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Subject: [Struc] crack propagation in fatigue
Author: Andre Beim
Date: 2008-10-09 18:30:31

I want to bring a new issue to an old topic. Some time ago, some people
told about a trend in fatigue analysis, to consider a small initial deffect
in the material (some say is 0.25 mm, others say 0.3, others say even 0.5
mm), and calculate the life with the fatigue propagation laws (Paris law). I
had recently a case in which a part was safe according to the ASME fatigue
curve (which is known to be very conservative), but unsafe when calculated
by this small crack propagation criteria. A metallurgist told me the reason
is that the propagation curves are determined with test specimens with large
cracks, and the propagation of a small crack is a completely different
phenomenon, which depends on the material (he said he had some experimental
curves). I did not find anything about this in the codes. BTW, the part I
designed did not fail. Does anybody know any code or published data showing
this difference?


Andre Beim
Tresca Eng., Brasil
e-mail: andre_at_tresca.com.br

Posts possibly associated with message #95392AuthorDateScore
95392[Struc] crack propagation in fatigueAndre Beim2008/10/09 
95403Re: [Struc] crack propagation in fatigueGuowei Li 2008/10/09 
95404Re: [Struc] crack propagation in fatigueChristopher Wright2008/10/10 
95424Re: [Struc] crack propagation in fatigueAndre Beim2008/10/10 
95432Re: [Struc] crack propagation in fatigueGuowei Li 2008/10/10 
95433RES: [Struc] crack propagation in fatigueAndre Beim2008/10/10 
95436Re: [Struc] crack propagation in fatigueRobin Borland 2008/10/12 
95438RES: [Struc] crack propagation in fatigueAndre Beim2008/10/13