NASA Scientific and Technical Aerospace Reports
NASA Scientific and Technical Aerospace Reports
NASA Scientific and Technical Aerospace Reports
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20040111390 <strong>NASA</strong> Glenn Research Center, Clevel<strong>and</strong>, OH, USA<br />
Modeling the Nonlinear, Strain Rate Dependent Deformation of Shuttle Leading Edge Materials with Hydrostatic<br />
Stress Effects Included<br />
Goldberg, Robert K.; Carney, Kelly S.; [2004]; 12 pp.; In English; 8th International LS-DYNA Users Conference, 2-4 May<br />
2004, Dearborn, MI, USA<br />
Contract(s)/Grant(s): 22-376-70-30-02; No Copyright; Avail: CASI; A03, Hardcopy<br />
An analysis method based on a deformation (as opposed to damage) approach has been developed to model the strain rate<br />
dependent, nonlinear deformation of woven ceramic matrix composites, such as the Reinforced Carbon Carbon (RCC)<br />
material used on the leading edges of the Space Shuttle. In the developed model, the differences in the tension <strong>and</strong> compression<br />
deformation behaviors have also been accounted for. State variable viscoplastic equations originally developed for metals have<br />
been modified to analyze the ceramic matrix composites. To account for the tension/compression asymmetry in the material,<br />
the effective stress <strong>and</strong> effective inelastic strain definitions have been modified. The equations have also been modified to<br />
account for the fact that in an orthotropic composite the in-plane shear response is independent of the stiffness in the normal<br />
directions. The developed equations have been implemented into LS-DYNA through the use of user defined subroutines<br />
(UMATs). Several sample qualitative calculations have been conducted, which demonstrate the ability of the model to<br />
qualitatively capture the features of the deformation response present in woven ceramic matrix composites.<br />
Derived from text<br />
Ceramic Matrix Composites; Composite Materials; Stress-Strain Relationships; Hydrostatics; Strain Rate; Viscoplasticity<br />
20040111396 QSS Group, Inc., Clevel<strong>and</strong>, OH, USA<br />
Robust Joining Technology for Solid Oxide Fuel Cells Applications<br />
Shpargel, Tarah P.; Needham, Robert J.; Singh, M.; Kung, S. C.; [2004]; 30 pp.; In English; 28th International Cocoa Beach<br />
Conference <strong>and</strong> Exposition on Advanced Ceramics <strong>and</strong> Composites, 25-30 Jan. 2004, Cocoa Beach, FL, USA<br />
Contract(s)/Grant(s): NAS3-00145; 22-708-87-07; Copyright; Avail: CASI; A03, Hardcopy<br />
Recently there has been a great deal of interest in research development <strong>and</strong> commercialization of solid oxide fuel cells<br />
(SOFCs). Joining <strong>and</strong> sealing are critical issues that will need to be addressed before SOFCs can truly perform as expected.<br />
Ceramics <strong>and</strong> metals can be difficult to join together, especially when the joint must withst<strong>and</strong> up to 900 C operating<br />
temperature of the SOFCs. The goal of the present study is to find the most suitable braze material for joining of yttria<br />
stabilized zirconia (YSZ) to stainless steel. A number of commercially available braze materials TiCuSil, TiCuNi,<br />
Copper-ABA, Gold-ABA <strong>and</strong> Gold-ABA-V have been evaluated. The oxidation behavior of the braze materials <strong>and</strong> steel<br />
substrates in air was also examined through thermogravimetric analysis. The microstructure <strong>and</strong> composition of the brazed<br />
regions have been examined by optical <strong>and</strong> scanning electron microscopy <strong>and</strong> eDS analysis. Effect of braze composition <strong>and</strong><br />
processing conditions on the interfacial microstructure <strong>and</strong> composition of the joint regions will be presented.<br />
Author<br />
Brazing; Ceramics; Metals; Oxidation; Sealing; Solid Oxide Fuel Cells<br />
20040111402 Winona State Univ., Winona, MN, USA<br />
Accelerated Testing of Polymeric Composites: Correlation of Scale-up Effects on Viscoelastic Behavior<br />
Abdel-Magid, Beckry; [2004]; 6 pp.; In English<br />
Contract(s)/Grant(s): NAG1-01054; No Copyright; Avail: CASI; A02, Hardcopy<br />
A major issue for many designers <strong>and</strong> engineers is the long-term mechanical properties of polymer matrix composites<br />
(PMC). These composites are being used more than ever in high-performance applications; <strong>and</strong> engineers need to underst<strong>and</strong><br />
the characteristics of polymeric behavior as they relate to the time-dependent mechanical properties, or viscoelastic properties.<br />
The viscoelastic nature of polymers dominates the mechanical properties of polymeric composites. Failure modes such as<br />
excessive deformation, creep rupture, <strong>and</strong> environmental aging are all related to the viscoelastic properties of these<br />
composites. Determining these time-dependent properties, <strong>and</strong> the factors that affect them, is crucial to underst<strong>and</strong>ing how a<br />
material will perform under high performance conditions. In this research project an accelerated method was developed using<br />
the dynamic mechanical analyzer (DMA) to measure the viscoelastic creep properties of polymeric composite materials. The<br />
objectives of the study are to: investigate the use of the DMA in finding creep properties of polymeric composites, compare<br />
results from DMA creep tests with data from conventional creep tests, assess the accuracy of results of the DMA sub-coupon<br />
level tests, <strong>and</strong> investigate the potential of using the DMA results to predict the long-term creep properties of composite<br />
materials.<br />
Derived from text<br />
Mechanical Properties; Polymer Matrix Composites; Viscoelasticity; Aging (Materials); Accelerated Life Tests<br />
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