8:3010:00 
AFGROW Release 5.02 Overview
James Harter, Alex Litvinov (LexTech, Inc)
Breaking down new features of upcoming AFGROW release 5.2

10:45 – 11:45 
Stress Intensity Factors And Fatigue Growth Of Irregular Planar Cracks Subjected To Arbitrary Mode I Stress Fields
Grzegorz Glinka, PhD., DSc. (Department of Mechanical and Mechatronics Engineering, University of Waterloo,
Waterloo, Ontario N2L 3G1, Canada)
Fatigue cracks in welded and notched machine components and structures are subjected to complex stress fields induced by the external load and residual stresses resulting from the manufacturing processes. The stress fields are often nonuniform and available handbook stress intensity factor solutions for such configurations are usually unavailable, especially in the case of surface breaking cracks at notches. Cracks in patch (welded and adhesive) repaired components are subjected to similarly complex stress fields. The proposed method makes it possible to calculate stress intensity factors for cracks subjected to arbitrary stress fields by using the generalized weight function technique. Therefore the mathematical and physical nature of available weight functions is to be discussed, including the principles of the weight function technique used for the determination of stress intensity factors. The general weight function and calculated stress intensity factors will be validated against various numerical and analytical data. The numerical procedure for calculating stress intensity factors for cracks subjected to nonlinear stress distributions such as those near notches and welds will be briefly discussed as well. It will be also shown that the proposed weight functions make it possible to calculate the Crack Opening Displacement field used in the evaluation of the critical load or the critical crack size. The method makes it also possible to calculate stress intensity factors for irregular nonelliptical cracks along the entire crack contour. The method is particularly suitable for modeling fatigue crack growth of arbitrary twodimensional surface and embedded cracks and the fatigue growth of cracks in welded structures.
Finally examples of the weight function application for the determination of the critical crack size and the simulation of fatigue crack growth will be demonstrated using inhouse computer software.

1:00 – 2:00 
Stress Intensity Factor Solutions for Narrow Plates
Matthew J. Hammond, Scott Fawaz (SAFE, Inc)
Accurate quantification of crack tip stress intensity values is paramount in the analysis of damage tolerant structures. The present analytical investigation seeks to determine the stress intensity solutions for crack geometries outside the existing valid solution space and expand the analyst’s ability to capture representative crack growth behavior. The primary focus of this investigation is to better quantify the crack growth behavior of single quarterelliptical corner cracks from centrally located holes in finite width plates under various loading conditions (remote tension, bending, and pin loading). Some current finite width corrections, such as the NewmanRaju corrections, have been calculated from straight through cracks and universally applied to all locations along the quarterelliptical crack front. Early investigations into the validity of this application seem to indicate that this correction procedure produces stress intensity values +/ 30% from reality for relatively narrow plates (width/depth<6). Furthermore, the crack depth to length ratio and depth to thickness ratio can significantly influence the applicability of the current finite width corrections. The analytical investigation utilizes the three dimensional virtual crack closure technique (3D VCCT) and a welluctured completely hexahedral element mesh. Stress intensity values are generated for a range of crack depth to crack length ratios (a/c = 0.01 to 10), crack depth to sheet thickness ratios (a/t = 0.01 to 0.99), hole radius to sheet thickness ratios (r/t = 0.1 to 10), and sheet width to hole diameter ratios (W/D = 1.1 to 20). This effort is being executed under a DoD Technical Corrosion Collaboration program.

2:00 – 2:30 
Crack Growth Retardation Parameter Sensitivity to Thickness of an Aluminum Alloy
Steffan M. Wilcox, 2LT (USAF), James M. Greer, Jr., Civilian (USAF, Center for Aircraft Structural Life Extension (CAStLE), United States Air Force Academy)
A series of tests were performed to empirically determine a shutoff overload ratio (SOLR) for varying thicknesses of 7075T7351 aluminum alloy using the Generalized Willenborg Retardation Model to provide data for aircraft wing crack growth analysis for a trainer aircraft. The test matrix consisted of three different plate thicknesses: 0.125 in. (3.18 mm), 0.375 in. (9.53 mm), and 0.625 in. (15.88 mm). Each 4 in. X 20 in. (102 mm X 508 mm) plate had a 0.25 in. (6.35 mm) center hole with a corner crack (EDM notch). All specimens were machined from the midthickness of the same 0.75in thick plate of material. A positive correlation was found between plate thickness and SOLR. The AFGROW software tool was used to model the tests which, through an iterative process, were matched to model results by changing the SOLR, thus generating an empirically determined SOLR value for each thickness. The SOLR for each respective thickness was found to be about 1.93 for the 0.125in thickness, 1.99 for the 0.375in thickness, and 2.09 for the 0.625in thickness for the clength cracks. The alength cracks were not found to be well correlated with the simulations, growing faster in the tests than in the AFGROW simulations.

2:30 – 3:00 
Recent improvements to the Advanced, Multiple Thru Crack KSolution
James Harter (LexTech, Inc)
The current Advanced Solution in AFGROW for multiple thrucracks is a collection of curve fit solutions to FEM results for a large matrix of geometric variables. The curve fits were based on a selection of parameters that appeared to have the most influence on the solution. The curve fit solution was reasonable for most cases, but was off by as much as 10% for some extreme cases. Recent User inquiries have prompted a review of the solution for the case of 2 through cracks in a plate, and significant improvements have been made. This presentation presents the current state of the solution, the new proposed solution, and the resulting improvement in accuracy.

3:30 – 4:00 
Fracture mechanics model width for nonflat geometries
Luciano Smith (SwRI)
Practical structural parts often have threedimensional cross sections, but are modeled as flat plates in AFGROW because the available fracture mechanics models do not include the true geometries. In order to determine the appropriate fracture model width to use when the true geometry is not flat, a study was performed comparing the stress intensities for flat plates of varying widths against those for T, L, Z, and J sections of various dimensions. From these results, guidance is given for determination of an appropriate flat plate (model 1030/2020) width to use in AFGROW depending on the actual structural configuration.
