A functionally graded syntactic foam material for high energy absorption under compression

A functionally graded structure for hollow particle (microballoon) filled syntactic foams is fabricated that is capable of withstanding compression for 60–75% strain without any significant loss in strength. The new functionally graded structure is based on creating a gradient in microballoon wall thickness. This material has the same volume fraction of microballoons throughout the structure, eliminating the undesirable effects of the present functionally graded composites containing a gradient of particle volume fraction. Three compositions of such material are fabricated and tested in the present study. Results show that the compressive modulus, strength, and total energy absorption of the new syntactic foams can be controlled by using appropriate type and volume fraction of microballoons.