Advanced Engineering Materials

Cover image for Vol. 8 Issue 5

Special Issue: 50 Years Materials Research at GKSS

May, 2006

Volume 8, Issue 5

Pages 309–445

Issue edited by: W. A. Kaysser, K. U. Kainer

    1. Cover Picture: The Effect of Grain Size on the Deformation Behaviour of Magnesium Alloys Investigated by the Acoustic Emission Technique (Adv. Eng. Mater. 5/2006)

      J. Bohlen, P. Dobron, E. Meza Garcia, F. Chmelík, P. Lukáč, D. Letzig and K. U. Kainer

      Article first published online: 11 MAY 2006 | DOI: 10.1002/adem.200690009

      Extruded round bars from magnesium alloys ZM21, ZK30, ZE10 and ZEK100 with various grain sizes were tested in tension and compression. The effect of grain size on the deformation behaviour of the alloys was investigated through the Hall-Petch relation. In-situ acoustic emission measurements were conducted during testing to evaluate the mechanisms of plastic deformation. The results are discussed with respect to twinning as one important deformation mechanism in magnesium alloys.

    2. Contents: Adv. Eng. Mater. 5/2006 (pages 309–313)

      Article first published online: 11 MAY 2006 | DOI: 10.1002/adem.200690008

    3. Structural Integrity Assessment of Thin-Walled Structures (pages 319–327)

      W. Brocks, K.-H. Schwalbe and U. Zerbst

      Article first published online: 11 MAY 2006 | DOI: 10.1002/adem.200600120

      As part of the concept of damage tolerant design, methods for the analytical and numerical simulation of ductile crack extension in thin-walled structures are presented and discussed. They comprise the application of an analytical flaw assessment procedure as well as finite element analyses based on the crack tip opening displacement (CTOD), δ5, and finite element simulations of crack extension based on the crack tip opening angle (CTOA), a cohesive zone model and a ductile damage model. All these methods are or will become part of the GKSS Structural Integrity Assessment Method (SIAM), which also provides test procedures for the experimental determination of the required material parameters.

    4. Developments in Membrane Research: from Material via Process Design to Industrial Application (pages 328–358)

      V. Abetz, T. Brinkmann, M. Dijkstra, K. Ebert, D. Fritsch, K. Ohlrogge, D. Paul, K.-V. Peinemann, S. Pereira-Nunes, N. Scharnagl and M. Schossig

      Article first published online: 11 MAY 2006 | DOI: 10.1002/adem.200600032

      Separation of materials is a fundamental issue in natural and technological processes. Membrane based separation processes offer the possibility to separate mixtures at low energy consumption, i.e. under isothermal conditions. The aim of this review paper is to give an overview of the research activities of GKSS in the field of polymer based membranes.

    5. Microstructural Investigations of the Mg-Sn-xCa System (pages 359–364)

      N. Hort, Y. Huang, T. Abu Leil, P. Maier and K. U. Kainer

      Article first published online: 11 MAY 2006 | DOI: 10.1002/adem.200600014

      New magnesium-tin-calcium alloys offer the potential to improve the property profile and to extend the range of applications for magnesium alloys. Alloy development is undertaken in accordance to the formation of intermetallic phases during casting or during subsequent heat treatment. These intermetallic phases may contribute to room temperature strength as well as to the improvement of creep properties. Therefore the behaviour and the structure of these phases needs to be understood in more detail when using these materials in the as-cast condition or after subsequent heat treatment.

    6. Advanced TiAl6Nb7 Bone Screw Implant Fabricated by Metal Injection Moulding (pages 365–370)

      E. Aust, W. Limberg, R. Gerling, B. Oger and T. Ebel

      Article first published online: 11 MAY 2006 | DOI: 10.1002/adem.200500134

      The innovative technology of metal injection moulding could be successfully applied to the titanium alloy TiAl6Nb7. For this reactive material the complex processing steps such as feedstock fabrication, injection moulding, debinding and sintering were optimised in the frame of the development of a bone screw implant.

    7. Nano-Scale Design of TiAl Alloys Based on β-Phase Decomposition (pages 371–376)

      F. Appel, M. Oehring and J. D. H. Paul

      Article first published online: 11 MAY 2006 | DOI: 10.1002/adem.200600013

      Phase decomposition and ordering reactions in β/B2-phase containing TiAl alloys were utilized to establish a novel, previously unreported, type of laminate microstructure. The characteristic constituent of this microstructure are laths with a nanometer-scale substructure that are comprised of several stable and metastable phases. Microstructural control can be achieved by conventional thermomechanical processing and leads to a structurally and chemically very homogeneous material with excellent mechanical properties. The physical metallurgy of this novel type of alloy has been assessed by transmission electron microscope investigations and mechanical testing.

    8. Tailoring Hydrogen Storage Materials Towards Application (pages 377–385)

      M. Dornheim, N. Eigen, G. Barkhordarian, T. Klassen and R. Bormann

      Article first published online: 11 MAY 2006 | DOI: 10.1002/adem.200600018

      A breakthrough in hydrogen storage technology was achieved by preparing nanocrystalline hydrides using high-energy ball milling and the use of suitable catalysts/additives. These new materials show fast or in case of Mg-based hydrides very fast absorption and desorption kinetics within minutes, thus qualifying lightweight Mg- or Al-based hydrides for storage applications. This article summarizes our current understanding of the kinetics of Mg-based light metal hydrides, describes an approach for a cost-effective processing technology and highlights some promising new developments in lightweight metal hydride research.

    9. Catalytic Polymer Membranes for high Temperature Hydrogenation of viscous Liquids (pages 386–389)

      D. Fritsch and G. Bengtson

      Article first published online: 11 MAY 2006 | DOI: 10.1002/adem.200600019

      Polymeric membranes with high oil fluxes were developed and catalytically activated by a new route of direct calcination of polymeric membranes charged by Pd or Pt catalyst precursors. High concentrations of citric acid mixed with the precursors afforded a decrease of the calcination temperature to 175 °C. Membrane reactor tests in the flow through contactor mode displayed high reactivities for sunflower oil hydrogenation.

    10. Polyimide Asymmetric Membranes for Hydrogen Separation: Influence of Formation Conditions on Gas Transport Properties (pages 390–397)

      S. Shishatskiy, C. Nistor, M. Popa, S. P. Nunes and K. V. Peinemann

      Article first published online: 11 MAY 2006 | DOI: 10.1002/adem.200600024

      An asymmetric flat sheet membrane was developed for separation of hydrogen from its mixtures with other gases. The composition of the casting solution and conditions of membrane preparation were optimized for pilot scale membrane production. The membrane is stable against mixtures of liquid hydrocarbons and can withstand heating up to 200°C. The non-woven fabric used as a support for the asymmetric membrane gives to the membrane excellent mechanical properties and allows to use the membrane in GKSS gas separation modules.

    11. Assessment of Fracture and Fatigue Crack Propagation of Laser Beam and Friction Stir Welded Aluminium and Magnesium Alloys (pages 399–406)

      W. V. Vaidya, M. Horstmann, E. Seib, K. Toksoy and M. Koçak

      Article first published online: 11 MAY 2006 | DOI: 10.1002/adem.200600015

      The new joining technologies and the development of new weldable alloys open perspectives for weight and cost savings in the aerospace and the automotive industries. However, fulfilment of property requirements can be a limiting factor for the application of such new technologies. In this paper we present our results from some recent and on-going investigations on the damage tolerance of 6XXX aerospace Al-alloys and AZ31B Mg-alloy, welded by using laser beam and friction stir processes. Particular emphasis is placed on fatigue crack propagation and fracture behaviour, and future areas for research in the damage tolerance behaviour of the strength undermatched Al-welds are identified while outlining possible solutions.

    12. Statistical Modelling of Fracture in Quasi-Brittle Materials (pages 406–410)

      J. Schicker and M. Pfuff

      Article first published online: 11 MAY 2006 | DOI: 10.1002/adem.200600022

      Different mesoscale finite element models were applied to damage and fracture of brittle or quasi-brittle heterogeneous materials. By combining elastic behaviour with local stochastic rupture criteria these models are able to reproduce some of the typical features of damage development and failure of such materials.

    13. Simulation of Crack Growth in Al Panels Under Biaxial Loading (pages 410–414)

      I. Scheider and M. Schödel

      Article first published online: 11 MAY 2006 | DOI: 10.1002/adem.200600029

      Safety and reliability are the most important issues in all engineering structures. In recent years the so-called damage tolerance has become a main requirement. The assessment of cracked structures can be performed using analytical methods. Two models are presented in the paper: the cohesive model and the CTOA model.

    14. Dissimilar Al to Mg Alloy Friction Stir Welds (pages 415–421)

      R. Zettler, A. A. M. da Silva, S. Rodrigues, A. Blanco and J. F. dos Santos

      Article first published online: 11 MAY 2006 | DOI: 10.1002/adem.200600030

      In the present study the microstructure and properties of a dissimilar friction stir weld between the magnesium alloy AZ31 and the aluminium alloy 6040 have been investigated. The intermetallic leads to a loss of strength and ductility of the join. In this study optical and scanning electron microscopy as well as energy dispersive spectroscopy (EDS) have been used to analyse the join interface as well as workpiece residues bonded to the joining tool. Dynamic recrystallisation was observed in the stir zone resulting in a substantial reduction in grain size particularly for the Al base material.

    15. The Effect of Grain Size on the Deformation Behaviour of Magnesium Alloys Investigated by the Acoustic Emission Technique (pages 422–427)

      J. Bohlen, P. Dobron, E. Meza Garcia, F. Chmelík, P. Lukáč, D. Letzig and K. U. Kainer

      Article first published online: 11 MAY 2006 | DOI: 10.1002/adem.200600023

      Extruded round bars from magnesium alloys ZM21, ZK30, ZE10 and ZEK100 with various grain sizes were tested in tension and compression. The effect of grain size on the deformation behaviour of the alloys was investigated through the Hall-Petch relation. In-situ acoustic emission measurements were conducted during testing to evaluate the mechanisms of plastic deformation. The results are discussed with respect to twinning as one important deformation mechanism in magnesium alloys.

    16. TiC-Based Cermet Coatings: Advanced Wear Performance by Nanocrystalline Microstructure (pages 427–433)

      X. Qi, E. Aust, N. Eigen, F. Gärtner, T. Klassen and R. Bormann

      Article first published online: 11 MAY 2006 | DOI: 10.1002/adem.200600031

      This paper highlights the influence of a refined microstructure on the wear behaviour of cermets by comparing TiC-Ni based, VPS-sprayed microcrystalline and nanocrystalline cermet coatings. The coatings are subjected to two-body and three-body abrasive wear at different loads. Fracture behaviour as well as mass loss and surface quality after the wear tests are evaluated. Although at low wear loads, the refined microstructure leads to a higher mass loss, at high loads the wear resistance of the nanocrystalline coating is superior. This behaviour is strongly related to a significantly higher toughness of the nanocrystalline coating. Independent of the wear load, the nanocrystalline microstructure leads to less surface roughness after wear.

    17. Molecular Modeling Investigations of Dry and Two Water-Swollen States of Biodegradable Polymers (pages 434–439)

      M. Entrialgo-Castaño, A. Lendlein and D. Hofmann

      Article first published online: 11 MAY 2006 | DOI: 10.1002/adem.200600021

      Biodegradable polymers have incessantly gained salience in medical technology and regenerative medicine during the past few decades. These biomaterials are used in temporary implant devices, wound sutures and drug delivery systems. The relation between characteristics of a material and its ability to degrade is still not sufficiently understood. Thus, improved biomaterial design is performed by time-consuming trial and error experimental procedures. Knowledge-based modeling techniques can provide a more systematic and efficient method.

    18. Synthesis, Shape-Memory Functionality and Hydrolytical Degradation Studies on Polymer Networks from Poly(rac-lactide)-b-poly(propylene oxide)-b-poly(rac-lactide) dimethacrylates (pages 439–445)

      N.-Y. Choi, S. Kelch and A. Lendlein

      Article first published online: 11 MAY 2006 | DOI: 10.1002/adem.200600020

      Amorphous, hydrolytically degradable, multi-phase block copolymer networks were obtained by photocrosslinking. The macrodimethacrylate precursors were prepared by ring-opening polymerisation (ROP). The aim of this investigation to tailor the materials' elasticity in the temporary shape could be achieved. Stress-controlled, cyclic thermomechanical tensile experiments showed the materials' excellent shape-memory properties with strain recovery rates up to 99 %. The presented amorphous, biodegradable polymer network system with shape-memory presents a new generation of multi-functional biomaterials enabling applications in keyhole surgery or controlled drug release.

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