Periodic cellular aluminum structures for space applications:from casting to additive manufacturing

Mass is one of the crucial parameters for hardware that has to be placed in Earth orbit. Due to its harsh environment, a material with highest specific properties is desired to achieve space missions. The rise and development of new technologies, such as additive manufacturing (AM), opened new opportunities in part-design complexity, periodic cellular structures (PCS) being one of them. The present thesis investigates the potential implementation of PCS in space applications, particularly for structures and micro-meteoroids and orbital debris (MMOD) impact shields. This was achieved in three steps: Four different types of AlSi12 PCS manufactured by selective laser melting (SLM) were tested under quasi-static compression to measure the mechanical properties dependency versus topology and to characterize the failure mode. Properties ranging from 3 to 4 GPa for the compressive modulus, 5 to 12 MPa for the yield stress, 12 to 20 MPa for the plateau stress, and 2 to 8 MJ/cm3 for the absorbed energy were obtained. An unexpected failure mode was observed when compared to classical cellular metals, namely a brittle failure occurring by global shearing. A predictive failure criterion was established based on topology considerations and correlated to most of the reported results in the literature. A preliminary test campaign on tensile specimens was performed to compute numerical models that were fed into a finite element analysis. Good agreement with experimental data was shown, and the importance of microplasticity effects in this class of material was highlighted. An alternative process was developed to produce AlSi1 PCS by investment casting. The process is based on replication of a polymer preform used to build a NaCl mold. It was observed that the quality of the final cast part depends mainly on the grain size of the salt, with an optimum identified for distributions between 125 and 180 um. Optimization of the process allowed to reduce the drying time by a factor 6. Main process parameters include a drying temperature of 80C and infiltration at 660C under 300 mbar. From this process, PCSs having an energy absorption capacity of 15 MJ/m3 with an efficiency of 80% were produced. Hypervelocity impact tests were conducted on cast PCS and stochastic structures. The objective being to hit the structures with a 2mm-diameter aluminum sphere at velocities close to 7 km/s. Influence of the sample topology, the orientation, and the bumper material was assessed. Stochastic structures successfully stopped the projectile in all configurations. The beneficial effect of the bumper was measured reducing the crater depth from 20 mm to 14 mm. This type of structure exhibited a comparable areal density (0.8 g/cm2) to simple Whipple shield design. PCS poorly performed in mitigating the impact as the debris passed through all the structures, independently of the test configuration due to the open-channels present. PCS are good candidates to be used in space hardware, but their design and the manufacturing process need to be carefully chosen depending on the specific application. AM PCS are suitable for structural application with a high compressive modulus and yield stress. Cast PCS would perfectly fit in shock absorbers. A more random design would be preferable for MMOD shielding applications

Synthesis of Zeolites from Fine-Grained Perlite and Their Application as Sorbents

The hydrothermal alteration of perlite into zeolites was studied using a two-step approach. Firstly, perlite powder was transformed into Na-P1 (GIS) or hydro(xy)sodalite (SOD) zeolites at 100 °C and 24 h using 2 or 5 M NaOH solutions. Secondly, the Si:Al molar ratio of the reacted Si-rich solution was adjusted to 1 by Na-aluminate addition to produce zeolite A (LTA) at 65 or 95 °C and 6 or 24 h at an efficiency of 90 ± 9% for Al and 93 ± 6% for Si conversion. The performance of these zeolites for metal ion removal and water softening applications was assessed by sorption experiments using an artificial waste solution containing 4 mmol/L of metal ions (Me(2+): Ca(2+), Mg(2+), Ba(2+) and Zn(2+)) and local tap water (2.1 mmol/L Ca(2+) and 0.6 mmol/L Mg(2+)) at 25 °C. The removal capacity of the LTA-zeolite ranged from 2.69 to 2.86 mmol/g for Me(2+) (=240–275 mg/g), which is similar to commercial zeolite A (2.73 mmol/g) and GIS-zeolite (2.69 mmol/g), and significantly higher compared to the perlite powder (0.56 mmol/g) and SOD-zeolite (0.88 mmol/g). The best-performing LTA-zeolite removed 99.8% Ca(2+) and 93.4% Mg(2+) from tap water. Our results demonstrate the applicability of the LTA-zeolites from perlite for water treatment and softening applications

Channeling Contraband: How States Shape International Smuggling Routes

Although smuggling is commonly assumed to happen in remote and difficult-to-access borderlands, in reality, smuggling is most prevalent in areas that states tightly control, including at formal border crossings. To understand this puzzle, this article explores the relationship between states and smugglers at international borders. Based on extensive empirical research in various borderlands in North Africa and Southeast Asia, it argues that different kinds of smugglers prefer different types of relationships with the state. The article outlines six ideal types of such relationships. It contends that these types of relationships are the dominant factor in how different smuggling networks choose routes along a border. The findings have implications for our understanding of smuggling and policies that aim at addressing smuggling, especially regarding the effects of border fortifications and corruption prevention

The Routledge Handbook of Smuggling

The Routledge Handbook of Smuggling offers a comprehensive survey of interdisciplinary research related to smuggling, reflecting on key themes, and charting current and future trends. Divided into six parts and spanning over 30 chapters, the volume covers themes such as mobility, borders, violent conflict, and state politics, as well as looks at the smuggling of specific goods – from rice and gasoline to wildlife, weapons, and cocaine. Chapters engage with some of the most contentious academic and policy debates of the twenty-first century, including the historical creation of borders, re-bordering, the criminalisation of migration, and the politics of selective toleration of smuggling. As it maps a field that contains unique methodological, ethical, and risk-related challenges, the book takes stock not only of the state of our shared knowledge, but also reflects on how this has been produced, pointing to blind spots and providing an informed vision of the future of the field. Bringing together established and emerging scholars from around the world, The Routledge Handbook of Smuggling is an indispensable resource for students and researchers of conflict studies, borderland studies, criminology, political science, global development, anthropology, sociology, and geography.Please note: this is a large file. Individual chapters can be downloaded from the link under "more details" below

Beyond greed: why armed groups tax

Based on a review of the diverse practices of how armed groups tax, we highlight that a full account of why armed groups tax needs to go beyond revenue motivations, to also engage with explanations related to ideology, legitimacy, institution building, legibility and control of populations, and the performance of public authority. This article builds on two distinct literatures, on armed groups and on taxation, to provide the first systematic exploration of the motivations of armed group taxation. We problematize common approaches toward armed group taxation and state-building, and outline key questions of a new research agenda

Humanitarian Smuggling in a Time of Restricting and Criminalizing Mobility

A remarkable finding from studies that take migrants’ perspectives on human smuggling into account is that smugglers’ services are often described in the context of ‘saving lives.’ Apart from smugglers who are in for profit, there are people involved in the smuggling industry who want to help migrants find protection. These ‘humanitarian smugglers’ range from religious organisations, charities, NGOs, private initiatives, celebrities, to migrant’s family members. In this chapter it is argued that criminalization of human smuggling and the lumping together of very different smuggling activities is morally unjust and involves serious human rights violations

Humanitarian Smuggling in a Time of Restricting and Criminalizing Mobility

A remarkable finding from studies that take migrants’ perspectives on human smuggling into account is that smugglers’ services are often described in the context of ‘saving lives.’ Apart from smugglers who are in for profit, there are people involved in the smuggling industry who want to help migrants find protection. These ‘humanitarian smugglers’ range from religious organisations, charities, NGOs, private initiatives, celebrities, to migrant’s family members. In this chapter it is argued that criminalization of human smuggling and the lumping together of very different smuggling activities is morally unjust and involves serious human rights violations