Under quasiperiodic fluctuating dynamic loads, a structure made of elastic
plastic material may fail by incremental collapse (ratcheting) or alternating
plasticity (fatigue). For the kinematic hardening materials considered, the only
two crucial material parameters needed are the initial and ultimate yield
stresses, but not the generally deformation-history-dependent hardening curve
between them. With the high-cycle loading we suggest taking the fatigue limit
as the initial yield stress, and taking the stress corresponding to a certain
allowable amount of plastic deformation from the empirical Ramberg–Osgood
curve (or the particular cyclic yield strength corresponding to the amount
of
plastic deformation) as the ultimate yield stress in our shakedown analysis of
structures. The approach is practical and well founded within our shakedown theory,
while the small deformation assumption framework of the classical plasticity theory is
kept. As illustrations, we derive explicit expressions of the working load limits for
the circular shaft and helical spring, which are based on the shakedown
analysis and can be used for safety design of the structures with given loading
conditions.
Keywords
shakedown, dynamic high-cycle loading, ratcheting, fatigue,
circular shaft, helical spring
