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Hence, the displacement of the loaded edge will be infinite. The plate is 0.2-in. The difference between F(u_EX) and the physical property it represents is called the "modeling error". Bolts are modeled with point constrains and the p-element order reaches eight.

But two mistakes do not make it right. Because FEA results combine effects of two errors: the modeling and discretization error, which may nearly cancel each other, producing seemingly correct results. close Technologies3D Printing Adhesives Batteries/Power Supplies Bearings Cables, Connectors, Enclosures CAD Controllers Embedded Fasteners FEA and Simulation Hydraulics IoT Linear Motion Materials Mechanical Drives Metals Motion Control Motors/Drives Plastics and Composites It automatically assesses both modeling and discretization errors.

Proper application of the art and science of FEA involves assessing and controlling these two types of errors. But good correlation can be misleading and does not necessarily prove that the model is correct. The spring rate of 3.0 3 108 lb/in. It has been put in commercial FEA software only recently in a code called StressCheck from ESRD, St.

Maximum deflections? The hierarchical approach to controlling modeling errors can be automated in special cases like plate analysis in which a series of models are formulated with progressively less restrictive assumptions. To model the cantilevered plate, an engineer might argue that the bolt diameter is small in relation to the plate, so bolts-as-point supports is a reasonable simplification. For example, a model based on the linear theory of elasticity is a special case of a model that accounts for geometric or material nonlinearities, or both.

By simply scaling the load, one finds that 28,115 lb produces the yield stress of 36,000 psi and therefore plastic yielding. A Reissner model of a plate in bending assumes that all in-plane displacements vary linearly across the thickness and that shear strains are constant across the thickness. Is the strain energy of the exact solution finite and not zero? At the same time, a coarse mesh produces a large discretization error masking the conceptual error by underestimating deflections.

The term mathematical model refers to a theory such as the theory of elasticity, the Reissner theory of plates, or deformation theory of plasticity, and to the information that defines the For this reason, the cutoff point for the fringe plot is 36,000 psi. The elastic, perfectly plastic material should be replaced with a more realistic model along with assumptions of geometric linearity (small strains and displacements) and more realistic support conditions. The sketch indicates a deformed shape in the cantilever plate at bolt F2 magnified 100 times.

Your cache administrator is webmaster. When data of interest do not appear to approach limiting values, then either the discretization is still too large (too few elements or too low p-order) or the model is not Another indicator of a faulty model comes by plotting the reaction forces at the bolts versus the number of DOF when the prescribed displacement is applied to the right edge of Using higher plate models forces one to think about the meaning of a simple support, and whether or not it provides an accurate description of a physical system.

Generated Sat, 15 Oct 2016 19:37:16 GMT by s_ac15 (squid/3.5.20) ERROR The requested URL could not be retrieved The following error was encountered while trying to retrieve the URL: http://0.0.0.4/ Connection Generated Sat, 15 Oct 2016 19:37:16 GMT by s_ac15 (squid/3.5.20) It often happens that the formulated model is conceptually wrong. The first step in a finite-element analysis selects a mathematical model to represent the object being analyzed.

Numerical convergence tests, however, do not always detect singularities and cannot be considered a foolproof singularity spotter. The modeling error here is the use of point constrains which are incapable of generating nonzero reactions in the linear theory of elasticity. Similarly, the Reissner theory of plates is a special case of the full 3D representation, with infinitely many possible plate models in-between. The two errors can have opposite signs and may nearly cancel.

Consider a higher model, one that uses a more complex theory to imitate the real world. How should we represent support conditions? How to 'relax' a finite-element model: Part 2 The graph Displacement versus DOF shows that in the limit (increasing DOF), the strains will be infinite on an area of zero size. Your cache administrator is webmaster.

Strain hardening will increase this figure. Maximum stress? How to 'relax' a finite-element model Several finite-element models show how easy it is to make bad modeling decisions and how to control modeling errors using a systematic approach. Why?

The analysis goal is to compute information from the exact solution u_EX and then calculate information from it such as the maximum von Mises stress, which could be F(u_EX). thick and fasteners are 0.4-in. Consider a cantilever plate of a constant thickness supported by four bolts. Top 10 Tips CompaniesCompany Directory Product Locator Part Search Advertisement Home > Technologies > FEA and Simulation > How to Find Errors in Finite-Element Models How to Find Errors in Finite-Element

The lowest member of the hierarchy is the Reissner model, the highest is a 3D representation. For instance, a hierarchic family of models is available for isotropic and laminated plates in bending. By repeating calculations using progressively higher hierarchic models, one can gradually "relax" modeling assumptions until the results no longer change significantly. ScienceDirect ® is a registered trademark of Elsevier B.V.RELX Group Download PDFs Help Help ERROR The requested URL could not be retrieved The following error was encountered while trying to retrieve

Model 2: Springs for Bolts ID=SOL_LN Run=8 Fac.=Seq Max=6.1601e+04 Min=4.6981e+01 3.6000e+04 3.2002e+04 2.8000e+04 2.4000e+04 2.0000e+04 1.6000e+04 1.2000e+04 8.0000e+03 4.0000e+03 0.0000e+00 The graph indicates that reaction at the bolts converges to zero, an illogical conclusion. Assume plane stress conditions. The system returned: (22) Invalid argument The remote host or network may be down.

It's also a good idea to distinguish between apparent and real errors in FEA results.