Interview Questions

Uploaded on

27 Jul 2022

Skill-Lync

The interview is the final hurdle that every student has to cross before starting their career. The very thought of having to face a panel of experts fills every potential job seeker with trepidation. Interviewers can ask questions that are common knowledge or they could frame queries that require industry expertise.

To help you ease your nervousness before an interview, we have compiled a list of frequently asked FEA engineer interview questions and their answers. Over the years, Skill-Lync’s FEA engineering students have answered these questions and cleared job interviews with flying colors. Recommended by our industry experts, these answers will establish you as a candidate, who is a class apart from the rest.

**What are the most common problems we face on two-wheelers?**

- High Brake/Brake pad wear
- High tyre wear
- Very high fuel consumption
- Strong vibrations at high speed
- Electrical problems

**Difference between petrol and diesel engine?**

**Define compression ratio?**

Compression ratio is defined as the ratio of the maximum to minimum volume in the cylinder of an internal combustion engine

**Why does a diesel engine have a high compression ratio?**

Diesel engines have a higher compression ratio in order to obtain a higher temperature for self-ignition. The self-ignition temperature of diesel engines (210°C) is generally lower than that of petrol engines (247°C to 280°C). 28. Where do we use the diesel cycle?

Automobiles, farm and construction equipment, aircraft, power generators, diesel engines, and trains/locomotives employing diesel engines

**Why is a diesel engine not used in bikes?**

- A heavier engine to accommodate for a higher compression ratio
- More space requirements to accommodate sub-systems (Fuel injection system manifold vs spark plug)
- High torque and less RPM result in slow acceleration.
- Increased noise and vibration
- Periodically toggling off/on is not ideal for diesel engine
- Priming issues with fuel injectors

**What is the Otto cycle?**

The Otto cycle describes the functioning of the spark ignition piston engine. The development of the Otto cycle was instrumental in establishing the movement of the four-stroke engine.

The ideal Otto cycle has four steps: Two isentropic (reversible adiabatic) (compression and power stroke) processes alternated with two isochoric(ignition and exhaust stroke) processes.

- The piston pressures the gas between stages 1 and 2 (isentropic compression).
- Ignition of the gas moves the piston between stages 3 and 4 (isentropic expansion).

The difference between the energy produced by the two stages corresponds to the area enclosed by the cycle curve

**Can you explain and give an example of an adiabatic process?**

The adiabatic process is a thermodynamic process in which there is no heat transfer from in or out of the system. An adiabatic process is a reversible process with constant entropy for an ideal gas. The mathematical representation of the adiabatic process is ΔQ=0.

**Example:** Turbines used in power plants are great examples of adiabatic systems as they utilize heat as a source to produce work, so any heat lost to the surroundings would reduce their efficiency.

** **

**What is the Poisson Equation?**

The ratio of lateral strain to longitudinal strain is Poisson's ratio. It ranges from 0 to 0.5 for metals, 0/3 for steel, and 0.5 for rubber.

A higher Poisson's ratio reduces the stiffness of axial load

** **

**Can you comment on the Torsion equation?**

The torsion equation is defined as the geometrical property of a bar’s cross-section that is involved in the axis of the bar. It is the relationship between the angle of twist and applied torque. The SI unit for the torsion equation is m4.

The numerical representation of the torsion equation is as follows:

**What is the equation for bending moment?**

I = Moment of inertia exerted on the bending axis.

σ = Stress of the fibre at a distance

y from the neutral/centroidal axis.

E = Young's Modulus of beam material.

R = Curvature radius of this bent beam.

M=Bending Moment

**If a bar is fixed at one end torsion is applied from the other end what would be the torsional stress?**

This causes the shaft to twist as shown in (b) and the outer elements of the shaft experience maximum shear stress, tmax = (TR/J) where R is the shaft radius and J is the polar moment of inertia of the shaft.

**Values for specific density and Modulus of elasticity for steel and aluminium?**

Steel

Modulus of elasticity: 190-215 GPa.

Specific Density: 7750-8050 Kg/m3

Aluminium:

Modulus of elasticity: 67-73 GPa

Specific Density: 2640-2810 Kg/m3.

**Can you briefly explain the Factors of Safety?**

The ratio of ultimate stress to the permissible stress

** **

Factor of safety = ultimate stress / permissible stress.

** **

The factor of safety, also known as Safety Factor (SF), is a term describing the structural capacity of a system beyond the expected load or actual load.

** **

**For Example: **

A bridge is made and it is required to carry a weight of vehicles up to 50 KN. But when the bridge is made it is made in such a way that it can carry vehicles of weight up to 100 KN, so we will say that the bridge has a safety factor of 2 (100 KN / 50KN).

** **

**What is the bulk modulus of elasticity?**

The ratio of direct stress to volumetric strain

** **

When a body is subjected to mutually perpendicular and equal direct stresses, the ratio of direct stress to the corresponding volumetric stress and strain is found to be constant for a given material when the deformation is within a certain limit. This ratio is known as the bulk modulus.

** **

**Define Strain Energy?**

** **

By the principle of work, the amount of strain energy in a body is found. When a load acts on a body there will be deformation, which causes movement of the applied load. This load is defined as strain energy.

** **

**What is the term for materials that have the same elastic properties in all directions?**

** **

Isotropic Materials

** **

**Explanation:**

**Note: **

- Isotropic refers to the properties of a material which is independent of the direction (e.g. Metals, Glass)
- whereas anisotropic is direction-dependent (e.g. woods)

** **

**Please provide an explanation of the different points in the stress-strain graph**

** **

The stress-strain graph represents the stress value against the strain value of the given material when the material is subjected to increasing pull from any of the cardinal directions.

There are mainly six points in the graph.

**Proportional limit:**It is the point up to which Hooke's law is applicable ie., stress is directly proportional to strain.**Elastic limit:**The limiting value of load up to which strain completely disappears on the removal of load. All materials possess elastic nature and exhibit properties until the elastic limit.**Yield point:**The stress after which materials become plastic and the load after which the permanent deformation of material starts.**Ductile point:**The point beyond which a neck forms at the local cross-sectional area.**Ultimate point:**The point beyond which material can withstand maximum load and ultimate strength with maximum elongation. The absolute maximum load that a material can withstand before large deformations occur resulting in failure.

**What are the ways materials can be classified in LS-Dyna?**

Materials can be classified based on the stress-strain graph.

- Elastic materials within the elastic limits
- Brittle materials where failure happens just beyond the
*max*elastic limit - Elastoplastic materials like steel and aluminum have a nonlinear plastic curve after the young’s modulus
- Hyperelastic materials which have 100 % strain like rubber

For these materials to be given as input in LS Dyna there are multiple material laws which:

MAT Elastic (1) is used for applications under the elastic limits with input parameters such as Elastic Modulus, Density, and Poisson’s Ratio.

MAT_Piecewise_Linear_Plasticity (24) for applications for elastoplastic (Steel, aluminum) materials beyond the elastic limit.

MAT_SPOTWELD (100) when defining spot welds with beam or solid elements with input data with failure criteria.

MAT_Ogden_Rubber (77) for Hyperelastic materials like rubber which has more than 100% strain with specimen dimensions.

**What is element formulation 16 in LS Dyna?**

Elemental formulation 16 is for fully integrated shell elements. The presence of 4 integration points improves the accuracy of the FEA analysis. When compared to a computational analysis method that only has one integration point the element formulation method is time intensive.

The elemental formulation 16 for a solid element is a tetrahedron with 10 nodes. Since there are 10 nodes in this element, all additional nodes will be formed on the edges of the mesh. The total nodes in a tetrahedron with 10 nodes is lesser than that of a regular tetrahedron with 4 nodes and so the time step is reduced.

**Can you comment on a head impact using the FEA tool LS-Dyna?**

This answer to this question can be simplified by using the standard model of a human head and a meshed car hood. The head impact simulation is further simplified by providing velocity to the model of the head instead of the car and the necessary boundary conditions are applied to the car hood. The head model is oriented so that it resembles a real impact. Head Impact Coefficient (HIC) is measured for the impact and is compared with standard references to estimate the severity of the injury.

**How will you define mesh for 2D and 3D components?**

2D components imply surfaces without thickness. The mid-surfaces in a 2D mesh are selected for the components if the thickness to area ratio is 1:20. The mid-surfaces are cleaned after considering the quality criteria.

The best way to create 3D meshes is to initially mesh the surfaces of the 3D components with 2D elements (quad and trias) and use this 2D mesh to generate a structured or unstructured mesh.

**What are the criteria which determine the quality of a mesh?**

Some of the mesh Quality Criteria

**Aspect Ratio:**It is the ratio of the maximum length to the minimum length of the element**Skewness:**It is the internal angle measured for a distorted element from the ideal element shape.**Warpage:**It is the angle of plane deviation in the element when the element is on a curved feature and the element is following the feature.**Minimum Length:**It is the minimum length of the element that can be present in the meshing of the component.**Jacobian:**It is the value by which the transformation matrix of the ideal element is compared to the transformation matrix of the distorted element in the natural coordinate system.

**What are the types of mesh elements?**

Mesh elements are based on dimensions:

1D elements like a bar element have two nodes and each node has 6 Degree Of Freedom(DOF) which is the limit an element can flex before snapping at the point of stress.

2D elements: There are two elements in the 2D mesh. Tria, is a triangle with three nodes. Quad, which is a quadrilateral with four nodes. Each of these two elements each has six DOF

3D elements: There are two elements in the 3D mesh as well. Hexa, is a brick element with eight nodes. Tetra, is a tetrahedron with four nodes. Each of these two elements has three DOF.

**What is the difference between structured and unstructured mesh?**

**Unstructured Mesh**

Unstructured meshes are meshes with general connectivity whose structure is arbitrary (random) and hence the connectivity between the elements must be defined and stored. The unstructured element types have triangular elements (2D) or tetrahedral (3D) elements

**Structured Mesh**

Structured meshes are meshes with implicit (absolute) connectivity whose structure allows for easy identification of elements and nodes. The structured meshes have quadrilateral elements (2D) or hexahedral (3D) elements.

**What are under-defined and fully defined elements?**

Under-defined: In these elements, a reduced number of integration points are used to decrease the computation time. This simplification generates zero energy deformation modes, called hourglass modes.

Fully Integrated: Elements with a higher number of integration points

**What do you know about Hypermesh?**

Hypermesh is an FEA preprocessing software where the CAD model is cleaned such that the model resembles the original CAD model. A mid-surface is then created from sheet metal or plastic components followed by 2D meshing that confirms to certain predetermined quality criteria.

**What is ANSA used for?**

ANSA stands for Automated Net generation for Structural Analysis, It is used for discretizing a CAD model after importing and cleaning the model.

**Is morphing possible in ANSA?**

Yes, Morphing is possible in ANSA using a morphing deck.

**What is morphing?**

Morphing is a process by which the shape of the model (CAD or FEA model) can be adjusted or changed.

**What is contact thickness?**

Contact thickness can be defined as the distance between two surfaces below which contact is calculated. It can also be defined as the combination of the thickness of the shell components when they are in contact with each other.

**How to define the thickness of contacts**

The thickness of the contacts can be defined using options available in the contact parameters in the respective solvers.

**Ansys**: Defining the pinball region can help set the contact thickness below which the parameters are considered.

**Radioss**: Engineers should define the gapmin value. After which initial contact thickness can be used for contact initiation.

**LS Dyna**: SST in the contact cards is used to define the thickness for the slave and master components which overrides the true thickness of shell components for contact thickness.

**What is mass scaling?**

Mass scaling is a technique in which non-physical mass is added to a structure in order to achieve an explicit timestep.

Mass scaling is used to increase the time step size in each cycle by reducing the processing load of the CPU while increasing the performance.

Examples of such cases may include the addition of mass to a few small elements in a non-critical area or quasi-static simulations in which the velocity has a low value and the kinetic energy is small relative to the peak internal energy.

In the end, it's up to the judgment of the analyst to gauge the effect of mass scaling. The engineer might have to eliminate mass scaling to determine the sensitivity of the results against the mass that has been added.

**What is the time step?**

The time step is the incremental change in time for which the governing equations are being solved.

Engineers should adjust the steps of analyses according to the loads, conditions, and response frequencies of a system.

Engineers can adjust the application of loads and conditions by toggling them on or off on time steps. This helps engineers derive precise values for the questions being solved.

There are four different types of time steps:

- Auto time stepping: Used in nonlinear and dynamic loads and responses.
- Initial Time Step.
- Maximum Time Step
- Minimum Time Step

**What are FMVSS regulations?**

FMVSS stands for Federal Motor Vehicle Safety Standards

FMVSS aims to protect the public by minimizing vehicle crashes, injuries, and deaths.

Vehicle manufacturers are required by the stipulations of The Vehicle Safety Act to certify their vehicle or equipment to demonstrate FMVSS compliance.

Some of the FMVSS norms that vehicle manufacturers have to abide by are:

201: Occupant protection in interior impact

208: Occupant crash protection

209: Seat belt assemblies

218: Motorcycle helmets

**Briefly discuss the various types of mesh contacts.**

Based on Behavior

- Bonded
- Frictionless
- Frictional
- No-separation
- Rough

Based on Contact points

- Tied interface
- Node to Node/ Node to the Surface surface (General Purpose contact)
- Edge to Edge contacts

We hope that this compilation of FEA interview answers will help you achieve your career goals.

These are just 35 potential FEA interview questions that you might be asked when applying for the position of an FEA analyst. The competition for an FEA analyst is intense and you will be competing with engineers across the country for top jobs. One of the ways to stand out from the competition is to showcase your expertise in software and tools used by engineering firms in this industry.

This is where having practical-oriented meticulous training becomes crucial. Skill-Lync’s Post Graduate Program in Finite Element Analysis is a 26-week intensive program that will train you in the fundamentals of FEA. Our program has been designed to help you start your career in the FEA domain in just 45-days.

In this program, you will train in the preprocessing software tool Hypermesh and improve your understanding of Partial Differential Equations and how it applies to various element types. You will learn how to create mid-surface, clean up the geometry of components, and apply 1D,2D, and 3D mesh elements. Our course modules will help you develop a portfolio of industry-relevant projects like the meshing of a door panel or the meshing of a car spare tyre floor panel.

Skill-Lync students benefit from the numerous mock interviews conducted by our in-house experts. With our rigorous training, you will be able to answer any interview question that comes your way with confidence.

There are only a limited number of seats allocated for this offline program in FEA.

Author

Anup KumarH S

Author

Skill-Lync

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