Shear History Extensional Rheology Experiment (SHERE) - 01.09.14

Overview | Description | Applications | Operations | Results | Publications | Imagery

ISS Science for Everyone

Science Objectives for Everyone Shear History Extensional Rheology Experiment (SHERE) is designed to investigate the effect of preshearing (rotation) on the stress and strain response of a polymer fluid (a complex fluid containing long chains of polymer molecules) being stretched in microgravity. The fundamental understanding and measurement of the extensional rheology of complex fluids is important for understanding containerless processing, an important operation for fabrication of parts (such as adhesives or fillers) using elastomeric materials on future exploration missions. This knowledge can be applied to controlling and improving Earth-based manufacturing processes, as well.

Science Results for Everyone

Complex fluids containing long chains of polymer molecules, called polymer fluids, experience stress and strain when stretched. Pre-shearing, or rotation, affects this stress and strain response when a polymer fluid is stretched in microgravity. Understanding and measuring pre-shearing is necessary for fabricating parts such as adhesives or fillers on future space missions. This investigation measured the material properties of these fluids, including temperature, midpoint diameter, and force on fluid flow at various stretch rates. The data will help researchers understand how to process flexible polymers, which are very resilient and so can be made very thin and lightweight.



This content was provided by Gareth H. McKinley, Ph.D., and is maintained in a database by the ISS Program Science Office.

Experiment Details

OpNom:

Principal Investigator(s)

  • Gareth H. McKinley, Ph.D., Massachusetts Institute of Technology, Cambridge, MA, United States
  • Co-Investigator(s)/Collaborator(s)
    Information Pending

    Developer(s)

    ZIN Technologies Incorporated, Cleveland, OH, United States

    Sponsoring Space Agency
    National Aeronautics and Space Administration (NASA)

    Sponsoring Organization
    Human Exploration and Operations Mission Directorate (HEOMD)

    Research Benefits
    Information Pending

    ISS Expedition Duration:
    April 2008 - April 2009

    Expeditions Assigned
    17,18

    Previous ISS Missions

    SHERE is a unique investigation which has not been performed in microgravity.

    ^ back to top



    Experiment Description

    Research Overview

    • The Shear History Extensional Rheology Experiment (SHERE) will obtain material property measurements of the fluid such as temperature, midpoint diameter, and force in the direction of fluid flow at various rotational preshear and axial extensional rates inside the Microgravity Science Glovebox (MSG).


    • This experiment will generate previously unattainable scientific data for dilute viscoelastic polymer solutions, materials that exhibit both viscous and elastic characteristics when undergoing deformation such as elongation (stretching).


    • Understanding extensional rheology (study of the deformation and flow of matter under the influence of an applied stress) is key in understanding how to process thermoplastic elastomers (flexible elastic polymeric materials), which are very resilient and can be made very thin, and hence, lightweight.


    • SHERE can provide data for engineering design tools that are part of computer-assisted manufacturing (CAM) systems to ensure the rheological properties of polymer parts have not been impacted in a variable gravity environment.

    Description
    The main objective of Shear History Extensional Rheology Experiment (SHERE) is to study the effect of rotational preshear on the extensional behavior of a fluid. The resistance of a fluid to an imposed flow is termed "viscosity", and it is a fundamental material parameter by which manufacturers characterize a material. Unlike common Newtonian fluids, like water for example, complex fluids such as polymers cannot be characterized by a single material parameter such as the Newtonian (shear) viscosity, Polymers are made up of long chains and when exposed to a rotational shearing flow, will align 45 degrees to the flow direction and flip over and over again to coil the polymer chain. When exposed to an extensional (stretching) flow, the coil extends in the direction the fluid is being stretched and can be tightly drawn if the flow is strong enough. Because polymers act like springs, more stress is required to stretch them to higher strains. This relationship between stress and extensional deformation rate (i.e., strain rate) is expressed as an extensional viscosity and is a fundamental material parameter independent of shear viscosity. Due to the coiling effect of rotational shear flow on the polymer chains, shearing on the fluid immediately before extension will have an effect on the extensional behavior of the fluid.

    A class of dilute polymer solutions collectively referred to as Boger fluids, have become a popular choice for fundamental rheological studies of non-Newtonian fluids and will be used in this experiment. These ideal elastic fluids exhibit a nearly constant shear viscosity, which allows a direct comparison of Boger fluids with Newtonian fluids having similar viscosities. The high viscosity of the suspending solvent results in long relaxation times and substantial normal stresses, and the low concentration of high molecular weight polymers facilitates modeling analysis.

    Gravitational body forces cause appreciable sagging of thin fluid filaments. This sagging is most notable for low deformation rates where strain-hardening is not significant. Removing these perturbative forces will allow one to probe a wider parametric range of strain rates while simultaneously measuring the total stress and velocity field (shape and diameter) in the deforming fluid element. These measurements will provide an idealized data set for comparison with theoretical models and will serve as a gold standard for ground-based extensional rheometry.

    ^ back to top



    Applications

    Space Applications
    Understanding the extensional rheology of a complex fluid such as a liquid polymer is key for containerless processing because the absence of the bounding walls of a container or vessel removes the shearing component of the deformation which typically dominates Earth-based processing operations. The resulting flow is thus shear-free or extensional in character. Containerless processing is a central component in the development of in-situ fabrication technology, such as a means of producing new parts on demand or replacing existing parts or tools. This represents a critical element in the evolution of an autonomous exploration capability. In-situ fabricated parts, which may include both new and recycled materials, will be composed of plastics, filled polymers, metals, ceramics and composites.

    SHERE plays a role in this area by measuring, in microgravity conditions, a material property that has a direct connection to in-situ manufacturing and fabrication of polymeric parts. In-situ manufacturing operations can occur in microgravity or reduced gravity levels (e.g. on the Moon or Mars) and may include for example, the extrusion and processing of thermoplastic elastomer films, which are very resilient and can be made thin and lightweight. These elastomeric materials may form the basis of adhesives and fillers utilized in a wide variety of repair applications, especially under a reduced gravity environment, such as the repair of space suits or other similar materials.

    Understanding and exploiting the ability to fabricate new parts in-situ from a limited number of precursor components is critical in future space missions where weight plays a critical role in the overall cost of a mission. Additionally, in-situ repair provides a means of maintaining systems during transport and while on the Moon, Mars, and other extraterrestrial bodies.

    Earth Applications
    Fundamental understanding and measurement of the extensional rheology of complex fluids also allows Earth-based manufacturing processes to be controlled and improved. Ground-based work using variants of the Filament Stretching Rheometer includes studies of spinnability, and the investigations of cohesive and adhesive instabilities which manifests themselves in adhesion and tackiness of materials. It has lead to the development of a Resin-spinning technology that allows the formation of ultra-fine elastic threads analogous to spider-silks. Control of the fluid shear history and extensional rheology of test fluid is essential to optimizing the ultimate web properties. Extensional rheology is of critical importance in optimization of polymer processing operations that involve complex flows, i.e. flows that contain both shearing (rotation) and elongation (stretching) components.

    ^ back to top



    Operations

    Operational Requirements
    On-orbit operations will consist of crew installation, hardware turn-on and checkout, fluid sample installation, experiment execution, and fluid sample removal. During experiment execution a test point is selected (with specified preshear and strain rates), and the experiment will then automatically execute.

    The fluid is presheared and stretched according to a pre-programmed exponential velocity profile. The stretch is stopped abruptly at 194 mm in length, and the tensile stress in the fluid thread is allowed to relax. Each experiment lasts approximately 5 minutes, most of which is spent waiting for the fluid column to drain to the end plates, and the fluid filament eventually breaks in the middle.

    Several key measurements will be made during the experiment. They include measuring the force induced due to shearing and stretching of the elastic fluid, recording the position of the moving plate to verify the imposed velocity profile, recording the fluid diameter at its midpoint , measuring the temperature of the fluid, and measuring the fluid filament shape and evolution. Afterwards, the translation slider is repositioned to the starting position, and the fluid column is reconstituted. If it is reusable (based on a criteria of temperature, bubble contamination, and previous strain encountered), then another test can be performed with the same fluid sample. Otherwise, the fluid sample is removed, and the next one is installed or the hardware is powered down.

    The SHERE hardware consists of the Rheometer, Interface Box, Camera Arm, Keyboard, Toolbox, Fluid Module Stowage Tray, and cabling.

    • The Rheometer is the heart of the SHERE and is where the preshear and elongational deformation of each fluid sample are performed. The Rheometer has a cover that opens to allow the fluid sample installation and closes to prevent accidental escape of the fluid during the test. Two windows allow the fluid to be observed inside the Rheometer. Inside the Rheometer are a rotational stepper motor mounted on a linear translation stage (slider), axial position sensor, laser micrometer, force transducer, electroluminescent panel, X-Y positioning stage, zeroing potentiometer, and thermistors.

    • The Interface Box provides power distribution, control, and data storage for all components.

    • The Camera Arm attaches to the back of the Rheometer, and a black and white video camera is mounted to the top of the arm to allow viewing through the top window of the Rheometer.

    • The Keyboard is used by the crew for data entry and experiment parameter selection and initiation.

    • The Tool Box contains miscellaneous parts and tools used during the setup and operation of the experiment.

    • The Fluid Module Stowage Tray contains twenty-five Fluid Modules, each of which contains an identical sample of a well-characterized model non-Newtonian fluid (a Boger fluid). The Fluid Modules are cylindrical containers with two layers. A split outer shell protects an inner shroud, which is manually retracted to deploy the fluid column between two coaxial, disk-shaped end plates.

    • There are seven cables providing power and signal interconnections between the Rheometer, Interface Box, Camera Arm, Keyboard, and MSG.

    Operational Protocols
    The crew will install the SHERE hardware into the MSG, power up the hardware, and perform hardware checkout using calibration tools. A Fluid Module is then installed into the Rheometer by attaching its two ends to the force transducer and preshear motor/slider, respectively. The crew then deploys the fluid by removing the outer shell and sliding back the inner shroud. The experiment execution automatically occurs once the crew has selected a test point on the keyboard. The fluid is presheared at a steady rotation rate and then stretched according to an exponentially-increasing velocity profile. Following the completion of a test, the fluid column is recombined by bringing the Fluid Module halves back together again. If possible, another test can be performed using the same sample (provided no bubbles are present within the fluid and the sample temperature remains below 25 degrees C). If not, the Fluid Module is sealed, removed, and a new Fluid Sample is prepared for testing or the hardware is powered down. Upon completion of testing, the hardware is removed from the MSG.

    Twenty-five tests will be performed in groups of five tests. Each test will nominally use one Fluid Module. Data downlink will be performed after each group of five tests, and the results will be analyzed before the next group is run. Sample return of the Fluid Modules is desired but not required. Data will also be stored on up to 25 digital video tapes for later return to the ground for more complete analysis.

    ^ back to top



    Results/More Information

    Data analysis continues for the test points performed. This analysis involves the computation of the time evolution in the cross-sectional area of the filament from the radius data, a temperature correction for the relaxation time and the zero-shear rate viscosity to correct for thermal fluctuations in the ISS Glovebox environment, and the computation of the extensional viscosity together with the Trouton ratio (Hall 2009, 2010).

    ^ back to top



    Results Publications

    ^ back to top


    Ground Based Results Publications

    ^ back to top


    ISS Patents

    ^ back to top


    Related Publications

    ^ back to top


    Related Websites

    ^ back to top



    Imagery

    image The SHERE hardware consists of the Rheometer, Interface Box, Camera Arm, Keyboard, Toolbox, Fluid Module Stowage Tray (not pictured), and cabling. Image courtesy of NASA.
    + View Larger Image


    image SHERE Fluid Module with outer shell in place. Image courtesy of NASA.
    + View Larger Image


    image NASA Image: ISS017E012286 - View of Expedition 17 flight engineer Gregory Chamitoff, in the European Lab, Columbus as he works with the Shear History Extensional Rheology Experiment (SHERE) rheometer is inside the Microgravity Sciences Glovebox (MSG).
    + View Larger Image


    image NASA Image: ISS017E012282 - View of the Microgravity Sciences Glovebox (MSG) in th European Lab, Columbus. The Shear History Extensional Rheology Experiment (SHERE) rheometer is inside the MSG.
    + View Larger Image


    image The Shear History Extensional Rheology Experiment (SHERE) operations team monitoring the progress of the experiment from the NASA Glenn Research Center Telescience Support Center in Cleveland, Ohio. Image courtesy of Glenn Research Center. Image courtesy of Glenn Research Center.
    + View Larger Image


    image The Shear History Extensional Rheology Experiment (SHERE) operations team monitoring the progress of the experiment from the NASA Glenn Research Center Telescience Support Center in Cleveland, Ohio. Image courtesy of Glenn Research Center.
    + View Larger Image


    image NASA Image: ISS018E013505 - Expedition 18 Commander Mike Fincke with the SHERE hardware inside of teh MSG.
    + View Larger Image


    image NASA Image: ISS018E017303View of the Microgravity Sciences Glovebox (MSG) with the Shear History Extensional Rheology Experiment (SHERE) inside.
    + View Larger Image


    image NASA Image: ISS017E012296 View of the Laser Micrometer,Deployment Tool,Preshear Motor,and Force Transducer on the Shear History Extensional Rheology Experiment (SHERE) rheometer within the Microgravity Science Glovebox (MSG). Photo was taken in the European Laboratory/Columbus during Expedition 17.
    + View Larger Image


    image NASA Image: ISS028E020679 - NASA astronaut Mike Fossum, Expedition 28 flight engineer, works with Shear History Extensional Rheology Experiment (SHERE) hardware inside the Microgravity Science Glovebox (MSG) located in the Destiny laboratory of the International Space Station


    + View Larger Image