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Title: Constitutive Models for the Viscoelastic Behavior of Polyimide Membranes at Room and Deep Cryogenic Temperatures

Abstract

Targets for ICF shots on NIF typically use ~500nm thin polyimide films with a coating of 25nm of aluminum as windows that seal the laser entrance hole or LEH. Their role is to contain the hohlraum gas and minimize the extraneous infra-red radiation getting in. This is necessary to precisely control the hohlraum thermal environment for layering inside the capsule with solid deuterium-tritium at 18K. Here, we use our empirical data on the bulging behavior of these foils under various different conditions to develop models to capture the complex viscoelastic behavior of these films at both ambient and cryogenic temperatures. The constitutive equations derived from these models give us the ability to quantitatively specify the film’s behavior during the fielding of these targets and set the best parameters for new target designs.

Authors:
 [1];  [2];  [2];  [2];  [2]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  2. Luxel Corp., Friday Harbor, WA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1343043
Report Number(s):
LLNL-JRNL-677537
Journal ID: ISSN 1536-1055; TRN: US1701814
Grant/Contract Number:
AC52-07NA27344
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Fusion Science and Technology
Additional Journal Information:
Journal Volume: 70; Journal Issue: 2; Journal ID: ISSN 1536-1055
Publisher:
American Nuclear Society
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 42 ENGINEERING

Citation Formats

Bhandarkar, Suhas, Betcher, Jacob, Smith, Ryan, Lairson, Bruce, and Ayers, Travis. Constitutive Models for the Viscoelastic Behavior of Polyimide Membranes at Room and Deep Cryogenic Temperatures. United States: N. p., 2016. Web. doi:10.13182/FST15-218.
Bhandarkar, Suhas, Betcher, Jacob, Smith, Ryan, Lairson, Bruce, & Ayers, Travis. Constitutive Models for the Viscoelastic Behavior of Polyimide Membranes at Room and Deep Cryogenic Temperatures. United States. doi:10.13182/FST15-218.
Bhandarkar, Suhas, Betcher, Jacob, Smith, Ryan, Lairson, Bruce, and Ayers, Travis. 2016. "Constitutive Models for the Viscoelastic Behavior of Polyimide Membranes at Room and Deep Cryogenic Temperatures". United States. doi:10.13182/FST15-218. https://www.osti.gov/servlets/purl/1343043.
@article{osti_1343043,
title = {Constitutive Models for the Viscoelastic Behavior of Polyimide Membranes at Room and Deep Cryogenic Temperatures},
author = {Bhandarkar, Suhas and Betcher, Jacob and Smith, Ryan and Lairson, Bruce and Ayers, Travis},
abstractNote = {Targets for ICF shots on NIF typically use ~500nm thin polyimide films with a coating of 25nm of aluminum as windows that seal the laser entrance hole or LEH. Their role is to contain the hohlraum gas and minimize the extraneous infra-red radiation getting in. This is necessary to precisely control the hohlraum thermal environment for layering inside the capsule with solid deuterium-tritium at 18K. Here, we use our empirical data on the bulging behavior of these foils under various different conditions to develop models to capture the complex viscoelastic behavior of these films at both ambient and cryogenic temperatures. The constitutive equations derived from these models give us the ability to quantitatively specify the film’s behavior during the fielding of these targets and set the best parameters for new target designs.},
doi = {10.13182/FST15-218},
journal = {Fusion Science and Technology},
number = 2,
volume = 70,
place = {United States},
year = 2016,
month = 6
}

Journal Article:
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  • Polyimide films has been used as insulating component in superconducting machinery. A full understanding of the property at low temperatures and the radiation effect is very important for stabilization of superconducting coils. The tensile properties of polyimide films have been measured at 4.2 K {approximately} 473 K. Stress-Strain curve profiles vary as a function of temperature. At cryogenic temperature, the elongation is much lower but the tensile strength is higher than that at room temperature. Also, polyimide film degradation performances after exposure of to an electron beam at very high dose level are examined. The test device for irradiation hasmore » a cooling system for preventing polyimide film from heating by electron absorption. The tests are performed at room temperature in He gas. After 80 MGy absorption, the elongation maintains about 60% level of the non irradiated film, and the tensile strength maintains about 85%.« less
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  • Flow-induced structural anisotropy could result when a complex fluid system is removed from equilibrium by means of hydrodynamic forces. In this paper, a general theory is developed to model flow induced anisotropic behavior of complex viscoelastic systems, e.g. polymer solutions/melts and suspensions. The rheological properties are characterized by viscosity and relaxation time tensors. We consider a second-rank tensor as a measure of the microstructure. We consider the effect of the flow on the structural changes: i.e. the evolution of the microstructure tensor is governed by a relaxation-type differential equation. We also propose that the viscosity and the relaxation time tensorsmore » depend on the second-rank microstructure tensor. That is as the microstructure tensor changes with the applied rate of deformation, the viscosity and relaxation time tensors evolve accordingly. As an example we consider elongational flow of two complex fluids.« less
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