To estimate the service fatigue life of dynamically loaded
components and structures, laboratory fatigue tests with simulated
loads must be carried out. The paper presents various methods of
on-line simulation of service loading processes, representing
inputs of computer controlled fatigue machines. Omitting the
fictitious sinusoidal loading, reproduction of any service process
can be based either on the probability density of amplitudes, or on
the power spectral density, or both of them, depending on the
fatigue damage hypothesis and philosophy of testing accepted.
The starting step of the simulation is generation of random
numbers /representing as usually uniformly distributed white
noise/, which are further transformed into the required probability
density shape. If the simulated process is stationary, this
transformation does not represent a principal problem /even when it
is non-linear/. There is, however, no general method available,
which would reproduce the non-stationary /time-dependent/
probability density and at the same time the non-stationary
/time-dependent/ power spectral density of non-stationary
processes. A partial success can be gained by simulating each of
them separately or supposing the process is Gaussian.
Examples of some simulated processes are shown, having been
programmed for the MTS fatigue machine, equipped with PDP8/e
computer.