Matthias Kröger

MRE Properties under Shear and Squeeze Modes and Applications

Magnetorheological elastomers (MREs) are smart materials whose mechanical properties, like their modulus and elasticity, can be controlled by an external magnetic field. This feature has resulted in a number of novel applications, such as adaptive tuned dynamic vibration absorbers for suppressing unwanted vibrations over a wide frequency range. MRE-based devices operate in different modes, such as shear mode and squeeze mode; however, the study of mechanical performances of MREs under squeeze mode is very rare. This article aims to investigate MRE performances under both shear and squeeze modes. Experimental studies and simulations were conducted to analyze the MR effect in both modes. These studies indicate a different working frequency ranges for both modes. In a case study, a MRE-based vibration absorber was built up in a simulation and its mechanical performances were analyzed, which demonstrated good capabilities in reducing vibrations.

Modeling of Process Machine Interactions in Tool Grinding

A systematic modeling approach to predict and manipulate the static and dynamic process machine interactions in tool grinding is described. The modeling approach is verified by experimental investigations gained by means of an industrial tool grinding machine and separate test stands. It combines models of the static and dynamic behavior of the grinding machine and its components with a microscopic grinding process model. Material removal algorithms are applied to cope with the changing shape and changing mechanical properties of the workpiece during grinding. The interaction model has been applied in the process planning phase to optimize tool paths and process parameters in order to reduce resulting shape errors in ground tools.

Simulation and Experimental Investigations of the Dynamic Interaction between Tyre Tread Block and Road

The dynamic behaviour of a tyre tread block is described by a modularly arranged model with a high numerical efficiency. Special emphasis is laid on the interaction between structural dynamics and contact mechanics. Parameter-dependent friction is implemented as well as a non-linear contact stiffness to consider the properties of the rough surface. The model includes local wear which influences the dynamic behaviour. The relevant parameters are obtained by experimental investigations. High-frequency stick-slip vibrations of the tread block occur e.g. on a corundum surface within a certain parameter range which are compared to simulation results. Furthermore, the model includes the rolling process of the tyre: the tread block follows a trajectory which is obtained from the deformation of the tyre belt. The results from simulations with a single tread block provide a deeper insight into highly dynamic processes that occur in the contact patch such as tyre squeal, run-in or snap-out effects.

Local effects between the tyre and the road

The tyre is the integral part of the vehicle that transmits all normal and tangential forces between the vehicle and the road. The tyre tread block is the only tyre component that is in direct contact with the road surface and is thus of special interest. However, the contact situation between the tyre and the road is a very complex one, and therefore all its details are usually unknown. The Institute of Dynamics and Vibration Research at Leibniz University Hanover (Germany) and the Insitute of Machine Elements, Design and Production of the Technical University Freiberg (Germany) investigate the local contact phenomena in the tyre/road contact and developed a modular model that describes the dynamic behaviour of tyre tread blocks, taking into account the contact effects.

An integrated model of tool grinding: challenges, chances and limits of predicting process dynamics

The objective of manufacturing technology, to reduce machining costs, increase product quality and optimize process setups, is only achievable by considering the entire manufacturing process and its interrelations. Especially in tool grinding, strong interactions exist between workpiece dynamics, grinding wheel engagement, structure deformations and cutting process conditions, which makes an integrated model necessary. This paper introduces a tool grinding model that combines time-dependent dynamical aspects of the grinding wheel and workpiece with local varying contact conditions to predict the final workpiece geometry and cutting forces with a high resolution in space and time. The model is capable to reproduce systemic effects on cutting forces and ground geometries which only occurs in the interplay of all system components. The model is also positively tested in representing influences of process parameters and in optimizing the machining. The excellent agreement of simulations and experimental data shows the model’s potential in manufacturing technology, but also in investigating grinding aspects, which are not fully understood yet.

Dynamic systems with rubber contacts in technical applications

Abstract This work deals with the experimental investigation and modelling of adhesion and friction of rubber. With the recently developed adhesion test rig, the contact partners can rapidly be separated while the contact force is measured. The results reveal a strong influence of the preload duration and preload level. Furthermore, a modular modelling concept for dynamic systems with rubber components undergoing sliding friction is presented and exemplified by a tyre tread block. The model considers the geometry of the rubber component, the parameter dependent friction, the roughness induced non-linear contact stiffness and the wear effects. The measurements of high frequency, self-excited tread block vibrations are performed on a tribometer test rig and compared to corresponding simulations with the proposed model.

Lokale Effekte zwischen Reifen und Fahrbahn

Der Reifen als integraler Bestandteil des Fahrzeugs ubertragt alle erforderlichen Normal- und Tangentialkrafte zwischen Fahrzeug und Fahrbahn. Der Reifenprofilblock ist die einzige Reifenkomponente mit direktem Kontakt zur Fahrbahn und ist somit von besonderem Interesse. Die genaue Kontaktsituation zwischen Reifen und Fahrbahn ist sehr komplex und deshalb in der Regel nicht im Detail bekannt. Das Institut fur Dynamik und Schwingungen der Leibniz Universitat Hannover und das Institut fur Maschinenelemente, Konstruktion und Fertigung der TU Bergakademie Freiberg untersuchen lokale Kontaktphanomene zwischen Reifen und Fahrbahn und stellen ein modular aufgebautes Modell vor, das unter Berucksichtigung der Kontakteffekte eine Beschreibung des dynamischen Profilblockverhaltens liefert.

An Experimentally Validated Model for Unsteady Rolling

The description of the tyre road contact is important for brake or drive stability systems working in modern vehicles. Steady models loose accuracy, if slip or normal force contain higher frequencies. This is the case during an ABS brake process.

Effects of the Grinding Wheel Eccentricity and Waviness on the Dynamics of Tool Grinding

The complex dynamics of grinding repeatedly cause critical or unstable process conditions. For a better understanding and prediction of such occurrences, the dominant excitation phenomena need to be identified and their interrelation with the system dynamics have to be analyzed.Based on measurements of the excited frequencies in several operation modes of the grinding machine, the grinding wheel rotation is identified as a major excitation source. Further analysis of the grinding wheel surface displays three main components that define the excitation frequencies of the system; these are the eccentricity, waviness and roughness (also named wheel topography). Moreover, the wheel topography and thus the excitation frequencies can change over time due to excessive wear.Following the experimental results, a grinding wheel topography and wear model are developed and included in an integrated simulation of tool grinding. The analysis of the calculated cutting forces in the frequency domain confirm the excitation due to the grinding wheel topography.Firstly, this work has extracted the grinding wheel as a prominent excitation mechanism and reproduced it with the developed grinding model. Secondly, we have evidence that a complete description of the complex grinding process is only possible when considering the interdependence between system dynamics, wheel kinematics and the grinding process.

Simulation of tire tread block dynamics with respect to complex contact phenomena

Vibrations of the tire structure are caused by the interaction between the rolling tire and the road surface. The tread block is the only tire component which is directly in contact with the cleft road surface texture and therefore of special interest. The contact due to the rough surface leads to complex contact phenomena e.g. friction characteristics depending on normal contact pressure and relative velocity, non-linear contact stiness and wear eects changing the tread block geometry and in hence the local contact forces. These contact phenomena strongly influence the dynamical behaviour of the tread block and the whole tire. A modular model based on a modal reduction method will be presented to investigate the tread block dynamics under consideration of the local friction characteristic, the non-linear contact stiness and wear which are also analyzed experimentally on a concrete road surface to identify the model parameters.