Using Gleeble constructed diagrams of deformation under compression at a high rate 100c-1.We got "toothed" diagram. What processes (mb Multicyclic DRX, Dynamic Recovery) reflect diagram, or it can be the instrument error Gleeble?
Thank you for attention!
To my knowledge, nobody investigated such serrated (jerky) diagrams obtained at so high strain rates, which in turn make the apparent Portevin-Le Chatelier (PLC) effect more probable even at so high deformation temperatures! I would suspect the PLC rather than DRX or related mechanisms because the strain amounts under first peaks on the diagrams are too small for the strain thresholds of DRX; more so with the enormous strain rates kept in mind. It is advisable, btw, to roughly indicate the material type like "medium-carbon martensitic steel", etc.
/////// The more challenging data, the more desirable to exclude possible artifacts, however. In particular, it could be the machine stiffness effect (find pls a Conclusion to paper by Measrovic, 1995, in your mail). More so that there are no strain gages on specimens COMPRESSED in Gleeble; instead, the strain is estimated in terms of grip displacements.
//////How to exclude artifacts (at least partly)? 1) Fix (quench) intermediate states at reasonably modest strains (say 0.1+ and 0.3+) where characteristic softening happen while the specimen is not extremely flattened. Then, IF LUCKY, you will detect traces of (macroscopic!) deformation bands on the external surface (to find information in the microstructure TRANSFORMED in cooling is not a way); such features are commonly accepted as one of the two main reasons of PLC. 2) To exclude the second reason (dynamic interaction of dislocations with alloying atoms) merely repeat the experiments on, say, pure iron (Armco-ferrum) or pure copper. 3) At least, try another material type, skip from martensitic to austenitic steels for example.
This is not toothed deformation. It is a natural phenomenon observed at high speed deformation known as Load Cell Ringing. This occurs when the deformation speed is near its resonance frequency. This is true with all dynamic testing systems.
Kindly note that PLC effect is not possible at such high speed deformation as available time for solute diffusion is very very small.
Dynamic Systems Inc. - the manufacturer of Gleeble Systems have prepared an Application Note APN019 to eliminate load cell ringing during high speed deformation by mathematical treatment. Application Note APN019 is attached for your reference.
Thanks a lot, Dr. Kumar. What you said is in a sense a (dynamic) KIND of machine stiffness effect, as I suspected
Yes, Dr. Zisman. It's like a impact of a ball on a hard surface which creates bounce and rebounce. This happens on the load cell which picks up and reflects in the load data.
We have been using Gleeble for last 15 years now for cariety of studies. Hot deformation simulation is the most sought after study. It is always my pleausre to interact with people working on Gleeble system and solve some of the issues they are facing. We have also created a Gleeble User Forum of India where all Gleeble owners and users meet, interact and discuss their issues.
It is interesting (forum) as our people repeatedly visit India due to our (CRISM "Prometey") collaboration with your metallurgists. We should reflect this issue anyway.
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