Kurzfassung Der Einfluss der Maschinensteifigkeit auf die Versuchsführung ist ein seit langem untersuchtes Thema. Von den in den Kraftfluss einbezogenen Komponenten hat das Maschinengestell wesentlichen Anteil an der Eigenfederung. Diese lässt sich an ausgeführten Prüfmaschinen durch Belastungsversuche messtechnisch ermitteln. Aus der Steigung typbezogener Federkennlinien geht außer der Größe der Formänderung die gespeicherte elastische Formänderungsenergie hervor. Um den dadurch bedingten Maschineneinfluss zu minimieren, ist das Merkmal „harte” Prüfmaschine eine unabdingbare Forderung jeder konstruktiven Auslegung. Der Schwerpunkt vorliegender Abhandlung liegt daher auf der voraussagenden Steifigkeitsermittlung. Hierfür lassen sich Bemessungsregeln anhand des Stabwerkmodells „Rahmentragwerk” angeben. Variable Bemessungsparameter werden nach ihrem Einfluss auf die Steifigkeit in der Prüfachse abgestimmt.
Kurzfassung Im vorliegenden Beitrag wird die Überprüfung der Dichtheit von Felgen gegossener Leichtmetallräder behandelt. Die Bedingungen für eine zuverlässige Dichtheitsprüfung und die Forderungen in den Spezifikationen und Werknormen einzelner Fahrzeughersteller werden erörtert. Die Ergebnisse der Erfassung von undichten Rädern im Betrieb in den Jahren 2011 bis 2015 eines Radherstellers wurden vorgestellt und bewertet. Abschließend wurde ein Vorschlag unterbreitet, die vorliegenden Normen einzelner Fahrzeughersteller an die Bedürfnisse der modernen, weitgehend automatisierten Dichtheitsprüfung anzupassen.
Kurzfassung Der vorliegende Fachartikel stellt die wichtigsten zerstörungsfreien Prüfmethoden zur Qualitätssicherung von dünnen Strukturklebungen vor. Auf diese Weise wird ersichtlich, welche Methoden neben der zerstörenden Prüfung von dünnen Strukturklebungen eingesetzt werden können, um einen Haftfestigkeitsverlust zu detektieren. Steigende Leichtbau- und Dämpfungsanforderungen an großflächige Blechbauteile sorgen trotz erhöhter Kosten für einen zunehmenden Einsatz von modernen hybriden Schichtverbundwerkstoffen in zahlreichen Konstruktionsanwendungen. In der Luft- und Raumfahrtindustrie gehören solche Werkstoffe seit geraumer Zeit zum aktuellen Stand der Technik, wohingegen diese Werkstoffkonzepte in der mobilen Großserie derzeit nur selten zum Einsatz kommen. Neben dem Materialversagen der einzelnen Schichten von Schichtverbundwerkstoffen spielt das interlaminare Versagen der Schichten untereinander eine entscheidende Rolle. In der Umformtechnik ist es möglich, dass die polymere Zwischenschicht und das Deckblech nach der Umformung noch in Kontakt stehen, obwohl die Scherfestigkeit bereits überschritten wurde. Dieser Kraftschluss der beiden Fügepartner resultiert aus den schwachen Van-der-Waals-Kräften, die eine eindeutige Detektion mit Hilfe von zerstörungsfreier Prüfung erschweren. Die vorliegende Publikation soll die Eignung diverser zerstörungsfreier Prüfverfahren auf die Detektion von sogenannten „kissing bonds“ (schwaches Anhaften der Schichten nach Versagen der Verbindung) überprüfen.
Use of laser welding is constantly increasing as it allows attainment of a high welding efficiency and weld quality. In this study, 5754 grade aluminum plates were joined on both sides by means of pulsed Nd: YAG power intensified micro scale laser welding method at three different laser powers in flat position by using supplemental welding wire. Mechanical properties of joints were examined by means of tensile and bending tests and by micro hardness measurements, and their structural changes were examined by means of optical microscope, SEM and EDS. As a result, it was determined that the welded joints could display an adequate tensile strength when exposed to tensile strain under action of static loads, but their bending strength remained relatively weaker. Mechanical properties of welded samples were observed to improve with increasing penetration depending on the increase in the laser power. It is believed that use of siliceous supplemental welding wire was also effective in strength improvement.
Abstract This contribution presents an estimation of the measurement uncertainty of coating thickness measurement results. The measurements were performed on a steel sheet sample with an outside shell plating. The sample is protected against corrosion with two layers of 100 ¼m thick dry film. In the present case, the criteria of “80-20” have been applied. The measurement uncertainty evaluation has been carried out using Monte Carlo simulations (MCS method) in accordance with the document OIML G 1-101 Edition 2008 (E) Evaluation of Measurement Data – Supplement 1 to the Guide to the Expression of Uncertainty in Measurement – Propagation of Distributions Using a Monte Carlo Method. The criteria “80-20” was evaluated based on the mean coating thickness measurement results, as well as, on the basis of the complete measuring information. Aside from the expected value, complete measuring information comprises the value of measurement uncertainty. In the case where measurement result is described only as the mean of the measurement values a wrong conclusion regarding the fulfillment “80-20” is reached.
The Influence of Fretting Corrosion on the Fatigue Life of Wheel-Hub Assemblies of Commercial Vehicles. The phenomena of fretting corrosion is influencing the fatigue behavior or the reduction of fatigue material properties of assembly interconnections. The following text shows the general effects of fretting fatigue on specimen. Results of the behavior of two different materials under constant and variable amplitude loading are shown as well as the influence of the design of the wheel-hub-assembly of commercial vehicles. For the simulation of operational field usage the biaxial wheel test procedure was used.
Fatigue Proof Design of Aluminium High-Pressure Die Casting Components Taking Into Consideration the Defect Distribution. Reliable computation of the fatigue lifetime of an aluminium high-pressure die casting (HPDC) component requires knowledge of the pore distribution in the material. An existing porosity model has been used to compute the pore distribution in a reference component. A comparison to the pore distribution in a real casting component shows a good agreement. The influence of the pores on the fatigue strength can be described by the Kitagawa-diagram. The sustainable local load can be derived by combining the results of the statistical porosity model and the Kitagawa-diagram.
Extended Material Test for the Characterization of Light Weight Design Materials in View of Their Edge Cracking Sensitivity. In the present contribution, a newly developed test procedure is highlighted, which a quantification of the edge cracking sensitivity of high strength sheet steels. Based on conventional bend tests, the present procedure has been modified in such a way that the maximum edge load can be introduced into the test materials. In the contribution, also the standardized material characterization procedures are adressed and test procedures are presented which allow evaluations of the bending capabilities of high strength sheet steels and their edge cracking sensitivity.
Short-time procedure for the calculation of Woehler curves of metallic materials on the basis of physical measurements. The reliable calculation of the fatigue life of highly stressed metallic materials and components requires the comprehensive understanding of the fatigue processes and the systematic investigation of the cyclic deformation behaviour. Beside mechanical stress-strain hysteresis measurements, temperature and electrical resistance measurements were performed at the Institute of Materials Science and Engineering at the University of Kaiserslautern for the detailed characterisation of metallic materials under cyclic loading. On the basis of this data the physically based fatigue life calculation method "PHYBAL(LSV)" was developed. This new short-time procedure requires data of only one load increase and two constant amplitude tests for a fast determination of Woehler curves. Consequently, the application of "PHYBALLSV" saves experimental time and costs compared to conventional test methods, leading to enormous scientific and economic advantages.
Stress corrosion cracking of high strength steels. In corrosion sustainability load tests, the influence of material hardening through cold-forming on the susceptibility of the material StE 480.7 TM to hydrogen-induced stress corrosion cracking (SCC) is investigated. The defined strength of the material is regulated through cold-forming in a rotary swaging machine. The susceptibility of the material to hydrogen-induced stress corrosion cracking is validated in sustainability load test stands at varying levels of load and cathodic polarization. As a result of the investigations it can be noticed that the time-to-rupture of the material RE 480.7 TM highly depends on the strength of the material and the level of load. The SEM investigations clearly show that the failure of broken samples can be traced back to hydrogen-induced stress corrosion cracking.
Operational Loads on Sport Bicycles. Numerous failure cases in the field show, that the existing standards for fatigue tests on bicycles cannot ensure the athletes safety. Therefore the Institute for Sport Equipment and Materials at the TU Munich carried out an extensive field test to obtain the operational loads placed on mountain bikes and road racing bikes. Simultaneously new multi-axial test stands have been built up, to determine the fatigue strength of safety relevant bicycle components.
A New Test Procedure to Investigate the Cracking Behaviour of Hot-Dip Galvanised Steel. A new test procedure has been developed for systematic research into the conditions conducive to liquid metal-assisted cracking (LMAC), a phenomenon which can occur when steel is hot-dip galvanised. U-bend specimens are used to achieve different tensile stress gradients and to allow an investigation of the influence of any pre-deformation. The procedure was used to test steels with different levels of susceptibility to LMAC, although the main focus was on S355 J2. Having established a broad range of parameters, closer attention was paid to the effect of the alloying elements of lead, tin and bismuth during zinc smelting on the potential risk posed by LMAC. Of the various procedures studied, the test involving constant stress (stress/time-to-rupture test) and the test where stress was continually increased (tensile test) offered the greatest indication of existing risk potential. Irrespective of the test procedure and of the variable used for the indication (time to crack formation, engineering stress or strain), comparable results were obtained with comparable risk potential for tests lasting between 5 min and 1 h. One important insight is that before any damage becomes evident on the basis of load curves and their analysis, micro-cracks occur in the outer layer which is subject to high stress, and these minute cracks cause an increase in the expansion as compared to a crack-free specimen subject to similar levels of stress. This must be factored into the calculation of the plastic expansion which can be withstood during the galvanising process as measured from the specimen expansion.
Fatigue Resistance of Completely Mounted Bicycles. In the present contribution test procedures are highlighted to evaluate the fatigue resistance of bicycles and to increase the safety of such sporting products.
Increased Efficiency of Multi-Endurance Tests of Axles by Using Standard Interfaces Between the Sub-Frame and the DAFA, and by Implementing a Fast, Well-Arranged Evaluation Tool for Iteration and Simulation. In the case of the multi-axis endurance strength test of axles there is no standard interface so far between the subframe and the DAFA mapping the stiffness of the body connecting points. The resulting changes in stiffness skew the test result of the crucial structural component sub-frame. In order to increase the significance in terms of quality of these tests via this component, ZF Lemforder developed a constructive solution and validation methodology in cooperation with a supplier. A further increase in efficiency is achieved by implementing a fast, well-arranged evaluation tool for iteration and simulation results. With the aid of the Excel-based calculation macro "Target-Response-Analyzer", it is possible to evaluate iteration results in a quick and clearly arranged manner. A channel-based damage summary about the share of individual proving ground sections in the total damage of a collective provides the iteration staff with a road map before start of work indicating which amount of work is reasonable for which tracks. After completion of the iteration, further evaluation tab sheets provide a coherent summary about the damage-based iteration result of as many tracks and load channels as requested.
Do Failures Make Clever? - The Extended VDI-Guideline 3822 "Failure Analysis" Generally, failures make more poor than clever. Only the systematic analysis of technological failure cases makes the original mechanisms visible which lead to the keys for failure future avoidance. The present contribution highlights the current state of the VDI-Guideline 3822 "Failure Analysis" which is also available in English language.
