1 / 30

Composites- Engineering Basics

Composites- Engineering Basics. Paul H. Miller, D.Eng., PE Naval Architecture Program United States Naval Academy. Outline. Blended properties/carpet plots Advanced analysis Tests to get properties or verify a structure Basic loads Safety factors An example Guides and references.

Leo
Télécharger la présentation

Composites- Engineering Basics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Composites- Engineering Basics Paul H. Miller, D.Eng., PE Naval Architecture Program United States Naval Academy IBEX 2004 - Session 102

  2. Outline • Blended properties/carpet plots • Advanced analysis • Tests to get properties or verify a structure • Basic loads • Safety factors • An example • Guides and references IBEX 2004 - Session 102

  3. Blending Properties • Taking a composite and treating it like an isotropic material (like aluminum) Two Basic Approaches • Approximate methods based on common laminates. Carpet plots, design data sheets, approximate equations. • Classical Lamination Theory (CLT) - Matrix math using unidirectional material data to come up with an equivalent stiffness and strength. This is much more accurate! IBEX 2004 - Session 102

  4. CLT Properties E = 5,530,000 Str= 54,000 Efy= 2,130,000 Efx= 8,910,000 Flex Str x= 20,800 Flex Str y= 87,000 Blended Props E = 5,000,000 Str= 50,000 Ef= 5,000,000 Flex Str= 50,000 Comparison of Blended and CLT For a 2 ply knitted (90/0/0/90) 0.25” Laminate With Unidirectional PropertiesEx=10,000,000 Ey=100,000 Str=100,000 IBEX 2004 - Session 102

  5. My Suggestions • You can use blended methods for wovens and mats in balanced or near balanced laminates (about the same amount of material on each side of the core) • You MUST use CLT for uni’s or unbalanced or asymmetric laminates • You should use CLT for knits IBEX 2004 - Session 102

  6. More Suggestions The “best” solution is to: • Test for uni properties • Preliminary design with CLT • Make a test laminate • Analyze the structure with finite element analysis • Prototype test #4 and possibly #5 if it is a “risky” design! IBEX 2004 - Session 102

  7. Determines which way the load goes in a structure Can use either blended (bad idea) or CLT (good idea) to analyze composites. Finite Element Analysis IBEX 2004 - Session 102

  8. FEA Example IBEX 2004 - Session 102

  9. Realities of FEA • Not for everyone! It takes practice. • It might be cheaper and faster and more accurate to test a prototype! • When you need a really accurate prediction, it is the only way to go. IBEX 2004 - Session 102

  10. Testing 1-2-3 • First, determine if you need basic material properties. If so, use standard tests. • Second, determine if you need to test for something special (fatigue, impact, high heels)? Design an appropriate test. • Third, do you need a prototype test? IBEX 2004 - Session 102

  11. Standard Test Methods • Primary Tests • Tensile- ASTM D3039 • Compressive – C364/D3410 • Shear – D4255 • Bending – C393/D790 • Secondary Tests • Peel, Void Content, Resin Content IBEX 2004 - Session 102

  12. D3039 Tensile C393 Flex Standard Tests IBEX 2004 - Session 102

  13. Impact – A hull panel IBEX 2004 - Session 102

  14. Prototype – a deck panel IBEX 2004 - Session 102

  15. Safety Factors • Example: • 3/4” three strand nylon has a breaking strength of 16,700 pounds • The design load for anchoring a 110’ boat in 60 knots is 3,500 pounds • The Safety Factor is 16,700/3,500 = 4.8 IBEX 2004 - Session 102

  16. Safety Factors • Overall Approach – All calculations use the same FOS. • “For Composite Materials Use FOS=4” • Is 4 too conservative? • Does one value fit all conditions? • Do you know the loads and strengths? • What if you went lower and guessed wrong? IBEX 2004 - Session 102

  17. “You've got to ask yourself one question: 'Do I feel lucky?‘” IBEX 2004 - Session 102

  18. Safety Factors • Based on Materials: • “For Polyester Laminates use 4” • “For Epoxy or Vinyl Ester use 3” • Why? • Epoxy and VE have greater strains to failure and therefore higher fatigue endurance limits (longer fatigue lives) IBEX 2004 - Session 102

  19. What about loads? • Assume the worst case loading! • If loads are static rather than dynamic, reduce SF by 33%. • If short lived, reduce by 15%. • Are boats ever static? IBEX 2004 - Session 102

  20. Safety Factor Adjustments • Decrease by 15% if using CLT • Decrease by 30% if using FEA (and the operator knows how to use it!) • Increase by 50% if the builder is not intimately familiar with the materials! • Increase by 25% if the material properties are not well known. • Increase by 10-200% if the loads are unknown! IBEX 2004 - Session 102

  21. Example SF Adjustment • A standard boat laminate of polyester will have a SF = 4 • An epoxy laminate designed using FEA for a competitive race boat could have a SF as low as: 3 x (1-0.3)x(1-0.15) = 1.8 A 55% Reduction! That’s a lot less weight! And no resale value! IBEX 2004 - Session 102

  22. Basic Loads to Consider • Tensile • Compression • Buckling • Shear • Bending IBEX 2004 - Session 102

  23. A Bending Example2’ x 3’ Hatch Cover WR/Poly Load is a 250 pound person in the middle. Might use a 2.0 dynamic factor if it could be jumped on! Safety Factor is 4. Material strength is 40,000 psi Moment is (WxL)/4 = 1500 in-lb Bending Stress is (M*t/2)/(bt3/12) and must be no more than material strength/safety factor. So t needs to be at least 0.26” (~8 plies 18 oz) (“blended”) With CLT it is ~7 plies and with FEA ~6 plies But it could be stiffness driven! IBEX 2004 - Session 102

  24. Guides and References • Everything you need to know about basic structural analysis? • My most-used reference! IBEX 2004 - Session 102

  25. Guides and References • The classic • Structural details • Basic properties • Carpet plots • OK if building to 60’s technology IBEX 2004 - Session 102

  26. Guides and References • A good, basic reference from the 70’s for low tech construction • A good alternative to Marine Design Manual IBEX 2004 - Session 102

  27. Guides and References • The most up-to-date and comprehensive of the basic guides • Great materials section! • My second most-used reference! IBEX 2004 - Session 102

  28. Guides and References • In case you want to really learn composites analysis! • Presents CLT! • Review your matrix math, then take the short course! IBEX 2004 - Session 102

  29. Guides and References • A $35 program that uses CLT. • My most-used composites software! • Works great with a spreadsheet. IBEX 2004 - Session 102

  30. If you want it done right… • Do it yourself! • Ask an expert! • All of the above! Cogito – Two time winner of the Little America’s Cup No breakdowns so far! IBEX 2004 - Session 102

More Related