Structural dynamics and damage detection of foam-rigidized deployable aerospace structures

The basic advantage of deployable structures, their compact stowed size relative to their final deployed size, presents a significant advantage to the aerospace designer. Extremely large structures that stow into very small volumes for launch are particularly feasible with one particular type of deployable, the inflated structure. However, it is difficult to advocate the use a purely inflated structure for an orbital mission because of the risk of micrometeor puncture. Rigidizing the structure in some fashion addresses this fragility issue. Design and operational issues with respect to foam- rigidized aerospace structures are investigated in this paper. The structures are fabricated from flexible Kapton film that is formed into a cylindrical shell. The shell is injected with a hardening urethane foam to form a composite strut. The results of both static and dynamic tests of four test coupons cut from foam rigidized struts are presented. The experimentally determined structural properties are then input into a finite-element model to gain insight into the dynamic behavior of a realistic inflated-rigidized structure. As with all structures touted for aerospace use, the survivability of foam-rigidized structures in the orbital environment is of interest. This issue is investigated by damaging the test coupons in a controlled fashion and then again experimentally evaluating the static and dynamic material properties. These properties are used for sections of the finite-element model to represent damage to the structure. An evaluation of the possibility of vibration-based damage assessment is included.