| 1. |
- Lange, Jonathan, et al.
(författare)
-
Novel lithographic printing techniques enabling sustainable and high quality multi material manufacturing process for future space outposts
- 2021
-
Ingår i: IAC 2021 Congress Proceedings, 72nd International Astronautical Congress (IAC), Dubai, United Arab Emirates. - : International Astronautical Federation (IAF).
-
Konferensbidrag (refereegranskat)abstract
- Several challenges remain before the full potential of on-orbit manufacturing can be realized. There may be some limitations to the types of items that can be manufactured in space. Such limitations could be caused by a variety of factors, including the materials required for a particular structure, the size of the object to be manufactured, the time required to execute the architecture, the configuration of the object being manufactured, and the raw material needed to support the manufacturing process. The complementary challenge to the relevant fabrication processes is the possibility to achieve the required precision demanded by geometrically complex structures and the ability to be versatile in processing a broad material spectrum. In this context, novel lithographic 3D printing techniques will be an asset to pave the way towards overcoming these challenges. Currently, the European Space Agency (ESA) is investigating the implementation of such technology in the context of a lunar base. In particular, two different applications are being studied: • Lithography-Based Ceramic Manufacturing (LCM), where the ceramic powder is distributed in a photocurable monomer formulation in presence of a photoinitiator. Ceramic materials are extensively used in a vast number of technological processes as well as in space applications. They are usually considered as the material of choice for applications where other materials such as plastic and metal fail to deliver the required performance. The LCM process will also allow processing lunar regolith simulant adding value to the current material portfolio of this technique, as well as to the range of processes potentially applicable on the lunar or Martian surface. • Lithography-based Metal Manufacturing (LMM) for processing metallic powders. In contrast to the currently predominantly used powder bed fusion (direct metal laser melting) techniques, this process uses a paste/suspension as feedstock and hence, does not rely on the use of highly spherical gas atomized powders. This will enable the utilization of recycled powders from scrap metals that are available at Moon bases or of metallic alloys reduced from lunar regolith, thus providing higher flexibility in accepting raw material with poor quality and purity. The paper addresses the results from both activities in terms of printed parts quality (roughness, density, resolution and accuracy) as well as the implementation requirements for the whole process chain, including suitable pre- and post-processing steps, with the aim to achieve a zero-waste flow in a lunar environment.
|
|
| 2. |
- Riede, M., et al.
(författare)
-
Material characterization of AISI 316L flexure pivot bearings fabricated by additive manufacturing
- 2019
-
Ingår i: Materials. - : MDPI. - 1996-1944 .- 1996-1944. ; 12:15
-
Tidskriftsartikel (refereegranskat)abstract
- Recently, additive manufacturing (AM) by laser metal deposition (LMD) has become a key technology for fabricating highly complex parts without any support structures. Compared to the well-known powder bed fusion process, LMD enhances manufacturing possibilities to overcome AM-specific challenges such as process inherent porosity, minor build rates, and limited part size. Moreover, the advantages aforementioned combined with conventional machining enable novel manufacturing approaches in various fields of applications. Within this contribution, the additive manufacturing of filigree flexure pivots using 316L-Si by means of LMD with powder is presented. Frictionless flexure pivot bearings are used in space mechanisms that require high reliability, accuracy, and technical cleanliness. As a contribution to part qualification, the manufacturing process, powder material, and fabricated specimens were investigated in a comprehensive manner. Due to its major impact on the process, the chemical powder composition was characterized in detail by energy dispersive X-ray spectroscopy (EDX) and inductively coupled plasma optical emission spectrometry (ICP-OES). Moreover, a profound characterization of the powder morphology and flowability was carried out using scanning electron microscopy (SEM) and novel rheological investigation techniques. Furthermore, quantitative image analysis, mechanical testing, laser scanning microscopy, and 3D shape measurement of manufactured specimens were conducted. As a result, the gained knowledge was applied for the AM-specific redesign of the flexure pivot. Finally, a qualified flexure pivot has been manufactured in a hybrid manner to subsequently ensure its long-term durability in a lifetime test bench.
|
|
| 3. |
- Cowie, A. L., et al.
(författare)
-
Applying a science-based systems perspective to dispel misconceptions about climate effects of forest bioenergy
- 2021
-
Ingår i: Global Change Biology Bioenergy. - : John Wiley and Sons Inc. - 1757-1693 .- 1757-1707. ; 13:8, s. 1210-1231
-
Tidskriftsartikel (refereegranskat)abstract
- The scientific literature contains contrasting findings about the climate effects of forest bioenergy, partly due to the wide diversity of bioenergy systems and associated contexts, but also due to differences in assessment methods. The climate effects of bioenergy must be accurately assessed to inform policy-making, but the complexity of bioenergy systems and associated land, industry and energy systems raises challenges for assessment. We examine misconceptions about climate effects of forest bioenergy and discuss important considerations in assessing these effects and devising measures to incentivize sustainable bioenergy as a component of climate policy. The temporal and spatial system boundary and the reference (counterfactual) scenarios are key methodology choices that strongly influence results. Focussing on carbon balances of individual forest stands and comparing emissions at the point of combustion neglect system-level interactions that influence the climate effects of forest bioenergy. We highlight the need for a systems approach, in assessing options and developing policy for forest bioenergy that: (1) considers the whole life cycle of bioenergy systems, including effects of the associated forest management and harvesting on landscape carbon balances; (2) identifies how forest bioenergy can best be deployed to support energy system transformation required to achieve climate goals; and (3) incentivizes those forest bioenergy systems that augment the mitigation value of the forest sector as a whole. Emphasis on short-term emissions reduction targets can lead to decisions that make medium- to long-term climate goals more difficult to achieve. The most important climate change mitigation measure is the transformation of energy, industry and transport systems so that fossil carbon remains underground. Narrow perspectives obscure the significant role that bioenergy can play by displacing fossil fuels now, and supporting energy system transition. Greater transparency and consistency is needed in greenhouse gas reporting and accounting related to bioenergy.
|
|
| 4. |
- Moritz, J., et al.
(författare)
-
Functional integration approaches via laser powder bed processing
- 2019
-
Ingår i: Journal of laser applications. - : Laser Institute of America. - 1042-346X .- 1938-1387. ; 31:2
-
Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing design rules are different from those of conventional fabrication techniques. These allow geometries that would not be possible to achieve otherwise. One example of application is the integration of functional parts as part of the manufacturing process. Conceivable applications range from mechanical functions like integration of moving parts or thermodynamic functions, for example, cooling channels or incorporation of electric circuits for electrical functionalization [J. Glasschroeder, E. Prager, and M. F. Zaeh, Rapid Prototyping J. 21, 207–215 (2015)]. Nevertheless, the potential of functional integration using powder-bed processes is far from being exhausted. The present approach addresses the generation of inner cavities and internal structures of titanium-based parts or components by the use of selective laser melting. This paper focusses on the investigation of voids and cavities regarding their capabilities to add new functions to the material. To this end, comprehensive characterization is performed using destructive as well as nondestructive testing methods. These include 3D scanning, computed tomography, and surface roughness measurements as well as microscopic analysis. Voids and cavities were filled with different thermoplastic materials, followed by the qualitative assessment of the mold filling and resulting material properties. Finally, applications are derived and evaluated with respect to the field of lightweight design or damping structures.
|
|
| 5. |
- Bartoli, A., et al.
(författare)
-
Coupling economic and GHG emission accounting models to evaluate the sustainability of biogas policies
- 2019
-
Ingår i: Renewable & sustainable energy reviews. - : Elsevier. - 1364-0321 .- 1879-0690. ; 106, s. 133-148
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this study is to evaluate and quantify the impacts of different biogas and related policies on the agricultural sector as well as their performance in terms of climate change mitigation and associated costs. To do so we coupled the partial equilibrium approach simulating the market clearing process with the perspective of Life Cycle Assessment of GHG applying it to the well-documented Lombardy case. Results show that the recent Italian biogas policy – prompting manure utilization and reducing the average subsidy per kWh – effectively increased the environmental sustainability of the system, which only now seems able to counteract global warming. Synergies are observed when the recent Common Agricultural Policy greening reform is simultaneously considered by the model.
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
- Dale, Virginia H., et al.
(författare)
-
Status and prospects for renewable energy using wood pellets from the southeastern United States
- 2017
-
Ingår i: Global Change Biology Bioenergy. - : Wiley-Blackwell. - 1757-1693 .- 1757-1707. ; 9:8, s. 1296-1305
-
Tidskriftsartikel (refereegranskat)abstract
- The ongoing debate about costs and benefits of wood-pellet based bioenergy production in the southeastern United States (SE USA) requires an understanding of the science and context influencing market decisions associated with its sustainability. Production of pellets has garnered much attention as US exports have grown from negligible amounts in the early 2000s to 4.6 million metric tonnes in 2015. Currently, 98% of these pellet exports are shipped to Europe to displace coal in power plants. We ask, 'How is the production of wood pellets in the SE USA affecting forest systems and the ecosystem services they provide?' To address this question, we review current forest conditions and the status of the wood products industry, how pellet production affects ecosystem services and biodiversity, and what methods are in place to monitor changes and protect vulnerable systems. Scientific studies provide evidence that wood pellets in the SE USA are a fraction of total forestry operations and can be produced while maintaining or improving forest ecosystem services. Ecosystem services are protected by the requirement to utilize loggers trained to apply scientifically based best management practices in planning and implementing harvest for the export market. Bioenergy markets supplement incomes to private rural landholders and provide an incentive for forest management practices that simultaneously benefit water quality and wildlife and reduce risk of fire and insect outbreaks. Bioenergy also increases the value of forest land to landowners, thereby decreasing likelihood of conversion to nonforest uses. Monitoring and evaluation are essential to verify that regulations and good practices are achieving goals and to enable timely responses if problems arise. Conducting rigorous research to understand how conditions change in response to management choices requires baseline data, monitoring, and appropriate reference scenarios. Long-term monitoring data on forest conditions should be publicly accessible and utilized to inform adaptive management.
|
|
| 9. |
|
|
