Jan Schwerdtfeger

Design of Auxetic Structures via Mathematical Optimization

The design of auxetic structures is traditionally based on engineering experience, see, for instance, refs. [1,2]. The goal of this article is to demonstrate how an existing auxetic structure can be improved by structural optimization techniques and manufactured by a selective electron beam melting (SEBM) system. Auxetic materials possess negative Poisson’s ratios ν which is in contrast to almost all engineering materials (e. g. metals ν ≈ 0.3). The negative Poisson’s ratio translates into the unusual geometric effect that these materials expand when stretched and contract when compressed. This behavior is of interest for example for fastener systems and fi lters. [ 2 , 3 ] It also results in interesting mechanical behavior like increased penetration resistance for large negative Poisson’s ratios [ 4 ] and in the case of isotropy for higher shear strength relative to the Young’s modulus [ 2 ] of the structure. The auxetic behavior can always be traced back to complex mesoor microscopic geometric mechanisms, e. g. unfolding of inverted elements or rotation of star shaped rigid units relative to each other. [ 5 – 7 ] These geometries can be realized on vastly different scales from specifi cally designed polymers to reactor cores. [ 2 , 8 ]

In situ flaw detection by IR‐imaging during electron beam melting

Purpose – The purpose of this paper is to investigate the possibility of in situ flaw detection for powder bed, beam‐based additive manufacturing processes using a thermal imaging system.Design/methodology/approach – The authors compare infrared images (IR) which were taken during the generation of Ti‐6Al‐4V parts in a selective electron beam melting system (SEBM) with metallographic images taken from destructive material investigation.Findings – A good match is found between the IR images and the material flaws detected by metallographic techniques.Research limitations/implications – First results are presented here, mechanisms of flaw formation and transfer between build layers are not addressed in detail.Originality/value – This work has important implications for quality assurance in SEBM and rapid manufacturing in general.

Efficient hydrogen release from perhydro-N-ethylcarbazole using catalyst-coated metallic structures produced by selective electron beam melting

A particularly suitable reactor concept for the continuous dehydrogenation of perhydro-N-ethylcarbazole in the context of hydrogen and energy storage applications is described. The concept addresses the fact that dehydrogenation is a highly endothermic gas evolution reaction. Thus, for efficient dehydrogenation a significant amount of reaction heat has to be provided to a reactor that is essentially full of gas. This particular challenge is addressed in our study by the use of a catalyst-coated (Pt on alumina), structured metal reactor obtained by selective electron beam melting. The so-obtained reactor was tested both as a single tube set-up and as a Hydrogen Release Unit (HRU) with ten parallel reactors. In stationary operation, the HRU realized a hydrogen release capacity of 1.75 kWtherm (960 Wel in a subsequent fuel cell) with up to 1.12 gH2 min−1 gPt−1 and a power density of 4.32 kWel L−1 of HRU reactor.