Mechanical system design based on statistical considerations. This slide deals with statistics while designing any machine or a system.

1. Design review of any product/ system for
statistical consideration
Monday, November 11,
2013
Mechanical System Design
1
Presented By:
Kuwar Sushil Ashok(B-88)

2. 1.
2.
3.
4.
Some definitions and a review of statistic
Distribution curves
Design and natural tolerances
Factor of safety, Margin of safety,
Reliability and design based on reliability
5. Sampling distribution
Monday, November 11,
2013
Index
2
Presented By:
Kuwar Sushil Ashok(B-88)

3. Population: The entire group of apparently identical
components or elements under study.
Sample: The small portion of population selected for study.
Random variable: Characteristic to be studied.
• Frequency distribution
• Central tendencies
1. Mean
2. Mode
3. Median
Monday, November 11,
2013
Some definitions and a
review of statistics
3
Presented By:
Kuwar Sushil Ashok(B-88)

4. Normal curve
Standard normal
curve
• Random variable is ‘x’
• Mean is any value
• Standard deviation is
any value .
• Area under curve
represent population
• Random variable is ‘z’
• Mean is equal to zero
• Standard deviation is
always equal to ‘1’.
• Area under curve is
equal to ‘1’.
Monday, November 11,
2013
Distribution curves
4
Presented By:
Kuwar Sushil Ashok(B-88)

5. Design Tolerances: The specification limits set which is
some what arbitrarily by the designer from the
consideration of functional requirements and process
constraints.
Natural Tolerances: Limits within which not all but a given
allowable fraction of components will fail.
• Natural tolerances should be within design tolerances.
• Percentage of rejection depends upon the relation
between these two tolerances.
Monday, November 11,
2013
Design and Natural tolerances
5
Presented By:
Kuwar Sushil Ashok(B-88)

6. Factor of safety: The ratio of material strength (ultimate,
yield or endurance) to the working or allowable stress.
Margin of safety: The difference between strength and
stress.
Reliability: The probability that a component, system or a
device will perform without failure for specified period of
time under specified operating conditions.
Reliability based design: It takes margin of safety into
consideration to avoid the probability of failure. The
resultant curve is normal distribution curve.
Monday, November 11,
2013
Factor of safety, Margin of
safety & Reliability
6
Presented By:
Kuwar Sushil Ashok(B-88)

7. • If the number of samples are tested with their means to
be µ1, µ2, µ3, µ4 of each, then frequency distribution of this
population of means is called as “Sampling distribution
of mean”.
• Population and samples must be related for
satisfactory results.
Monday, November 11,
2013
Sampling distribution
7
Presented By:
Kuwar Sushil Ashok(B-88)

8. Monday, November 11,
2013
Thank you
very much…..!
8
Presented By:
Kuwar Sushil Ashok(B-88)

9. Monday, November 11,
2013
Questions…..!
9
Presented By:
Kuwar Sushil Ashok(B-88)