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Recent content by RPstress

  1. RPstress

    Ply-Splicing Requirements

    Double bias fabric seems to be two plies, one at + 45 and one at - 45, stiched together, the two together can be called a 'layer' of double bias fabric. It's basically two plies of UD. See jloncomposite.com and merrittsupply.com . If this comes on a roll then I don't see why it needs...
  2. RPstress

    Thumb rule for honeycomb,corrugated structures.

    It's usually best to take an example H/C panel and assess its performance. Use one of the usual stressing guides. Hexcel's are free and quite good ( https://www.hexcel.com/Resources/Technology-Manuals - a bit of googling will yield many more). You can calculate properties such as weight vs...
  3. RPstress

    Frame configurations for an aircraft fuselage

    Option 2 should be most weight efficient and lowest cost too.
  4. RPstress

    Tie Rod Double Lug Fitting Bushing Holes

    Usually this is done so that the inner bush on the big side can be full length, allowing the clamp-up to put the bush into compression rather than bend the forkend lugs together.
  5. RPstress

    Bulkhead-Longeron Connections?

    The longitudinal joint as shown appears flexible and weak. If you HAVE to break a longeron the joint should be made with extruded cleats (or maybe C-fittings) joined longitudinally by bolts. A normal longeron is continuous through a simple bulkhead and joined to it by shear cleats with at least...
  6. RPstress

    Composite modelling with solid elements

    You can put properties in if you know them (most test programs find adequate through-thickness stiffnesses and strengths). However, you will have a problem finding adequate failure criteria accounting for both inplane and through-thickness forces at the same time. Combinations of inplane...
  7. RPstress

    Balanced and Symmetric Layups with PW Fabric

    Plain weave is pretty symmetric (although beware, some manufacturers use different weight plies in the 0 and 90 directions) but 5 harness or, worse, 8 harness satin weaves will curl up if cured as a single ply and should be laid up warp-side down below laminate centerline and warp-side up above...
  8. RPstress

    Help required in Spec Interpreation and possibly more...

    Re Q. 2, most SMCs are short fiber reinforced rather than cloth (usually fibers are less than a mm long, but some are 'long short' fibers, several mm long) and the properties are pretty much isotropic, at least in 2 dimensions. The example you supply can be injection molded which will give a...
  9. RPstress

    How can I reduce ply maximum shear stress using tailoring

    We don't know how detailed your model is. Are the high stresses predicted in the curved part of the corners or in some corners that are modelled more simply? A crude hand sketch would allow sensible answers. P.S.: is the FE model simple and linear static? Are the high stresses definitely...
  10. RPstress

    How can I reduce ply maximum shear stress using tailoring

    A sketch or at least a view of the FE model with the loading and restraints will help considerably. Usually shear is helped by 45 deg plies but the fibers must be in the directions of high stress. An open-sided box will not be much good at carrying torsion. Sketch of loading and restraints...
  11. RPstress

    Clarification on my thought process about FE load path needed.

    The level of detail implies you are interested in details of the beam's behavior which will only be revealed by nonlinear analysis. If so, then yes, you need axial fastener stiffness. If you're linear-static, then no, but you also don't need such a complicated model. What are you trying to...
  12. RPstress

    Thin machine cover made from light and shape stable material

    You could try AlBeMet, see http://www.materion.com . AlBeMet's a beryllium/aluminum alloy that's about as stiff as steel but quite a bit less dense. There are a few alloy variants. Materion are a useful reference for some fairly exotic alloys and claim to have advice for handling them. They also...
  13. RPstress

    Thin machine cover made from light and shape stable material

    It's worth mentioning that all metals' young's moduluses divided by their densities are the same for all useful metals (and many useful composites), except beryllium (high stifness for its density), Al-lith (a tiny bit high stiffness for its density) and copper alloys (copper, brass, bronze...
  14. RPstress

    Thin machine cover made from light and shape stable material

    If you want it lighter and stiffer than steel your options are pretty much limited to small benefits from aluminum and titanium, slightly bigger ones from an advanced aluminum-lithium alloy or larger ones from beryllium or HM or UHM continuous carbon epoxy (there are other resins but epoxy is...
  15. RPstress

    Thin machine cover made from light and shape stable material

    Plastic filled with short carbon fibers will not be stiffer than steel and at best will typically be about as stiff as aluminum if 40% fibers are used (50% of the highest modulus short carbon fibers available (hard to get) might give a modulus of about 80 (maybe 100) GPa). Continuous high...
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