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16th International Conference on Composite Structures (ICCS16)
Analysis of Crushing Response of Composite Crashworthy Structures
Matthew David and Alastair JohnsonDLR Institute of Structures and Design, Stuttgart
16th International Conference on Composite Structures , ICCS 16Analysis of Crushing Response of Composite Crashworthy Structures
M. David & A. JohnsonSlide 2
Overview
Introduction
Experimental Investigation (Strain rate)Testing and Analysis MethodologyIdentification of varied crush response modes
Experimental Investigation (Stacking sequence)
Conclusion
Outlook
16th International Conference on Composite Structures , ICCS 16Analysis of Crushing Response of Composite Crashworthy Structures
M. David & A. JohnsonSlide 3
IntroductionCrashworthy structures
During a crash scenario, the role of a crashworthy structure is to utilize energy absorbing mechanisms to absorb crash loads in a controlled progressive manner.
Goals of a crashworthy structure are: 1. Limit deceleration on occupants
2. Allow the safe evacuation of occupants by maintaining sufficient structural integrity
Full scale drop test conducted at CIRA (HeliSafe TA)
Bell UH-1D fitted with 3 dummies
Impact conditions (Vx = 11.1 m/s2, Vz = 9.3 m/s2)
16th International Conference on Composite Structures , ICCS 16Analysis of Crushing Response of Composite Crashworthy Structures
M. David & A. JohnsonSlide 4
IntroductionMotivation
Cooperation between CRC-ACS & DLR – Crashworthy Design (2007-2010)
Concepts for helicopter subfloor structures with improved energy absorption
Numerical design tools for predicting crash response of composite aircraft structures
Stiff Survivalspace
Energy absorbing structure
Drop tower test of a crashworthy structure (C. Kindervater et al., 2011)
16th International Conference on Composite Structures , ICCS 16Analysis of Crushing Response of Composite Crashworthy Structures
M. David & A. JohnsonSlide 5
IntroductionEnergy absorbing coupon specimen
Developed to understand the energy absorption and failure mechanisms of energy absorbing structures at an coupon level
Easy to fabricate and gives reproducible axial crush failures under quasi-static and dynamic loading conditions
Sub-floor box structure(CRASURV)
Coupon specimen
16th International Conference on Composite Structures , ICCS 16Analysis of Crushing Response of Composite Crashworthy Structures
M. David & A. JohnsonSlide 6
Experimental Investigation – Strain rateMethodology
Test Methodology
Crush load curves extracted from test machines
Video and still images of crushing process and specimens
High Resolution Computed Tomography (HRCT) scan
Analysis Methodology
Quasi-static crush test at a cross head velocity of 1.0 mm/s
Dynamic crush test at an impact velocity of 10.0 m/s
Dynamic crush test setup
Loading platen
16th International Conference on Composite Structures , ICCS 16Analysis of Crushing Response of Composite Crashworthy Structures
M. David & A. JohnsonSlide 7
Experimental Investigation – Strain rateTest specimen specifications
Material : Hexply M18/1/43%/G939/1230 five harness fabric pre-peg material system
Ply Layup : [(0/90)2/0/(90/0)2] configuration
Trigger Mechanism : 45º outside chamfer
Sketch of specimen Specimen affixed in clamp
16th International Conference on Composite Structures , ICCS 16Analysis of Crushing Response of Composite Crashworthy Structures
M. David & A. JohnsonSlide 8
Experimental Investigation – Strain rateCrushing process
Quasi-static
Dynamic
16th International Conference on Composite Structures , ICCS 16Analysis of Crushing Response of Composite Crashworthy Structures
M. David & A. JohnsonSlide 9
Experimental Investigation – Strain rate High-Resolution Computed Tomography (HRCT)
Non destructive analysis (NDT)
Nanotom® CT system by phoenix ׀ xray
Acquisition phase (2-D) to the reconstruction of the volumetric data (3-D) took ca. 5 hours
Voxel resolution of 7 microns
HRCT-scan image slices
Detailed analysis of cross section
16th International Conference on Composite Structures , ICCS 16Analysis of Crushing Response of Composite Crashworthy Structures
M. David & A. JohnsonSlide 10
Experimental Investigation – Strain rateHRCT-scan image of crushed coupon specimen
Quasi-static loading condition Dynamic loading condition
16th International Conference on Composite Structures , ICCS 16Analysis of Crushing Response of Composite Crashworthy Structures
M. David & A. JohnsonSlide 11
Experimental Investigation – Strain rateEnergy absorption performance parameters
Typical force-displacement curve(progressive failure mode)
Crush force efficiency (CE) : Peak Crush Force / SSCF
Energy Absorbed (EA) :Area under Crush Force-Displacement curve
Specific Energy Absorbed (SEA) :EA / Mass of crushed portion
16th International Conference on Composite Structures , ICCS 16Analysis of Crushing Response of Composite Crashworthy Structures
M. David & A. JohnsonSlide 12
Experimental Investigation – Strain rateEnergy absorption comparison
16th International Conference on Composite Structures , ICCS 16Analysis of Crushing Response of Composite Crashworthy Structures
M. David & A. JohnsonSlide 13
Experimental Investigation – Strain rateVaried crush response
Inter and intra molecular interaction during the load bearing phase
Quasi-static loading condition
Dynamic loading condition
Inter molecular interactions between polymer chains only due to time scale of the test
Difference attributed to the strain rate dependency of the epoxy resin :where the time scale of the load bearing phase dictates the extent of changes in the polymer chains
Brittle Behavior
Ductile Behavior
16th International Conference on Composite Structures , ICCS 16Analysis of Crushing Response of Composite Crashworthy Structures
M. David & A. JohnsonSlide 14
Experimental Investigation – Strain rateDynamic material properties (carbon-epoxy)
Tensile stress-strain curve Shear stress-strain curve
(K.S Raju et al. 2011)
16th International Conference on Composite Structures , ICCS 16Analysis of Crushing Response of Composite Crashworthy Structures
M. David & A. JohnsonSlide 15
Experimental Investigation – Strain rateSummary of varied crush responseGlobal splaying failure crush mode Local fragmentation failure crush mode
16th International Conference on Composite Structures , ICCS 16Analysis of Crushing Response of Composite Crashworthy Structures
M. David & A. JohnsonSlide 16
Experimental Investigation – Stacking sequenceTest specimen specifications and methodology
Material : ACG MTM44-1FR/468 four harness fabric pre-preg material system
Ply Layup : [(0/90) 2] s configuration[(+45) 2] s configuration
Test methodology : Dynamic crush test at an impact velocity of 10.0 m/s
Analysis methodology : As previously described
16th International Conference on Composite Structures , ICCS 16Analysis of Crushing Response of Composite Crashworthy Structures
M. David & A. JohnsonSlide 17
Experimental Investigation – Stacking sequenceCrushing process
Quasi-static
Dynamic
16th International Conference on Composite Structures , ICCS 16Analysis of Crushing Response of Composite Crashworthy Structures
M. David & A. JohnsonSlide 18
Experimental Investigation – Stacking sequenceEnergy absorption comparison
16th International Conference on Composite Structures , ICCS 16Analysis of Crushing Response of Composite Crashworthy Structures
M. David & A. JohnsonSlide 19
Conclusion
Successful experimental methodology implemented in testing and analysis of crush coupon specimens
Identification and detailed study of varied crushing response and failure modes (Global and Local) from increasing compression strain rates
Importance of understanding the role of strain rate dependency in the design of crashworthy structures highlighted from the work presented
Future outlook includes the adoption of the experimental methodology to study the crush response of crush coupons consisting of varied:
Dynamic loading ratesGeometriesMaterial systems
16th International Conference on Composite Structures , ICCS 16Analysis of Crushing Response of Composite Crashworthy Structures
M. David & A. JohnsonSlide 20
Acknowledgements
The authors would like to thank CRC-ACS for the supply of specimens, valuablediscussions and exchanges throughout the collaboration.
16th International Conference on Composite Structures (ICCS16)
Analysis of Crushing Response of Composite Crashworthy Structures
Matthew David and Alastair JohnsonDLR Institute of Structures and Design, Stuttgart