Detonation and Detonation-Driven Tube Fracture

1. Detonation and Detonation-Driven Tube Fracture Joe Shepherd, Aeronautics, Caltech Personnel Faculty: J. E. Shepherd A. Khokhlov (U Chicago) J. Austin (UIUC) Staff Scientists: F. Cirak R. Deiterding P. Hung M. Arienti (-> UTRC May 2004) Graduate Students: T.-W. Chao (PhD March 2004) F. Pintgen S. Browne FY04 Review October 19-20, 2004

2. Detonation-Driven Fracture

3. Structure of Detonations Simulation Experiment Regular Irregular Poster

4. Connection with VTF Three connections: • Detonation wave propagation, structure of the front • Requires AMR, reduced chemistry, turbulence modeling • Dynamic fracture, plastic deformation • Multiscale modeling, advanced FEM methods (shells) • Coupled fluid-solid problem • Benchmark problem for VTF techniques • Strong coupling of solid and fluid motion • Multiple interpretations: • Engineering models for material response and detonation with the focus on the coupling between fluid and solids. • Research multiscale models of individual processes, i.e., detonation, fracture propagation, plasticity, etc.

5. Validation Aspects • Models that are being tested: • Dynamic fracture, contact, plastic deformation • Compressible, reacting, turbulent flow: detonation • Integrated simulations, fluid-structure interaction • Measurements that are being performed: • Strain History • Crack speeds • Digitized crack paths • Pressure (detonation and post-rupture blast) • Detonation front structure: • Wave shape • Density (schlieren) • OH concentration measurements • Precisely controlled initial conditions and boundary conditions

6. Previous work: 2002-2003 • Elastic wave propagation driven by detonations • Shear-wave resonance study • Detonation-driven fracture in Al tubes (6061T6) • No prestress control • Effect of initial crack length studied • Crack bifurcation and curving observations • Fractography • Fracture threshold model • Comparison of static and dynamic fracture

7. Progress: Oct 2003 – Oct 2004 • Fracture experiment series completed in new facility (T.-W. Chao) • 36 experiments accurately controlling prestress • Measurements: • Strain • Crack paths • Blast pressure • Crack Speeds • Visualization of initial crack opening • Validation of elastic wave propagation (F. Cirak) • Diffraction experiments (F. Pintgen, R. Deiterding, P. Hung) • 100+ experiments completed with two mixtures – weakly and strongly unstable • Measurements • OH PLIF and schlieren • Multiple exposure luminosity • Stereoscopic imaging and 3D reconstruction • Analysis of role of diffusion in detonations (M. Arienti) • Examination of 3-step models for detonation chemistry (S. Browne)

8. Validation of elastic wave propagation Measured Hoop Strain and Detonation Pressure Comparison of Measured Hoop strain and Simulation (resolution study)

9. Issues in validation • Simulation amplitude about 20% higher than experiment • Parametric examination of possible sources of error: • Resolution (number of shell elements) • Eccentricity and thickness variations of tube • Wave speed • Pressure decay rate • Detonation structure • Systematic error in experiment • Frequency response of strain gauges • Nonsteady detonation wave Poster

10. Using Prestress to Control Crack Propagation Path Test Fixture Design criteria: • Compliance of the fixture is orders of magnitude lower than that of the specimen • Minimize bending due to misalignment • Precisely prescribe torque to control crack propagation path Detonation direction Test Matrix (36 shots): • Pressure series • Torsion series • Crack length series • Repeat series

11. Incipient Crack Kinking Detonation Direction Initial Notch Hoop Stress Shear Stress Hoop Stress Shear Stress Torque Direction (right-hand rule) Initial Notch Image from Shot 153 Kinked Incipient Forward and Backward Cracks

12. Effect of Reflected Shear Wave: Crack Path Direction Reversal • Cracks initially kinked at angles consistent with principal stresses • The cracks then reversed directions due to reflected shear waves • Shear wave travel time: 150 ms Shot 143

13. Effect of Reflected Shear Wave: Crack Path Direction Reversal Shear Strain Reversal Rosette 1 (solid) Rosette 2 (dotted) Detonation Wave Direction

14. High-Speed Video Visualization Shot 148 Shot 147 Shot 146 Poster

15. Detonation Diffraction • complex flow field-especially in critical regime • short time scales • two mixture types studiedin criticalregime accoustic corner disturbance signal t4 t3 t1 t2 D UCJ diffracting shock

16. Optical Diagnostics Simultaneous use of: • Schlieren system • PLIF system to detect OH radical distribution • Multiple exposure chemiluminescence • imaging

17. Qualitative comparison with simulation sub-critical reignition event 2H2+O2+70%Ar 10kPa, D/l=12 2H2+O2+70%Ar 10kPa, D/l=8 R. Deiterding, (AMROC) flow direction PLIF - schlieren overlay 2H2 +O2+22%N2 , 100kPa, D/l=13 detonation wave traveling into shocked but unreacted fluid image-height 130mm OH PLIF Poster 2H2+O2+70%Ar, 100kPa, D/l=12

18. Quantitative differences in mixture type low activation energy, q=4.8 high activation energy, q=9.5 Measurements of reaction front velocity from multiple exposure chemiluminescence images 2H2+O2+67%Ar, 100kPa

19. Further measurements • Shape of shock • front in sub-critical • case q=4.8 q=9.5 • velocity of shock on center line and along wall • induction zone length on center line and wall (from PLIF-schlieren overlays) • 3-dimensional image construction for re-ignition event 2H2+O2+67%Ar, 100kPa

20. Summary • Fracture: • Experimental data base available for validation testing • http://www.galcit.caltech.edu/~tongc/ • Detonation: • Experimental database on detonation structure available • Diffraction experiments completed • PLIF and schlieren images available for validation of AMR • Analysis of chemistry and diffusion in progress • 3-step model for treating competition effects • Preliminary shear layer ignition modeling • Future work • Higher resolution and precision strain measurements • Combined effects experiments • Simultaneous imaging of blast waves and fracture