Damage Tolerance Test Method Development For Sandwich ......Damage Tolerance Test Method Development...
Transcript of Damage Tolerance Test Method Development For Sandwich ......Damage Tolerance Test Method Development...
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Damage Tolerance Test
Method Development For
Sandwich Composites
2012 Technical Review
Brad Kuramoto, Dan Adams
University of Utah
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FAA Sponsored Project Information
• Principal Investigator: Dr. Dan Adams
• Graduate Student Researcher: – Brad Kuramoto
• FAA Technical Monitor – David Westlund
• Collaborators: Boeing
Materials Sciences Corporation
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BACKGROUND: DAMAGE TOLERANCE
Damage Resistance Versus Damage Tolerance
Damage Resistance: “Concerned with the creation of damage due to a specific impact event” *
Variables: Facesheet: material, layup, thickness
Core: type, density, thickness
Test specimen: size, shape, boundary conditions
Damage Tolerance: “Concerned with the structural response and integrity associated with a given damage state of a structure” *
Variables: Damage state: type, extent, location
Sandwich configuration: same facesheet and core variables as above
Test type: loading, specimen size, support conditions
* Tomblin, Lacy, Smith, Hooper, Vizzini, and Lee, “Review of Damage Tolerance for Composite
Airframe Structures, DOT/FAA/AR-99/49 , August, 1999.
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BACKGROUND:
Damage Tolerance Test Methods for Sandwich Composites
• Damage tolerance test methods for monolithic composites have reached a relatively high level of maturity
– Damage Resistance: ASTM D 7136 – Drop-Weight Impacting
– Damage Tolerance: ASTM D 7137 – Compression After Impact
• Less attention to sandwich composites…until recently
– SAMPE/ASTM D30 Panel at Joint Meeting October 2009
“Damage Resistance and Damage Tolerance of Sandwich Structures”
Dan Adams, organizer, panelist Carl Rousseau, moderator
– ASTM D30 publishes standard for sandwich damage resistance
ASTM D7766 (2011) “Standard Practice for Damage Resistance Testing of Sandwich Constructions”
– SAMPE/ASTM D30 Panel at Joint Meeting October 2011
“Damage Resistance of Composite Sandwich Structures”
Dan Adams, organizer Carl Rousseau, moderator
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RESEARCH OBJECTIVES:
Damage Tolerance Test Methods for Sandwich Composites
• Evaluate candidate test methodologies
• Develop a standardized ASTM test method
• Compare residual strength results of sandwich
panels using proposed test methods
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Where Do We Start?
What is the intended usage of a damage tolerance test
method for sandwich composites?
Ideas from “relevant” test methods, discussions with
industry personnel, and the literature:
• Quality assurance
• Material ranking/selection/specification
• Establishing design properties/allowables
• Research and development activities
• Product development
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Intended Usage Likely to Affect Test Method
• Material ranking/selection/specification – Specify a sandwich panel configuration
Example: D 7137: Specified lay-up and target laminate thickness for CAI testing
• Establishing design properties/allowables – Allow a wide range of sandwich panel
configurations Example: C 364: Edgewise compression strength of
sandwich panels
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Edgewise Compression
• Preferred DT test method for monolithic laminates
• High interest level for sandwich composites
CANDIDATE TEST CONFIGURATIONS:
Damage Tolerance of Sandwich Composites
Four-Point Flexure
• Constant bending moment and zero shear in damaged section of panel
• Damaged facesheet can be placed under compression or tension
Pressure Loading
• Simply supported
sandwich panel
• Distributed load
• Of interest for
pressure loaded
applications
Boeing Gougeon Brothers, Inc.
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Edgewise Compression Testing For Damage Tolerance:
Testing Considerations
• Test fixture support of sandwich specimen
– End supports
Clamping of top and bottom
Potting of core
– Side edge supports
Knife edge (pinned)
Clamped (reduce rotation)
• Method of specimen alignment
• Strain measurement
– Alignment
– Determination of load paths
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Edgewise Compression Testing For Damage Tolerance:
Scaling of Test Results
Applying results to composite sandwich structures
• Sandwich configuration
• Specimen size
• Specimen support conditions
• Type of damage
• Extent of damage relative to
specimen size
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Edgewise Compression Testing
Testing with Supported Gage Section
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University of Utah
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Edgewise Compression Testing
Testing with Unsupported Gage Section
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NASA Langley NASA Langley
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Damage Tolerance Testing:
Four-Point Flexure Testing
V
P/2 P/2
P/2 P/2
L1 L1 L2
P/2
P/2 PL1/2
M
Within central test region:
• No shear forces/stresses
• Uniform bending moment
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Four-Point Flexure Testing For Damage Tolerance:
Testing Considerations • Location of Damage: tension or compression loading?
• Required length of central test section of panel – Minimum distance from damage region to loading points
• Required length of outer regions of panel – Sufficient distance to develop bending moment
• Core requirements for shear stress - outer panel sections
• Facesheet /core requirements at loading points
• Overall panel length P/2 P/2
P/2 P/2
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Four-Point Flexure Testing For Damage Tolerance:
Examples of Efforts to Date
Boeing University of Utah
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Four-Point Flexure Testing:
Undesirable Failures
Failure at core material splice Failure at loading point
Core failure in
outer region
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Four-Point Flexure Testing:
Acceptable Failures
Delamination/buckling of facesheet Failure of facesheet
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Uniform Pressure Test
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• Simulates hydrostatic pressure loading
• Pressure loading of sandwich panel
using pressure bladder
• Test machine used to press bladder
against test panel
• Quasi-static or cyclic fatigue loading
• Size of sandwich panel dependent on
sandwich properties
• Current usage primarily in marine industry
Based on Existing Standard: ASTM D 6416
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Uniform Pressure Test
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Gougeon Brothers, Inc.
12 in. x 12 in. test panel
22-kip test machine (Gougeon Brothers, Inc.)
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Development of an ASTM Standard:
Damage Tolerance of Sandwich Composites
Process Includes:
• Review of Similar/Relevant Standards
• Establish intended usage(s)
• Develop suitable test fixturing
• Establish suitable range of sandwich configurations
• Facesheet parameters
• Core parameters
• Specify suitable specimen geometries
• Develop proper test procedures
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• Investigate all three proposed test methods
– Edgewise compression
– Four-point flexure
– Uniform pressure loading (D6416)
• Determine residual strength of sandwich panels
using the three test methods
• Initial comparison : Sensitivity to idealized impact
damage
Initial Experimental Evaluation
Damage Tolerance of Sandwich Composites
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• G11 glass/epoxy facesheets & Nomex honeycomb core
• “Idealized” damage: 1 in. and 3 in. hole in facesheet
• Develop a recommended procedure for each method
• Initial assessment of damage tolerance
– Develop familiarity with each test method
– Identify additional issues requiring investigation
– Initial assessment of each test method
– Identification of test method limitations
Initial Experimental Evaluation
Use of Idealized Impact Damage
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Summary
Benefits to Aviation Include… – Standardized damage tolerance test method for
sandwich composites
– Test results used to predict damage tolerance of
sandwich composites
– Research results on scaling of results towards
composite sandwich structures
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Thank you for your attention!
Questions?