Cloth on Cloth

Discussion in 'Fiberglass and Composite Boat Building' started by titan22, Jan 28, 2011.

  1. ondarvr
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    ondarvr Senior Member




    We did lab testing for a marine customer that was having fracture problems in a certain section of the hull, we tested 3 resins with roving and biax, back to back and with mat between each layer. What it clearly showed was that every time mat was used between each layer the laminated could withstand a much greater force before fracturing, and when it did fail there was less over all damage to the laminate.

    These boats had been using several 24 oz roving back to back applied all at one time, then they went to biax to help with the fracturing and it really didn't help much. The solution was to use a very light layer of chop between each roving, this increased the fracture resistance dramatically.

    While the bond between cured layers can be less than a laminate done all at one time, its the weak resin rich layer between stitched or woven fabrics that is typically the failure point in hand lamination when no mat is used.
     
  2. rxcomposite
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    rxcomposite Senior Member

     
  3. ondarvr
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    ondarvr Senior Member

    Right now I can only recall two of the resins, one was an ortho DCPD blend and other was a straight ortho, I can't remember if the third was a straight ISO or a blend.

    The overall thickness of the laminate was kept the same and there was so little chop used between each layer it would have had a minimal affect on the thickness.

    A few of my friends have a particular boat that is made locally and they advertise the improved strength and lighter weight of back to back roving (all done at one time). The problem is that when I go to repair these boats I find large sections that have delaminated at the roving to roving bond, it can actually be somewhat difficult to repair because as you grind, the new edge of the roving will continue delaminate. Years later when I repair these boats again the repaired areas that used mat are fine, its the roving to roving areas that continue to fail.

    I also built very large structures (85ft long) out of VE, these were frequently heavily modified and at one time they were designed with back to back roving and back to back knits. What I found was at any cut edge all I had to do to remove a layer was find one of these back to back layers and drive a small wedge into it, as I did the entire laminate could be split apart at the bond line. Mat was used as a first layer when going over a cure layer and these bonds held up fine. The design was later changed so that mat was used between each layer and you couldn't split the laminate as easily.

    The better the resin used, the better it will hold up, but the bond line is still stronger when a small amount of mat is used between layers.
     
  4. rxcomposite
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    rxcomposite Senior Member

    Ondarvr,

    You did it right. That is one approach to flexing/cracking problem.

    Ortho, Iso, and DCPD are classified as brittle resins with an elongation in 1.5 to 2%. Prone to cracking with greatly reduced ultimate strength. Use of pure WR’s will reduce overall thickness due its high fiber packing factor. Reduced thickness will result to flexing.

    Increasing thickness by adding bulking materials (CSM) will increase thickness and reduce flexing. Even a CSM 225 with 33% resin content will be about 0.47 mm. thick, Multiply that by the number of CSM in between layers. It might look minimal but has a multiplying effect on load bearing.

    The resin is the weakest part of the link. As in the case of the wedge test in VE, you are prying the strong part (laminate) from the weak link. VE, at room temperature curing is at the 3% elongation range.

    I have always believed in cloth-mat-cloth combination but have been re educating myself to keep abreast with current technology, Resin Infusion. RI focuses on creating a laminate with high fiber content such as Biax’s, Uni’s, WR’s and eliminating CSM in the process..

    Coupled with this are designs for faster and faster boats with higher impact loads. I believe this was covered in another thread http://www.boatdesign.net/forums/ma...ongation-cores-hype-real-world-use-36170.html. The choice of resin, fiber, and core become critical. Ad Hoc also highlighted an issue about “fitting the resin curve” on the fiber on http://www.boatdesign.net/forums/materials/divinycell-vs-core-cell-35996-4.html thread. He was right, as always. Refer to the graph on the attached spreadsheet where the fiber fails before the resin.

    Attached is a study I am making on resin performance based on numerous articles recently surfacing and the availability of various resins with improved performance. Not quite done yet (I am finding the time) but I am posting this as the articles backs up what I am saying. The final version will predict laminate performance with various matrix/fiber combination. This will include modulus to gauge how the laminate will react to slamming.

    BTW, my post on “cloth on cloth” is an LR rule, Part 8 Chapter 2 Section 3.3.8 to 3.3.11. Note that there is mention of interlaminar strength. This focuses on the resin shear properties.

    Regards,

    Rx
     

    Attached Files:

  5. tunnels

    tunnels Previous Member

    Over the years have built some interesting hulls , the most interesting were hulls used for surf life saving boats . I came on the scene late in the excise after composite engineers had had a go and failed , after university wizz kids had graphed and predicted and rebuilt the hulls to the strenght of a 40 ft offshore powerboat but still they failed ! The owner of the company had reached a point of despiration when i happened on the scene .
    Went for a test run and saw first hand what and where and how these boats were being used . They should have been light enough to be dragged on the beach by two burly life savers but had reached a point where 3 were required to do the job of simply getting the boats into the water so two crew could go rescue a downing person .
    I was given a free hand on a no questions asked basis to come up with a solution to there never ending problem. to solve first the failure and then the weight . To me the two went hand in hand , flex and twist were the two things that they were trying to combat against ! Instead of working with and not against .
    Only two tpes of glass i used and just the everyday poly resin . I had come straight from working with offshore power boats and also F1 tunnels and seen what and how they were being built so pooled some of that knowledge and some of my own and came up with a unidirectional glass with a 225 gram csm between the 4 layers and set it loss on the waves . They ran down the beach and were in the water with smiles because it was 1/3 the weight of what they had been using . it flew on the water and they spent a whole day of pushing to almost beyond the limits of what the crew could take . bought it back and we checked the boat from end to end and not one single sign of a crack anywhere . they were asked to test the boat for a month all day every day and not spare any abuse to the point of distruction if need be . It came back to the factory and we took the tube off and stripped it of all its stuck on bits looking for signs of damage but there wasnt any .
    Simply I had built it to flex and twist and take shock loads to be beached half full of water and to the point where a ordinary boat would have simply burst wide open from the water inside trying to get out . After it was thoroughly inspected and given a clean bill of health a new better and lighter tube was fitted and it went even faster than before . It lasted 3 years before the club put it up for tender to be sold . I built 4 more the same way and they also lasted twice as long as the older boats they had been using .
    Its understanding the materials limitations and what and how its going to be used for, uni is a wonderful material to use just no one takes the time to try and understand it and what it is capabilities . even with a good quality poly resin its fantastic, with Vinylester it amazing .
    The key is the oriantation of the fibres and how they are laid to get the best from them . I worked on other things as well and did some work on progressive distruction laminants specially for life saving equipment used in exstreme conditions . During all this i never found it nessasary to even think about using epoxy of any sort for anythin i was making !. :D:p:p
    Not knocking computers to predict lay ups but at the end of the day you simply need to pull the plug and go get your hand dirt and get some practical exsperiance .Know whats good and what isnt , what works well and whats **** and not worth the effort !.
     
  6. ondarvr
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    ondarvr Senior Member

    It may not have been clear in my explanation, but in the testing the laminate schedule was designed so the thickness was the same with each combination of materials. What it showed was even though on paper the all woven and/or stitched laminates should have been stronger, it was the resin failure between the fabrics that failed. You could improve the test results by removing a layer of fabric and then place a very thin mat or chop between each layer.

    Yes DCPD blends are somewhat brittle, they have other good properties, but this can be a shortcoming for some applications. In much of the marine industry these are the workhorse resins though, and are used for just about every application, skin coats of VE or at least better resins are used, but the bulk of the boat is built from these GP resins. This why we tested these resin types, straight VE construction typically isn't an option in production boat building.
     
  7. jim lee
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    jim lee Senior Member

    Really? We must be fancy! Ours is 100%VE.

    -jim lee
     
  8. ondarvr
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    ondarvr Senior Member

    You have a boat built for a specific purpose and it will be purchased by someone that wants it light and strong, they will also pay extra for that. Most production boats are built to a price point (cheap) and the customer wants it to be shiny. You build quality, the others...well...not so much.
     
  9. tunnels

    tunnels Previous Member

    You could improve the test results by removing a layer of fabric and then place a very thin mat or chop between each layer.
    Well done to any one that has been in the laminating game for a while and been and seen lots a damaged boats and looked closely at how lay ups stay together and or fall apart etc etc and what works and what dosent knows csm in thin layers between layers of stitched or woven its not there for the ride it reinforces the resin layer be it polyester or vinylester .Be it 125 gram or 225 gram its there for a purpose !.
    Resin is needed to hold the glass together, somewhere the is a thin line of to much ,just right, or to little!. Finding that line is not easy . In all the work i do i use peel ply where ever possible .
    This helps to find the line i am looking for and feel comfortable with of just enough resin . Viscosity of resin helps in all this as well so check your resin !!
    Resin thinning is not an option !!. :confused:
     
  10. jim lee
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    jim lee Senior Member

    ondarvr, That reminds me, did you go to the Seattle boat Show?

    -jim lee
     
  11. ondarvr
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    ondarvr Senior Member

    No, I was out of town, I cover all of the West Coast and part Mexico and Canada now, so I'm on the road a lot.
     
  12. rxcomposite
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    rxcomposite Senior Member

    The 24 oz/yd2 (800 gr/m2) is a heavy boat cloth. The fiber undulations create a large gap in between layers for the resin to fill in. See fig A of the attached.

    Inserting a CSM in between reinforces the resin in the bondline and helps the laminate to nestle better as shown in fig B. It is the bondline that is reinforced and is a solution when laminating heavy bulky cloth.

    Several thin layers to build up thickness reduces the weak resin bondline as shown in fig c and d.

    Don’t get me wrong, a boat can be built out of ortho resin and boat cloth. It will be just heavier to compensate for the weaker resin. Switching to a better resin such as ISO and thinner WR will increase strength and reduce weight. As always, the higher the fiber content, the higher the strength of the laminate.

    Only higher performance laminate will need VE and EP.
     

    Attached Files:


  13. ondarvr
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    ondarvr Senior Member

    We do a great deal of testing with what the industry uses most, which is 24oz roving and CSM or chop, although more and more companies do use stitched fabrics. One of the problems the companies run into when they switch to knits is although the physical properties increase, the laminate is thinner and flexes more, so they end up using more glass or something like core mat to regain some of the stiffness they lost. Since knits cost more and they need to add more products to increase the stiffness, the material and labor cost can increase a great deal just to duplicate what they previously had.

    I don’t trust the lighter weight cloth any more than a I do the heavier ones when used back to back, in fact I’ve seen more frequent failures with lighter cloth when used with polyesters. One other problem with the lighter products is the cost climbs rapidly as the fabric weight goes down. So not only does the labor cost increase due to more layers of fabric being laid down, the actual cost in glass is higher too. Remember, I’m talking production boats, not custom or semi custom construction, so the speed of building the boat and cost are very important.
     
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