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Mullen, R. L.

Publications and source records attributed to Mullen, R. L..

41 records · Page 3

Analogy between fluid cavitation and fracture mechanics

When the stresses imposed on a fluid are sufficiently large, rupture or cavitation can occur. Such conditions can exist in many two-phase flow applications, such as the choked flows, which can occur in seals and bearings. Nonspherical bubbles with large aspect ratios have been observed in fluids under rapid acceleration and high shear fields. These bubbles are geometrically similar to fracture surface patterns (Griffith crack model) existing in solids. Analogies between crack growth in solid and fluid cavitation are proposed and supported by analysis and observation (photographs). Healing phenomena (void condensation), well accepted in fluid mechanics, have been observed in some polymers and hypothesized in solid mechanics. By drawing on the strengths of the theories of solid mechanics and cavitation, a more complete unified theory can be developed.

Hendricks, R. C.↗

The effect of annealing on the creep of plasma sprayed ceramics

The creep of plasma sprayed ZrO2-8Y2O3 was measured at temperatues from 98 to 1250 C (180 to 220 F), and compared to creep of identical samples after annealing at temperatures from 98 to 1316 C (1800 to 2400 F). Loads and temperatures which produced significant creep of as sprayed ceramics produced no creep after annealing.

Hendricks, R. C.↗

Correlation of compressive stress with spalling of plasma sprayed ceramic materials

Ceramics on metal substrates for potential use as high temperature seals or other applications are exposed to forces originating from differences in thermal expansion between the ceramic and the metal substrate. This report develops a relationship between the difference in expansion of the ceramic and the substrate, defines conditions under which shear between the ceramic and the substrate occurs, and those under which bending forces are produced in the ceramic. The off-axis effect of compression forces resulting from high temperature plastic flow of the ceramic producing buckling of the ceramic is developed. Shear is associated with the edge or boundary stresses on the component while bending is associated with the distortion of an interior region. Both modes are significant in predicting life of the ceramic.

Mullen, R. L.↗

Residual stress in plasma sprayed ceramic turbine tip and gas path seal specimens

The residual stresses in a ceramic sheet material used for turbine blade tip gas path seals, were estimated. These stresses result from the plasma spraying process which leaves the surface of the sheet in tension. To determine the properties of plasma sprayed ZrO2-Y2O3 sheet material, its load deflection characteristics were measured. Estimates of the mechanical properties for sheet materials were found to differ from those reported for plasma sprayed bulk materials.

Hendricks, R. C.↗