Everyone, of course, has heard the Biblical story of the Flood of Noah. Well, we weren't around for that, but it almost felt like it on one of our projects many years ago. Actually, we're using the editorial "we" here because this particular project was over 40 years ago, and although we remain close to some of our former employees who were here at the time, none of the current "we" were present. But since it's our 70th birthday (really you ask? yes indeed--see Last Story), we thought we'd share a story from way back when we were just kids.

Back in the early 60's, MEI-C was one of the few companies in the United States working with strain gages to measure the stress in large fabricated components. At the time, the U.S. was deep in the throes of the Cold War, and only five years after Sputnik, we were also engaged in a Space Race. MEI-C was retained to assist a fabricator in measuring the stresses in an experimental, solid-fuel rocket motor case being built for the U.S. Air Force.

The motor case consisted of two hollow, high-strength steel cylinders joined end-to-end. The cylinders were 200 inches in diameter, and joined together, measured some 40 feet tall. So it was quite an imposing sight, especially after we got through installing nearly 200 strain gages and attaching several thousand feet of lead wire.

The test protocol was pretty straight forward. Fill the motor case with water, then pressurize it and measure the resulting strains, from which the stresses could be calculated. Recognizing there was some uncertainty in the design (why else would they be testing it, right?), the government had specified that the motor case be enclosed in a giant, double-wall wooden structure to isolate it from the test operators (that would be us) during the test--just in case something went wrong (who knew... keep reading).

Oh, and because the water supply system couldn't supply the desired pressure, the client was using oil to pressurize the water-filled cylinder, creating, of course, a nice and messy emulsion of water and oil.

So there we were, with our many weeks of labor and our shiny new recording equipment (which, by the way, was brand new for the job), dutifully measuring the stresses while the client slowly increased the pressure. Everything was going according to plan at first, but gradually we noticed that several strain gages seemed to be reading quite a bit higher than all the others. We reported this to the client, and the test continued on. Pretty soon, however, these gages were approaching yield-level stresses, at which point we were becoming increasingly alarmed. (Did we mention that this was high strength, low ductility material, as in material with not much of a range between its yield strength and ultimate strength?)

Us, believing in our test instruments, told the client there was a major problem, and we recommended holding up on the pressurization until things could be sorted out. The client, believing in his design, said it must be a problem with our instrumentation and chose to continue.

Well, as you've probably guessed, the instruments were right. Some areas of the rocket case were under a lot of stress. In fact, too much stress.

With an enormous Crack!, the motor case failed in a catastrophic and most spectacular manner, instantly releasing its pressurized mixture of oil and water--all 65,000 gallons of it!

The ensuing wall of water smashed through the wooden encasing structure and engulfed the twenty or so engineers, scientists, technicians, and other workers who were on site helping with the test. Not only was our equipment totally soaked, but a nearby electrical distribution panel was also flooded, sending a stiff electrical shock to those folks unfortunate enough to be still in contact with the water.

Amazingly, no one was seriously hurt, but our equipment was totally destroyed by the water/oil-soaking, and of course, the rocket motor case was a complete write off.

Was there a lesson here? We like to think so: The next time someone says, "That's a bit odd... these gages seem to be reading kind of high..." Well, you get the idea.

Strain gage work has progressed a long way since then, but it's still very much a specialty activity in the engineering community, requiring not only good engineering knowledge but also high level technician skills. And we still find it to be one of the more interesting activities we're engaged in.

Strain Gage Basics We've discussed some of our interesting strain gage projects in several past newsletters, but we've never really explained just what a strain gage is or how it works. So we thought those of you who may not be familiar with the technology might be interested in knowing just what we're talking about--and fear not! We're going to keep this nice and simple. First of all, you may be wondering why they're called "strain" gages if we're always talking about measuring stress. That's pretty easy to explain. "Strain" is simply a measure of how much something (like a girder in a bridge, for example) stretches (or compresses) as you pull (or push) on it. So strain is what we're actually measuring; that is, we measure how much the material stretches (or compresses) in response to a load. Once you've measured the strain, it's pretty easy to calculate the stress through a little simple arithmetic, which we don't really need to go into here. So, back to strain. How do we go about measuring that? Well, guess what happens if you take a piece of wire, say copper for example, and pull on it? It stretches of course. But while it's stretching, it's also necking down. That is, its cross section is getting smaller. And guess what happens when its length increases and its cross section decreases? Here's the key: Its electrical resistance increases. So, if we take a fine grid of wire and glue it to the surface of a part; then, when we load the part and cause it to stretch, the wire grid stretches right along with it, and when it does, its resistance changes. And as you've probably guessed, we simply measure the change in resistance in the wire grid, from which we can calculate the strain in the part, from which, in turn, we can calculate the stress. Sound simple enough? It is, actually. Well, in principal anyway. Like all things in the real world, there are a number of technical considerations to take into account if you want to obtain accurate, reliable data, but in principle, that's all there is to it. Way back in the "old days" engineers had to make their own strain gages out of very fine copper wire sandwiched between insulating layers of paper. Now, there's a huge range of commercially produced foil gages available, in all sizes and configurations, for use on a variety of materials and in a variety of environments. We've been using a lot of weld-on gages lately. They're a bit quicker to apply than the glue-on type, and they're more rugged. Also, they're available fully encapsulated, which allows them to withstand severe operating environments. For example, on one project we installed them in a recovery boiler, then monitored the stresses after the boiler was brought back on line. In another application we installed them inside a hydroelectric project penstock, then monitored the stresses after the penstock was filled with water and pressure tested.

For example, we recently completed a strain gage project for the Oregon Department of Transportation (ODOT) in which we instrumented the drive shafts for the mechanism that opens and closes the leaves on a Bascule bridge. ODOT engineers will use the information we gathered to evaluate the balance between the counterweights and the leaves and make adjustments if necessary.

Currently, we have two more assignments pending with ODOT to instrument two freeway bridges and measure the stresses and deflections in the support beams.

At the other end of the size spectrum from highway bridges, we've recently had several strain gage assignments for clients in the microelectronics industry who've been experiencing brittle fracture-type failures on printed circuit boards.

The failures have been occurring on boards containing ball grid array (BGA) components, which, because of their stiffness, don't bend with the board during assembly, processing, and testing. To evaluate the problem, we mounted small strain
gages on the boards around the BGAs, then monitored the strains while the boards were subjected to a variety of processing and testing regimes. Using the results of the strain gage tests, our clients were able to modify their procedures to reduce the strains to an acceptable level.

For those of you interested in strain gage testing on printed circuit boards, SMT magazine recently published an article in which they discussed the use of strain gage testing as a means for predicting and preventing brittle fracture of BGAs. Interestingly, while reading through the article, we noticed the client and results they referenced were from one of our projects. The article is available on SMT's website at www.smtmag.com.

Intel International Science and Engineering Fair

This past May, the Intel International Science and Engineering Fair was held in Portland at the Oregon Convention Center. With more than 1,300 finalists from 40 countries, the fair is a showcase of talent for pre-college students in engineering, science, and math. The students compete for scholarships, tuition grants, internships, scientific field trips, and a grand prize of a $50,000 college scholarship and a high-performance computer.

The fair was founded in 1950 by Science Service, a nonprofit organization based in Washington, DC, whose mission is to advance public understanding and appreciation of science.

And if you're thinking "Science Fair? Whoopee... another round of Jello volcanoes, bean plants on turntables, and mice in a maze," you're mistaken. There was some very serious, high level science and engineering going on at the fair.

Consider, for example, "Real-Time Remeshing with Optimally Adapting Domain: A New Scheme for View-Dependent Continuous Levels-of-Detail Mesh Rendering," or "Increased Channel Capacity in Fiber Optics Through Transmission of Multiplexed Orbital Angular Momentum States," to name just a couple of the winning projects.

We were proud to support the Fair through Dr. Chakrapani's participation as one of approximately 1,200 judges.

Yikes! We're 70!

That is, our company is 70 years old, even though none of us are. (Anyone want to guess which of our current employees has been here the longest? see answer below)

Indeed, MEI-Charlton, Inc. was founded in 1934 by David B. Charlton, PhD. Originally, we were known as Charlton Laboratories, and we specialized in chemical analysis. Then in 1946, Harry Czyzewski founded Metallurgical Engineers, Inc., specializing in metallurgical and failure analysis. When the two companies merged in 1973, we took our present name, MEI-Charlton, Inc.

"So what?," you're thinking, "So you did a project for my grandfather way back when... what's that do for me now?" Well, we think it's noteworthy because it shows the stability of our organization and the ongoing need for the services we provide. (And actually, it wasn't us doing the project for your grandfather way back then... it was our grandfathers doing the project for your grandfather.)

In the aftermath of the dotcoms (remember them?) and the flurry of acquisitions and mergers of small businesses into large conglomerates, we're still here providing personalized engineering services on a one-on-one basis.

But of course, resting on past achievements is probably the quickest way of becoming obsolete, or worse yet--extinct. So we prefer to look forward. Forward to the next 70 years. Forward to new growth, and to the ongoing challenge of adapting and bringing new skills to meet the changing needs of our clients.

Answer:

Our most "seasoned" veteran? Ralph Hudson, who's been here since 1966, or 38 years now. Bob Hodel and Dr. Chakrapani are a bit "greener", with only 29 and 28 years of service, respectively. In total, more than half our employees have been with us for over ten years.

MEI-C People

Bob Hodel, vice president, and Corinne Gauthier were married on July 24 in Portland. A honeymoon in Maui followed. Congratulations, Bob and Corinne!

Richard Garber, Senior Metallurgical Engineer, has been busy lately with technical presentations. In March, he presented a paper at the NACE International Corrosion 2004 conference in New Orleans. The paper, co-authored by Dr. Chakrapani, was titled "Some Recent Failures of Fire Sprinkler System Components: Corrosion Case Histories." In April, Richard gave a presentation on internet research at a meeting of the American Society of Women Accountants. In May, he gave a presentation titled, "Metallurgical Problems in Sprinkler Systems," at the Cascade Chapter of the Society of Fire Protection Engineers.

MEI-CHARLTON, INC. IS A CONSULTING ENGINEERING FIRM WHICH SPECIALIZES IN QUALITY ASSURANCE, FITNESS-FOR-PURPOSE EVALUATIONS, CORROSION, METALLURGY, WELDING, AND ENVIRONMENTAL AND ANALYTICAL CHEMISTRY
©1999 MEI-Charlton, Inc.