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A Griffith theory for fatigue from Delft group?

Mike Ciavarella's picture

I came across an interesting theory for fatigue crack propagation from collegues in Delft, I think the group of prof Benedictus, but I have mixed feelings about it, because while there seems to be something very interesting experimentally, there seems to be some confusion between concepts of energy balance like Griffith seminal theory of fracture (which do not apply in fatigue) and Paris type of law, which are only weak forms of power law scalings which depend on all dimensionless parameters of the problem, so that C and m in Paris are not material constants, and there is no energy balance at all.   

I wrote a short draft the way I see the problem,

I am looking forward for some discussion perhaps to work on the draft with other collegues, is anyone in Imechanica working on this topic?



Mike Ciavarella's picture

PS There was another theory from Delft in the past from Kassapoglou in fatigue which was surprising and perhaps interesting. Kassapoglou's approach was so elementary that I got curious, he claimed that you don't need to do fatigue testing, but simply get the fatigue curve from a statistic of static tests!!!! These papers were peer reviewed by good journals, but clearly they cannot be correct. If you are interested about that, see my paper which was peer reviewed here It did attract independent investigation by the FAA (Tomblin and Seneviratne, 2011 [5]), and others, who found that the theory was --- unconservative for the vast majority of data (10 sets), of which 5 perhaps by 1-2 orders of magnitude, 3 by 2-3 orders of magnitude, and 2 by 4-5 orders of magnitude. But nobody, except me, discussed why the theory was obviously theoretically misleading and not simply wrong. The theory has disappeared and will not resist the test of time. It will be forgotten.I am happy that Kassapoglou nevertheless is a good teacher, and for example has written an excellent book.So the main point is not "peer review" which is just the judgement of 2-3 people sometimes made in 5 minutes, and not "funding", which depends on ability to attract money, but the test of time, and validation by the large scientific community. This is at least what I believe.

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