Air Force Awards VEXTEC® SBIR PH II to Develop Corrosion Prediction Software for the Lifetime Assessment of Airborne Systems


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.

Quantification of corrosion damage is important to the management of the structural integrity of an airframe, and current corrosion damage modeling methods are expensive and provide only rough estimates of damage. Cracking due to corrosion is a complex problem that needs to integrate multiple physics-of-failure modes for accurate simulation of the damage state and better prediction of failure risk. VEXTEC’s Virtual Life Management® (VLM®) proprietary software is a multi-disciplinary, multi-scale systems engineering software in which failure models are developed for all of the important components in a system, such as an airframe. The result of this Phase II program will be an integrated computational software that combines state-of-the-art corrosion and structural integrity models, and demonstrates prediction of a corrosion-assisted failure on an aircraft component.

“VEXTEC is in an extraordinary position to develop a probabilistic corrosion assisted cracking tool capable of determining the locations and intervals for inspection of current aircraft along with improving the structural designs for future aircraft,” stated Dr. Animesh Dey, VEXTEC Chief Product Development Officer (CPDO). “VLM services and software have helped clients accelerate product development, reduce physical testing costs, improve product designs and material specification during development, and helped clients resolve field performance issues.”

It is envisioned that the software will be used to optimize inspection and maintenance of aging aircraft. It will also aid in the design of corrosion-tolerant structures. The capability will enhance the overall scope of VLM to become a general purpose, multi-disciplinary virtual design, analysis and inspection tool. VEXTEC will work closely with the USAF, in particular the Aircraft Structural Integrity Program (ASIP) managers in this Phase II. The collaboration will help to commercialize the technology being developed in Phase II via integration with ASIP sustainment practices.


VEXTEC’s Virtual Life Management (VLM) is a unique integration of engineering analysis, computational materials science and condition monitoring protected by seven patents. The VLM process helps companies predict and enhance the reliability and performance of critical components during design, testing, manufacturing and service. Since 2000, VEXTEC’s Virtual Twin® has provided predictive analytics prognostics and life extension for hundreds of different products. To learn more, visit

The Comet’s Resonance

aircraft window design has improved fatigue resistance

A Modern Aircraft Window (Image courtesy of podpad at

A couple of months ago, there was an anniversary that might not be very well-known: July 27, 1949. It is a date as momentous for air travel as it is for the advancement of the field of fatigue and fracture mechanics. On this date, the de Havilland Comet, the world’s first jet airliner designed and built for commercial passengers, underwent its first test flight in Hertfordshire, England. The prototype performed admirably, and paved the way for the Comet’s entry into service by the British Overseas Airways Corporation in 1952. The designs of the Comet 1 and 1A aircraft were revolutionary, with two de Havilland Ghost turbojet engines built into each wing, a pressurized cabin for the comfort of 44 passengers, and large square windows yielding a generous visual perspective that was rarely seen by civilians before that time. Unfortunately, it was the convergence of the last two features (pressurization and square-shaped windows) that led to a series of fatal crashes in the first two years of the Comet’s service. The entire fleet was grounded in 1954 while investigations took place, the results of which concluded that repeated pressurization/re-pressurization caused cracks to initiate and grow at the corners of the planes’ square windows. During each pressurization cycle, the fuselage’s metal was being further “fatigued” with cracks originating from locations of high “stress concentration” at these window corners. The terms “fatigue” and “stress concentration” were relatively new at the time, as materials science (as we now know it) was still a new field of study. The Comet was redesigned in subsequent years, with oval windows and other safety improvements, but by then (the late 1950s) the market had been overtaken by Boeing’s larger and longer-range 707 model. Boeing went on to dominate the commercial airliner industry for decades to come.

The Comet’s legacy is not completely negative however; these early failures helped develop the backbone of fatigue and fracture mechanics that would be used, refined and evolved over the next 70 years. Indeed, it was only 20 years after that first test flight of the Comet that NASA’s engineering team supported a successful moon landing! Industries beyond aviation and space exploration have benefited from this science as well: heavy machinery, transportation, naval, energy, medical devices…all have been fundamentally changed by the furtherance of materials science principles.

VEXTEC continues this evolutionary effort, by incorporating these “physics of failure” principles into our probabilistic Virtual Life Management® technology. We differentiate ourselves from other computational fatigue methods, by combining a component’s inherent microstructural variability with physics-based damage mechanisms and realistic loading histories to accurately predict fatigue life. As structures become increasingly more complex, with continual demands for lighter-weight materials (for both manufacturing and operational cost savings) and better performance, the need for a comprehensive reliability simulation technology becomes clear. No one wants to be the next disastrous chapter in this Comet’s Tale.

Corrosion as the “Good Guy”


Permanent Bio-Implantable Plates and Screws (Image courtesy of Praisaeng at

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.

Corrosion as the “Bad Guy”

Corrosion of a can

Image courtesy of sakhorn38 at

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.


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