Question

1. a What are the most important aspects to be considered in preparing reliability specifications?

b Write an outline reliability specification for (i) a domestic TV set, (ii) a fighter aircraft, and (iii) a gearbox bearing.

Answer 1

Answer

There are various important aspects which needs to be considered while making the reliability specification. Out of them all are given below step by step and in a detailed manner for easy understanding.

1. A QUALITATIVE STATEMENT FOR THE REQUIREMENT OF RELIABILITY

whenever there is reliability specification requirement, it should be defined quantitatively. And there are generally 4 basic ways in which the quantitative reliability requirement can be defined and as given below

• At the very first step mean time between failure is required, as the degree of failure always vary relative to the specified mean life
• Probability of survival over the time is required for the very delicate and important equipments and parts to know the exact reliability of that perticular specification
• Probability of success, actually probability of success is independent of time and generally used in the items which have launch reliability and used in missile and flights
• Failure rate

2. ENVIRONMENT

Reliability specification should consider all the impact of environmental factor which can affect the probability of failure of any part component or assembly. As environmental factors seriously affects the reliability of products and some environmental aspects are as given below

• Skills of operator
• Pressure
• Temperature
• Weather
• Shock
• Humidity
• Light of ambient
• Vibration

3. TIME MEASURES

Time is the independent variablle of the reliability function and in any reliability specification it is very important to specify the time requirement and the span of the perticular product to use it properly . If in some systems, if they are not used for continuos operation, in that case the time should be defined in term of duty cycle

4. DEFINATION OF FAILURE

All important functional parameters to be defined with the proper failure criteria and cause. It should also be included in the demonstration test of the product. This can defined the Go/No go strategy easily to pick the product by the customers easily. If in case the acceptance level is below the highest failure point, in that case product can be eliminated for the use can be decided accordingly

5.DEMONSTRATION OF RELIABILITY

only reliability requirement specification is not enough in any general case, one has to perform the specific tests also to know whether the specified specifications will meet the requirement or not. Reliability specification should also include these below point

• How to test the system
• Test will be conducted by whom means by government, contractor or by organisation
• When to perform the test means the stage
• Where to do the test means to specify the premise where test will be done

So all are the important aspects which need to be considered while making the reliability specification.

(b)

1. RELIABILITY SPECIFICATION OUTLINE FOR DOMESTIC TV SET

The reliability specifications can be given as per the requirements for the perticular product and are as given below: all the reliability specification tells about the success of product

• Light weight
• Low price
• High precise control
• Contamination resistance
• Low noise
• High reliability
• High response
• Ling life time

2. RELIABILITY SPECIFICATION OUTLINE FOR FIGHTER AIRCRAFT

• Probability of success
• Durability
• Life
• Fault diagnosis
• Ease of maintenance
• Specification for the speed
• Striking capacity during wars
• Development test and result data
• Structure load bearing capacity
• Ease of service
• Load capacity
• Understanding of physics behind the failure

3. RELAIBILITY SPECIFICATION OUTLINE FOR GEARBOX BEARING

• Life of bearing
• Dynamic load rating of the bearing
• Designed power at which it can be used
• Service life
• Load bearing capacity
• Maximum speed at which it can be used
• Bearing size
• Ease of maintenance
• No of cycles
• Material used
• Reliability
• Contamination specifics such as hardness, size and particle count
• Lubrication type and bearing geometry