Computational Fracture Mechanics of Concrete Structures: A Retrospective through Multiple Lenses

1. PetaFLOPS TeraGrid Computational Fracture Mechanics of Concrete Structures: A Retrospectivethrough Multiple Lenses ACI 446/447 J. M. Emery, J. D. Hochhalter & A. R. Ingraffea Cornell University, Ithaca, NY www.cfg.cornell.edu

2. Outline of This Presentation A Retrospective and a View Forward through 4 Lenses: • The Lens of Computational Resources • Demand < supply, why? • The Lens of Software • Great numerical innovations, better science? • The Lens of Physics • Multiscale: physics, mechanics, stochastics • The Lens of Practice • Practice is one thing, failure analysis another • The Lens of Dimensionality • Not much happens in 2D, use all that power in 3D • Observations and Predictions

3. Through the Lens of Computational Resources Compared to sister disciplines, ComFraMCoS has made little demand on modern cyberinfrastructure. - at the structural length-scale - at the material length-scale

4. 1000 processors, 330 Million DOF Courtesy B. Anderson, Swedish Defense Agency S. Fawaz, USAF Academy Fracture Mechanics in Aging Aircraft Through the Lens of Computational Resources …at the structural length-scale

5. 1 mm Through the Lens of Computational Resources …at the material length scale: A Digital Material model of an aluminum polycrystal 8 million elements, 33 million DOF

6. CU Through the Lens of Computational Resources • National Science Foundation TeraGrid (www.teragrid.org) deploys 100’s of unused teraflops on a relatively low-traffic 10 Gbps network. Science should not be limited by the computer on your desk.

7. Outline of This Presentation • The Lens of Computational Resources • Demand < supply, why? • The Lens of Software • Great numerical innovations, better science? • The Lens of Physics • Multiscale: physics, mechanics, stochastics • The Lens of Practice • Practice is one thing, failure analysis another • The Lens of Dimensionality • Not much happens in 2D, use all that power in 3D • Observations and Predictions

8. Through The Lens of Software Our ComFraMCoS community has made innovative contributions to • Representations of cracking: • smeared; • discrete with adaptive remeshing; • particle and lattice; • meshfree; and • enriched element. • Constitutive models for cracking: • fictitious cracking concept; • cohesive zone models; • non-local plasticity; and • damage mechanics.

9. Through The Lens of Software However: Have we perhaps been a bit too distracted by the novelty of variations in numerical methods for software implementation rather than finding ways of applying it to answer fundamental questions of cracking behavior? What new physical insights at the micro or meso length scales have arisen from application of meshfree or enriched element methods? • Commercial software has improved in GUI, postprocessing, speed. • But it appears to be locked into the early 1990’s in: • not avoiding mesh dependencies and instabilities associated with • smeared cracking • non-representation of bond degradation • inability to be used for failure analysis due to cracking

10. Outline of This Presentation • The Lens of Computational Resources • Demand < supply, why? • The Lens of Software • Great numerical innovations, better science? • The Lens of Physics • Multiscale: physics, mechanics, stochastics • The Lens of Practice • Practice is one thing, failure analysis another • The Lens of Dimensionality • Not much happens in 2D, use all that power in 3D • Observations and Predictions

11. Through The Lens of Physics • Physics underpins mechanics • Continuum geometrical representations and constitutive models are surrogates for physics which we can’t or don’t want to include in our models • Multiscale approaches are proving useful in sister disciplines • Purposes of multiscale simulation are to: • Start modeling with best physics at lowest feasible length scale, • Identify sources of variability at nano/micro/meso length scales and to quantify their effect at the structural scale. • Multiscale simulations conjoin physics, mechanics, and stochastics Why are we not seeing more multiscale simulations in ComFraMCoS ?

12. Micro-scale: the interface with physics and chemistry (Stutzman 2001) Meso-scale: most difficult mechanics (Roels et al. 2002) Structure-scale: most time spent! Through The Lens of Physics

13. Through The Lens of Physics Why has it taken over 20 years to build on this innovative work? Wittmann, etal., 1984 Wittmann, etal., 1981

14. Outline of This Presentation • The Lens of Computational Resources • Demand < supply, why? • The Lens of Software • Great numerical innovations, better science? • The Lens of Physics • Multiscale: physics, mechanics, stochastics • The Lens of Practice • Practice is one thing, failure analysis another • The Lens of Dimensionality • Not much happens in 2D, use all that power in 3D • Observations and Predictions

15. Through The Lens of Practice • Two branches of practice: • Design: to engineer against failure • Forensic analysis: to understand failure when it occurs • These branches require different software, different mindset, for example….

16. Beam-Column Joint Failures Through The Lens of Practice

17. Region shown in (b) 2 (a) 3 1 Influence of steel bar (b) Through The Lens of Practice

18. A B Through The Lens of Practice 300 mm 300 mm Killer crack should appear along this line Smeared crack analysis, with 100 mm elements, showing wildly oscillating value of tensile stress along line A-B. Note that stress pattern follows boundaries of finite elements.

19. Through The Lens of Practice Blunt crack band approach CAN NOT solve this problem: where eucr = ultimate cracking strain GF = fracture energy h = element size measure ft= tensile strength • Must make h small enough to resolve local high stress gradient • But with reasonable values of GF and ft , eucr then so large critical • cracking event never predicted ! Smeared crack representation is appropriate for design, might be useless for failure analysis.

20. Through The Lens of Practice • ACI/ASCE 446 • Update ACI 446.3R-97 • Please, the personalities should give way to the science

21. Outline of This Presentation • The Lens of Computational Resources • Demand < supply, why? • The Lens of Software • Great numerical innovations, better science? • The Lens of Physics • Multiscale: physics, mechanics, stochastics • The Lens of Practice • Practice is one thing, failure analysis another • The Lens of Dimensionality • Not much happens in 2D, use all that power in 3D • Observations and Predictions

22. Through the Lens of Dimensionality Continuum-2D is for class project type work “these-days”

23. Through the Lens of Dimensionality Continuum-2D is for class project type work “these-days” sxx in rebar (ksi) sxx in concrete (ksi) y x

24. We’ve come a long way since 1982! Through the Lens of Dimensionality Continuum-2D is for class project type work “these-days” sxx (ksi) y x

25. Through the Lens of Dimensionality Continuum-2D is for class project type work “these-days”

26. Multiscale SimulationRealistic-3D is for research type work “these-days” 3-D Realistic Microstructure Model 3-D Continuum Field Analysis 3-D Continuum Model Simulate Microscopic Damage Processes: Crack Incubation in Particles Crack Nucleation into Matrix Intra/Intergranular Crack Propagation Analyze Microstructure for Higher Physical Fidelity, Update Continuum Damage State and Fields Apply B.C.’s from Macroscale Model

27. Generate First-Phase Realization 2nd Phase Constituent Particles Cause Cracking 7075-T651 10 mm ND RD TD ~100 mm 145 mm SEM scans of 7075-T651 along 3 orthogonal planes (R. Campman, CMU) First-phase realization Observation Representation “Digital Material”

28. Sample Particle Distribution Nearest Neighbor CDF Surface Area CDF Aspect Ratio CDF 1 mm 28 Particle distribution realization

29. ND ND RD RD Mesh Microstructure 33 million DOF

30. Multiscale Simulation in RC Structure 3-D Realistic Mesostructure Model 3-D Continuum Field Analysis 3-D Continuum Model Simulate Microscopic Damage Processes: Crack Incubation in/around Particles Crack Nucleation into Matrix Intra/Intergranular Crack Propagation Analyze Microstructure for Higher Physical Fidelity, Update Continuum Damage State and Fields Apply B.C.’s from Macroscale Model

31. Sample Aggregate Distribution Shape Adjacency Probability 150 mm Size Probability

32. Forward through the Lens of Dimensionality Observation Digital Concrete 150 mm 850,000 DOF, 1.5 million elements 20 min wall clock time 150 mm

33. Forward through the Lens of Dimensionality

34. Outline of This Presentation • The Lens of Computational Resources • Demand < supply, why? • The Lens of Software • Great numerical innovations, better science? • The Lens of Physics • Multiscale: physics, mechanics, stochastics • The Lens of Practice • Practice is one thing, failure analysis another • The Lens of Dimensionality • Not much happens in 2D, use all that power in 3D • Observations and Predictions

35. Observations andPredictions (For the young at heart) • Computational Resources • Science should not be limited by the computer on your desk. • Software • Less time on numerics, more time on physics/mechanics. • Physics • Why not more multiscale simulations? • Practice • Know whether you are designing or explaining! • ACI 446 will … • Dimensionality • Little more to be learned via 2D simulation. • Unleash the power: conjoin physics, mechanics, stochastics.

36. ND RD Filter Particles: Retain Most Damaging Surface particles on RD-ND face adjacent to stress riser 36

37. Sample Aggregate Distribution ? ? Probability

38. Nearest Neighbor CDF (from Lehigh) Surface Area CDF Sample Particle Distribution Aspect Ratio CDF (from Lehigh)