Aircraft Fatigue and Creep
Aircraft Fatigue and Creep
(OP)
I was wondering weather anyone could help me with a problem I have. I been asked to comment on the implications of creep and fatigue in a Rudder control cable. I think it could be both but i'm a bit unsure because the decription I have of fatigue is fatigue is caused by a number of things such as, atmospheric turbulence, the transfer of weight between undercarriage and wing or rotors on take off and landing, manoeuvring and taxing on the ground and manoeuvring during flight. I know there is a transfer of weight when the rudder is moved so does that mean it will suffer from fatigue? and creep well the decription i have is creep is caused by a static or dead load applied to a material or component over a period of time. Is the load on the rudder a staci or dead load. Please could someone help.
RE: Aircraft Fatigue and Creep
RE: Aircraft Fatigue and Creep
My understanding of creep is it involves temperature as well. I doubt your control cable sees the kind of temperature required for creep.
The biggest problem I've seen in cables is wear. This wear can weaken the cable which gives way to a static failure at a lower load.
RE: Aircraft Fatigue and Creep
Creep - Plastic strain induced by temperature and stress for a period of time - normally for steels below 400 deg C not a problem. Failure = accumataled creep strain = strain at rupture. Creep more responsive to temperature than stress. Not easily analysed as stress redistribution and sometimes stress relaxation occurs.
Fatigue - Material degradation as a result of cyclic loading. Sensitive to mean tensile stresses, notches, temperature, number of cycles, stress range, etc. etc. etc
More easily analysed by linear damage theories etc, etc.
Creep - Fatigue - complex interaction of creep and fatigue very conservative approaches exists in the pressure vessel industry. Not very nice.
Regards.
Gerrie
RE: Aircraft Fatigue and Creep
RE: Aircraft Fatigue and Creep
I don't mean to be offensive but if you need to ask these questions in relation to this problem, you should not be the person conducting this engineering investigation. This field carries far too much legal liability for anyone but experienced, qualified aircraft engineers to answer. Pass it on.