Composite tubing material properties 1

[bsdhr]

Hello Everyone;

I am putting together weight saving proposition for upcoming Boeing 787 part. The intended design is all Stainless Steel and the proposed design would be combination of Steel and Composite material.

We are currently the selected supplier for this part and hence have all required and generated engineering information to design the part. However, we don't have work expereience with composite materials. So help/suggestions on below would be greatly appreciated;

1.Part made out of composite material would be in form of round tube about 12 inches long. The outside diameter is 1.10in and inside diameter is obtained from stress calculations. I need material properties, to simulate via hand calculations axial, bending and torsional stresses.

2. Preliminary work scope for structural stress calculations would assume linear elastic isotropic properties. This is for simplicity as I understand composite layup can be tailored.

3. My calculations on current design indicates, 50% of Stainless Steel material can be removed without affecting functionality. However, lost material has to be compensated by composite tube to account for lost structral strength. If the weight savings upto 25% can be justified without loss of structural strength, i will like to procure few pieces to build prototype. So please suggest something off-the shelf for low cost concept feasiblity check

Again thanks for taking interest in my quest.

Bye.

 

[rb1957]

without any slight implied or intended, i suspect that the designer/analyzt working on it was the stuff regularly ... such is often the way !

 

[RPstress]

A word of caution: Hansmeister's allowables appear not to be damage tolerant. All composite airframe must be stressed with damage.

For composite secondary structure, you can get away with hot/wet open hole allowables. For primary you need hot/wet compression after impact (CAI).

Bsdhr's 125 deg C environment is pushing it for a 180 deg C cure epoxy. You can do it, but your compression allowables begin to drop significantly at 125 deg C/wet.

125 deg C will also give strong Al alloys a problem. However, you should find that for secondary structure the strength/weight compromise is in favor of Al if the part does not have large fatigue loading. The Al can potentially be being sized to 60 ksi (400+ MPa). If it's primary (will have crack growth done on it eventually) the ultimate allowable for rough initial sizing needs to be about 35 ksi (240 MPa) for good Al.

 

[graemew]

Interesting thread.
When using a mix of different materials bonded together, please do not forget to consider that the different materials will experience the same stain under load and that this strain will result in quite different stress levels in each different material. For instance it is possible that metallic materials will reach yield while the non-metallics are still at significantly lower stress levels. It becomes more complicated (and the differences more noticeable) when considering off-axis lay-ups.
Why do you need to consider using any CRES in the design at all?