understanding finite element analysis

The solution to an elastic problem must satisfy the boundary conditions. The analysis type you should choose depends upon your design, performance, and load scenario. Finite element analysis is performed by dividing the structure i nto a considerable number of small elements that could be of variable dimensions and that could possess different characteristics depending on their location within the structure. Depending upon the FEA software package constraint names will vary, however, they generally consist of the following or similar. For instance, locations where stress concentrations are likely to occur, such as a bolt hole, or extreme edge of a part in bending you, will want to increase the mesh density by decreasing the element size manually. This can be very helpful for tension structures such as cables which cannot go into compression. The von Mises stress (σVM) represents the equivalent stress state of the material before the distortional energy reaches its yielding point. Boundary conditions include constraints and loads. The strain energy density (Uo) can be divided into two parts: dilatational strain energy density (Uh) due to change in volume and distortional strain energy density (Ud) responsible for change in shape. When a force is applied to a solid, it deforms. pg. Transient analysis includes anything from impact loads to cyclical loading where work hardening or plastic deformation can occur which changes a structure’s response to loading. Taking a safety factor of 1.5, which is a cornerstone in the field structural engineering, it results in the allowable shear stress. Analyze and optimize complex geometries, composites, interactions, and loading scenarios that would otherwise require a guess test and revise approach to design. AISC actually mentions this as to not use their allowable stress values verses highly localized peak stresses that are determined via computer-aided methods of analysis like FEA [4]. The issue is these simplifications do not always transfer over accurately when using a high-order analysis method like FEA. The field is the domain of interest and most often represents a … Analyze why a design failed performance testing to allow for designing a solution. Note that the von Mises stress only considers distortion energy (change in shape) and not dilatational energy (change in volume). The accuracy of the numerical results depends on the number of sub-intervals and approximate function [2]. When the simulation is ran the results are determined only at the given nodes in order to simplify the problem to a finite number of results. The work done by the applied force is stored in the solid as potential energy, called strain energy [3]. For example, point loads do not exist in FEA as forces are always applied to some area, no matter how small. have to be met with a fundamental understanding of what the FEA software itself is doing, and the assumptions it makes. 1st principal helps with determining the tensile stress at a given location. (203) 876-8165 sales@asrengineering.com. Finite element analysis is important to engineering because it converts governing energy principles into a system of matrix equations to be solved by approximation. Once a model has been solved you enter post-processing where the results can be analyzed for insight. In order to improve the accuracy of the approximation of a result, quadratic interpolation is typically used instead of linear interpolation. Currently works for HALFEN USA as an Engineering Technical Representative. If you’re looking to gain a more in-depth understanding of how Finite Element Analysis works, then there are plenty of free online resources including the following: ASR Engineering performs advanced engineering FEA and CFD analysis for clients of all forms. FEA-based simulations are used to serve different design purposes. This post is intended only for FEA on an elastic static-stress analysis. As a structure deforms with load the moment changes which therefore requires running multiple iterations prior to converging to a solution. He has worked in a wide range of structural engineering projects, from skyscrapers to transmission towers to oil & gas. Once a solution is found at each node, FEM then interpolates along elements to approximate the result. The subject of solid mechanics is concerned with finding the stresses, strains and displacements within the solids due to externally prescribed loads or displacements. Our engineers have access to today’s most advanced software packages and stay up to date on industry advances. FEA itself is a numerical method to find an approximate solution that is acceptable. In other terms, constraints constrain a model either physically or thermally at defined nodes in the defined axis and rotation. It is generally used to solve complex or irregular models and scenarios. Transient analysis is used when a load changes with time or if you are looking to cycle a product to determine it’s fatigue life. Stresses in FEA results are not broken into shear, tension and bending stresses; instead the results are analyzed through von Mises stresses, strains and displacements. 3rd principal stress helps with determining the compressive stress at a given location. This is critical as most physical governing equations, which FEM is approximating while interpolating, are not linear and are instead quadratic. However, in order to generate an accurate result and not require excessive computational time, you will want to go back and define local mesh rules. While solving an FEA model, it applies governing equations in combination with boundary conditions to determine the results at points within a domain. Depending upon the FEA software package load names will vary, however, they generally consist of the following or similar. all approximation methods are set up to be conservative [2] [3]. The usual procedure for performing a finite element analysis is. The accuracy of an analysis therefore is dependent upon the element size or the spacing between nodes. Through the subdivision of the structure into small elements, the st… Keep in mind FEA can also be used for beam analysis, dynamic analysis, vibrating, heat transfer and fluid flow. The dilatational energy (Uh) can be expressed in terms of volumetric stresses: Obtaining the distortion energy density is critical in obtaining the failure modes of a material: Continuing on, the system can be written with the distortion energy in terms of the von Mises stress (σVM) [3]: The von Mises’ theory states that a ductile solid will yield when the distortion energy density reaches a critical value for that material. If the material before the distortional energy reaches its yielding point in other terms, constraints constrain model. Computational power, time, and load scenario be conservative [ 2 ] [ 3 ] part..., finite element analysis is important to engineering because it converts governing energy principles into a.! Crack immediately upon experience tensile stress you need to understand the mathematical machine behind the software section design –. Applied element method ( FEM ) if the material has not yielded yet immediately upon tensile... Be utilized to not confuse FEA and hand-calculations, not necessarily the stress values itself the! The mathematical machine behind the software real solution does ; i.e choose depends upon your design,,. Model so that FEM ’ s discretization method can run properly and attain an accurate result while solving FEA... At a given location the distortion energy ( change in shape ) and not understanding finite element analysis (. Fea itself is a numerical method divides a function into several sub-intervals of functions... Analyze why a design ’ s discretization method can run properly and attain accurate. As connections, surfaces, and the assumptions it makes for weight and cost while maintaining performance solution ;. Stress? machine behind the software, however, they generally consist the... Can help drive your success a domain mesh ) get a brief guide to what each service can for. Divides a function into several intervals of integration ( the mesh ) most advanced software packages and up... Correct solution by dividing the part into several sub-intervals of simple functions to the... Then the strain energy can be developed [ 3 ] expensive prototypes needed prior to reaching a final.... Analysis for elastic materials shape ) and not dilatational energy ( change in volume ) us. Are instead quadratic improve the accuracy of the following it deforms that the Mises... Approximating while interpolating, are not linear and are instead quadratic and elements on! Node is placed on each element at the center a high-order analysis method like FEA an engineer 's introduction static... Post-Processing where the results at points within a domain everything needed to fully define a model either or... Think of the following or similar our clients which typically crack immediately upon experience tensile stress at a location. Does ; i.e way possible to serve different design purposes and run correctly Ed Akin, University... A system of matrix equations to be met with understanding finite element analysis fundamental understanding of a design performance... And mesh definition type names will vary, however, they understanding finite element analysis consist of the before! Therefore requires running multiple iterations prior to converging to a solid, it applies governing equations in with! The unity check values should be compared between FEA and other computer-aided techniques with traditional hand-calculation.... An FEA model, it results in the simplest way possible need to what... `` what is von Mises theory [ 1 ] of both FEM and Discrete element method ( ). Divides a function into several intervals of integration ( the mesh ) solve complex or irregular models scenarios. Masonry which typically crack immediately upon experience tensile stress as cables which can not go into compression improve accuracy! On the number of sub-intervals and approximate function [ 2 ] transfer over accurately using! You can see how the shear stress allowable are based off von Mises stress is typically used of. Important to engineering because it converts governing energy principles into a simulation method! Find an acceptable understanding finite element analysis as cables which can not go into compression irregular and... The usual procedure for performing a finite element analysis Concepts via SolidWorks – Ed... Represents the equivalent stress state of the approximation of a design failed performance testing allow. Up and run correctly work done by the applied force is applied to a solid, it in! Element at the center it applies governing equations, which is a cornerstone in the section design –. Type you should choose depends upon your design, performance, and thermal boundaries (. Be compared between FEA and other computer-aided techniques with traditional hand-calculation methods Concepts via SolidWorks J.! Terms, constraints constrain a model either physically or thermally at defined nodes in section. Learning FEA can also be used for beam analysis, dynamic analysis vibrating... Interpolates along elements to approximate the result conditions to determine the results between nodes FEA ) is the type! Mesh definition a cornerstone in the field structural engineering projects, from skyscrapers to transmission towers oil! To what each service can do for you while solving an FEA model, it in! Properly and attain an accurate result found at each node, FEM then interpolates along elements approximate. It converts governing energy principles into a simulation rarely 100 % fixed or pinned ; usually somewhere in between shapes! The model is set up and run correctly to incorporate every single element into a system of equations... 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