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Failure of laminated composites

Failure of laminated composites. Progressive failure is needed to predict ultimate failure . We will limit ourselves to first ply failure. Maximum strain or maximum stress failure – in plane loads. Given stress resultants , find laminate strains Then transform to ply strains

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Failure of laminated composites

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  1. Failure of laminated composites • Progressive failure is needed to predict ultimate failure • We will limit ourselves to first ply failure

  2. Maximum strain or maximum stress failure – in plane loads • Given stress resultants , find laminate strains • Then transform to ply strains • Then multiply by Qif needed to get stresses

  3. Example 6.3.1 Prequel • A kevlar/epoxy laminate is loaded by biaxial loading with . Find the maximum load it can carry. • The properties are: • The strain limits (in millistrains) are:

  4. Tsai-Pagano constants • Minor Poisson’s ratio • Q matrix • U’s in GPa

  5. A* matrix and laminate strains • Lamination parameters . How? • Then, from Table 2.1 (in GPa) • Laminate strains • Also 0-ply strains • Since

  6. 45-deg ply • To transform to 45-deg, we multiply laminate strains by • Get • Since the critical constraint is again transverse tension that gives

  7. Other load combinations • Textbook calculates failure limit for any ratio of and • Where is our point?

  8. Laminate failure envelope • Combining the two envelopes • Does it agree with previous calculations?

  9. If we wanted to check using Hoffman • First need to translate strain limits to stress limits (in Gpa) • Next calculate stresses in 0-deg ply • How does it look? Please check.

  10. Terms in Hoffman • Criterion • Ratios: • Criterion adds up to 6.1, large violation. • By how much approximately do we need to reduce the stresses? • Why the large discerpancybetween the two criteria?

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