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Using vibration to control stress during martempering
6

Using vibration to control stress during martempering

Using vibration to control stress during martempering

(OP)
We know you can use sub to low sonic waves to relive stresses in carbon, alloy steel cased by machining, welding etc.

When martempering, (marquenching), carbon alloy steels, is it possible to use the same vibrational frequencies that reduce stress, to reduce the built in stresses caused by the transformation of austenite to martensite? Could vibration be used to reduce retained austenite during martempering?
Metastable austenite is very plastic. It seems you could take advantage of this state and manipulate crystal formation with sound waves.
Any studies out there? I can not seem to find any myself. Thanks

RE: Using vibration to control stress during martempering

Vibrational stress relief, if it happens at all, is of low intensity, i.e. the degree of stress relief would be low. With marquenching, the whole idea is to relieve thermal stresses caused during cooling to the marquench temperature. But, you are still going to have the austenite to martensite transformation stresses. Since the transformation time is so short, there is not time for any kind of stress relief to help during transformation (which I think is the gist of your question). Anything that is going to be done to alleviate the transformation stresses has to wait until after transformation.

RE: Using vibration to control stress during martempering

I agree with Swall, every metallurgist I've discussed this with says it is either an "old wives tale"/voodoo or if it happens at all it is so minimal as to be useless.

RE: Using vibration to control stress during martempering

(OP)
What is exactly the "wives tale" you refer to?

RE: Using vibration to control stress during martempering

(OP)
If vibrational stress relief is a wives tale, than my company believes it, as I am starting to write a BAC spec for vibrational stress relive with the controlling engineer in the near future. I've done a lot of work with this the last 12 years or so.

I just wanted to know if it could work on metastable austenite to improve grain.

RE: Using vibration to control stress during martempering

Old Wives tale: aka urban legend, Snake oil, false statement, junk pseudo-science. In other words, no metallurgist I have ever discussed this purported phenomeona with believes it actually happens, or if it does happen, it is of such low intensity as to be not worth trying. I have discussed this with metallurgists who have been part of internal company studies trying to substantiate this phenomeona and they have been unable to prove it does anything. The claims of vibrating a weldment or casting to relieve internal stresses have been circulating for years but the only claims I've seen are by people who sell shaker equipment....

RE: Using vibration to control stress during martempering

(OP)
A little off topic but yes, if you judge claims made by manufactures, just hype.
We actually discovered this by accident several years ago when we received a bad batch of castings from a vendor. The flaws would show up at a certain process and would  consistently manifest themselves. We did many controlled experiments, and found out that a certain freq. and process, does indeed relive internal stresses caused by heavy machining etc. MRD was impressed enough to design a similar device, (currently one is 1 of a kind ) to be used for large, single machined components.
They spent the time and the money and decided it works. By the way, we don’t sell shakers.

RE: Using vibration to control stress during martempering

2
Gentlemen,

I wrote a paper, soon to be published by the ASM, on Vibratory Stress Relieving.  My coauthors in this effort were:

   - Dr. C. Mel Adams, PhD, Metallurgy, MIT.  Dr. Adams cofounded the Welding Research Department at MIT, has been the Dean of Engineering at the U. of Wisc. and the U. of Cincinnati, and Chief Staff Metallurgist at Forensic Technologies Int'l.  Amongst his discoveries is the hydrogen embrittlement properties of T1, a problem that is common amongst low-carbon, high-strength steels (such as ASTM 514, B, H, and Q), HY80 and HY100, ASTM 710, and similiar steels.

   -  Dr. John T. Berry, Coleman Chair of Engineering at Mississippi State University.  Dr. Berry has taught at Georgia Tech and the U. of Alabama, and is an expert at FEM simulations of complex material behavior, such as dendrite formation and fluid motion.

The paper was recently presented at ASM Int'l's Trends in Welding Research, held every 3 years, this time in Pine Mountain, GA.

Agreed, far too many salesmen are out there pushing vibratory stress relief upon applications that are inappropriate.  AT THE SAME TIME, the VSR Process can be used to assure the dimensional stability of a wide array of components, especially if they are large, and works extremely well on many stainless steel grades.  This type of experience was undoubtedly what has caused Greenleader to ask the question he has. Indeed, for some applications, the only way to do it effectively is with the VSR Process.

In my opinion it should be approached experimentally.  

RE: Using vibration to control stress during martempering

(OP)
Thank you bklauba. I look forward to your paper. The process we use is an internal, tailor made system. We find it works quite well on complex parts, with very thick, and very thin cross-sections.

You mentioned stainless, I would also like to add aluminum alloy as being very effected by this.

As to my original question, do you know of any studies concerning the application of sound waves on carbon steel to effect grain during thermal processing?

RE: Using vibration to control stress during martempering

3
Is Vibratory Stress Relief a hoax?  Some say yes others say no.  I think that the misnomer is to include “Relief” as part of the title.  I suggest that four publications gives one a proper perspective:

    1. G. Gnirss, Vibration and vibratory stress relief.
           Historical development, theory
           and practical application.  Welding in the World,
           Vol. 26 No. 11/12, pp284-291, 1988.

        2. R. Dawson and D.G. Moffat, Vibratory Stress
           Relief:  A Fundamental Study of Its
           Effectiveness, J. Engr. Matl, and Tech., Vol 102
           pp 169-176 Apr 1980.

        3. T.E. Hebel, Sub-Resonant stress relief: what it
           is; when it’s used.  Heat Treating, pp 29-31,
           Sept. 1989.

        4. Y.P. Yang, G. Jung and R Yancey, Finite Element
           Modeling of Vibration Stress Relief after
           Welding, Proc. 7th Int. Conf. on Trends in
           Welding Research, Pine Mountain, Georgia, May 19,
           2005.

I’ll let the readers read and draw their own conclusions.  

It is my opinion that Ref. 3 has no verifiable engineering basis while Ref. 4 gives us a complete insight as to the true effects of VSR.  Clearly, VSR is a masking of additional stresses over an existing stress state.  Plastic strains are introduced at specific points along the work piece and through the thickness.  The amount of plastic strain is dictated by the load level and duration imposed.  Further, the path of effective stress to effective strain is different for loading and unloading.  This is called the Bauschinger effect.  The instantaneous tangent modulus changes for different cycles along a portion of this path.  Therefore, one has a different structure for each cycle to consider. With these changes in material behavior, the actual natural frequency of the structure changes—slightly lower.  This is demonstrated in BKlauba’s paper.  Although, there is no discussion as to the change in compliance of the supporting blocks.   

If one uses the natural frequencies as a guideline for developing the plastic strains, the pattern of strains will be dictated by each normal mode pattern of the individual component which in turn is being affected by its surrounding structural elements.  You are not assured that you can “treat” a specific point on the structure.  Further, points that do not require “treatment” may develop unwanted plastic strains.

VSR is therefore a cold work process not a relief process.  VSR can not change the basic material properties as can heat treat stress relieving.  VSR does not change the phase, bond or crystalline structure of the material as do heat treat stress relieving.  Luder’s lines, stretcher strains or worms will form in the grain structure during the cold working process.  VSR does allow the dimensional stability of the structure to eventually take place.  VSR does have an effect on the fatigue life of the structure.  The degree is dependent upon the duration and number of cycles the structure experiences during treatment.  In BKlauba’s case, only 24,000 cycles were needed.

RE: Using vibration to control stress during martempering

(OP)
Very interesting. I need to read all the papers before I can comment though. Probably a couple of times.
Vibration is only half of the equation for our purposes at work. We found you could even induce stress by "masking" the part in certain areas.

Thanks for the interest, but would heat and vibration TOGETHER be able to improve crystal structure in carbon steel?

RE: Using vibration to control stress during martempering

We use VSR for dimensional stability.  While I can't say exactly how or why it works - there appear to be enough experts in the room to explain their opinions.  

However, consider we are using this to hold dimensional tolerances that are 0.0015 included (or +/- 0.00075) on a 19.75 inch diameter.  This is a complex welded part that is made from high tensile strength steel (A514).

The parts are used in a service subject to fatigue loading with no problems to date.  We have no basis to say it does or doesn't work - except our parts don't move.  

jackboot

RE: Using vibration to control stress during martempering

Greenleader:   

The source of residual stresses should not be an issue.  I see no reason why, providing the geometry of the part and its condition are appropriate, that an effective vibratory stress relief cannot be performed.  

Geometry (together with setup) will determine what opportunities you have to resonate the part, along with the limitations of your equipment.  Max frequency and unbalance, speed regulation, and instrumentation of your gear are the parameters that limit its applicability.  The physical condition of the material is also a factor, in that ductility is required.  Severely through hardened or tempered materials resist the VSR Process, often to the degree of no benefit.  On the other hand, as cast, welded or forged conditions are highly suitable.

To mtnengr:

I have taken a poll of my metallurgist friends, and they all agree that interpretting the modus operandi of vibratory stress relief as cold working is "wierd".  (Some were less polite.)  Few, if any, of the overall effects of cold-working can be detected on a real-life, large precision workpiece that has been VSR Processed.  Rather, the workpiece appears to have undergone the benefits of long term storage (if it were a casting it would be called "curing".)

At the ASM Conference, one of the first questions asked after the paper was presented was, "Would not a better description of the VSR Process be vibratory stress redistribution?"  My coauthors agreed with this point, as did I.

But here the dichomoty 'tween those operating out of a lab, and those "in the trenches" dealing with large, complex parts bearing exacting dimensional tolerances, starts becoming apparent.  In response to the Q at the ASM, I added, "If I showed up at a machine shop manager's office, and stated that I was there to talk about vibratory stress redistribution, for the purposes of dimensional stability, I think that the manager was scratch his head, give me a confused look for a moment, but then say, 'Oh, you mean stress relieving.  Why didn't you say so?  Sit down, and have some coffee.  Can you help us with this?'

Some describe this problem as one of semantics. I think it is a bit more than that, and the differences in benefits and limitations of both PWHT and the VSR Process should be both kept in mind and continue to be explored.  In the paper we presented two of the many case histories that we have (at the conference, we presented five) where PWHT-ing was either unable or highly inappropriate to solve problems that were resolved with the VSR Process.

Picking up on the semantic arguement approach, some of the guys in the office have conjured up some alternative names for vibratory stress relief, which have been crafted so as to both minimize offending those who are so quick to engage in this arguement, plus add a comic perspective.  My favorite (this week, at least) is:  Kumquats on parade.  

Shifting back to a serious discusion:  In our private email coorespondance, I posed the following situation and question:  If a company employing you as a consultant asked if the VSR Process would be a viable choice to enhance the dimensional stability of a production run of semi-trailer sized stainless steel or lo-C, hi-strength steel (say ASTM 514, Grade Q), what would you say?  Would you answer that the, in your opinion, vibratory stress relief is cold working? . . or that it would be better to label it as vibratory stress redistribution?  (Your answer to me directly was that this is a sales problem, not a technical one.  You stated that you would tell it like it is.)  But you didn't answer the question:  WHAT WOULD YOU SAY to the company as to their selection/choices/options of processes to consider when faced with the challenge of machining such parts to respectable dimensional tolerances?  

YES or NO (within the context described) to vibratory stress relief (or whatever you wish to call it)??

The work of Dawson & Moffat (Doug Moffat sent me a fresh copy of the paper, with his compliments), is sited in the ASM Paper, along with Yang's.  Yang's work bears some resemblence to Bill Hahn's work, which can be seen at:

  ceer.alfred.edu/research/vibatory.html

When the ASM paper is posted on the net, I will add/post the website address as a followup to this corresopondance.  It should be out within 60 days. (The lawyers are still haggeling over security/proprietary/patent issues.)

Bruce Klauba
Airmatic Inc.

RE: Using vibration to control stress during martempering

To B Klauba:

You have a product.  That product was hopefully developed by some engineer.  In that process, the engineer tested the product to determine just what could be said about the functionality, its limitations and purpose of the product.  ABC company buys your product (Kumquats on parade) and uses it for relieving stresses on a cast steel gondola they manufacture.  Due to your product, stresses are introduced that change the state so that the critical transition temperature is above 40F. Your engineer did not investigate this case.  The environmental service temperature drops, the part fails and many people are killed.  If you did not warn ABC company not to use your product for that environment or did not disclose the fact that its properties could be dramatically altered to a near failure position, your legal staff would be active for many years trying to defend your company.  A similar scenario can be envisioned for your semi-trailer customer.

The point is that you are making a claim that VSR is better than sliced bread.  Prove it—under all of the circumstances that you envision.  Define the intent and purpose of the product.  Use accepted engineering terminology to describe the process.  Some of your competitors just say “I don’t know how it works, but it does.”  In my opinion, this is worse than saying nothing at all.

The problem I have with your present discussion is that you are not using nor referring to terms I am familiar with.  For over fifty years, I have heard most of the ubiquitous statements provided to me by my customers during my long term consultancy.    “Trust me” is one of them, but not accepted. It appears that we are at that point in re-evaluating VSR.  

I hope that we can agree that VSR is a method that introduces vibratory stresses in a part and in turn suggests the following items need to be considered:
  
1.    These stresses can only affect the final state of stress (strain) at any given point.  At low amplitudes, the stresses do not alter the bond strength of the grain structure and do not change the basic crystalline structure of the material.
  
2.    Because of the limitations of forces needed to excite the structure, VSR dwells at a natural frequency of the structure.  Therefore, it can only be effective at specific nodal patterns associated with that natural frequency.  Forces can be introduced that are proportional to the damping ratio, 1/2?.  This natural frequency may become nonlinear due to the softening of the material resulting from plasticity.  Otherwise, very large shaker systems would be required to introduce adequate stress levels.

3.    The final (superposed vibratory stresses and the original residual stresses) stress state at these nodal patterns often approach the presumed elliptical failure surface for that material.  Other failure surfaces are possible and its shape is dependent upon the class of material.  The failure surface (that relates the three principle stresses) can be considered to be fixed in space and ever expanding and convex or the entire surface can shift in space.

4.    There is no evidence that VSR alters the creep characteristics of the material.  If VSR does, then a relaxation function needs to be defined as a function of VSR levels.

5.    If VSR is the process as you have described and if you believe that the material does not experience plasticity, you need to describe the mechanism that alters the residual stresses within the body.  Heretofore, the referenced finite element approaches are on the presumed thesis that inelastic behavior is that mechanism.  It should be noted that with the recent demise of Dr. Hahn, his study can not be effectively examined.

You are only discussing the effects of VSR on dimensional stability and not the other possible side effects.  If you have not established the true limits of the process, you had better clearly define what the limitations are.  Otherwise there will be a new class of lawyers on your heels.

With respect to your question (YES or NO, within the context described), it would be NEITHER if I did not have laboratory proof of the limitations under those exact (or near) circumstances or it would be YES or NO if I did have proof.

Prior to 1980, VSR had not been “accepted” as a stress relief process.  Twenty-five years later, there are more suppliers in the field, but I have not seen any advancement on the definition of its limitations.  The fact that you tie down some eccentric mass to a part (no matter how massive) and vibrate that part near or at a resonant frequency really does not demonstrate the effectiveness of the process.  Since dynamic stresses are introduced throughout the part and not just at one locale, the sparseness of the induced stresses needs to be addressed.  If the resulting stresses are below the proportional limit of the material, no change in the material properties or dimensions can take place.  It is though you had done nothing.  The only possible change in the structure’s dimension would be due to creep or a change in load—like transporting and/or material handling.  The magnitude and direction of these new principle residual stresses under these new conditions would have to be known and their effects on the dimensional stability needs to be determined.

There has been a review of studies by H. Mughrabi and H. Christ, “Cyclic Deformation and Fatigue of Selected Ferritic and Austenitic Steels: Specific Areas”, ISIJ Intl, Vol. 37 (1997), No. 12, pp. 1154-1169.   I would hardly classify Dr. Christ as “weird.”  They make the same claim (as I) about the presence of Luders bands ( a result of the cold work process).  They go on further to describe the behavior of steels when they approach their fatigue limit.  And Yes, plastic strains are observed and the grain structure is changed into what is called “dislocation arrangements.”  Thermomechanical fatigue is also touched on.

It has been suggested that using VSR during the welding process, residual stresses are greatly reduced.  (S. Aoki, T. Nishimura and T. Hiroi, “Reduction of Residual Stress of Welded Joint Using Vibrational Load,” SMiRT 16, Wash. D.C., Aug. 2001).  This would suggest that the material properties are being accelerated during the solidification of the weld material over the “normal” VSR process.  The mechanism that reduces these residual stresses has yet to be identified.

It would be interesting to have a blind test as to the effectiveness of VSR.  If one had the resources, prepare six identical specimens for each material class.  Produce three specimens that have residual stresses built in, three that are virgin.  Using transmission electron micrographs or X-ray diffractometer, establish the residual stresses before and after treatment for each specimen.  Pass these specimens to VSR suppliers, but do not tell them which specimen is treated.  Let the results fall where they may.  I tried this challenge, twenty-five years ago and got no takers.  I wonder if now we have any advocates that would take the bait.  NIST, are you interested?
  
How does VSR affect these “dislocation arrangements”?  Does VSR reduce or enhance the fatigue life of the structure? Does VSR reduce the impact strength?  Worried?  I would be.

RE: Using vibration to control stress during martempering

mtnengr:

I would say you know a great deal about metallurgy.

Would you explain the phenomenon whereby highly stressed steel parts will slowly "stress relieve" themselves over a period of time (with no thermal stress relief)?  I recognize that the time span may well be years, decades, or possibly greater.  

How would this mechanism be any different than that of VSR?

Why does thermal energy allow for "slippage" in the crystaline structure but kinetic energy does not?

The second law of thermodyanmics allows for everything to seek a "lower state".

Please explain.  I would think the two mechanisms would be the same.

jackboot


RE: Using vibration to control stress during martempering

To Jackboot:

For thirty years, I was V.P. Engineering of a lab that performed failure analysis on a variety of structures and conditions.  My principal job was to determine or oversee the determination of mechanical stresses these structures would experience.  Why did the part fail?  The metallurgists would provide me with the mechanical properties, the modes of failure and alike.  Maybe some of that information rubbed off.

Your second point is answered by my point (4) above.  If VSR affects the creep properties of the part, provide me with the new creep relaxation function with respect to VSR vibration levels.  But, others have suggested that the level of plastic strain affects the condition of the material.  Can both be right?

The use of temperature on a part can directly change the phase of the material.  Any elementary metallurgy textbook should give you a phase diagram for the presence of Ferrite and Austenite and what the grain structure would look like.  Similarly, non-ferrous alloys have equivalent phase diagrams.  The content of steels has a direct effect on the mechanical properties and hardness at these temperatures.  There is a process called aging or age hardening.  Aging may take place at room temperature or at elevated temperatures.  Just how these changes are made can be best described in a “Bain-S Curve” relating phase change over time at specific temperatures.

Slippage of the grain structure generally has to do with the shear stress properties of the material.  When a cold-worked material is subject to prolonged annealing temperature, the material recrystallizes.  Grain structure improves and many of the mechanical properties also improve.

Kinetic energy can be transformed into work.  The work done has to do with the determination of stress and strain over the volume less any thermal work being done either through internal or external losses.  The work done is conditioned by the physical properties of the material.  So in a round about way, kinetic energy can affect the slippage properties.

Dealing with the 2nd Law of Thermodynamics and material properties is well beyond by expertise and comprehension.  I might suggest M. E. Gurtin, “Modern Continuum Thermodynamics”, Mechanics Today, Vol. 1, 1972, pp 168-213, Edited by S. Nemat-Nasser.

RE: Using vibration to control stress during martempering

(OP)
This has been a very interesting thread.
I'm dying to share what we found, and our solution, but they didn't use any of my money on the R and D, so I hope you all understand I'm not at liberty to say much.
Like I mentioned, vibration is only half the energy that we utilize. Metengr's point #2 is spot on. Our "apparatus" are very large, and can be adjusted both amplitude and frequency, among other adjustments. The shape and the size dictate nodes, or you can cheat by "masking" part of it. Keep in mind we use them strictly for aluminum forgings, and for "dimensional stability"

That being said, I would love to participate in metengr's experiment, I really have an opened mind, but alas I work in a production shop, that rarely has time for good R & D.
We have been doing fairly well recently, and have a new CEO as of today. Mayyyybe he is a good ole' engineer.

Now, how about vibes on metastable steel? Would it help austenite "slip" into martenste?

RE: Using vibration to control stress during martempering

Greenleader

He probably brought some tape with him to stick the vibrating parts back togather when they break.

RE: Using vibration to control stress during martempering

(OP)
Your post is a classic example why letterman doesn't hire engineers to write jokes.
At least metengr addressed specific points.
KMA, Greenleader

RE: Using vibration to control stress during martempering

b]Greenleader[/b],
My post was in relation to your comment on the new CEO and your apparent relation to the aircraft industry were a highly publicized CEO swap occurred.  

I hope you understand that vibrations and aircraft are not normally considered good bed mates. One of the foremost airframe designers of my time, not yours, was once asked how to keep the wings of new design from cracking from vibration and falling off at a specific point.  His answer was we need to perforate it like toilet paper, since it doesn't ever tear where it supposed to.

Now that we are the same level we can let the thread continue.

RE: Using vibration to control stress during martempering

(OP)
You need to understand that you don't understand. I am not in a position to explain our process in any detail that would satisfy. It was discovered as a "byproduct" of a process that has nothing to do with VSR. The machine was custom made for a certain part.One of a kind that produced one of a kind conditions. We had a rather large batch of forgings that the vendor took a shortcut on. After years of producing good parts, suddenly my department was accused of damaging high cost machined forgings. Process A. Process B had similar warping show up after processing in their shop.Process B produces no vibrations. I had an idea for a test and since heat lots and dimensions are carefully recorded as the norm, it was easy to accurately control an experiment. I had everything CMM'd before and after. I had been masking part of the component in question. I unmasked it and processed normally.

Long story short, the vendor was putting unnecessary strain in the forgings and showing up consistently in process A and B. Especially A. Tons of testing later they concluded that, no my process has no negative effect on parts and the unique conditions somehow relived certain strains. There is a low amount of heat involved, but very low.

MR&D did lots of testing, flying to this country and that country etc. They came up with their own conclusions. They gathered enough to write a future spec to relieve stress or strain what ever you wish to call it, using very low intensity/frequency vibrations in conjunction with process B.

In the meantime, I kind of took your comments personally. We do not build faulty products. We really don't care about the debate about VSR. We often times take off the shelf processes and "make them our own" so to speak. It's a tradition we are proud of.

In a few days, I will celebrate 20 years with the company. I am considered a newcomer, in the shop anyway. You can see why I got a little hot. Especially when my original question really had nothing to do with VSR. I admit I was naive about VSR and had no idea of the debate going on outside.
What I really wanted, was to know if ultra sound, low freq. sound, any kind of sound waves could help austenite crystals "slip" into martensite crystals when carbon alloy steel is in metastable austenite during marquench. They use sound waves to refine grain in solidifying aluminum, and wondered if something similar could work for steel. http://www.tms.org/pubs/journals/JOM/9802/Vives/

If you don't mind, I would like to bow out of anymore discussion about VSR, as I am not a metallurgist, and am bound by non disclosure. Hopefully I haven't got my tit in the wringer already.

RE: Using vibration to control stress during martempering

Understand been there and done that.  No problem.

Again no reflection on the information in your post, in fact it was intriguing and something that I was going to look into as I’ve seen a little information on warming a material prior to forming.  As for a low level of heat affecting a part we have a large SS rotating element that if allowed to be heated by the sun and rolled 180° and heated again it achieves a degree of RT stability, measured by TIR, that we had never seen before.  This was a serendipitous discovery as I understand yours is.  Serendipitous discoveries are usually made by a very observant person with a practical and analytic mentality. The old “How Come?”.    

Having worked with a large complex legacy process and the let's do it like grandpa did, don't rock the boat, put it back to OEM conditions attitude,  I hope you achieve your Eureka moment as they are few and far between these days.   

If you get to complete your investigations  and are able to publish anything please let the Forum
know.  As if you have probably noticed there is always a question on the stability of metals in one form or the other.  

We tried VSR several times in it’s infancy and got absolutely no verifiable results on some pretty controlled tests.  The current project that I’m involved with could use such a procedure if there convincing proof it would work.

RE: Using vibration to control stress during martempering

A couple years ago it was found that VSR effects were dramatically increased with applied heat.  This approach was subsequently patented and a company formed.  See http://www.acceledyne.com/ for some limited information.

RE: Using vibration to control stress during martempering

To help clarify some of the issues, I have posted the paper published by the ASM on the web:  http://www.msnusers.com/VSRUsersResearch    then click on Documents, and open the ASM 04-2005.pdf.  

Much of the research cited by mtnengr is also cited in this paper, especially note the work of Dawson & Moffat.  The most distinctive aspect of their work was their success in relieving 90% of the residual stresses in numerous samples of three different alloys.  

What we consider to be an extension/continuation of this work is that of Walker, Waddell and Johnston (also cited in the paper), in which they showed that stress relieving by vibration can be achieved at load levels significantly lower than previously thought.  They offer this as a likely explanation of the failure (at least thus far) to find real-life examples of workpieces that have suffered fatigue damage from vibratory stress relief.  In our efforts to find some (the survey of users of vibratory stress is summarized at the end of the paper), we only were able find users who reported reduced incidents of cracking, which they attribute to using vibratory stress relieving.  One user of the method does so for purely to minimize fatigue damage that otherwise occurs to their products (vibratory screening systems) during use.

We also continue to get feedback from users who have switched to using vibratory stress relief, due to quality improvement, i.e., specifically, tighter achieved dimensional accuracy, on their stream of precision production components.  This is true not only of 300 series stainless steel fabs (which respond marginally to PWHT, due to their robust high-temperature strength), or lo-C, high-strength steels, which manufacturers are reluctant to PWHT, but mild steel fabrications.  Much of this improvement might well be due to the ease of performing a vibration treatment both before and after rough machining.

As nematic's posting shows, vibratory stress relief appears to fall into the catergory of "working in practice, but not in theory".  A number of us are busy crafting new theory, to help explain the practice.

bklauba

RE: Using vibration to control stress during martempering

Gentlemen,
I've been researching VSR for use in MFG.  We currently own a unit that we've been using for 15 years.  We use it during welding and with reasonable results.  We are trying to use it for VSR of machining shaft stresses.  Is there any suggests on how we can be successful with this method?

RE: Using vibration to control stress during martempering

You should start a new thread on this subject, rather than "piggyback" on this one, both for your benefit in getting answers directed at your specific questions, and sharing the discussion with the community.

When you start your thread, perhaps you can supply details, such as materials, sizes and tolerances.

BK

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