Membrane or Membrane+Bending when assessing local failure protection per ASME VIII-2

[YuJie_PV]

hi All,

i have a question regarding local failure criteria in the example of ASME PTB-3, shown as below:
"5.3.2 Example E5.3.2 – Elastic Analysis
In addition to demonstrating protection against plastic collapse, the following elastic analysis criterion
shall be satisfied for each point in the component. The sum of the local primary membrane plus
bending principal stresses shall be used for checking this criterion........."

it mention "The sum of the local primary membrane plus bending principal stresses".
which subtype of principal stress shall i choose in ANSYS to retrieve the data of linearized primary stress?
Membrane or Membrane+Bending, or depending on the location of the path defined?

Thanks in advance.

 

[IdanPV]

Most commercial FEA software includes an option to plot the Triaxial Stress (σ₁ + σ₂ + σ₃), and I am confident that ANSYS offers this capability as well.
Note that if the total principal stress summation meets the allowable limit (4S), linearization is not required.

 

[YuJie_PV]

Thanks IdanPV,
i know that method you mentioned,
my question is how to retrieve linearized primary stress in case that (S1 + S₂ + S₃) is larger than 4*S。
i guess maybe Table 5.6 " exmples of stress classfication" in VIII-2 shall be also used to identify if the stress is primary according to the location of a path.
is my philosophy correct?

Thanks in advance.

 

[IdanPV]

Whenever I encountered a situation where (σ₁ + σ₂ + σ₃) was larger than 4S, I applied the procedure described in 5.3.3.

 

[YuJie_PV]

@IdanPV, what is the reason? worries on the the categorization of stresses which requiring significant knowledge and judgment?

 

[IdanPV]

Yes, mainly 5.2.1.2.

 

[YuJie_PV]

thanks IdanPV
same worries with me, thus i believe selection of "Membrane+Bending" as a default in ANSYS would lead to a conservative result, because secondary stress may be included the stress。
i agree elastic-plastic is better, i just not quite get used to it presently.

Thanks for your reply.