Paper Number
BC12 

Session
Blends, Composites and Multiphase Systems

Title
Effect of thermal history on the behavior of thixotropic elasto-visco-plastic materials

Presentation Date and Time
October 7, 2014 (Tuesday) 1:55

Track / Room
Track 5 / Washington B

Authors (Click on name to view author profile)

1. Geri, Michela (Massachusetts Institute of Technology, Mechanical Engineering - HML)
2. McKinley, Gareth H. (Massachusetts Institute of Technology, Department of Mechanical Engineering)
3. Venkatesan, Rama (Chevron Energy Technology Company)
4. Sambath, Krishnaraj (Chevron Energy Technology Company)

Author and Affiliation Lines (in printed abstract book)
Michela Geri¹, Gareth H. McKinley¹, Rama Venkatesan², and Krishnaraj Sambath^2
1Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139-4307; ²Chevron Energy Technology Company, Houston, TX

Speaker / Presenter 
Geri, Michela

Text of Abstract
During the last decade a lot of interest has been built around what are now known in the literature as Elasto-Visco-Plastic (EVP) materials. These are soft materials that show a complex behavior characterized by both a plastic component, due to the presence of a yield stress below which there is no detectable flow, and a viscoelastic component. Many metals and alloys formed at medium or high temperatures fall into this category as well as waxy crude oils at extreme thermodynamic conditions, such as those experienced during deep-water drilling and transport. Recently, attention has also been focused on EVP materials for bio-inspired applications related to high-performance structural materials. From a modeling prospective, the simplest constitutive responses that capture the canonical behavior are of Bingham-Maxwell or Bingham-Voigt type. However, several different constitutive equations have been proposed in recent years that attempt to capture key features of EVP materials such as waxy crude oils, even in cases where the thixotropy interplays with the strongly non-linear mechanical response of the system. Notwithstanding the substantial progress that has been made, all of the models available in the literature have been developed for the situation of isothermal flows or quasi-equilibrium conditions. Such constraints must be relaxed for many applications such as flow assurance of crude oils in which rapidly quenched non-equilibrium wax microstructures can be developed near the walls of pipes. We show how thermal history influences the rheological response of EVP materials by a series of experiments performed in both steady and oscillatory shear. In particular, we show how spatial temperature gradients can, under some conditions, induce large stress overshoots even in the absence of a shear-induced strong gel network. We also describe modeling efforts to incorporate such behavior in the existing constitutive models for the limit of both small and large temperature gradients.