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More than 400 iron hydrogen storage containers (also called bottles or cylinders exploded on the air strip Berlin-Tempelhof on May 25, 1894, leaving immense destruction. The Royal Prussian Materials Testing Institute was requested to investigate the material properties and to furnish an expertise, how an increased safety of such cylinders might be achieved for the future under protection of the interests of the air ship service, as for instance by improvement of delivery specifications or respective material inspections.
The studies conducted personally by the director Prof. Adolf Martens and his deputy Prof. M. Rudeloff represent one of the first comprehensive failure case investigations in history and initiated BAMs long tradition in failure analysis. Martens and his colleague elaborated quite detailed specimen plans and investigated original failure parts with a special emphasis on conspicuous fracture appearance, but also made comparison experiments with hardened as well as annealed samples. Experienced investigators might identify some first routines how to conduct failure analyses and the importance of Adolf Martens as a pioneer in this field becomes evident.
Martens publications about the original expertise Martens, 1896 [1] and [2] include detailed descriptions about the experimental procedures and specimen preparation. Also, quite modern materials testing technologies and machines have been utilized, as for instance light microscopy as well as the tensile testing machines developed by Werder and Pohlmeyer. As special features developed by Martens, precision strain measurements have been applied during respective tensile tests and the so-called micro-photographic apparatus has been adopted to produce photos of the investigated microstructures. Additionally, the publications contain at that time very valuable advices regarding appropriate materials selection for gas storage cylinders.
The present contribution provides a nearly complete and as exact as possible translation of the original report Martens, 1896 [1] written in Old German language. Only little changes have been made in the text for a better understanding.
Grain refinement is an important possibility to enhance the mechanical properties such as strength, ductility and toughness of aluminium weld metal. In this study, grain refinement was achieved through the addition of commercial grain refiner Al Ti5B1 to gas tungsten arc weld metal of the aluminium alloys 1050A (Al 99.5) and 5083 (Al Mg4.5Mn0.7). The grain refiner additions led to a significant reduction of the weld metal mean grain size (Alloy 1050A, 86 %; Alloy 5083, 44 %) with a change in grain shape from columnar to equiaxed. Tensile tests showed for Alloy 5083 that the weld metal's ductility can be increased through grain refinement. No improvement in weld metal strength (i.e. yield strength and ultimate tensile strength) was observed. Furthermore, tear tests with notched specimens revealed that the resistance against initiation and propagation of cracks in the weld metal can be enhanced through grain refinement. The toughness was observed to increase clearly by grain refinement in weld metal of commercial pure Al (Alloy 1050A). In Alloy 5083 weld metal, the toughness was not improved through grain refinement, likely because of a semi-continuous network of brittle intermetallic phases that facilitate crack propagation.
Fabrication of modern microelectronic components requires miscellaneous solder materials for joining. In order to guarantee the quality of the manufacturing process and the reliability of the resulting solder joint it is necessary to know the material properties of the joining parts and of the solder materials. In particular Youngs modulus, yield stress, and the hardness are of great interest. Moreover, a complete stress-strain curve is important for a detailed material characterization and simulation of a component, e.g., by Finite Elements (FE). The miniaturization of modern electronic products with small solder joints allows only fabrication of very small-sized specimens. Because of this miniature tests are used for measuring the mechanical properties of the solders in the experimental investigations of this paper. More specifically two miniature tests are presented and discussed, a mini-uniaxial-tension-test and a nanoindenter experiment. In the tensile test the axial loading is prescribed, the corresponding extension of the specimen length is recorded, both of which determines the stress-strain- curve directly. The stress-strain curves are then mathematically analyzed by assuming a non-linear relationship between stress and strain of the Ramberg-Osgood type and fitting the corresponding parameters to the experimental data by means of an optimization routine. For a detailed analysis of very local mechanical properties nanoindentation is used, resulting primarily in load vs. indentation-depth data. According to the procedure of Pharr and Oliver this data can be used to obtain hardness and Youngs modulus but not a complete stress-strain curve, at least not directly. In order to obtain such a stress-strain-curve, the nanoindentation experiment is combined with FE and the coefficients involved in the corresponding constitutive equation for stress and strain are obtained by means of the inverse method. Finally in this paper, the stress-strain curves from nanoindentation and tensile tests are compared for two materials, namely aluminum and steel and differences are explained in terms of the locality of the measured properties.