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Innovative Materials for Novel Concepts for Internal Heat Exchangers
(2018-07-27)
Internal heat exchangers are often employed in solar thermal applications as well as in many other applications that involve heat, and, for the most part, consist of metallic materials (copper, stainless steel). Corrugated stainless steel tubes are easy to assemble, and are commonly used in various storage geometries. In order to significantly reduce costs, alternative materials, such as plastics, can function as excellent substitutes. Alternative heat exchangers for the following examinations using various materials ...
Aufsatz
Influence of the Miniaturisation Effect on the Effective Stiffness of Lattice Structures in Additive Manufacturing
(2020-10-29)
Thin-walled and cellular structures are characterised by superior lightweight potential due to their advantageous stiffness to weight ratio. They find particular interest in the field of additive manufacturing due to robust and reproducible manufacturability. However, the mechanical performance of such structures strongly depends on the manufacturing process and resultant geometrical imperfections such as porosity, deviations in strut thickness or surface roughness, for which an understanding of their influence is ...
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Damage Tolerance Evaluation of E-PBF-Manufactured Inconel 718 Strut Geometries by Advanced Characterization Techniques
(2020-01-06)
By means of electron beam powder bed fusion (E-PBF), highly complex lightweight structures can be manufactured within short process times. Due to the increasing complexity of producible components and the entangled interplay of damage mechanisms, common bulk material properties such as ultimate tensile or fatigue strength are not sufficient to guarantee safe and reliable use in demanding applications. Within this work, the damage tolerance of E-PBF-manufactured Ni-based alloy Inconel 718 (IN 718) strut geometries ...
Aufsatz
Determination and Validation of Residual Stresses in CFRP/Metal Hybrid Components Using the Incremental Hole Drilling Method
(2020-09-21)
Lightweight materials contribute to an efficient decrease in fuel consumption in the automotive and aircraft industries. Hybrid components made of metal and carbon fiber-reinforced plastics (CFRP) have a high potential in lightweight applications due to their high strength-to-weight ratio. For cost-effective processing of hybrid materials, advanced manufacturing processes such as the prepreg-press-technology have been developed, in which the bonding between a metallic component and a fiber compound is exclusively ...
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The Manufacture of Hot-Compacted Layered Composite Systems Made of Oriented Semifinished PP-Films
(2014-03-04)
Monoaxial stretched PP-films are used for the manufacture of hot-compacted layered composites. These are layered with stretched co-extruded coupling agent films, and are consolidated to laminates by means of a hot-compaction process, which employs pressure and temperature. This paper aims to examine the influence of the process settings on the properties of the composites during the hot-compaction process. For this purpose, the mechanical values will be determined by means of tensile testing variously compacted and ...
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Promoting abnormal grain growth in Fe-based shape memory alloys through compositional adjustments
(2019-05-28)
Iron-based shape memory alloys are promising candidates for large-scale structural applications due to their cost efficiency and the possibility of using conventional processing routes from the steel industry. However, recently developed alloy systems like Fe–Mn–Al–Ni suffer from low recoverability if the grains do not completely cover the sample cross-section. To overcome this issue, here we show that small amounts of titanium added to Fe–Mn–Al–Ni significantly enhance abnormal grain growth due to a considerable ...
Aufsatz
On the structural integrity of Fe-36Ni Invar alloy processed by selective laser melting
(2020)
Specimens made from pre-alloyed Invar (Fe-36Ni) powder were fabricated by selective laser melting and stress-relief heat treated afterwards. A relative density of the fabricated parts of 99.6 % was determined by computed tomography. The microstructure and mechanical behavior under monotonic and particularly cyclic loading at ambient temperature were investigated. Results reveal a bimodal microstructure containing columnar and equiaxed grains with an average grain size of 75 μm and pronounced texture 〈001〉 || BD. The ...
Aufsatz
Cyclic degradation of Co49Ni21Ga30 high-temperature shape memory alloy - On the roles of dislocation activity and chemical order
(2015)
Conventional shape memory alloys (SMAs), such as binary Ni-Ti, are typically limited to service temperatures below 100 °C. Recent studies on Co-Ni-Ga high temperature (HT) SMAs revealed the potential that these alloys can be used up to temperatures of about 400 °C. Analysis of the cyclic functional properties showed that degradation in these alloys is mainly triggered by intensive dislocation motion. However, data on the cyclic stress-strain response and the mechanisms leading to functional degradation of Co-Ni-Ga ...
Aufsatz
On the Effect of Quenching on Postweld Heat Treatment of Friction-Stir-Welded Aluminum 7075 Alloy
(2019)
This work focuses on the effect of postweld heat treatment (PWHT) on the mechanical properties and microstructural evolution of aluminum 7075 alloy processed via friction stir welding (FSW). FSW is known to be capable of grain refinement in the nugget zone (NZ). Two different quench media (water and air) were employed for PWHT. Regardless of the quench media, the PWHT led to the occurrence of grain growth in the NZ of the FSWed aluminum 7075 alloy. Abnormal grain growth occurred in the water quenched specimen. It is ...
Aufsatz
Cyclic Deformation Response of Ultra-fine Grained Titanium at Elevated Temperatures
(2019)
This study focuses on the high-temperature cyclic deformation response (CDR) of ultra-fine grained (UFG) titanium of commercial purity (grade 4) processed via equal channel angular extrusion as a severe plastic deformation method. Low-cycle fatigue experiments were conducted at elevated temperatures up to 600 °C and at strain amplitudes ranging from 0.2% to 0.6%. Besides temperature and strain amplitude, the influence of two processing routes (8BC and 8E) on the fatigue characteristics of UFG Ti was examined. It is ...