Chacterization of CU tube filled with Al alloy foam by means of X-ray computer tomography

Copper tubes filled with aluminium foams were prepared by directly foaming metal powder compacts inside them. Compressive behaviour and foam-shell interface, that characterizes mechanical properties of reinforced tubes, were investigated by means of variable focus X-ray computer tomography. Compression tests were performed on empty and filled samples at increasing deformation steps: at each stage the samples were observed by tomography. A geometric evaluation of porosity on 2D sections was performed by calculating, for each pore, its area, equivalent diameter and circularity

High Strain Rate Reloading Compresson Testing of a Closed-Cell Alumnum Foam

Aluminum (Al) closed-cell foams are materials of increasing importance because they have good energy absorption capabilities combined with good thermal and acoustic properties. They can convert much of the impact energy into plastic energy and absorb more energy than bulk metals at relatively low stresses. When used as filling materials in tubes, they increase total energy absorption over the sum of the energy absorbed by foam alone and tube alone [1]. In designing with metallic foams as energy absorbing fillers, mechanical properties are needed for strain rates corresponding to those created by impact events. Quasi-static mechanical behavior of metallic foams has been fairly extensively studied, but data concerning high strain rate mechanical behavior of these materials are, however, rather sparse [2,3]. This study was initiated, therefore, to study and model the high strain rate mechanical behavior of an Al foam produced by foaming of powder compacts and to compare it with quasi-static behavior and, hence, determine any effect on energy absorbing capacity

Bestimmung der Materialeigenschaften in der Wärmeausbreitungszone S355J2 und AlMgSi 0.6

Das Ziel dieser Arbeit war die Bestimmung der Materialeigenschaften der Wärmeeinflußzone (WEZ) von geschweißten Aluminium- und Stahlkonstruktionen aus warmgewalztem S355J2 und aus extrudiertem AA 6008 T4, um reale Input-Daten der lokalen Deformationen der Bauteile für die rechnerische Simulation zu erhalten. Dazu wurde die WEZ durch in-situ Temperaturmessungen während des Schweißprozesses, durch Mikrohärtemessungen und durch mikroskopische Untersuchungen charakterisiert. Ausgehend von diesen Ergebnissen wurden Zugproben so wärmebehandelt, daß das Gefüge der WEZ entspricht um deren mechanische Eigenschaften zu bestimmen. Einerseits wurde die Gefügeverteilung der WEZ mit den entsprechenden Fließkurven ermittelt (S355J2) und andererseits wurden durch optische Dehnungsmessungen während des Belastungsvorganges die lokalen Dehnungsfelder um die Schweißungen bestimmt (AA 6008 T4). Unter Berücksichtigung der ermittelten Dehnungen der wärmebehandelten Zugproben aus Aluminium wurden die plastifizierten Regionen der WEZ in Übereinstimmung mit den lokalen Bruchfestigkeiten gebracht, die für die Dehnungsverteilung verantwortlich sind. Die Zonen, in denen die lokalen maximalen Festigkeiten überschritten wurden konnten als Orte der Rißentstehung identifiziert werden

Crushing of Axially Compressed Steel Tubes Filled with Aluminium Foam

Summary This study, with the emphasis on experiments, investigates the applicability of aluminium foam as filler material in tubes made of mild steel having square or circular cross sections, which are crushed axially at low loading velocities. In addition to the experiments finite element studies are performed to simulate the crushing behaviour of the tested square tubes, were a crushable foam material model is shown to be suitable for describing the inelastic response of aluminium foam with respect to the considered problems. The experimental results for the square tubes reveal efficiency improvements with respect to energy absorption of up to 60%, resulting from changed buckling modes of the tubes and energy dissipation during the compression of the foam material itself. The principal features as well as the changes of the crushing process due to filling can also be studied by the numerical simulations. A global failure mechanism due to a high foam density can be observed for filled circular tubes. Aluminium foam is shown to be a suitable material for filling thin-walled tubular steel structures, holding the potential of enhancing the energy absorption capacity considerably, provided the plastic buckling remains characterized by local modes. Dedicated to Prof. Dr. Dr. h. c. Franz Ziegler on the occasion of his 60th birthda

Strain fields of tensile and shear loaded weldments of AlMgSi0.6 extrusions

The goal of this work is to determine the mechanical properties required for computation of the deformation of welded Al-extrusions. The heat affected zone (HAZ) is characterized by the temperature exposure during welding, by hardness testing, and by microscopy. Tensile specimens are heat treated according to the microstructure of the HAZ. The local strain fields of the specimens are determined during overloading. The distribution of plastic regions depends on the local yield strenght. The zones surpassing the local maximum strength indicate the location of crack formation

Experimental studies on the quasi-static axial crushing of steel columns filled with aluminium foam

Experimental investigations are carried out in order to study the effects of different tube and filler arrangements on the crushing behaviour of axially compressed tubular crush elements. To this end quasistatic experiments are performed on monotubal and bitubal, empty and filled steel profiles with different materials, dimensions and cross-sectional shapes. Aluminium foam, produced by a powder metallurgical production process, is applied as filler material. The test results confirm that considerable mass efficiency improvements with respect to energy absorption may be obtained, even if reduced stroke lengths, caused by the presence of foam, are taken into account. Distinct differences are pointed out between the different cross-sectional shapes. Bitubal arrangements, consisting of outer and inner profiles with foam in between, are shown to be particularly efficient crush elements, as long as global failure can be avoided. Explanations for the experimental observations are obtained by a simplified analysis of interaction effects. Constraints concerning the appropriate choice of Al-foam densities are summarized, too, in order to provide an aid for the future design of 'optimally tuned' crush elements composed of tubular members and Al-foam. Author Keywords: Axial crushing; Empty profiles; Filled profiles; Aluminium foam; Metal foa