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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

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detonation and detonation driven tube fracture

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

structure of detonations
Structure of Detonations

Simulation

Experiment

Regular

Irregular

Poster

connection with vtf
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.
validation aspects
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
previous work 2002 2003
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
progress oct 2003 oct 2004
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)
validation of elastic wave propagation
Validation of elastic wave propagation

Measured Hoop Strain

and Detonation Pressure

Comparison of Measured Hoop strain

and Simulation (resolution study)

issues in validation
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

using prestress to control crack propagation path
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
incipient crack kinking
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

effect of reflected shear wave crack path direction reversal
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

effect of reflected shear wave crack path direction reversal1
Effect of Reflected Shear Wave: Crack Path Direction Reversal

Shear Strain Reversal

Rosette 1 (solid)

Rosette 2 (dotted)

Detonation Wave Direction

high speed video visualization
High-Speed Video Visualization

Shot 148

Shot 147

Shot 146

Poster

slide15

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

slide16

Optical Diagnostics

Simultaneous use of:

  • Schlieren system
  • PLIF system to detect OH radical distribution
  • Multiple exposure chemiluminescence
  • imaging
slide17

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

slide18

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

slide19

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

summary
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