Search
Now showing items 11-20 of 26
Aufsatz
Optimal attitude maneuvers in the presence of prohibited directions
(2023-05-31)
We consider the problem of realigning a space telescope from one observation target to the next in the presence of prohibited directions. More specifically, we want to steer the space telescope – modelled as a gyrostat – from an initial attitude at rest to a final attitude at rest within a fixed time interval. During the motion, the line of sight of the telescope must be kept away from forbidden directions towards bright objects like the sun, moon or earth due to power or thermal requirements. The kinematics of the ...
Aufsatz
Influence of Mean Stress on Lifetime Prediction of Adhesive Bonds
(2023-05-31)
The importance of adhesive bonds in the field of joining technology is increasing due to their advantageous properties. One of these attributes is the possibility to reduce the weight compared to welded joints in group of components. For a safe design, the knowledge of the lifetime of these components is essential. Various methods are used for the prediction of the lifetime under cyclic loading. On the one hand there are test-based methods, on the other hand simulation-based approaches. Test-based ones are often ...
Aufsatz
Hybrid modeling of viscoelastic and switching–induced heating in ferroelectrics
(2023-03-24)
This contribution focuses on two effects causing a temperature change in electrically loaded ferroelectrics. These materials are often subjected to cyclic loading, where viscoelasticity prevails at lower electric fields, whereas dissipative heating by domain switching dominates above the coercive field. While viscoelasticity is modeled within a phenomenological, rheological framework, the ferroelectric constitutive behaviour is described based on a microphysical model. Merging both approaches results in the hybrid ...
Aufsatz
Effect of Crystallographic Orientation and Grain Boundaries on Martensitic Transformation and Superelastic Response of Oligocrystalline Fe–Mn–Al–Ni Shape Memory Alloys
(2021-07-26)
In situ tensile tests employing digital image correlation were conducted to study the martensitic transformation of oligocrystalline Fe–Mn–Al–Ni shape memory alloys in depth. The influence of different grain orientations, i.e., near-〈001〉 and near-〈101〉, as well as the influence of different grain boundary misorientations are in focus of the present work. The results reveal that the reversibility of the martensite strongly depends on the type of martensitic evolving, i.e., twinned or detwinned. Furthermore, it is ...
Aufsatz
Simultaneous impact modified and chain extended glass fiber reinforced poly(lactic acid) composites: Mechanical, thermal, crystallization, and dynamic mechanical performance
(2021-02-05)
Herein, glass fiber (GF) reinforced binary, ternary, and quaternary poly(lactic acid) (PLA) composites were prepared. Toughening, and chain extension of PLA was achieved through the incorporation of impact modifier and chain extender and their concurrent effects on the spectroscopic, crystallization, mechanical, thermal, and thermomechanical properties of the composites were investigated. High mechanical properties of GF influenced the mechanical performance of the composites. However, GF alone could not restrict the ...
Aufsatz
On the Reliability of Automated Analysis of Fracture Surfaces Using a Novel Computer Vision-Based Tool
(2023-08-05)
Fracture surface analysis is of utmost importance with respect to structural integrity of metallic materials. This especially holds true for additively manufactured materials. Despite an increasing trend of automatization of testing methods, the analysis and classification of fatigue fracture surface images is commonly done manually by experts. Although this leads to correct results in most cases, it has several disadvantages, e.g., the need of a huge knowledge base to interpret images correctly. In present work, an ...
Aufsatz
Cyclic Superelastic Behavior of Iron-Based Fe-Ni-Co-Al-Ti-Nb Shape Memory Alloy
(2023-01-03)
Iron-based shape memory alloys came into focus as promising candidate materials for large-scale structural applications owing to their cost-efficiency. In the present work, the superelastic properties of a recently introduced Fe-Ni-Co-Al-Ti-Nb shape memory alloy are investigated. For 〈001〉-oriented single-crystalline material in aged condition (650 °C/6 h), an incremental strain test reveals excellent superelasticity at −130 °C with fully reversible strains up to about 6%. Under cycling loading at different test ...
Aufsatz
Influence of Microstructure and Defects on Mechanical Properties of AISI H13 Manufactured by Electron Beam Powder Bed Fusion
(2021-08-04)
Electron beam powder bed fusion (E-PBF) is a well-known additive manufacturing process. Components are realized based on layer-by-layer melting of metal powder. Due to the high degree of design freedom, additive manufacturing came into focus of tooling industry, especially for tools with sophisticated internal cooling channels. The present work focuses on the relationships between processing, microstructure evolution, chemical composition and mechanical properties of a high alloyed tool steel AISI H13 (1.2344, ...
Aufsatz
On the Impact of Build Envelope Sizes on E-PBF Processed Pure Iron
(2021-11-17)
In additive manufacturing, the thermal history of a part determines its final microstructural and mechanical properties. The factors leading to a specific temperature profile are diverse. For the integrity of a parameter setting established, periphery variations must also be considered. In the present study, iron was processed by electron beam powder bed fusion. Parts realized by two process runs featuring different build plate sizes were analyzed. It is shown that the process temperature differs significantly, ...
Aufsatz
Hot Work Tool Steel Processed by Laser Powder Bed Fusion: A Review on Most Relevant Influencing Factors
(2021-03-26)
As a representative of a common carbon-bearing hot work tool steel AISI H13 is in focus of the present review paper. Most relevant details for processing of AISI H13 by laser powder bed fusion (L-PBF) are systematically investigated. Three common stages of process parameter development and material assessment, respectively, are in focus: general processibility, process refinement, and deduction of process–microstructure–property relations, i.e., understanding of the interplay of relevant elementary mechanisms. On the ...