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A Very Brief History of Fatigue Research- Part 2 – August Wöhler and the Late 19th Century

This is the second of a three-part series on the history of fatigue analysis.  It has been adapted from the upcoming Ph.D. dissertation of VEXTEC’s Robert McDaniels. You can read Part 1 here.

While early and important work was being done by Wilhelm Albert, Jean-Victor Poncelet, William Rankine, and other researchers in the growing field of fatigue in the 1800’s, by far the most influential person at the beginning of the systematic study of fatigue was August Wöhler.  His influence on early fatigue research is so great that an entire section of Walter Schutz’s paper on the history of fatigue [6] and an entire section of Stepan Timoshenko’s book “History of Strength of Materials” are dedicated to Wöhler’s work [9].  Wöhler was a railroad engineer who worked his way from the machine shop manager to the head of all rolling stock and machine shops of the railroad in Frankfurt, Germany [9, 13].   During his long and influential career he established materials specifications for the metals that were used in railroad applications, fostered the creation of a network of material testing laboratories in Germany, and standardized those labs’ testing and reporting procedures [9].  He also designed and built many different types of fatigue testing machines, and performed many different types of tests [6].  He was the first to understand the importance of both stress amplitude and mean stress on the fatigue life of components [6].  He differentiated between safety factors for components that had finite-design lives and components that were designed for infinite life [6].  Wöhler was also the first researcher to seriously consider the effect of residual stresses on fatigue [9].  He also published the results of his rotating bend fatigue test results in tabular form, and he is generally credited as the originator of the concept of the “endurance limit” [3].  His influence was so great that many years later, this rotating bend fatigue data (and other fatigue data) were presented as curves that his successors called Wöhler curves in his honor [6].

The next significant contributor to our understanding of fatigue was Johann Bauschinger [6].  His main contribution was the discovery and description in 1886 of the effect which bears his name.  The Bauschinger effect is the effect whereby induced strains beyond the elastic limit in one loading direction decreases the elastic limit in the opposite direction [3, 14].  This was an important discovery because it led the way to the theories of L.F. Coffin Jr. and S.S. Manson in the 1950’s, and for understanding both the low cycle fatigue phenomena and damage accumulation theories that are still used today [6].

REFERENCES

  1. Turnbull, H.W. ed., The Correspondence of Isaac Newton: 1661-1675, Volume 1, London, UK: Published for the Royal Society at the University Press. p. 416 (1959).
  2. “Wilhelm Albert”, Wilhelm Albert. Wikipedia. created 06 February 2016, accessed 31 Dec 2016.
  3. Suresh, S. Fatigue of Materials. pp. 1-11 (1998).
  4. Hansson, T.J. “Fatigue Failure Mechanisms and Fatigue Testing” NATO Science and Technology Organization Educational Notes. EN-AVT-207-14 (2012).
  5. Albert, W. A. J. “Über Treibseile am Harz” Archive für Mineralogie Geognosie Bergbau und Hüttenkunde, vol. 10, pp. 215-34 (1838).
  6. Schutz, W. “A History of Fatigue,” Engineering Fracture Mechanics, vol. 54. No. 2, pp. 263-300 (1996).
  7. Bhat, S. and Patibandla, R. “Metal Fatigue and Basic Theoretical Models: A Review,” Alloy Steel -Properties and Use. Dr. Eduardo Valencia Morales, ed. (2011).
  8. Mitchell, M.R. Fatigue, ASM Handbook, Vol. 19, 554-555. Materials Park, Ohio (1996).
  9. Timoshenko, S.P. History of the Strength of Materials. pp. 162-173 (1983).
  10. Bathias, C., and Pineau, A. Fatigue of Materials (2010).
  11. “The Versailles Rail Accident,” Versailles Rail Accident. Wikipedia. Created 22 November 2016, accessed 31 Dec 2016.
  12. ASM HANDBOOK. Vol 19, Fatigue and Fracture.  ASM International. pp.76-86 (1996).
  13. “August Wohler,” August Wohler. Wikipedia. Created 21 October 2016, accessed 02 January 2017.
  14. ASM dictionary, ASM International. p. 454 (1992).
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A Very Brief History of Fatigue Research- Part 1- The Beginning

This is the first of a three-part series on the history of fatigue analysis.  It has been adapted from the upcoming Ph.D. dissertation of VEXTEC’s Robert McDaniels.  You can read Part 2 here.

Isaac Newton wrote to Robert Hooke “If I have seen further, it is because I have stood on the shoulders of giants.”[1]   Since the first research on metal fatigue began in the 18th century, a very large number of researchers from all over the world have contributed to the knowledge base that has been amassed.  Some workers have contributed to the characterization of fatigue failures, the discovery of the mechanisms of fatigue, and the testing of materials. Other researchers have contributed by adding to the theoretical and mathematical models that allow us to make predictions about how components will behave in the future when subjected to periodic loading under different conditions.  Fatigue research is truly a multidisciplinary field that incorporates:

  • Mechanical engineering expertise to understand the stresses and strains to which components are subjected;
  • Materials science expertise to understand how the stresses and strains affect, and are affected by, the microstructure of the components; and
  • Statistical expertise to recognize and mathematically describe the microstructures, loads, and geometries of the components that are all inherently variable, and how these variabilities will affect the fatigue behavior of an individual component, or a fleet of components.

The first person to observe and report what we now know as metal fatigue was a German mining administrator named Wilhelm Albert.[2]  He investigated the failure of mine hoist chains.  He then built a machine which subjected lengths of chain to repeated loads of up to 100,000 cycles.[3]  He authored the first paper on metal fatigue in 1838.[4-6]

The importance of fatigue in transportation was well established by the 1850’s.[6]  The failure of axles of both horse drawn and railroad carriages were investigated by Arthur Morin in France, and William Rankine and J.O. York in Great Britain.[6]  The actual usage of the term “fatigue” has been attributed to most often to Jean-Victor Poncelet [7-9], but also to Morin, Frederick Braithwaite, and his colleague Mr. Field.[3, 6]  Whoever coined the term, the historical record is clear that by the mid-19th century, it was already well-established that fatigue was a significant problem in all modes of transportation, and in many industries as well.

Unfortunately, it is often catastrophic accidents that provide the impulse and direction of fatigue testing and research.  One of the first accidents that spurred the growth and direction of fatigue research was the famous railroad mishap that occurred in 1842, on the railroad from Versailles to Paris, France.[3, 6, 7, 10, 11]  While transporting revelers back to Paris from King Louis Phillipe I’s birthday celebration at Versailles, a locomotive suffered an axle failure, which caused a derailment.  The trailing carriages ran into the engine, and they all caught fire.[11]  The crash killed over 60 people, and was the one of the worst railroad accidents that occurred during the 19th century.[7]  A failure analysis investigation was conducted by Rankine, who found brittle cracking of the shaft.  Railroad mishaps, many caused by fatigue failures, were so commonplace that newspapers in Great Britain were reporting “the most serious railway accidents of the week” even into the late 1880’s.[6, 12]  By the mid 1800’s, several engineers in the British railroad industry had conducted tests of axles and members used in railroad bridges, and had already determined that even a load of half the ultimate strength of iron and steel components was sufficient to cause failure of metal components.  They had also created a predecessor to what engineers now call the endurance limit or “safe life” of components used in the railroad industry.[9]  In addition, they also identified sharp notches and corners as locations where cracks were likely to form, a precursor to the modern concept of stress risers, and had begun to investigate the idea of microstructural changes in the metal, [9] although they were decades too early to be able to explore microstructure the way that we currently can.

References

  1. Turnbull, H.W. ed., The Correspondence of Isaac Newton: 1661-1675, Volume 1, London, UK: Published for the Royal Society at the University Press. p. 416. (1959)
  2. “Wilhelm Albert”, Wilhelm Albert.Wikipedia. created 06 February 2016, accessed 31 Dec 2016.
  3. Suresh, S. Fatigue of Materials. Pp. 1-11. (1998).
  4. Hansson, T.J. “Fatigue Failure Mechanisms and Fatigue Testing” NATO Science and Technology Organization Educational Notes. EN-AVT-207-14. (2012)
  5. Albert, W. A. J. “Über Treibseile am Harz” Archive für Mineralogie Geognosie Bergbau und Hüttenkunde, vol. 10, pp 215-34 (1838)
  6. Schütz, W. “A History of Fatigue,” Engineering Fracture Mechanics, vol. 54. No. 2 pp 263-300 (1996).
  7. S. Bhat and R. Patibandla. “Metal Fatigue and Basic Theoretical Models: A Review”, Alloy Steel -Properties and Use, Dr. Eduardo Valencia Morales (Ed.), (2011).
  8. Mitchell, M.R. Fatigue, ASM Handbook, Vol. 19., 554-555. Materials Park, Ohio. (1996).
  9. Timoshenko, S.P. History of the Strength of Materials. Pp. 162-173. (1983).
  10. Bathias, C., and Pineau, A. Fatigue of Materials.,  (2010)
  11. “The Versailles Rail Accident”, Versailles Rail Accident. Wikipedia. Created 22 November 2016, accessed 31 Dec 2016.
  12. ASM HANDBOOK Vol 19 Fatigue and Fracture.  ASM International. pp.76-86. (1996).
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Air Force Awards VEXTEC® SBIR PH II to Develop Corrosion Prediction Software for the Lifetime Assessment of Airborne Systems

FOR IMMEDIATE RELEASE:

USAF SealOctober 5, 2016 -The United States Air Force (USAF) recognizes that rising procurement cost and shrinking budgets require sustainment of existing aircraft. An improved life cycle management tool that helps inform sustainment decisions and extends remaining useful life of aircraft is essential for decreasing total ownership costs. To facilitate this effort, the USAF has awarded a new Phase II Small Business Innovation Research (SBIR) contract to VEXTEC to develop a software that can be used to predict the effect of corrosion on the lifetime assessment of airborne systems. Read more

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Corrosion as the “Good Guy”

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Permanent Bio-Implantable Plates and Screws (Image courtesy of Praisaeng at FreeDigitalPhotos.net)

While plenty of industries abhor corrosion and its consequences, another sector has welcomed it as a step in the healing process: medical devices. Devices have evolved over the decades to be less-intrusive during (and after) implantation. The bio-inert nature of titanium (along with its weight and strength characteristics) has made it the go-to material for structural orthopedic implants (hip and knee joints, bone plates and screws, etc.). These implants are made to go into the patient’s body and remain there, hopefully performing well for an extended period of time without the need for replacement. But what about implantable devices that have a finite life of medical functionality, and afterwards can become detrimental to the patient’s quality of life?

Such is the case with attaching soft tissues to bone during ACL repairs, as described in a recent issue of Advanced Materials & Processes. Stainless steel or plastic attachments have been the accepted materials in the past because of their strength and biocompatibility behaviors. However, once these devices have done their job they can be hard to remove, or can (in the case of stainless steel) cause metal sensitivity in the patient. Implanted screws made of polymer-based biocomposites have been shown to degrade at a safe rate in living bone and tissue. This allows the repaired ligament to heal, while the tool itself is slowly absorbed by the body using its own metabolic conversion system (the Krebs cycle).

Another example is the performing of a balloon angioplasty to unblock clotted arteries. The device employed in this procedure is a balloon-tipped catheter, which widens the artery. A metallic mesh stent is placed in the area where the work was performed, to keep the artery open as it heals from the procedure. The mesh stent never goes away, which can have an unintended outcome as time progresses. In an ideal world, the stent would remain properly positioned in the artery and cause no further damage. In reality, the stent has the opportunity to create major issues in the body after the artery’s healing time (localized inflammation, or structural breakdown resulting in stent fracture and arterial wall damage). A research group at Michigan Tech is looking to take the bio-corrodible nature of zinc and use it to their advantage in stent design. An alloyed zinc stent would perform the necessary function of propping the blood vessel open as it heals, and then would break down into products that are harmless to the body after its function is complete. The degradation rate for zinc in the body has been shown to be approximately 0.015 millimeters/month for the first three months (the crucial timeframe for stent functionality), with an accelerated rate after that.

VEXTEC’s past success with modeling corrosion-induced damage propagation (previously used for corrosion mitigation purposes) provides an exciting opportunity to repurpose this methodology to model the corrosion state in materials and devices in which degradation is in fact encouraged. Whether seen as detrimental or beneficial, the processes of corrosion and fatigue are interrelated. The key to merging the two phenomena lies in reducing the size of the initial flaw (as described by traditional damage tolerance analysis) to better reflect the size ranges that are observed in corroded surfaces. In the realm of bioabsorbable medical devices, the ongoing degradation due to corrosion can be explicitly accounted-for during the service life of the implanted devices. The randomized load patterns of a given virtual patient (or a population of patients) can provide the external loads necessary to perform simulated damage progression. This analysis could provide insights into the reliability of a temporary implant and its effect on a patient’s wellbeing.

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Corrosion as the “Bad Guy”

Corrosion of a can

Image courtesy of sakhorn38 at FreeDigitalPhotos.net

The topic of corrosion makes recurring appearances in the media; it seems that when you hear about one corrosion-related problem, invariably there will be others reported-on at around the same time. There has recently been a spate of articles confirming that corrosion is currently a headache to the oil and gas sector (undersea bolt failures), as well as to the aviation sector (corrosion-induced fatigue of turbine engine blades in the new Dreamliner aircraft). Oftentimes these stories are first published by financial-leaning news outlets (Wall Street Journal, CNN Money, Bloomberg), a result of the high visibility and cost that these incidents bring in terms of replacement and downtime to their respective industries. Enough of these stories circulating over the span of a few news cycles will make any investor wary, and will prompt questions on what is being done from a regulatory standpoint to restore confidence in companies’ operations. This is particularly true when these reports of corrosion failures have impacts (real, or perceived) on public and environmental safety.

Of course, corrosion is not a new phenomenon. We have been observing the process of corrosion for centuries in our manmade structures, and have developed ways to physically mitigate its effects (painting, inspection methods, et cetera). However, it has only been in recent history that we a) have deeper understanding of the electrochemical processes that describe corrosion, and b) have the industrial engineering prowess to design and build ever greater machines and superstructures that help make modern life possible (economically-available energy sources and air travel, being prime examples). The confluence of these two factors drive the need for more development of mechanistic approaches to corrosion mitigation, through the use of computer-assisted modeling and simulation.

To that end, more and more resources are being appropriated for the research of these corrosion mechanisms in many of the materials that are used today. For example, members of the LIFT Consortium (Lightweight Innovations for Tomorrow) have begun work on the development of new models and a material properties database that will allow for more accurate simulations of corrosion in aluminum alloys used in aerospace and other transportation sectors (focusing on aluminum alloys containing copper, lithium, magnesium, manganese, and zinc). The materials database will be characterized to such a degree so that precise information is obtained about the interaction between microstructure and corrosion. The team will begin with the characterization of the industry’s workhorse alloys, and then extend work to evaluate newer alloys crated using various manufacturing techniques. The goal is to mitigate corrosion in a broad spectrum of aluminum alloys through improved simulator capabilities.

However, only half of the equation is being studied by LIFT: the corrosion impact on metals…with no discussion of how that corrosion introduces damage states, from which stress corrosion cracking and other types of corrosion-fatigue can arise. VEXTEC has pioneered development of a software for the U.S. Navy that predicts the statistical distribution of stress corrosion cracking in an alloyed aluminum microstructure that has been exposed to a corrosive environment. This software serves as a basis for all types of materials that are impacted by corrosion: the material modelers can provide the inputs of the corroded damage states into the VEXTEC software, which will in turn simulate the result of in-service loading on the durability of the critical structures of interest.

Until such time as corrosion has been completely removed as a mechanism in a critically-stressed component (and that time is not approaching anytime soon), it is enough to just model the corrosion characteristics…we must also be able to effectively model the subsequent damage growth throughout the component’s service life.