP. The maximum von Mises stress, maximum principal stress, and maximum displacement of the components of the models were evaluated. ResultsBoth external and internal connection systems resulted in higher maximum von Mises stress and maximum principal stress values in the presence of preload in the abutment screw. The internal connection system showed higher displacement values than the external system with or without occlusal loading, and values tended to increase with the preload condition. ConclusionsThe presence of a preload condition significantly affected the biomechanical behaviors of the components of 2 different connection systems. The preload condition should be included in FEA to achieve more realistic results.

Finite-element analysis of mandibular first molar with two marginal designs of endocrown for the repair of different defects

This study aimed to evaluate the stress distribution of the mandibular first molar with different thicknesses and heights of the axial wall restored by the endocrown with two marginal designs and thus provide a theoretical basis for selecting clinical preparation through the finite-element method. Two marginal endocrowns of the mandibular first molar with different axial-wall thicknesses (t=1, 2, 3 mm) and heights (h=2, 3, 4 mm) were established. Group A was the butt-joint design, whereas group B was the shoulder-surrounded design. After applying vertical and oblique loads , the size and distribution of the maximum principal stress and equivalent stress of residual tooth tissue were recorded. The maximum principal stress and equivalent stress distribution of residual tooth tissue were similar among different models. Group A showed a lower maximum principal stress and equivalent stress than group B at the same thickness and height under vertical load. Meanwhile, under oblique load, the maximum principal stress values of groups A and B decreased with increased thickness at constant height. Group A showed lower equivalent stress than group B at the same thickness and height of 2 and 3 mm. However, when the height was 4 mm, the trend was reversed. In mastication, when bearing the vertical force, the retention of the butt-joint marginal endocrown preferred to the shoulder-surrounded one. Given the higher axial wall of the shoulder-surrounded marginal endocrown, it showed better ability to bear the oblique force than the butt-joint one.

Combined crystal plasticity and grain boundary modeling of creep in ferritic-martensitic steels: II. The effect of stress and temperature on engineering and microstructural properties

This paper describes a series of physically-based crystal plasticity finite element method (CPFEM) simulations of long-term creep and creep rupture of Grade 91 steel. It is Part 2 of a two part series of papers. Part 1 describes the simulation framework; this part focuses on specific simulations and on how the predicted long-term creep properties of Grade 91 compare to the assumptions used in current high temperature design practices. This work extends the model developed in Part 1 to look at creep properties at different temperatures, principal stresses, and multiaxial stress states. The simulations show that empirically extrapolating creep rupture stresses from short-term experimental data may substantially over predict the actual long-term creep properties of Grade 91. Additionally, the CPFEM calculations predict a transition from notch strengthening creep behavior for high values of maximum principal stress and moderate notch severity to notch weakening behavior for low principal stresses and more severe notches. The latter regime better categorizes conditions in engineering components designed for long term elevated temperature use, which implies Grade 91 may be a notch weakening material in actual service. This would have a significant impact on high temperature design practices, though confirmatory test data on long-life, low stress notched specimens is difficult to obtain. Finally, one advantage of the physically-based modeling approach adopted here is that the simulation results also elucidate the microstructural mechanisms causing the macroscopic trends in engineering properties predicted by the simulations. This paper shows that the detailed micromechanical mechanisms predicted by the CPFEM simulations can be abstracted with a simple micromechanical model that can be used to both explain the detailed results and make improved predictions of engineering properties from experimental data.

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.