On a hybrid method to characterize the mechanical behavior of thin hollow glass microspheres

Hollow glass microspheres possess niche markets and future research areas due to their high strength-to-density ratio and low thermal conductivity. For example, these qualities make them a viable alternative insulation medium. For this study, Scotchlite((TM)) k1 hollow glass microspheres (HGMs) manufactured by 3M((TM)) were used; however, one of the challenges in investigating their mechanical properties was due to the limited availability of published data. Most importantly, the thickness (or the range of thicknesses) of produced thin hollow microspheres is not measured by the manufacturer, so the authors needed to develop a hybrid characterization method that depended on both experiments and simulations to estimate the HGMs mechanical properties. The experimental method utilizes a nano-indenter with a spherical sapphire tip of 500 mu m in diameter. Each HGM was uniaxialy compressed under the indenter to yield the stiffness, diameter, and the force-displacement at fracture of each HGM tested. ABAQUS((TM)) was used to numerically model an HGM of mean diameter and stiffness to obtain a relation between the mechanical and geometrical properties of each HGM to its thickness, and investigate the development of stresses on an HGM during its uniaxial compression. The data show large scatter in the measured stiffness of each HGM as a function of diameter. The authors conjecture this is due to a large fluctuation of the microsphere thickness. Finally, the work necessary to deform an HGM was successfully correlated to its radius-to-thickness ratio. This gives us a unique insight on the force-displacement behavior against the geometrical features of HGMs.