Evaluating Formability of Sheet Metal at IIT

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Evaluating Formability of Sheet Metal at IIT

• Tensile parameters and new ductility criteria
  based on continuous bending under tension (CBT)
  test to correlate with sheet formability in
  production

By Professors Joseph Benedyk Sheldon Mostovoy
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Local elongation in conventional tensile testing
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Schematic of CBT apparatus developed at IIT
Schematic Drawing of CBT Test for Sheet Metal
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CBT apparatus installed on an Instron machine at
IIT
Click the picture for movie
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Close-up of CBT apparatus
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Rolled arrangement of CBT apparatusduring testing
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Commercial sheet materials used in tensile and
CBT elongation trials
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Tensile and CBT properties of 3004-H19 aluminum
alloy sheet compared
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CBT and tension test comparison
Photos of annealed mild steel (0.010 in thick)
tested to fracture by CBT (top 140 elongation)
and by conventional tension (bottom 40
elongation).
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Strain pattern on 5xxx sheet after tension and
CBT testing
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Comparative tensile CBT elongations
Tensile and CBT elongations for aluminum alloy
sheet
Tensile and CBT elongations for steel sheet
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CBT test advantages

• CBT test is easy to perform and CBT elongation
  avoids necking failure mode characteristic of
  uniaxial tension
• CBT elongation correlates better with formability
  in various sheet metal production processes
• CBT test can be modified to study shape and
  surface roughness parameters in sheet metal
  forming dies
• CBT test can be modified to study lubrication
  effects in sheet metal forming
• CBT test duplicates Bauschinger or strain
  softening effects in sheet metal forming