Design, Engineering and Processing of Functionally Graded Syntactic Foam Structures for Impact Energy Absorption Applications

Author: Ajibola Adewole, Department of Chemical and Biological Engineering

Mentor: Dr. David Salem, CAPE Laboratory, CNAM Center, and Department of Chemical and Biological Engineering

Syntactic foams and functionally graded syntactic foams (FGSF) have been widely studied for use in energy absorption applications but most of the foam designs and fabrications reported in the literature are based on empiricism rather than rational design. In addition, the traditional methods of fabricating FGSF lack the precision needed to produce seamless, well-integrated foam structures.

The design of protective material for impact energy absorption requires an understanding of the features of an impact that can cause damage to protected structures and how these features can be effectively dissipated by the protective material. These features are peak force/pressure and the impulse transmitted to a protected structure. The peak force/pressure can be reduced by introducing a large acoustic impedance mismatch between two elastic layers while the transmitted impulse can be attenuated in the protective material via viscous dissipation. This study utilizes a rational design concept called impact tuning, where a multilayered protective structure is used to tune impact-induced stress waves to narrow frequencies that match the damping frequencies of viscoelastic layers, to engineer lightweight multilayer protective structures. To ensure a seamless, well-integrated monolithic structure, a process based on vacuum assisted transfer molding (VARTM) developed at Composite and Polymer Engineering Laboratory at SDSMT is adapted to produce these layered protective structures. Geometrical and material properties of carbon fabric, hollow microspheres, solid particles, and polymer matrix resins are used to design layering sequences of the constituent materials such that mechanical/impact-resistant properties of the protective materials are modulated through the thickness direction.

Initial drop-tower impact tests on three-layered protective structures show reduced peak force and higher energy-absorbing capabilities compared to neat resin and homogenous syntactic foams of comparable thickness.