Unique Features and Capabilities

There are a number of unique features and capabilities that set AFGROW apart from other fatigue crack growth life prediction software. Brief descriptions of these capabilities are given below for your consideration:

AFGROW Analysis Framework Philosophy

AFGROW is a user-friendly 64-bit, object-oriented life prediction tool. Linear Elastic Fracture Mechanics analysis methods form the foundation of the code, but a strain-life crack initiation capability is also included in the framework. AFGROW is designed to be a flexible analysis tool for Engineers who have a good understanding of the principles and methods used in the code. The code includes several options and features including:

• 5 Crack Growth Rate Models
• 5 Load Interaction (Retardation) Models
• 26 Classic Application Defined Geometry Models
• 9 Classic Weight Function Models
• User-Defined Geometry Models
• Beta Correction Capability
• Advanced, Multiple Crack Models
• Optional, User-Defined Plug-In Models
• Bonded Repair Analysis Capability
• Corrosion Prediction Capability
• Spectrum Management Tool
• Spectrum Filtering
• Microsoft COM Automation
• Fracture Mechanics Database with Downloadable Growth Rate Data Curve Fits

AFGROW works within the Microsoft Windows environment to allow it to easily interface with other Windows applications. This includes an extensive copy/paste capability. Spectrum creation/management and cycle counting tools are also included with AFGROW

Although AFGROW is a very user-friendly analysis framework, we strongly advise users to read the manuals provided on our web page and to use the help provided in the code. One hour of e-mail or phone-based help is also available each year to users with a current license.

Many of these capabilities/features are demonstrated on our You Tube Channel
https://www.youtube.com/user/AFGROW

Ability to Model Crack Growth Rate Data for Different Environments and Growth Directions

AFGROW allows for the use of tabular crack growth rate data for different environmental conditions and different crack growth directions.

In the case of environmental conditions, the loading spectrum for AFGROW, Version 5.3 may be tagged to identify spectrum levels that will use the appropriate crack growth rate data. Our current tagging system is given as a temperature, but we expect to use other tags in the future. The default (checked) data set is used for any spectrum level without a tag that corresponds to a tag assigned to other data sets. There is no limit to the number of data sets that may be used.

Crack growth rate data for different growth directions (currently, the a and c-direction for part-through cracks) may be used by selecting the box shown at the bottom of the figure above. It is possible to use this option and the environmental capability at the same time.

Crack Initiation Material Parameter Data

Local Material Database in the Tabular Lookup Format

• Based on AFMAT Raw Data
• Searchable by material name and type
• Database can not be modified
• AFGROW can be configured to be used the database on local computer, network server or company intranet
• There are currently tabular curve fits for 85 materials in the local database

Beta Correction

The beta correction capability may be used to obtain an unknown K-solution for a unique and/or specific geometry by modifying a similar, known stress intensity factor solution for a given geometry (or loading case) that is available in AFGROW. This is implemented through a modification to the non-dimensional geometry correction factor (β).

The correction is calculated based on a Gaussian integration of the ratio of the normalized unflawed stress distribution ratios of the unknown/known geometries. An example of the input required for a through cracked case is shown below:

Spectrum Filtering

The spectrum filtering capability allows tension and compression values to be adjusted independently to account for external or internal effects which may behave differently under tensile and compressive loading.

The spectrum filtering capability is a function of the crack length in the c-direction, and may be entered in tabular format or by using AFGROW’s new embedded java script engine.

Stress Intensity Filters

Stress intensity (K) solutions are typically provided in terms of the geometry correction factor (β), where:

β=K/(σ √(πx )) , where x is the crack length of interest

The K-filtering capability permits the beta values to be adjusted independently for tensile and compressive loading for all load cases (axial, bending, and bearing). This allows for independent beta values to be applied for tension and compression spectrum stresses.

One example of the application of this capability is the classic lug geometry.

The beta values for this case should be zero for compressive spectrum loads.

The K-filtering capability is a function of the current crack length, and may be entered in tabular format or by using AFGROW’s new embedded JavaScript engine.

API 579 Stress Intensity Factor Solutions

COM Automation

In addition to operating as a stand-alone, interactive life analysis tool, AFGROW can also be executed from any Windows© application using COM technology. This feature allows users to pass information to AFGROW and execute nearly all of its capability via another application. One of the most common applications is the use of MS Excel. AFGROW input parameters for any number of life calculations may be passed to AFGROW from Excel using the VBA for applications option. This also allows a user to write code to control how AFGROW uses this data in an automated environment.

Information on the use of AFGROWs COM capability (including sample applications) is available in the Component Object Model manual.

Plug-In Stress Intensity Factor Modules

Users can develop addition stress intensity solutions to add to the existing AFGROW. These solutions may be shared with other users, or kept as proprietary models as desired. AFGROW has built-in drawing tools to allow these modules to be animated during execution as is done for all of the native AFGROW solutions. The modules must be compiled as Dynamic Link Libraries (DLLs).

This capability, along with the AFGROWs COM capability was used to demonstrate the use of an external stress intensity solver to solve very complex problems in an interactive manner. Geometric data was sent to a 3rd party finite element code (i.e. StressCheck), and stress intensity data was passed back to AFGROW on an incremental basis during the life prediction process.

Information and step-by-step instructions on the development and use of AFGROWs Plug-In capability (including a sample plug-in module) is available in the Building AFGROW Plug-Ins presentation in the document download section

Advanced Multiple Crack Analysis Capability

AFGROW has the ability to perform crack growth analyses for multiple cracks. Each crack tip in AFGROW is treated as a separate object so that all life prediction operations may be performed independently for each object. This capability has been utilized in AFGROWs Advanced Model interface to for two, independent cracks in a plate (including holes).

Detailed information on the multiple crack solutions (corner and through-the-thickness cracks) is available in the references provided in the document download section. The User’s Manual includes the capabilities and limitations of the currently available solutions.

Bonded Repair (U.S. Customers Only)

A bonded repair design wizard can be used to create several repair patch options using the existing material database, or a user can manually design a repair patch. The database includes properties for graphite epoxy, boron epoxy, and several options for fiberglass/aluminum (Glare) repair patches.

New Special Case Multi-Site Damage solutions (MSD)

Multiple Through Cracks in an Infinite Plate

• Axial load case
• 3 to 9 through cracks in an Infinite Plate (Continuing Damage)

Multiple Holes in an Infinite Plate (Multisite Damage)

• Axial and Bearing load cases
• 3 to 9 cracked holes in an Infinite Plate
• Primary and Secondary Crack at the Center Hole
• Single Secondary Crack on Outside of each adjacent hole (2, 4, 6, or 8 holes)

Spectrum Management Tool

The Spectrum Management Tool is a separate software tool that may be downloaded and used by anyone with a current AFGROW, Version 5.3 (or newer) license. This tool allows users to build new loading spectra by creating any number of sub-spectra files that may be sequenced/repeated in any order.

Data may be entered manually or copy/pasted from any Windows software tool. Once a spectrum has been created, the program provides basic spectrum statistics, and tools are included to clip or truncate the spectrum. In addition, any level of the spectrum may be tagged so that different crack growth rate data may be applied. Files may be saved in the legacy AFGROW text format, or in our new, XML format.

Please note: For the tagging option, the XML format must be used with AFGROW, Version 5.3 or later.

Fracture Mechanics Database (AFMAT)

The AFMAT database is available on the AFGROW web site for all to browse, but user’s must login to the AFGROW web site and have a current AFGROW license to use the database search and download capability. All new AFGROW purchases are current for one year, and maintenance may be purchased on a yearly basis.

The database currently contains fracture mechanics related data for 655 materials. These data include: da/dN vs. Delta K, da/dt vs. Kmax, Fracture Toughness, KISCC, and R-Curves. Complex Boolean searches may be constructed to query the database using our search engine. Data may be downloaded directly in MS Excel format.

In addition, we have tabular lookup crack growth rate model curve fits for over 50 materials available in AFMAT, and we plan to add more with each new AFGROW release.

The curve fits are shown with the raw test data to provide the total context of each fit. Each component of the plot can also be removed/replaced by clicking on the item in the legend to de-clutter the image for better resolution. These tabular lookup files may be downloaded and used directly in AFGROW.

Damage Tags

In AFGROW version 5.3.4.23 we have added the ability to track the amount of crack growth resulting from each sub-spectrum as well as individual spectrum levels. Damage tags are used in AFGROW to determine how much a specific level within a spectrum contributes to the total amount of predicted crack growth. Damage tags are labels that can be assigned to spectrum levels using Spectrum Manager.

The spectrum with damage tags for user specified levels is opened with AFGROW. After running a prediction, a short summary (By Source) lists the percentage of crack growth damage resulting from both non-tagged and tagged spectrum levels. In addition, a damage summary (By Sub Spectra) is displayed within the Output window.

For more information about AFGROW ability to track the amount of crack growth resulting from each sub-spectrum as well as individual spectrum levels please visit our blog.