A slideshow about operating conditions and their effects on Reliability . the emphasis is to comprehensively identify various operating conditions and their effects on the strength, hence reliability of an element / system. the conclusion is that the stress and stress overlap must be avoided. The slides are based on a NASA Technical Memorandum.

1. Effect of Operating Conditions
on
Reliability of an Equipment
Major General Prabal C Sen
Major Genral Prabal C Sen

2. Effect of Operating Conditions
on
Reliability of an Equipment
Aim
To expose students to the effects of operating conditions on
reliability
A NATO Technical Memorandum on preferred reliability practices
&
The Report by a Commission to investigate Space Shuttle Challenger
accident
have been usedMajor Genral Prabal C Sen

3. Severe
Operating Conditions
Twenty Severe Conditions
As listed by
National Aeronautics & Space
Administration
USA
( NASA Technical Memorandum 106313 )
Major Genral Prabal C Sen

4. NASA/TM-106313, NASA TECHNICAL MEMORANDUM (TM)
DESIGN FOR RELIABILITY
NASA reliability preferred practices for design and test can be
downloaded form the net ( including this TM)
These practices were collected from various NASA field centres and were
reviewed by a committee of senior technical representatives from the
participating centres. The material was taken from the publication issued by the
NASA Reliability and Maintainability Steering Committee (NASA Reliability
Preferred Practices for Design and Test. NASA TM-4322, 1991).
Reliability must be an integral part of a systems engineering process.
It should start at the design stage itself.
Major Genral Prabal C Sen

5. OPERATING CONDITIONS & EFFECT on STRENGTH
(EXTRACTED FROM NASA Tech Memo 106313)
Reliability parameters for Design & Test
ENVIRONMENT PRINCIPAL EFFECTS TYPICAL FAILURES INDUCED
High Temperature
( one )
Thermal aging:
Oxidation
Structural Change
Chemical Reaction
Softening, melting and
sublimation
Viscosity reduction/
evaporation
Physical expansion
Insulation failure;
Alteration of Electrical Properties
Structural Failure
Loss of lubrication properties
Structural failure;
Increased mechanical stress;
Increased wear on moving parts
Low Temperature
(Two)
Increased viscosity and
solidification
Ice formation
Embrittlement
Physical contraction
Loss of lubrication properties
Alteration of electrical properties
Loss of mechanical strength;
cracking; fracture
Structural failure; increased wear
on moving partsMajor Genral Prabal C Sen

6. OPERATING CONDITIONS & EFFECTS
ENVIRONMENT PRINCIPAL EFFECTS TYPICAL FAILURES INDUCED
High relative humidity
(Three)
Moisture absorption
Chemical reaction
Corrosion
Electrolysis
Swelling, rupture of container;
physical breakdown; loss of
electrical strength
Loss of mechanical strength;
interference with function; loss
of electrical properties;
increased conductivity of
insulators
Low relative humidity
( Four)
Dessication
Embrittlement
Granulation
Loss of mechanical strength;
structural collapse; alteration
of electrical properties;
Major Genral Prabal C Sen

7. OPERATING CONDITIONS & EFFECTS
ENVIRONMENT PRINCIPAL EFFECTS TYPICAL FAILURES INDUCED
High pressure
Not applicable for
CV
(Five)
Compression Structural collapse;
penetration of sealing;
Low pressure
Not applicable for
CV
(Six)
Expansion
Outgassing
Reduced dielectrical
strength
Fracture of container; explosive
expansion
Alteration of electrical
properties; loss of mechanical
strength
Insulation breakdown and arc-
over;
Major Genral Prabal C Sen

8. OPERATING CONDITIONS & EFFECTS
ENVIRONMENT PRINCIPAL EFFECTS TYPICAL FAILURES INDUCED
Solar radiation
(Seven)
Actininc (photo-chemical
reactions ): embrittlement
Surface deterioration; alteration
of electrical properties;
Discoloration of materials
Sand and dust
(Eight)
Abrasion
Clogging in moving parts
Increased wear
Interference with function;
Alteration of electrical properties
Salt spray
(Nine)
Chemical reactions:
corrosion
Electrolysis
Increases wear
Loss of mechanical strength;
alterations of electrical
properties; interference with
function
Surface deterioration; structural
weakening; Increased
conductivity
Major Genral Prabal C Sen

9. OPERATING CONDITIONS & EFFECTS
ENVIRONMENT PRINCIPAL EFFECTS TYPICAL FAILURES INDUCED
Wind
(Ten)
Force application
Deposition of materials
Heat loss (low velocity)
Heat gain (high velocity)
Structural collapse; interference
with function; loss of mechanical
strength
Mechanical interference and
clogging; abrasion accelerated
Acceleration of low-temperature
effects
Acceleration of high temperature
effects
Rain
(Eleven)
Physical stress
Water absorption and
immersion
Erosion
Corrosion
Structural collapse
Increase in weight; electrical failure;
structural weakening
Removal of protective coatings;
structural weakening; surface
deterioration
Enhancement of chemical reactions
Major Genral Prabal C Sen

10. OPERATING CONDITIONS & EFFECTS
ENVIRONMENT PRINCIPAL EFFECTS TYPICAL FAILURES INDUCED
Temperature shock
(Twelve)
Mechanical stress Structural collapse or weakening;
seal damage
High-speed particles
(nuclear irradiation)
Not applicable for
CV
(Thirteen )
Heating
Transmutation and
ionisation
Thermal aging; oxidation
Alteration of chemical, physical
and electrical properties;
production of gases and secondary
particles
Zero gravity
Not applicable for
CV
(Fourteen)
Mechanical stress
Absence of convection
cooling
Interruption of gravity-dependent
functions
Aggravation of high temperature
effects
Major Genral Prabal C Sen

11. OPERATING CONDITIONS & EFFECTS
ENVIRONMENT PRINCIPAL EFFECTS TYPICAL FAILURES INDUCED
Ozone
Not applicable for
CV
(Fifteen)
Chemical reactions:
Crasing, cracking
Embrittlement
Granulation
Reduced dielectrical
strength of air
Rapid oxidationl alteration of
electrical properties
Loss of mechanical strength
Interference with function
Insulation breakdown and arc-over
Explosive de-
compression
Not applicable for
CV
( Sixteen)
(Sixteen)
Severe mechanical stress Rupture and cracking structural
collapse
Dissociated gases
Not applicable for
CV (Seventeen)
Chemical reactions:
Contamination
Reduced dielectric strength
Alteration of physical and electrical
properties
Insulation breakdown and arc-over
Major Genral Prabal C Sen

12. OPERATING CONDITIONS & EFFECTS
ENVIRONMENT PRINCIPAL EFFECTS TYPICAL FAILURES INDUCED
Acceleration
Not applicable for
CV
(Eighteen)
Mechanical stress Structural collapse
Vibration
(Nineteen)
Mechanical stress
Fatigue
Loss of mechanical strength;
interference with function;
increased wear
Structural collapse
Magnetic fields
Not applicable for
CV
(Twenty )
Induced magnetisation Interference with function;
alteration of electrical properties;
induced heating
Major Genral Prabal C Sen

13. Operating condition
and
Loss of reliability
A case study
Major Genral Prabal C Sen

14. LAUNCH of SPACE SHUTTLE CHALLENGER IN
EXTREME OPERATING CONDITIONS
January 28, 1986
January 28, 1986 was the day when all 7 US
astronauts died when their shuttle exploded
73 seconds after launch
Major Genral Prabal C Sen

15. Solid (Propellant ) Rocket Booster
Imparts Thrust for lift off
Major Genral Prabal C Sen

16. 60 seconds after lift off
Major Genral Prabal C Sen

17. 73 seconds after lift off
Major Genral Prabal C Sen

18. .
EXTREME COLD TEMPERATURE CAUSED
FAILURE
OF O RING
It was the coldest day in history that a shuttle has
been launched
Major Genral Prabal C Sen

19. Member of the Comission included Neil Armstrong
Major Genral Prabal C Sen

20. Cause for the explosion
failure of the right SRB aft joint sealing
Due to the extremely cold temperature on the morning 28/1/1986.
Out of the two SRBs that were used, the one that was in the
extreme cold( due to shadow).
O-rings when they are cold contract & do not expand as quickly
as ones that are warmer. Therefore the O-rings were nearly frozen
in place during ignition, Challenger left launch pad and headed
for space with frozen O rings in one Solid Rocket Booster.
Since the joints were not sealed, hot gases leaked through and
ignited liquid hydrogen.
Lesson: Lack of foresight in Operating Conditions
.
Major Genral Prabal C Sen

21. Strength Distribution of Standard and
substandard components
Major Genral Prabal C Sen

22. Stress and Strength Distribution
Major Genral Prabal C Sen

23. Strength Stress Gap
• Likely Failure Zone is depicted by overlapped area under the curves
• The overlap between stress & strength curves should be as less as possible
• This is possible with
Catering for Larger factor of Safety , this would distance the curves – But it is an
expensive option, also may make the component heavier ( redundancy being one
option ) with complex circuitry / structure or more rugged components being used.
Reduction of tolerance in manufacture – The strength curve should be as peaky as
possible , being measured by Kurtosis formulae.
Avoiding overdesign : carrying out audit or much closer examination of the likely
operating conditions . Question and verify user expectations .
Major Genral Prabal C Sen

24. Sources and Credits
• NASA Technical Memorandum 106313
• NASA Report to the President
Actions to Implement Recommendations of the
Presidential Commission on the Space Shuttle
Challenger Accident.
Major Genral Prabal C Sen

25. Author
• Major General Prabal C Sen, VSM
• Master in Technology in Industrial Engineering ( IIT Delhi)
• Master in Engineering in Guided Weapons ( Control Systems) from Poona
University
• M Phil form Madras Engineering.
• Forty years experience in maintenance of equipment, mainly electronics,
Radars and Guided Weapons, also teaching.
Major Genral Prabal C Sen