NASA Scientific and Technical Aerospace Reports
NASA Scientific and Technical Aerospace Reports
NASA Scientific and Technical Aerospace Reports
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weldments [1]. The flaw detection mechanism of the flux focusing electromagnetic probe can help alleviate these difficulties<br />
<strong>and</strong> provide a unique capability for detecting longitudinal fatigue cracks in critical tube structures. The Flux Focusing<br />
Electromagnetic Flaw Detector, originally invented for the detection of fatigue <strong>and</strong> corrosion damage in aluminum plates<br />
[2-3], has been adapted for use in testing steel tubing for longitudinal fatigue cracks. The modified design allows for the probe<br />
to be placed axisymmetrically into the tubing, inducing eddy currents in the tube wall. The pickup coil of the probe is fixed<br />
slightly below the primary windings <strong>and</strong> is rotated 90 so that its axis is normal to the tube wall. The magnetic flux of the<br />
primary coil is focused through the use of ferromagnetic material so that in the absence of fatigue damage there will be no<br />
flux linkage with the pickup coil. The presence of a longitudinal fatigue crack will cause the eddy currents induced in the tube<br />
wall to flow around the flaw <strong>and</strong> directly under the pickup coil. The magnetic field associated with these currents will then<br />
link the pickup coil <strong>and</strong> an unambiguous increase in the output voltage of the probe will be measured. The use of the flux<br />
focusing electromagnetic probe is especially suited for the detection of flaws originating at or near tube welds. The probe is<br />
shown to discriminate against signals due solely to the weld joint so that flaw signals are not hidden in the background in these<br />
locations. Experimental <strong>and</strong> finite element modeling results are presented for the flaw detection capabilities of the probe in<br />
stainless steel tubes.<br />
Derived from text<br />
Winding; Magnetic Fields; Ferromagnetic Materials; Magnetic Flux; Crack Propagation; Fatigue (Materials)<br />
20040112013 <strong>NASA</strong> Langley Research Center, Hampton, VA, USA<br />
Buckling Behavior of Compression-Loaded Composite Cylindrical Shells With Reinforced Cutouts<br />
Hilburger, Mark W.; Sarnes, James H., Jr.; September 2004; 25 pp.; In English; Original contains color illustrations<br />
Contract(s)/Grant(s): 719-20-30<br />
Report No.(s): <strong>NASA</strong>/TM-2004-212656; L-19009; No Copyright; Avail: CASI; A03, Hardcopy<br />
Results from a numerical study of the response of thin-walled compression-loaded quasi-isotropic laminated composite<br />
cylindrical shells with unreinforced <strong>and</strong> reinforced square cutouts are presented. The effects of cutout reinforcement<br />
orthotropy, size, <strong>and</strong> thickness on the nonlinear response of the shells are described. A nonlinear analysis procedure has been<br />
used to predict the nonlinear response of the shells. The results indicate that a local buckling response occurs in the shell near<br />
the cutout when subjected to load <strong>and</strong> is caused by a nonlinear coupling between local shell-wall deformations <strong>and</strong> in-plane<br />
destabilizing compression stresses near the cutout. In general, reinforcement around a cutout in a compression-loaded shell<br />
is shown to retard or eliminate the local buckling response near the cutout <strong>and</strong> increase the buckling load of the shell. However,<br />
some results show that certain reinforcement configurations can cause an unexpected increase in the magnitude of local<br />
deformations <strong>and</strong> stresses in the shell <strong>and</strong> cause a reduction in the buckling load. Specific cases are presented that suggest that<br />
the orthotropy, thickness, <strong>and</strong> size of a cutout reinforcement in a shell can be tailored to achieve improved buckling response<br />
characteristics.<br />
Author<br />
Buckling; Composite Structures; Cylindrical Shells; Reinforcement (Structures); Compression Loads; Openings; Numerical<br />
Analysis<br />
20040112014 <strong>NASA</strong> Langley Research Center, Hampton, VA, USA<br />
Parametric Study on the Response of Compression-Loaded Composite Shells With Geometric <strong>and</strong> Material<br />
Imperfections<br />
Hilburger, Mark W.; Starnes, James H., Jr.; September 2004; 29 pp.; In English<br />
Contract(s)/Grant(s): 719-20-30<br />
Report No.(s): <strong>NASA</strong>/TM-2004-212676; L-19008; No Copyright; Avail: CASI; A03, Hardcopy<br />
The results of a parametric study of the effects of initial imperfections on the buckling <strong>and</strong> postbuckling response of three<br />
unstiffened thinwalled compression-loaded graphite-epoxy cylindrical shells with different orthotropic <strong>and</strong> quasi-isotropic<br />
shell-wall laminates are presented. The imperfections considered include initial geometric shell-wall midsurface<br />
imperfections, shell-wall thickness variations, local shell-wall ply-gaps associated with the fabrication process, shell-end<br />
geometric imperfections, nonuniform applied end loads, <strong>and</strong> variations in the boundary conditions including the effects of<br />
elastic boundary conditions. A high-fidelity nonlinear shell analysis procedure that accurately accounts for the effects of these<br />
imperfections on the nonlinear responses <strong>and</strong> buckling loads of the shells is described. The analysis procedure includes a<br />
nonlinear static analysis that predicts stable response characteristics of the shells <strong>and</strong> a nonlinear transient analysis that predicts<br />
unstable response characteristics.<br />
Author<br />
Shells (Structural Forms); Compression Loads; Parameterization; Cylindrical Shells; Composite Structures; Fabrication<br />
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