FEA Interview questions in Strength of materials

      1.Why we need to study the Strength of material subject?

·         Strength of materials, also called mechanics of materials, is a subject which deals with the behavior of solid objects subject to stresses and strains.

·         To predict the response of a structure under loading condition and its susceptibility to various failure modes.

·        Predicting  properties of the materials such as  yield strength, ultimate strength, Young's modulus, and Poisson's ratio by various method

·       Helps calculate the stresses and strains in structural members, such as beams, columns, and shafts.

2. What is Load? Its classifications?

·         A load is defined as combined effect of external force acting on a body.

Classification of loads.

·         Point load

·         Distributed load

Other classification is

·         Tensile load

·         Compressive load

·         Torsional or twisting loads

·         Bending loads and shearing loads

·         Static load

·         Dynamic load

3. Classification of structure based on the type of load they resist?

·         Bar- Resist axial loads both tensile and compressive

·         Beam- Resist transverse loads

·         Truss (Collection of bars) - Resist axial loads both tensile and compression

·         Shaft- Resist torsional loads

·         Columns- Resist axial compressive loads only

4. What is mean by rigid body?

·         A rigid body does not undergo any deformation.

·         It is hypothesis only. In real life all bodies are elastic and deformable up to a certain limit.

      5. Define an elastic body.

·         The strains which disappear with the removal of load, this type of body is called elastic body.

      6. Define stress.

           

                 The internal resistance which the body offers to meet with the load is called Stress.

                                

           Ratio between Internal resisting forces per area perpendicular to the direction of force.

                                       σ =P/A

7.What type of stresses occurring in a structure?

    1.       Direct stress or simple stress

o   Tension stress

o   Compressive stress

o   Shear stress

2.       Indirect stress

o   Bending stress

o   Torsional stress

3.       Combined stress

      8. What is shear stress?

·         Ratio of Internal resisting force (shear force) to area parallel to the direction of force.

Ratio between Internal resisting forces per area perpendicular to the direction of force.

                                       τ=V/A

       9. Explain strain.

           Deformation produced by the stress

               

          Ratio of Change in length to the original length.

          Normal strain = Change in length / original length    

                      ϵ  = δL / L

           Where,

             ϵ - Normal strain

             δL - Change in length

              L   - Original length     

10. Various types of strain.

·         Tensile Strain

·         Compressive strain

·         Shear strain

·         Volumetric strain

Engineering mechanics interview questions

              1. What are the various Types of friction?

                         Dry friction or Coulomb friction
                         Fluid friction
                         Lubricated friction
                         Skin friction
                         Internal friction

              2. Characteristics of dry friction?

 Friction is a force that resists the movement of two contacting surfaces that slide relative to one another.

This force always acts tangent to the surface at the points of contact and is directed so as to oppose the possible or existing motion between the surfaces.

             3. Friction is depends on Degree of roughness and area of contact?

                      No, friction force independent of these two.


              4. What is limiting friction?

                     The maximum resistance offered by the body is called limiting friction.

              5. What is coefficient of friction?

                      Ratio of limiting friction to the normal reaction.

                         Co-efficient of friction µ=Limiting friction /Normal reaction

              6. What is angle of friction?

                    Tangent of ratio of limiting friction to the Normal reaction.

                    tanɸ = limiting friction/Normal reaction

             7. What is meant by impending motion?

Just about to move or slide is called impending motion.

When the maximum frictional force is attained and if the applied force exceeds the limiting friction, the body start to slide or roll, that motion is called impending motion.

             8. Angle of repose?

The plane at which the body tends to slide down is known as angle of repose.

             9. State parallel axis theorem?

The moment of inertia of an area around any axis in its plane is equal to the moment of inertia of the same area around a parallel axis passing through the area’s centroid, plus the product of the same area and the square of the distance between the two axes.

I=I_G+Ah²

            10. State perpendicular axis theorem?

If I_xx is the area moment of inertia of a lamina about x-x axis in the plane of the lamina and I_yy is the area moment of inertia of a lamina about y-y axis (Perpendicular to the x-x axis) in the plane of the lamina, then I_zz, the polar area moment of inertia of the lamina about an axis perpendicular to the plane of the lamina (and perpendicular to the x-x axis and y-y axis) is given by

I_zz=I_xx +I_yy

            11. Write general equation for finding area moment of inertia?

I_xx=y²dA                        I_yy=X²dA

           12. Write general equation for finding area moment of inertia?

J=r²dA

Where

r-radius of the circle.

FEA interview questions in Engineering mechanics

1.Define: Moment of a force

• Moment of force is the Product of magnitude of force and distance between line of action of force, point about which the force causing rotation.

2.What is moment of inertia?

• Moment again multiplied by distance between line of action of force point about which the force causing rotation.     
• The moment of inertia which forms the basis of dynamics of rigid bodies and strength of materials.

3.What is area moment of inertia? What is it significance and its conjunction?

• Moment of inertia for plane figures is called area moment of inertia.
• When examined by itself there is no physical important for moment of inertia. It’s a just mathematical expression usually denoted by I.
• Structural meaning of Moment of inertia Measure ability of the beam to resist bending.
• Area moment inertia is conjunction with deflection or deformation.

4.What is mass moment of inertia? And it’s the structural meaning?

• Moment of inertia for Solid or 3D figures is called mass moment of inertia.it is conjunction with rotation of rigid bodies.
• Structural meaning of mass moment of inertia Measure of resistance of a body to rotation.

5.What is Polar moment of inertia? And it’s the structural meaning?

• Polar moment of inertia is equal to the sum of area moments of inertia about any two mutually perpendicular axes in its plane and intersecting on the polar axis.
• Structural meaning of Polar Moment of inertia Measure ability of the Shaft to resist torsion

6.What is Radius of gyration or radius of rotation?

Distance from that axes at which all the elemental parts of the lamina would have to be placed

                   

  r =√ I/A

       Where,

                   r – Radius of gyration

                   I – Moment of inertia

                   A – Area

7.What is centroid?

• The point where the whole area of the figure is assumed to be concentrated.
• It is also called as Centre of area.
• Which is same as Centre of gravity when the bodies have area only and not weight.
• The weightless lamina’s, plane figures have Centroid.

8.What is centre of gravity?

• The point through the whole weight of the body assumed to act.
• The position of the c.g depends upon the shape of the body. C.g may be within the boundary of the body or outside of the boundary of the body.

9.How to determine centre of gravity of object?

  There are two methods to find the centre of gravity.

1. Balancing method
2. Suspension method

FEA interview questions in Engineering mechanics

1. What is force?

• A force can affect both the motion and the deformation of the body on which it acts. Forces may arise from direct contact between bodies, or they may be applied at a distance (such as gravitational attraction).
• Contact forces are distributed over a surface area of the body, whereas forces acting at a distance are distributed over the volume of the body.

2. Classification of force?

3. What are Characteristics of a force?

There are two Characteristics of force.

Magnitude

Direction

This makes force as a vector quantity. Having both magnitude and direction.

4. What is meant by Resultant Force?

N number of the forces acting in a system, can be replaced by a single force, Which could produce the same effect as produced by the all the forces, that single force is called resultant force.

5. State Lami's theorem?

• If three coplanar, concurrent and non-collinear forces acting on a particle keep it in equilibrium, each is proportional to the sine of the angle between the other two.
• According to the theorem, where A, B and C are the magnitudes of three coplanar, concurrent and non-collinear forces, which keep the object in static equilibrium, and α, β , γ are the angles directly opposite to the forces A, B and C respectively.
A/sinα =B/ sin β = c/ sin γ

6. Triangle law of forces?

Triangle law of forces states that, If two forces acting at a point are represented in magnitude and direction by the two adjacent sides of a triangle taken in order, then the closing side of the triangle represents the resultant of the force.

7. Polygon law of forces?

If a number of forces acting at a point be represented in magnitude and direction by the sides of a polygon in order, then the resultant of all these forces may be represented in magnitude and direction by the closing side of the polygon taken in opposite order.

8. What is the procedure to draw the free-body diagram?

• Isolation of a part from the system
• Show all the forces acting on the part
1. Active forces – tends to set the particle in motion.
2. Reactive forces – Results of constraints or supports that tend to prevent motion.
• Identify each forces
1. The forces that are unknown must labeled with their proper magnitude and directions.

FEA Interview Questions in Engineering Mechanics:

1. What is mechanics and its classifications?

• Mechanics is a branch of the physical science that is concerned with the state of rest or motion of bodies that are subjected to the action of forces.
• In general, this mechanics can be classified as below:

2. What is rigid body?

A rigid body can be considered as a combination of a large number of particles in which all the particles remain at a fixed distance from one another, both before and after applying a load.(No deformation)

In most cases the actual deformations occurring in structures, machines, mechanisms, and the like are relatively small, and the rigid-body assumption is suitable for analysis.

3. State: Newton’s Three Laws of Motion.

First law:
• If a particle is at rest (or moving with constant velocity in a straight line), it will remain at rest (or continue to move with constant velocity in a straight line) unless acted upon by a force.

Second law:

• A particle acted upon by a force will accelerate in the direction of the force. The magnitude of the acceleration (a) is proportional to the magnitude of the force(F) and inversely proportional to the mass (m) of the particle.

F=ma Where F - Applied force M - Mass of the particle A- Acceleration of the particle

Third Law:

• For every action, there is an equal and opposite reaction; that is, the forces of interaction between two particles are equal in magnitude and oppositely directed along the same line of action.

4. What is equilibrium of a particle or system?

• A particle is said to be in equilibrium if it remains at rest if originally at rest, or has a constant velocity if originally in motion
• Static equilibrium” is used to describe an object at rest.
• To maintain equilibrium, it is necessary to satisfy Newton’s first law of motion, which requires the resultant force acting on a particle to be equal to zero.
• This condition may be stated mathematically as
  
  ∑F = 0
  

5. What is the difference between scalar and Vector?

A scalar is a quantity that has magnitude only.	A vector is a quantity that possesses magnitude and direction and obeys the parallelogram law.
E.x. Length, Mass, Pressure	E.x. Weight, Force

6. What is free body diagram?

• A free body diagram is a graphical illustration of an isolated section or member of a part or a system.
• Used visualize the applied forces and moments and resulting, reactions, on a body in steady state condition (not in accelerated condition).
• Free body diagram must satisfy the equations of static equilibrium in the principles of statics.

7. What is moment?

• When a forces are applied to the body, it rotate about a Center point which is not in the line of action of force is called moment.
• This tendency is called “torque”.

Moment=force Χ distance which is perpendicular the direction of force

M= Fd

Where, M- Moment F- Force d- Distance which is perpendicular the direction of force

8. What is couple?

• Two parallel, noncollinear forces that are equal in magnitude act in opposite direction is called couple .
• Its effect is to produce pure rotation or tendency for a rotation in a specified direction.
• Resultant force value of a couple is zero.

9. What is Friction?

When two surfaces are in contact with each other one surface tend to move with respect to the other, tangential force will be developed at the contact surface in the opposite direction of motion is called friction.

10. Friction is advantage or disadvantage? Justify?

Friction force has both advantage and disadvantage.

Advantage:

• Friction between floor and feet, Enable us to walk on floor(less friction makes us to slide)
• Friction between road and Vehicle, help us to ride vehicles on road.
• Transmission of power using belt…and the like.

Disadvantage:

• Wear between components in a system
• Tear
• Loss of power, Loss of energy…etc.

Finite element method

Finite Element Method (FEM)

Finite element method is modern method to solve Physical problems in Aeronautical, Automobile, Bio mechanical, Civil, Electromagnetic, Mechanical, Mining, Nuclear, Ocean….Engineering and the relevant field. But, Finite element method is widely used for Structural engineering problems.

The finite element method involves modeling the structure using small interconnected elements called finite elements. This process is called discretization or meshing.

Finite element Method has three steps to solve any Physical problem

Viz

1. Preprocessing
2. Processing
3. Post processing

or

1. Defining problem by Finite element model
2. Solving or solution
3. Interpreting the results or reviewing the results

Pre Processing

1. Model Designing
2. Discretization or Meshing
3. Selection of elements
4. Geometrical properties (For 1-D, 2-d)
5. Material selection
6. Constrains or Boundary conditions
7. Loads
8. Type of analysis

Processing or solution

There are two general direct approaches used in the finite element method as applied to structural mechanics problems to get Solution. i.e.

1. Force or flexibility method
2. Displacement or stiffness method

Force or flexibility method

Internal forces as the unknowns of the problem. To obtain the governing equations, first the equilibrium equations are used. Then necessary Additional equations are found by introducing compatibility equations. The Result is a set of algebraic equations for determining the redundant or unknown forces.

Displacement or stiffness method

Displacements of the nodes as the unknowns of the problem. For instance, compatibility conditions requiring that elements connected at a common node, along a common edge, or on a common surface before loading remain connected at that node, edge, or surface after deformation takes place are initially satisfied. Then the governing equations are expressed in terms of nodal displacements using the equations of equilibrium and an applicable law relating forces to displacements.

Most of the Finite element software programs uses the Displacement or stiffness method to solve the Problems.

During the solution phase, finite element software assembles the governing algebraic equations in matrix form and computes the unknown values of the primary field variable(s).

The equation is

[k] [u] = [F]

Where

K- Stiffness matrix from material property and geometrical shape

u- Results needs to be calculated (Unknown)

F- Applied force

S.no	Domain	Property [K]	Result [u]	External action [F]
1	Structural	Stiffness	Displacement	Force
2	Thermal	Conductivity	Temperature	Heat source
3	Fluid flow	Viscosity	Velocity	Body force

The computed values are then used by back substitution to compute additional, derived variables.

• Reaction forces
• Element stresses
• Heat flow

As it is common for a finite element model to be represented by tens of thousands of equations, special solution techniques are used to reduce data storage requirements and computation time.

Post processing

Evaluation of the solution results is referred to as post processing. Postprocessor software contains sophisticated routines used for sorting, printing, and plotting selected results from a finite element solution.
Various operations in the post processing

• Visualization of Deformed structure
• Displacements magnitude in three directions
• Nodal stress magnitude
• Element stress magnitude
• Check equilibrium
• Factor of safety
• Strain energy
• Natural frequency
• Amplitude
• Time history
• Thermal stress and strain
• Plot deformed structural shape
• Animate dynamic model behavior
• Produce color-coded temperature plots

While solution data can be manipulated many ways in post processing, the most important objective is to apply sound engineering judgment in determining whether the solution results are physically reasonable.

Generally in FEA industry two terms are in normal usage about the analysis results:
Garbage in and garbage out. The finite element method software program will solve the given input. But, it can’t justify the results.

List of popular FEA software’s according to its purposes

Preprocessing tools

• ANSA
• HyperMesh
• Patran

Processing tools

• Abaqus
• ADINA
• Algor
• ANSYS
• COSMOS
• LS-Dyna
• MSC/NASTRAN
• NISA
• Optistruct
• RADIOSS
• SAP
• STARDYNE

Postprocessing tools

• Hyperview
• µETA