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Help - Second Moment of Area
John P - 15/8/06 at 04:25 PM

I need to calculate the buckling load for a vertically mounted hydraulic cylinder in accordance with an agreed formulae from a British Standard.

Trouble is I need the Second Moment of Area of the cylinder rod in 4th power milimetres.

Sounds easy but I'm getting confused.

The cylinder rod is 60mm diameter.

Thanks,
John.

RazMan - 15/8/06 at 04:54 PM

quote:
Originally posted by John P
Sounds easy but I'm getting confused.


You're confused - that goes way beyond my City & Guilds Engineering Certificate! You lost me after the word 'calculate'

[Edited on 15-8-06 by RazMan]

Aboardman - 15/8/06 at 05:18 PM

is this any good

Area: 2827.4334
Perimeter: 188.4956
Bounding box: X: -30.0000 -- 30.0000
Y: -30.0000 -- 30.0000
Centroid: X: 0.0000
Y: 0.0000
Moments of inertia: X: 636172.5124
Y: 636172.5124
Product of inertia: XY: 0.0000
Radii of gyration: X: 15.0000
Y: 15.0000
Principal moments and X-Y directions about centroid:
I: 636172.5124 along [0.7071 0.7071]
J: 636172.5124 along [-0.7071 0.7071]

TangoMan - 15/8/06 at 05:36 PM

quote:
Originally posted by Aboardman
is this any good

Area: 2827.4334
Perimeter: 188.4956
Bounding box: X: -30.0000 -- 30.0000
Y: -30.0000 -- 30.0000
Centroid: X: 0.0000
Y: 0.0000
Moments of inertia: X: 636172.5124
Y: 636172.5124
Product of inertia: XY: 0.0000
Radii of gyration: X: 15.0000
Y: 15.0000
Principal moments and X-Y directions about centroid:
I: 636172.5124 along [0.7071 0.7071]
J: 636172.5124 along [-0.7071 0.7071]


That's just what I was going to say

jon_boy - 15/8/06 at 05:44 PM

some one else has to retake somecourse work then?!

matt_claydon - 15/8/06 at 07:23 PM

Second moment of area for a solid circular section is (Pi)*(r^4)/4.

Using your diameter of 60mm this gives

Ixx = Iyy = 636200 mm^4

HTH,
Matt.

[Edited on 16/8/06 by matt_claydon]

Aboardman - 15/8/06 at 07:49 PM

quote:
Originally posted by matt_claydon
Second moment of area for a solid circular section is (Pi)*(r^4)/4.

Using your diameter of 60mm this gives

Ixx = Iyy = 10180000 mm^4

HTH,
Matt.


are you sure on the answer

pi * (30^4) / 4 =636172.51235

easy way to check second moment of any shape if you have autocad.
draw your shape, box circle, i beam, some fancy shape what ever you want.
make it a closed polyline, then turn the shape into a region, by using the region command.
then by using the tools/inquiry/region mass properties this will give you the values i gave before, however this is incorrect, you then need to reset the ucs to the Centroid of the object. so that the values for the centroid are x0,y0

once you have done this redo the mass properties and there you go.

matt_claydon - 16/8/06 at 07:29 AM

Yep, thanks for pointing that out - small mistake on my part ; corrected now!

Simon - 17/8/06 at 12:24 AM

quote:
Originally posted by RazMan
You lost me after the word 'calculate'


Lost me after the word Help



ATB

Simon