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Defect migration in supercrystalline nanocomposites
No full textSupercrystalline nanocomposites (SCNCs) are nanostructured hybrid materials with a variety of unique functional properties. Given their periodically arranged building blocks, they also offer interesting parallels with crystalline materials. They can be processed in multiple forms and at different scales, and cross-linking their organic ligands via heat treatment leads to a boost of their mechanical properties. This study shows, via X-ray and in situ scanning transmission electron microscopy (STEM) analyses, how each of these processing steps plays a distinct role in the generation, migration, interaction, and healing of supercrystalline defects. Pressing of SCNCs into bulk pellets leads to a distortion of the otherwise fcc superlattice, while emulsion-templated self-assembly yields supraparticles (SPs) with stacking faults and size-dependent symmetries. Heat treatment at the same temperatures as those applied for the organic cross-linking has significant effects on planar defects. Stacking faults migrate and get healed, as also confirmed via molecular dynamics simulations, and intersupercrystalline “grain” boundaries migrate via anisotropic motion of disconnections. These rearrangements of defects at the supercrystalline scale (tens of nanometers) in nanocomposites with high mechanical properties (compressive strength of 100–500 MPa) provide insights into the formation and evolution of ordered assemblies of functionalized nanoparticles
Robust design optimization of structures with multimodal responses using Taylor expansions
No full textThis paper shows how a combination of multiple linear approximations can efficiently capture nonlinear and non-smooth response functions in the framework of robust design optimization. The basic idea is to split the domain of random parameters into multiple subdomains along discontinuities of the response. For each subdomain, a linear approximation is used to determine the stochastic moments of the response function due to the scatter in that subdomain. The total stochastic distribution of the structural response is considered to be a multimodal distribution, and its moments are composed of the approximations in the subdomains. The application to use cases shows that indeed the structural response is multimodal in these cases, and the stochastic moments are shown to be sufficiently accurate using the proposed method
Supporting medical phantom design through a comprehensive design catalogue for phantom materials
No full textMedical phantoms are models used for imaging and therapy, enabling research, quality assurance, and training without human test subjects. Their development relies on selecting tissue-mimicking materials, however the lack of a holistic overview to guide this process poses challenges. This work presents a comprehensive design catalogue for phantom materials, offering a structured overview of materials and their imaging properties for computed tomography (CT), magnetic resonance imaging, and ultrasound, including parameters such as CT numbers, relaxation times, and acoustic properties. It is implemented as a digital tool with filtering options, enhancing usability and decision-making. Despite limitations from incomplete data in the literature, the catalogue establishes a groundwork for a standardized, expandable resource to support future phantom design
Effects of new ways of working in product development - a systematic evaluation in an engineering simulator
No full textThis study explores the impact of new work practices on product development in an Engineering Simulator by comparing traditional practices with new ways of working in a compressed product development process. By introducing flexibility, digital tools, and autonomy, the study highlights improvements in individual productivity and innovation. For example, teams employing new work practices developed their first prototypes 30% faster than control groups. However, challenges in communication and team dynamics emerge, underscoring the need for structured support systems. The findings further suggest that while these modern practices foster creativity and efficiency, successful implementation at the organizational level requires balancing autonomy with clear guidelines and effective management. This study provides actionable insights for adapting new work methods to engineering environments
Causal analyses on entrepreneurial intention, success, and failure
No full textThis dissertation embarks on two complementary paths: (i) it investigates how contextual and structural factors influence entrepreneurial intention, success, and recovery from failure, and (ii) it highlights recent advancements in causal inference, focusing on the identification of treatment effects through valid and robust research designs. The work offers new insights into key phenomena across the entrepreneurial life cycle and proposes methodological approaches to address empirical challenges in entrepreneurship and management science.Diese Dissertation verfolgt zwei zentrale Zielsetzungen: (i) sie untersucht, wie kontextuelle und strukturelle Faktoren unternehmerische Intentionen, Erfolg sowie den Umgang mit dem Scheitern prägen, und (ii) sie greift aktuelle Entwicklungen der kausalen Inferenz auf, um mithilfe robuster Forschungsdesigns kausale Effekte valide zu identifizieren und zu schätzen. Die Arbeit liefert neue Einblicke in zentrale Phänomene des unternehmerischen Prozesses und präsentiert methodische Ansätze der empirischen Analyse in der Entrepreneurship- und Managementforschung
The tasks and traps of sustainability certification organizations
No full textAlthough sustainability certifications are widespread, the challenges confronting the sustainability certification organizations (SCOs) who develop, promote and administer such certifications have received less attention. We argue that SCOs face three task domains: legitimacy management, organizational learning, and stakeholder engagement. Critically, these domains are interdependent; a preoccupation with one domain poses limitations on the others. First, an emphasis on legitimacy management can inhibit organizational learning, leading to the advocacy trap. Second, an emphasis on stakeholder engagement can inhibit learning processes, leading to the inertia trap. Third, an emphasis on legitimacy management can inhibit stakeholder engagement, leading to the mobilization trap. Collectively, these challenges constitute the trap triangle. Building on our theoretical model, we develop propositions about how SCOs fall into these traps and how they can overcome them. Finally, recognizing SCOs vary in terms of their movement, market or mission orientations leads to propositions about the traps each type of SCO is most likely to fall into. We close the article by discussing our contributions to the literature on sustainability certifications and environmental governance
HOOU an der TU Hamburg : Jahresbericht 2024
No full textIn diesem Bericht stellt die Hamburg Open Online University an der TU Hamburg (HOOU@TUHH) ihre Arbeit im Jahr 2024 vor
Flame-retardant composites and analysis of their residual strengths after tailored flame tests
No full textIn recent decades, fibre-reinforced polymers (FRPs) have become a key factor to realise lightweight design, e.g., to safe fuel in mobility applications. As FRPs are usually combustible, flame retardants (FRs) are necessary to fulfil critical requirements. On the one hand, FRs can negatively affect thermo-mechanical properties of composites and should therefore used as little as possible. On the other hand, frequently used infusion processes to manufacture FRPs are no longer possible due to filtration effects, if the FRs are present as particles. However, novel in this study is the use of a combined prepreg and infusion process to solve both challenges by implementing FRs only in the most exposed plies. Simultaneously, this method enables the manufacturing of large parts with implemented FR particles, without compromising the lightweight potential or causing adhesion challenges through the use of FR gel-coats. As part of this study, tailored flame tests with adequate reproducibility were developed for qualitative comparisons between different configurations and the residual compressive strength was determined afterwards, because the structural integrity in fire scenarios is of special importance in mobility applications. It was found, that despite a very low global amount of ≈ 1.5 - 3 % red phosphorus leads to significant improvements in the residual strength compared to unmodified configurations
Computational fluid dynamics technologies and applications for offshore floating structures: Progress and perspectives
No full textOffshore floating structures face intricate multiscale flows, making their design a significant engineering challenge. Computational fluid dynamics (CFD) has become indispensable in designing these structures and their components. Beyond design purposes, CFD deepens fundamental understanding by revealing fluid dynamics in previously poorly characterized flows. This paper reviews current CFD technologies and their applications in offshore floating structures while exploring future prospects. The key challenges are identified to guide professionals in extending technology lifecycles and enhancing capabilities. These insights underscore a crucial research direction for developing the next generation of offshore floating structures
Ansatz zur mechanischen Schwingungsbeeinflussung mittels Dynamisch Adaptiver Impedanzelemente in der Versuchstechnik
No full textThe interface properties are a key factor in the vibration behaviour of technical systems, making it relevant in vibration testing. The potential of Dynamically Adaptive Impedance Elements (DAIEs) as interfaces between the test bench and the test object is derived from two distinct fields of application: the vibration reduction of lightweight structures in the aircraft cabin and the vibration analysis of handheld devices in the human-machine interaction. DAIEs are semi-active interface elements that enable the adaptation of the interface stiffness and damping during test-ing, thus facilitating the replication of multi-steady-state as well as transient behaviour in the testing environment.Deutsche Forschungsgemeinschaft (DFG