Characterization of Carbon Fiber and Glass Fiber Fabrics by Drape Fixture

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Characterization of Carbon Fiber and Glass Fiber
Fabrics by Drape Fixture

• By Aaron Holmberg

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Scope of Project

• The following parameters must be determined
  through experimentation
• Force needed to deform fabric in shear related to
  the fabrics characteristics
• Locking Angle The angle at which the shear force
  increases rapidly and the fabric begins to
  wrinkle related to the fabrics characteristics
• Determining these characteristics will help in
  predicting the drapability / formability of these
  fabrics which is useful knowledge when
  determining manufacturability of curved
  components with a particular fabric

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Fixture Design

• A fixture was designed to help determine the lock
  angle and force vs. fiber angle of fabrics
• Fabric is clamped between two ridged steel plates
• A rubber gasket was used between the plates to
  distribute clamping force evenly along the
  fabrics edge
• Universal ball transfer unit (not pictured) were
  attached to the side of the bottom clamp to
  reduce friction on the glass guides (shown in
  green) during shearing test.
• Dowel pins were install on the bottom clamp for
  alignment and tensile fiber attachment point.

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Fixture Design

• The back was cut out to allow for convective heat
  transfer during tested performed in the oven
• The simple design allowed most of the fixture to
  be build at Sicomp

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Installation of Fabric

• Tip fixture on its side
• Lay spacers into place

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Installation of Fabric

• Lay fabric blank and tensile fiber into place
  with a sheet of glass on top of fabric to
  eliminate fabric wrinkles
• Clamp jaws are set in place and tightened while
  holding the bottom clamp edge against the spacer

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Installation of Fabric

• Flip fixture upright
• Remove spacers
• Set guide in place

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Experiments

• Various fabrics were cut into 200mm x 210mm
  pieces
• After installing the fabric sample, an
  incremental increase of tension was applied by
  adding weights to a receptacle attached to the
  tensile fiber
• The lower jaw displacement was measured by hand
  after each incremental increase in tension

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Fabrics Tested

• Five different fabrics were loaded into the
  fixture.
• Devold AMT - glass fiber 90o
• Sigmatex - carbon fiber 90o Light 0o glass fiber
  weave
• CS-Interglass 0o-90o small tight weave
• Sparas till VAC - carbon fiber 0o-90o heavy weave
• No Label - carbon fiber 0o-90o light loose weave
• Additional information on these fabrics can be
  found in the table at the end of this Power Point
  presentation

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Results

• Devold AMT - glass fiber 90o
• Very stiff during loading
• Instantaneous wrinkling
• No load data taken because of wrinkling

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Results

• Sigmatex - carbon fiber 90o light 0o glass fiber
  weave
• Little resistance to shear
• No locking angle found
• No wrinkling experience at higher angles
• Fiber compression at higher angles created fabric
  thickening without wrinkles of the fabric
• Louver fiber formations were observed in the
  fabric near the clamps

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Results

• Photo of Louvers observed during experiment
• Fibers would rotate out of plane only near the
  clamping surfaces

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Results

• No Label - carbon fiber 0o-90o light loose weave
• First fabric tested
• Load was incrementally applied and displacement
  measured
• Tensile fiber was 317mm long at 0mm displacement
  which created large variations in tensile angle
  (angle of tensile fiber relative to horizontal)
  as displacement was increased due to a fixed
  pivot point
• Tensile angle was compensated for in calculations
  found in Excel file
• Future experiments were performed with a longer
  tensile fiber (1.920m) do decrease angle
  variation
• Experimental results were inconclusive due to
  inaccuracy of measuring by hand and variation in
  tensile angle

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Results

• CS-Interglass 0o-90o small tight weave
• The only fabric tested with a significant
  historysis
• Historysis could be related to a combination of
  relatively greater friction between GF compared
  to CF and / or the tighter weave constricting
  sliding motion between fibers
• Load incrementally applied and displacement
  measured
• Locking angle determined to increase with greater
  tension on fabric as shear is applied
• It is assumed low angle wrinkles are related to
  the friction between fibers overcoming tension
  applied by the weight of the lower clamp jaw
• Additional downward force applied to the lower
  clamp jaw by hand allowed greater angles to be
  reached before fabric wrinkled

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Results

• With 7.9 Newtons of downward force due to the
  weight of the lower clamp jaw a locking angle of
  9 degrees was found
• When additional downward force was applied by
  hand to the lower clamp jaw a locking angle of 16
  degrees was found
• The locking angle is defined as the point just
  before wrinkles are observed

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Results

• Sparas till VAC - carbon fiber 0o-90o heavy weave
• Binder was removed from this fabric by placing it
  in an oven at 400 C for two hours
• Shear force was incrementally increase and
  displacement measured
• Wrinkles were observed at approximately 50
  degrees

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Results

• 0-90 Heavy Carbon Fiber Tensile Force vs.
  Fabric Angle
• Note Tensile angle is not compensated for in
  the graph below

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Additional Equipment Desired

• More accurate data could be gathered using the
  following equipment in parallel with the drape
  fixture
• Variable speed linear actuator with 200mm of
  travel and 20 N of force
• 20 N load cell
• Linear displacement transducer
• Hand measurements proved to be extremely
  inaccurate

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Conclusion

• Additional testing will be needed before good
  fabric characterization results can be gathered
• Fixture was proven to have potential in testing
  0-90 woven fabrics.
• Variation of lock angle results relative to
  fabric tension may be a concern in future
  experiments
• Compensation for tensile angle resulted in
  questionable calculation results hens why it was
  excluded from the graph
• Uncertainty may be associated with louvers
  observed near clamp surfaces. Additional testing
  may be needed to determine its effects.

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