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A Very Brief History of Fatigue Research- Part 4 – 1950’s to Today

This is the final installment of a four-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, Part 2 here, and Part 3 here.

The 1950’s brought another of the seminal events in the history of fatigue.  The world’s first commercial airliner, the DeHavilland Comet, suffered a series of catastrophic crashes in 1953-1954 that resulted in the deaths of all of the crew and passengers [3, 16-18].   After a thorough investigation that included both the analysis of recovered aircraft, and the testing of an entire aircraft that simulated the pressurization and depressurization of the entire aircraft during flight, it was determined that the cause of the mishaps was fatigue cracks that had originated in rivet holes near the square portholes in the fuselage [3].  The cause of the crashes was found to be the stress concentration factor of the corners of the square portholes, along with the procedure used to manufacture the holes [3, 16-18].  The year 1954 saw two researchers, S.S. Manson and L.F. Coffin, simultaneously determine that fatigue damage is always the result of plastic strain [3, 6], which advanced the study of low-cycle fatigue, and led to the fatigue analysis model that bears their names.  The mechanisms of fatigue crack initiation that are now commonly understood were first proposed and identified in the late 1950’s by W.A. Wood [19, 20].

In 1957, George Irwin extended the previous work of Alan Griffith to include ductile materials, such as metals, using linear elastic fracture mechanics [3].  Irwin also introduced the concept of the Stress Intensity Factor [6, 14].  The pioneering work of Griffith and Irwin was fulfilled in 1961, when Paul Paris developed the fatigue crack growth law which bears his name [3, 6].  This revolutionized the field of fatigue research and analysis because it allowed engineers to analyze and assess the growth of cracks with only a knowledge of the far-field stresses and the material geometry [3]. Also in 1961 was the observation by P.J.E. Forsyth that fatigue crack growth can be divided into 2 separate phase, which he called Stage I and Stage II. [21]

The fledgling field of fracture mechanics research was further advanced in 1970, when Wolf Elder introduced the concept of crack closure [6].  In crack closure, the rate of fatigue crack growth is reduced due to the fact that the crack tip is wedged open by surface roughness in the fracture surface in the wake of the crack tip, or another mecanism, such as corrosion, or plastic deformation [3, 6].  A series of aircraft mishaps in the late 1960’s caused the study of fracture mechanics to gain new followers in the USAF [6], when an F-111 aircraft suffered a mishap after only 100 hours of flight due to a crack in the wing structure. The USAF then embarked on an extensive program to improve the durability of its aircraft structures [6].   The outcome of this program was a new set of specifications for all structural metals in the “Damage Tolerance Design Handbook”, and a series of conferences on “Structural Integrity” that have been held regularly since the 1980’s [6].  As a continuation and expansion of that work, the Defense Advanced Projects Development Agency (DARPA), a research organization within the Department of Defense (DoD), created a program called the Structural Integrity Prognosis System (SIPS).  The purpose of SIPS was to develop better ways to predict the fatigue durability of complex aviation structures.  VEXTEC was one of the companies that participated in the SIPS program [22-24].

The next significant contribution to fatigue research came in 1968, when Tatsuo Endo and M. Matsuishi first introduced the concept of rainflow counting [6, 19, 25, 26].  This would lead to another direction of research, which concentrated on variable loading, and the effects of the sequencing of loads, through such concepts as power spectral density, which expand on the work that resulted in Miners’s rule [6].  Another avenue of research that arose in the late 1970’s was the idea of multi-site fatigue damage, which is now called widespread fatigue damage [6].  This work took on new importance in 1988 after the mishap of Aloha Flight 243 [27].  In this incident, a Boeing 737 suffered a casualty in which a large section of the fuselage separated during flight, which resulted in the death of a flight attendant [27].  The investigation revealed that cause of the incident was multiple site fatigue damage in the skin panels near rivet holes at a lap joint [27].

This is not the end of the story of fatigue research.  In fact, this blog series has only illustrated the most historically-significant contributions that have been made in since Wilhelm Albert reported his first observations in 1838 [5, 6].  A brief search in a database of academic papers yields over 34,000 papers written on topics related to fatigue, nearly 17,000 of those being written just since the year 2000.  This illustrates the expanding interest in the many aspects of fatigue research, and the accidents and mishaps described in this short history demonstrates the importance of continuing this research, and how much more work needs to be done in this field.  As demands of fuel efficiency and environmental concerns increase, the need for lighter structures to carry more weight will put tremendous pressure on engineers and operators of all types of vehicles to design and maintain components that operate more economically, while simultaneously being safer.

 

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).
  15. “Sir James Alfred Ewing,” Sir James Alfred Ewing. Wikipedia. Created 05 August 2016, accessed 29 January 2017.
  16. “de Havilland Comet,” de Havilland Comet. Wikipedia. Created 26 January 2017, accessed 28 January 2017.
  17. “BOAC Flight 781,” BOAC Flight 781. Wikipedia. Created 09 January 2017, accessed 28 January 2017.
  18. “South African Airways Flight 201,” South African Airways Flight 201. Wikipedia. Created 05 January 2017, accessed 28 January 2017.
  19. Suresh, S. Fatigue of Materials. pp. 132-162 (1998).
  20. Dieter, G. Mechanical Metallurgy. pp. 394-398 (1986).
  21. Bannantine, J. Fundamentals of Metal Fatigue Analysis. pg. 244 (1990).
  22. Papazian, J., Agnagnostou, E., et al. Structural Integrity Prognosis System (SIPS) Final Report. Northrup Grumman Corporation (2009).
  23. Line, K., McDaniels, R, Pulikollu, R, Tryon R. Crack Nucleation Prediction Through Surface Roughness Measurement Phase I Final Report. VEXTEC Corporation (2008).
  24. Tryon, R., McDaniels, R., Oja, M., Matthews, R.  Crack Nucleation Prediction Through Surface Roughness Measurement Phase II Final Report. VEXTEC Corporation (2011).
  25. Hertzberg, R.W. Deformation and Fracture Mechanics of Engineering Materials. pp. 570-572 (1996).
  26. Bannantine, J. Fundamentals of Metal Fatigue Analysis. pp. 189-196 (1990).
  27. National Transportation Safety Board Summary Report on Aloha Flight 243 (June 14, 1989).
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A Very Brief History of Fatigue Research- Part 3 – The 20th Century through WWII

This is the third of a four-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, Part 2 here, and Part 4 here.

The beginning of the 20th century saw the introduction of metallurgy to the study of fatigue. In 1903, Sir James Alfred Ewing and his colleagues in Scotland were the first to observe and describe slip bands.[3, 6, 15]  Ewing also invented the term “hysteresis.”[3, 6, 15]  While his discovery was initially limited to electromagnetism, it was later extended to many other phenomena, including mechanical fatigue.  The idea of dislocations was first introduced by Michael Polyani in 1934.[6]  Another important discovery in the analysis of fatigue data was made by Olin Basquin in 1910, when he observed that when fatigue data (in terms of stress and number of cycles to failure) is plotted in log space, there is a linear relationship between stress and fatigue life over a large range of stress.[3]  Work and study into fretting fatigue was begun by E.M. Eden and his colleagues in 1911.[3]

The period from the 1920’s through the 1940’s saw rapid growth in the field of fatigue research.[3]  The first book devoted to the study of fatigue, “The Fatigue of Metals” was published by Herbert Gough in 1924 in the U.K. and another book with the same title was published by Herbert Moore and Jesse Kommers in the U.S. in 1927.[3, 6]  The influence of surface roughness on fatigue life was first discussed in Gough’s book.[6]  Also in this period, the effects of corrosion and heat treatment on fatigue behavior were first studied.[3]  The study of fracture mechanics, which describe the physics and mathematics behind the growth of cracks in brittle solids, was begun by Alan Griffith in 1920.[6]

The next major advance in the statistical treatment of fatigue data occurred with the work of Waloddi Weibull in the late 1930’s.[6]  The first damage accumulation model was proposed by Arvid Palmgren in 1924, then extended and improved by M.A. Miner in 1945.[3, 6]  During the period of 1924-1956, one of the most important contributors to fatigue research was August Thum.  He authored or co-authored over 500 papers on nearly every aspect of fatigue, including:  stress-concentration factors, the effects various factors on the fatigue limit of metals, the effect of heat treatments on fatigue, corrosion fatigue, fretting fatigue, fatigue at cryogenic temperatures, welded joints, and many other diverse aspects of fatigue.[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. 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).
  13. “August Wöhler”, August Wöhler. Wikipedia. Created 21 October 2016, accessed 02 January 2017.
  14. ASM dictionary, ASM International. pg,. 454. (1992)
  15. “Sir James Alfred Ewing”, Sir James Alfred Ewing. Wikipedia. Created 05 August 2016, accessed 29 January 2017.
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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 four-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, and Part 3 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 four-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.