Short ED in Graphite Composite

[aerohead56]

Does anyone know how to analyze short ED conditions in Graphite Composites? Any guidance would be greatly appreciated.

 

[SWComposites]

Conservative appoach is to draw a straight line between the strength at e/d=2.5 and zero strength at e/d=0.5. Otherwise test data is needed. There was some data published by McAir in Air Force reports in the '80s for one of the early CFRP material systems.

 

[aerohead56]

Not a bad idea. We are assuming that full bearing strength is developed at 3D, so I will start at that and calculate 0 strength at .5D like you suggested.

 

[Aerodesign]

I agree with the approach SWComposites suggests. However dont forget the laminate composition may effect the directional bearing properties.
We clear a lot of structures using a spreadsheet based OHT method, this takes into account the local laminate composition, including any drape induced shearing, local bypass loads, gives choice of failure criteria. Outputs an RF and a failure envelope. It currently works for only some CFRP materials.
This approach is probably only worthwhile if you are designing 'down to the wire' but it has proven very effective for us.

 

[SouthernManCT]

SWComposites approach should produce a reasonable answer. But a word of caution on using data from testing done in the 80's. Material systems, particulary the resin systems most commonly in use today, are superior to those first generations resins, particularly for bearing and bearing bypass.