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

Abstract

Hollow glass microspheres possess niche markets and future research areas due to their high strength-todensity ratio and low thermal conductivity. For example, these qualities make them a viable alternative insulation medium. For this study, Scotchlite™ k1 hollow glass microspheres (HGMs) manufactured by 3M™ 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 µm 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™ 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.

Fabrication of syntactic foam fillers via integrated on/off-chip microfluidic methods for optimized geopolymer composites

“…The snap-through region represents the buckle away of the constrained area that is in direct contact with the indenter, the filler thus releases the accumulated compressive membrane stress. 41 Another noteworthy characteristic is that the slope of the force–displacement line basically remains the same except for the snap-through region, which is speculated to be the sequential fracture of the shell. This assumption is supported by three reasons: (i) the much larger size of the indenter can guarantee sequential contact with the filler outer wall; (ii) the PVA film can lock the exact position of the filler regardless of possible vibration or shock during the test; (iii) the calcined filler is mechanically tough to avoid the occurrence of longitudinal cracks.…”

Glass Microspheres

“…The properties to be mentioned here are density, strength, thermal and electrical features, which are limited to those being a straight forward consequence of glass microspheres hollow nature [18,21].…”

Characterization

“…Reasons for this may include (1) a thin-walled HGM is statistically less likely compared to a thicker-walled bubble to contain a flaw of critical size that would initiate a crack under a given load, and (2) larger spheres have a smaller radius of curvature relative to smaller spheres, so as the uniaxial compression test proceeds, the contact area between the larger bubble and the platen increases, lowering the stress on the sample by distributing a comparable load over a larger area [7,9,10]. In other words, larger and presumably thinner-walled bubbles break at higher failure loads than their smaller, thicker-walled counterparts.…”