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Aufsatz
Additive manufacturing of Co-Ni-Ga high-temperature shape memory alloy - Processability 3 and phase transformation behavior
(2019)
Co-Ni-Ga high-temperature shape memory alloy is additively processed by selective laser melting for the first time. Reversiblemartensitic transformation of the as-built material is proven by differential scanning calorimetry. Microstructural analysis reveals a columnar-grained microstructure due to epitaxial solidification. Columnar-grained microstructures are characterized by a very low degree of constraints being beneficial for superior functional performance in numerous shape memory alloys. However, process-induced ...
Aufsatz
Investigations on Tightness of Polymer-Metal Hybrids in Environments with Thermal, Media, and Mechanical Loads
(2017-07-31)
With polymer-metal hybrids becoming more commonly used as structural components it was investigated how they perform in complex environments with combined thermal, media, and mechanical loads. Special attention was put on media tightness under said loads. This paper sums up the activities of the polymer technology research group of the University of Kassel on hybrids produced by overmolding metal inserts. Investigations concerning joint strength and influence of (cyclic) temperature loads and chemical corrosion on ...
Aufsatz
Mechanical Properties of Polydimethylsiloxane as a Function of the Amount and Type of Crosslinking Agent
(2017-06-13)
In this investigation, a high-consistency rubber (HCR) was mixed with five different, typically used crosslinking agents that are based on organic peroxide. Furthermore, the amount of crosslinking agent was varied in order to quantify the effect on the mechanical properties. All materials were processed in a hot pressing process, and, subsequently, post-cured. The properties were characterized by the measurement of the swelling ratio, shore A-hardness, rebound resilience and tensile test. We successfully proved that ...
Aufsatz
Microstructure of an additively manufactured Ti-Ta-Al alloy using novel pre-alloyed powder feedstock material
(2023-05-01)
Binary Ti-Ta and ternary Ti-Ta-Al alloys attracted considerable attention as new potential biomaterials and/or high-temperature shape memory alloys. However, conventional forming and manufacturing technologies of refractory based titanium alloys are difficult and cost-intensive, especially when complex shapes are required. Recently, additive manufacturing (AM) emerged as a suitable alternative and several studies exploited elemental powder mixing approaches to obtain a desired alloy and subsequently use it for complex ...
Aufsatz
Pathways towards grain boundary engineering for improved structural performance in polycrystalline Co-Ni-Ga shape memory alloys
(2018)
Co-Ni-Ga high-temperature shape memory alloys attracted a lot of scientific attention due to their superior functional material properties in recent years. In the single crystalline state Co-Ni-Ga HT-SMAs feature a good pseudoelastic response up to 500°C. However, in the polycrystalline condition Co-Ni-Ga suffers significant grain constraints and premature fracture at grain boundaries. In this regard, crystallographic orientation of the grain being involved as well as morphology and geometrical orientation of the ...
Aufsatz
Influence of ethylene oxide and gamma irradiation sterilization processes on the degradation behaviour of poly(lactic acid) (PLA) in the course of artificially accelerated aging
(2024-02-10)
To promote the application of bio-based materials in the field of medical technology, it is essential to conduct additional research, focusing on their long-term performance after sterilization. For this purpose, the study examines the aging behaviour of three poly(lactic-acid) (PLA) materials, sterilized with either ethylene oxide or gamma irradiation, over a two years aging period, in accordance with ASTM F1980-21. During these investigations, a direct correlation between moisture absorption and degradation progression ...
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
In-situ full-field deformation analysis of injection-molded microcellular polycarbonate according to foam morphology patterns
(2023-06-02)
Deformation behavior of microcellular foam materials are sensitive to microstructural details. Therefore, the distinctive foam morphology patterns of foam injection-molded Polycarbonate are identified. These morphology patterns are investigated regarding their cell size, distance between cells, cell density, density reduction, homogeneity of cell size distribution, sphericity of cells and cell volume. Consequently, the predefined foam morphologies, the resulting modulus of elasticity and the elongation at break are ...
Aufsatz
Shape Memory Effect and Superelasticity of [001]-Oriented FeNiCoAlNb Single Crystals Aged under and without Stress
(2021-06-10)
The two-step ageing of Fe-28Ni-17Co-11.5Al-2.5Nb (at.%) single crystals under and without stress, leads to the precipitation of the γ′- and β-phase particles. Research has shown that γ–α′ thermoelastic martensitic transformation (MT), with shape memory effect (SME) and superelasticity (SE), develops in the [001]-oriented crystals under tension. SE was observed within the range from the temperature of the start of MT upon cooling Mₛ, to the temperature of the end of the reverse MT upon heating Af, and at temperatures ...
Aufsatz
Experimental Analysis of Residual Stresses in CFRPs through Hole-Drilling Method: The Role of Stacking Sequence, Thickness, and Defects
(2023-05-09)
Carbon fiber reinforced plastics (CFRPs) gained high interest in industrial applications because of their excellent strength and low specific weight. The stacking sequence of the unidirectional plies forming a CFRP laminate, and their thicknesses, primarily determine the mechanical performance. However, during manufacturing, defects, e.g., pores and residual stresses, are induced, both affecting the mechanical properties. The objective of the present work is to accurately measure residual stresses in CFRPs as well ...