Ultrasonics to monitor liquid metal melt pool dynamics for improving metal 3D printing

Christopher Kube – kube@psu.edu
Twitter: @_chriskube

Penn State University, 212 Earth and Engineering Sciences Bldg, University Park, PA, 16802, United States

Tao Sun, University of Virginia
Samuel Clark, Advanced Photon Source, Twitter: @advancedphoton

Find the authors on LinkedIn:
www.linkedin.com/in/chriskube
www.linkedin.com/in/suntao

Popular version of 3pID2-Acoustics for in-process melt pool monitoring during metal additive manufacturing, presented at the 183rd ASA Meeting.

3D printed or additively manufactured (AM) metal parts are disrupting the status quo in a variety of industries including defense, transportation, energy, and space exploration. Engineers now design and produce customizable parts unimaginable only a decade ago. New geometrical or part shape freedom inherent to AM has already led to part performance often beyond traditionally manufactured counterparts. In the years to come, another revolutionary performance jump is expected by enabling the AM process to control the grain layout and structural features on the microscopic scale. Grains are the building blocks of metal parts that dictate many of the performance metrics associated with the descriptors of bigger, faster, and stronger.

The second performance revolution of AM metal parts requires uncovering new knowledge in the complicated physics present during the AM process. 3D printed metals are born from an energy source such as a laser or electron beam to selectively melt feedstock material at microscopic locations dictated by the computerized part drawing. Melted locations temporarily form liquid metal melt pools that solidify after the energy source moves to another location. Resulting grain structure and pore/defect formation strongly depends on how the melt pool cools and solidifies.

Over the past five years, high-energy X-rays only available at particle accelerators are used for direct real-time visualization of AM melt pool dynamics and solidification. Figure 1 shows an example X-ray frame, which captured a laser-generated melt pool moving in a single direction with a speed of 800 mm/ms.

This situation mimics the laser and melt pool movement found during 3D printing metal parts. Being able to directly observe melt pool behavior has led to new and improved understanding of the underlying physics. Unfortunately, experiments at such X-ray sources is difficult to ascertain because of extremely high demand across the sciences. Additionally, the measurement technique relegated to high-energy X-ray sources is not transferrable to metal 3D printers that exist in normal industrial settings. For these reasons, ultrasonics are being explored as a melt pool monitoring technology that can be deployed within real 3D printers.

Ultrasound is commonly used for imaging and detecting features inside of solid materials. For example, ultrasound is applied in medical settings during pregnancy or for diagnostics. Application of ultrasound for melt pool monitoring is made possible because of the tendency of ultrasound to scatter from the melt pool’s solid/liquid boundary. The development of the technique is being supported alongside X-ray imaging at the Advanced Photon Source at Argonne National Laboratory. X-ray imaging is providing the extremely important ground truth melt pool behavior allowing for easy interpretation of the ultrasonic response. In Figure 1, the ultrasonic response from the exact same melt pool given in the X-ray video is being shown for two different sensors. As the melt pool enters the field of view of the ultrasonic sensors (see online video), features in the ultrasound response confirms their sensitivity to the melt pool.

In this research, high-energy X-rays are being used to develop the ultrasonic technique and technology. In the coming year, the knowledge developed will be leveraged such that ultrasound can be applied on its own for melt pool monitoring in real metal 3D printers. Currently, no existing technology can capture the highly dynamic melt pool behavior through the depth of the part or substrate.

Practical benefits and value of melt pool monitoring within 3D printers are significant. Ultrasound can provide a quick check to determine the optimal laser power and speed combinations toward accelerated determination of process parameters. Currently, determination of the optimal process parameters requires destructive postmortem microscopy techniques that are extremely costly, time-consuming (sometimes more than a year), and wasteful. Ultrasound has the potential to reduce these factors by an order of magnitude. Furthermore, metal 3D printing processes are highly variable over many months, across different machines, and even when using feedstock powder from different suppliers. Ultrasonic melt pool monitoring can provide period checks to assure variability is minimized.

Assessment of road surfaces using sound analysis

Andrzej Czyzewski – andcz@multimed.org

Multimedia Systems, The Faculty of Electronics, Telecommunications and Informatics, Gdansk University of Technology, Gdansk, Pomorskie, 80-233, Poland

Jozef Kotus – Multimedia Systems, The Faculty of Electronics, Telecommunications and Informatics,
Grzegorz Szwoch – Multimedia Systems, The Faculty of Electronics, Telecommunications and Informatics],
Bozena Kostek – Audio Acoustics Lab., Gdansk Univ. of Technology, Gdansk, Poland

Popular version of 3pPAb1-Assessment of road surface state with acoustic vector sensor, presented at the 183rd ASA Meeting.

Have you ever listened to the sound of road vehicles passing by? Perhaps you’ve noticed that the sound differs depending on whether the road surface is dry or wet (for example, after the rain). This observation is the basis of the presented algorithm that assesses the road surface state using sound analysis.

Listen to the sound of a car moving on a dry road.
And this is the sound of a car on a wet road.

A wet road surface not only sounds different, but it also affects road safety for drivers and pedestrians. Knowing the state of the road (dry/wet), it is possible to notify the drivers about dangerous road conditions, for example, using signs displayed on the road.

There are various methods of assessing the road surface. For example, there are optical (laser) sensors, but they are expensive. Therefore, we have decided to develop an acoustic sensor that ‘listens” to the sound of vehicles moving along the road and determines whether the surface is dry or wet.

The task may seem simple, but we must remember that the sensor records the sound of road vehicles and other environmental sounds (people speaking, aircraft, animals, etc.). Therefore, instead of a single microphone, we use a special acoustic sensor built from six miniature digital microphones mounted on a small cube (10 mm side length). With this sensor, we can select sounds incoming from the road, ignoring sounds from other directions, and also detect the direction in which a vehicle moves.

Since the sound of road vehicles moving on a dry and wet surface differ, performing frequency analysis of the vehicle sounds is recommended.

The figures below present how the sound spectrum changes in time when a vehicle moves on a dry surface (left figure) and a wet surface (right figure). It is evident that in the case of a damp surface, the spectrum is expanded towards higher frequencies (the upper part of the plot) compared with the dry surface plot. Colors on the plot represent the direction of arrival of sound generated by vehicle passing by (the angle in degrees). You can observe how the vehicles moved in relation to the sensor.

Plots of the sound spectrum for cars moving on a dry road (left) and a wet road (right). Color denotes the sound source azimuth. In both cases, two vehicles moving in opposite directions were observed.

In our algorithm, we have developed a parameter that describes the amount of water on the road. The parameter value is low for a dry surface. However, as the road surface becomes increasingly wet during rainfall, the parameter value becomes more extensive.

The results obtained from our algorithm were verified by comparing them with data from a professional road surface sensor that measures the thickness of a water layer on the road using a laser beam (VAISALA Remote Road Surface State Sensor DSC111). The plot below shows the results from analyzing sounds recorded from 1200 road vehicles passing by the sensor, compared with data obtained from the reference sensor. The data were obtained from a continuous 6-hour observation period, starting from a dry surface, then observing rainfall until the road surface had dried.

A surface state measure calculated with the proposed algorithm and obtained from the reference device

As one can see, the results obtained from our algorithm are consistent with data from the professional device. Therefore, the results are promising, and the cheap sensor is easy to install at multiple points within a road network. Hence, it makes the proposed solution an attractive method of road condition assessment for intelligent road management systems.

Explosions Help Probe Elusive Atmospheric Waves

Explosions Help Probe Elusive Atmospheric Waves

Infrasound pulses from munitions plant explosions used to study gravity waves, atmospheric events

Media Contact:
Larry Frum
AIP Media
301-209-3090
media@aip.org

DENVER, May 25, 2022 – Infrasound waves can probe some of the most complex weather patterns hidden to normal observations, but finding a powerful enough source of infrasound waves can be a challenge unless there is a munitions factory nearby.

During the 182nd Meeting of the Acoustical Society of America, Stephen Arrowsmith, from Southern Methodist University, will discuss a method for using infrasound pulses from detonated munitions to probe atmospheric phenomena. His presentation, “The use of infrasound from repeating explosion sequences in Oklahoma to probe the atmosphere,” will take place May 25 at 10:55 a.m. Eastern U.S. at the Sheraton Denver Downtown Hotel.

Infrasound waves are acoustic waves at frequencies too low for humans to hear, but they can be invaluable for studying atmospheric phenomena. One example is gravity waves, which are small-scale waves in the atmosphere driven by buoyancy. These waves are small and transient, making them challenging to study with traditional methods. Infrasound waves have the speed and resolution to track those gravity waves.

“The sound that we record propagates upward into the atmosphere and is refracted back down to the ground,” said Arrowsmith. “The information they provide on the upper atmosphere can tell us about the winds aloft, and these can affect the weather at the ground.”

These infrasound waves need to be strong enough to reach the atmosphere and bounce back, which requires a sizeable source. Fortunately for Arrowsmith, an Oklahoma munitions factory routinely sets off large explosions multiple times per day. He and his team set up detectors in the area around the factory to measure infrasound reflections from the troposphere and stratosphere.

They were able to use the data to study short-term atmospheric fluctuations and tie those fluctuations to gravity waves and other events. They then compared their data across multiple days to study longer-term trends and compare those to meteorological models.

Arrowsmith intends this result to serve as a demonstration of the power of infrasound to probe the atmosphere and study some of its more elusive elements. He hopes infrasound could one day be used as a tool to better understand and predict weather patterns.

———————– MORE MEETING INFORMATION ———————–
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WORLDWIDE PRESS ROOM
In the coming weeks, ASA’s Worldwide Press Room will be updated with additional tips on dozens of newsworthy stories and with lay language papers, which are 300 to 500 word summaries of presentations written by scientists for a general audience and accompanied by photos, audio and video. You can visit the site during the meeting at https://acoustics.org/world-wide-press-room/.

PRESS REGISTRATION
We will grant free registration to credentialed journalists and professional freelance journalists. If you are a reporter and would like to attend, contact AIP Media Services at media@aip.org. For urgent requests, staff at media@aip.org can also help with setting up interviews and obtaining images, sound clips, or background information.

ABOUT THE ACOUSTICAL SOCIETY OF AMERICA
The Acoustical Society of America (ASA) is the premier international scientific society in acoustics devoted to the science and technology of sound. Its 7,000 members worldwide represent a broad spectrum of the study of acoustics. ASA publications include The Journal of the Acoustical Society of America (the world’s leading journal on acoustics), JASA Express Letters, Proceedings of Meetings on Acoustics, Acoustics Today magazine, books, and standards on acoustics. The society also holds two major scientific meetings each year. See https://acousticalsociety.org/.

On Mars, NASA’s Perseverance Rover’s Playlist Like No Other

On Mars, NASA’s Perseverance Rover’s Playlist Like No Other

Microphones on the rover capture, characterize sounds from red planet’s atmosphere

Media Contact:
Larry Frum
AIP Media
301-209-3090
media@aip.org

DENVER, May 25, 2022 – Since NASA’s Perseverance rover landed on Mars, its two microphones have recorded hours of audio that provide valuable information about the Martian atmosphere.

Baptiste Chide, of Los Alamos National Lab, will discuss the importance of this acoustical information in the presentation, “Mars soundscape: Review of the first sounds recorded by the Perseverance microphones,” at the 182nd Meeting of the Acoustical Society of America on May 25 at 3:45 p.m. Eastern U.S.at the Sheraton Denver Downtown Hotel.

After more than a year of recording on the surface, the team reduced the data to a Martian playlist that features about five hours of sounds. Most of the time, Mars is very quiet. Sounds are 20 decibels lower than on Earth for the same source, and there are few natural noises except for the wind.

“It is so quiet that, at some point, we thought the microphone was broken!” said Chide.

However, after listening carefully to the data, the group uncovered fascinating phenomena. There was a lot of variability in the wind, and the atmosphere could abruptly change from calm to intense with rapid gusts. By listening to well-characterized and intentional laser sparks, Perseverance calculated the dispersion of the sound speed, confirming a theory that high-frequency sounds travel faster than those at low frequencies.

“Mars is the only place in the solar system where that happens in the audible bandwidth because of the unique properties of the carbon dioxide molecule that composes the atmosphere,” said Chide.

The red planet’s seasons impact its soundscape. As carbon dioxide freezes in the polar caps during winter, the density of the atmosphere changes and the environment loudness varies by about 20%. That molecule also attenuates high-pitched sounds with distance.

Perseverance continues to collect audio recordings as it moves across different regions of Mars. Chide believes this technique will be even more informative on planets and moons with denser atmospheres, such as Venus and Titan, where sound waves interact more strongly and propagate farther.

———————– MORE MEETING INFORMATION ———————–
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Main meeting website: https://acousticalsociety.org/asa-meetings/
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Press Room: https://acoustics.org/world-wide-press-room/

WORLDWIDE PRESS ROOM
In the coming weeks, ASA’s Worldwide Press Room will be updated with additional tips on dozens of newsworthy stories and with lay language papers, which are 300 to 500 word summaries of presentations written by scientists for a general audience and accompanied by photos, audio and video. You can visit the site during the meeting at https://acoustics.org/world-wide-press-room/.

PRESS REGISTRATION
We will grant free registration to credentialed journalists and professional freelance journalists. If you are a reporter and would like to attend, contact AIP Media Services at media@aip.org. For urgent requests, staff at media@aip.org can also help with setting up interviews and obtaining images, sound clips, or background information.

ABOUT THE ACOUSTICAL SOCIETY OF AMERICA
The Acoustical Society of America (ASA) is the premier international scientific society in acoustics devoted to the science and technology of sound. Its 7,000 members worldwide represent a broad spectrum of the study of acoustics. ASA publications include The Journal of the Acoustical Society of America (the world’s leading journal on acoustics), JASA Express Letters, Proceedings of Meetings on Acoustics, Acoustics Today magazine, books, and standards on acoustics. The society also holds two major scientific meetings each year. See https://acousticalsociety.org/.

Acoustic Sensors Pinpoint Shooters in Urban Setting

Acoustic Sensors Pinpoint Shooters in Urban Setting

Modeling and optimizing sensor networks for a specific environment will help missions narrow in on shooter locations

Media Contact:
Larry Frum
AIP Media
301-209-3090
media@aip.org

DENVER, May 23, 2022 – During a gunshot, two sound events occur: the muzzle blast and the supersonic shock wave. Acoustic sensors, such as single or arrays of microphones, can capture these sounds and use them to approximate the location of a shooter.

As part of the 182nd Meeting of the Acoustical Society of America at the Sheraton Denver Downtown Hotel, Luisa Still, of Sensor Data and Information Fusion, will discuss the important factors in determining shooter localization accuracy. Her presentation, “Prediction of shooter localization accuracy in an urban environment,” will take place May 23 at 12:45 p.m. Eastern U.S.

In an urban setting, buildings or other obstacles can reflect, refract, and absorb sound waves. The combination of these effects can severely impact the accuracy of shooter localization. Preemptively predicting this accuracy is crucial for mission planning in urban environments, because it can inform the necessary number of sensors and their requirements and positions.

Still and her team used geometric considerations to model acoustic sensor measurements. This modeling, combined with information on sensor characteristics, the sensor-to-shooter geometry, and the urban environment, allowed them to calculate a prediction of localization accuracy.

“In our approach, the prediction can be interpreted as an ellipse-shaped area around the true shooter location,” said Still. “The smaller the ellipse-shaped area, the higher the expected localization accuracy.”

The group compared their accuracy prediction to experimental performance under various geometries, weapons, and sensor types. The localization accuracy depended significantly on the sensor-to-shooter geometry and the shooting direction with respect to the sensor network. The smaller the distance between the shooting line and a sensor, the more accurate they could be with their prediction of the source. Adding more sensors increased the accuracy but had diminishing returns after a certain point.

“Each urban environment is too individual (e.g., in terms of layout, building types, vegetation) to make a general recommendation for a sensor set up,” said Still. “This is where our research comes in. We can use our approach to recommend the best possible setup with the highest accuracy for a given location or area.”

———————– MORE MEETING INFORMATION ———————–
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Main meeting website: https://acousticalsociety.org/asa-meetings/
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Press Room: https://acoustics.org/world-wide-press-room/

WORLDWIDE PRESS ROOM
In the coming weeks, ASA’s Worldwide Press Room will be updated with additional tips on dozens of newsworthy stories and with lay language papers, which are 300 to 500 word summaries of presentations written by scientists for a general audience and accompanied by photos, audio and video. You can visit the site during the meeting at https://acoustics.org/world-wide-press-room/.

PRESS REGISTRATION
We will grant free registration to credentialed journalists and professional freelance journalists. If you are a reporter and would like to attend, contact AIP Media Services at media@aip.org. For urgent requests, staff at media@aip.org can also help with setting up interviews and obtaining images, sound clips, or background information.

ABOUT THE ACOUSTICAL SOCIETY OF AMERICA
The Acoustical Society of America (ASA) is the premier international scientific society in acoustics devoted to the science and technology of sound. Its 7,000 members worldwide represent a broad spectrum of the study of acoustics. ASA publications include The Journal of the Acoustical Society of America (the world’s leading journal on acoustics), JASA Express Letters, Proceedings of Meetings on Acoustics, Acoustics Today magazine, books, and standards on acoustics. The society also holds two major scientific meetings each year. See https://acousticalsociety.org/.

LEGO Down! Focused Vibrations Knock Over Minifigures

LEGO Down! Focused Vibrations Knock Over Minifigures

Time reversal technique focuses wave energy to knock over minifigure targets in museum demonstration

Media Contact:
Larry Frum
AIP Media
301-209-3090
media@aip.org

SEATTLE, December 2, 2021 — A tabletop covered in miniature LEGO minifigures. There is a whooshing sound, a pause, and then a single minifigure in the center of the table topples over, leaving the remaining minifigures standing.

Brian Anderson, of Brigham Young University, will discuss how this is achieved in his presentation at the 181st Meeting of the Acoustical Society of America, “Knocking over LEGO minifigures with time reversal focused vibrations: Understanding the physics and developing a museum demonstration.” The session will take place on Dec. 2 at 5:15 p.m. Eastern U.S. in the Elwha B Room, as part of the conference running from Nov. 29 to Dec. 3 at the Hyatt Regency Seattle.

Anderson and his team use speaker shakers to generate vibrations in a plate. They place LEGO minifigures on the plate, choose a target, and measure the impulse response between each shaker and the target location. Playing that very response from the shakers, but reversed in time, creates sound waves that constructively interfere at the target minifigure. The focused energy knocks over the single LEGO minifig without disrupting the surrounding minifigs.

This demonstration was transformed into a two-player game for a museum exhibit in a wave propagation museum hosted by ETH Zurich in Switzerland. Two visitors take turns focusing vibrations and attempting to knock over the LEGO minifigures on the other team.

The technique also has numerous applications beyond LEGO, and Anderson said it shows the power of focused vibrations.

“Time reversal has been used to focus sound in the body that is intense enough to destroy kidney stones or brain tumors without requiring surgery,” Anderson said. “I have used time reversal to locate cracks or defects with ultrasound in metal structures, such as storage canisters for spent nuclear fuel. Time reversal can also be used to locate and characterize earthquakes or locate gun shots within an urban city environment.”

———————– MORE MEETING INFORMATION ———————–
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Main meeting website: https://acousticalsociety.org/asa-meetings/
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WORLDWIDE PRESS ROOM
In the coming weeks, ASA’s Worldwide Press Room will be updated with additional tips on dozens of newsworthy stories and with lay language papers, which are 300 to 500 word summaries of presentations written by scientists for a general audience and accompanied by photos, audio and video. You can visit the site during the meeting at https://acoustics.org/world-wide-press-room/.

PRESS REGISTRATION
We will grant free registration to credentialed journalists and professional freelance journalists. If you are a reporter and would like to attend, contact AIP Media Services at media@aip.org. For urgent requests, staff at media@aip.org can also help with setting up interviews and obtaining images, sound clips, or background information.

ABOUT THE ACOUSTICAL SOCIETY OF AMERICA
The Acoustical Society of America (ASA) is the premier international scientific society in acoustics devoted to the science and technology of sound. Its 7,000 members worldwide represent a broad spectrum of the study of acoustics. ASA publications include The Journal of the Acoustical Society of America (the world’s leading journal on acoustics), JASA Express Letters, Proceedings of Meetings on Acoustics, Acoustics Today magazine, books, and standards on acoustics. The society also holds two major scientific meetings each year. See https://acousticalsociety.org/.