On the Paris coefficient and crack closure effects of Alporas aluminum foam

Fatigue Crack Growth experiments are performed on M(T)-samples made of Alporas aluminum foam. This foam is a commercially available closed cell aluminum foam, which is made from a technically pure aluminum. The Alporas foam has a rather high Paris exponent of about 15. The Paris crack growth region is from ∆K = 0.095 MPa√m up to 0.13 MPa√m. An existing model, the so-called Beam Bending model, for Fatigue Crack Growth in metal foams is verified. A good agreement between predicted values and experimental values was found. A novel form of crack closure occurs in the Alporas aluminum foam during Fatigue Crack Growth. The behavior deviates from solid metals, due to the larger influence of the compressive part of the fatigue loading on the crack growth. It is hypothesized that the structure of the foam transforms macroscopic compression loads into surface tension loads on a microscopic scale.