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## Robot Structural Analysis

Contributor
Posts: 15
Registered: ‎05-30-2012

# Section Definition stress analysis - stresses symbols

491 Views, 8 Replies
11-28-2012 04:16 AM

Hello! I am Ricardo Dias.

I have a doubt relative to the stress results given in the section definition module. In the attached image, it can be seen two highlighted "items": |t|max and Si,max.

I search for the meaning of the symbols, but I didn't found it. I know that corresponds to tangencial and normal stresses, respectively, but that values are based in which calculus? What are they referred to?

In the |t|max, the Ylocal is different from the Ylocal above (|t|xy,max and |t|xz,max. I don't understand this.

If anyone can give me a help. Many thanks.

Ricardo Dias.

Ricardo Dias
Product Support
Posts: 529
Registered: ‎06-23-2008

# Re: Section Definition stress analysis - stresses symbols

11-28-2012 08:54 AM in reply to: Ricardo.Dias

Ricardo,

your guess concerning |t|max and Si,max stresses was correct: they correspond to maximum shear and normal stresses - shown in the attached screen capture.

Maximum shear stress is resulting in your case from shear forces Fy and Fz (torsion moment Mx is set to zero).

The different position of maximum of |t|, |t|xz and |t|xy is resulting from their variability and positions of extreme values.

|t|max is dominated by |t|xy and maximum value of |t|xy is constant along connection of slender horizontal wall with the rest of the section (z=-36.7 with possible discretization inaccuracy). It would be visible when displaying the map of |t|xy. So any y coordinate along the thickness of the slender wall results in the same maximum value of |t|xy

In this area |t|xz is maximum in the middle of the thin wall, i.e. for y=0 . That is why the maximum total shear stress |t|max is reported for y=0  (and for z=-36.7 as for maximum  |t|xy).

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Regards,

Pawel Pulak
Contributor
Posts: 15
Registered: ‎05-30-2012

# Re: Section Definition stress analysis - stresses symbols

11-28-2012 09:20 AM in reply to: pp2008

Ok. Understand it.

One more doubt: Si,max corresponds to Von Mises comparison stress, or the Von Mises verification has to be made using the Si,max and the |t|max? (as stated in attached file)

Thanks.

Ricardo Dias.

Ricardo Dias
Product Support
Posts: 529
Registered: ‎06-23-2008

# Re: Section Definition stress analysis - stresses symbols

11-29-2012 12:44 AM in reply to: Ricardo.Dias

Si,max corresponds to Von Mises stress so it is also considering shear stresses

In your screen capture Si,max is equal to Sx,max because the applied forces and moments result in flexural state dominating and maximum Von Mises stress is observed on the edge of section where shear stress from shear forces is zero.

If you very significantly increase shear forces Fy or/and Fz you will see that Si,max will be bigger from both Sx,max and |t|max. In such case maximum von Mises stress will be observed probably in the place of maximum shear stress..

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Regards,

Pawel Pulak
Contributor
Posts: 15
Registered: ‎05-30-2012

# Re: Section Definition stress analysis - stresses symbols

11-29-2012 01:47 AM in reply to: pp2008

Yes, I understand that.

In the attached document "A", it is another example. I tried different combinations of stresses, maintaining the Si,max always the same (Von Mises has to be that, no matter what), but I was unable to reach a value equal to one of the calculated by the program.

In the attached document I also have a verification of Von Mises stresses. Shouldn't the program to do that calculation or does it chooses the place (a specific point of the section) to do the verification?

Thank you.

Ricardo Dias
Product Support
Posts: 529
Registered: ‎06-23-2008

# Re: Section Definition stress analysis - stresses symbols

11-29-2012 02:47 AM in reply to: Ricardo.Dias

Ricardo,

von Mises Stress is calculated using normal and shear stresses in the same location in section (the same coordinates).

In your last screen capture  |t|max is reported for Y local = -30.7 mm    Z local = 13.2 mm

while in the formula you have used Sx,min = -190.81 MPa for Y local = 115.2 mm    Z local = -18.4 mm

and |t|max = 179.42 MPa  for Y local = -30.7 mm    Z local = 13.2 mm

|t|max is calculated using Sx for Y local = -30.7 mm    Z local = 13.2 mm

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Regards,

Pawel Pulak
Contributor
Posts: 15
Registered: ‎05-30-2012

# Re: Section Definition stress analysis - stresses symbols

11-29-2012 03:44 AM in reply to: Ricardo.Dias

Yes, of course. I was defocused from that.

Many thanks.

One more thing: it is possible to save the created file in section definition, in order to open later, with the results calculated?

I calculated a section and saved the file, but when I am going to open again the file, the results didn't appear, not even the defined section.

Ricardo Dias
Product Support
Posts: 529
Registered: ‎06-23-2008

# Re: Section Definition stress analysis - stresses symbols

11-29-2012 04:06 AM in reply to: Ricardo.Dias

You can save the defined section without results of stress analysis as a *.SEC file - but repeating calculation for single section does not take a lot of time:

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Regards,

Pawel Pulak
Contributor
Posts: 15
Registered: ‎05-30-2012

# Re: Section Definition stress analysis - stresses symbols

11-29-2012 04:27 AM in reply to: pp2008

Yes, that kind of saving I know.

But is just not the time of repeating the calculation, the forces also have to be introduced again.

Once again thank you for the clarifications.

Kind regards.

Ricardo Dias