Uniaxial Compressive Properties of Bismaleamid-coated Carbon Microballoons

A uniaxial compression technique employing a nanoindenter equipped with a flat-ended cylindrical tip is used to evaluate the performance of carbon microballoons (CMBs) precipitation-coated with a bismaleamid (APO-BMI) polymer. This coating will eliminate the size and density induced segregation of APO-BMI and CMBs during mold filling and the potentially damaging mixing step wherein CMBs and powdered binder pre-polymer are blended prior to foam molding. To augment the molding of syntactic foams directly from coated CMBs and to aid in the development of a constitutive model for a three-phase syntactic foam, mechanical property evaluation of the coated CMBs is needed. Cured, APO-BMI coated and uncoated CMBs (0.192 g/cm³ tap density) are compressed uniaxially using a modified nanoindenter to obtain the compressive properties of the CMBs in both conditions. These properties included strain-to-failure, failure load, displacement-at-failure, and work of fracture. The 0.192 g/cm ³ tap density CMBs' behavior followed the prior inter-tap density trends between compressive strain and diameter and failure load versus stiffness. The coating is determined to have no statistically significant effect on the mechanical properties of the CMBs. From the combination of this information, the effect of an APO-BMI coating on CMBs of any tap density is inferred.