Definition Of Terms-fea

Definition of Terms 1. Aspect ratio - the ratio of measurements (length to width, for example) of an element must be within certain limits to ensure accuracy. 2. axisymmetric - element type that can be used to model a solid of revolution. Can only be used when geometry, material, constraints, and loads are all axisymmetric. 3. Beam element - element whose geometry is defined by a curve, cross-section is input by user as a property 4. Brick element - type of solid element defined by the volume between six faces (cubeshaped). In H-codes, these elements are more accurate than tetrahedral elements. This is not the case for the P-method. 5. Composite shell - common element used to model sandwich composite materials. Material properties may be defined on multiple layers, with different orthotropic properties within each layer. Used often in the aerospace industry. 6. Convergence - the act of honing in on the correct answer in a numerical simulation. In the H-version of the FEA method, this is a difficult, manual process of mesh refinement. In Pro/MECHANICA, it is automatic, achieved by the selective raising (adaptive Pmethod) of polynomial orders of the approximating equations. 7. degree-of-freedom (dof) - name given to the freedom of movement for an object in any given direction. Any unconstrained object has six degrees-of-freedom (translation in three directions and rotation in three directions). 8. gap element - element used in H-codes that allows for contact between two bodies. 9. H-method - original version of the finite-element method. Elements are flat-edged and flat-faced, giving faceted representation of geometry. Accuracy is dependent upon mesh size and shape. 10. Element - one individual piece used in a finite-element analysis model. 11. Geometric nonlinearity - type of nonlinearity in structural analysis caused by large deformation. If the geometry changes enough during the course of the analysis, the stiffness will also change (even if the material property does not). Imagine a thin piece of sheet metal. It may stay within the linear range of the material property, but still show a

large deflection. This results in nonlinearity because the stiffness (which is a function of both material and geometry), changes during the simulation. 12. Material nonlinearity - type of nonlinearity in structural analysis caused by nonlinear relationship between stress and strain for the material used. The material property (Young’s Modulus) changes over the course of the analysis, and cannot be input as one number. This can be caused by a material (such as a metal) being loaded above it’s yield stress value. It can also be caused by a material that has an inherently nonlinear stress-strain curve. This nonlinearity requires an iterative solution (performed in many steps). 13. Matrix algebra - a form of mathematics where sets of simultaneous equations are represented by rows and columns of numbers. 14. Mesh - collection of finite-elements that together represent a geometric body for FEA mid-plane compression - the act of transforming a thin-walled solid CAD model into a surface model, located at the mid-plane of the solid, ready for shell meshing. 15. Nonlinear - term used to describe a function whose slope is not constant. The graph of such a function is not a straight line. In structural analysis, used to describe a problem where the relationship between load and deflection is not constant. This usually occurs when the stiffness (K) of the structure changes over the course of the simulation. The problem must usually be solved in an iterative fashion, updating the stiffness along the way. Nonlinearity is common in contact problems, problems with certain materials, and problems with large deflections 16. P-method - polynomial-based version of the finite-element method. Elements are geometrically represented by polynomials (curved edges and faces) to more accurately represent the geometry. Accuracy is not dependent upon element size and shape, because convergence is achieved automatically. 17. Optimization - design study where software automatically finds the best design 18. Sensitivity - design study where multiple solutions are performed for a problem, each using a variation on the model. Results are graphs that illustrate which design variables are important.

19. shell element - element whose geometry is defined by a surface, thickness is a userdefined property, good for thin-walled structures 20. Solid element - element whose geometry is defined by a volume, good for bulky structures 21. Symmetry - term used to describe using part of the geometry of a model (1/2, 1/4, etc.) to simulate a situation that is equal on either side of an imaginary plane. Special boundary conditions are required along the symmetry planes. 22. Tetrahedral element - solid element defined by the volume between four faces (pyramid-shaped). In H-codes, these elements are generally not as accurate as brick elements. They are widely used, however, because automatic meshing schemes create tets more easily than bricks. 23. Two-dimensional element - element whose geometry is defined by a 2-d area. Represents a solid whose cross-section is unchanging in the direction into the page. Can be used for linearly extruded cross-section solids or axisymmetric solids of revolution. Only valid if geometry, loads, and boundary conditions are symmetric.