Modeling non-uniform aluminum foams as sacrificial layers for blast mitigation of protected structures - A theoretical approach

Aluminum Foams (AFs) are cellular materials that exhibit energy absorption capabilities, making them desirable to use as sacrificial protective cladding applied on structural members. Thereby, the structural resistance to blast loads is increased. During the foam compaction, inner and local buckling of the material walls occur. The described phenomenon reduces the peak overpressure of the blast load and increases its positive duration while maintaining the impulse and transmitting the plateau stress of the foam to the Protected Structure (PS). The plateau stress is commonly significantly lower than the peak overpressure of the blast load. Available analysis approaches typically neglect the coupling between AF and PS and mostly consider uniform -density foams. Moreover, the efficiency of adding AF has been commonly evaluated by comparing the structural response with and without AF. However, such a comparison may not be adequate for studying energy absorption due to the role that the added mass affects the behavior of the structural system due to inertia forces. In this study, using the shock front theory, a numerical solution to a non -uniform density foam as protective cladding is developed, considering both the foam densification and the PS response. A parametric study is performed using this approach to investigate the efficiency of non -uniform density foam compared to a uniform density foam. Calculation and discussion of the efficiency of uniform and non -uniform foams are presented using a more adequate proposed approach, mainly concluding that under loads considered to be impulsive, the non -uniform AF with certain specimens considerably reduce the Peak Displacement (PD) of the PS significantly more than uniform AF.