Texas A&M mechanical engineering student, John Mayo, wondered if it’s true what they say about ceramics - that they are strong in compression. Armed with his pick-up truck and four trade show coffee mugs, he set to find out. Credit: John Mayo.

John Mayo, who is finishing his second year as a mechanical engineering student at Texas A&M, is a “show me, don’t tell me” kind of guy.

This spring he’s been taking a class, Materials and Manufacturing Selection in Design, and came across this in the textbook:

“Since cracks and flaws tend to remain closed in compression, brittle materials such as concrete are often incorporated into designs so that only compressive stresses act on the part. Often, we find that brittle materials fail at much higher compressive stresses than tensile stresses This is why it is possible to support a fire truck on four coffee cups; however, ceramics have very limited mechanical toughness. Hence, when we drop a ceramic coffee cup, it can break easily.”

Which got him thinking — was this a true statement? John says, “I am one to test the limits, and this statement certainly captured my attention.”

Because (legal) access to fire trucks is limited, he decided to test the statement using his Ford Ranger pick-up truck weighing just over 3000 pounds and four ceramic coffee mugs gleaned from trade shows.

Here is his description of the experiment (I especially like the mechanical engineering details):

A wood sandwich helped distribute the load and protected the tires in case of fracture. Credit: John Mayo.

I cut pieces of scrap wood to place above and below the cups, to provide a uniform surface. The wood also would insulate the ceramic from unevenness of the concrete driveway, especially if the truck shifted and put excessive pressure on only one edge of a cup. With a jack, two jack stands and wood blocks to keep the truck from rolling, I began at the front, left wheel. After ensuring that the transmission was set to ‘park’ and the parking brake engaged, I jacked up the wheel and gently lowered it back on the cup between two wood pieces. The cup did not break, so I added one under the front, passenger side next. The truck seemed stable, so I jacked the rear end under the differential, lifting both tires simultaneously. As soon as the tires rose from the concrete, the truck rolled forward slightly, so I let it back down and checked on the front cups. Surprisingly, the coffee cups had not broken, even though they were both titled with only one point on their rims supporting the truck.

I quickly jacked the front end up again, and supported it slightly above the cups with jack stands. Next, I jacked the rear end up again and successfully installed the cup and wood ‘sandwiches’ under each tire. Then I used the jack to remove the jack stands at each front wheel, thus getting all four wheels supported on cups.

After leaving the truck on the cups for the entire, windy night and most of the next day, I decided to test the cups further by jumping up and down in the truck bed. The cups seemed to be magically strong, so to prove to myself and others that these were ordinary ceramic cups, I used my phone to record a video clip of me breaking one of them. Wearing safety glasses and using a glass shield for the phone proved to be a wise decision, because the weight of the truck helped create an intense explosion of ceramic pieces when I tapped the cup with a hammer. The video clearly demonstrates that the cup is indeed ceramic and that the truck’s weight is substantial.

I asked John whether he often takes up ‘extracurricular’ experiments like this. He said, “I do not usually think of them as “experiments,” more of just an “I wonder if” idea put into action.”

Once, for example, he and a buddy wondered whether they could harness some of Texas’ high winds to pull their bicycles down the road using parachute-like kites. Another time he and some pals decided that $200 was over their budget for a small catamaran mast float. Instead, they gathered up some floating duck decoys and modified them into a workable substitute.

A self-described tinkerer John says, “I’m always “doing something” which I find much more interesting than merely sitting in front of a TV or video games.”

In fact, this coffee mug experiment made him wonder what would happen if he did the same experiment using unopened soft drink cans. That experiment can be viewed here, and in the background you can here him definitively state his conclusion, “OK. Soda cans do not work.”

‘Nuff said.

He spends his spare time helping out the local high school and middle school robotics teams or restoring his 1978 CJ7 Jeep. In the future, plans to pursue a MS in mechanical engineering and hopes to work on robotics-related technology such as unmanned ground or aerial vehicles.

This summer he’ll be working for Boeing in Mesa, Ariz., on tooling mechanisms for Apache helicopters.

I hope they can provide a coffee cup for him. He’s running out.

The textbook that triggered the experiment was The Science and Engineering of Materials, Sixth Edition, Askeland, D. R., Pradeep, P. F., and Wendelin, J. W. 2006, Cengage Learning, Stamford, CT, pp. 220.

Share

Distributions of surface height and in-plane strain of an angle interlock C/SiC composite at 1,200°C, measured by DIC. Line scans (in red) are used to correlate strains with the underlying fiber weave. (Material provided by D.B. Marshall, Teledyne Scientific.) Credit: Frank Zok; UCSB.

Last August DARPA conducted the second test flight of its hypersonic technology vehicle, the Falcon HTV-2. The test ended when the vehicle sent itself into the Pacific Ocean nine minutes into the flight. At the time, the reasons for the abort were unclear and frustrating. The project’s program manager, Maj. Chris Schulz, USAF said then, “We’ll learn. We’ll try again. That’s what it takes.”

To help figure out what it takes, DARPA enlisted the aid of an independent engineering review board comprised of government and academic experts to evaluate the data collected during the flight. The vehicle was built not only to demonstrate the technology, but also as a data-gathering platform. Thus, the ERB had plenty of data telling the story of what happened.

The goal of the program is to develop a vehicle that can reach any location in the world within an hour, which requires hypersonic speeds. According to a story on the DARPA website, the August 11 test flight successfully achieved stable, aerodynamically-controlled speeds up to Mach 20 for the first three minutes. The vehicle appears to have experienced a series of “shockwave disturbances” that were more than 100 times more intense than it was designed to withstand. The vehicle recovered from these first shockwaves and maintained control, which DARPA’s acting director, Kaigham Gabriel observed, was in itself a successful outcome, “That’s a major validation that we’re advancing our understanding of aerodynamic control for hypersonic flight.”

So, how did the vehicle eventually lose control? The ERB conclusion was that “the most probable cause of the HTV-2 Flight 2 premature flight termination was unexpected aeroshell degradation, creating multiple upsets of increasing severity that ultimately activated the Flight Safety System,” which triggered a controlled descent and ocean ditch of the vehicle.

Vehicle design engineers knew there would be a “gradual wearing away of the vehicles skin as it reached stress tolerance limits,” however, more of the vehicle skin separated from the vehicle than was expected. The gaps created by the peeling “created strong, impulsive shock waves around the vehicle,” which caused it to roll suddenly. Eventually, the shockwave-induced rolls became more than the vehicle could overcome.

The old maxim that we learn more from our failures than our successes applies here. Schulz said in the DARPA story, “Data collected during the second test flight revealed new knowledge about thermal-protective material properties and uncertainties for Mach 20 flight inside the atmosphere.” That is, the data collected during the flight showed that the assumptions and extrapolations used to design the vehicle were not enough to predict accurately the extreme environment experienced at Mach 20. Schulz says, “The result of these findings is a profound advancement in understanding the areas we need to focus on to advance aerothermal structures for future hypersonic vehicles. Only actual flight data could have revealed this to us.”

The DARPA story says the next step for the program is to improve models for “characterizing the thermal uncertainties and heat-stress allowances for the vehicle’s outer shell.”

However, accurately characterizing materials at high temperatures is not easy. Last week we summarized a review article on methods for measuring thermophysical properties above 1,500°C, a laboratory capability that is being driven largely by aerospace and nuclear applications. Even the business of accurately measuring temperature for those tests is as much art as science.

These materials are not easy to work with, either. The materials under investigation are refractory nonoxide composites, like C/SiC, sometimes with refractory borides mixed in. The cover story of the January/February issue of The Bulletin gives an overview of materials, processes and properties of UHTC composite materials under investigation for hypersonic vehicles in the UK. In the US, a multi-university and industry partnership is working on the problem under the umbrella organization, National Hypersonic Science Center for Materials and Structures.

A recent paper (abstract only) by a research team at the University of California, Santa Barbara—one of the partner universities—describes a method for measuring strain at high-temperatures. The authors, Mark Novak and Frank Zok, note that development of materials for extreme environments requires the ability to reproduce conditions in the laboratory, which is not trivial.

In their paper, they use digital image correlation to measure displacement and strain. DIC is an optical, non-contact method that can be used at high temperatures.

Displacements are measured by correlating speckle pattern images of specimen surfaces in the deformed state to the undeformed state. Strains are determined by differentiating between displacement fields. The technique eliminates strain gauges, and they report, is accurate with excellent spatial resolution. It has the further advantage of being useful for specimens subject to thermal gradients or mechanical loads because it can recognize out-of-plane displacements.

The trick is in the imaging, which requires an illumination source that can be distinguished from the glow of thermal radiation. Also, heat haze is a problem when the measurements are made in ambient air. Finally, the speckle pattern itself has to be thermally stable and have enough contrast in the test temperature interval.

The paper describes a technique Novak and Zok devised using a CO₂ laser as the illumination source, which they demonstrated on a C/SiC composite and a nickel base superalloy (Inconel 625). Alumina or zirconia paints were used to enhance the speckle contrast on the composite; the superalloy was oxidized to create a dark background.

Heat haze was managed by using an “air knife,” which blows air across the surface of the sample, minimizes turbulence and mixes the air in the sight lines of the imaging instruments. The air knife did not completely eliminate heat haze, but their results show that using it led to sharper images and reduced the standard deviation of strain values by a factor of three.

They were able to demonstrate full-field strain mapping up to 1,500°C, and suggest that the upper-temperature limit for measuring thermomechanical properties could be extended by modifying the illumination and filtering out longer wavelengths.

Share

There is some pretty interesting work underway on ceramic materials for ultra-high temperature applications. Service temperatures of more than 1,500°C requires the use of ceramic materials rather than refractory alloys. Development of these ceramics is driven mostly by aerospace applications, such as hypersonic vehicles and thermal barrier coatings for jet engines, and nuclear energy applications, such as nuclear fuels and accident scenarios.

At those temperatures, the pool of candidate materials is not large. For example, a material system being considered for hypersonic vehicles is refractory (Zr, Hf) boride-silicon carbide composites, which will experience temperatures above 2,000°C where they are sure to form zirconium and hafnium oxides at the leading edges. A proper understanding of zirconia formation is important, too, to understanding (and thus controlling) how zirconium alloys passivate in loss-of-coolant nuclear accidents.

Sophisticated modeling techniques have accelerated the pace of development for these materials and allow researchers to test scenarios that are experimentally challenging. However, the old computer engineer’s maxim still applies, “Garbage in — garbage out.” That is, a simulation is only as good as the data it uses.

In a new paper in the Journal of the American Ceramic Society (available online in Early View), Sergey Ushakov and Alexandra Navrotsky reviews methods for measuring high temperature thermophysical properties. In the paper, the duo says, “The free energy change for an reaction can be calculated if the heat capacities, standard enthalpies and entropies of formation, and enthalpies and temperatures of phase transformations are known for all products and reactants.” But, they go on to observe that such data are often not available at temperatures over 1,500°C, and even when they are, they are subject to revision as better methodologies improve. They give the example of the melting temperature of MgO, which has been revised by hundreds of degrees in the last decade. Nevertheless, they note, “Thermodynamics is the most reliable tool for scientific predictions of materials stability we have at our disposal.”

They also warn that simulation has its limits, especially (in this context) with regard to calculated phase diagrams (CalPhaD) and first-principles ab initio calculations. They cite Saunders and Miodownik, authors of a definitive book on CalPhaD, who point out that very accurate CalPhaD diagrams of multicomponent systems can be generated provided that the binary and ternary subsystems are available. They note that Saunders and Miodownik say, “it is in reality impossible to make predictions for the phase diagrams of binary systems to any degree of accuracy, which would be acceptable for practical purposes.” Similarly, first-principles calculations require some approximations that compromise their accuracy.

The first essential requirement for measuring high temperature properties is accurate measurement of temperature, and the key is to choose the right method for the temperature regime. Temperatures can be measured by thermocouples or by optical pyrometry, and at these high temperatures, there are subtleties to be aware of with both, and Ushakov and Navrotsky review them thoroughly.

The paper goes on to review how to measure melting point and how to determine phase diagrams in refractory systems. Calorimetry measures “heat effects from reaction or during heating and cooling,” and is used to measure heat capacities and standard entropies and enthalpies of formation. It also locates phase transformation and melting points. There are a number of calorimetric methods, and the paper reviews their use, set-up, calibration and limitations. Included are drop calorimetry, combustion calorimetry, solution calorimetry and the flash method. The authors also discuss other important high temperature measurements including vapor pressure measurement and volume measurement (using high temperature dilatometry).

The authors present two case studies to illustrate. The first is a determination of fusion enthalpy of La₂O₃. It has been known for some time that below the melting point, rare earth oxides from lanthanum to samarium undergo reversible phase transformations from hexagonal A-type to H-type to cubic X-type, but the transformation enthalpies have not be measured. The authors show us the experimental set-up, and offer an analysis of the uncertainty and accuracy of the outcome. The experimental temperatures were 2,000-2,300+°C. They present a similar evaluation for a premelting phase transition in Y₂O₃ that occurs at about 2,400°C.

The article covers a lot of ground in just 16 pages and 190 references. While it is not a review article in the strict sense, it is a thorough, very readable summary of the issues and challenges that attend high temperature thermophysical data. Researchers who need to use, evaluate and interpret such data will find this article is a handy and useful tutorial.

The paper is titled, “Experimental Approaches to the Thermodynamics of Ceramics above 1,500°C” (doi: 10.111/j.1551-2916.2012.05102.x).

Share

Check ‘em out:

Thermodynamic glass transition in a spin glass without time-reversal symmetry

(PNAS) Spin glasses are a longstanding model for the sluggish dynamics that appear at the glass transition. However, spin glasses differ from structural glasses in a crucial feature: they enjoy a time reversal symmetry. This symmetry can be broken by applying an external magnetic field, but embarrassingly little is known about the critical behavior of a spin glass in a field. In this context, the space dimension is crucial. Simulations are easier to interpret in a large number of dimensions, but one must work below the upper critical dimension (i.e., in d < 6) in order for results to have relevance for experiments. Here we show conclusive evidence for the presence of a phase transition in a four-dimensional spin glass in a field. Two ingredients were crucial for this achievement: massive numerical simulations were carried out on the Janus special-purpose computer, and a new and powerful finite-size scaling method.

Conference fosters innovation of materials

[Brown University's] School of Engineering hosted a conference over spring break that brought together academics, professionals and representatives from the federal government to discuss the future of new materials technologies and the Materials Genome Initiative. The MGI, announced by President Obama last June, aims to assist American institutions and companies in the development of cheaper and more effective new materials. “The president calls for an expansion of opportunities for American workers,” said Cyrus Wadia, assistant director for clean energy and materials research and development in the White House Office of Science and Technology Policy. “Materials are going to be at the heart of all new technologies.” Wadia said he was impressed by the broad range of departments working together [at Brown] on material design, specifically citing the mechanical, biomaterial, applied math and physics departments. These researchers rely on computational tools, experimental tools and digital data to create new materials, Wadia said.

The printed world: Three-dimensional printing from digital designs will transform manufacturing and allow more people to start making things

(Economist) Filton, just outside Bristol, is where Britain’s fleet of Concorde supersonic airliners was built. In a building near a wind tunnel on the same sprawling site, something even more remarkable is being created. Little by little a machine is “printing” a complex titanium landing-gear bracket, about the size of a shoe, which normally would have to be laboriously hewn from a solid block of metal. Brackets are only the beginning. The researchers at Filton have a much bigger ambition: to print the entire wing of an airliner. Far-fetched as this may seem, many other people are using three-dimensional printing technology to create similarly remarkable things. These include medical implants, jewellery, football boots designed for individual feet, lampshades, racing-car parts, solid-state batteries and customised mobile phones.

Tinted windows that generate electricity

(Technology Review) A startup in Germany has developed a new kind of solar panel made of small, organic molecules deposited on polyester films. The panels are flexible, and far lighter than conventional solar panels, yet in some locations -particularly where it’s hot or cloudy - they can generate just as much electricity as a conventional solar panel. Heliatek, based in Dresden, is funded by Bosch, BASF, and others, and has raised €28 million so far. The company, which recently started making its panels on a small, proof-of-concept production line , hopes to raise an additional €60 million part of which will be used to build a 75-megawatt factory. Heliatek’s panels will cost more per watt than conventional solar panels, says CEO Thibaud de Séguillon. But in four to five years, by which time Heliatek should reach large-scale production, the cost could drop to around 40 to 50 cents per watt, which would make them competitive with conventional solar panels, he says.

And two stories related to the 100th anniversary of the sinking of the Titanic:

Science Xplained: The Titanic’s Metal Mysteries

The iceberg wasn’t the only culprit in the Titanic’s sinking; In this edition of Science Xplained, Yale University’s materials science educator Ainissa Ramirez demonstrates in this video how the metal rivets that held the ship together became brittle in the frigid waters and broke apart on impact with the iceberg, likely contributing to the enormity of the tragedy.

In 1990s, Missouri S&T researchers studied secrets of Titanic steel

The steel definitely played a role, because it was not as “impact-resistant” as modern steel, said the late Phil Leighly, who studied steel from the Titanic in 1996 and 1997. A professor emeritus of metallurgical engineering Leighly said the steel was so brittle that in the chilly waters of the North Atlantic it could shatter easily. But it also was the best steel available at the time, he said. Leighly spent five months examining samples of the Titanic wreckage. Assisting him was F. Scott Miller, now an associate teaching professor of materials science and engineering at Missouri S&T. While working on his PhD, Miller conducted X-ray microanalysis of the samples of Titanic steel that Leighly had obtained from RMS Titanic Inc., the steward of all artifacts from the luxury ocean liner. In September 1996, Leighly received three wooden crates containing more than 400 pounds of the three-quarter-inch steel plate of the Titanic’s hull.

dsfas

Share

An ultrasonic phased array setup. Credit: Techno Inc.

A hat tip to Quality Magazine on this. As part of their PhD thesis work, Steve Bottiglieri and Andrew Portune, graduate students at Rutgers, worked with equipment suppliers to develop a novel and relatively quick non-destructive testing approach that seems to be well suited for inspecting certain high-performance ceramic products that are so critical (such as armor) that each must be evaluated.

One commonly used inspection tool for ceramic manufactures is conventional ultrasound inspection which typically relies on a single probe. Some manufacturers use an operator to direct the probe and others use a linear automated probe to conduct the testing.

Bottiglieri and Portune, working under the guidance of Richard Haber, director of Rutgers Ceramic, Composite & Optical Materials Center, wondered if there was a way to accelerate the inspection process. (Haber, an ACerS fellow, and Portune presented a related paper at the ICACC 2010 conference on “Advanced Nondestructive Ultrasound Characterization of Transparent Armor Ceramics.”)

In brief, according to QM, the Rutgers team found a way to integrate an Olympus OmniScan phased array flaw detection probe, composed of 64 piezoelectric elements, with a Techno Inc. gantry machine, which can be programmed to automatically sweep over the ceramic object. A OmniScan unit captures the ultrasonic data simultaneously with positional information. The net effect is that the phased array system can measure ceramic properties while sweeping over large sample areas, and data from the gantry allows inspectors to develop accurate property maps of each object.

Bottiglieri says his team’s tool is 10-times faster than conventional ultrasonic inspection.

In a summary of his PhD thesis, Bottiglieri explains the role of ultrasonc testing, noting that the performance of critical ceramic products is dependent on the products’  microstructure. “Microstructural variations or heterogeneities throughout large sample volumes can severely degrade the physical properties of alumina-based materials. Variations and heterogeneities in this case refer to variations in density and grain size, unreacted sintering additives, unwanted secondary phases, or large porosity. The ability to predict the performance of not just alumina-based materials but any ceramic material will be dictated by the ability to understand the type, size, and concentration of all features present throughout the bulk microstructure. Ultrasound nondestructive testing was chosen as the method for characterizing the microstructures of dense, polycrystalline, high hardness, aluminum oxide materials,” he writes.

Portune’s graduate work specifically focused on nondestructive characterization of armor grade silicon carbide. He writes, “Predicting the performance of armor grade ceramic materials depends on knowledge of the absolute and relative concentration and size distribution of bulk heterogeneities. Ultrasound was chosen as a nondestructive technique for characterizing the microstructure of dense silicon carbide ceramics. Acoustic waves interact elastically with grains and inclusions in large sample volumes, and were well suited to determine concentration and size distribution variations for solid inclusions.

Much of the work of the Rutgers groups was to write the software to control the motion of the Techno gantry. Their system allows for the input of basic parameters for the parts being inspected and the generation of a tailored set of instructions “that guides the machine through the intricate series of motions required to produce the scaffold.”

Bottiglieri and Portune also worked with Techno and Omniscan to craft a way to pass the gantry spatial location into the Omniscan recorders to such that it correctly corresponds with the collected ultrasonic sample information correspond to a spatial location.

The Rutgers researchers validated their inspection system by setting up an experimental inspection of 4″ x 4″ glass-ceramic tiles, which purposely contained a variety of compositions. Some sample tiles were also laminated. Tile thickness varied from 0.5-1 inch.

For the ordinary tiles, they compared the ultrasonic data to results obtained through the use of conventional microstructural testing, including field emission scanning electron microscopy  imaging and X-ray diffraction, and found strong correlations. For laminated samples, the researchers focused on identifying the location and severity of delaminations.

“The integration of the gantry machine and the phased array provides a major advancement in ultrasonic inspection of ceramic material,” Bottiglieri concludes in the QM story. “This new approach can inspect a large number of parts in considerably less time than is required by conventional methods. It also delivers excellent material property maps, making it possible to locate anomalous defects with a high degree of accuracy.”

In his thesis summary, Bottiglieri has high hopes for the ultrasonic techniques and predicts the novel characterization methods “can be proliferated for use with a wide range of other high density materials.”

Portune also tested the system on silicon carbide, using commercial and custom-engineered SiC materials. As in the tile experiments, Portune found excellent correlations between the ultrasonic data and results from electron microscopy. He, too, believes the phased array technique “should be extended to a wide range of dense polycrystalline heterogeneous materials.”

Share