Aluminium foam represents a new class of materials characterized by a large variability due to its porous structure. A simple and easy-to-use indicator of foam inhomogeneities is represented by apparent density, but this parameter does not give indications about differences existing in structural stiffness. To overcome this limit, the variability of natural frequency has been considered in this work in the case of commercial closed-cell aluminium foam. Moreover, fatigue and fracture properties of aluminium foam are not well studied. In this work standard three-point bend specimens SE(B) have been used to determine critical Crack-Tip Opening Displacement. The pre-crack phase, consisting in the application of appropriate fatigue load, has been monitored through modal analysis. Experimental results confirm the possibility of using this technique also in the initial step of fatigue failure process to quantify the amount of fatigue damage induced by repeated loads.