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Foundation :: Engineering Applications :: NASA FLAGRO v2


Fatigue Crack Growth Computer Program

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Total downloads from Open Channel to date: 2
source code available SOURCE CODE AVAILABLE

Structural flaws and cracks may grow under fatigue inducing loads and, upon reaching a critical size, cause structural failure to occur. The growth of these flaws and cracks may occur at load levels well below the ultimate load bearing capability of the structure. The Fatigue Crack Growth Computer Program, NASA/FLAGRO v2, was developed as an aid in predicting the growth of pre-existing flaws and cracks in structural components of space systems. NASA/FLAGRO provides the fracture mechanics analyst with a computerized method of evaluating the "safe crack growth life" capabilities of structural components. NASA/FLAGRO could also be used to evaluate the damage tolerance aspects of a given structural design.

The propagation of an existing crack is governed by the stress field in the vicinity of the crack tip. The stress intensity factor is defined in terms of the relationship between the stress field magnitude and the crack size. The propagation of the crack becomes catastrophic when the local stress intensity factor reaches the fracture toughness of the material. NASA/FLAGRO predicts crack growth using a two-dimensional model which predicts growth independently in two directions based on the calculation of stress intensity factors. The analyst can choose to use either a crack growth rate equation or a nonlinear interpolation routine based on tabular data. The growth rate equation is a newly modified Forman equation which can be converted to a Paris equation by substituting different values into the exponent. This equation provides accuracy and versatility and can be fit to data using standard least squares methods. Stress-intensity factor numerical values can be computed for making comparisons or checks of solutions. NASA/FLAGRO can check for failure of a part-through crack in the mode of a through crack when net ligament yielding occurs.

NASA/FLAGRO has a number of special subroutines and files which provide enhanced capabilities and easy entry of data. These include:
  • crack case solutions,
  • cyclic load spectrums,
  • nondestructive examination initial flaw sizes,
  • table interpolation,
  • and material properties.
The material properties files are divided into two types, a user defined file and a fixed file. Data is entered and stored in the user defined file during program execution, while the fixed file contains already coded-in property value data for many different materials. Prompted input from CRT terminals consists of initial crack definition (which can be defined automatically), material properties (if they are not in the built-in tables of material data), load spectrum data (if not included in the loads spectrum file), and design limit stress levels. NASA/FLAGRO output includes an echo of the input with any error or warning messages, the final crack size, an indication as to whether or not critical crack size has been reached for the specified stress level, and a life history profile of the crack propagation.

NASA FLAGRO v2 carries the NASA case numbers MSC-22550 and COS-10073. It was originally released as part of the NASA COSMIC collection.
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