Monotonic and Cyclic Loading Behavior of Closed-cell Aluminum Foams and Sandwich Structures

Despite the fact that most aluminum foam products are used mainly due to their energy-absorption and damping capabilities, the respective Al-foam-containing structures may undergo fatigue damage to some extent. The present paper reviews the general issues of cyclic loading behavior of cellular metals, including their particular sensitivity to tensile loads. It was shown that nearly all aluminum foam products show poor ductility during testing. Correspondingly, fully-reversed rotating-bending tests on ALPORAS and FOAMTECH specimens revealed fatigue strength values at 107 cycles of only 10% of the respective tensile strength. The deformation mechanisms of the aluminum metal foams have been further analyzed for various stress ratios, R=-1, R=0.1 and R=10 under uniaxial loading using an optical 3D strain analysis system (ARAMIS by GOM). The strain analysis system allows identifying positions of strain localization and ongoing fatigue damage. Fracture surfaces were analyzed by scanning electron microscopy (SEM). It has been found that morphological and microstructural defects, like relative large pores, silicon precipitates and grains within the cell walls lead to crack initiation and promote easy fatigue crack propagation and cell-wall fracture. The results are discussed within the scope to provide design guidelines for fatigue-loaded aluminum-foam-including structures.