Re: [PSUBS-MAILIST] acrylic cylinder

[Jon Wallace <jonw@psubs.org>]

Sean,

According to the text under 13.3.3 (pgs 726,727), the graphs are 
supposed to show the elastic instability of a cylinder supported by 
bulkheads or stiffeners spaced L apart (page 727, first sentence under 
the formula).  So aren't the curved plots showing the number of 
stiffeners present at a particular failure pressure?

Jon


Sean T. Stevenson wrote:
> OK - I can understand the confusion, as Figure 13.15 puts a lot of information 
> in one diagram.  The each plotted curve corresponds to a t/D value, indicated 
> by a text label beneath each plot.  Each plot is a series of joined arcs, with 
> each curved segment corresponding to a particular number of lobes expected 
> during failure.  These are the text labels above each plot - omitted on a few 
> of the lower ones because the text would be too dense, but you can count in 
> from the edges.
>
> The X coordinate is L/D as you surmised, but the Y coordinate is not pressure 
> - at least, not directly.  Actually, using your L/D value, look up to the 
> appropriate t/D plot (where you will find the number of lobes expected at 
> failure) and then read across to the Y axis, to get a value of "eta" used in 
> the following equation:
>
> Pc = eta * 0.035  
> (Pc = eta * E * 10^-7 for non-acrylic material)
>
> Where Pc is the short term critical pressure in psi.
>
> Three separate plots are presented, but you can think of these as simply 
> stacking on top of one another.  The plot is log-log, showing two orders of 
> magnitude in X and six in Y.
>
> -Sean
>
>
>   




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