8-Harness Satin vs Plain Weave Directional strength

Discussion in 'Materials' started by abosely, Oct 18, 2015.

  1. abosely
    Joined: Mar 2015
    Posts: 136
    Likes: 1, Points: 18, Legacy Rep: 10
    Location: Big Island Hawaii

    abosely Senior Member

    Is there a difference in directional strength between 8-Harness Satin weave and plain weave glass cloth of same wt per oz cloth?

    Building a Dierking Ulua strip plank outrigger with my nephews.
    It gets 6oz glass on inside and outside of hull.

    I know they're different as far as handling and conforming.
    But is there a strength direction bias with the 8-Harness Satin weave since it is over 7 and under 1?

    Or is it the same in both directions like a plain weave?

    Cheers, Allen
  2. rxcomposite
    Joined: Jan 2005
    Posts: 2,552
    Likes: 476, Points: 83, Legacy Rep: 1110
    Location: Philippines

    rxcomposite Senior Member

    The strength is in the number of fibers or tows in the longitudinal and transverse direction. Even plain weave is seldom balanced with more fibers in one direction.

    Assuming it is balanced, a plain weave will have equal strength in both direction. A harness satin will have more strength in the direction where the fibers do not bend or undulate.

    This is because the moment the fibers go out of misalignment from the straight direction, it loses some of its strength. Thus a plain weave will have less strength than a harness satin because there are many "bends" along the direction.

    Unidirectional has the greatest strength in the longitudinal directions because the fibers are straight and it tends to lay flat, decreasing the resin content. It has drawback of course. The moment the load is misaligned. the strength goes down rapidly as the fibers are held only together by resin. It splits. At 90 degree load, you get only about 17-20% of the original strength.

    Thus, plain weave is the weakest of the weave but retains its off axis load better. Harness satin drapes easily, but its strength is biased towards the fibers where there are less bends. Uni's is the strongest but in only one direction. It starts degrading at about 7 degrees of load misalignment.
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.