design philosophy

Question 1

3 design philosophies and describe them

Answer 1

safe life - assumption that cracking will develop at areas that are susceptible to extreme fatigue

fail safe - sufficient strength and stiffness remains in primary structure even if one member fails

damage tolerance - accept the flaws and anticipate their growth rate

Question 2

what is safe fatigue life

Answer 2

operational period which the possibility of fatigue failure of the part is extremely rare

Question 3

what is fail safe

Answer 3

structure is designed such that after failure in ops to a part of a primary structure, such that;

sufficient strength and stiffness remains in primary structure

permits operation for a limited amount of time

level of safety is decreased but still acceptable until next repair time

Question 4

2 designs of fail safe philosophy

Answer 4

alternate load path (another member on standby to take over all the load)

multiple load path (remaining members take on the shared load)

Question 5

fail safe design features

Answer 5

material thickness must have:

• low level of stress
• reduce fatigue failure

material must have good resistance to crack propagation (slow increase in crack) & limit the length of crack developed

Question 6

damage tolerant design

Answer 6

ability of structure to sustain operation load in the presence of damages

Question 7

info needed to calculate safe life

Answer 7

magnitude of loads

frequency of loads