Q: Why does MOSES not follow the standard scaling rule for damage?
REV 7.04

A: The standard scaling rule to which you refer says that if the damage for a stress concentration SCF1 is D, then the damage for a stress concentration SCF2 is D*(SCF2/SCF1)**M where M is the slope of the SN curve and the all of the contributions to the damage are within the curve. An important thing to notice here is that almost all SN curves have more than one slope and the above is valid only for a single slope SN curve.

All published SN curves all have limits, and what are we to do

outside these limits? Before Rev 5.06, we actually computed the

damage based on the curve. We found that this can be seriously

wrong. In particular, if one has a beam with really large stresses,

then the larger the stresses, the smaller the CDR! This is because

as the stress becomes large, more of it is outside the range

of the SN curve. We have now changed this so that if the

probable maximum stress in greater than the first point in the

SN curve, damage is accumulated as if it were all at the first

point on the curve. This gives some discontinuities in the CDRs,

but it is better than overly optimistic results.