Joint between Aluminium and Composite Sandwich

Discussion in 'Boatbuilding' started by Cacciatore, May 9, 2020.

  1. rxcomposite
    Joined: Jan 2005
    Posts: 2,058
    Likes: 206, Points: 63, Legacy Rep: 1110
    Location: Philippines

    rxcomposite Senior Member

    There are many who have tried mating a composite superstructure to a steel or aluminum hull and was successful. The problem would be the difference in thermal expansion of the composite and the metal part depending on the range of operating temperature. The materials have different CTE with steel having the highest and Carbon fiber being zero or negative. As one of the material tries to expand more, it will create a shear force on the bond/bolted connection or in case of embedded hard points, internal stress.

    A flange is welded to the base metal and the composite structure is bolted to the flange. The bolt hole is a loose fit on the center and elongated on the others emanating from the center. To seal/watertight, flexible silicone adhesive/sealant is used in between. Silicon sealant has high shear strength and is flexible enough to take up some of the strain during expansion and contraction. There will be some compromises on the short side of the structure but the thermal strain can be calculated if it is workable.
     

    Attached Files:

    • TL1.jpg
      TL1.jpg
      File size:
      112.9 KB
      Views:
      6
    • TL2.jpg
      TL2.jpg
      File size:
      160.4 KB
      Views:
      6
    fallguy likes this.
  2. Cacciatore
    Joined: Oct 2008
    Posts: 66
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: Italy

    Cacciatore Junior Member

    Thank you so much for reply. I would to save some weight of the superstructure of the new area to avoid to add several tons of solid ballast (due stability compliant ) in the bottom that can worsen the speed and seakeeping performance. I would like to build the new area fully carbon sandwich (8 kg/m^2) removing the several aluminium stiffeners (span 400 mm ) and using only primary stiffeners like the following pictures image https://ibb.co/C6Jx47S . Do you know if IACS have some rules about these joints ? The vessel is only 45 meters.
     
  3. Ad Hoc
    Joined: Oct 2008
    Posts: 6,379
    Likes: 503, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Only see 1 image in the link?

    Only that:
    i) you must demsotrate that the joint can transfer the load effectively and not yield beyond the design allowable by Class;
    ii) you have sufficient fire protection (A60) to ensure the structure is now the equivalent to what it is replacing.
     
  4. Cacciatore
    Joined: Oct 2008
    Posts: 66
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: Italy

    Cacciatore Junior Member

    Thanks for reply . There i have only thermal insulation and not A60 so it is easy for core. Have you some pictures of your previous works like it ?
     
  5. DCockey
    Joined: Oct 2009
    Posts: 4,562
    Likes: 258, Points: 83, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    Do not forget about corrosion. Carbon and aluminum can be used to make a battery.
     
  6. gonzo
    Joined: Aug 2002
    Posts: 14,132
    Likes: 538, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Have you compared carbon fiber sandwich panels to other commercially available materials? For example, comparing fiberglass/end grain balsa panels or Coosa Board vs carbon fiber for material properties and cost? The savings in cost may easily pay for an engineering firm.
     

  7. Ad Hoc
    Joined: Oct 2008
    Posts: 6,379
    Likes: 503, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    If I understand you correctly... you just install the A60 as per the suppliers approval officiate for composite.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.