Basics in FEA

1. What do you understand by FEA?

Finite element analysis is defined as a numerical analysis method which provides solutions to problems that would otherwise be difficult to obtain. In simple terms, FEA is a faster way to get results to problems that are hard to solve. FEA uses software based numerical methods to analyse and understand the practical behaviour of parts which are subjected to any kind of internal or external load.

2. What are other similar techniques available & how are they different?

To solve the engineering problems, the techniques similar to Finite Element Analysis are ‘Real Time Solution’ and ‘Analytical Solution’. They are very different from FEA. In ‘Real Time Solution’ technique, to find solution on any engineering problem, the real time experimental data is used or studied, such as external forces practically applied on the beam. This method is time consuming and cost effective. In the other technique, the engineering problem is solved based on a formula that resembles the problem. This method of solving problem is called the analytical method and the solution obtained in analytical method is called as analytical solution. Comparing FEA to these techniques, FEA has better overall accuracy and it is less time consuming and it involves less cost.

3. What do you mean by linear & nonlinear analysis?

Linear Analysis – Linear analysis is a case where the Load - Displacement response is linear. There is a linear relationship between the applied forces and the response of the system. It is also called as linear static analysis because the load is not changing with respect to time or the load applied is constant and also there are no net forces or moments acting on a body. This also implies that the object is in equilibrium.

Non-Linear Analysis – A nonlinear analysis is an analysis where a nonlinear relation holds between applied forces and displacements. The non-linear analysis is performed when the stress and strain values are outside the yield point. It is basically performed on non-metals such as rubber or plastic as they do not have a relationship between stress and strain. This is a dynamic based analysis.

4. Where is nonlinear analysis needed?

Nonlinear analysis becomes necessary when the stiffness of the part changes under its operating conditions. Non-Linear Analysis is preferred when large deformations occur in a model due to dynamic loads. It is also preferred when there is contact between the parts. Basically the information comprised of ultimate loads, failure modes, and load-displacement relationships as well as any other required data can be obtained from materially nonlinear analysis.

5. What is the existing type of nonlinearity?

The types of nonlinearities are :

• Geometric nonlinearities – Geometric nonlinearities involve nonlinearities in kinematic quantities such as the strain-displacement relations in solids. Such nonlinearities can occur due to large displacements, large strains, large rotations, and so on.
• Contact nonlinearities – Contact can also be classified as a geometric nonlinearity because the area of contact is a function of the deformation. So contact nonlinearities also occur due to forces such as translation or rotation.
• Material nonlinearities – Material nonlinearities occur when the stress-strain or force-displacement law is not linear, or when material properties change with the applied loads.

6. What are Node & Elements?

Node – A node is a coordinate location in space where the degrees of freedom (DOFs) are defined. The results of a finite element analysis such as deflections and stresses are usually given at the nodes. These are the points where properties are to be determined for an element.

Element – The entities joining nodes and forming a specific shape such as bar, triangle or quadrilateral is known as finite element. Every element has one or more nodes. The elements are connected to each other at the nodes only. More the number of elements, more accurate are the results.

7. What types of elements are available in Hypermesh & application of the different type of elements?

The different types of elements available in Hypermesh are 1D elements, 2D elements, 3D elements and Special elements.

• 1D elements are used for modelling line-type members such as columns, piers, beams or poles.
• 2D elements are commonly used for plate-type members such as walls, slabs, shells, bridge abutments, tanks, domes.
• 3D elementsare used for structure with complex geometry which cannot be simplified for analysis.
• Special elements are usedto apply boundary conditions. For example special elements might include gap elements to specify a gap between two pieces of geometry.

8. What do you understand by 1d element & what are the special engineering applications of it?

When configurations of elements are expressed in terms of one coordinate only, then the element is termed as 1D element or line element.

1D elements have less number of nodes in the geometry compared to 2D and 3D elements. Each node has six degrees of freedom and hence 1D elements have less degrees of freedom compared to other elements. This results in smallest stiffness matrix which in turn results in a smallest computational time.

9. How you discretize a model?

Discretization is the process through which we can transform continuous variables, models or functions into a discrete form. In the process of discretization, we take the original geometry and divide it into individual elements or volume. Then the analysis is carried out for each of these elements.

10. How do you decide element size & density?

In order to establish suitable finite element size:

• Perform chosen analysis for several different mesh sizes.
• Notice where high deformations or high stresses occur, perhaps it is worth to refine mesh in those regions.
• Collect data from analysis of each mesh: outcome, number of nodes in the model, computing time

Mesh density is the number of elements per unit area in a mesh. Higher density meshes usually produce more accurate analysis results, but take longer to analyse.

11. What do u mean by stress concentration & how will you mesh for such regions?

The stress concentration in a body happens because of sudden change in the geometry of the body due to cracks, sharp corners, holes, decrease in the cross section area. Due to these irregularities, there is an increase in the intensity of stress in the body. To mesh the stress concentrated areas, we can reduce the factors that causes the stress concentrations, such as fillet the sharp corners, etc. or we can choose a finer mesh density for stress concentrated regions.

12. What are 2D shell elements?

A 2D shell is a one-dimensional element that has constant thickness and represents a shell. 2D shell elements are linear but can be curved or straight, much as a beam element would be in a 3D model. Basically shell elements are used to model structures in which one dimension, the thickness, is significantly smaller than the other dimensions.

13. What are 3D elements?

3D elements are usually used to mesh the volume of the part. They are derived from 2D elements are used when the problem is unable to be simplified. A 3D solid element can be a tetrahedron or hexahedron in shape with either flat or curved surfaces.

14. What is the difference between BAR, ROD and Beam?

Rod/Bar - The rods or bar is any member which is subjected to axial loads only. But rods are definitely circular cross section whereas bars may or may not have circular cross section.

Circular Rod Square Bar

A long structural member, mostly in a horizontal position, supported on one (fixed) or more supports and a load is placed on it at one or more points then the member is called a beam. It could be any cross section including circular, square or anything. However a specific cross section that has more material at the top and bottom gives a better strength to weight ratio. Hence most common beam is an I beam.

I Beam