Professional Resources

A Highly Stretchable and Self-healing Strain Sensor for Motion Detection

Strain sensors are devices that can convert force, pressure, tension, and weight into a change in electrical resistance (i.e., capacitance), which can then be measured. Such sensors can be used to create a variety of devices that can detect motion in their surroundings, including robots, health monitoring devices, and smart human–machine interfaces.

Researchers at Fudan University, Tongji University, and the Chinese Academy of Sciences have recently developed a new strain sensor that is highly stretchable, efficient, and sensitive to motion-related changes in its environment and can monitor a variety of human motions in real time. When combined with silicon integrated circuits, it can then transfer the data it recorded directly to a smartphone or another smart device via Bluetooth. The sensor can thus be used to monitor and keep track of human body motions, which is particularly useful for the development of health and fitness tracking devices. This sensor also has self-healing capabilities, as it is made of an ionic and conductive poly(acrylamide) hydrogel, and can quickly and effectively repair itself when torn or damaged.

A highly stretchable and self-healing strain sensor for motion detection. Hang et al.

The new strain sensor can also be used to create technology that recognizes human gestures. The smart glove created by the researchers can express and recognize American sign language. This means that it could be used to enable more engaging interactions between deaf individuals who use ASL and machines. Moreover, the smart glove can be used to wirelessly control a robotic hand, by performing the desired hand gestures while wearing the glove.

The sensing device developed by the researchers has already shown great potential for a wide range of applications, including human–machine interfaces, interactive robots, health monitoring systems, and fitness trackers. In the future, it could be used to fabricate a number of new smart devices with advanced motion sensing capabilities.

For more information: https://techxplore.com/news/2020-07-highly-stretchable-self-healing-strain-sensor.html.

Experimental Physicists Study Steel on Board the International Space Station

For many years, the Institute of Experimental Physics at Graz University of Technology and the Styrian industrial company Böhler Edelstahl have been conducting joint research on the surface tension and temperature dependence of different types of steel. Steel in particular is the focus of interest here, because it will be needed in metallic laser 3D printing to produce steel components using this new remelting technology in the future. Conventional examination methods only work up to a certain upper temperature limit. At higher temperatures, problems can occur with the sample container, such as interactions between the container and the sample, and this would falsify the measuring results.

For the experiments, the Styrian team works together with Japanese and U.S. researchers and uses the electrostatic levitation furnace at the international space station (ISS). “We let the samples hover electromagnetically or electrostatically and thus avoid contact with the sample container.” A laser then heats and melts the floating steel sample, and various sensors measure the density, surface tension, and viscosity of the molten material. When the material cools down again, the researchers can observe and measure this process closely, too. The experiment is controlled from Earth, where the team follows the event live while data is passed on directly via downlink.

Credit: Baustädter - TU Graz

Peter Pichler (left) with working group leader Gernot Pottlacher (right). From the steel rod in their hands, they cut the small balls that are now being examined on the ISS.

Once the tests have been completed, the data will be published by Graz University of Technology as part of a wide-ranging dissertation, as G. Pottlacher explains: “In his dissertation, Peter Pichler is looking into a complete data set of a material in liquid form. He has already analyzed it in many different ways for this purpose. Now the data from the ISS is being added, and in the autumn the steel sample will be examined once again in zero gravity on board a reduced-gravity aircraft.”

For more information: https://phys.org/news/2020-07-experimental-physicists-steel-board-iss.html.

Fusing Technology and Expertise to Solve Inspection Challenges in Additive Manufacturing

Olympus Corp. recently showcased work done at ASM International that speeds up inspection of parts made by laser powder bed fusion (L-PDF), an additive manufacturing process where a laser is used to weld powdered material to form a 3D object.

The entire L-PBF process is controlled by a computer, and about 200 parameters need to be properly set up for each part being created, or poor part quality will result. A major challenge is how to assess the quality of such 3D printed parts.

A common technology available to evaluate the quality of such parts is computed tomography (CT), using x-rays to capture a series of 2D cross-sectional slices which can then be reconstructed into a 3D rendering, which takes about 3 h.

John Peppler, a senior metallurgist and laboratory manager at ASM International’s Training Center, used an Olympus LEXT OLS5000 laser confocal microscope to help speed up the L-PBF process by characterizing the weld shape and comparing the results with those from the CT scan, taking about 1 h to scan a 3 × 3 mm area. In addition, Peppler used the microscope to capture simple line profile measurements of the part—scans which took only a couple of minutes.

Left: A color image of the 3 × 3 mm scan captured using a long working distance, 50 × objective. Right: A height map of the same area shown in the image to the left

Each L-PBF machine has parameters that need to be properly set to enable it to produce the best possible parts. The rapid linear roughness measurement capabilities of the OLS5000 microscope can help speed this process.

Laser powder bed fusion and similar additive manufacturing techniques are rapidly gaining in popularity. The ability to print 3D metal parts with complex shapes and geometries without forging or milling is attractive to many manufacturers, but they must be supported by advanced inspection technologies. Olympus and ASM International aim to help by combining advanced equipment with skilled educators and researchers who work together to develop solutions to emerging challenges.

For more information: https://www.olympus-ims.com/en/microscopes/laser-confocal/ols5000/.

Holographic Beam Shaping to Deliver a Boost to Metallic 3D Printing

Cambridge engineers have begun a three-year research program to help speed up the manufacture of metallic 3D printed parts and products by using computer-generated holography.

With funding from the Engineering and Physical Sciences Research Council, Professor Tim Wilkinson and his team aim to strengthen metallic 3D printing by using computer-generated holography to improve not only the quality of finished parts and products, but also to allow greater control over the metallic powder during the additive manufacture (AM) process.

Credit: Peter Christopher

The department’s set-up for additive manufacturing (AM).

State-of-the-art machines use a laser spot to melt the powder before adding thin layers of the material to make up a part. The localized nature of the laser spot makes controlling thermal energy difficult, leading to unpredictable stresses and distortions. Computer-generated holograms can help bring this distribution of energy under control in three dimensions rather than two as a result of optical diffraction.

Credit: Peter Christopher

Current additive manufacturing machines that make use of just the single laser.

The research team has begun working with plastic and resin AM to develop the algorithms needed to control the hologram and will move on to using metal powder.

Ph.D. student Peter Christoper said the aim is to melt an entire layer of metal powder simultaneously, thereby improving the speed of manufacture as well as removing many of the thermal-related issues.

“During the COVID-19 pandemic, we have seen thousands of scientists, engineers, researchers, and medical professionals, 3D printing parts for ventilators in mere hours, whereas traditional approaches would have taken months or years to set up.” He added, “As a result of our holographic technique, we can use multiple light beams at the same time in order to build up a structure in a more three-dimensional way, and we can control the direction in which the light is traveling. This allows us greater control over any imperfections. We also hope that a new generation of liquid crystal displays will be produced as a result of this research, designed specifically for high-power laser illumination in AM processes.”

For more information: https://phys.org/news/2020-07-holographic-boost-metallic-d.html and https://phys.org/partners/university-of-cambridge/.

Materials Scientists Drill Down to Vulnerabilities Involved in Human Tooth Decay

Northwestern University researchers have cracked one of the secrets of tooth decay. In a study of human enamel, they have identified impurity atoms that may make the material more soluble. This discovery could lead to a better understanding of human tooth decay as well as genetic conditions that affect enamel formation.

“Enamel has evolved to be hard and wear-resistant enough to withstand the forces associated with chewing for decades,” said Derk Joester, who led the research and whose study was published on July 1 by the journal Nature. “However, enamel has very limited potential to regenerate. Our fundamental research helps us understand how enamel may form, which should aid in the development of new interventions and materials to prevent and treat caries. The knowledge also might help prevent or ameliorate the suffering of patients with congenital enamel defects.”

One major obstacle hindering enamel research is its complex core–shell structure, with features across multiple length scales. Enamel, which can reach a thickness of several millimeters, is a three-dimensional weave of rods. Each rod, approximately five microns wide, is made up of thousands of long, thin hydroxylapatite crystallites.

Each crystallite has a continuous crystal structure with calcium, phosphate, and hydroxyl ions arranged periodically (the shell). At the crystallite’s center, two magnesium-rich layers flank a mix of sodium, fluoride, and carbonate ions (the core).

“Surprisingly, the magnesium ions form two layers on either side of the core, like the world’s tiniest sandwich, just 6 billionths of a meter across,” said Ph.D. student Karen DeRocher.

Credit: Northwestern University)

Two views of the “world’s tiniest sandwich” (with scalebar). The left panel shows the magnesium (magenta) sandwich at the enamel crystallite’s core from data acquired by atom probe tomography. The right panel shows an atomic resolution scanning transmission electron microscopy image of an enamel crystallite looking down the long axis of the crystal. The dark areas are distortions in the crystal lattice due to the presence of impurities such as magnesium and sodium, identified by atom probe tomography (left panel).

The researchers found strong evidence that the core–shell architecture and resulting residual stresses impact the dissolution behavior of human enamel crystallites while also providing a plausible avenue for extrinsic toughening of enamel.

“The ability to visualize chemical gradients down to the nanoscale enhances our understanding of how enamel may form and could lead to new methods to improve the health of enamel,” said postdoctoral fellow Paul Smeets.

For more information: https://phys.org/news/2020-07-materials-scientists-drill-vulnerabilities-involved.html.

New Method Measures Temperature Within 3D Objects

University of Wisconsin-Madison engineers have made it possible to remotely determine the temperature beneath the surface of certain materials using a new technique they call depth thermography, with potential uses where traditional temperature probes won’t work, like monitoring semiconductor performance or next-generation nuclear reactors.

“We can measure the spectrum of thermal radiation emitted from the object and use a sophisticated algorithm to infer the temperature not just on the surface, but also underneath the surface, tens to hundreds of microns in,” says Mikhail Kats, a UW-Madison professor of electrical and computer engineering.

Kats, his research associate Yuzhe Xiao, and colleagues described the technique this spring in the journal ACS Photonics.

For the project, the team heated a piece of fused silica and analyzed it using a spectrometer, measuring temperature readings from various depths of the sample using computational tools previously developed by Xiao in which he calculated the thermal radiation given off from objects composed of multiple materials. Working backwards, they used the algorithm to determine the temperature gradient that best fit the experimental results.

Credit: Mikhail Kats

An infrared image of the fused silica window used to test the depth thermography concept. For the project, the team heated the silica, a type of glass, and analyzed it using a spectrometer. They then measured temperature readings from various depths of the sample.

Eventually, Kats wants to use depth thermography to measure semiconductor devices to gain insights into their temperature distributions as they operate. This type of 3D temperature profiling could also be used to measure and map clouds of high temperature gases and liquids.

“For example, we anticipate relevance to molten-salt nuclear reactors, where you want to know what’s going on in terms of temperature of the salt throughout the volume,” says Kats. “You want to do it without sticking in temperature probes that may not survive at 700 degrees Celsius for very long.”

“This is a completely remote, non-contact way of measuring the thermal properties of materials in a way that you couldn’t do before,” Kats says.

For more information: https://phys.org/news/2020-07-method-temperature-d.html.

Researchers Report 3D Printed Latex Rubber Breakthrough

Virginia Tech researchers have discovered a novel process to 3D print latex rubber, unlocking the ability to print a variety of elastic materials with complex geometric shapes.

The team, including Timothy Long, a professor of chemistry, and Christopher Williams, the L.S. Randolph Professor of mechanical engineering, overcame some long-standing limitations of 3D printing, chemically modifying liquid latexes to make them printable and building a custom 3D printer with an embedded computer vision system to print accurate, high-resolution features of this high-performance material. Their initial results are detailed in a journal article published in ACS Applied Materials and Interfaces.

Credit: Virginia Tech

An interdisciplinary group of chemistry and mechanical engineering researchers developed a novel process to 3D print latex rubber. Latex rubber parts, such as this impeller printed at 100 micron resolution, allow nondestructive reuse of complex molds because the parts exhibit a unique combination of flexibility and toughness.

After unsuccessful attempts to synthesize a material that would provide the ideal molecular weight and mechanical properties, Phil Scott, a student in the Long Research Group, turned to commercial liquid latexes.

The researchers ultimately wanted this material in a solid 3D printed form, but Scott first needed to augment the chemical composition to allow it to print.

“Latexes are in a state of Zen,” said Viswanath Meenakshisundaram, a student in the lab who collaborated with Scott. “If you add anything to it, it’ll completely lose its stability and crash out.”

Then, the chemists came up with a new idea: What if Scott built a scaffold, similar to those used in building construction, around the latex particles to hold them in place? This way, the latex could maintain its great structure, and Scott could add photoinitiators and other compounds to the latex to enable 3D printing with ultraviolet light.

Needing a printer capable of printing high-resolution features across a large area, Meenakshisundaram built a new printer with an embedded camera, enabling the printing parameters to be updated based on his code.

Meenakshisundaram and Scott discovered their final 3D printed latex parts exhibited strong mechanical properties in a matrix known as a semi-interpenetrating polymer network, which hadn’t been documented for elastomeric latexes in the prior literature.

For more information: https://phys.org/news/2020-07-d-latex-rubber-breakthrough.html.

Researchers Solve a 60-Year-Old Puzzle About a Superhard Material

Skoltech researchers have cracked a 1960s puzzle about the crystal structure of a superhard tungsten boride that can be extremely useful in industrial applications, including drilling technology. The research, supported by Gazpromneft Science and Technology Center, was published in the journal Advanced Science.

Tungsten borides first captured the imagination of scientists in the mid-20th century due to their hardness and other fascinating mechanical properties. One longstanding puzzle has been the crystal structure of the highest W-B phases, the so-called WB₄, which varied widely between experimental models and theoretical predictions.

In 2017, a collaboration began between Skoltech and the Vereshchagin Institute for High Pressure Physics of the RAS, searching for superhard materials to be used for producing composite cutters installed on bits, which are used for drilling oil and gas wells. Researchers led by Artem R. Oganov of Skoltech and MIPT predicted the existence of WB₅, tungsten pentaboride, which was expected to be harder than the widely used tungsten carbide and have comparable fracture toughness. The compound was successfully synthesized in the lab at Vereshchagin Institute to complete the research loop. In the new paper, Oganov and his colleagues show that the long-debated WB₄ and the newly predicted WB₅ are actually the same material.

The researchers synthesized this new material and revealed a connection between the two compounds: the new material has a crystal structure derived from the WB₅ structure, with some amount of disorder and nonstoichiometry (the proportions of its elemental composition cannot be represented by a ratio of small integer numbers). Thus, the new material was denoted not as WB₄ but as WB_5−x.

Credit: Pavel Odinev/Skoltech

Researchers have cracked a 1960s puzzle about the crystal structure of a superhard tungsten boride.

Since WB_5−x is relatively easy to synthesize, its excellent mechanical properties and stability at high temperatures make it a very promising material for many technologies where tungsten carbide-based composites dominated in the last 90 years.

For more information: https://phys.org/news/2020-07-year-old-puzzle-superhard-material.html.

World Auto Steel Releases Report on Potential Liquid Metal Embrittlement in Welded AHSS

World Auto Steel, Middletown, OH, has just released the results of a three-year study on liquid metal embrittlement (LME), a type of cracking that can occur in the welding of advanced high-strength steels.

The study results add important knowledge and data to understanding the mechanisms behind LME and thereby finding methods for controlling and establishing parameters for preventing its occurrence. The study also investigated possible consequences of residual LME on part performance, as well as nondestructive methods for detecting and characterizing LME cracking, both in the laboratory and on the manufacturing line.

As with most of its study results, World Auto Steel makes its reports freely available for download on its website in hopes that it will provide valuable information to steel users around the world.

For more information: www.worldautosteel.org.