History. NASA/FLAGRO was originally developed at the NASA Johnson Space Center in the early 1980s to perform fracture control for manned space programs. The name was changed to NASGRO with the release of version 3 in 1999. Southwest Research Institute and NASA have been jointly developing NASGRO since version 4 in 2001.
Different Modules. NASGRO is actually a suite of different computer programs for different types of fatigue and fracture mechanics analysis:
- NASFLA (the main module) calculates fatigue crack growth lifetimes
- NASSIF calculates stress intensity factors from a library of solutions
- NASCCS calculates critical crack size at failure, or threshold crack size for no growth
- NASFAD assesses flaw criticality using the Failure Assessment Diagram (FAD)
- NASGLS calculates time-dependent crack growth in glass-like materials
- NASMAT fits fatigue crack growth and fracture toughness equations to test data
- NASFORM calculates crack formation lifetime using stress-life or strain-life methods
- NASBEM calculates stress intensity factors for 2D bodies using the boundary element method
All of these modules have user-friendly graphical interfaces to facilitate data entry and results visualization.
Stress Intensity Factors. The stress intensity factor (K) library is one of the greatest strengths of NASGRO. NASGRO has over 110 different K solutions for cracks in plates, lugs, cylinders, spheres, fasteners, stiffened panels, and structural sections, plus cracks at holes, notches, or cutouts. Most of these solutions are exclusive to NASGRO. Some K solutions are formulated for remote tension, bending, pin, and/or pressure loading, while more than 30 other solutions employ a weight function formulation for arbitrary stress distributions (univariant or bivariant) on the crack plane in the corresponding uncracked body. Most of the weight function solutions allow residual stresses or localized yielding to be included in the model. Users can input their own K solutions through tables, and they can include compounding factors with nearly all of the library solutions. A complete listing of all the K solutions is available here.
Material Properties. NASGRO also includes a large library of material properties. FCG and fracture toughness properties are available for nearly 500 different metallic materials. A complete listing of all these materials is available here. The NASMAT module contains the original FCG data that supports all of these properties, including 3000 sets of FCG data and 6000 toughness values. NASMAT can also be used to fit FCG equations to user data, or to re-fit NASGRO data. Material properties and crack analyses can be expressed in US units or several different metric unit systems.
Models for Crack Growth and Failure. The NASGRO 4 FCG equation is a comprehensive model that includes the effects of stress ratio on FCG rate; the effects of crack size, stress ratio, and fanning on threshold; and the effects of constraint on toughness. Properties can be described as functions of temperature. Users can also select a Walker equation or enter FCG rate data directly in tabular form. Several different load interaction models are available including three Willenborg models and two crack closure models, including a detailed strip yield model. NASGRO automatically performs crack transitioning from one crack model to another as the crack reaches geometry boundaries. Several different failure criteria are available, including toughness, net section yield, plastic limit load, the Failure Assessment Diagram, residual strength, HCF threshold, and environmental cracking threshold. Inverse modes allow calculation of initial crack size or stress scale factors for a specified FCG life.
Load Histories. A variety of flexible options are available to enter load histories, including several different file formats. Complex load histories can easily be built up from different sources. Many options are available for load spectrum visualization and editing.
User Manual. A comprehensive user manual in PDF form describes NASGRO features, including many appendixes with technical details about K solutions, net section stress solutions, crack transitioning, failure assessment diagrams, and much more.
Operating System and Hardware Requirements. NASGRO has been successfully installed and tested on a variety of different Windows operating systems. Current development and testing activity is focused on Windows 10 implementations. NASGRO requires installation on a 64-bit Windows operating system with at least 4GB of RAM to execute. NASGRO requires approximately 500MB of disk space for NASGRO program and data file installation. NASGRO Consortium members and site licensees may install NASGRO in a server environment. Disk space requirements are a function of user data files (e.g. load spectrum files) and program output files (dependent on user-selected frequency of writing output to file). For graphics display, a minimum vertical screen resolution of 800 pixels is needed; for example, a resolution of 1280x800 (width x height) is sufficient. A main display setting of 100% is also recommended. Complete details regarding the NASGRO installation process and system requirements are available here.
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