In reality CoF is a function of many parameters such as load, speed, materials, lubrication, etc. However, in particular process conditions these conditions are constant and therefore CoF may be assumed to be constant too.

Many thanks for your response Sergei!

Ebrahimi et al [1] developed a work by Prof. Avitzur and concluded that CoF for perfectly plastic materials is purely a geometric parameter; given the barrelled geometry configuration, CoF can be found easily based on their formulation.

I need to know if a similar work exists for comparison or an existing theory which can explain WHY using CoF as a constant or variable during the barrelling compression test.

Regards

Shahin

[1] Ebrahimi, R., and A. Najafizadeh. "A new method for evaluation of friction in bulk metal forming." Journal of Materials Processing Technology 152.2 (2004): 136-143.

Actually no one knows exactly the value of the CF, and whether it is constant at all contact Die/material points or at different moments along the simulation. CF is actually frequently used as an "adjustment parameter" that will make the FE element apprach lead to reasonable results.

In relation to compression, there are some geometrical configurations where increasing the CF the load actually drops.... See the old 1949 paper by Polakowski,

please refer to the following link:

https://www.jim.or.jp/journal/e/pdf3/51/07/1210.pdf

there the friction is  determined  as  a function of strain.

b.r. Hartwin Weber

You can avoid barreling by  neally  ideal friction  by machining an outer ring a the ends  of the cylinder and fill it with MOS or graphite (depending on temperature) Then you have  a cushion on both  sides which is capable  to care for nearly zero friction. If you compare that with your barreling trial then you can get some answer for your problem.

b.r.  wb

 I am aware of the work of Yunping et al as suggested by Hartwin. The points made by Prof. Cetlin are also interesting. Thank you both.

Yunping's work is essentially similar to that of Ebrahimi-Avitzur and no significant theoretical development has been made by the former.

Two issues with Ebrahimi-Avitzur work:

I have developed a similar theory that complies reasonably well with the FE and accounts for the effect. However, I am hoping that there are other similar THEORETICAL works which can be used as a reference and would like to hear what others have to say on this.

Looking forward to seeing more contributions

Shahin

[2] Solhjoo, Soheil. "A note on “Barrel Compression Test”: A method for evaluation of friction." Computational Materials Science 49.2 (2010): 435-438.

Really do hope a nice approach is developed. This is a really complex area. Concerning strain distributions in the product, we often find that FC does not have a lot influence. Perhaps it affects only a very superficial material layer?

People also use the ring test for finding an experimental FC, but it's not certain that such FC is valid for a real forging situation, for example.

Friction between sample and platen may cause subsurface curving instead of barreling. In general this friction results in triaxial stress-strain state in the subsurface of the sample. Therefore ductile fcc materials like copper or nickel develop a lip or a fold under compression instead of barreling. In this case uniaxial stress state is developed only in the central part of the sample. We observed this on the copper single crystals both under compression and in sliding.

As correctly noted by prof. Cetlin, this topic is a quite undeveloped area due to its extreme complexity. Observations by Sergei are interesting but my aim is to deal with friction in a very general sense such that the results can be used for Materials characterisation in general.

Many indirect measurement methods in materials engineering rely on flow curves of materials and their slopes. There is an amazing body of research conducted in many years which have been relying on such flow curves and their slopes. It is such a shame that they have constructed such a large empire on a very simplistic model of hot compression test. Friction, as far as flow curve identification and indirect measurement of phenomenon such as SRX, DRX MDRX etc are concerned is quite important and the curves are quite sensitive to friction. It has been known that the flow curves obtained by the hot torsion test and compression are quite different in shape, magnitude and slopes. Friction is highly responsible for the discrepancy of the curves.

My derivations on CoF are quite promising however I am hoping similar works, hopefully more concise, are available somewhere which can be used in general sense. Ebrahimi-Avitzur model is purely geometrical, bringing a few general material parameters in the model makes it a lengthy formulation but still manageable in a non-FE fashion using spread sheets, subroutines etc.

Flow curve characterization has a long way to develop. To produce the research outputs based on accurate flow curves, we have to develop the theoretical front. The friction part for this has proved to be very challenging.

Thanks for all contributions and looking forward to hear more comments

Shahin

Friction is a function of operating parameters I have compiled number of friction models suitable for extrusion process one model is highly suitable for thermal plz refer my paper

'Efficient friction models in extrusion-a review'

Thanks Pankaj

These models need experimental verification. This is why I am currently developing more detailed closed form solutions of the barrelling compression test to enable a platform for experimental observations on friction and deformation under combined shear and compression.