Von Mises Stress Criterion Research Articles

Tensile properties of 3D multi-layer wrapping braided composite: Progressive damage analysis

An experimental and numerical study on mechanical properties and damage behavior of 3D multi-layer wrapping braided composite under axial tensile load is presented. The braiding process of this material is introduced and its tensile properties are obtained in tensile tests. Numerical simulations employ periodical boundary conditions, with interface elements between yarns and matrix added to improve the accuracy of prediction. 3D Hashin-type criteria and Von-Mises stress criterion are employed as damage initiation criteria for yarns and matrix, respectively. The obtained numerical results show a good agreement with the experimental data. The load-bearing capacity and failure mechanisms of 3D multi-layer wrapping braided composites under axial tensile loading are also discussed. A stress distribution shows that the axial yarns are the main load-bearing component of the composite. The main failure mode of the yarns is the yarn-matrix tensile cracking in the width direction, followed by the yarn-matrix tensile cracking in the thickness direction and fibre tensile failure. When the fibres in axial yarns begin to break, the material loses its load-bearing capacity.

Influence of Abutment Collar Height and Implant Length on Stress Distribution in Single Crowns.

This in silico study evaluated the influence of the abutment collar height and implants length on the biomechanical behavior of morse taper single dental implants with different crown-to-implant ratio. Six virtual models were constructed (S11, M11, L11, S13, M13 and L13) by combining short (S: 2.5 mm), medium (M: 3.5 mm) or long (L: 4.5 mm) abutment collar heights with different implant lengths (11 or 13-mm). An upper central incisor of 11-mm height was constructed on top of each abutment. Each set was positioned in a virtual bone model and exported to analyze mathematically. A 0.60-mm mesh was created after convergence analysis and a 49 N load was applied to the cingulum of the crown at an angle of 45°. Load-generated stress distribution was analyzed in the prosthetic components according to von Mises stress criteria (σvM) and in the cortical and cancellous bone by means of shear stress (εmax). The use of longer collar abutments (L11) increased the stress on the abutment by 250% and resulted in 40% higher stresses on the screw and 92% higher cortical shear stresses compared to short collared abutments (S11). Increasing the implant length produced a slight stress reduction on cortical bone. Cancellous bone was not affected by the crown-to-implant ratio. Longer abutment collars concentrate stresses at the implant level and cortical bone by increasing the crown-to-implant ratio.

Numerical investigation of influence of defects of the dentition small extent on the stress-strain state of bridge prosthesis and periodontium

The investigation aim is numerical evaluation of polymethylmethacrylate dental bridge and periodontal ligament stres-strain state in the case of tilted premolar and molar in mandible. Plain strain formulation is used via finite element method. Effect of dental cement on results is also studied. Equivalent stresses in dental bridge and periodontal ligament are determined using von Mises and maximum principal stress criteria. Equivalent stresses in cement are determined using Mohr criterion. The study investigated no difference in stres-strain state of dental bridge with and without consideration of cement. The results showed that dental bridge implantation in the case of tilted teeth redistribute and reduce forces acting on periodontal ligament in comparison with tilted vital teeth.

A stress-based topology optimization method for heterogeneous structures

In this work, we introduce a method to incorporate stress considerations in the topology optimization of heterogeneous structures. More specifically, we focus on using functionally graded materials (FGMs) to produce compliant mechanism designs that are not susceptible to failure. Local material properties are achieved through interpolating between material properties of two or more base materials. Taking advantage of this method, we develop relationships between local Young’s modulus and local yield stress, and apply stress criterion within the optimization problem. A solid isotropic material with penalization (SIMP)–based method is applied where topology and local element material properties are optimized simultaneously. Sensitivities are calculated using an adjoint method and derived in detail. Stress formulations implement the von Mises stress criterion, are relaxed in void regions, and are aggregated into a global form using a p-norm function to represent the maximum stress in the structure. For stress-constrained problems, we maintain local stress control by imposing m p-norm constraints on m regions rather than a global constraint. Our method is first verified by solving the stress minimization of an L-bracket problem, and then multiple stress-constrained compliant mechanism problems are presented. Results suggest that good designs can be produced with the proposed method and that heterogeneous designs can outperform their homogeneous counterparts with respect to both mechanical advantage and reduced stress concentrations.

Determination of optimal residual stress profiles for improved rolling contact fatigue resistance

A theoretical framework is developed for the evaluation of favorable residual stress profiles, suppressing fatigue damage initiation in rolling contact fatigue. Non-metallic inclusions at the microstructure of bearings are one of the most important reasons for fatigue damage initiation since they act as stress risers. In order to evaluate the stress state around such inclusions at the micro-scale, macroscopic stress histories are determined by Hertzian contact theory at different depths below the raceway for a typical roller bearing. These stress distributions are then used as far-field stresses for a micro-scale model accounting for single inclusions of different geometries and orientations. Eshelby’s method is used to relate far-field and local stresses in the vicinity of inclusions. The von Mises stress criterion is then used as a conservative estimator of crack initiation due to micro-scale plasticity. The effect of compressive residual stresses added to the axial and circumferential normal stress components at different depths is analyzed. The von Mises stress field around different inclusions at different depths is investigated in order to determine the most critical case in terms of micro-scale plastic deformation. Finally, an optimization process is carried out in order to determine the residual stresses that minimize the maximum observed von Mises stress as a function of depth.

The effect of different irrigation protocols on elastic modulus of dentine and biomechanics of single-rooted premolar tooth: A nano-indentation and finite element analysis study.

This study evaluated the effect of different irrigation protocols on elastic modulus and biomechanics of single-rooted premolar tooth using with nano-indentation and finite element analysis (FEA). Root canals of single-rooted human teeth were prepared, divided into eight groups, and irrigated with (1) 2.5% NaOCl + 17% EDTA; (2) 2.5% NaOCl + 17% EDTA + 2.5% NaOCl; (3) 2.5% NaOCl + SmearClear; (4) 2.5% NaOCl + 2% chlorhexidine; (5) 1.3% NaOCl + MTAD; (6) 5.25% NaOCl; (7) 17% EDTA; and (8) saline. The roots were vertically sectioned, and elastic modulus of the root dentine was measured using nano-indenter device at coronal, middle, and apical third. Data were recorded as megapascal and statistically analyzed (one-way analysis of variance, Tukey tests). Three-dimensional FEA model of a premolar tooth was created, and the inner root dentine was modified to simulate the effect of irrigation protocols on root dentine. The elastic properties of inner root dentine layer in the FEA models were modified for each group according to the data obtained with nano-indentation. A 300-N load was applied at the buccal cusp and central fossa of the models with a 45° angle. The stresses were calculated using von Mises stress criteria. All irrigation protocols affected the elastic modulus of root dentine. Groups 2 and 3 showed similar elastic modulus values (P > 0.05), whereas the lowest values were obtained in group 7 (P < 0.05). No statistically significant differences were found between groups 4, 5, and 8 (P > 0.05). Despite the effect of different clinically used irrigation protocols on elastic modulus of the inner dentine, this does not affect the biomechanics of the roots.

Influence of Geometric Design Variable and Bone Quality on Stress Distribution for Zirconia Dental Implants-A 3D Finite Element Analysis

This study aims to investigate the effects of variable thread pitch on stress distribution in bones of different bone qualities under two different loading conditions (Vertical, and Horizontal) for a Zirconia dental implant. For this purpose, a three dimensional finite element model of the mandibular premolar section and three single threaded implants of 0.8 mm, 1.6 mm, 2.4 mm pitch was designed. Finite element analysis software was used to develop the model and three different bone qualities (Type II, Type III, and Type IV) were prepared. A vertical load of 200 N, and a horizontal load of 100 N was applied at the abutment surface. The von-Mises stress criterion was used to analyze the results. The crestal bony-region of the mandibular section was subjected to maximum von-Mises stresses for all bone qualities. The outcome of this study indicates that, horizontal loading had more influence on stress distribution than vertical loading, regardless of the bone qualities and pitch values. Varying the dental implant pitch does not cause any decrease in stress distribution in bone, when the bone density decreased. The study concluded that implants with minimum pitch values induced lesser stress values at the implant-bone interface.

Surface mechanical properties of shot-peened CNT/Al–Mg–Si alloy composites

A carbon nanotube (CNT)-reinforced Al matrix composite was fabricated and treated by shot peening. After shot peening, isotropic compressive residual stress fields were induced in surface shot-peened layers. As the mechanical properties of the peened layers were improved and therefore varied from the base metal, a specific in-situ X-ray stress analyzer combined with the tensile test technique was used to measure the stress–strain relationship of the strengthened surface layer. On the basis of the measurement and the Von Mises stress criterion, the surface yield strength was calculated and improved by 25% relative to that of the matrix. Moreover, a relaxation behavior of compressive residual stress was observed under cyclic loading. The results showed that the rapid relaxation of surface residual stress chiefly occurred in the first few cycles and then stabilized gradually in subsequent cycles. The retained residual stress under all given applied cyclic loadings possibly occurred in the compressive state consistently.

Topology optimization for microstructural design under stress constraints

This work aims at introducing stress responses within a topology optimization framework applied to the design of periodic microstructures. The emergence of novel additive manufacturing techniques fosters research towards new approaches to tailor materials properties. This paper derives a formulation to prevent the occurrence of high stress concentrations, often present in optimized microstructures. Applying macroscopic test strain fields to the material, microstructural layouts, reducing the stress level while exhibiting the best overall stiffness properties, are sought for. Equivalent stiffness properties of the designed material are predicted by numerical homogenization and considering a metallic base material for the microstructure, it is assumed that the classical Von Mises stress criterion remains valid to predict the material elastic allowable stress at the microscale. Stress constraints with arbitrary bounds are considered, assuming that a sizing optimization step could be applied to match the actual stress limits under realistic service loads. Density–based topology optimization, relying on the SIMP model, is used and the qp–approach is exploited to overcome the singularity phenomenon arising from the introduction of stress constraints with vanishing material. Optimization problems are solved using mathematical programming schemes, in particular MMA, so that a sensitivity analysis of stress responses at the microstructural level is required and performed considering the adjoint approach. Finally, the developed method is first validated with classical academic benchmarks and then illustrated with an original application: tailoring metamaterials for a museum anti–seismic stand.

Investigation of Titanium Material Deformation for Positioning Stereotactic Navigation System by von Mises Stress Criteria and Finite Element in Engineering

Investigation of Titanium Material Deformation for Positioning Stereotactic Navigation System by von Mises Stress Criteria and Finite Element in Engineering

Surface mechanical property and residual stress of peened nickel-aluminum bronze determined by in-situ X-ray diffraction

As one of the most important surface strengthening method, shot peening is widely used to improve the fatigue and stress corrosion crack resistance of components by introducing the refined microstructure and compressive residual stress in the surface layer. However, the mechanical properties of this thin layer are different from the base metal and are difficult to be characterized by conventional techniques. In this work, a micro uniaxial tensile tester equipped with in-situ X-ray stress analyzer was employed to make it achievable on a nickel-aluminum bronze with shot peening treatment. According to the equivalent stress-strain relationship based on Von Mises stress criterion, the Young’s modulus and yield strength of the peened layer were calculated. The results showed that the Young’s modulus was the same as the bulk material, and the yield strength corresponding to the permanent plastic strain of 0.2% was increased by 21% after SP. But the fractographic analysis showed that the fracture feature of the surface layer was likely to transform from the dimple to the cleavage, indicating the improved strength might be attained at the expense of ductility. The monotonic and cyclic loading were also performed via the same combined set-up. In addition, the specific relaxation behavior of compressive residual stress was quantified by linear logarithm relationship between residual stress and cycle numbers. It was found that the compressive residual stress mainly relaxed in the first few cycles, and then reached steady state with further cycles. The relaxation rate and the stable value were chiefly depended on the stress amplitude and number of cycles. The retained residual stress kept in compressive under all given applied stress levels, suggesting that the shot peening could introduce a more stable surface layer of compressive residual stress other than the elevated strength of nickel-aluminum bronze alloy.

A critical analysis of the Mises stress criterion used in frequency domain fatigue life prediction

Multiaxial fatigue failure criteria are formulated in time and frequency domain. The number of frequency domain criteria is rather small and the most popular one is the equivalent von Mises stress criterion. This criterion was elaborated by Preumont and Piefort on the basis of well-known von Mises stress concept, first proposed by Huber in 1907, and well accepted by the scientific community and engineers. It is important to know, that the criterion was developed to determine the yield stress and material effort under static load. Therefore the direct use of equivalent von Mises stress criterion for fatigue life prediction can lead to some incorrectness of theoretical and practical nature. In the present study four aspects were discussed: influence of the value of fatigue strength of tension and torsion, lack of parallelism of the SN curves, abnormal behaviour of the criterion under biaxial tensioncompression and influence of phase shift between particular stress state components. Information contained in this article will help to prevent improper use of this criterion and contributes to its better understanding. KEYWORDS. Mises stress; Frequency domain; Multiaxial fatigue.

Fatigue Life Prediction of a Commercial Vehicle Radiator under Internal Pressure Cycling Loading

Objectives: The study is conducted to find the hot spot stresses in the commercial vehicle heavy duty radiator subjected to internal pressure loading and predict the pressure cycle life. Methods/Statistical Analysis: The finite element analysis technique is employed to predict the hot spot stress and pressure cycle life of the radiator. Finite element model of the radiator is built by the including the mass and stiffness of the radiator component. Header tube joint is the critical area which affects the pressure cycle life and needs to be analyzed. The critical joint area is captured with a good mesh pattern and better element quality to avoid stress singularities and spurious stresses. Findings: Deformation and stresses are the studied in detail to evaluate the finite element analysis result. The radiator deformation shows core side to side expansion which correlates well with the pressure cycle test. Then von-mises stresses are measured at various locations, the header tube stress is found to at 75MPa. Since the radiator core material is ductile material, von-mises stress criterion is employed. To calculate the pressure cycle life, three components such as geometry, loading and material are required. The geometry component is represented by the stress concentration factor (kt) at the header tube joint. The Kt value can be measured based on test failure history. The loading is represented by the internal pressure loading. The S-N curve and cyclic stressstrain properties for the aluminium material is required. Once the above three parameters are known, we can calculate the pressure cycle life at the header tube joint using strain life approach. Calculated pressure cycle life at the critical joint is found to be 150,000 cycles to failure. The virtual life meets the typical pressure cycle life at the header tube joint. Application/Improvements: Prototypes for the pressure cycle test can be reduced. The approach identifies the weak areas early in the design phase. Approximate pressure cycle life at header tube joint is estimated.

English

The aim of this study was to analyze the biomechanical behavior of lower premolars regarding the non-carious cervical lesion (NCCL) depth, load type and restoration status, using finite element analysis. Two-dimensional virtual model simulating a healthy lower premolar were created using the CAD software. Based on this image, five models were generated: healthy (H), three types of NCCLs: small lesion (SL – 0.5 mm deep), medium lesion (ML – 1.0 mm), deep lesion (DL – 1.5 mm), and restored lesion (RL). The models were export to a CAE software (ANSYS Finite Element Analysis Software), the areas of all structures were plotted and each model was meshed using a control mesh device. All of the virtual models were subjected to two occlusal load types, (100N each): occlusal load (OL) and buccal load (BL) on buccal cusp. The magnitude and the stress distribution were obtained using the von Mises and maximum principal stress criteria (σ1), in MPa. The quantitative analysis of stress (MPa) was identified at three points of the NCCLs: enamel surface on its upper wall , dentin at the bottom wall and dentin on the lower wall. The results showed a direct relation between sequential removal of cervical structure and higher stress concentration for any groups and for both loads types. For OL the highest value of stress was 8.8 MPa for DL on upper wall of NCCLs.The BL exhibited higher stress values in comparison to the OL for all models.In addtion, the BL was responsible for providing the highest stress accumulation on the bottom wall, 38.2 MPa for DL. The restoration with composite resin was able to restore a stress distribution close to the healthy model, for both load types. In conclusion, the extent of non-carious cervical lesion and loading conditions influenced the stress distribution pattern of lower premolar. The outer load seems to be more critical in affecting the biomechanical behavior of lower premolars, regardless of the lesion size . The restoration of NCCLs with composite resin appears to recover the biomechanical behavior, similar to healthy model.

Modeling and deformation analyzing of InSb focal plane arrays detector under thermal shock

A higher fracture probability appearing in indium antimonide (InSb) infrared focal plane arrays (IRFPAs) subjected to the thermal shock test, restricts its final yield. In light of the proposed equivalent method, where a 32×32 array is employed to replace the real 128×128 array, a three-dimensional modeling of InSb IRFPAs is developed to explore its deformation rules. To research the damage degree to the mechanical properties of InSb chip from the back surface thinning process, the elastic modulus of InSb chip along the normal direction is lessened. Simulation results show when the out-of-plane elastic modulus of InSb chip is set with 30% of its Young’s modulus, the simulated Z-components of strain distribution agrees well with the top surface deformation features in 128×128 InSb IRFPAs fracture photographs, especially with the crack origination sites, the crack distribution and the global square checkerboard buckling pattern. Thus the Z-components of strain are selected to explore the deformation rules in the layered structure of InSb IRFPAs. Analyzing results show the top surface deformation of InSb IRFPAs originates from the thermal mismatch between the silicon readout integrated circuits (ROIC) and the intermediate layer above, made up of the alternating indium bump array and the reticular underfill. After passing through both the intermediate layer and the InSb chip, the deformation amplitude is reduced firstly from 2.23μm to 0.24μm, finally to 0.09μm. Finally, von Mises stress criterion is employed to explain the causes that cracks always appear in the InSb chip.

Root Canal Filling: Fracture Strength of Fiber-Reinforced Composite-Restored Roots and Finite Element Analysis

The aims of this study were to evaluate the effect of root canal filling techniques on root fracture resistance and to analyze, by finite element analysis (FEA), the expansion of the endodontic sealer in two different root canal techniques. Thirty single-rooted human teeth were instrumented with rotary files to a standardized working length of 14 mm. The specimens were embedded in acrylic resin using plastic cylinders as molds, and allocated into 3 groups (n=10): G(lateral) - lateral condensation; G(single-cone) - single cone; G(tagger) - Tagger's hybrid technique. The root canals were prepared to a length of 11 mm with the #3 preparation bur of a tapered glass fiber-reinforced composite post system. All roots received glass fiber posts, which were adhesively cemented and a composite resin core was built. All groups were subjected to a fracture strength test (1 mm/min, 45°). Data were analyzed statistically by one-way ANOVA with a significance level of 5%. FEA was performed using two models: one simulated lateral condensation and Tagger's hybrid technique, and the other one simulated the single-cone technique. The second model was designed with an amount of gutta-percha two times smaller and a sealer layer two times thicker than the first model. The results were analyzed using von Mises stress criteria. One-way ANOVA indicated that the root canal filling technique affected the fracture strength (p=0.004). The G(lateral) and G(tagger) produced similar fracture strength values, while G(single-cone) showed the lowest values. The FEA showed that the single-cone model generated higher stress in the root canal walls. Sealer thickness seems to influence the fracture strength of restored endodontically treated teeth.

Effects of non-carious cervical lesions and coronary structure loss association on biomechanical behavior of maxillary premolars

Introduction: Dental lesions and cavity preparations can impact the biomechanical behavior of teeth due to tooth structure loss. Objective: Analyze the influence of tooth structure loss associated to non-carious cervical lesions (NCCLs) and coronary preparations on biomechanical behavior of maxillary premolars, restored or not, using finite element analysis (FEA). Material and methods: Virtual models were generated using a longitudinal cut image of a maxillary premolar, exported to a finite element software (Ansys 12.0) and analyzed as follows: sound tooth (S); MOD preparation (P); MOD preparation restored with composite resin (PR); cervical lesion (L); cervical lesion restored with composite resin (LR); and combinations, PR+LR; P+L; PR+L; P+LR. The areas corresponding to each structure were plotted and then meshed with eight-node isoparametric plane elements (PLANE183) in accordance to mechanical properties of each structure and materials. The materials and structures were assumed elastic, isotropic, homogeneous and linear, except for enamel and dentin, considered orthotropic. Oblique load (45N) was applied on buccal and palatal cusps, simulating an experimental tooth-sphere contact. Von Mises (VM) and maximum principal stress (S1) criteria were applied for analyzing the results. Results: FEA using VM criterion revealed similar stress distribution patterns for groups S, PR, LR and PR+LR. Models L, P+L, P+LR and PR+L presented the highest stress at the center of NCCLs, with S1 levels of 0.22, 0.2, 0.25 and 0.31 MPa, respectively. For groups P and P+LR, Von Mises stress concentration was observed at internal angles of preparation and at base of cusps. Conclusion: NCCLs and intracoronal structure loss associated promoted high stress concentration in dental structure and at center of lesion. The load application influenced the stress distribution, and the models of groups restored with composite resin tend to mimic the biomechanical behavior of sound tooth model.

Polyamide worm gear: manufacturing and performance

The focus of this paper is to establish a characterisation method for seven polyamide (PA) grades to determine the major material to manufacture an automotive worm gear. The composite properties were measured according to the worm gear loadings: tensile strength, Young's modulus, abrasion and impact resistance. They were also correlated to the PA moisture absorption and its glass fibre (GF) reinforcement. The data from mechanical tests were applied in the finite element analysis (FEA) using the von Mises stress criterion. Before the rig tests of the PA worm gears, the injection process was evaluated, through the capillary rheometry. A higher difficulty to process PA 6/6 30% GF was found, due to its lower apparent viscosity. In the end, the influence of moisture absorption was as decisive to the gear's material selection as the GF to the pinion. Thus, the PAs with the best performance were: PA 6 with 30% GF (gear) and with PA 60% GF (pinion).

Numerical analysis of an osseointegrated prosthesis fixation with reduced bone failure risk and periprosthetic bone loss

Currently available implants for direct attachment of prosthesis to the skeletal system after transfemoral amputation (OPRA system, Integrum AB, Sweden and ISP Endo/Exo prosthesis, ESKA Implants AG, Germany) show many advantages over the conventional socket fixation. However, restraining biomechanical issues such as considerable bone loss around the stem and peri-prosthetic bone fractures are present. To overcome these limiting issues a new concept of the direct intramedullary fixation was developed. We hypothesize that the new design will reduce the peri-prosthetic bone failure risk and adverse bone remodeling by restoring the natural load transfer in the femur. Generic CT-based finite element models of an intact femur and amputated bones implanted with 3 analyzed implants were created and loaded with a normal walking and a forward fall load. The strain adaptive bone remodeling theory was used to predict long-term bone changes around the implants and the periprosthetic bone failure risk was evaluated by the von Mises stress criterion. The results show that the new design provides close to physiological distribution of stresses in the bone and lower bone failure risk for the normal walking as compared to the OPRA and the ISP implants. The bone remodeling simulations did not reveal any overall bone loss around the new design, as opposed to the OPRA and the ISP implants, which induce considerable bone loss in the distal end of the femur. This positive outcome shows that the presented concept has a potential to considerably improve safety of the rehabilitation with the direct fixation implants.

Periodontal ligament influence on the stress distribution in a removable partial denture supported by implant: a finite element analysis

ABSTRACTObjectiveThe non-homogenous aspect of periodontal ligament (PDL) has been examined using finite element analysis (FEA) to better simulate PDL behavior. The aim of this study was to assess, by 2-D FEA, the influence of non-homogenous PDL on the stress distribution when the free-end saddle removable partial denture (RPD) is partially supported by an osseointegrated implant. Material and MethodsSix finite element (FE) models of a partially edentulous mandible were created to represent two types of PDL (non-homogenous and homogenous) and two types of RPD (conventional RPD, supported by tooth and fibromucosa; and modified RPD, supported by tooth and implant [10.00x3.75 mm]). Two additional FE models without RPD were used as control models. The non-homogenous PDL was modeled using beam elements to simulate the crest, horizontal, oblique and apical fibers. The load (50 N) was applied in each cusp simultaneously. Regarding boundary conditions the border of alveolar ridge was fixed along the x axis. The FE software (Ansys 10.0) was used to compute the stress fields, and the von Mises stress criterion (σvM) was applied to analyze the results. ResultsThe peak of σvM in non-homogenous PDL was higher than that for the homogenous condition. The benefits of implants were enhanced for the non-homogenous PDL condition, with drastic σvM reduction on the posterior half of the alveolar ridge. The implant did not reduce the stress on the support tooth for both PDL conditions. ConclusionThe PDL modeled in the non-homogeneous form increased the benefits of the osseointegrated implant in comparison with the homogeneous condition. Using the non-homogenous PDL, the presence of osseointegrated implant did not reduce the stress on the supporting tooth.