Abstract

The present work aims at advancing an innovative computational methodology
that simulates steel and composite material fracture under cyclic loading following
a phenomenological approach, with calibration from both small scale and
large scale testing. This work addresses fatigue processes ranging from High Cycle
to Ultra-Low-Cycle Fatigue. An assessment of the current state of the art is done
for all the di erent fatigue types. Following, for Ultra-Low Cycle Fatigue a new
constitutive law is proposed and validated with experimental results obtained
on small scale samples. Industrial applications are shown for a large diameter
straight pipe under monotonic loading conditions and for a bent pipe under cyclic
loading. Emphasis is made on the capacity of the model to represent di erent
failure modes depending on the loading conditions. The research regarding this
part has been used in the frame of the European Project: \Ultra low cycle fatigue
of steel under cyclic high-strain loading conditions" (ULCF).

Regarding High Cycle Fatigue, a classic damage model is presented in combination
with an automatic load advancing strategy that saves computational time
when dealing with load histories of millions of cycles. Numerical examples are
shown in order to demonstrate the capabilities of the advancing strategy and a
validation of the model is done on small scale samples.

A new constitutive model is presented for Low Cycle Fatigue that uses the classic
plasticity and damage theories and simultaneously integrates both processes
in the softening regime. The capabilities of the model are shown in numerical
examples.

Finally, the High Cycle Fatigue damage model is applied to the constituents of
a composite material and the structural behaviour is obtained by means of the
serial/parallel rule of mixtures. Validation of the constitutive formulation is done
on pultruded glass ber reinforced polymer pro les.