SHEAR-OUT/BURST-OUT IN COMPOSITE PANELS 1

[StressMan2506]

Calling composite stressers...

Does anyone know of a method for calculating shear-out/burst-out strength in composites where the fibres are orientated at other than 0, 45 or 90 dgerees to the subject edge?

Thanks in anticipation.

 

[SWComposites]

Are you referring to a "shear-out" failure mode due to a bearing load on a hole near a laminate edge? or something else? (I have never heard of "burst-out").

SW

 

[StressMan2506]

Thanks for getting back to me, SW. I do mean shear-out of a loaded fastener through an edge. I used the expression "burst-out" because such an edge failure is not really a plug of material simply shearing out...

 

[SWComposites]

As far as I am aware (and I have been involved in several methods development projects and thru piles of test data), there are no accurate methods to predict bearing, shear-out, end-splitting, etc failure modes. You need a test database, or very conservative design values.

SW

 

[StressMan2506]

Well, SW, I work with a legacy method of calculating shear-out strength which includes a parameter which is dependent upon, firstly, the percentage of fibres at 45 deg to the edge and, secondly, the percentage of the remainder parallel to it. I do not have access to the data upon which it is based. Later methods treat edge strength as being the bearing strength if edge distance > N times fastener shank dia; if edge dist < N x dia, edge strength is bearing strength times an empirical reduction factor. N is 3 for countersinks & 2.5 for plain.

As a concessions engineer, I often have to use the legacy method to account for short edge distances or cases where a ply or two are considered ineffective. If the plies align conveniently with the edge in question, I can follow the method. If they do not, I calculate two values of the parameter, and hence strength. In the first, the edge is treated as parallel to one of the fibre directions. The second alignment is at 45 deg to the first. I would like to be able to do better than this.

 

[SWComposites]

Well, someone would a) have to get the legacy data to see how the current method was derived, and b) get some test data for short edge margin bearing strength with other fiber angles.

SW

 

[StressMan2506]

OK, SW, so, as far as you know, the means to do what I would like to be able to do is not readily available. Thanks for responding. I will find a work-around.

 

[Aerodesign]

Try this nice method.

http://files.engineering.com/getfile.aspx?folder=a6eec873-bd4f-4378-9304-c80169f5be3b&file=C8-1.jpg

http://files.engineering.com/getfile.aspx?folder=41176c67-94ee-4ea9-a95d-468b8ae424a8&file=C8-2.jpg

Regards

 

[StressMan2506]

Thanks, Aerodesign, but I am very familiar with those two figures. Unfortunately, the method embodied does not allow for fibre angles other than 0 deg, 45 deg & 90 deg to the subject edge.