NASA Scientific and Technical Aerospace Reports

B and A(sup *) could only be made when the starting slow crack growth equation was transformed and the coefficients of
variation of the input parameters were not too large. This was partially a result of the skewered distributions of B and A(sup
*). Parametric variation of the input parameters was used to determine an acceptable range for using closed form approximate
equations derived from propagation of errors.
Author
Stress Analysis; Crack Propagation; Error Analysis; Fatigue Tests
20040120876 NASA Langley Research Center, Hampton, VA, USA
Application of Self Nulling Eddy Current Probe Technique to the Detection of Fatigue Crack Initiation and Control
of Test Procedures
Namkung, M.; Nath, S.; Wincheski, B.; Fulton, J. P.; [1994]; 7 pp.; In English; No Copyright; Avail: CASI; A02, Hardcopy
A major part of fracture mechanics is concerned with studying the initiation and propagation of fatigue cracks. This
typically requires constant monitoring of crack growth during fatigue cycles and the knowledge of the precise location of the
crack tip at any given time. One technique currently available for measuring fatigue crack length is the Potential Drop method.
The method, however, may be inaccurate if the direction of crack growth deviates considerably from what was assumed
initially or the curvature of the crack becomes significant. Another popular approach is to optically view the crack using a high
magnification microscope, but this entails a person constantly monitoring it. The present proposed technique uses an
automated scheme, in order to eliminate the need for a person to constantly monitor the experiment. Another technique under
development elsewhere is to digitize an optical image of the test specimen surface and then apply a pattern recognition
algorithm to locate the crack tip. A previous publication showed that the self nulling eddy current probe successfully tracked
a simulated crack in an aluminum sample. This was the impetus to develop an online real time crack monitoring system. An
automated system has been developed which includes a two axis scanner mounted on the tensile testing machine, the probe
and its instrumentation and a personal computer (PC) to communicate and control all the parameters. The system software
controls the testing parameters as well as monitoring the fatigue crack as it propagates. This paper will discuss the
experimental setup in detail and demonstrate its capabilities. A three dimensional finite element model is utilized to model the
magnetic field distribution due to the probe and how the probe voltage changes as it scans the crack. Experimental data of the
probe for different samples under zero load, static load and high cycle fatigue load will be discussed. The final section
summarizes the major accomplishments of the present work, the elements of the future R&D needs and the advantages and
disadvantages of using this system in the laboratory and field.
Derived from text
Crack Propagation; Eddy Currents; Fatigue (Materials); Mathematical Models; Fracture Mechanics; Detection; Probes
20040120950 NASA Langley Research Center, Hampton, VA, USA
Multi-Terrain Impact Testing and Simulation of a Composite Energy Absorbing Fuselage Section
Fasanella, Edwin L.; Lyle, Karen H.; Sparks, Chad E.; Sareen, Ashish K.; [2004]; 12 pp.; In English; American Helicopter
Society 60th Annual Forum, 8-10 Jun. 2004, Baltimore, MD, USA; Original contains color illustrations; No Copyright; Avail:
CASI; A03, Hardcopy
Comparisons of the impact performance of a 5-ft diameter crashworthy composite fuselage section were investigated for
hard surface, soft soil, and water impacts. The fuselage concept, which was originally designed for impacts onto a hard surface
only, consisted of a stiff upper cabin, load bearing floor, and an energy absorbing subfloor. Vertical drop tests were performed
at 25-ft/s onto concrete, soft-soil, and water at NASA Langley Research Center. Comparisons of the peak acceleration values,
pulse durations, and onset rates were evaluated for each test at specific locations on the fuselage. In addition to comparisons
of the experimental results, dynamic finite element models were developed to simulate each impact condition. Once validated,
these models can be used to evaluate the dynamic behavior of subfloor components for improved crash protection for hard
surface, soft soil, and water impacts.
Author
Impact Damage; Fuselages; Impact Tests; Simulation; Crashworthiness; Terrain; Velocity
20040120964 Sandia National Labs., Albuquerque, NM
Status and Integrated Road-Map for Joints Modeling Research
Segalman, D. J.; Paez, T.; Smallwood, D.; Sumali, A.; Urbina, A.; Mar. 2003; In English
Report No.(s): DE2004-809623; SAND2003-0897; No Copyright; Avail: National Technical Information Service (NTIS)
The constitutive behavior of mechanical joints is largely responsible for the energy dissipation and vibration damping in
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