The NASGRO 3.0 computer program is an advanced version of a program used by NASA and the European Space Agency for fracture-control analysis of space-system structures and other hardware. The prior version, NASA/FLAGRO 2.0, was described in “Updated Fatigue-Crack-Growth and Fracture-Mechanics Software” (MSC-22550), NASA Tech Briefs, Vol. 19, No. 12 (December 1995), page 74. NASGRO 3.0 affords additional capability for durability and damagetolerance analysis of aircraft structures and other mechanical systems. Because this code offers state-of-the-art and general capabilities in fracture mechanics and crack-propagation analysis, its usefulness extends beyond aerospace to numerous industrial applications: For example, it can provide guidance for prevention of catastrophic failures that originate in cracklike flaws in offshore oil structures, pressure vessels, pipes, diesel engines, and railroad tank cars. The program is also useful as an instructional device for courses in fatigue and fracture mechanics.

The objective in developing NASGRO 3.0 was to extend NASA/FLAGRO 2.0 (which was released in 1994) to accommodate more recent advancements in fracture mechanics and crack-propagation theory, to meet needs for damage-tolerance and durability analysis of aircraft, and to enable the program to function within the Windows 95/98, Windows NT, and Unix operating systems. The changes made in pursuit of this objective were the following:

• A graphical user interface (GUI) was developed to make input of data easier and more intuitive.

• Load-interactive or retardation routines were added to account for changes in crack-growth rates due to fatigue spectrum (nonconstant) loading. Five different mathematical models have been included: the generalized Willenborg, the modified generalized Willenborg, the Walker- Chang-Willenborg, the strip-yield, and the constantclosure models.

• New and improved crack solutions were added for cases of bolts, cracks from holes, and nonlinear stress distributions.

• Spectrum-input routines have been improved to provide more flexibility in the use of pre-existing spectrum files.

• A materials database has been added, along with a GUI that gives users access to the data from which the materialproperty curves are derived. A software module called “NASMAT” contains a base of experimental data that are available for easy access, viewing, and use in deriving crack-growth material constants required for safe-life analysis.

• The threshold equation has been improved by incorporation of a newer, more accurate mathematical model of fatigue- crack-growth thresholds.

This program was written by Royce G. Forman of Johnson Space Center; V. Shivakumar, Sambi Mettu, Joachim Beek, and Feng Yeh of Lockheed Martin; and Leonard Williams of GB Tech, Inc., and is available at MSC-23082

NASA Tech Briefs Magazine

This article first appeared in the April, 2002 issue of NASA Tech Briefs Magazine.

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