Publications without final theses

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Petrich, Martin; Kletzin, Ulf; Krehan, Tom-Luis; Feld, Julius; Otto, Christian
Design methodology for fiber-reinforced polymer composite springs and experimental study on a volute spring. - In: Composites and advanced materials, ISSN 2634-9833, Bd. 33 (2024), S. 1-16

Fiber-reinforced polymer (FRP) composites are particularly suitable for spring applications due to numerous advantages like lightweight design, intrinsic damping, or chemical resistance. Although there are many studies on the properties of FRPs and even some on springs made out of these materials, there is no holistic method for FRP spring design. Therefore, this article focuses on a new approach that combines all relevant design steps. This includes a spring-related overview of requirements and associated FRP properties, as well as recommendations regarding material and spring type selection with a specialization on polymer composite volute springs. Thereupon, a mountain bike rear suspension spring was designed and produced. These carbon fiber-reinforced polymer (CFRP) lightweight spring, which weighs only half of the metal spring, was examined in static and cyclic experiments. Important results of the tests are a lower spring rate than theoretically expected as well as a loss of stiffness of the spring of about 25% after 25,000 full deflections just before failure. Downhill riding tests were carried out and showed comparable driving characteristics as when using conventional steel springs. The research is a contribution to FRP spring design considerations as well as to extend the range of applications for composite springs, and especially volute springs, in the future.
Petrich, Martin; Kletzin, Ulf
Practical fatigue strength diagrams for compression springs based on the FKM-guideline “Analytic Strength Assessment for Springs“. - In: Journal of physics, ISSN 1742-6596, Bd. 2692 (2024), 012031, S. 1-7

Today’s helical compression springs are designed according to DIN EN 13906-1. The fatigue diagrams contained there are outdated and essential influences on fatigue strength are not taken into account. In order to resolve these circumstances, endurable stresses were calculated with the FKM guideline “Analytic Strength Assessment for Springs and Spring Elements”, which was published in 2020. The application of the included safety concept results in characteristic curves for permissible stresses that are conservative with regard to real test data. Therefore, the new fatigue strength diagrams can be used directly for standard applications. This article gives an overview of the method and accompanying experiments. The presented results enable spring designers to design competitive springs in a shorter time and with less testing effort according to the current state of research.
Petrich, Martin; Kletzin, Ulf
Practical fatigue strength diagrams for compression springs based on the FKM-guideline “Analytic Strength Assessment for Springs“. - In: International journal of fatigue, Bd. 183 (2024), 108273, S. 1-8

Metal springs are used extensively in technical products. The mathematical relationships and Goodman diagrams contained in the DIN EN 13906-1 standard form the essential basis for the design and calculation of cylindrical helical compression springs. They are used not only nationally, but internationally in the spring industry and by spring users. However, the diagrams are more than 50 years old and no longer reflect the current status of modern spring materials and spring manufacturing technologies. This results in great uncertainty for users of the standard, which currently has to be compensated by costly fatigue tests. In order to overcome the problems, the research project IGF 19693 aimed to renew the Goodman diagrams of the DIN EN 13906-1 standard in accordance with the state of spring technology. Therefore, the FKM guideline “Analytic Strength Assessment for Springs and Spring Elements“ was used to calculate permissible fatigue strength values for standard springs. Additionally, an extensive experimental program was carried out with fatigue tests on cold-formed helical compression springs to validate the calculations. The main results of the project are presented in this manuscript, which strengthens SMEs in designing competitive springs, which they can offer in a shorter time and at a lower cost due to lower development costs.
Reich, René; Kletzin, Ulf
Möglichkeiten zur Erweiterung der FKM Richtlinie für Federn und Federelemente. - In: Neueste Erkenntnisse zu Funktion, Berechnung, Prüfung und Gestaltung von Federn und Werkstoffen, (2023), S. 181-191

Petrich, Martin; Weimann, Tom-Luis; Feld, Julius; Thein, Ludwig; Ziems, Otto; Sauer, Adrian; Otto, Christian; Kletzin, Ulf
Entwicklung einer Auslegungsmethode für Federn aus faserverstärkten Kunststoffen. - In: Neueste Erkenntnisse zu Funktion, Berechnung, Prüfung und Gestaltung von Federn und Werkstoffen, (2023), S. 143-164

Schleichert, Johannes; Reich, René; Kletzin, Ulf; Geinitz, Veronika
Vorhersage des Vorsetzbetrages von Schraubendruckfedern unter Berücksichtigung von Geometrieänderungen und Rückfederungsverhalten. - In: Neueste Erkenntnisse zu Funktion, Berechnung, Prüfung und Gestaltung von Federn und Werkstoffen, (2023), S. 83-100

Schleichert, Johannes; Kletzin, Ulf
Relaxation behavior of (cylindrical) helical compression springs. - In: Engineering for a changing world, (2023), 4.1.091, S. 1-13

This paper deals with the relaxation behavior of helical compression springs made out of different types of spring steel wire. The starting point of the examinations marks the creep and relaxation behavior of similar preprocessed wires prior to the cold forming under torsional stress. In this context the main influencing factors regarding creep deformations and relaxation losses are discussed and the particular findings contrasted, which allows for transfer factors to be deducted. The mathematical models forming the evaluation basis of the experimental data are based upon the NORTON-BAILEY creep law and utilized to determine creep specific characteristics and identify material constants. Doing so enables the deviation of calculating instructions to estimate the relaxation losses of helical compression springs based on numerous influencing factors. Applying those calculation methods facilitates the deduction of relaxation figures as well as recommendations regarding the manufacturing process in order to achieve springs with favorable relaxation behavior.
Petrich, Martin; Weimann, Tom-Luis; Thein, Ludwig; Kletzin, Ulf
Behaviour of FRP-sandwich structures for lightweight composite springs in static and cyclic torsional load cases. - In: Engineering for a changing world, (2023), 4.1.064, S. 1-13

Fiber-reinforced polymers (FRP) are established as high-tech materials for special purposes such as racing cars, planes or bicycles. Nowadays, they are increasingly used for functional parts and machine elements. For lightweight optimization, FRP sandwich structures can be used, which also appear to be suitable for spring applications. But material data availability is often limited for UD-specimen or specific load cases, which makes it difficult to use FRPs for technical springs. In order to reduce this gap and to facilitate the development of new applications, this paper deals with the basic static and cyclic behavior of FRP sandwich strips under torsional load. Therefore, manufacturing methods have been developed, to produce FRP strip specimens with GFRP and CFRP shells containing various core materials. An analytical model was used to describe the static behavior, which shows decent agreement with test results. Initial studies on fatigue characteristics of these strips were carried out as well as tests on associated volute springs. The results contribute to composite lightweight spring design and could extend the range of applications for composite springs in the future.
Otto, Christian; Geinitz, Veronika; Kletzin, Ulf; Reich, René
FEM simulation of wire drawing. - In: Engineering for a changing world, (2023), 4.1.022, S. 1-12

The paper deals with the finite element simulation of wire drawing processes with focus on unalloyed carbon steels. Based on the development of suitable material models as a basis for the simulation model, the forming processes are analyzed over several drawing stages for different drawing regimes. The simulation model is validated by comparing the simulation results with measured values. For the description of the forming behavior, the damage developments of the wire during the multi-stage forming are specifically analyzed. Subsequently, forming limits are derived by correlating the calculated damage with mechanical parameters of the wires. The validation of the damage models used is made possible by an FE parameter study, within which a targeted variation of the drawing die geometry takes place at a specific drawing stage. The paper is concluded by the verification of the results obtained theoretically by practical tests on a wire drawing machine using critical drawing die geometries.
Geinitz, Veronika; Otto, Christian; Kletzin, Ulf
Drahtziehen ohne Bleibadpatentierung. - In: Draht, ISSN 0012-5911, Bd. 74 (2023), 4, S. 14-16