In this interview AZoM talks to Dr. Vern Wedeven about the Revolutionary Tribology course which is being conducted by the MIT Professional Education.
Can you explain why friction and wearing are so important to address in mechanical and electromechanical systems?
All mechanical systems have motions and stresses associated with their motions. Robotics, drive systems, and propulsion systems transmit forces across contacting bodies, including bearings and gears. The friction at these intimate interfaces generates heat and requires extra power for motion. That is what we call frictional losses. Friction and wear are important to address because they can help make mechanical and electromechanical systems more efficient, effective and durable – which in turn saves resources, money and time.
What impact do friction and wearing have on industry?
Friction reduces useful work, and wear diminishes precision positioning and useful life. The net effect is the consumption of precious resources and disruption of economic productivity and safety. The economic impact is vast. By one estimate, proper tribological procedures save 1.3% to 1.6% of a nation’s gross, resulting in hundreds of billions of dollars of savings.
Indeed, friction and wear pose incredible challenges to 21st Century mechanical and electromechanical systems, particularly in the fields of nanotechnology, aerospace, and biotechnology, and the financial benefits of tribology advances should not be overlooked.
How has your approach changed over the past two decades?
Despite tribology’s obvious importance, to date, most engineers have not had effective ways of including it in their design processes. The reason so many engineers lack suitable methods of including tribology in design is partly due to its complexity.
In some applications, bearings and gears have contact points that must carry enormous loads at low and high speeds, and the stresses are unbelievably high. Motions are also extreme, and contact areas are small — the size of a pinhead, in some cases. Heat is also generated, which brings chemistry into the equation, in addition to hydrodynamics.
All of this happens on a micro-scale, which controls performance on a macro-scale. Factor in new and sometimes unfamiliar tribology interface materials and manufacturing requirements, and things get even more complicated.
Over the past 20 years, tribology experts have worked to better understand pieces of the fundamental tribology puzzle. Our revolution has been a decades-long journey to assemble those fundamental pieces into a comprehensive framework. We have developed engineering parameters that now enable tribology to be put into the design realm so that they can design for life and durability under extraordinary circumstances.
What is tribology?
Tribology is the science of friction, lubrication, and wear associated with contacting surfaces in relative motion. We experience tribology in action every day. For example, when we lace up our running shoes and hit the road or trail. The soles of our shoes are in relative motion to the street or trail. The friction between our shoe soles and the running surface provides traction that allows us to move forward. This same friction wears down our shoe soles, eventually needing to be replaced.
Lubrication between the shoe sole and running surface reduces wear and interferes with our forward movement. You might slip on a wet sidewalk, for example. These are situations where we trade shoe sole wear for the advantages of friction. In mechanical systems, friction results in wear and heat generation, both of which limit the efficiency and useful life of system components.
Image Credit: Shutterstock // Andrey V
What is Tribology-by-Design (T/D), and how has it helped engineers?
T/D combines a theory, a set of test and analysis tools, and a methodology. It was developed to get powerful tribology mechanisms into engineering design to let engineers design and develop component contact interfaces that can carry loads and transmit power under extreme conditions.
In the future, T/D will be taught to engineers around the globe as part of the Massachusetts Institute of Technology’s Professional Education course, “Tribology: Friction, Wear and Lubrication.” I will be an instructor for a session that explores how T/D connects and compliments axiomatic design (AxD), a newly adopted design methodology developed by the course’s lead instructor, Dr. Nam Pyo Suh, Cross Professor Emeritus at MIT.
AxD uses matrix methods to systematically analyze the transformation of customer needs into functional requirements, design parameters, and process variables. It is used to design the best possible solution for planned features and functions.
T/D methodology is complimentary. It differs in that it targets the operating conditions or duty cycle of a critical component within its operating system with specially designed test and analysis tools. T/D predicts and solves tribology problems to save time on testing and redesign.
The theory characterizes critical tribology interfaces in terms of motion, stress, and temperature and how these parameters activate the tribology interface materials and mechanisms during operation (MST-Tm). The T/D process extracts and delivers the targeted MST-Tm to a virtual TRL 4 (Technology Readiness Level 4), where innovative tribology R&D can be conducted using T/D test and analysis tools.
The three T/D tools represent component analysis, single contact models (SCM), and single contact simulation testing. These tools provide, respectively, a component digital twin, a digital interface twin, and an interface simulation twin.
Why is it important to integrate tribology into design?
The development of major (and minor) mechanical systems, some of which I have been involved with in the aerospace community, have experienced significant setbacks due to a lack of tribology design guidelines during the development process.
When engineers solve tribology problems in mechanical systems, the result is typically increased system efficiency. It also improves the useful life of the component or system by reducing wear and heat, all of which improve service life and save money. Moreover, if we can solve tribology problems faster, we can promote faster innovations and greatly reduce the costs and risks of mistakes and unforeseen events.
What tribology problems can arise in engineering? Can they turn dangerous or even deadly? Are there any famous examples of this? How have these incidents shaped your approach to this area?
Some projects do not go as well as hoped. There are delays, mistakes, and missteps because of the complex tribology challenges that come into play.
Take, for instance, the Apollo 17 mission. NASA officials agreed that lunar dust was one of the greatest hurdles to nominal operation on the moon because of the mechanical problems it causes. In a previous mission, lunar grit clogged radiators and even wore a hole in the knee of an astronaut’s spacesuit.
NASA is now planning an experiment for next year, the Regolith Adherence Characterization mission. Its goal is to determine how and why dust sticks to materials during lunar landings and other operations. The findings will help determine how to design equipment that repels dust and make spacesuits that do not break under the wear and tear of contact with the moon’s sandpaper-like grit.
This is an excellent example of the problems that can arise in the world of tribology and how it can take a long time to solve those problems.
Tribological failure can also be dangerous or even deadly, as demonstrated when a wind-turbine gearbox caught fire in Scotland in 2011 or when Alaska Airlines flight 261 crashed in 2000 due to excessive wear on a jackscrew in the flight control system.
New designs for high-powered systems are at risk with insufficient design knowledge for interface speed, stress, and temperature limits. Although no disasters happened, the Space Shuttle Main Engine (SSME) turbopump bearings had to be replaced after every launch, due to excessive wear, during the first 15 years of its 30-year operation. The astronauts were keenly aware of the problem. It took more than a decade to solve this risky and expensive problem, which involved harmonizing tribology materials with complex design and manufacturing.
Safety and the high cost/time required to successfully launch new bearing/gear materials and lubricants into aerospace applications has been a great motivating factor for T/D.
What are the benefits of being able to solve tribology problems faster?
Time, cost, and scope of innovation.
Tribology is enormous, and it is everywhere. Increasing demands for more performance and energy savings continue to drive innovation in mechanical systems. Introducing new materials, designs, and test methods will play an important role in future progress.
But relevant tribology design parameters are urgently needed to support new bearing and gear materials, lubricants, and designs for transportation, energy, and industrial components. Using T/D theory, test, and analysis tools and methods to discover and apply new technologies will open the door to a much more rapid response to tribology challenges, faster innovation, reduced costs, and mitigating risk.
Engineers can benefit greatly from implementing T/D. It will let them keep pace by providing a systematic way to cover all the bases.
How does Tribology-by-Design lead to the best possible systems?
T/D operates within the Technology Readiness Level (TRL) system, which is now commonplace for major mechanical system design and development, particularly in aerospace.
The test and analysis tools enable designs on a pseudo-virtual basis that covers lots of options and “leaves no attribute behind.” Within the TRL system of design, T/D targets the application (TRL 8) and identifies the motion, stress and temperature (MST) of the targeted application and its duty cycle.
We have developed physics-based engineering parameters for MST that allow the interface of the targeted application to be explored and designed on a virtual level (TRL 4). The unique and key tools are: (1) testing with a patented Wedeven Associates Machine (WAM), and (2) the development of a single contact model (SCM). The SCM becomes the centerpiece for design, development, manufacturing, and application monitoring.
How does Tribology-by-Design differ from other approaches to these problems?
Design and life theories for bearings and gears are based on stress and contact-fatigue stress-cycle criteria and a “material life factor.” In contrast, the T/D theory is based on motion-driven mechanisms for lubrication and performance, which is more consistent with physical reality.
“Tribology” by definition is the science and technology associated with contacting bodies in relative motion. It is all about motion. Consider a violin. A bow resting on a string does nothing but add motion to the bow, and you get a frictional mechanism or a motion-driven mechanism to make harmony. We need motion to activate the interface materials and T/D to engineer the interface ingredients to achieve functional harmony.
Image Credit: Shutterstock// cass1976
What elements of Tribology-by-Design have been successful with engineers?
Understanding the fundamentals and the engineering parameters that control performance. Through T/D, the mechanical designers, metallurgists, and chemists suddenly realize their role and their value to the enterprise. T/D is the glue that holds the team together. To make T/D work requires the engagement of the entire technology supply chain.
What improvements have engineers suggested, and how are you considering implementing these?
Now that we have launched T/D, we are getting excellent feedback. Those who have worked with us on recent projects have become totally engaged and actively innovative. At the moment, there is enthusiastic “engagement” as well as good “suggestions.” The suggestions are mostly an expression of their technical needs and objectives.
About L.D. Wedeven, PhD
Dr. Vern Wedeven is the founder and President of Wedeven Associates, Inc. He is the author of over 90 technical publications and co-instructor of the MIT Professional Education course, “Tribology: Friction, Wear and Lubrication.”
This information has been sourced, reviewed and adapted from materials provided by MIT Professional Education.
For more information on this source, please visit MIT Professional Education.
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