Safety Test 1 September 9

Question 1

Derating

Answer 1

• parts are rated by manufacturers for specific conditions and stress
• reducing stresses of operations will reduce failure rate
• reducing load factor (ratio of actual to rated load) will reduce failure rate

Question 2

screening

Answer 2

• close control of component quality
• reliability tests eliminating components that will fail with unacceptable times
• visual inspection and measurements

Question 3

types of reliability tests used in screening

Answer 3

• normal pressure or voltage - short periods
• accelerated - much greater stress, short period
• “burn-in” - entire period of expected life
• statistical sampling of finished product

Question 4

decision coincidence

Answer 4

3 to 5 system outputs monitored and decisions made based on the combination of results (ex. - vehicle airbags)

Question 5

standby redundancy

Answer 5

operative unit functions until failure and then another unit is turned on automatically, semi-automatically, or manually

Question 6

Monitoring

Answer 6

monitoring system is of no value unless corrective action is taken when necessary - example is the “empty box solution”

Question 7

Rule about emergency/safety devices and monitoring

Answer 7

dont use an emergency/safety device as a part of your regular control, but they should be tested regularly

Question 8

material/structural failures

Answer 8

• cause many accidents and injuries
• failures often caused by forces of too great in magnitude for the structure/material (often these include more than just the forces the object is designed to withstand - must consider external possibilities)

Question 9

Designer method for safety factors

Answer 9

• final design = required design X safety factor
• designer determines SF
• calculate required final design value

Question 10

Test method (observational) for safety factors

Answer 10

• SF = (critical load) / current load

- calculate SF and compare to required SF values

Question 11

strain

Answer 11

• the change in physical shape or deformation caused by stress
• failure usually occurs after some amount of strain

Question 12

stress

Answer 12

• force per unit area - internal to object

- fluids have pressure, solids have stress

Question 13

Static failures

Answer 13

• due to forces applied by structures that re not moving prior to failure
• shearing, tension, compression, bearing, bending, buckling

Question 14

dynamic failures

Answer 14

due to forces applied due to movement

- fatiguing, impacting

Question 15

instability failures

Answer 15

• structure does not fail through breaking, etc.

- it tips over, slides, rolls, etc. undesirably

Question 16

Creep (type of failure)

Answer 16

• very slow, permanent deformation (usually occurs within a range of temperature)
• usually occurs in materials with high plasticity