Teachers Recruitment Board Tamilnadu Multiple Choice Questions for Mechanical Engineering

No cutting fluid is used in the following operation:
  1. Planning and shaping
  2. Broaching
  3. Honing
  4. Thread rolling
Answer:

Planning and shaping

Hint:

In planning and shaping operation, cast iron work piece machined. Graphite in the cast iron acts as a lubricant in itself. But machining cast iron will get you fine powders everywhere that tend to sneak into your machines nooks and corners and get lodged there. The stuff later becomes very difficult to remove especially after mixing up with machine lube or oil.

 

Which one of the following is not a decision taken during the aggregate production planning stage?
  1. Scheduling of machines
  2. Amount of labour to be committed
  3. Rate at which production should happen
  4. Inventory to be carried forward
Answer:

Scheduling of machines

Hint:

The aggregate planning is particularly useful for organizations that experience seasonal or other fluctuations in demand or capacity. Planners must make decisions on output rates, employment levels and changes, inventory levels and changes, back orders, and subcontracting. So Aggregate production planning is a short term decision making process.

  • It is usually possible to
  • hire or lay off workers
  • increase or decrease number of shifts
  • increase / decrease number of working days in a week
  • decrease or increase working hours (overtime or under time)
  • subcontract work to other firms
  • build up or deplete inventory levels

 

Which of the following is incorrect regarding template in layout design?
  1. Templates are three dimensional representation of machines (or) equipments
  2. Templates are virtual picture of layout
  3. Templates are used for storage areas
  4. Templates shows the area occupied by machine
Answer:

Templates are three dimensional representation of machines (or) equipment’s

Hint:

Two dimensional plan – Templates

Three dimensional plan – Miniature Models

 

Arrival rate of telephone calls to a telephone book is 9 minutes between two consecutive arrivals and length of the telephone call is assumed to be exponentially distributed with mean 3 minutes. The probability that a person will have to wait:
  1. 33
  2. 333
  3. 33
  4. 33
Answer:

0.333

Hint:

Here, N and Nq are the number of people in the system and in the queue respectively. Also W and Wq are the waiting time in the system and in the queue respectively. ρ is the ratio of arrival rate to service rate. Also the probabilities can be given as :

where, p0 is the probability of zero people in the system and pk is the probability of k people in the system.

Given:

Arrival rate λ = 1/9 minutes

Service rate μ = 1/3 minutes.

Probability that a person will have to wait

= (1/9)/(1/3) = 0.333

A dummy activity is used in PERT network to describe:
  1. Precedence relationship
  2. Necessary time delay
  3. Resource restriction
  4. Resource idleness
Answer:

Precedence relationship

Hint:

A CPM/PERT network consists of branches and node. The arrows in between the nodes indicated the precedence relationships between activities. A dummy activity inserted into the network to show a precedence relationship, but it does not represent any actual passage of time.

 

Slow cooling rate in solidification of casting results in:
  1. Fine dendrite with large arm spacing
  2. Coarse dendrite with large arm spacing
  3. Coarse dendrite with smaller arm spacing
  4. Fine dendrite with smaller arm spacing
Answer:

Coarse dendrite with large arm spacing

Hint:

Solidification mechanism is essential for preventing defects due to shrinkage. During solidification, cast forms develops cohesion and acquires structural characteristics. Since heat loss is more rapid near the mold walls than any other place, the first metal crystallizes called ‘nuclei’. Slow cooling makes the dendrites to grow long whereas fast cooling causes short dendrite growth. So slow cooling results in larger grain structure and fast cooling results in small grain structure in the solidified metal.

Finite Element Analysis | FEA

In this article Introduction to Finite Element Analysis is discussed. FEA is a computerized method for analysis / simulation for the engineering structures or Components. They are widely used in Automotive and various fields to replace the experimental design / testing.

Finite Elements in Analysis and Design

Finite Element Analysis is a way to simulate loading conditions on a design and determine the design’s response to those conditions. FEA is based on the idea of building a complicated object with simple blocks, or, dividing a complicated object into small and manageable pieces, application of this simple idea can be found everywhere in everyday life as well as in engineering.

FEA Elements

In FEM a complex domains divided / discretized into simple geometric shapes called “elements“.

FEA Nodes

The properties and the governing relationships assumed over these elements and expressed mathematically in terms of unknown values at specific points in the elements called “nodes“.

Finite Element Method

An assembly process used to link the individual elements to the given system. When the effects of loads and boundary conditions considered, a set of linear or nonlinear algebraic equations usually obtained.

Solution of these equations gives the approximate behavior of the continuum or system. The continuum (any system is considered for analysis) has an infinite number of degrees of freedom (DOF), while the discritized model has a finite number of DOF. This is the origin of the name, “Finite Element Method“. The number of equations is usually rather large for most real – world applications of the FEM, and requires the computational power of the digital computer. The FEM has a little practical value if the digital computer were not available.

Advances in and ready availability of computers and software has brought the FEM within reach of engineers working in industries, and even students.

Two features of the finite element method are worth noting:

  1. The piece-wise approximation of the physical field on finite elements provides good precision even with simple approximating functions.
  2. Simply increasing the number of elements can achieve increasing precision.One method to solve a wide variety of problems, including problems in Solid Mechanics, Fluid Mechanics, Chemical Reactions, Electromagnetic, Bio-mechanics, Heat transfer and Acoustics, to name a few.
FEA Model

A typical representation of a FEA model with reference to its original system is as shown below:

Why is FEA needed?

FEA needed for the following reasons –

  1. To reduce the amount of prototype testing
    1. Computer simulation allows multiple “what-if” scenarios to be tested quickly and effectively.
  2. To simulate designs that are not suitable for prototype testing
    1. Example: Surgical implants such as an artificial knee etc
  3. The bottom line:
    1. Cost savings
    2. Time savings
    3. Reduced time to market
    4. Create more reliable, better quality designs

List of Industries using FEA:

Following are the Industries using FEA-

  1. Aerospace
  2. Automotive
  3. Biomedical
  4. Bridges & Buildings
  5. Electronics & Appliances
  6. Heavy Equipment & Machinery
  7. MEMS – Micro Electro mechanical Systems
  8. Sporting Goods