Dear All,

As per defination of local Primary membrane stress in ASME SECTION VIII - DIV-II

Average stress across any solid section. Considers DISCONTUNITY but not CONCENTRATIONS produced only by mechanical loads.

I thought because of discontinuties, stress concentrations will occur.

But After reading the defination. I am confused.

Please explain: What is the difference between discontunity and concentrations??

Durga,

I will try to explain this as far as what I understood from the code.

As the ASME Code, the stress indices provided in Code measures the PEAK Stress components induced by the internal pressure action at the inside and at the outside "Shell - Nozzle" junction wall. Consequently, when we multiply the general primary membrane stress components by the ASME stress indices, we obtain the peak stresses developed under the internal pressure loading, in the near vicinity of the "Shell - Nozzle" junction.
The peak stresses quantify the following effects, developed under the internal pressure loading:

a) The nozzle orifice discontinuity effect;
b) The general stress concentration effect (Gross structural discontinuity effect)
c) The local stress concentration effect (Local structural discontinuity effect)

Briefly, the peak stress components quantify the result of the general and of the local stress concentration effects, developed under the internal pressure loading.

While when it comes to primary/secondary stresses individually effect cannot be checked for stress concentration.

I could be wrong but this is my understanding. If anyone can comment on this then always welcome.

Regards,
R.K.

RK,

what I know:: Peak stress: Its an incremental addition to primary or secondary stress by concentrations.

Peak stress is only due to internal pressure or due to mechanical loading( pressure or weight which ever is govern) ???

Again why in your explination discontinuity came, so in peak stress discontinuty is considered?

what I understand is:

Discontunity: at junctions between two dismillar materials or thickness change, trunnions, nozzles, any reformentpad.

concentrations: notches, sharp corners.

bend: comes under concentration (I doubt)

now in peak stress what it considers concentration or both concentration and discontinuty.

please correct me if I am wrong.

Hi Again,

Discontinuities are of basic two types,

Local Structural Discontinuity; which is a source of stress/strain intensification and will affect the small volume of material and have no significant effect on stress-strain pattern.

While the Gross Structural Discontinuity a source of stress or strain intensification which affects a moderately large portion of a structure and has a momentous effect on the overall stress or strain prototype or on the structure as a whole.

A general primary membrane stress is one which is so distributed in the structure that no redistribution of load occurs as a result of yielding so for this the discontinuities and concentration are excluded.

Local Primary Membrane Stress, arise in which a membrane stress produced by pressure or other mechanical loading and associated with a discontinuity would, if not limited, produce excessive distortion in the transfer of load to other portions of the structure. That was the reason discontinuity (purely because of mechanical loads) is included but not the stress concentration, as this is not only a primary function of mechanical loading, but also affected by the secondary stresses.

The peak stresses is those part of total stress that are produced by thermal gradients and discontinuities. But when we perform the detail analysis it gives a combination of primary and secondary stresses directly and not only the peak stress.

Again you can comment if you have other opinion.

Regards,
R.K.

RK,

Thanks for your Explination.

Primary - secondary - peak ==> another topic.

But my doubt remains same. difference between discontinuity and concentration.

I am unable to understand the exact difference.

Please give me any examples reg discontinuity and concentrations.

Hi Durga,

The relation is both are dependant, but if you check you’re above post where you were referring for ASME Section table, I was trying to explain that to you.

It was only at those places where the discontinuity will have an impact with the stress concentration factor, not at all the loading condition. Also it does matter where is your discontinuity is located. I will suggest you to try and run one simple FEA model and apply the stresses at different axis e.g. parallel to the major axis of cylinder, or perpendicular to major axis of cylinder and locate the discontinuity at different location.

Because in Caesar-II you will not get the visual effect as it's a simple beam equation we are using.

If still having doubt kindly send your mail ID.

Regards,
R.K.

Regards,
R.K.

RK,

my mail Id: durgamanikonda@lntchiyoda.com

Ok Durga,

I will try to put up something for you and send you the details.

Regards,
R.K.

Thank you.