Finite Element Analysis And Design Of Metal Structures Pdf 11 Extra Quality
Intravascular stents are small tube-like structures expanded into stenotic arteries to restore blood flow perfusion to the downstream tissues. The stent is mounted on a balloon catheter and delivered to the site of blockage. When the balloon is inflated, the stent expands and is pressed against the inner wall of the coronary artery. After the balloon is deflated and removed, the stent remains in place, keeping the artery open. Hence, the stent expansion defines the effectiveness of the surgical procedure: it depends on the stent geometry, it includes large displacements and deformations and material non-linearity. In this paper, the finite element method is applied (i) to understand the effects of different geometrical parameters (thickness, metal-to-artery surface ratio, longitudinal and radial cut lengths) of a typical diamond-shaped coronary stent on the device mechanical performance, (ii) to compare the response of different actual stent models when loaded by internal pressure and (iii) to collect suggestions for optimizing the device shape and performance. The stent expansion and partial recoil under balloon inflation and deflation were simulated. Results showed the influence of the geometry on the stent behavior: a stent with a low metal-to-artery surface ratio has a higher radial and longitudinal recoil, but a lower dogboning. The thickness influences the stent performance in terms of foreshortening, longitudinal recoil and dogboning. In conclusion, a finite element analysis similar to the one herewith proposed could help in designing new stents or analyzing actual stents to ensure ideal expansion and structural integrity, substituting in vitro experiments often difficult and unpractical.
finite element analysis and design of metal structures pdf 11
Abstract:A parameterization modeling method based on finite element mesh to create complex large-scale lattice structures for AM is presented, and a corresponding approach for size optimization of lattice structures is also developed. In the modeling method, meshing technique is employed to obtain the meshes and nodes of lattice structures for a given geometry. Then, a parametric description of lattice unit cells based on the element type, element nodes and their connecting relationships is developed. Once the unit cell design is selected, the initial lattice structure can be assembled by the unit cells in each finite element. Furthermore, modification of lattice structures can be operated by moving mesh nodes and changing cross-sectional areas of bars. The graded and non-uniform lattice structures can be constructed easily based on the proposed modeling method. Moreover, a size optimization algorithm based on moving iso-surface threshold (MIST) method is proposed to optimize lattice structures for enhancing the mechanical performance. To demonstrate the effectiveness of the proposed method, numerical examples and experimental testing are presented, and experimental testing shows 11% improved stiffness of the optimized non-uniform lattice structure than uniform one.Keywords: lattice structures; additive manufacturing; infilled structure finite-element-mesh based method; MIST method
To design a new subperiosteal implant structure for patients suffering from severe Maxillary Atrophy that lowers manufacturing cost, shortens surgical time and reduces patient trauma with regard to current implant structures. A 2-phase finite-element-based topology optimization process was employed with implants made from biocompatible materials via additive manufacturing. Five bite loading cases related to standard chewing, critical chewing force, and worst conditions of fastening were considered along with each specific result to establish the areas that needed to be subjected to fatigue strength optimization. The 2-phase topological optimization tested in this study performed better than the reference implant geometry in terms of both the structural integrity of the implant under tensile-compressive and fatigue strength conditions and the material constraints related to implant manufacturing conditions. It returns a nearly 28% lower volumetric geometry and avoids the need to use two upper fastening screws that are required with complex surgical procedures. The combination of topological optimization methods with the flexibility afforded by additively manufactured biocompatible materials, provides promising results in terms of cost reduction, minimizing the surgical trauma and implant installation impact on edentulous patients.
Recently, new design and manufacturing techniques have redeveloped the way edentulous patients are treated. Several Additive Manufacturing techniques, such as Electron Beam Melting6,7 (EBM), Selective Laser Melting8,9 (SLM), or Selective Laser Sintering10,11,12 (SLS), use biocompatible implantable materials to facilitate the manufacturing of implants with the required mechanical properties13,14. Individuals who may have lost .all their teeth and suffer from Cawood and Howell class V-VI bone atrophy are able to benefit from the progress made in the fields of Finite Element (FE) analysis and metal additive manufacturing. Additively Manufactured Sub-periosteal Jaw Implants or purposed Additively Manufactured Subperiosteal Implant Structures (AMSISs) associated to the surgical procedure and postoperative recovery15 may prove to be promising enhancement channels for severe atrophic cases stemming from maxillary bone loss and/or poor bone quality.
The production of implant structures through additive manufacturing yields a large flexibility in the design of the implant since many shapes and geometries are more easily achievable than by using traditional or alternative production methods. Combining this with a finite element analysis, the critical points of the implant structure can be identified and reinforced while reducing the number of fastening points and optimizing their location. Moreover, the simplification of manufacturing restrictions facilitates the reduction of the contact surface between the implant and the maxillary bone, condensing the amount of bone subjected to contact and lessening the potential difficulties derived from bone loss. Eventually, this treatment may lead to shorter surgical incisions, reduce pain and surgery difficulties, facilitate screw fixation by osteosynthesis of the implant, and reduce post-operation recovery, enabling patients to adapt more quickly to their daily activities.
3D finite element analysis is a numerical stress analysis technique that is widely used to study engineering and biomechanical problems. Its combination with new manufacturing techniques, such as Additive Manufacturing, results in considerable improvements in the design and performance of implants when compared with more traditional approaches. In this study, an optimization of the original design of a sub-periosteal jaw implant has been carried out using these tools. The optimized implant structure has an individualized titanium network shape, with six implant-like connections fixed directly to the bone of the upper jaw by means of micro-screws. This design makes it possible to produce a biocompatible structure with optimal biomechanical characteristics for the subsequent fixation of a fully functional dental prosthesis.
The finite element method (FEM) is a popular method for numerically solving differential equations arising in engineering and mathematical modeling. Typical problem areas of interest include the traditional fields of structural analysis, heat transfer, fluid flow, mass transport, and electromagnetic potential.
The FEM is a general numerical method for solving partial differential equations in two or three space variables (i.e., some boundary value problems). To solve a problem, the FEM subdivides a large system into smaller, simpler parts that are called finite elements. This is achieved by a particular space discretization in the space dimensions, which is implemented by the construction of a mesh of the object: the numerical domain for the solution, which has a finite number of points. The finite element method formulation of a boundary value problem finally results in a system of algebraic equations. The method approximates the unknown function over the domain.[1]The simple equations that model these finite elements are then assembled into a larger system of equations that models the entire problem. The FEM then approximates a solution by minimizing an associated error function via the calculus of variations.
In the first step above, the element equations are simple equations that locally approximate the original complex equations to be studied, where the original equations are often partial differential equations (PDE). To explain the approximation in this process, the finite element method is commonly introduced as a special case of Galerkin method. The process, in mathematical language, is to construct an integral of the inner product of the residual and the weight functions and set the integral to zero. In simple terms, it is a procedure that minimizes the error of approximation by fitting trial functions into the PDE. The residual is the error caused by the trial functions, and the weight functions are polynomial approximation functions that project the residual. The process eliminates all the spatial derivatives from the PDE, thus approximating the PDE locally with
While it is difficult to quote a date of the invention of the finite element method, the method originated from the need to solve complex elasticity and structural analysis problems in civil and aeronautical engineering.[4] Its development can be traced back to the work by A. Hrennikoff[5] and R. Courant[6] in the early 1940s. Another pioneer was Ioannis Argyris. In the USSR, the introduction of the practical application of the method is usually connected with name of Leonard Oganesyan.[7] It was also independently rediscovered in China by Feng Kang in the later 1950s and early 1960s, based on the computations of dam constructions, where it was called the finite difference method based on variation principle. Although the approaches used by these pioneers are different, they share one essential characteristic: mesh discretization of a continuous domain into a set of discrete sub-domains, usually called elements.