Strain Isolator Pad (SIP)

Name: Strain Isolator Pad (SIP)
Database: NASA Ames Thermal Protection Materials
Category: Silicon-Based Reusable Composites: Cloths
Composition: Aramid fibers
Manufacturer: Albany International
Technical Readiness Level: 9
Last Modified: 2001-10-01

Description:

  • SIP, or Strain Isolation Pad, is a Nomex felt pad used to prevent stress failure in rigid TPS ceramic tiles. The SIPs are thermal isolators typically supplied in thicknesses of 0.090, 0.115 or 0.160 inch. SIPs are bonded to the tiles, and the SIP and tile assembly is bonded to the shuttle orbiter structure using an RTV adhesive. <BR><BR> SIP can introduce stress concentrations at the needled fiber bundles. This has resulted in localized failure in the tile just above the RTV bond line causing loss of the tile during flight. To solve this problem, the inner surface of the tile is densified to distribute the load more uniformly and increase tile strength at the bondline.

Point of Contact:

  • Marc Rezin
  • NASA Ames Research Center
  • mrezin@mail.arc.nasa.gov

Pictures:

  • N/A

Properties at Standard Conditions
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Property Value Units Uncertainty Source STP Reference Last Modified Additional Data
Density 5.40e+00 lbm/ft^3 2.70e-01 unknown assumed/assumed 1 2006-01-05
Thermal Conductivity (Thru-the-Thickness)1 6.52e-06 Btu/ft-s-R 2.97e-08 unknown interpolated(T) 1 2006-01-05
Specific Heat2 3.12e-01 Btu/lbm-R 1.56e-03 unknown TRUE 1 2006-01-05
Multiple Use Temperature Limit 9.10e+02 R 4.55e+01 unknown assumed/assumed 1 2006-01-05
Single Use Temperature Limit 1.16e+03 R 5.80e+01 unknown assumed/assumed 1 2006-01-05
Tensile Strength (Isotropic)3 3.96e+03 psf 1.98e+01 unknown TRUE 2 2006-01-05

Notes:

  • 1. Value is Per MB0135-051, Type II, Class 3 SIP with .0075 RTV-560 each side.
  • 2. Values extracted from graph of data.
  • 3. Values are flatwise tensile strength vs temperature, for 0.160 inch thick SIP transfer coated per MA0106-316, grades A and B.. SIP is highly sensitive to strain rates and previous loading history.

Property References:

  • 1. anon: Space Shuttle Program Thermodynamic Design Data Book. Penetrations.:SD73-SH-0226:Rockwell International, Downey, CA:Jan. 1981:TPSX Ref. #23.
  • 2. anon: Materials Property Manual, Vol.3, Thermal Protection System Materials Data:Rockwell International Publication:Sep. 1980:TPSX Ref. #24.

General References:

  • 1. anon: Space Shuttle Program Thermodynamic Design Data Book. Penetrations.:SD73-SH-0226:Rockwell International, Downey, CA:Jan. 1981:TPSX Ref. #23.
  • 2. anon: Materials Property Manual, Vol.3, Thermal Protection System Materials Data:Rockwell International Publication:Sep. 1980:TPSX Ref. #24.
  • 3. J. Sawyer: Mechanical Properties of the Shuttle Orbiter Thermal Protection System Strain Isolator Pad:23rd Structures, Structural Dynamics and Materials Conference, New Orleans, LA:May 10-12, 1982:TPSX Ref. #25.