Finite Element Method Stress Analysis Research Articles

Suppressing methods of cracking on inter-metallic silicon oxide films

We investigated the mechanism of cracking between the inter/intra-metallic dielectric (IMD) silicon oxide films after anneal process. The cracks were initiated at the top corner of aluminum lines, then propagated through the silicon oxide films. Thus, the extrusion of melted Al along the IMD cracks, caused metal line bridge. These cracking conditions involve the stresses of the IMD films as well as their thickness. Namely, the cracking was suppressed not only by decreasing the magnitude of compressive stress but also increasing the film thickness on silicon oxide films. These results are in accordance with the finite element method stress analysis using silicon oxide film stress and thickness. In this paper, we focused on the analysis of crack formation mechanism on the IMD film, and finally proposed an empirical criterion for crack-safety condition.

FEM Stress Analysis and the Evaluation of Sealing Performance of the Box-Shaped Flange Connections with Gaskets Subjected to Internal Pressure (In the Case Where the Wavy Oil-Pan Shaped Flange Connection is Used)

The contact gasket stress distribution in a wavy oil-pan shaped flange connection under the internal pressure was examined using finite element method (FEM) for estimating a location where a principal leakage occurred and for calculating the amount of leakage. Leakage tests were also conducted to validate the estimated results using an actual connection under the internal pressure. The effects of flange shape on the contact gasket stress distributions were examined. The sealing performance for the difference types of inner fluid (gas/liquid) was evaluated from the contact gasket stress distributions. It was seen that the estimated amount of leakage was in a fairly good agreement with the measured results. The difference of the contact gasket stress distribution and the sealing performance were shown between the box-shaped flange and the wavy oil-pan shaped flange connections. In addition, a method how to determine the bolt preload taking into account the allowable amount of the leakage was demonstrated. Furthermore, discussion was made on the effect of the bolt pitch on the sealing performance.

The Effect of Framework Design on Stress Distribution in Implant-Supported FPDs: A 3-D FEM Study

The biomechanical behavior of the superstructure plays an important role in the functional longevity of dental implants. However, information about the influence of framework design on stresses transmitted to the implants and supporting tissues is limited. The purpose of this study was to evaluate the effects of framework designs on stress distribution at the supporting bone and supporting implants. In this study, the three-dimensional (3D) finite element stress analysis method was used. Three types of 3D mathematical models simulating three different framework designs for implant-supported 3-unit posterior fixed partial dentures were prepared with supporting structures. Convex (1), concave (2), and conventional (3) pontic framework designs were simulated. A 300-N static vertical occlusal load was applied on the node at the center of occlusal surface of the pontic to calculate the stress distributions. As a second condition, frameworks were directly loaded to evaluate the effect of the framework design clearly. The Solidworks/Cosmosworks structural analysis programs were used for finite element modeling/analysis. The analysis of the von Mises stress values revealed that maximum stress concentrations were located at the loading areas for all models. The pontic side marginal edges of restorations and the necks of implants were other stress concentration regions. There was no clear difference among models when the restorations were loaded at occlusal surfaces. When the veneering porcelain was removed, and load was applied directly to the framework, there was a clear increase in stress concentration with a concave design on supporting implants and bone structure. The present study showed that the use of a concave design in the pontic frameworks of fixed partial dentures increases the von Mises stress levels on implant abutments and supporting bone structure. However, the veneering porcelain element reduces the effect of the framework and compensates for design weaknesses.

Conservative restoration of severely damaged endodontically treated premolar teeth: a FEM study

The aim of this finite element method (FEM) study was to test two different restorative techniques used for construction of severely damaged endodontically treated premolar teeth using Finite Element Stress Analysis Method. In this study, four types of three-dimensional (3-D) FEM mathematical models simulating (1) a sound lower single rooted premolar tooth with supporting structures; (2) a root-filled lower premolar tooth without lingual cusp, restored with resin composite; (3) a root-filled lower premolar tooth without lingual cusp restored with resin composite in combination with a polyethylene fiber which is placed circumferentially to help to create a composite lingual wall; (4) a root-filled lower premolar tooth without lingual cusp restored with resin composite in combination with a glass fiber post, were modeled. A 300-N static vertical occlusal load was applied on the node at the center of occlusal surface of the tooth to calculate stress distributions. Solidworks/Cosmosworks structural analysis programs were used for FEM analysis. The analysis of the von Mises stress values revealed that maximum stress concentrations were located at loading areas for all models. Root dentine tissue, lingual cortical bone, and apical bone structures were other stress concentration regions. There were stress concentration differences among the models at root dentine tissue. Although the distribution pattern was similar with composite resin restored tooth model, highest stress values were observed at root dentine in the model restored with post-and-core. Post structure accumulated more stress on its own body. Stress distribution patterns of sound tooth and fiber-reinforced restoration models were found as similar. The present study showed that the use of post material increased the stress values at root dentine structure while reinforcing the restoration with a fiber decreases stress transmission. Fiber-reinforced restoration provided stress distributions similar to sound tooth.

Finite element analysis of maxillary central incisors restored with various post-and-core applications

The purpose of this study was to investigate the effect of rigidity of post core systems on stress distribution by the theoretical technique, finite element stress-analysis method. Three-dimensional finite element models simulating an endodontically treated maxillary central incisor restored with a zirconia ceramic crown were prepared and 1.5 mm ferrule height was provided. Each model contained cortical bone, trabecular bone, periodontal ligament, 4 mm apical root canal filling, and post-and-core. Six combinations of three parallel type post (zirconia ceramic, glass fiber, and stainless steel) and two core (Paracore and Tetric ceram) materials were evaluated, respectively. A 50 N static occlusal load was applied to the palatal surface of the crown with a 60� angle to the long axis of the tooth. The differences in stress transfer characteristics of the models were analyzed. von Mises stresses were chosen for presentation of results and maximum displacement and hydrostatic pressure were also calculated. An increase of the elastic modulus of the post material increased the stress, but shifted the maximum stress location from the dentin surface to the post material. Buccal side of cervical region (junction of core and crown) of the glass fiber post restored tooth was subjected to the highest stress concentration. Maximum von Mises stress in the remaining radicular tooth structure for low elastic modulus resin core (29.21 MPa) was slightly higher than that for high elastic modulus resin core (29.14 MPa) in case of glass fiber post. Maximum displacement of glass fiber post restored tooth was higher than that of zirconia ceramic or stainless steel post restored tooth. [J Kor Acad Cons Dent 34(4):324-332, 2009]

The finite element analysis of the effect of ferrule height on stress distribution at post-and-core-restored all-ceramic anterior crowns

The purpose of this study was to compare the effect of ferrule with different heights on the stress distribution of dentin and the restoration-tooth complex, using the finite element stress analysis method. Three-dimensional finite element models simulating an endodontically treated maxillary central incisor restored with an all-ceramic crown were prepared. Three-dimensional models were varied in their ferrule height (NF: no ferrule, 1F: 1-mm ferrule, and 2F: 2-mm ferrule). A 300-N static occlusal load was applied to the palatal surface of the crown with a 135 degrees angle to the long axis of the tooth. In addition, two post and core materials with different elastic modulus were evaluated. The differences in stress transfer characteristics of the models were analyzed. Maximum stresses were concentrated on force application areas (32.6-32.8 MPa). The stress values observed with the use of a 2-mm ferrule (14.1/16.8 MPa) were lower than the no-ferrule design (14.9/17.1 MPa) for both the glass fiber-reinforced and zirconium oxide ceramic post systems, respectively. The stress values observed with zirconium oxide ceramic were higher than that of glass fiber-reinforced post system. The use of a ferrule in endodontically treated teeth restored with an all-ceramic post-and-core reduces the values of von Mises stresses on tooth-restoration complex. At rigid zirconium oxide ceramic post system, stress levels, both at dentin wall and within the post, were higher than that of fiber posts.

A Modified Technique for FEM Stress Analysis in Practical Problem

Finite element method (FEM) is used widely for various structural problems. However, in general, it is difficult to guarantee the accuracy of results obtained by commercial software of FEM. In this paper, a practical finite element technique for calculating the stress concentration factors with high accuracy is proposed in consideration of physical meaning of stress concentration, and applied to a 2-dimentional stress problem.

FEM Stress Analysis and an Evaluation of the Sealing Performance in Non-circular Box-shape Bolted Flange Connections with Gaskets Subjected to Internal Pressure

The contact gasket stress distribution of a non-circular box-shape flange connection with a compressed sheet gasket subjected to internal pressure was analyzed taking account a hysteresis of the gasket using finite element method (FEM). Leakage tests were also conducted using an actual non-circular box-shape flange connection with a compressed sheet gasket under internal pressure. By using the contact gasket stress distributions and the results of the leakage tests, the new gasket constants were calculated. The difference in the new gasket constants was substantial between the values obtained from the present study and those from the PVRC procedure. In addition, a method to determine the initial clamping bolt force (bolt preload) for a given tightness parameter was demonstrated. It was found that a higher bolt preload was needed for a given tightness parameter in the more safety design of box-shape flange connections.

2818 頚椎障害を有する関節リウマチ患者の椎間板における力学的挙動評価(J08-2 バイオメカニクス,J08 生体・環境適合材料の創製・強度評価技術開発)

The purpose of this study was to establish a finite element stress analysis method of intervertebral discs in a rheumatoid arthritis (RA) patient with cervical involvement using a three dimensional (3D) computer model reconstructed from computer tomography (CT) and magnetic resonance (MR) images. Intervertebral disc 3D finite element models were created using point cloud data of endplates of cervical spine (C2-C7) vertebral bodies in three different positions; neutral, flexion, and extension positions. Transformations of each endplate in flexion and extension positions were determined using a volume merge method. Changes in stress/strain distribution during flexion and extension were analyzed using displacement data of the endplate as input data. Stress concentration was noted at both lateral regions in C2/3 and C3/4 intervertebral discs. However, no significant changes in stress distribution during motion were observed at C4/5, C5/6, and C6/7 intervertebral discs.

The influence of various occlusal materials on stresses transferred to implant‐supported prostheses and supporting bone: A three‐dimensional finite‐element study

The aim of this numerical analysis was to evaluate the amount and localization of stress that occurs with various materials used in implant-crown design under functional forces. Computer-aided design techniques and a finite-element stress analysis method were used for evaluation. A 4.1 x 10-mm implant placed in the mandibular second premolar area was simulated and analyzed. Simulation and analysis were performed with the use of COSMOS/M software and Pro/Engineer 2000i on a Dual Pentium III 1-GHz computer. Crown designs were as follows: porcelain fused to noble metal crown, porcelain fused to base metal crown, In-Ceram porcelain crown, and IPS Empress 2 porcelain crown. A 300-N vertical force was applied to the centric relation stop points of the crowns. The results of this study indicated that different types of restorative materials play an important role in the amount and distribution of the stresses in the superstructure and the implant. The highest stress values were observed in the IPS Empress 2 porcelain crown design (600 MPa). Porcelain fused to base metal and In-Ceram framework designs transferred less stress to abutment. Type of restorative materials used in implant crown designs are significant factors in the amount and distribution of the stresses on superstructure and implant under functional forces. Porcelain fused to base metal (149 MPa) and In-Ceram (173 MPa) crown designs induced higher von Mises stress values within the framework than porcelain fused to noble metal (108 MPa) and IPS Empress 2 (119 MPa) porcelain crown designs.

FEM Stress Analysis and Sealing Performance Evaluation in Pipe Flange Connections with Spiral Wound Gaskets Subjected to External Bending Moments (Case where Internal Fluid is Liquid)

The leakage evaluation when gas is used is more severe than that when liquid is used in pipe flange connections. In a practical design, it is also necessary to examine the leakage in the connections under liquid internal pressure application. The contact gasket stress distributions in the connection with a spiral wound gasket subjected to internal pressure and bending moment were analyzed by using elasto-plastic finite element method (FEM) taking account hysteresis and nonlinearity in the stress-strain curve of the gasket. The effects of the initial clamping bolt force (bolt preload), the nominal pressure and the nominal diameter of the pipe flange and the equivalent pressure on the contact gasket stress distributions were examined. The leakage tests for the connections under the bending moment and the internal pressure were also conducted by using liquid (water). By using the results of the leakage tests and the calculated contact gasket stress distributions, the sealing performance of the connections was evaluated. It was found that the sealing performance of the connection can be estimated when liquid (water) was used. In addition, a method for determining the bolt preload in the connections under the bending moments was proposed for the reliable design.

Fusion-Driven Sub-Critical Dual-Cooled Waste Transmutation Blanket: Design and Analysis

The Fusion-Driven Sub-critical System (FDS) is one of the Chinese programs to be further developed for fusion application. Its Dual-cooled Waste Transmutation Blanket (DWTB), as one the most important part of the FDS is cooled by helium and liquid metal, and have the features of safety, tritium self-sustaining, high efficiency and feasibility. Its conceptual design has been finished. This paper is mainly involved with the basic structure design and thermal-hydraulics analysis of DWTB. On the basis of a three-dimensional (3-D) model of radial-toroidal sections of the segment box, thermal temperature gradients and structure analysis made with a comprehensive finite element method (FEM) have been performed with the computer code ANSYS5.7 and computational fluid dynamic finite element codes. The analysis refers to the steady-state operating condition of an outboard blanket segment. Furthermore, the mechanical loads due to coolant pressure in normal operating conditions have been also taken into account. All the above loads have been combined as an input for a FEM stress analysis and the resulting stress distribution has been evaluated. Finally, the structure design and Pb-17Li flow velocity has been optimized according to the calculations and analysis.

Generalized multi-domain method for fatigue analysis of interconnect structures

This paper describes a generalized multi-domain finite element stress analysis method to obtain the stress and strain fields for a variety of packaging styles under cyclic thermal environments. The elastic–plastic analysis was demonstrated on ceramic chip component, gull-wing, plated-through hole, and plastic ball grid array solder joints. The solder joints were modeled by colonies of sub-domains at stress risers identified in advance by finite element analysis. In this approach, the physical domain was mapped into isoparametric regions, which were divided into nested sub-domains according to projected high-stress gradients. The previous multi-domain method, based on Rayleigh-Ritz energy principle, utilized polynomials to interpolate the displacement within sub-domains. On the other hand, the displacements in the main and sub-domains, for the improved method used in this paper, are represented by the nodal displacements through isoparametric interpolation, which is similar to the finite element method. The solution at each domain was formed as the superposition of the results corresponding to their sub-domains. The Broyden-Fletcher-Goldfarb-Shanno (BFGS), a quasi-Newton method with line search, was used for fast convergence. All results were compared with finite element analyses (FEA) for the same loading conditions. The demonstration concluded that the proposed multi-domain method decreases the presented (example) problem's solution time by a factor ranging from 3.4 to 4.5 compared to finite element model (FEM) at a comparable accuracy.

Finite element analysis of the influence of implant inclination, loading position, and load direction on stress distribution.

The selection of the appropriate alignment of an implant and the position of implantation are vital for its longterm success. Excessive load is generated around inclined implants, causing microcracks in the bone, which result in implant loosening and eventual failure. This study was designed to analyze the stress distribution caused by varying the degree of inclination of an implant body and varying the loading position and direction, using the finite-element method of stress analysis. Buccal and lingual two-dimensional simulation models of a cylinder implant, embedded in the first molar edentulous cross-section of the mandible, were prepared, and the stress distribution and maximum principal stresses were recorded. Regardless of the point and direction of loading, compressive stresses were relatively greater when the implant was inclined. This tendency became more pronounced when a 45 degrees loading direction and eccentric loading were tested. For the inclined model, with a 45 degrees loading direction, the compressive stress was observed on the cortical bone adjacent to the direction of inclination, while tensile stress was observed on the opposite side.

Analysis on stress field of the dual-cooled waste transmutation blanket for the FDS

This paper mainly deals with stress field numerical calculations and analysis of the Dual-cooled waste transmutation blanket (DWTB). A comprehensive finite element method (FEM) structure analysis has been performed with the computer code ANSYS5.7. The analysis refers to the steady-state operating condition of an outboard blanket segment. Thermal stresses caused by the temperature gradients in the blanket structure have been calculated. Furthermore, the mechanical loads due to coolant pressure in normal operating conditions have been also taken into account. All the above loads have been combined as input for a FEM stress analysis and the resulting stress distribution has been evaluated.

FEM Stress Analysis and Sealing Performance Evaluation in Pipe Flange Connections with Gaskets Subjected to External Bending Moments

The stresses in a pipe flange connection with a gasket subjected to an internal pressure and an external bending moment are analyzed taking account the non-linearity and hysteresis of a spiral wound gasket and a joint sheet gasket by using an elasto-plastic finite element method (FEM). The effects of the internal pressure and the external bending moment on the contact gasket stress distributions are examined. Leakage tests were also conducted using an actual pipe flange connection with a gasket under an external bending moment. As a result, a difference in the new gasket constants is substantial between the PVRC values and the estimated values when the external bending moment is applied to the connection. The hub stress and variation in axial bolt force were also measured. Fairly good agreements are found between the calculated and experimental results. In addition, a method for determining the bolt preload in the pipe flange connection under the external bending moment is demonstrated for a given tightness parameter.

FEM stress analysis and sealing performance improvement of box-shaped bolted flanged joints using silicone sealant under internal pressure and thermal conduction conditions

Interface stresses and sealing performance of thin-wall box-shaped bolted flanged joints using silicone sealant under internal pressure and thermal conduction conditions are analyzed by the thermo-elastic finite element method. The flexible flanges were fastened by M8 bolts and nuts with an initial clamping force (bolt preload) after being joined with the silicone sealant. In the elastic and thermo-elastic Finite Element Method (FEM) calculations, the effects of the bolt pitch distance, flange rigidity and flange thickness were examined on the interface stress distributions. In addition, the effects of the linear thermal expansion coefficient and Young's modulus of the silicone sealant in the steady temperature state were also examined from a design standpoint. In the experiments, leakage pressure was measured when the silicone sealant was applied between an aluminum flexible flange with 1 mm thickness and an aluminum flange (body) with 10 mm thickness. Measurements of sealing performance with the silicone sealant and a sheet gasket were also conducted. In addition, strains in the joint in steady temperature states were also measured by strain gauges to understand the effect of the operative temperature on the sealing performance. The experimental results were found to be in fairly good agreement with the calculated results. From the results, it was found that the effect of the thermal conduction condition was greater than that of the internal pressure on both the interface stress distributions and the sealing performance. In addition, the sealing performance was found to be better in the joint with the silicone sealant than that with the sheet gasket.

Single crystal silicon nano-wire piezoresistors for mechanical sensors

A p-type silicon (Si) nano-wire piezoresistor, whose minimum cross-sectional area is 53 nm/spl times/53 nm, was fabricated by combination of thermal diffusion, EB (electron beam) direct writing and RIE (reactive ion etching). The maximum value of longitudinal piezoresistance coefficient /spl pi//sub l[011]/ of the Si nano-wire piezoresistor was found to be 48/spl times/10/sup -5/ (1/MPa) at surface impurity concentration of 5/spl times/10/sup 19/ (cm/sup -3/) and it has enough sensitivity for mechanical sensor applications. The longitudinal piezoresistance coefficient /spl pi//sub l[011]/ of the Si nano-wire piezoresistor increased up to 60% with a decrease in the cross sectional area, while transverse piezoresistance coefficient /spl pi//sub t[011]/ decreased with a increase in the aspect ratio of the cross section. These phenomena were briefly investigated based on a hole energy consideration and FEM (finite element method) stress analysis.

FEM stress analysis and strength of adhesive butt joints of similar hollow cylinders under static and impact tensile loadings

The stress wave propagations in butt adhesive joints of similar hollow cylinders subjected to static and impact tensile loadings are analyzed in elastic and elasto-plastic deformation ranges using the finite-element method (FEM). The impact loading is applied to the joint by dropping a weight. The upper end of the upper adherend is fixed and the lower adherend of which the lower end is connected to a guide bar is subjected to the impact loading. The FEM code employed is DYNA3D. The effects of the adhesive thickness and Young's modulus of the adhesive on the stress wave propagation at the interfaces are examined. In addition, the characteristics of the joints subjected to impact loadings are compared with those of the joints under static loadings and the joint strengths are estimated by using the interface stress distributions. It is found that the maximum value of the maximum principal stress, σ1 occurs at the outside edge of the interface of the lower adherend to which the impact loading is applied. The maximum value of the maximum principal stress, σ1 increases as Young's modulus of the adhesive increases when the joints are subjected to impact loadings. It is found that the characteristics of the joints subjected to impact loadings are opposite to those subjected to static loadings. In addition, experiments were carried out to measure the strain response of the butt adhesive joints subjected to impact and static tensile loadings using strain gauges and the joint strengths were also measured. Fairy good agreements are observed between the numerical and the measured results.

Design of a steam-heated sterilizer based on finite element method stress analysis

A steam-heated sterilizer is a pressure vessel of rectangular cross section externally reinforced by members welded to the flat surfaces of the vessel. These members are pressure vessels too with rectangular cross section. The ASME code provides alternative rules (Division 2) for the design of pressure vessels based on a Design By Analysis route. The stresses on the sterilizer were computed by the finite element method followed by the calculation of the stress fields according to the classification established in the ASME code. Structural members with shell intersections (as in the present case) present difficulties due to problems of linearisation and categorisation. In the present work the shell stress resultants were used instead of smoothed stresses. The operating conditions of the vessel involve cyclic application of loads requiring design based on fatigue analysis.