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Lawrence Livermore National Laboratory (LLNL) researchers have developed an efficient method to measure residual stress in metal parts produced by powder-bed fusion additive manufacturing. This 3D printing process produces metal parts layer by layer using a high-energy laser beam to fuse metal powder particles. When each layer is complete, the build platform moves downward by the thickness of one layer, and a new powder layer is spread on the previous layer.
While this process is able to produce quality parts and components, residual stress is a major problem during the fabrication process. Large temperature changes near the last melt spot—rapid heating and cooling—and the repetition of this process result in localized expansion and contraction, factors that cause residual stress.
Aside from their potential impact on mechanical performance and structural integrity, residual stress may cause distortions during processing resulting in a loss of net shape, detachment from support structures and, potentially, the failure of additively manufactured (AM) parts and components.
An LLNL research team, led by engineer Amanda Wu, has developed an accurate residual stress measurement method that combines traditional stress-relieving methods (destructive analysis) with modern technology: digital image correlation (DIC). This process is able to provide fast and accurate measurements of surface-level residual stresses in AM parts. A paper describing their method is published in the journal Metallurgical and Materials Transactions A.
The team used DIC to produce a set of quantified residual stress data for AM, exploring laser parameters. DIC is a cost-effective, image analysis method in which a dual camera setup is used to photograph an AM part once before it’s removed from the build plate for analysis and once after. The part is imaged, removed and then re-imaged to measure the external residual stress.
In a part with no residual stresses, the two sections should fit together perfectly and no surface distortion will occur. In AM parts, residual stresses cause the parts to distort close to the cut interface. The deformation is measured by digitally comparing images of the parts or components before and after removal. A black and white speckle pattern is applied to the AM parts so that the images can be fed into a software program that produces digital illustrations of high to low distortion areas on the part’s surface.
In order to validate their results from DIC, the team collaborated with Los Alamos National Laboratory (LANL) to perform residual stress tests using a method known as neutron diffraction (ND). This technique, performed by LANL researcher Donald Brown, measures residual stresses deep within a material by detecting the diffraction of an incident neutron beam. The diffracted beam of neutrons enables the detection of changes in atomic lattice spacing due to stress.
Although it’s highly accurate, ND is rarely used to measure residual stress because there are only three federal research labs in the US—LANL being one of them—that have the high-energy neutron source required for this analysis.
The LLNL team’s DIC results were validated by the ND experiments, showing that DIC is a reliable way to measure residual stress in powder-bed fusion AM parts.
Their findings were the first to provide quantitative data showing internal residual stress distributions in AM parts as a function of laser power and speed. The team demonstrated that reducing the laser scan vector length instead of using a continuous laser scan regulates temperature changes during processing to reduce residual stress. Furthermore, the results show that rotating the laser scan vector relative to the AM part’s largest dimension also helps reduce residual stress. The team’s results confirm qualitative data from other researchers that reached the same conclusion.
By using DIC, the team was able to produce reliable quantitative data that will enable AM researchers to optimally calibrate process parameters to reduce residual stress during fabrication. Laser settings (power and speed) and scanning parameters (pattern, orientation angle and overlaps) can be adjusted to produce more reliable parts. Furthermore, DIC allowed the Lawrence Livermore team to evaluate the coupled effects of laser power and speed, and to observe a potentially beneficial effect of subsurface layer heating on residual stress development.
LLNL’s findings eventually will be used to help qualify properties of metal parts built using the powder-bed fusion AM process. The team’s research helps build on other qualification processes designed at LLNL to improve quality and performance of 3D printed parts and components.
Wu and her colleagues are part of LLNL’s Accelerated Certification of Additively Manufactured Metals (ACAMM) Strategic Initiative. The other members of the Lawrence Livermore team include Wayne King, Gilbert Gallegos and Mukul Kumar.
Amanda S. Wu, Donald W. Brown, Mukul Kumar, Gilbert F. Gallegos, Wayne E. King (2014) “An Experimental Investigation into Additive Manufacturing-Induced Residual Stresses in 316L Stainless Steel,” Metallurgical and Materials Transactions A Volume 45, Issue 13, pp 6260-6270 doi: 10.1007/s11661-014-2549-x
At the Los Angeles Auto Show this week, Marc Lichte, Head of Design, is presenting the Audi prologue concept car. Lichte is giving the Audi brand a new styling direction in the large coupe. Among the many advanced technology features of this “foretaste of the future of Audi” is a new 48‑volt subsystem of the vehicle electrical system—this is a technology that will soon be introduced to production cars at Audi. (Earlier post.)
The 48‑volt system is supplied by a powerful belt starter generator, which turns the powertrain into a mild hybrid and has an energy recovery output of up to 12 kW during braking. An eight‑speed tiptronic directs engine power to the quattro permanent all-wheel drive, which works closely with torque vectoring.
The prologue is powered by a biturbo V8 4.0 TFSI producing 445 kW (605 hp) and 700 N·m (516.3 lb‑ft) of torque; in overboost mode, which the driver can call up for around 15 seconds, a boosted torque of 750 N·m (553.2 lb‑ft) is available. The V8 accelerates the two‑door coupe, which has an unladen weight of 1,980 kilograms (4,365 lbs) from 0 to 100 km/h (62.1 mph) in 3.7 seconds.
Despite that performance, the show car’s combined fuel consumption is still only 8.6 liters per 100 kilometers (27.4 US mpg), which equates to CO2 emissions of 199 grams per kilometer (320.3 g/mile). One contributor to this high efficiency is the 48‑volt subsystem.
Dynamic all‑wheel steering, in which the rear wheels can turn up to five degrees, makes the large couple extremely responsive and stable while driving.
A study by a doctoral student in epidemiology at the Indiana University Richard M. Fairbanks School of Public Health at Indiana University-Purdue University Indianapolis showed that vehicle inequities have a significant impact on survivability in head-on collisions. Motor vehicle crashes are the most common cause of unintentional life lost around the world, with about 30,000 deaths occurring annually in the US due to motor-vehicle crashes.
Uzay Kirbiyik conducted a study of risk factors associated with drivers’ survival in head-on vehicle collisions by examining Fatality Analysis Reporting System database records in 1,108 crashes.
The results showed that the driver’s chance of survival was increased by driving a vehicle with a higher mass, driving a newer vehicle, being younger, being a male, using a seatbelt and having the airbag deployed in the crash.
Kirbiyik said his study found that more women die in head-on collisions, but deferred to medical trauma experts to explain why.
The study concludes that “vehicle inequity”, which includes differences like height and rigidity as well as weight, was a major cause of drivers’ fatalities. According to Kirbiyik, if you are in an automobile, given that other variables are equal, you are 17 times more likely to die compared to a driver of a light truck. This ratio is about nine times for a collision with an SUV.
According to the study, there were more young people between the ages of 15 and 24 involved in head-on collisions than any other age group. That age group accounts for 21% of the collisions, and the rate of death among that age group is 39%, the lowest among all age groups.
An intervention that reduces the involvement of younger drivers will likely help reduce the death rate of other age groups. This shouldn't be a surprise, but it is not an easy task to do.—Uzay Kirbiyik
Kirbiyik presented his study, “Factors affecting survival in head-on vehicle collisions” on 17 Nov. at the annual meeting of the American Public Health Association in New Orleans.
The European Advanced Lead-Acid Battery Consortium (EALABC) is delivering a paper this week outlining the consortium’s approach to 48V hybridization at the 2nd International Conference on Advanced Automotive 48V Power Supply Systems in Düsseldorf. The EALABC focus is on the environmental and cost benefits of current and future advanced lead-carbon batteries for 48V hybrid vehicles.
The state-of-charge (SoC) of current lead-carbon batteries is typically maintained at between 30 and 50%, with the voltage and amperage meeting VDA requirements by not exceeding 54V at 150A when recovering joules of energy from vehicle deceleration (kinetic energy recovery) and exhaust gas energy recuperation (thermal energy recovery), also dropping not less than 38V at 180A when discharging energy for engine starting and torque assist. Advanced lead-carbon batteries for vehicles currently under development will be capable of operating in the 30 to 70% SoC range at 12.5kW.
Additionally, says Allan Cooper, European projects coordinator for ALABC, as with conventional starter-motor batteries, advanced lead-carbon batteries can be charged at minus 30 °C (-22°F), which is not possible with lithium-ion batteries.
Significant emissions reduction and major improvements in fuel efficiency can be achieved with advanced lead-carbon batteries using materials that can be fully recycled into new batteries. This electrochemical breakthrough provides the most cost effective solution for 48V hybrids, which have a unique requirement for a battery demanding a high rate partial state-of-charge (HRPSoC) capability.—Allan Cooper
Augmenting its existing LC Super Hybrid program (earlier post), which deploys a downsized gasoline-electric powertrain, ALABC is working on advanced diesel-electric applications in development programs being undertaken with car makers including Ford and Kia.
Other industry partners comprise AVL Schrick, Controlled Power Technologies, East Penn, Exide, Faurecia, Furukawa, InnovateUK (previously known as the UK Technology Strategy Board), Mubea, Provector, Ricardo, University of Nottingham, US Department of Energy, and Valeo.
The Consortium’s global initiative is supported by test and validation programmes carried out at high and low altitudes in Arizona, and at Millbrook proving ground in the UK.
Future battery developments will most likely combine advanced lead-carbon electrochemistry with other types of battery design, for example bi-polar technology, which will reduce the lead content by as much as 40 percent, substantially reducing the size of a 1 kWh battery required for mild electrification of the powertrain. Meanwhile, advanced lead-carbon batteries, with their high levels of carbon in the negative active mass, already represent an exciting development that is truly state of the art, resulting in much improved battery performance ideally suited to 48V hybrids.—Allan Cooper
The additional functionality of a 48V hybrid vehicle fitted with a Belt Integrated Starter Generator (BISG), compared with simple 12V stop-start systems, characteristically includes torque assist as well as kinetic energy recovery. This is achieved effectively using electronically controlled switched-reluctance motor-generators, which avoid the need for rare earth permanent magnets.
These compact electrical machines can be rated up to 12.5 kW in a package little larger than a conventional alternator. Connected to the powertrain belt system, they avoid the cost and complexity of directly driving the road wheels.
ALABC has employed commercially available Exide Orbital batteries as well as Furukawa and East Penn UltraBattery packs in its technology development programs. The Exide Orbital absorbent glass mat battery is of spiral wound construction enhanced with added carbon in the negative plate.
The UltraBattery is a hybrid energy storage device invented by Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO). (Earlier post.) It combines ultra-capacitor technology with lead-carbon electrochemistry in a single cell with a common electrolyte. The result is an economical, fast-charging and discharging battery with high power and a long life, and can be made using existing manufacturing facilities. The technology has been licensed to East Penn, which is working on 14V modules as a building block for nominal 42V batteries required for 48V hybrid vehicles.
With further development of 48V powertrain technology, we anticipate being able to reduce CO2 emissions by as much as 30 percent compared with today’s baseline. Moreover, the low additional cost of €50-60 [$63-75] for each 1 percent of CO2 reduction achieved is as little as one-tenth the premium of high voltage (200-400V) hybrids and pure battery electric vehicles—which presently are deemed unaffordable by the average motorist.—Allan Cooper
The European Advanced Lead-Acid Battery Consortium (EALABC) is the London-based arm of its parent Advanced Lead-Acid Battery Consortium (ALABC) international research and development organisation based in North Carolina. Formed in 1992, the ALABC is dedicated to enhancing the capabilities and competitiveness of the advanced lead-carbon battery in various energy storage markets. These markets include telecommunications, remote area power supply (RAPS), 12V micro-hybrid stop-start systems, 48V mild hybrids with their torque assist and regeneration energy capabilities, as well as full hybrid vehicle applications.
TÜV SÜD Japan Ltd. is partnering with ESPEC Cooperation to build a test center for large battery systems in Japan. The aim is to offer a complete range of testing for traction batteries for electric vehicles in Japan in 2015. The new Japan lab will become the seventh in TÜV SÜD’s international network of battery labs.
Testing will range from cells to modules to packs, following international specifications and standards. Some of the standards that TÜV SÜD tests to include (but are not limited to): DOE/ID-11069; DOE/ID-11173; IEC 62660-1/2; IEC 62133; ISO 12405-1/2; SAE J2464; SAND 2005-3123; SBA S1101; and UN 38.3.
There will be a special focus on the new extension level 2 of the UN-ECE-R100. The revised UN-ECE R100 standard entered into force in July and is internationally mandatory as of July 2016. For the first time destructive testing of battery systems is required.
The new site in Japan will bring to 7 the number of TÜV SÜD laboratories (Germany, USA, Canada, China, Korea, Singapore, Japan) with identical test equipment and test procedures.
The TÜV SÜD Group in Japan was founded in 1993 with the aim to meet the growing demand in the Japanese market for modern quality and safety testing and certification requirements.
Good morning. Its great to be here in northern Texas to celebrate this important milestone. Id like to thank our partners from the airlines, NATCA, PASS, ALPA and APA (Allied Pilots Association), as well as the cities of Dallas and Fort Worth.
Just a little more than 40 years ago, leaders in Dallas and Fort Worth celebrated a great success when they opened what was then the largest airport in the world some 18,000 acres of Texas prairie that was destined to also become one of the worlds busiest airports.
Time and again, the aviation community in northern Texas has played a major role in advancing aviation safety. It was here that lifesaving technologies were developed and tested, such as wind-shear detection and radar that can track the movements of airplanes on busy taxiways and runways. Working with NASA and D/FW Airport, the FAA has looked to northern Texas to serve as a test bed for many satellite-based NextGen technologies that are now transforming our nations airspace.
A few weeks ago, the FAA flipped the switch on 80 new NextGen air traffic procedures in northern Texas. Overnight, we saw significant benefits to the complex airspace around northern Texas. Planes are flying fewer miles and burning less fuel. Flights are arriving a little earlier than before, and departures are able to get on their way even faster.
It was the most ambitious airspace optimization project that the FAA has undertaken in recent years. We estimate these procedures in the North Texas Metroplex could save airlines 4.1 million gallons in fuel each year, and allow aircraft to descend to the runway from cruise altitude with engines almost at idle.
It saves a lot of fuel because its like sliding down the banister rather than walking down the stairway, one stair at a time. A traditional descent requires an aircraft to level off at each new altitude, burning up fuel at each new step. Weve optimized the departure routes as well, to make optimum climbs and shorter routes. These departures also save fuel.
These new routes are the result of a collaborative effort with the airlines and our workforce. Using satellite-based NextGen technology, we have turned some of the most complex airspace in the country into some of the most efficient.
We created more efficient routes that separate traffic flowing into Love Field from that headed to D/FW. As a result, both airports can expect to operate more efficiently, and the flights taking off and landing at both airports are flying more precise flight paths.
We estimate jetliners will fly 1 million fewer nautical miles each year in northern Texas, based on flight plans.
Together, these new procedures and routes will prevent 41,000 metric tons of carbon dioxide from entering our atmosphere each year. Thats like taking 8,000 cars off the streets of Dallas and Fort Worth. NextGen improves efficiency and makes aviation greener.
This project takes into consideration the flight paths into not only the large commercial airports Dallas/Fort Worth and Love Field but also Alliance, Meacham, Dallas Executive, Arlington and Addison as well as other satellite airports to make the entire system work better.
NextGen is delivering significant benefits in northern Texas now. Around the United States, we are creating similar new airways that will relieve bottlenecks, improve safety, and foster the flow of commerce in more than a dozen major metropolitan areas.
Back in the 60s, the leaders in Dallas and Fort Worth had a vision to create a better air transportation system for future generations. We are carrying that commitment forward, with the North Texas Metroplex air traffic system.
I want to again thank the many people who worked so hard to modernize the northern Texas airspace. It took teamwork from all areas controllers, technicians, pilots, environmental specialists, managers, airlines and airports-to achieve such a great outcome. You have laid the groundwork for a modern air transportation system that will benefit generations to come.