Three-dimensional Finite Element Stress Research Articles

ANNFAA: artificial neural network-based tool for the analysis of Federal Aviation Administration’s rigid pavement systems

ABSTRACT Three-dimensional Finite Element (3D-FE) stress computations involved in the current rigid airport pavement design methodology, are time consuming when considering top-down cracking failure mode. In this study, Artificial Neural Network (ANN) models are integrated into a tool called ANNFAA to replace such 3D-FE computations. ANNFAA makes use of the best ANN models developed in MATLAB for 156 different airplanes without requiring any additional software installation or cumbersome learning of a new program. Within ANNFAA development, about 4,000 of 3D-FE simulations and many ANN models have been developed for each of these airplanes. Three useful tools were also developed using C# and MATLAB for implementing the 3D-FE analysis, post-processing the results, training the ANN models, and determining accuracy and performance of the ANN models. ANNFAA provides an accurate and rapid procedure for practitioners, engineers, and researchers for computing the critical stress responses associated with top-down cracking in multiple-slab rigid airfield pavements. This should make pavement design and analysis more practical, especially when a significantly large number of different cases that include top-down cracking failure mode are investigated. Also, this will help when currently used bottom-up cracking mode in the FAA standard rigid pavement design procedures is being considered in a design.

Integrated Approach for Steam Turbine Thermostructural Analysis and Lifetime Prediction at Transient Operations

In order to achieve the highest power plant efficiency, original equipment manufacturers continuously increase turbine working parameters (steam temperatures and pressures), improve components design, and modify start-up cycles to reduce time while providing more frequent start-up events. All these actions result in much higher levels of thermostresses, a lifetime consumption of primary components and an increased demand for accurate thermostructural and low cycle fatigue (LCF) simulations. In this study, some aspects of methodological improvement are analyzed and proposed in the frame of an integrated approach for steam turbine components thermostructural analysis, reliability, and lifetime prediction. The full scope of the engineering tasks includes aero/thermodynamic flow path and secondary flows analysis to determine thermal boundary conditions (BCs), detailed thermal/structural two-dimensional and three-dimensional (3D) finite element (FE) models preparation, components thermal and stress–strain simulation, rotor–casing differential expansion and clearances analysis, and finally, turbine unit lifetime estimation. Special attention is paid to some of the key factors influencing the accuracy of thermal stresses prediction, specifically, the effect of “steam condensation” on thermal BC, the level of detailing for thermal zones definition, thermal contacts, and mesh quality in mechanical models. These aspects have been studied and validated against test data, obtained via a 30 MW steam turbine for combined cycle application based on actual start-up data measured from the power plant. The casing temperatures and rotor–stator differential expansion, measured during the commissioning phase of the turbine, were used for methodology validation. Finally, the evaluation of the steam turbine HPIP rotor lifetime by means of a LCF approach is performed.

A three-dimensional finite-element stress analysis and strength evaluation of stepped-lap adhesive joints subjected to static tensile loadings

Stress distributions in stepped-lap adhesive joints subjected to static tensile loadings are analyzed using three-dimensional finite-element calculations. For establishing an optimum design method of the joints, the effects of the adhesive Young's modulus, adhesive thickness and number of steps on the interface stress distributions are examined. The results show that the maximum value of the maximum principal stress σ 1 occurs at the edge of the adhesive interfaces. The maximum value of the stress σ 1 decreases as the adhesive Young's modulus and number of steps increase and as the adhesive thickness decreases under static loadings. A method for estimating the joint strength under static loadings is proposed using interface stress distributions. For verification of the finite-element method calculations, experiments were carried out to measure the strains and the joint strengths under static loadings. Fairly good agreements were found between the numerical and the experimental results.

418 インプラントオーバーデンチャーの3次元FEAモデルの構築と応力解析(OS6-2:硬組織のバイオメカニクス(2),OS6:硬組織のバイオメカニクス)

418 インプラントオーバーデンチャーの3次元FEAモデルの構築と応力解析(OS6-2:硬組織のバイオメカニクス(2),OS6:硬組織のバイオメカニクス)

Mixed Mode Stress Intensity Calibrations for an Angled Crack Bend Specimen

Abstract Test specimens with angled or inclined cracks are frequently used to investigate mixed mode fatigue and fracture properties. A full three-dimensional (3-D) linear elastic finite element stress analysis has been performed for a beam with an angled single edge crack subjected to three-point bend loading. Crack angles of 45°, 60°, 75°, and 90° to the longitudinal axis of the beam have been considered. The resulting geometric correction terms to the linear elastic fracture mechanics (LEFM) mode I, II, and III stress intensity factors are presented.

A three-dimensional finite-element stress analysis of an endodontically prepared maxillary central incisor

This study is an application of a three-dimensional Finite-Element Method to investigate the changes in stress characteristics of a prepared maxillary central incisor. The purpose of this study was to analyze stress distributions in this tooth after simulated canal preparation and static loading. A maxillary central incisor was embedded in acrylic, sectioned, photographed, and digitized. A three-dimensional finite-element model was generated by a computer and appropriately modified to simulate canal preparation. Data identified the highest stress magnitudes to be located between the middle and coronal thirds of the root; an area clinically observed to be prone to fracture during treatment. In addition, the magnitude of generated stresses was directly correlated with the simulated prepared canal diameter. The development of a validated three-dimensional finite-element method could identify areas that may predispose a tooth to structural failure during condensation loads.

Iterative study for three-dimensional finite-element stress analysis

Iterative study for three-dimensional finite-element stress analysis

Non-self-similar crack growth in elastic-plastic finite thickness plate

Abstract This work is concerned with non-self-similar crack growth in medium strength metal plates while the loading step, plate thickness and material properties are altered. The three-dimensional elastic-plastic finite element stress analysis is combined with the strain energy density criterion for modeling the material damage process from crack initiation to final global instability including the intervening stage of slow crack growth. Both inelastic deformation and crack growth are accounted for each increment of loading such that the redistribution of stresses and strains are made for each new crack profile. Numerical results are obtained for the center cracked plate configuration under uniform extension with twenty-seven (27) different combinations of specimen thickness, loading step and material type. The fracture toughness S c being related to K 1c for three different materials are predicted analytically from the corresponding uniaxial tensile test data. Effective strain energy density factor S and half crack length a are defined so that the results can be compared with their two-dimensional counterparts. Crack growth resistance curves ( R- curves ) are constructed by plotting S as a function of a . The condition d S / d a = const. is found to prevail during slow crack growth. Translation and/or rotation of the S − a lines can yield results other than those calculated and serve a useful purpose for scaling component size and test time. The minimum thickness requirement for the ASTM valid K 1c test is also discussed in connection with predictions based on the strain energy density criterion. The corresponding K 1c for smaller specimens that exhibit moderate ductility and nonlinearity can also be obtained analytically. In such cases, the influence of loading step can be significant and should not be neglected. Notwithstanding the shortcomings of the theory of plasticity, the qualitative features of non-self-similar crack growth are predicted by the strain energy density criterion. Any refinements on the analytical modeling of the material damage process would only affect the results qualitatively, a subject that is left for future investigation.

A comparative evaluation of tibial component designs of total knee prostheses.

Three-dimensional finite-element stress analyses were used to compare the fixation of tibial component configurations of surface-replacement-type total knee prostheses, bases on the stresses in the cancellous bone, in the polymethylmethacrylate, and at the bone cement-bone interface. The results indicate that, in general, metal components provide lower system stresses than polyethylene components, particularly in the methacrylate and the cancellous bone, and that one-piece designs give lower bone cement-bone interface stresses compared with those with separated condylar components. Of the designs considered, a single-post, metal-backed design provided the lowest system stresses over-all. a great and confusing variety of tibial component design exists today, with more in the process of development. Short of long term clinical trials, there are few objective methods by which these designs can be evaluated and long-term performance predicted. There is evidence from clinical results that excessively high stresses in the systems can lead to loosening of the tibial component. The finite-element method provides a method for comparing prosthetic designs using system stresses a s a design criterion. On this basis, we analyzed the stress distribution for several types of tibial components and discuss the advantages and disadvantages of their designs.

An analysis of femoral component stem design in total hip arthroplasty.

A comparative study of the various aspects of the design of the femoral components of total hip replacements was done using three-dimensional finite-element stress analysis. The aspects of deisgn that were considered included: length, cross-sectional size, and material properties of the stem; presence or absence of a medial collar; and material properties of the cement. We found that increasing the length of the stem generally increased the stress present in the stem while decreasing the stress present in the cement. Increasing the cross-sectional size of the stem decreased the stress in both the stem and the cement. Decreasing the modulus of elasticity of the stem material decreased the stress in the stem but increased the stress in the cement. Increasing the modulus of elasticity of the cement decreased the stress in the stem and increased the stress in the cement. Contact of the collar of a femoral prosthesis with the calcar femorale increased the longitudinal component of stress within the region of the calcar femorale. The mechanical longevity of a total joint reconstruction is related to the stress distribution throughout the prosthesis, cement, and bone. The stress distribution is related to a number of factors, including the design of the prosthetic components (for example, stem size, stem length, stem modulus of elasticity, and cement modulus of elasticity). Reducing the stresses in prosthetic components to minimize the risk of failure can be accomplished only through systematic analysis of all components of the reconstruction.

Three-Dimensional Optimization of a Gas Turbine Disk and Blade Attachment

A new three-dimensional finite-element stress simulation is described and applied to design optimization of a turbine disk/blade attachment. Isoparametric elements are employed, with the standard elements being a general parabolic conoid and a variable thickness triangle. The stress field obtained is improved with the use of a conjugate approximation. A parametric study is used to select optimum attachment geometry. The analysis model includes complex airfoil geometry and a nonzero broach angle.