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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Failure analysis of flaw growth characteristics of 6Al-4V titanium forgings used in Apollo spacecraft propellant tanks
Ultrasonic radiography for weld flaw detection in butt joints of Saturn 5 S-1C stage
Cyclic and sustained load flaw growth properties of titanium alloys for pressure vessels
Plane strain cyclic flaw growth in aluminum and titanium specimens
Stress intensity factors for surface flawed fracture specimens
Reliable and accurate Delta technique, a nondestructive ultrasonics method, uses redirection of energy to detect randomly oriented imperfections in fusion butt welds. Data on flaws can be read from either an oscilloscope or a printout.
Growth of deep surface flaws in thin wall tanks of aluminum and titanium base metals
Comparison of flaw growth characteristics under cryogenic proof and ambient test conditions for Apollo titanium pressure vessels
Fracture and sustained load flaw growth characteristics for titanium alloy evaluated in nitrogen tetroxide
Growth behavior of surface-flaw type cracks in titanium alloys
Radiographic flaw detection evaluation in aluminum TIG welds
Stress analysis of multilayered composite structures with flaws, emphasizing application to fracture studies
Stress intensity factors and strain energy rate for bonded layered composites with interface flaw /crack/
A description is given of a computer program for analyzing the crack propagation in cyclic loaded structures. By using equations for the stress intensity factors for surface and embedded flaws, the capability of ascertaining lengthwise crack growth as well as crack growth through the thickness of the structure was determined. Equations used are written in general form so that many other types of crack growth problems, such as through the thickness type cracks, can be analyzed. Provisions have been made in the computer program to analyze crack growth for repeated blocks of variable-amplitude fatigue load spectra. Additional features of the computer program include a variable print interval and a variable integration interval to minimize computer printout and computer run time. A source listing and instructions for using the computer program are included.
Recent experimental findings related to the surface deformation and plastic zones associated with a deep surface flaw in Mode I tension loading are surveyed. Results of front and back surface dimpling, as determined by replica profiling and interferometry, are presented. The stresses required to initiate back surface dimpling are inversely related both to the crack depth and to the crack length. The plastic zone at the crack tip is described using results obtained from Fe-3Si specimens which have been studied with the electrolytic etching technique. It is shown that the plastic zone may be identified with a state of plane strain around the entire crack perimeter, except for the very thin layer near the crack tips on the front surface, where the deformation state approximates plane stress.
Small structures are checked by monitoring samples for acoustical signal count. Flaws are located by observing relatively high acoustical activity within given area. Acoustical monitoring has been extended to large structures by dividing large samples into small areas and then monitoring each area separately.
The crack-closure and crack-growth characteristics of the titanium alloy Ti-6Al-4V were determined experimentally on surface-flawed plate specimens. Under cyclic loading from zero to tension, cracks deeper than 1 mm opened at approximately 50 percent of the maximum load. Cracks shallower than 1 mm opened at higher loads. The correlation between crack-growth rate and the total stress-intensity range showed a lower threshold behavior. This behavior was attributed to the high crack-opening loads at short cracks because the lower threshold was much less evident in correlations between the crack-growth rates and the effective stress-intensity range.
Multicomputer configurations and redundancy management techniques used in various airborne systems were investigated to determine methods to prevent and/or treat generic design flaws. The findings are intended for use in the design of a computer system for use in the space shuttle orbiter.