Betriebsfestigkeit in der Fahrzeugentwicklung – von der Theorie zum Produkt

Durability Evaluation in the automotive engineering – from theory to product The procedures for durability evaluation in the automotive engineering are represented, especially the methods, load assumption, fatigue testing and the regulations for the release and quality control. By practical examples of the vehicle development from chassis, aggregate and body the procedure is described, in particular the used experimental and virtual simulation methods     

HiFIT – Technische Entwicklung und Anwendung

Das Verbundprojekt REFRESH bot in den vergangenen drei Jahren eine ideale Plattform für die theoretische und experimentelle Weiterentwicklung des HiFIT (high frequency impact treatment)‐Verfahrens. So konnten sowohl die Behandlungsparameter an umfangreichen Schweißproben optimiert als auch ein industrietaugliches Gerätedesign unter Einbeziehung zahlreicher Anwendungsfälle aus der Praxis der Industriepartner entwickelt werden. Effizienz, Ergonomie und die Qualitätssicherung standen bei der Entwicklung im Vordergrund. Die Beurteilung der Anwendbarkeit des Verfahrens und die Anwendung selbst sollten im Sinne einer allgemeinen Qualitätssicherung und zur Quantifizierung des zu erwartenden Behandlungserfolgs von geschultem Personal durchgeführt werden. Letzteres gilt nicht nur im Speziellen für das HiFIT‐Verfahren, sondern generell für alle Nachbehandlungsverfahren. Hinter dem Markennamen HiFIT steht ein ganzheitliches Lösungskonzept mit rechnerischen Analysetools, Nachbehandlungswerkzeugen, Schulung und Consulting zur effizienten Steigerung der Betriebsfestigkeit neuer und bereits im Einsatz befindlicher Schweißkonstruktionen. HiFIT – Technical development and application. In the past three years the HiFIT technology for application on welded parts has been investigated in the REFRESH project. Many treatment parameters have been tested. Using prototype devices a lot of experience has been gained by treatment of several parts in cooperation with the project partners. The design of the HiFIT device is optimized for industrial application where efficiency, ergonomics and quality assurance are the main topics. An application benchmark of HiFIT and the treatment should be done only by specially trained employees. This restriction is not only HiFIT specific. The trademark HiFIT means a solution for improvement of fatigue strength of new and cyclic pre‐damaged welded structures. The solution contains assessment of fatigue strength, treatment devices, training and consulting.     

Current developments and trends on structural durability

Basic approaches for assessment of Structural Durability are outlined in principle. Some of their limits in actual application fields and new solutions are shown. Multiaxial Fatigue remains as to be treated very carefully. The superposition of damaging processes known as “Very High Cycle Fatigue” and “Corrosion Fatigue” might be a key for assessment of components at very high load cycles.     

Ermüdungsverhalten von Schraubendruckfedern bei konstanten und variablen Beanspruchungsamplituden bei sehr hohen Schwingspielzahlen

A test rig for simultaneous testing of up to 88 compression springs under constant as well as variable amplitude loading is presented in this paper. The test rig utilizes a servo‐hydraulic testing machine. The results of long‐term fatigue tests of compression springs under constant and variable amplitude loading up to 5 ? 10⁸ and 1.4 ? 10⁷ cycles are presented. Experimental Woehler‐ and Gassner‐curves are obtained using the maximum likelihood method. Theoretical Gassner‐curves are generated using Miner's rule and experimental Woehler‐curves. The theoretical Gassner‐curves are compared to the experimental ones. The results of the constant amplitude loading tests are compared to literature data. The possibility to increase the testing frequency in variable amplitude loading tests is discussed. Thereto, the comparability of results from fatigue tests of material specimens using torsional ultrasonic fatigue testing equipment to results from fatigue tests on compression springs is addressed.     

Light‐weight design chances using high‐strength steels

In order to make effective use of high‐strength steels for designing light‐weight structures, it is necessary to consider the interaction between the service loading, material, geometry and manufacturing technology. This interaction determines durability. The fatigue performance of high‐strength steels can be better exploited if high stress concentrations are reduced through geometry improvement and manufacturing process control. With regard to their capability for high energy absorption, high‐strength steels offer the best solutions for designing against impact loads and crash. These advantages of high‐strength steels are realised in modern vehicle structures through the multi‐material concept, where materials selection is made according to expected service loads and locally required strengths.     

Modeling and fatigue assessment of weld start‐end locations based on the effective notch stress approach

The present paper contains a methodology for modeling and life assessment of fatigue loaded welded components providing distinct weld start and end locations. The proposed methodology follows the IIW recommendation regarding modeling and finite element meshing of weld toe and root by means of an effective notch radius and uses the corresponding Wöhler curve (FAT class) to assess the durability. Geometrical singularities and, therewith, numerical discontinuities, can be overcome especially when 3D weld root problems are treated. The fatigue life assessment is performed on the basis of normal stresses acting at the failure‐critical weld toe and root locations. Comprehensive experimental database containing stress and fatigue life results derived from motor truck's hypoid rear axles providing complex 3D welds subject to vertical, longitudinal, and torsional loading is used to verify the calculation accuracy of the proposed methodology. The agreement between experimentally determined and calculated fatigue results is satisfactory.     

Neue Methoden zur Beurteilung der Betriebsfestigkeit im Fahrzeugauslegungs‐ und ‐absicherungsprozess

Advanced durability evaluation in vehicle design and validation process The modern process of evaluation and validation conducted in the automotive industry uses experimental, metrological, and calculation‐based methods. Offering various examples, the present paper describes new developments in the determination and evaluation of operating strength, particularly in terms of virtual methods and their application in practice. The first point considered is the virtual determination of load data, the second is the improvement of calculated fatigue life. Two current examples in the development of methods are presented in this context: The first example examines the inhomogeneity of materials in calculating aluminium castings. The second example describes the approach taken in the configuration of components made of short‐fibre‐reinforced polymers, applying a new method of calculation.