Hello Naveen. Let me attend this discussion. Regarding ratcheting phenomena and related modeling concepts please consult a series of papers published by N. Ohno.  You find the following definition there: "ratcheting is the accumulation of secondary deformation, proceeding cycle by cycle under stress-controlled conditions". According to this, ratcheting is always "strain ratcheting" as the cyclic force is the input and strain us the output. "Creep ratcheting" is, in my view, a particular case of ratcheting if the temperature is in the range of 0.3-0.7 Tm. Here, you have to consider additional phenomena, like loading rate, aging etc. These high-temperature phenomena have an essential effect on the cyclic strain accumulation.

A more complicated thing is the analysis of structural behavior. Since the deformation may be partly constrained, you should take into account both strain ratcheting and cyclic changes in stress state, for example, cyclic relaxation, if a component is loaded by a cyclic force.

Dear Naveen,

Creep and strain are different. Creep is the time dependent behavior of material under loading but strain is reaction of material under stress. If the material is under loading for long time, so you should consider its creep behavior.

Strain ratecheting occurs under stress controlled loading in the elastic plastic regime this is the reason for which cyclic strain behavior is carried out under stain contolles tests with zero mean stress.

Under low stress amplitudes, the hysterisis loops can stabilize.

Creep ratcheting is time dependent.

Creep ratcheting occurs when a material is subjected to a constant stress. Strain ratchetting is observed when a cyclic stress-controlled loading with a non-zero mean stress is applied.

Hello Naveen. Let me attend this discussion. Regarding ratcheting phenomena and related modeling concepts please consult a series of papers published by N. Ohno.  You find the following definition there: "ratcheting is the accumulation of secondary deformation, proceeding cycle by cycle under stress-controlled conditions". According to this, ratcheting is always "strain ratcheting" as the cyclic force is the input and strain us the output. "Creep ratcheting" is, in my view, a particular case of ratcheting if the temperature is in the range of 0.3-0.7 Tm. Here, you have to consider additional phenomena, like loading rate, aging etc. These high-temperature phenomena have an essential effect on the cyclic strain accumulation.

A more complicated thing is the analysis of structural behavior. Since the deformation may be partly constrained, you should take into account both strain ratcheting and cyclic changes in stress state, for example, cyclic relaxation, if a component is loaded by a cyclic force.

Dear Konstantin thank you very much for the reply….

since I posted this question I also tried to find the answer of this question….here are some of the findings…

You may also find the attached papers useful…

Regards

Hi Naveen,

I had a look on your question. I think a lot of interesting things have already been said on ratcheting in the former posts, especially by Konstantin and by you in your last post. Concerning Chaboche’s model, connecting it to results obtained with ANSYS is not so easy because the basic principles are according to me different. At least, as far as I remember both of them ! Finally, regarding the O’Donnell Porowski diagram, you might be interested in reading an alternative method as presented in chapter 6 of joined document (see also p. 95).

Kind regards

Navin, a very good question indeed...strain ratcheting and creep ratcheting are two words should be used littlebit cautiously..ratcheting is not strain controlled but it is stress controilled..when you do a test with asymmetric fatigue cycles..like a mean stress and a superimposed cyclic stress controlled loading...materials start accumulating strain..and this is called ratcheting strain..this is called dynamic creep too by some researchers...so this is a room temperature phenomena and as Dr. Konstantin said creep ratcheting interaction is a high temperature ratcheting..or you can say high temperature dynamic creep...it can happen

(i) If you do a pure stress controlled sustained peak test...creep fatigue test with zero mean

(ii) Pure stress controlled sustained peak test...creep fatigue test with non-zero mean

In first case during the peak holding i.e compressive or tensile holding..strain accumulation occur and depending you are holding at which position, peak tensile or peak compressive...direction of strain accumulation is dependent on that

Whether in second case, the sign of non zero mean determines the direction, whether there can be compressive accumulation or tensile accumulation...Actually a competition between peak stress hold and mean stress which should be the direction....I also don't know is there any study discussing this or not...but from our experience this is the case..where ther is peak hold dominance and where there is mean stress dominance...  

The discussed problem has bothered me since a few years. I notice a big nomenclature mess in the literature about ratcheting, dynamic creep, cyclic creep and we could find a few more names on the same or maybe not a phenomenon. It is really necessary to be clarified. According to my personal experience, the creep phenomena should be associated with time (loading rate influence, etc.) and the ratcheting with a stress asymmetry. Obviously, the both phenomena could occur simultaneously. I suppose that physical mechanisms are different, but there is very little literature concerning this problem.  

Dear Aleksander,

I also feel the necessity of this type of clarification. ASME (NH) provides definitions of every term used in elevated temperature design, some clarity comes from it. But in papers I have also felt that mess and it confuses a lot.

Also, I have come across very less books  on elevated temperature component design which attack the problem from mechanical design point of view. I like the books like ‘Design for creep’ by Penny & Marriott. I am searching for more books which are written in same mode, if some are in your knowledge please inform me.

Regards

Dear Naveen,

I know you posted this question a long time ago and I apologize for this late reply. If you are still interested in learning more about this topic, I would suggest you this paper by me:

https://www.researchgate.net/publication/235998943_Cracking_and_creep_role_in_displacements_at_constant_load_Concrete_solids_in_compression

where I faced the problem of the difference between creep and strain ratcheting in unusual way. The idea underlying this paper is that damage phenomena could play a role in increasing the acquired displacements at constant loads. Therefore, time-dependence is an effect observed in the displacement field that does not necessarily correspond to a property of the strain field, i.e., the creep.

Elena

Dear Elena,

Thank you very much for replying and sharing your research. I will go through the paper, it seems interesting.

Regards

Naveen