NASA Scientific and Technical Aerospace Reports

ehavior and the resulting damage metrics. The parametric study conducted using the finite element model confirmed the
observed experimental trends and further indicated that the damage formation is the dominant energy dissipation mechanism
when the ratio of the impactor mass to that of the target is greater than 2 and vibrational energy transfer is dominant for ratios
less than 2. The effects of the ratio of specimen width to planar damage size on the compressive residual strength and failure
modes were investigated for two sandwich configurations. A subsurface damage state was considered for the study and
inflicted using a 3 diameter impactor. The scaling effects were characterized in terms of the residual strength and strain
distributions in the vicinity of the damage region. The latter was measured using a photogrammetry method. The residual
strength was found to increase by 12% when the ratio of the specimen size to damage size was increased from 4.6 to 12.4
for sandwich specimens with two-ply facesheets. No trends were, however, observed for sandwich specimens with four-ply
facesheets. The strain and displacement distributions indicated bending of the facesheet within the damage region leading to
a strain concentration-driven failure mode resembling an open hole configuration for the two-ply facesheet sandwich panels.
The 6.5 wide sandwich specimens with four-ply facesheets failed by global buckling initiated by an unstable dimple
propagation. For wider specimens, there was a dimple growth-arrest mechanism that lead to eventual facesheet fracture. The
increase of the specimen height resulted in a slight decrease in residual strength. This study showed that the results obtained
from small specimens are valid as far as the compressive residual strength obtained experimentally. However, larger specimen
sizes will sustain less impact damage for equivalent impact energy levels. Thus, it is valid to test smaller panels if the damage
is simulated correctly from the larger specimens. The effects of specimen height were not investigated but could effect the
buckling response of the panels.
NTIS
Composite Structures; Sandwich Structures; Damage
20040068371 NASA Marshall Space Flight Center, Huntsville, AL, USA, Sverdrup Technology, Inc., Huntsville, AL, USA,
NASA Marshall Space Flight Center, Huntsville, AL, USA
Measuring Permeability of Composite Cryotank Laminants
Oliver, Stanley T.; Selvidge, Shawn; Watwood, Michael C.; [2004]; 1 pp.; In English; 45th AIAA/ASME/ASCE/AHS/ASC
Structures, Structural Dynamics, and Materials Conference (Special Session): Cryogenic Propellant Tanks and Integrated
Structures for a Next Generation Reusable Launch Vehicle, 10-22 Apr. 2004, Palm Springs, CA, USA
Contract(s)/Grant(s): NAS8-00187; No Copyright; Avail: Other Sources; Abstract Only
This paper describes a test method developed to identify whether certain materials and material systems are suitable
candidates for large pressurized reusable cryogenic tanks intended for use in current and future manned launch systems. It
provides a quick way to screen numerous candidate materials for permeability under anticipated loading environments
consistent with flight conditions, as well as addressing reusability issues. cryogenic tank, where the major design issue was
hydrogen permeability. It was successfully used to evaluate samples subjected to biaxial loading while maintaining test
temperatures near liquid hydrogen. After each sample was thermally preconditioned, a cyclic pressure load was applied to
simulate the in-plane strain. First permeability was measured while a sample was under load. Then the sample was unloaded
and allowed to return to ambient temperature. The test was repeated to simulate reusability, in order to evaluate its effects on
material permeability.
Author
Permeability; Cryogenic Tanks; Carbon; Laminates
20040070723 NASA Glenn Research Center, Cleveland, OH, USA
Assessment of Erosion Resistance of Coated Polymer Matrix Composites for Propulsion Applications
Miyoshi, Kazuhisa; Sutter, James K.; Horan, Richard A.; Naik, Subhash K.; Cupp, Randall J.; April 2004; 22 pp.; In English
Contract(s)/Grant(s): WBS 708-31-14; WBS 714-30-01
Report No.(s): NASA/TM-2004-212911; E-14102; No Copyright; Avail: CASI; A03, Hardcopy
The erosion behavior of tungsten carbide-cobalt (WC-Co) coated and uncoated polymer matrix composites (PMCs) was
examined with solid particle impingement using air jets. Erosion tests were conducted with Arizona road dust impinging at
20 degrees, 60 degrees, and 90 degrees angles at a velocity of 229 meters per second at both 294 and 366 K. Noncontact optical
profilometry was used to measure the wear volume loss. Results indicate that the WC-Co coating enhanced erosion resistance
and reduced erosion wear volume loss by a factor of nearly 2. This should contribute to longer wear lives, reduced related
breakdowns, decreased maintenance costs, and increased product reliability.
Author
Coatings; Cobalt; Erosion; Polymer Matrix Composites; Tungsten Carbides; Jet Propulsion; Corrosion Resistance
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