Paper Number
DA11 

Session
Design of Applied Materials

Title
Characterizing the weakly elastic rheological behaviors of automotive lubricants through an improved capillary breakup extensional rheometer

Presentation Date and Time
October 16, 2018 (Tuesday) 4:35

Track / Room
Track 5 / San Felipe Room

Authors (Click on name to view author profile)

  1. Du, Jianyi (Massachusetts Institute of Technology, Department of Mechanical Engineering)
  2. Ohtani, Hiroko (Ford Motor Company, Structures & Stamping Department)
  3. McKinley, Gareth H. (Massachusetts Institute of Technology)
  4. Ellwood, Kevin (Ford Motor Company, Structures & Stamping Department)

Author and Affiliation Lines (in printed abstract book)
Jianyi Du1, Hiroko Ohtani2, Gareth H. McKinley1, and Kevin Ellwood2
1Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139; 2Structures & Stamping Department, Ford Motor Company, Dearborn, MI 48121

Speaker / Presenter 
Du, Jianyi

Text of Abstract
Elongational flows of complex fluids are important in a wide range of everyday phenomena such as jetting, drop impact and fragmentation. Even if the fluid is only weakly elastic, the extensional rheology of the fluid can control the final stages of the thinning process because of the large strains and singular strain rates that develop near pinch-off. Here we aim to develop an improved device to study the extensional rheology of complex fluids such as weakly-viscoelastic motor oils, paints, as well as metalworking waxes with yield stresses. In order to do so, we utilize the experimental technique of capillary thinning, and introduce an improved design of the Capillary Breakup Extensional Rheometer (CaBER) with better-controlled plate actuation and a novel environmental temperature control system. In this setup, a liquid sample is rapidly stretched by two coaxial plates, leading to a liquid bridge connecting two hemispherical liquid reservoirs at each plate. The temporal evolution of the resulting liquid bridge is controlled by inertial, viscous, elastic and capillary effects. By measuring the evolution in the mid-plane radius and the filament shape we can probe the underlying fluid properties. We first validate our setup and demonstrate this new system’s capabilities using a Newtonian calibration fluid and a series of well-studied aqueous food thickeners. We then consider a number of lubricants of importance in automotive applications: first we consider two commercial synthetic 10W-30 motor oils that appear to be identically Newtonian in shear flow. Capillary thinning measurements show that these fluids can be differentiated by onset of strain-hardening close to breakup. This weakly elastic response can be understood using a second order fluid model; second we consider a commercially available waxy metalworking lubricant which exhibits a yield stress below wax appearance temperature (of 47°C) altering the filament profiles, but then behaves as a simple Newtonian liquid even at high strain rates close to breakup.