Corrosion as the “Good Guy”

ID-100162304

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.

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.

 

VEXTEC Presenting at Trelleborg’s 2016 Global FEA Meeting

August, 2016 – Dr. Sanjeev Kulkarni (VP, Sales & Business Development) and Dr. Robert Tryon (CTO) from VEXTEC Corporation will be presenting at the 2016 Global Finite Element Analysis (FEA) meeting for Trelleborg Sealing Solutions (TSS) to be held in Boston, MA on September 15. The presentation will discuss the “Implementation of ‘Integrated Computational Materials Engineering’ or ‘ICME’ towards Managing the Fatigue Life of Components and Assemblies”.

ICME combines computational modeling and materials engineering, and considers materials at multiple length scales, processes that produce these materials and the properties to predict and optimize the performance of components. VEXTEC characterizes materials at the microstructural level and uses its Virtual Life Management®  (VLM®) technology to understand material damage, flaw initiation and crack propagation towards estimating fatigue life in components and assemblies subject thermal / mechanical cyclic loads. The talk will discuss VLM in the context of industry recognized structural design philosophies: Safe Life and Damage Tolerance.

VEXTEC Presenting Uncertainty Management at the 2015 ASME Verification & Validation Symposium

ASME V&V Symposium 2015 Program

ASME V&V Symposium 2015 Program

Brentwood, TN May 7, 2015 – Dr. Sanjeev Kulkarni, Vice President of Sales & Business Development of VEXTEC Corporation, will be presenting at the fourth annual ASME Verification & Validation Symposium in Las Vegas, NV on May 15, 2015.  The symposium, which runs from May 13 – 15, 2015, is entirely dedicated to verification, validation and uncertainty quantification (VVUQ) of computer simulations bringing together the foremost experts to exchange ideas and methods around for verification of codes and solutions, simulation validation and management of uncertainties in mathematical models, computational solutions and experimental data. Dr. Kulkarni is also chairing two sessions in the symposium, Validation Methods for Solid Mechanics and Structures (May 13) and Validation Methods for Impact, Blast, and Material Response (May15).

 

Dr. Kulkarni will be presenting, “VVUQ of Computational Modeling and Simulation Software To Predict The Durability Of Medical Devices”  which will discuss VEXTEC’s system reliability method and software, called Virtual Life Management® (VLM®). The VLM software considers the uncertainty of model parameters and acquired data to serve as a framework to incorporate realism with multi-scale statistical characterization using probabilistic and parallel computational simulation techniques.  The model itself, called a Virtual Twin®, characterizes parametric design sensitivity and uncertainty; both factors included in the proposed ASME V&V 40 Standard for Medical Devices. The talk will make that connection between VLM and ASME V&V 40.

 

The Virtual Twin, successfully implemented across multiple industries, starts with the initial preliminary design where it supports verification and validation activities and then is refined as the device moves through the detailed design, manufacturing, testing, launch and post market segments of the product life cycle. At any phase of the life cycle, the model considering uncertainty of any or all of the inputs to prognosticate the probability of device success in the future phases of the life cycle.

 

Founded in 2000, VEXTEC Corporation has developed patented technology on virtual material modeling and predicting product durability. As a senior strategic member of VEXTEC’s Leadership Team, Dr. Kulkarni leads commercial Sales & Business Development with a focus on Healthcare/Life Sciences/Medical Devices and Strategic Alliances. Dr. Kulkarni is an industry recognized leader and expert in Computational Mechanics and Computer Aided Engineering, and has supported many industries (Automotive, Aerospace, Defense, Energy, Consumer Products and Medical Devices) and in a variety of roles that include 5 years with Boston Scientific (as R&D Fellow), 10 years with KB Engineering (as President) and 6 years with TRW Automotive (as Principal Engineer).

DESIGN FOR RELIABILITY – THE GOLDEN AGE OF SIMULATION DRIVEN PRODUCT DESIGN

Posted by: EETimes.com

Author: Arvind Shanmugavel

The design and implementation process for integrated circuits (ICs) has been honed and perfected for decades by the design and the electronic design automation (EDA) community. However, the reliability verification process has been slow to catch up, especially due to the complex nature of failure mechanisms. Read more