OVERVIEW

The primary objective of the original SHERE experiment was to study the effect of torsional pre-shear on the subsequent extensional behavior of a model well characterized viscoelastic fluid in a microgravity environment aboard the international space station (ISS). Due to the vorticity induced by a rotational shear flow, shearing of a viscoelastic fluid (which has a ‘fading memory’ of its deformation history) immediately before uniaxial extension will have an effect on the subsequent extensional behavior of the fluid. Of specific interest was the transient evolution in the filament profile and in the viscoelastic tensile stresses that are developed during the extension of the fluid. The SHERE experiment has allowed us to obtain accurate measurements of the extensional viscosity of dilute polymer solutions without sagging of the fluid under gravitational body forces that restricts measurements made on earth.

As a logical extension to the SHERE project, SHERE II looks to study the effect of torsional pre-shear on the extensional behavior of a different non-Newtonian fluid. We specifically chose to study dilute suspensions of rigid micro-particles in dilute polymer solutions (0.025 wt. %). The suspending particles used are rigid inert poly(methyl methacyrlate) (PMMA) spheres, 6 µm in diameter, and the polymeric matrix is narrow polydispersity high molecular weight polystyrene dissolved in oligomeric styrene, which is the same fluid used in SHERE. 100 g of the prepared suspension was shipped to NASA Glenn Research Center (GRC) on May 27^th 2010. Following the successful completion of SHERE increment 18 operations, the 25 fluid modules (FM) were returned to earth, emptied, cleaned and inspected, and refilled with the SHERE II test fluid. The 25 FM’s were launched to the ISS aboard shuttle mission STS-134 on May 16th 2011. Astronauts Mike Fossum and Satoshi Furukawa completed the SHERE II checkout tests, dry-runs and fluid testing between July and August 2011. Analysis of the data is currently underway.