NASA Scientific and Technical Aerospace Reports

close-contact particle/interface region. It also shows that the increase of the temperature gradient diminishes the effect of the
disjoining pressure. The analysis of the numerical results obtained for a large range of processing conditions and materials
parameters has led to the development of an analytical solution for the critical velocity of pushing/engulfinent transition. The
theoretical results will be discussed and compared with the experimental measurements performed under microgravity
conditions.
Author
Metal Matrix Composites; Ceramics; Liquid-Solid Interfaces
20040050394 Arkansas Univ., Fayetteville, AR, USA
Repair of Damaged Concrete Structures Using Prepreg Composites
2003; 40 pp.; In English
Report No.(s): PB2004-103413; MBTC-2033; No Copyright; Avail: CASI; A03, Hardcopy
In this study, two fast curing resins were used to repair predamaged RC columns. They were 1.5-hour heat activated
curing prepreg and 20-minute ultraviolet curing resin. A 24-hour curing epoxy was also used for comparison purposes. A total
of 24 steel reinforced Phi 152.4 mm x 609.6 mm small-scale concrete columns were designed, cast, cured, surface prepared,
and predamaged. The damaged samples were repaired using the three types of E-glass fabric reinforced resins. An accelerated
conditioning using boiling seawater and ultraviolet radiation was also conducted to investigate the hygrothermal durability of
the repaired samples. Uniaxial compression test was conducted on both control samples and conditioned samples. The test
results and cost/benefit analysis results show that the two fast curing resins can replace the currently used long-time curing
resins in repairing damaged RC columns. A finite element analysis using ANSYS was also conducted to investigate the effect
of fiber orientation on the stress-strain distributions of FRP wrapped concrete columns. A total of twenty-one Phi 152.4 mm
x 304.8 mm concrete columns were prepared and tested to validate the analysis. The test and analysis results show that
aligning some fibers in axial direction may be more preferable for real columns.
NTIS
Concrete Structures; Durability; Curing; Fabrics; Fiber Orientation; Maintenance; Stress-Strain Relationships
20040050582 Ohio Aerospace Inst., Cleveland, OH, USA
SiC/SiC Life Modeling at Intermediate Temperatures under NASA UEET
Morscher, Gregory N.; [2003]; 9 pp.; In English; No Copyright; Avail: CASI; A02, Hardcopy
Within the NASA UEET program, physics-based residual strength and rupture life models are being developed for a
variety of time-temperature-stress-environment conditions for SiC/SiC components such as combustor liners and vanes.
During service, a tensile stress condition that could be life-limiting typically occurs on the ‘cold side’ of these components
due to thermal gradients and attachment schemes. An intermediate temperature (600 to 1000 C) stress-rupture model has been
developed based on the underlying physical processes, i.e., oxygen penetration through matrix cracks, oxidation of the BN
interphase, and subsequent fiber-fiber fusion within crack-bridging tows that eventually fail in time due to time-dependent
strength degradation of the weakest fibers. Modifications to the model will be discussed to incorporate different environmental
conditions as well as changes in oxidation kinetics due to improved interphase concepts.
Author
Silicon Carbides; Ceramic Matrix Composites; Life (Durability); Residual Strength; Rupturing
20040051019 California Inst. of Tech., Pasadena, CA, USA
Global Failure Modes in Composite Structures for High Altitudes
Knauss, W. G.; March 2004; 2 pp.; In English
Contract(s)/Grant(s): NAG1-02029; No Copyright; Avail: CASI; A01, Hardcopy
This report summarizes the accomplishments under the referenced grant. The work described was started under the
guidance and supervision of the late Dr. James Stames as the technical contact. It was aimed at investigating the development
of analysis tools to deal with the problem of rupture in reinforced structural skin of future composites-based aircraft. It was
of particular interest to assess methods by which failure features reminiscent of cracks in metallic structures would develop
and propagate in fiber reinforced structures in interaction with the reinforcing frame. To eventually achieve that goal it was
necessary to first understand the stress or strain distribution at the front of such features so that interactions between such
features and reinforcing agents could be assessed computationally. Thus the major emphasis here was on the assessment of
damage front and methods on how to assess or characterize it. During the conduct of this research program Dr. Stames changed
to a different NASA- internal assignment, which divorced him of the direct supervision of this grant. A student who was
24