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Progressive failure of laminates

Progressive failure of laminates. After first-ply failure, the stiffness of failed plies is degraded. A conservative approach is to set their stiffness very low. A less conservative approach is to degrade stiffness based on the type of failure. Fiber failure would degrade E 1

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Progressive failure of laminates

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  1. Progressive failure of laminates • After first-ply failure, the stiffness of failed plies is degraded. • A conservative approach is to set their stiffness very low. • A less conservative approach is to degrade stiffness based on the type of failure. • Fiber failure would degrade E1 • Matrix failure would degrade E2and G12

  2. Example 6.3.2 • Calculate the ultimate x-load that a graphite-epoxy laminate can carry. • What is another way to define the laminate? • Use max-strain criterion • Elastic properties , t=0.25mm • Strength • Which part of the data is not needed?

  3. Missing preliminaries • Same material was used in Example 2.4.1 where we obtained • This is also the Q for the 0-deg plies. For 90-deg what do we get? • Altogether

  4. First-ply failure • Laminate strains • Strain limits millistrains • Obviously , so failure will be due to 90-plies when . Why? • From second equation we calculate 0.0117 millistrain • Then from first equation

  5. What happens if we throw away the 90 plies? • Thickness will reduce to 1.5mm. • First-ply failure load is • This would also be the ultimate failure load of our laminate. • Textbook carries on a more complex calculation based on the assumption that the strain will remain the same when the 90’s fail.

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