Stiffness reduction caused by vibration fatigue

This thesis deals with the fatigue behaviour of a composite laminate under bending cyclic load. It is provided an initial theoretical introduction on how fracture in composite materials behave, with particular attention on the phenomena of "delamination", which will be the object of the software simulation in the second part of the thesis. The dissertation will guide the reader through the modelling of the laminate on a finite element software named Abaqus, focusing on modal dynamics theory and non linear dynamics. Since the composite laminate requires too much computation time, a steel laminate is considered in the simulation with the crack opening path pre defined in order to simulate the delamination phenomena. Furthermore there will be considered different stiffness condition for the specimen. In particular a comparison between linear stiffness and non linear stiffness behaviour during the crack opening will be taken into account. In the end all the results are collected with relative interpretations.