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Viva Questions

1. Discuss the need for the finite element analysis.

2. Discuss the steps involved in Linear static finite element analysis. 3. List few commercial FE analysis packages. 4. Explain pre-processor, processor/solver and post processor in an FEA package.

5. Highlight the capabilities of Ansys package( version 10.0) 6. what does multiphysics stand for in Ansys package. 7. list few line elements, 2-D elements and solid elements. Sketch them

indicating their degrees of freedom. 8. sketch and indicate the degrees of freedom of following elements

a.) Bar element b.) 2-D truss element ( link1) c.) Beam3 d.) Beam4 e.) plane42 f.) solid 45 g.) pipe 16 h) Tetrahedron

9. What are the real constants for the above elements? 10. what do you understand by higher order elements. List a few of them.

11. 12. Explain the terms discretisation, node numbering and connectivity. 13. what do you understand by the term shape function. 14. Explain the procedure for obtaining element stresses and Shear force

and bending moments for line elements in ANSYS 15. what is the relationship between the degrees of freedom of an element

and the size of element stiffness matrix. 16. Explain types of displacement constraints.

17. Write the displacement constraints for a.Cantilever beam,b. Simply

supported beam,c.fixed beam,d.Proped cantilever beam 18. Explain statically determinate and indeterminate beams.

19. what happens when a body is not given displacement constraint in FEA? 20. Explain the terms aspect ratio, mapped mesh and free mesh.

21. Explain ax symmetric, bi-axial and single axial symmetry with examples.

22. How many independent constants does an isotropic material has?. What are they?

23. Write the relationship between Modulus of Rigidity,modulus of elasticity and Poisson’s ratio.

24. Explain Plane stress and plane strain problems.Give examples. 25. What do understand by the term Convergence studies?

26. Explain H convergence and P convergence 27. Write the basic formula associated with a.)Axial loading

28. b.)bending and c.) torsion and explain them.

29. What are the assumption in the derivations of the bending and torsion Equations.

30. What are the assumption in SOM? 31. What are the assumptions in Truss analysis.?

32. What do you understand by linear static analysis? 33. Explain shear force and bending moments.

34. Write SFD and BMD for the beam problems in the exercises .

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35. Can you obtain deflection in beams using double integration? 36. What stress is induced in a member subjected to free Thermal

expansion? 37. Explain principal stress, maximum shear stress and Von –Misses stress.

Important points

• Steps in FEM

Modeling. Discritisation of continuum. Selection of displacement model.

Derivation of element stiffness matrix. Assembly of algebraic equations.

Solution for unknown displacements. Calculate of element stress and strain.

• Plane stress

A thin planar body subjected to in-plate loading on its edge surface is said to be in plane stress. Here stresses σz, τxz, and τyz are set as zero.

• Plane strain If a long body of uniform cross section is subjected to transverse loading along its length, a small thickness in the loaded area can be treated as subjected to plane strain. εz, γzx, γyz are taken as zero. Stress σz may not be zero in this case.

• Principle of minimum potential energy. For conservative systems, of all the kinematically admissible displacement fields, those

corresponding to equilibrium extremize the total potential energy. If the extremum condition is a minimum, the equilibrium state is stable. Total potential energy (Π) = Strain energy (U) + Work potential (WP)

• Principle of virtual work A body is in equilibrium if the internal virtual work equals the external virtual work for every kinematically admissible displacement field (φφφφ,εεεε(φ)).

• Modeling : Creating the geometry. • Meshing : The given geometry is dicritised into Finite number of elements, each

element is connected with other element at a common point is called as node. • Dof : It is used to define the displacements (Ux, Uy, Uz) and rotations (Rx, Ry, Rz) at a

node.

• Shape function Shape functions are used to define the unknown displacement field and the geometry of

the element by using interpolated functions. • Isoparametric

Both the displacement u and the coordinate (geometry) x are interpolated within the

element using the same shape functions N1 and N2. This is referred to as the isoparametric formulation.

• Order of the element Used to incorporate complexity of the geometry. Order 1: Linear interpolation function

Order 2: Parabolic interpolation function Order 3: Cubic interpolation function

• Multipoint constraints

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The types of boundary conditions used in modeling inclined roller supports, rigid connections, or shrink fits are known as multipoint constraints. (Multipoint constraints of the type β1Qp1 + β2Qp2 = β0 where β0,β1, and β2 are known constants)

• Local coordinate system In the local numbering scheme, the two nodes of the element are numbered 1 and 2.

The local coordinate system consists of the x' axis, which runs along the element from node 1 towards 2. All quantities in this system will be denoted by a prime (').

• Global coordinate system

The global x-, y- coordinate system is fixed and does not depend on the orientation of the element. Note that x, y, and z form a right-handed coordinate system with the z-axis

coming straight out of the paper. Connectivity will be established by local and global coordinate systems.

• Assembly of matrix • Convergence criteria

To obtain the correct and accuracy of the results, increase the number of elements in

multiplication of two for each run. The results should converge for any two consecutive runs, further by increasing the number of elements, it is observed that there is no

significant changes in the results and is called as convergence criteria. • CST element

For constant strain triangle, the shape functions are linear over the element.

N1 + N2 + N3 = 1, where N1 , N2 , N3 are shape functions at node 1,2,3 respectively. • Different type Boundary conditions (Displacements)

1. Fixed 2. Roller 3. Cantilever

4. Overhang Force, moments

• Type of material properties 1. Isotropic 2.Orthotropic 3. Anisotropic

• Property data: Beam, shell

• Post results: Used to get the Deformations, stress contours, animation etc.,