Question

Mid-semester test MEC4426 Date: 17/04/2014 1. Briefly (one or two sentences) answer the following questions: (10 marks) a). What is an isoparametric element? b). What are the meanings of the Abaqus element codes T2D2 and C3D8R? c). The following figure shows a second order brick element for structural analysis with 20 nodes. What are the degrees of freedom at one node of the element? How many degrees of freedom does the element have? face 2 8 15 face 5 7 face 6 16 20 5 13 6 14 19 face 4 12 11 17 18 10 1 face 3 2. 9 face 1 20 - node element d). Why should we avoid using first order triangular and first order tetrahedral elements ? e). What is shear locking and what is hourglassing?

Answer 1

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Sulir 10) a) what is an iso parametric element ? isoparametric elements have curved sides. The Same shape function for the interpolation function is used to define the ric shape is also used to define the displacement of the element. Exampler 3 8 6 4 . s So when the edges are curred, there is a need for higher-order polynomials to represent the edges of the element, b) what are the meanings of the Aboqus element Codes T202 & C3DSR? sol? :) (3D&R in each element in Abaqus has a unique name where (3088 meaning is. C Continuum, 3-0 8-node and Ro Reduced Integration. There are all linear, reduced integration elements, a farsily of corresponding out C3D8R has only integration point, T202: Two node 20 truss element is simply called as 1202 _. This element is internally replaced by one a T3D2 element

and it is treated as such. This is obtained by inserting hinges in coch node ) the element, first overly sky and elements. If they d) why should we avoid using first ander triangular and first order tetrahedral elements? oreler triangular and detrahedral elements should be avoided as much as possible in stress analysis problems; the elements are on exhibit slow convergence with Mesta refinement, which is especially a problem with first-crdos tetrahedral are required extremely fine mesta may be needed to obtain results of sufficient acuracy. Second erder elements can capture stress concentratos more effectively and are better for modelling genebile features. what is shear locking le soll shear locking :- fully integrated linear bricks of Nastran, Abaque are overly styf in bending applicated and modal analysis. This numerical problem is called as Sheen booking fully integrated first order elements, such as Solid elements may suffer from locking. FEA Coules could therefore give false results when this type of element is used. what is haunglassing

Hourglassing : The use of the reduced eed-integration Scheme has a draudback. It can result in mesh instablity, which is most commonly called as Hourglassing. - The hourglas mole does not cause any hence does not contribute to the energy integral. It behaves in a manner that is similar to that of a rigid body mode. Example - Rubber block compressed diagonally by a sigid Sunface strainę please prolde thank you thembsup have a nice day!