抄録
The distributions of stress and strain in some notched plates or bars in creep had been already calculated by means of the finite element method. Based on these previous results, the behavior of stress relaxation at the notch root and the relationship between stress or strain concentration factor of creep and elastic stress concentration factor were examined in the present study.
The stress at the notch root relaxes from the initial elastic stress in the course of creep, and reaches its steady state. The time for the stress to reach the steady state is the time period until the magnitude of creep strain becomes equal to the magnitude of elastic strain under the same nominal stress in the plane stress condition. It is also the time period until the creep strain becomes about ten times of the elastic strain in the plane strain condition. The stress and strain concentration factors for the steady state of stress in creep can be estimated through the elastic stress concentration factor by using the Neuber's equation in the case of plane stress. However, the Neuber's equation overestimates the magnitude of the stress and strain concentration factors for notched bars. The following equations seem to be applicable for the relationship between stress or strain concentration factor, Kσ or Kε, and elastic stress concentration factor, Kt.
Kσ=√1-k+k2Kt2/(α+1), Kε=(√1-k+k2)αKt2α/(α+1),
where k=σzmax/σymax, √1-k+k2=1 in plane stress and 0.866 in plane strain, and α is a creep exponent.
