Air Force Life Cycle Management Center

NX Crack and J- Integral Evaluation

Lawrence “Charlie” Stoker AFLCMC/WWA, A-10 Analysis [email protected]

Distribution A: Approved for Public Release Case Number 75ABW-2019-0048 Outline

 History  Benchmark Problems  Goals  FT01  FT02  CP4  Corner crack c=0.1”  Corner crack c=0.2”  Thru-crack c=0.4”  Case Study  F-15 Application  Summary of Recommendations  Conclusion  Questions Acknowledgements

 Siemens  SwRI  Mark Donley  Marcus Stanfield  Pat O’Heron  Hill Engineering  Nicolas Schutz  Joshua Hodges  Barry Nance  Robert Pilarczyk  Olivier Zone  USAF  Kaylon Anderson  Mark Thomsen  Jacob Warner  LexTech  Jim Harter  Alex Litvinov History

J-Integral is available in Nastran with the CRACKTP elements  NX user interface does not currently allow creation/access to those Requested Siemens look into implementing a UI for crack tip analysis in 2016 Siemens created a crack analysis app through NX Open and provided it to the USAF for evaluation in January 2019 USAF evaluation began April 2019 History

Crack tip analysis is currently performed in StressCheck by the USAF A-10 Analysis group Other crack tip FEA tools include:  ANSYS  ABAQUS  BEASY  FRANC3D (plug-in to ABAQUS, ANSYS, and NASTRAN)  MARC3D (MSC.Nastran/Patran)  ZenCrack History

Desired crack analysis within NX because:  A-10 has Model Based Definition (MBD) within a Product Lifecycle Management (PLM) framework which is NX-native  NX handles large assemblies very well  NX handles multiple bodies very well  NX handles multiple materials very well  NX handles geometry changes very well  NX and NX Nastran are very stable BENCHMARK PROBLEMS Benchmark Problems

Goals  Compare FRANC3D “Handbook solutions” to Beasy, StressCheck, and NX J- integral  Identify issues and potential sources of error Notes  CP4 comparison was performed first •Many lessons learned were incorporated from this section into benchmark comparisons •See convergence and meshing comparison  Comparison data provided by Hill Engineering, LLC •Presented at AFGROW 2016 •Benchmarking Problems in Fatigue Crack Growth Analyses, R. Pilarczyk, C. Morrison, and J. Hodges Benchmark, FT01

FT01/TC02 Geometry

Dimensions h = 5 b = 5 a = 0.5 t = 5

Material: E = 3.0e7, ν = 0.30 Loading: Uniform unit stress Benchmark, FT01

Edge crack W=L=5” H=10” c=0.5” (thru-crack) Stress=10ksi Fixed constraint at bottom  True plane strain model fixed y-direction on opposite faces Benchmark, FT01, 45 elements thru-thickness Benchmark, FT01, 45 elements thru-thickness, sides free Benchmark, FT01, 45 elements thru-thickness, sides free

J-integral, note integration at midnodes Benchmark, FT01, 45 elements thru-thickness, sides constrained (plane strain)

Note sensitivity to surrounding mesh Benchmark, FT01, 45 elements thru-thickness, sides constrained (plane strain), all brick

Too many elements! Didn’t solve (terminated at 25min) Also didn’t solve (terminated at 25min) 91080 elements 75330 elements “Mod” denotes plane strain SIF Benchmark, FT01 formulation:

퐽 ∙ 퐸 15500 퐾 = 1 − 푣2 15300

15100

14900

NX 10 Layer Ring 1 14700 NX 10 Layer Ring 2 NX 10 Layer Ring 2 Mod 14500

NX 10 Layer Ring 3 K (psi√in) K NX 10 Layer Ring 4 14300 NX 10 Layer Ring 2, 100 elements

14100 NX 10 Layer Ring 2, 300 elements NX 10 Layer Ring 3 Plane Strain 13900

13700

13500 0 1 2 3 4 5 6 Thickness (in) Added elements along crack front Attempted to converge (no convergence found) Benchmark, FT01

KI vs Crack Front Position 1.55 Handbook

FRANC3D 1.53 FRANC3D Plane Strain

1.51 Beasy Beasy Plane Strain

1.49 StressCheck

StressCheck Plane Strain KI 1.47 StressCheck - Fine Mesh

NX 10 Layer 45 Element Plane Stress 1.45 NX 10 Layer 45 Element Plane Stress Mod

NX 10 Layer 100 Element Plane Stress Mod 1.43 NX 10 Layer 45 Element Ring 2 Plane Strain

1.41 NX 10 Layer 45 Element Ring 3 Plane Strain 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Normalized Crack Front Length FT01 Conclusions

No convergence based on element number along crack front  J-integral is choppy  Influenced by surrounding elements outside of crack ring  Appears to be accented on “thick” models No smoothing in the extraction of data  Maybe this is a good thing? Near-edge peaks are close Middle of crack is close to handbook Benchmark, FT02

FT02/TC01 Geometry

Dimensions

h = 5 b = 5 a = 0.5 t = 5

Material: E = 3.0e7, ν = 0.30 Loading: Uniform unit stress Benchmark, FT02

Internal crack W=L=5” H=10” c=0.5” (thru-crack) Stress=10ksi Fixed on bottom Symmetric constraint on symmetry plane Benchmark, FT02, 45 elements thru-thickness Benchmark, FT02, 45 elements thru-thickness

J-integral, note integration at midnodes “Mod” denotes plane strain SIF Benchmark, FT02 formulation:

퐽 ∙ 퐸 14000 퐾 = 1 − 푣2

13500

13000 NX 10 Layer Ring 1 NX 10 Layer Ring 2

NX 10 Layer Ring 2 Mod K (psi√in) K NX 10 Layer Ring 3 12500 NX 10 Layer Ring 4 NX 10 Layer Ring 3 Plane Strain

12000

11500 0 1 2 3 4 5 6 Thickness (in) Benchmark, FT02

KI vs Crack Front Position 1.38 Handbook 1.36 FRANC3D FRANC3D Plane Strain 1.34 Beasy Beasy Plane Strain 1.32 StressCheck 1.3 StressCheck Plane Strain NX 10 Layer 45 Element Plane Stress

I 1.28 NX 10 Layer 45 Element Plane Stress Mod K NX 10 Layer 45 Element Plane Strain 1.26 1.24 1.22 1.2 1.18 0 0.2 0.4 0.6 0.8 1 Normalized Crack Front Position FT02 Conclusion

Closer than FT01 Solution is still “choppy” Local maxima are close Lower than handbook Benchmark Conclusions

Plane Strain formulation necessary to bring J-integral into general agreement with benchmark StressCheck consistently overestimates SIFs J-integral is influenced by larger global elements  Not as apparent on thinner models (see CP4 section) CP4 COMPARISON Model Summary

W=26.94” t=0.3” L=50”

Dhole=0.625” Hole offset=1.41” (hole center to edge of part) Stress=31.2ksi Model Summary

Crack front creation process tedious. Would be easier to have a “crack face” option instead of using mesh mating conditions. Model Summary Issues

Parameters/expressions set in geometry (like crack size) don’t up-flow into FEM expressions Can work around this using mesh controls, using number of elements on edge or biasing. These will update based on an edge’s length which can be controlled with an expression in the *.prt. Issues

Straight forward geometry failed to mesh (other side of crack tip) Mesh mating conditions was the culprit Recommend meshing crack first, then remaining bodies Issues

Changed crack “tube” diameter Mesh fails and deletes seed Issues

Meshing requires manual labor and foresight Geometry abstraction can go unstable quickly An easier way to make the element transitions smoother is desirable C=0.1”, SEMI CIRCULAR FLAW CP4, Sol 101 Check CP4, Sol 101 Check CP4, Sol 101 Check Notes

 When adding crack face region, only 1 side is required (not 2)  For 0.1” crack, 900 elements to be collapsed  t0=0.2475*c (0.02475”)  4 “rings” or layers, each ¼ of t0 (0.0061875”)  # of elements on 1 half of the circumference: 10  Time to collapse: 11.5 min  Solve time: •4 layers: 1.5 min •10 layers: 2.5 min  Post-Processing  Heavy editing time to pull tables from *.f06, associate to another edited grid location table, and then plot  Data modification time: 60 minutes for 1 crack size  Added crack tip group for faster extraction •Extracts 1 ring at a time, but can be performed in seconds •Have to recreate for every new crack size/crack modification • Can create after a simulation has been run Notes

Small elements create bad edges that are difficult to clean  tTotal=0.00225” CP4, Sol 401 J integral (c=0.1”, tTotal=0.02475”, 4 layer) CP4, Sol 401 J integral (c=0.1”, tTotal=0.05”, 4 layer) StressCheck

Solution time: p-level=3, 20sec p-level=4, 55sec p-level=5, 2min 20sec CP4, Sol 401 J integral (c=0.1”, tTotal=0.02475”, 10 layer)

Not pictured. See results in later charts. CP4, Sol 401 J integral (c=0.1”, tTotal=0.02475”, 10 layer), Glue

Checked gluing the crack refinement region for cases where geometry is ill -behaved (see F-15 application at end of presentation) Source: Crack refinement “tube” Target: Remaining body Used NX Glue defaults Solve time similar (2.5 minutes) CP4, Sol 401 J integral (c=0.1”, tTotal=0.02475”, 10 Layer), Glue

Stress/Displacement CP4, Sol 401 J integral (c=0.1”, tTotal=0.02475”, 10 Layer), Glue

J-integral c=0.1”, semi circular flaw summary “Mod” denotes 퐽 ∙ 퐸 퐾 = plane strain SIF 1 − 푣2 c=0.1", semi circular flaw formulation: 36000 K1 Run #1 StressCheck K1 Run #2 Plevel=3,4,5, respectively 34000 K1 Run #3 NX 4 Layer t02475 Ring 1 NX 4 Layer t02475 Ring 2 32000 NX 4 Layer t02475 Ring 3 NX 4 Layer t02475 Ring 4 AFGROW Classic NX 10 Layer t02475 Ring 1 30000 NX 10 Layer t02475 Ring 2 NX 10 Layer t02475 Ring 3 NX 10 Layer t02475 Ring 4 28000 NX 4 Layer t05000 Ring 1

NX 4 Layer t05000 Ring 2 SIF (psi (psi SIF √in) NX 4 Layer t05000 Ring 3 26000 NX 4 Layer t05000 Ring 4 NX 10 Layer t05000 Ring 1 NX 10 Layer t05000 Ring 2 24000 NX 10 Layer t05000 Ring 3 NX 10 Layer t05000 Ring 4 NX 10 Layer t02475 Ring 2 Mod 22000 NX 10 Layer Glue t02475 Ring 1 NX 10 Layer Glue t02475 Ring 2 NX 10 Layer Glue t02475 Ring 2 Mod NX 10 Layer Glue t02475 Ring 3 20000 270 280 290 300 310 320 330 340 350 360 370 NX 10 Layer Glue t02475 Ring 4 AFGROW Advanced Angle Newman-Raju c=0.1”, semi circular flaw summary “Mod” denotes 퐽 ∙ 퐸 퐾 = plane strain SIF 2 c=0.1", semi circular flaw 1 − 푣 formulation: 36000

34000

32000 K1 Run #3 30000 NX 4 Layer t02475 Ring 2 AFGROW Classic 28000 NX 10 Layer t02475 Ring 2

NX 4 Layer t05000 Ring 2 SIF (psi (psi SIF √in) 26000 NX 10 Layer t05000 Ring 2 NX 10 Layer t02475 Ring 2 Mod

24000 AFGROW Advanced Newman-Raju NX Ring 2 22000 Angle NX Ring 2 mod 275 -7.91% -2.44% 20000 280 -9.71% -4.35% 270 280 290 300 310 320 330 340 350 360 370 285 -10.56% -5.25% Angle 330 -9.29% -3.90% 345 -9.04% -3.64% 350 -9.39% -4.01% 355 -8.55% -3.12%

Error compared to SC at… SC to compared Error Avg -9.21% -3.82% c=0.1”, semi circular flaw summary, glue “Mod” denotes 퐽 ∙ 퐸 퐾 = plane strain SIF 2 c=0.1", semi circular flaw 1 − 푣 formulation: 36000

K1 Run #3 34000 NX 4 Layer t02475 Ring 2 AFGROW Classic 32000 NX 10 Layer t02475 Ring 2 NX 4 Layer t05000 Ring 2 30000 NX 4 Layer t05000 Ring 4 NX 10 Layer t05000 Ring 1 28000 NX 10 Layer t05000 Ring 2

NX 10 Layer t05000 Ring 3 SIF (psi (psi SIF √in) 26000 NX 10 Layer t05000 Ring 4 NX 10 Layer t02475 Ring 2 Mod

24000 NX 10 Layer Glue t02475 Ring 1 NX 10 Layer Glue t02475 Ring 2

22000 NX 10 Layer Glue t02475 Ring 2 Mod NX 10 Layer Glue t02475 Ring 3

20000 NX 10 Layer Glue t02475 Ring 4 270 280 290 300 310 320 330 340 350 360 370 AFGROW Advanced Angle

Glue with default parameters appears to behave similarly c=0.1”, semi circular flaw summary

Use crack diameter tTotal=0.2475*c Use 10 layers  Run time is similar to that p=5  Prep work is high Extract Ring 2, modify for plane strain  Based on Benchmark cases, Ring 3 may be better Agrees nicely with AFGROW advanced solutions for bore and surface C=0.2”, SEMI CIRCULAR FLAW Issues

Larger crack sizes can require seed mesh on both bore and surface faces CP4, Sol 401 J integral (c=0.2, tTotal=0.0495”, 10 layer) c=0.2”, semi circular flaw summary “Mod” denotes 퐽 ∙ 퐸 퐾 = plane strain SIF 2 c=0.2", semi circular flaw 1 − 푣 formulation: 48000

46000 K1 Run #1 K1 Run #2 44000 K1 Run #3 42000 AFGROW Classic NX 10 Layer t02475 Ring 1 40000 NX 10 Layer t02475 Ring 2

38000 NX 10 Layer t02475 Ring 3

NX 10 Layer t02475 Ring 4 SIF (psi (psi SIF √in) 36000 NX 10 Layer t02475 Ring 2 mod

34000 AFGROW Advanced AFGROW Newman-Raju 32000 NX Ring 2 30000 Angle NX Ring 2 mod 275 -8.58% -3.16% 28000 280 -8.69% -3.28% 270 280 290 300 310 320 330 340 350 360 370 285 -9.41% -4.03% Angle 330 -8.97% -3.57% 345 -9.42% -4.04% 350 -8.81% -3.40% 355 -8.94% -3.54%

Error compared to SC at… SC to compared Error Avg -8.98% -3.57% C=0.4”, THRU-CRACK Issues

Watch for coincident nodes! Double check by making sure there are 2 polygon edges at open edges. MMCs sometimes overstep their bounds. Turn off “keep imprinted edges” Issues

MMCs which automatically populate create this problem.  “Keep imprinted edges” needs to be turned off Subtract out works, but is cumbersome (and not necessarily accurate) Issues

Make sure crack edge and crack face come from the same body, otherwise it may create coincident nodes at the outer crack tip refinement diameter. Gives J in negative values if the CSYS is pointed opposite of global  Negative J should only be provided if the crack tip is in compression  If no way to fix programmatically, need to make users aware  Presents a problem with complex crack shapes in structure with non- standard orientation (most aircraft structures) NX c=0.4, thru-crack NX c=0.4, thru-crack

Note negative J StressCheck c=0.4, thru-crack c=0.4”, thru crack summary “Mod” denotes 퐽 ∙ 퐸 퐾 = plane strain SIF 2 t=0.4", thru-crack 1 − 푣 formulation:

49000

47000

K1 Run #1 45000 K1 Run #2 K1 Run #3 43000 AFGROW Classic & Advanced

NX 10 Layer t02475 Ring 1 SIF (psi (psi SIF √in) 41000 NX 10 Layer t02475 Ring 2 NX 10 Layer t02475 Ring 3 39000 NX 10 Layer t02475 Ring 4 NX 10 Layer t02475 Ring 2 mod 37000

35000 0 0.05 0.1 0.15 0.2 0.25 0.3 Z coord (in)

Z Coord NX Ring 2 NX Ring 2 mod Error compared to StressCheck at… 0.15 -6.95% -0.36% F-15 Longeron Cracking CASE STUDY/APPLICATION F-15 General Comments

“Legacy” FEM, not created in NX Numerous issues with the FEM, including some material inaccuracies Not editable Representative of many aerospace FEMs currently in use Issues

Complicated geometry adds tiny edges Reset face doesn’t work Starts due to MMC Issues Issues

Can’t resolve geometry idealization errors  Suspect it has something to do with loft geometry and/or tiny edges? Resort to NX Glue Edge-to-Surface Glue not allowed in Solution 401  Will ignore since these connection points are far away from location of interest F-15 CSL Detail (*.afm) F-15 CSL Detail (*.fem) F-15 CSL Detail (*.sim) Issues

Can’t create crack tips when an assembly FEM is used Complex aircraft application not possible in current iteration Summary of Recommendations

 Provide XYZ and/or degree from a CSYS in the *.f06 tables  Allow nodal displacement visualization when looking at J-int  Fix J-int negative values for CSYS disagreement  Is there a way to print the J-int table without manually extracting and editing through notepad?  Give crack ID, node ID, x coord, y coord, z coord, angle from a CSYS, J-int  All ready to interrogate and plot  Workaround using groups • Only gives 1 ring per interrogation  Streamline meshing so that a geometry change (“c”) can be made and the remesh updates flawlessly  Allow meshing of collapsed hex elements in FEM rather than through dialog in SIM  Retains mesh associativity for geometry changes (i.e. crack size changes), makes remeshing faster  May allow use in *.afm?  Consider modifying J-integral for tetrahedrals. Negates any crack tip definition/creation  Consider more robust meshing algorithms for cracks  There is no non-linearity in Linear Elastic Fracture Mechanics (LEFM). Consider moving the J-integral capability into Solution 101  Allows for more robust gluing techniques (i.e. edge gluing which is not available in SOL401) Conclusion

J-integral within NX/Simcenter could be a valuable tool in large, multi-body, multi-material models  Needs some UI/UX improvements J-integral converges quickly, within the first 3 rings  Crack refinement size has some effect, but is small. The solution appears to be more dependent on number of rings.  Global meshing has a significant influence on “thick” components StressCheck consistently over-predicts SIFs All solvers have a different approach Questions