We added an Installation Notes document on our Documentation and Supporting Information Page.

If you are experiencing problems saving or reading an AFGROW input file, you need to download and install MSXML 4.0 Service Pack 3 (Microsoft XML Core Services), as described in the AFGROW Installation Notes document.

The capabilities available in AFGROW Predict, Preferences menu are often missed by many casual AFGROW users. One very important preference is the growth increment option. The growth increment controls how often AFGROW will recalculate the normalized stress intensity solution (beta value) as a function of the amount of crack growth since the previous calculation. There is a trade-off between the accuracy of the prediction and the total run time. For cases in which crack extension per cycle is very small (say, 1e-6 in.), the change in the beta-value will be minimal (for most cases). For this reason, computer run times can be substantially reduced by taking advantage of the growth increment option.

The default growth increment is set to be 5% of the crack length since the last calculation. This means that the growth increment for each calculation will increase with the crack size. Since most of the calculated life is expended at the shorter crack lengths, this is a reasonable approach. Many users may not realize that the output beta (and associated K) values depend on the growth increment selected. If a user desires the "exact" beta (or K) for each cycle, then it is important to select the appropriate cycle x cycle growth increment. Please refer to the User's Guide or on-line help for more information.

 For example:

Advanced Model (Double Corner Cracked Hole)

Plate Width = 3.25 in., Thickness = 0.25 in., Hole Dia. = 0.15 in., Hole Offset = 1.625 in.

C = 0.0534, A = 0.0655

Constant Amplitude Loading, Smax = 20, R = 0 

The following run times resulted as a function of growth increment (shown for AFGROW Version 4.11.14 and 4.12.15):

Note: The decrease in run times for the new version of AFGROW is attributed to the faster CPU used. Also, the growth increment of 0.0 is the cycle x cycle option. 

As can be seen, there can be a very substantial run time penalty for running a cycle x cycle prediction. However, the increase in prediction accuracy may not warrant the increase in run time. This, of course, can vary from case to case. If a low growth increment is resulting in long run times, it may be helpful to experiment with a larger increment.

The bottom line is that users should be aware of this and use a growth increment that is suited to a given problem.

The following suggestions have been made for ways to improve AFGROW and the AFGROW Web Site:

AFGROW Improvements:

• Add Residual Strength Plotting Capability
• K-Solution for an Offset Loaded Lug
• Stress-Life Crack Initiation Model
• Expand Multi-Crack Capability
• Include the Bending Stress Fraction in the Bearing Stress Fraction Calculator Option
• Ability to Model Cracks in a Bonded Metallic Repair Patch
• Ability to Edit Parameters by Selecting an Item in the Status View
• Include Warning to Save Data Before Closing AFGROW

Web Site Improvements

• Publish AFGROW Tips and Tricks
• Retardation Parameter "Rules of Thumb"
• Add Material Data/Documentation

This will allow users to adjust spectrum tension and compression values independently. The primary purpose of this capability is to allow users to model interference fit pins as a pre-load which may be considered to be a function of crack length. The modifications will be in either equation or tabular form. The general capability will allow for a number of input parameters to be used in order to make the capability as flexible as possible.

Compression Factors for Stress Intensity Solutions

Stress intensity solutions for the crack opening mode are applicable under tensile loading conditions. Examples include a crack at an open hole, and a crack at a hole under bearing load. In the first case, the stress field in the assumed crack plane under remote tension, is quite different in magnitude under remote compression. In the second case, the crack will not see any compression due to the geometry. Although K is not defined under compression loading, the K-values calculated under compression use the same solution as the values calculated under tension loading. These values are then used to determine a crack growth rate for the resulting R-value. The ability to correct this situation may help improve crack growth life predictions for load spectra that includes significant amount of compression loading.

Beta Correction for Advanced Through-the-Thickness Cracks

AFGROW currently allows users to apply beta correction factors to classic models and corner cracked advanced models. The capability will be added to the advanced through crack cases. This will provide additional modeling flexibility for these cases.

K-Solution for an Edge Notch in a Plate

A new advanced solution for corner or through crack at an edge notch in a plate is being developed. This will permit users to continue life predictions for continuing damage cases in which a crack has grown from a hole to the near edge, and another crack was growing simultaneously on the opposite side of the hole. Some have reported using an edge crack to simulate this continuing damage condition, but the result will be extremely conservative since the hole radius will tend to reduce the actual K-value for this geometry. The availability of this new solution will provide better accuracy for these types of problems.

Comments/suggestions are welcome