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Bolted joints are one of the most used joining technologies in engineering. It is possible to join different kind of materials and to transmit heavy loads. Nevertheless, they are vulnerable to fatigue cracks. The present research investigates the dependency between the preload of the bolt and the initiation of a fatigue crack in the bolted sheet. Therefore, a representative bolt connection with a bolt of size M22 was selected in combination with a 5 mm thick sheet made of steel S355MC (1.0976). The bolted sheet was loaded by a fluctuating tension load and a load ratio of 0.1. The test results show a strong correlation of the preload and the number of load cycles to crack for preloads from 0 kN to 30 kN. The load cycles to crack are increased by about factor 20 by using a preload in contrast to the sheet without any preload. For higher preloads, the load cycles to crack does not change considerably. However, the crack initiation location changes by increasing the preload. For small preloads, the crack starts at the bolt hole, and for high preloads, the crack starts at the fretting zone.

At the IMKF, eight different elastomer compounds with different polymer compositions were examined for their demolding characteristics and mold fouling. Ten demolding cycles were carried out for each compound and the fouling of the mold was photo-technical recorded after ten demolding cycles. The used polymer composition does not seem to have any significant influence. However, the components of the compound have a significant influence on the friction characteristics while removing of the vulcanizate from the mold. Crosslinking that begins very early has an initiating influence on mold fouling. The measurable fluctuations in the maximum demolding force that occur could correlate with the internal friction of the polymer with the filler.

Ropeways are one of the most effective way to transport passengers or goods within minimum space requirements and with high transportation capacities in conjunction with a high safety level. Hence, ropeways are preferably used in mountainous regions as well as for urban transport. However, due to their functional principle, ropeways dissipate plenty of energy based on damping and friction effects. This paper focuses on the analysis of the energy consumption of ropeways and presents possible improvements, which may reduce the total energy consumption up to 20%. In terms of climate change and green marketing this could be one key point to implement sustainable tourism in ski regions. First, an analytical model is described, which enables the analysis of monocable ropeway systems in a stationary state. The model delivers physical values like the forces at the towers and the power consumption, which is separated into parts for transportation, the power loss of the drive, the power consumption of the stations and the power loss of the sheaves. As an improvement to the ropeway standard DIN EN 12930, the rolling resistance coefficient will be considered as velocity-dependent. The model is parametrized by measurement data of a representative ropeway. Second, the main parameters of the mechanical system such as the velocity or the number of vehicles are analyzed concerning their influence on the energy consumption. Finally, three possible energy-saving strategies are described, which provide a significant reduction of the energy consumption without any modifications in the mechanical system or by reducing the transport capacity.

Introduction Due to the COVID-19 crisis or any other mass casualty situation it might be necessary to give artificial ventilation to many affected patients. Contrarily, the worldwide availability of emergency ventilators is still a shortage, especially in developing countries. Methods Modes of artificial ventilation were compared and the most safe, easy to use, and lung protecting principle was optimized to fit all requirements of both emergency ventilation and cost-effective mass production. Results The presented research results describe a simplified device for a pressure-controlled ventilation which works without electricity according to a known principle. Just pressurized gas and a patient connection is required. The device enables the control of basic ventilator parameters such as peak inspiratory pressure, positive end-expiratory pressure and the ventilation frequency. Further, the device is semiadaptive to the patient's lung stiffness and automatically maintains minute volume through frequency adjustment. The machine can be manufactured by turning, milling and drilling and needs purchased components with costs less than 100 USD. A sterilization and thus a reuse is possible. Discussion The presented development does not describe a ready-to-purchase ventilator, it rather outlines a refined working principle for emergency ventilation and its easiest methods of production with a minimum of requirements. The presented research aims on providing an open-source guideline for production of an emergency ventilator using worldwide available methods and thus should inspire local researchers to do a reverse engineering and eventually to put it into operation following country-specific regulations. For long-term ventilation exceeding emergency purposes, a monitoring of alarms for disconnection and violation of desired ventilator parameters should be established. The ventilator is limited to a fixed ratio between PIP and PEEP. Moreover, the ventilation frequency depends on two parameters, which needs some training. Nevertheless, the ventilator provides basic features to enable an emergency ventilation with minimal prerequisites.

The treatment of autoimmune disorders such as multiple sclerosis (MS) so far relies largely on the use of non-specific immunosuppressive drugs, which are not able to cure the disease. Presently, approaches to induce antigen-specific tolerance e.g. by peptide-based tolerogenic “inverse” vaccines regain interest. We previously have shown that coupling of peptides to carriers can enhance their capacity to induce regulatory T cells in vivo. We here investigated in an experimental autoimmune encephalomyelitis (EAE) model for chronic MS (MOG C57BL/6) whether the tolerogenic potential of immunodominant myelin T cell epitopes can be improved by conjugation to the synthetic carrier polyethylene glycol (PEG). Indeed, preventive administration of the PEGylated antigenic peptide could almost completely protect mice from EAE development, which was accompanied by reduced immune cell infiltration in the central nervous system (CNS). Depletion of Tregs abrogated the protective effect indicating that Tregs play a crucial role in induction of antigen-specific tolerance in EAE. Treatment during the acute phase was safe and did not induce immune activation. However, treatment at the peak of disease was not affecting the disease course, suggesting that either induction of Tregs is not occurring in the highly inflamed situation, or that the immune system is refractory to regulation in this condition. Thus, PEGylation of antigenic peptides is an effective and feasible strategy to improve tolerogenic (Treg-inducing) peptide-based vaccines, but application in overt disease might require modifications or combination therapies that simultaneously suppress effector mechanisms.

In recent years, Non-small cell lung cancer (NSCLC) has evolved into a prime example for precision oncology with multiple FDA-approved &ldquo, precision&rdquo, drugs. For the majority of NSCLC lacking targetable genetic alterations, immune checkpoint inhibition (ICI) has become standard of care in first-line treatment or beyond. PD-L1 tumor expression represents the only approved predictive biomarker for PD-L1/PD-1 checkpoint inhibition by therapeutic antibodies. Since PD-L1-negative or low-expressing tumors may also respond to ICI, additional factors are likely to contribute in addition to PD-L1 expression. Tumor mutation burden (TMB) has emerged as a potential candidate, however, it is the most complex biomarker so far and might represent a challenge for routine diagnostics. We therefore established a hybrid capture (HC) next-generation sequencing (NGS) assay that covers all oncogenic driver alterations as well as TMB and validated TMB values by correlation with the assay (F1CDx) used for the CheckMate 227 study. Results of the first consecutive 417 patients analyzed in a routine clinical setting are presented. Data show that fast reliable comprehensive diagnostics including TMB and targetable alterations are obtained with a short turn-around time. Thus, even complex biomarkers can easily be implemented in routine practice to optimize treatment decisions for advanced NSCLC.

The increasing importance to predict the storage and flow behavior of granular materials and the need to optimize the processing leads towards ever more complex discrete element models. To parametrize these models, simulation parameters are often iteratively varied until the macroscopic particle behavior corresponds to experimental findings. However, this technique is not always practicable and does not consider the microscopic particle behavior. To study local and microscopic phenomena using the discrete element method, a parameter identification procedure is developed, which solely needs standardized and simple experiments and no supplementary parameter adaptation process. The experimentally identified parameters can be directly transferred to a complex discrete element model, in this case: a ring shear cell. After this the results have been compared to measurements. The validation displays that the developed parametrization procedure is sufficient to identify the model parameters experimentally and makes the numerical parameter adaptation unnecessary. Additionally, all identified parameters are related to physical quantities which facilitates the interpretation of the simulation. Hence, the presented parameter identification procedure extends the actual parametrization technique and especially helps to develop discrete element models where an alignment with experiments is impossible, or local and microscopic phenomena play a key role.

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.

Magnesium is the structural metal with the lowest density and hence a perfect lightweight material. This research investigates the crashworthiness of triggered and non-triggered welded tubes made of AZ31. Therefore, drop tower tests were performed to observe the crashworthiness under axial impact load. An improved crashworthiness was observed by using a trigger at the top end. The reached specific energy absorption is about 78 kJ/kg and similar to aluminum. For the first time, the tapering principle was investigated with tubes made of magnesium in an analytical, experimental and numerical way. It is shown that tapering works with a low degree of deformation.

Background: Therapeutic treatment options for chronic autoimmune disorders such as multiple sclerosis (MS) rely largely on the use of non-specific immunosuppressive drugs, which are not able to cure the disease. Presently, approaches to induce antigen-specific tolerance as a therapeutic approach; for example, by peptide-based tolerogenic ‘inverse’ vaccines have regained great interest. We have previously shown that coupling of peptides to carriers can enhance their capacity to induce regulatory T cells in vivo. Method: In this present study, we investigated whether the tolerogenic potential of immunodominant myelin T-cell epitopes can be improved by conjugation to the synthetic carrier polyethylene glycol (PEG) in an experimental autoimmune encephalomyelitis (EAE) mouse model for chronic MS (MOG C57BL/6). Results: Preventive administration of the PEGylated antigenic peptide could strongly suppress the development of EAE, accompanied by reduced immune cell infiltration in the central nervous system (CNS). Depletion of regulatory T cells (Tregs) abrogated the protective effect indicating that Tregs play a crucial role in induction of antigen-specific tolerance in EAE. Treatment during the acute phase of disease was safe and did not induce immune activation. However, treatment at the peak of disease did not affect the disease course, suggesting that either induction of Tregs does not occur in the highly inflamed situation, or that the immune system is refractory to regulation in this condition. Conclusion: PEGylation of antigenic peptides is an effective and feasible strategy to improve tolerogenic (Treg-inducing) peptide-based vaccines, but application for immunotherapy of overt disease might require modifications or combination therapies that simultaneously suppress effector mechanisms.

Crash absorbers made of fibre-reinforced plastics becoming more and more popular to reduce the mass in the front section of cars. Various research projects analysed the high specific energy absorption and the stable crushing behaviour of this material, however without examining the connection to other car body components. This paper focuses on the connection of the crash absorbers to the bumper system, particularly regarding to the crushing behaviour. An initial step focused on the development of a crash absorber made of carbon-fibre-reinforced plastic, which shows similar energy absorption compared to absorbers made of aluminium. A following step investigated various connection concepts using a drop tower. These first connection concepts resulted in unstable crushing behaviour. The finite element simulation of the tests delivered additional information about the reasons for the insufficient crushing behaviour. Subsequently, a simulation of various connection concepts turned out suitable connection concepts. A final drop tower test investigated the best connection concept. The developed connection system shows similar to the unmodified crash absorber stable crushing behaviour.

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.

Increasing competition and short product life cycles make it necessary to optimize and evaluate the outcome of manufacturing processes. In tool grinding, models for the final workpiece geometry and cutting forces are of particular interest. To establish a valid general grinding model, we investigated the cutting process and the influence of local grinding wheel engagements on the material removal. We consequently developed models of material removal and grinding wheel topography, which capture the main correlations in grinding. In combination, temporal cutting forces and final workpiece geometry are predictable and are in excellent agreement with experimental data. The introduced models are valid for grinding in general, since they are solely based on the geometry and process parameters, and hence are applicable for manufacturing process optimization.

Tool grinding is a complex process in which temporal dynamics of workpiece and grinding wheel, and the material removal process itself, affect the quality of the workpiece. Many existing models already provide the option to study the dynamics of workpiece and grinding wheel or cutting forces and material removal processes, but mostly do not combine these aspects. Here, workpiece dynamics are studied in relation to its structural and geometrical changing properties during machining, and are used to simulate the vibrations and deformation of the workpiece during grinding. In combination with models for the grinding wheel and the material removal process, dependencies of the workpiece dynamics on the workpieces quality are studied and results from this hybrid model are in excellent agreement with empirical measurements. Furthermore, the results demonstrate the significant effects of deformations of the workpiece on its final geometry.

In many industrial fields granular raw material is stored in silos until it is transported to machines for processing. During transportation complex interactions between particles and surrounding structure occur. To be able to investigate the dependency of particle movement on different parameters a reduced problem is investigated on a tribometer test-rig. Therefore, a box is filled with particles and pressed on a rotating disc. Interactions between process parameters, like particle shape, roughness or velocity of disc, can be observed clearly. Beside, a discrete element simulation is built up and validated with these experiments. Beside the particle behavior is analyzed under additional conditions like varying load and material properties. These investigations are necessary to transfer results to more complex systems.

The manufacturing of high performance cutting tools, like drills and chamfers, is done by a deep grinding process. This tool grinding process shows nonlinear relations between predefined process parameters, as cutting depth, feed speed and cutting speed, and the process characteristics, as process forces, surface properties and stability. Within an interdisciplinary research project a process model is built up to represent the process machine interaction and to predict process forces, deformation of the workpiece and geometry errors caused by this deformation. In this paper, the process model and the coupling of the included submodules will be described. The focus is thereby on the explanation of the contact module and the implementation in the dynamical model. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

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.

This article presents an overview of current simulation methods describing the interaction of grinding process and grinding machine structure, e.g., vibrations, deflections, or thermal deformations. Innovative process models which describe the effects of the grinding wheel–workpiece interaction inside the contact zone are shown in detail. Furthermore, simulation models representing the static and dynamic behaviour of a grinding machine and its components are discussed. Machine tool components with a high influence on the process results are modelled more detailed than those with low influence. The key issue of the paper is the coupling of process and machine tool models for predicting the interactions of process and machine. Several coupling methods are introduced and the improvements of the simulation results are documented. On the basis of the presented simulation approaches, grinding processes and machines can be designed more effectively resulting in higher workpiece quality and process stability.

Dynamic crash tests are performed in order to determine the crash behavior of thermoplastic composite crash boxes. The specimens are made from woven fiberglass/polyamide plates. Recently developed thermoforming and welding methods are used to construct the crash boxes. The crash experiments show that the tubes are crushed in progressive manner start from one end of the tubes and delamination takes place between the layers. To better understand details of the crash process, the LS-DYNA explicit finite element code is used. Thin shell elements are used to model the walls of the crash box. To simulate the delamination between the composite layers, the tube walls are modeled as multi layer shell elements. An adequate contact algorithm is implemented to model the adhesion between the layers. Finally the multi design optimization MDO technique is implemented to find an optimum composite crash box that absorbs the most energy and has minimum weight. The crash performance of the optimum composite crash box is compared with an optimum aluminum tube.

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.

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.

Axial and oblique impact crash tests on empty and honeycomb filled aluminum square tubes have been performed. Furthermore, in order to find more detail about crash process, finite element simulation of the experiments has been performed. In terms of finding more efficient and lighter crash absorber in this research, two steps have been done: First, multidesign optimization (MDO) technique has been applied to maximize the energy absorption and specific energy absorption of square, rectangular and circular tubes. Results of MDO have shown that the circular tubes have the best response. Results of previous works have indicated that filling of tubes with light filler often improve the crashworthiness behavior, and when the density of filler is higher than critical filler density the structure will lose its weight efficiency. Therefore, selection of an appropriate honeycomb density and tube thickness is unavoidable. In the second step, the MDO technique has been used to optimize honeycomb filled aluminum.

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.

In many technical applications sliding contacts with multiple contact points or engagements exist, like between seals and rough surfaces, between grinding wheel and workpiece, or between granular material and storage box. In a simplified way these contacts can be represented by a friction oscillator with multiple bodies. The behavior of the friction oscillator with one body is already well known. However only few studies exist on the behavior of a friction oscillator with multiple bodies. In this study especially the dynamical behavior depending on the number of bodies, the friction characteristic and the velocity of the belt has been investigated. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

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.

Self-excited vibrations are observed in many technical applications. Frictional contacts are often involved in the mechanism which generates vibrations. Reasons for the excitation mechanisms are decreasing friction characteristics depending on the sliding velocity, fluctuating normal loads or different geometrical effects. First, the mechanisms are explained using simple examples. The practical relevance of self-excited, friction-induced vibrations is exemplified with three technical systems: a system with an axial seal; a tread block of a tyre; and a disc brake. The knowledge of the excitation mechanism is necessary to introduce successfully design countermeasures. These measures to avoid self-excited vibrations are important to solve practical problems. They are the main focus of this work. Further, additional passive and active subsystems are described and validated experimentally. Therefore, a large range of design, active and passive solutions are given.

In the present paper dynamic friction processes in seals are investigated. The undesired stick-slip effect of these components under real technical conditions is analyzed. Starting with the basics of stick-slip vibrations the development of an advanced seal design with improved properties is presented that prevents stick-slip. Finally, an optimization based on the extensive but simple stability analysis is shown by an expanded theory of stick-slip simulations.Copyright © 2004 by ASME