Pocketed Panel Shear Buckling 1

[edbgtr]

Good Day Eng-Tippers

I am looking for help on the subject of shear buckling of pocketed panels.

Does anyone here have FEA or lab-test results from a systematic investigation into shear buckling of rectangular panels with varying percentages of edge thickening across the length and width of the panel and with varying thickening of the these edges relative to the basic host panel? The results, if correctly presented, should be “carpet” data of (ts/to) thickness ratios of the pad-up portion of the panel relative to the host panel and (bs/bo) and/or (as/ao) fractions of the pad-up width and length respectively. Alternatively, the carpet data could be reduced to chart/graph form that covers the range of thickness and edge widths investigated.

Typically the buckling equation has the following modified form: -

fcr = Kso*Kpocket*E*(to/bo)^2

Where: - Kso = Normal shear buckling coeffs based on panel AR = a/b and edge support boundary conditions
Kpocket = Function [(ts/to) ; (bs/bo)]

The Kpocket function is the actual trend that is sought which represents the effective thickness of the panel in terms of the thickness and width ratios.

Any data on this topic, including “spot” or single combination point data, will be welcome. A lead to a public domain, accessible research paper or journal article on the subject would also be most welcome. To date I have been unable to find any such data on the web.

Thanks,
Ed

 

[rb1957]

nothing in NACA or ESDU ?

 

[edbgtr]

rb1957

I think the NACA data is too early for doubler bonded or machined spar webs and as far as I recall, I have not seen this in the ESDUs, but correct me if I am wrong. This form of web reinforcement is now "in vogue" because of the large speeds at which such spars can be cut. I expect this kind of analysis is quite recent and not much has been published on it yet. I was hoping some enterprizing engineer on this forum had done some recently and was willing to share his/her results.

Ed

 

[40818]

edbgtr:

The analysis your looking for has been used by Airbus and its previous incarnations in SOR51 in its original form. The pad up at the panel edges effectivley reduce the panel size if i remember it at its most basic. The theory and application goes way back in time long before machined panels were utilised. Unfortunately as its propriety you wont find it unless you have been working in industry. Its now available in later mathcad application formats from the original paper then VAX systems.

 

[rb1957]

that is how i've dealt with padded webs too

 

[Sparweb]

How about old NACA papers:

TR 1195
TN 3059
RM-L52E05
RM-L53E13a
RM-L53J27

The language used in these papers is "integral waffle-like stiffening". Very descriptive title, but not very tasty.

The TR and TN are math-heavy and mostly about stress-strain analysis, while the RM's are concerned with buckling test results.

Hope that helps!


Steven Fahey, CET

 

[edbgtr]

40818, rb1957 & Steve

Thank you for your responses they're much appreciated.

I am aware of the Airbus approach as laid out in their new static manual, but I find it a little too broad-brush that the panels can be reduced to the inner size when the edge padding is 3 times the thickness of the inner panel. What happens in between? With machined and bonded doublers the ratio is rarely 3:1. This doesn't seem quite right when one considers the edge stiffening requirement for an SS condition.

Thank you Steve, I have downloaded the waffle stiffened panel reports from the NACA website and will see if I can get some guidance from their mathematical approach.

Ed.