Safety Test 1 September 9 Flashcards Preview

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Flashcards in Safety Test 1 September 9 Deck (16):
1

Derating

- 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

2

screening

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

3

types of reliability tests used in screening

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

4

decision coincidence

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

5

standby redundancy

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

6

Monitoring

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

7

Rule about emergency/safety devices and monitoring

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

8

material/structural failures

- 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)

9

Designer method for safety factors

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

10

Test method (observational) for safety factors

- SF = (critical load) / current load
- calculate SF and compare to required SF values

11

strain

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

12

stress

- force per unit area - internal to object
- fluids have pressure, solids have stress

13

Static failures

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

14

dynamic failures

due to forces applied due to movement
- fatiguing, impacting

15

instability failures

- structure does not fail through breaking, etc.
- it tips over, slides, rolls, etc. undesirably

16

Creep (type of failure)

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