Nov. 9, 2006 DDSim: A Next Generation Damage and Durability Simulator Presenting: John Emery Advising and Supporting: Prof. Tony Ingraffea, John Dailey Jr., Gerd Heber, Wash Wawrzynek funded through NASA’s Constellation University Institutes Project.

2 John Emery & Tony Ingraffea Cornell University ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator Outline for the Talk  The Big Picture & Overview  DDSim Level I – Reduced-order filter  Input  Approach  Results & Performance  Level II – Automated crack insertion  Approach  Results  Level III – Multiscale simulation  Statistically accurate microstructural geometry  Multiscale implementation  Conclusions

3 John Emery & Tony Ingraffea Cornell University ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator DDSim Finite element model of structure including boundary/environmental conditions Material system & pertinent microstructural statistics Best available physics-based damage models Random input Time to failure, N Probabilistic life prediction The Big Picture PP

4 John Emery & Tony Ingraffea Cornell University ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator Overview of the Hierarchical Approach  Level I: A fast, analytical, reduced-order filter to determine life- limiting hot-spots in complex structures  Level II: Traditional continuum fracture mechanics, FRANC3D, to compute the life of the structure consumed by growth of microstructurally large cracks (N MLC )  Level III: Multiscale simulation to compute the life of the structure consumed by incubation, nucleation and propagation of microstructurally small cracks (N MSC ) Assumption: N total = N MLC + N MSC A multiscale approach with 3 hierarchical levels:

5 John Emery & Tony Ingraffea Cornell University ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator Models and Parameters for Fracture and Damage Mechanics Models for fatigue crack growth (NASGRO equation*) Statistical material data & initial damage size Database from FEM without damage Mesh Field information Boundary conditions Stress field contour plot: Rib-stiffened element *Forman & Mettu, Fracture Mechanics: Twenty-second Symposium, Vol. 1, ASTM STP 1131 A (slide 6) DDSim Level I: Input B (slide 9)

6 John Emery & Tony Ingraffea Cornell University ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator Life prediction contour plot on original FE Mesh (29,072 surface nodes, average a i =2.76e-4 in) Analytical solutions & field data from undamaged FEM used to estimate service life limited by damage at a large number of possible origins (mesh nodes). Key Ideas for Level I: High Volume, High Automation, Probabilistic, & Conservative First Order Analysis These damage origins do NOT become part of the geometrical model in Level I. These damage origins do NOT interact with each other. These simplifications readily allow parallel processing. How to map: Stress  Life prediction? Initial flaw size from statistical distribution (eg. particle x- sectional area). Stress field contour plot: x-section A (previous), Rib-stiffened element DDSim Level I

7 John Emery & Tony Ingraffea Cornell University ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator Conservative SIF History Crack length, (in) Stress intensity factor, (ksi  in) Principal stress on a thermomechanically loaded part (courtesy of FAC) DDSim Level I is designed to provide conservative estimates of K (compared with FRANC3D here). a b

8 John Emery & Tony Ingraffea Cornell University ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator  Under Fatigue spectrum  Nodes (i.e. initial flaw locations): 63,974  Random initial flaws (from particle filter): 10,000  No. of 3.6GHz w/ 2GB RAM: 16  Min & Max computed life (cylces): ,999  Processing time (hr:mm): 5:48 Level I Results & Performance Particle diameter, (in) Probability of occurrence Life prediction contour plot w/ 10,000 initial flaws

9 John Emery & Tony Ingraffea Cornell University ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator Fully 3D crack growth simulation at “hot spots”: Explicit representation of crack surface in FE model geometry Automatically inserted at “hot spots” determined by Level I analysis Level I Life prediction contour plot (x-section B slide 5) Automatically inserted, grown and remeshed crack DDSim Level II

10 John Emery & Tony Ingraffea Cornell University ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator Level II Results Crack paths b m a Low fidelity N MLC = 803 cycles, High fidelity N MLC = 4070 cycles Crack length, (in) N, (load cycles) N MLC = 4070 Level I predictions

11 John Emery & Tony Ingraffea Cornell University ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator Representative digital microstructure With a first order, probabilistic analysis completed, focus on the “hot spots” to increase the accuracy of the N MSC prediction using: Representative digital microstructure Best available physics Multiscale simulation High performance parallel computing DDSim Level III: Multiscale Simulation Life contour plot from initial prediction Focusing on a “hot spot”, rectangular void for PC model

12 John Emery & Tony Ingraffea Cornell University ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator Crack IncubationCrack NucleationCrack Propagation Level III: Microstructurally Small Damage  Important geometrical features:  Grains  Particles  Damage processes and events:  (a) Crack incubation process – damage accumulation until the particle cracks  (b) Crack nucleation event –  (c) Microstructurally small crack propagation – process of crack growth within grains and across grain boundaries a b c 10  m

13 John Emery & Tony Ingraffea Cornell University ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator Level III: Current Microstructural Geometry Models The lumber model (right) approximates the average grain size and aspect ratios of AA 7075 in a randomly assorted stack The rolled Voronoi model (right) is our most statistically accurate geometry for rolled AA 7075, approximating grain morphology and average size. The Voronoi model (left) approximates random crystallographic structure of an unrolled alloy

14 John Emery & Tony Ingraffea Cornell University ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator DDSim Level III: Multiscale Simulation Life contour plot from initial prediction Focusing on a “hot spot”, rectangular void for PC model Multiscale model = Continuum +  structure! Representative digital microstructure

15 John Emery & Tony Ingraffea Cornell University ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator  DDSim Level I provides a high volume, highly automated, probabilistic, and conservative life prediction (N total ) for real structures & locates areas of high interest for the Level II & III simulations  Level II uses the current best practice fracture mechanics life predictions methodologies for high fidelity N MLC  The Level III microstructural models incorporate state-of- the-art physics and accounts for microstructural stochasticity for high fidelity N MSC.  DDSim, as a multiscale system, will provide microstructurally educated life predictions for real structures. Conclusions Our assumption is: N total = N MLC + N MSC

16 John Emery & Tony Ingraffea Cornell University ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator Safety slides  Intentionally blank

17 John Emery & Tony Ingraffea Cornell University ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator Metallic Composite 0.6 mm Dissimilar materials…similar microstructural geometrical features Level III: Microstructural Geometry and Damage 50  m Metallic micrographs courtesy of A. Rollett, CMU. Composite micrographs from: Nicoletto G., Enrica R., Composites: Part A, 35, 2004, 787 – 795, & S. Stanzl-Tschegg, personal communication

18 John Emery & Tony Ingraffea Cornell University ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator Level III: Particle Crack Incubation Criterion Affect of grain orientation on particle stress, 3 categories:  High stress orientation  Intermediate stress orientation  Low stress orientation     xx High orientation Low orientation Intermediate orientation Particle aspect ratio Grain orientation Strain level Probability Particle Tensile Stress (σ xx ) Probability Density Function Particle Tensile Stress Probability

19 John Emery & Tony Ingraffea Cornell University ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator Currently, we have these loose ends:  Monte Carlo simulation is feasible for the low fidelity life prediction of DDSim Level I, however, it is NOT feasible for the multi-scale simulation  One microstructural model requires millions of DOF  Required number of samples makes MC intractable  Level II computes the life consumed by continuum length scale damage evolution  Level III computes the life consumed by micro-scale damage evolution Putting It All Together Recall our assumption was: N total = N macro + N micro

20 John Emery & Tony Ingraffea Cornell University ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator Low fidelity life predictor: DDSim Level I Low fidelity life prediction Damage site iterator: DDSim Level II, N macro Combine conditional probabilities “predictor” “corrector” Multi-scale simulation: DDSim Level III, N micro Bayesian estimation Low fidelity “prior” conditional life cdf High fidelity “post” conditional life cdf Random input High fidelity life prediction Putting It All Together N PP N PP N PP N PP

21 John Emery & Tony Ingraffea Cornell University ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator 3-D Continuum Model 3-D Continuum Field Analysis 3-D Realistic Microstructure Model Analyze microstructure for to capture microstructural damage evolution, update continuum damage state and fields Apply B.C.’s from Macroscale Model Simulate damage evolution: steam enhanced delamination (with models from collaborating CUIP IFST teams) particle debonding/cracking crystal plasticity/cohesive constitutive models intra/intergranular microcracking Level III: Multi-scale

22 John Emery & Tony Ingraffea Cornell University ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator Close-Up of Bolt-Hole  x (ksi) Continuum Scale Continuum Model E=10,500 ksi = ksi Gather Boundary Conditions and Apply to Polycrystal Model Polycrystal Model Polycrystal Scale  x (ksi) Calculate New Modulus for Each Gauss Point in the Continuum Model Grain Boundary Decohered E=10,500 +/- 1,000 ksi =0.33 t p =72.5 ksi Update Stiffness Level III: Multi-scale, 2D Example x y

23 John Emery & Tony Ingraffea Cornell University ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator xx Updated Continuum Model Smeared Crack Level III: Multi-scale, 2D Example x y