Daniel Juhre
Prof. Dr.-Ing. Daniel Juhre
Institute of Mechanics (IFME)
Current projects
Modular peristaltic surface conveyor with AI based digital twin for polybags
Duration: 01.04.2024 bis 31.12.2027
The Modular Peristaltic Surface Conveyor (MPSC) is an entirely new device that conceptually enables the separation and sorting of flexible small packages (polybags) for the first time, providing an alternative to costly manual processing. For the first time, alongside the development of the actual MPSC, an AI-based Digital Twin (DT) is to be developed, which, based on AI-optimized simulation models, will allow predictions of system behavior and automated parameterization of the actuators and sensor data processing.
Integration of physically motivated material models for filled elastomers in multi-body simulations of highly dynamic systems
Duration: 01.05.2024 bis 30.04.2027
The DFG-funded research project aims to increase the numerical prediction capability for technical systems by implementing a holistic simulation methodology that enables efficient coupling between a multi-body simulation and a non-linear FE model. An extension of the physically motivated dynamic flocculation model is used to fully and precisely map the non-linear material behavior of elastomeric bearing elements. The focus here is primarily on the changes in the properties of the bearings under multi-axial loading, which are often neglected in current modeling approaches at . Since the integration of a detailed FE model leads to an increase in the necessary computing resources, different levels of detail of the solver coupling are implemented and analyzed in this project with the aim of allowing a reduction in computing time with an acceptable loss of accuracy. The resulting different levels of complexity of the developed methodology are comprehensively compared with conventional modeling strategies. The individual coupling strategies are evaluated with regard to the implementation and parameterization effort as well as the physical interpretability and the required computing resources. The developed and validated FE models based on the DFM are also examined with regard to their suitability, to what extent and with what reliability certain material parameters can be transferred once to other geometries and load scenarios. Finally, the accuracy of all investigated strategies for coupling the FEM and MBS is assessed with the aid of test results from real applications. The FEM is integrated into the MBS both directly via various solver couplings and indirectly by generating a characteristic map or a surrogate model with the aid of the FE model for use within the MBS. The first application example is a laboratory centrifuge, whose vibration amplitudes and operating resonances are measured and compared with the numerically obtained results of the respective coupling strategies. Furthermore, the developed methodology is applied and validated in the context of a vibration analysis of chassis components of an electric vehicle.
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26591_ SOFINA -Simulation-based optimization of flow diverters for the treatment of intracranial aneurysms
Duration: 01.04.2023 bis 31.03.2026
The aim of the project is to research ways of optimizing the fluid dynamic treatment of intracranial aneurysms in order to shorten the occlusion time, reduce the need for follow-up treatment and eliminate the risk of ruptures. To this end, novel neurovascular implants with improved flow-modelling properties are to be developed (target values: locally reduced porosity, optimized adaptability to the anatomy). Possible individualized solutions include the further development of braided structures or the use of novel polymer nonwovens on the support structure. On the other hand, "intelligent" software tools are being developed that enable improved planning and implantation based on virtual catheter guidance through complex 3D vessel models of patients. Deformation states of both the catheter and the crimped implant are simulated on their way to the brain aneurysm. In addition, a blood flow simulation is carried out to assess the effectiveness (intra-aneurysmal thrombosis) of the implant. The results will be used to provide interventionalists with information on handling the implant before and during treatment. Such software enables targeted optimization of the implant properties, for example to achieve localization-dependent reductions in velocity and vertebral strength of up to 50 % compared to the untreated state.
Strategies for the dynamic adaptation of discretization based on higher-order transition elements for the analysis of wave propagation processes using high-performance computers
Duration: 01.11.2023 bis 31.10.2025
Adaptive mesh refinement (AMR) methods are absolutely essential in many industrial and scientific applications in order to reduce the numerical effort and thus make complex problems manageable in the first place. However, a look at the current literature on AMR reveals a number of shortcomings that still need to be resolved. In order to achieve local mesh refinement, either hybrid meshes consisting of simplex and tensor product elements or constraints must be used. However, both approaches inevitably lead to local accuracy losses. Furthermore, in industrial applications, linear approach functions are often used, which is why only algebraic convergence can be achieved. In the scientific environment, there are of course also approaches for complete hp-adaptivity. However, due to the complexity of their implementation, these methods are designed for networks with one hanging node per element edge/surface and have weaknesses when applied to highly dynamic processes (explicit time integration), as diagonal mass matrices are not available. It should be noted, however, that exponential convergence rates can be achieved compared to simple h-refinements. The mentioned problems can easily be eliminated by higher-order transition elements derived on the basis of the so-called mixed (transfinite) interpolation. The element formulation is based on quadrilateral or hexahedral elements in the reference domain and can couple arbitrary discretizations. In principle, a wide variety of element families can be coupled, which differ not only in size or order of approach. Since the functional space does not have to be restricted by constraints, there is no need to compromise on accuracy. For high-frequency, transient calculations, suitable methods for diagonalizing the mass matrix are also being developed in this project. The resulting element family forms the basis for dynamic mesh refinements. The special feature of this approach is the targeted combination of refinement and coarsening steps, which are carried out in each time step of the simulation. This allows optimal convergence rates to be achieved with the lowest possible numerical effort . In order to further increase the efficiency of the developed technique, the algorithms are prepared for high-performance computers. The outstanding properties of the proposed methodology are illustrated using selected examples of wave propagation. For this purpose, continuous structural monitoring by means of guided waves in microstructured materials and the analysis of seismic activities are used.
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26088_ Design and evaluation of a novel dynamic ankle-foot orthosis using silicone/SMA materials
Duration: 01.10.2022 bis 30.09.2025
Ankle-Foot Orthoses (AFOs) are those devices used for rehabilitation of a pathological gait, which is caused for instance by a stroke. This research aims to design, model, simulate, manufacture, and test a novel AFO, which is designed to ensure ease of use, freedom of movement, and high performance for high-level activities at relatively low costs. Research problems are inherent in the increasing demand for AFOs based on polymers, which have relatively low biomechanical properties and may cause skin sweating and irritation in the long term. Furthermore, there are problems related to the high costs of recent AFOs made of advanced composites or carbon fiber, the market needs (orthopedic workers) and users alike, and the necessity of a novel AFO that meets the demands and helps to produce orthoses for fitting each patient. Therefore, orthotists could save time and obtain a more convenient AFO prototype, which helps them in patients' treatment.
This study includes, from an applied point of view, the design, modeling, and simulation of a novel ankle-foot orthosis based on silicone, shape memory alloy (SMA), and elastic bands. This, in turn, ensures freedom of movement and high performance for high-level activities. It also includes, in practical terms, the manufacturing of the ankle-foot orthosis, based on the aforementioned design and materials, and conducting appropriate mechanical and biomechanical tests. This study also includes a literature review and description of the materials, methods, and equipment used in the design, modeling, simulation, manufacturing, and testing of a novel dynamic ankle-foot orthosis.
26174_ Autoregressive neural networks for predicting the behavior of viscoelastic materials
Duration: 01.09.2022 bis 31.08.2025
Neural networks are already used extensively in the field of data analysis. Common material models consist of physically based equations to describe the real behavior as good as possible. Measurements are used to adjust the material parameters, but the accuracy of the model depends on the complexity of the constitutive equations. Neural networks offer the possibility to describe a material with the same test data without the necessity to derive complex and physically based material laws.
Considering a uniaxial stress-strain curve of a hyperelastic material, a classical neural network can be easily set up to describe this behavior. During training, the network finds a good fitting function that depends mainly on the number of weights and biases and the amount of training data. These overall parameters are not physically motivated, as they only connect the stress values to the strain values via multiplication and the sigmoid transfer functions in the range of the trainings set. This is the reason why classical neural networks have a very poor extrapolation performance.
In contrast, autoregressive neural networks can train a time series, such as the stress curve with a constant strain rate, using previous stress values to calculate the next one. Instead of training a stress-strain function, these networks attempt to find a recursive formulation between stress values. With external inputs, other variables can also be used in the recursive formulation, such as the strain rate. If the training data contains different strain rates, the network can take them into account. In addition, other variables are possible, for example, different temperatures.
Due to the recursive or regressive functionality, the network can calculate stress-strain curves, even beyond the range of the training data. With a sufficiently large training data set, it is thus possible to describe more complex material behavior better than with classical material models.
In this project the properties of viscoelastic materials shall be estimated with an autoregressive neural network. Calculating a stress-strain curve with different strain rates and training the networks can be done in a few minutes. Prediction with different strain rates and stress values outside the range of the training data works very well with only a small error and much less computation time. In addition to optimizing the network architecture, the possibility of other external inputs such as temperature or training with a real measurement data set will also be investigated.
Extension of fictitious domain methods for vibroacoustic issues - analysis of heterogeneous insulation materials
Duration: 01.08.2022 bis 31.07.2025
Predicting the acoustic behavior of systems containing materials with complex microstructure is a major challenge for several reasons. On the one hand, it is very time-consuming to build high-resolution numerical models using geometry-conforming discretizations and, on the other hand, all physically relevant interactions of the structure with both the surrounding and the enclosed fluid must be taken into account. The geometry-conform discretization of heterogeneous materials with complex microstructure usually leads to a very high number of finite elements and thus to unacceptable computing times. In recent years, fictitious domain methods, such as the Finite Cell Method (FCM), have emerged as an effective alternative. To capture the acoustic or vibroacoustic properties, the FCM must be extended in some aspects for the new field of application. First, the acoustic wave equation for calculations in the time domain and the Helmholtz equation for analyses in the frequency domain must be discretized using fictitious domain methods. Furthermore, suitable coupling strategies between the structural and fluid domains must be developed. The subfields can be coupled both weakly (without feedback) and strongly (with feedback). The advantage of fictitious domain methods is, in addition to the highly accurate resolution of the geometry (despite non-conformal discretization), the possibility of superimposing structural and fluid elements. This makes it possible to develop an effective strategy for the vibroacoustic coupling of heterogeneous materials. The numerical effort of these complex simulations is still very high, even when using fictitious domain methods. Therefore, another goal is to derive simplified models based on numerical homogenization methods in addition to the microstructurally resolved models. Despite the strong abstraction of reality, it is expected that useful results can be achieved for various applications. The final focus of the project is the experimental validation of the numerical methods developed. Various test rigs will be used for this purpose. The vibration behavior of the structure is crucial for the implementation of the vibroacoustic coupling. This can be investigated using a 3D laser scanning vibrometer. In addition, the frequency-dependent acoustic parameters are measured using various simple measurement setups, such as a Kundt's tube, and compared with the simulated results. Furthermore, the sound radiation is measured in a free-field room using microphone arrays and far-field microphones. On the basis of this data, the performance of the implemented models can be verified. Finally, guidelines for their use are derived.
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Completed projects
26592_ Extension of fictitious domain methods for vibroacoustic issues - analysis of heterogeneous insulation materials
Duration: 01.04.2023 bis 31.03.2025
The project is dedicated to the development of an efficient calculation method for solving three-dimensional vibroacoustic problems using porous insulation materials. The aim is to resolve the microstructure of the insulation material in order to overcome the current limitations of Biot's theory, which is often used and seems particularly unsuitable for modeling closed-cell foams. In order to enable the extremely complex geometry-resolved modeling we are aiming for, fictitious domain methods with higher-order approach functions are to be used. On the one hand, these can be applied very advantageously to voxel data and, on the other hand, a high efficiency for wave propagation problems can be expected.
"COCOON" - aCOustiC Optimized hOusiNg
Duration: 01.06.2022 bis 30.11.2024
Simulation-based and sensor-based functionalized housing design
The ZIM network INSTANT is primarily concerned with medical issues. Within the network, the COCOON R&D project focuses on reducing noise pollution during diagnostic and interventional image-guided procedures.
Various medical studies show that persistently high noise levels can lead to poor concentration, stress, impaired memory, a general reduction in performance and other symptoms, including burnout syndrome. Such stress and anxiety situations are detrimental to the recovery of patients and lead to longer treatment times and therefore increased costs. On the part of clinical/medical staff, noise pollution can lead to loss of concentration and treatment errors, for example during interventions lasting several hours or several consecutive interventions.
In many machines, the generation of loud noises cannot be prevented or can only be prevented by interfering with the existing structure. However, technical measures can be taken to hinder the propagation and transmission of noise and thus minimize the disturbing noise emissions. The COCOON project is researching methods for designing and manufacturing acoustically optimized housings for large medical devices, which also results in very high standards with regard to approval and the materials used.
Furthermore, the ambitious approach of researching a "diagnostic system" for recording the status of product functionality is being pursued. The early alerting of malfunctions is intended to minimize device failures and can thus contribute to product monitoring after the product has been placed on the market.
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23482_ Evaluation of Phase Morphology and its Impact on the Viscoelastic Response of Elastomer Blends
Duration: 01.01.2020 bis 31.12.2023
Filler reinforced elastomer blends play a key role in the design and optimization of high performance rubber goods like tires or conveyor belts. In most cases, a phase separated, anisotropic blend morphology develops during the last processing steps (extrusion, calendering, injection molding), which lowers its free energy by coagulation and relaxation processes, before the morphology is frozen by cross-linking. The development of the detailed phase morphology and its influence on the high-frequency viscoelastic response, affecting e.g. friction, fracture and wear properties, is not well understood at present but of high technological and scientific interest.
Accordingly, one main objective is the physically motivated modeling and numerical simulation of the thermo-chemically driven phase separation of filled elastomer blends with realistic, microscopic input parameters obtained from independent physical measurements. Beside the chemical compatibility of the polymers and the fillers, also the effect of mechanical stress on the phase dynamics shall be investigated. In combination with elaborated experimental methods, the phase field modeling for Cahn-Hilliard and Cahn-Larché type diffusion shall be applied. The local phase field equations, considering at the end three phases, must be implemented into the isogeometric analysis, allowing for the study of complex interaction of multi-phase materials with different material characteristics. The experimental focus lies on the evaluation of thermodynamic polymer-polymer- and polymer-filler interaction parameters that govern the phase morphology and filler distribution. For the simulation of phase boundary dynamics, the collective chain mobility shall be estimated as an input parameter of the Cahn-Hilliard type dynamic equation.
A second objective is the modeling and numerical simulation of the high-frequency linear viscoelastic response of unfilled and filled elastomer blends, which shall be based on the distinct phase morphology including domain and interphase size, filler distribution and cross-linking heterogeneities. The non-linear response will be analyzed in a future project.
The results of phase field simulations shall be compared to experimental investigations of phase mixture processes and numerically evaluated viscoelastic moduli shall be correlated with experimentally constructed viscoelastic master curves.
The sum of the both objectives leads to a complete numerical procedure with which it is possible to simulate the complete cycle of producing and using a new polymer blend for later engineering applications by optimizing the involved process and distinctive material parameters.
24608_ Development of FE technologies in the field of mixed formulation based on industrial applications
Duration: 02.11.2020 bis 31.10.2023
The aim of the dissertation is the development and further development of finite element technologies in the field of mixed formulation. The focus here is on the displacement-compression-strain formulation (u/p/e), as it enables both the mastering of incompressible material behavior and increased accuracy in the calculation of stresses and strains.
DampedWEA - Innovative concepts for vibration and noise reduction of gearless wind turbines
Duration: 01.12.2019 bis 30.04.2023
The aim of the joint project DampedWEA is to increase the acceptance of wind turbines. The aim is to open up new regions for wind turbines, particularly in the vicinity of inhabited areas. This requires a reduction in the radiated noise level. In this joint project, the focus is on tonal emissions, which are increasingly coming to the fore due to the successful optimization of aeroacoustic emissions and now pose a problem. In order to reduce these sufficiently, innovative concepts for vibration and noise reduction are used. The main source of tonal noise is the generator, as the vibrations from the generator propagate via the bearings and the drive train or via the generator support structure into the entire wind turbine and are ultimately emitted as sound. Tonal noises are particularly critical for public acceptance, as they are perceived as much more annoying than broadband noise.
The aim of this project is to investigate transmission paths where research into the potential for noise reduction is promising. In addition, many different concepts will be tested, some of which go far beyond the current state of the art. The project is being carried out in a consortium consisting of WRD/Enercon with the research partners DLR, Fraunhofer IFAM, Otto von Guericke University Magdeburg and Leibniz University Hanover.
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Coupling of fictitious domain methods with the boundary element method for the analysis of acoustic metamaterials
Duration: 01.08.2019 bis 30.04.2023
This project proposal focuses on innovative acoustic metamaterials. These are, for example, acoustically effective foam materials in which local resonance effects are to be generated by additionally introducing solid bodies with high rigidity. The aim is to significantly improve the insulating and damping effect of these materials, particularly in the low-frequency range. However, general guidelines on how an acoustic metamaterial should be designed in order to achieve the best possible and in particular a broadband effect are still lacking. The aim of the proposed project is to develop a reliable and efficient numerical tool in order to carry out a comprehensive analysis of the mechanisms, influencing factors and design parameters as well as targeted topology optimizations of acoustic metamaterials in further research work. A coupling of the finite cell method (FCM) and the boundary element method (BEM) is to be developed for the vibroacoustic analyses . The FCM is to be used for the structural-dynamic calculations in order to adequately and efficiently map the heterogeneous structure of the metamaterials. The resulting sound pressure in the surrounding air volume and the radiated sound power are used to evaluate different acoustic metamaterials. The sound radiation is calculated using the BEM, as this is an efficient way of calculating the acoustic field, particularly for evaluation in the far field, compared to volume-discretizing methods. The advantages of higher-order approach functions are also to be utilized within the scope of the project. After successful implementation, commercial FE-based calculation programs, analytical comparison solutions and experimental investigations will be used to verify and validate the developed methods in detail.
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Optimization of the design of mesoscale piezoelectric motors for robotic applications
Duration: 01.01.2021 bis 31.12.2022
Robotics has developed by leaps and bounds over the last few decades and many of the challenges of medium to large scale robotics have found suitable solutions. However, at the mesoscale, on the order of a millimeter to centimeters, few of these challenges have been addressed, chief among them, fabrication and actuation. Due to favourable scaling characteristics, piezoelectric actuation becomes more appropriate than electromagnetic actuation at small scales. Piezoelectric materials provide an actuation as they are materials that generate strain when a voltage is applied to them. They also generate a voltage when strained, which gives them the capability to operate as sensors or actuators, or both simultaneously. Due to their small total displacement, large bandwidth, and lack of friction, they have the ability to generate fast and precise movements.
The overall goal is to optimize a new class of piezoelectric motors based on a series of unimorph (a piezoelectric material bonded to a substrate) arms. The Canadian partner, Assistant Prof. Dr. Ryan Orszulik, has recently designed and fabricated a series of prototypes of a piezoelectric motor which has a planar rotor diameter of 9 mm, stator diameter of 8 mm, a total integrated motor thickness of 0.8 mm, weighs approximately 200 milligrams, and is capable of producing bidirectional motion with relatively low rotational speeds but high torque. However, a number of challenges remain, the most important of which is optimizing the torque density of the motor. For this purpose a numerical optimization will be used, which considers the mass and volume limitations, in order to achieve much higher torques without compromising structural integrity. This multi-objective optimization is a very challenging task, especially on such small scales. For mesoscale robotic applications, it is the torque that is of the greatest interest as it mitigates the need for a gearbox, which is very difficult to manufacture and integrate at these small scales. The unimorph based piezoelectric motor that is the focus of this project is simpler to construct, as it relies on non-standard planar fabrication techniques, and requires only a single drive source at a lower frequency to produce a high torque. In this research program, the goal is to leverage new fabrication techniques to create and miniaturize these piezoelectric motors, test them, and optimize them via analytical and finite element techniques. By employing the developed design, modeling, and fabrication techniques, a number of applications will be pursued including miniature autonomous vehicles and surgical instruments. The most promising possible application, which would create further opportunities for collaboration with the satellite design laboratory at York University, is to use these motors as the actuator for single gimbal control moment gyroscopes in pico to femto class satellites.
Innovative simulation methods for the acoustic design of automobiles
Duration: 01.07.2019 bis 30.09.2022
This project is a cooperation between the Chair of Multibody Dynamics and the Chair of Computational Mechanics with one research assistant from each partner. The core objective of the project is the development of a practical simulation methodology for calculating the noise emissions of engines and their psychoacoustic evaluation. This makes it possible to directly trace the effects of structural modifications (stiffness, mass distribution) and tribological system parameters (bearing clearances, viscosity, deaxialization and filling level) back to the excitation mechanisms and the internal structure-borne sound paths and to preventively combat them in terms of acoustic optimization through design and tribological measures. This purely virtual engineering approach is intended to do entirely without real prototypes and thus enable an acoustic evaluation early on in the engine development process. In this way, design measures to improve acoustic quality can be implemented in coordination with the development groups of adjacent subject areas without negatively influencing other important design criteria such as performance, pollutant emissions or total mass.
In contrast, passive measures to combat noise emissions through insulation, for example, are generally cost-intensive, as they require additional material as well as additional assembly steps and therefore have an impact on the production process. At the same time, this runs counter to the idea of lightweight construction, reduced consumption and environmental friendliness and leads to additional installation space being required, which is usually a very scarce resource in the development of modern engines and automobiles. The fundamental problem with these insulation measures, which are being used more and more frequently these days, is their symptomatic approach, which combats the effect but ignores the causes of the acoustic disturbance.
The holistic methodology that is the focus of this project, on the other hand, makes it possible to directly analyze and combat the cause of the disruptive noise emissions. In addition, the psychoacoustic evaluation of the sound emission allows it to be categorized into disturbing and less disturbing sound emissions. In this way, the design can be specifically modified so that the resulting noise is classified as more pleasant by people; after all, a quiet noise can still be perceived as more disturbing than a loud one.
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25675_ FE simulation of a vehicle joint from Siemens Mobility GmbH
Duration: 09.11.2021 bis 31.05.2022
The aim of the project is a comprehensive investigation of elastomer pads that are used in a vehicle joint from Siemens Mobility GmbH. For this purpose, finite element analyses are carried out to qualitatively evaluate the deformation properties of the joint and in particular the installed elastomer pads. In addition, experimental investigations are to be carried out on the elastomer pads from Siemens Mobility GmbH in order to characterize the corresponding material properties more precisely. This will allow more precise correlations between material selection and structural properties to be determined in the FE analyses.
26069_ Visual compression and reconstruction of patient-specific 3D vascular models for use in simulation methods
Duration: 15.10.2021 bis 14.04.2022
The aim of the project is to develop a method for generating simple geometries of vessel models that contain only essential information that can be used for the subsequent reconstruction of simplified simulation models for the finite element and CFD methods.
The focus here is on the geometry compression and reconstruction of the inner vessel wall with the help of parameterized NURBS. The centerline of the vessel is represented by the NURBS. Other important parameters (such as the vessel diameter, the curvature of the vessel and also the vessel thickness) are stored parameterized at the individual support points of the NURBS. In this way, the geometry is reduced to the essentials, but contains the most important information for recovering the required 3D geometry of the vessel model in a reconstruction process. This geometry can then be used for a wide variety of software systems to carry out corresponding simulations. Furthermore, it is possible to vary the parameters as required in order to generate new realistic vessel models for comparative simulations.
22760_ Competence Center eMobility - Powertrain research area: Sub-project AR4: "Lightweight construction and acoustics of electric motors"
Duration: 01.01.2019 bis 31.12.2021
The eMobility Competence Center project addresses the structural challenges and develops solutions in key areas as part of a newly established competence center, which will significantly strengthen cooperation between SMEs and university research and teaching. The knowledge can be transferred directly to the affected supplier industry, where it can help to successfully manage structural change and exploit new economic opportunities. In addition to the primary objective of building up and transferring core know-how, the main focus is on the long-term anchoring of the knowledge gained in economic structures that create jobs.
Based on a multi-patented, globally unique lightweight engine concept developed by OVGU, the work in the DRIVE TRAIN research area focuses on the further development and prototypical presentation of the new engine technology, its integration into the drive train and its operation in accordance with given safety and comfort requirements (driving dynamics). At the same time, there are further innovative steps in the area of basic research to increase the performance of the engine technology, which are to be developed and implemented in prototypes during this funding period.
Content of the AR4 sub-project:
The emitted noise is a central problem of all electrical machines. This is mainly due to the fact that the typical sound emission of an electric motor is very tonal and very high-frequency and is therefore, on the one hand, in the range of the auditory surface in which humans hear best and, on the other hand, is perceived as particularly annoying. For this reason, methods and solutions are to be developed as part of this sub-project in order to significantly improve the acoustic behavior of electric machines. The aim is not only to reduce the sound pressure level but also to achieve a noise that is as unobtrusive or pleasant as possible, which is why human perception is included in the considerations. State-of-the-art commercial simulation methods and proprietary software extensions are used for the developments, as well as extensive experimental studies and listening tests. The experimental investigations include vibration analyses using laser vibrometry in a stationary and rotating system (derotator measurements), sound pressure measurements with far-field microphones and measurements with microphone arrays (acoustic camera) in an anechoic chamber. The aim of the experimental investigations is to validate the simulation models on the one hand and to demonstrate the added value of the solutions developed on the other. In addition to acoustics, the focus is on lightweight construction. The concepts to be developed should be both acoustically inconspicuous and have a minimal mass.
Among other things, alternative materials (aluminum foam structures, metamaterials, GFRP, CFRP), innovative damping strategies, novel construction designs (e.g. additive manufacturing), as well as the inclusion of add-on parts (e.g. gearboxes) in terms of additional excitation sources are investigated. Stress analyses and strength calculations are carried out to ensure that structural integrity is guaranteed despite the lightweight construction measures taken. These include both static and dynamic load cases. The dynamic stress analyses are absolutely essential in order to take account of the inertial forces acting as a result of the highly variable processes over time and the impulsive excitations during typical operating scenarios.
22249_ Numerical analysis of crack propagation based on phase field method in welded steel structures
Duration: 01.11.2018 bis 31.10.2021
Welding is considered as one of the most indispensable processes in many industrial sections for joining. In many structures, welds are known as a critical sections led to mechanical failures. There are a variety of physical defects such as undercut, insufficient fusion, excessive deformation, porosity, and cracks that can affect weld quality. Of those defects, cracks are considered to be the worst since even a small crack can grow and lead to failure. All welding standards show zero tolerance for cracks whereas the other defects are tolerated within certain limits. There are three requirements for cracks to form and grow: a stress-raising defect, tensile stress, and material with low fracture toughness. Microscopic defect locations are available in practically all welds including geometric features and weld chemistry that can raise the local stress enough to induce a crack. That leaves the engineer to work with the stress environment and toughness: if either of the two can be effectively controlled then cracks can be prevented from initiating and growing. Toughness is a measure of resistance to crack growth; resistance can be provided by blunting of the crack tip in ductile materials. However, if applied strain rate is very high (as would be the case when a spot weld cools at the end of the pulse) and the stress field is multi-axial, even ductile materials exhibit poor toughness and produce rapid crack growth. Hard materials, such as martensite formed during cooling of steels, are brittle and have poor toughness. Having a deep understanding of the residual stresses in welding, micro structure and mechanical behavior of HAZ, multi axial fatigue strength, crack progress behavior and the effect of improvement techniques on welded structures will result in manufacturing more reliable and minimizing weight and increasing structural strength.
The following objectives of this project are:
- Modeling welding process by considering the phase transformation changes occurred in base and weld metal during the heating and cooling process.
- Effect of weld material strength and number of weld passes on the fatigue strength.
- Influence of heat treatment process like stress releasing, annealing hardening on fatigue behavior.
- Development of damage mechanics rules based on numerical analysis for predicting the ductile failure, fatigue life crack initiation.
- Numerical modeling of fatigue crack initiation and propagation based on phase field theory.
- Achieving experimental data by carrying out on universal servo hydraulic machine to investigate the influence of multi axial stresses on fatigue strength and fatigue life.
- The effect of residual stresses caused by welding on the fatigue life.
- Investigating HFMI process on residual stresses and fatigue strength by means of numerical and experimental work.
22068_ Individualized flow diverter treatment (Belucci) - Development of a design tool for the computer-aided design of individual flow diverters (IFD)
Duration: 01.09.2018 bis 31.08.2021
The aim of the BELUCCI project is to establish and validate a novel approach for the treatment of intracranial aneurysms with flow diverters, which includes individualized and simulation-based planning, implant selection/manufacturing and consultation based on patient-specific anatomical selection parameters. The project aims to develop a standardized individualization process in order to provide each patient with the optimal implant for the individual aneurysm and thus substantially improve the efficacy and safety of the procedure. The approach will be clinically evaluated as part of the project using patient-specific aneurysm models. In the sub-project at IFME, a computer-aided design tool for the numerical investigation and design of individualized flow diverters is being developed.
Quality and driving comfort rank among the top criteria of potential car buyers. Even though small dimensional deviations of exterior parts would not necessarily attract someone's attention, protruding parts or irregular gap sizes can cause, among other topics, interfering noises, degradation of driving experience or increase in the aerodynamic resistance. The Meisterbock (master jig) serves, primarily before the start of serial production of cars, as widespread test equipment for exterior parts. These include, among others, the sheet metal parts of fenders, doors, engine hood, trunk lids and side panels. In order to evaluate those assemblies and their interactions, each part is mounted on the Meisterbock and aligned according to the standardized Reference-Point-System (RPS). As a result, deviations from nominal geometries are determined and corrective actions for the manufacturing process can be derived. Due to the time and resource consuming activities of the physical installations, this iterative qualification method requires additional costs.
Duration: 27.04.2018 bis 30.04.2021
The Meisterbock is primarily used for new vehicle start-ups as a means of measuring and analyzing exterior components. These include sheet metal add-on parts such as fenders, doors, front and tailgates and side panels. In order to evaluate and qualify these components and their interaction in the installed state, each part is mounted on the master jig and aligned with repeat accuracy using the standardized reference point system (RPS). The aim of this project is to optimize this qualification process through the use of numerical simulation using the finite element method (FEM) in order to reduce the effort required for physical assembly and thus increase efficiency.
23483_ FE analysis of a multilayer adhesive system
Duration: 01.08.2019 bis 31.12.2019
The aim of the project is a comprehensive parameter study as part of deformation analyses of a new type of high-performance adhesive tape. The main point here is the selection of a suitable material model for the core and the adhesive layers. In subsequent FE analyses of the face tensile test, the material parameters and layer thicknesses are varied in order to assess its influence on the overall behavior both qualitatively and quantitatively.
19598_ Phase field simulation of crack initiation and propagation in metals under thermomechanical loadings
Duration: 01.05.2016 bis 31.10.2019
Fracture under thermomechanical load is a complex failure pattern that has serious consequences in materials and components. The prediction of fracture behavior through crack initiation and propagation in metals using numerical methods has become increasingly important in technical applications. The classical theories of fracture mechanics only include the criteria for crack propagation, but cannot be used to predict crack initiation. Furthermore, no statements can be made about curved cracks or crack branching. Over the past ten years, the phase field method has been transferred and further developed to describe crack formation and propagation. This method offers a powerful and flexible framework for investigating the fracture behavior of materials under arbitrarily complex thermomechanical loads. By defining an additional degree of freedom, the so-called order parameter, the crack description is carried out in the model. The heat conduction equation can also be included, for example if thermal stresses dominate the crack propagation. Both slow and sudden heating can be considered here. Analogous to the crack analysis, the temperature field is treated as an additional degree of freedom. The resulting equations can be solved using the finite element method. The aim of this doctoral thesis is to develop a model that can describe the mathematical relationship between thermomechanical loads and crack initiation and propagation at high temperatures. The starting point of the multiphysical model is formed by the constitutive equations of thermoelastoplasticity, which are solved using the phase field method. The degrees of freedom of the model include the displacement, the temperature and the phase field for the crack description.
19900_ Finite element analysis and service life prediction of fabric-reinforced elastomer membranes
Duration: 01.06.2016 bis 31.05.2019
Elastomer diaphragms are used as flat diaphragms in oscillating pumps or for pressure-actuated short-stroke actuators and control elements. Compared to metal diaphragms, elastomer diaphragms are very soft and flexible. Fabrics are often inserted into the elastomer to make elastomer diaphragms stronger and more resistant. The diaphragms are often exposed to a large number of complex and highly stressed switching cycles and must have optimum service life properties due to their important function.
Due to the complexity of elastomer membranes, it is hardly possible to reliably estimate the mechanical and service life properties based on empirical values alone. The aim of this project is to use the finite element method (FEM) to develop a simulation tool that can be used for the realistic deformation and service life analysis of fabric-reinforced elastomer membranes.
A mixed multi-field representation of gradient-type problems in solid mechanics
Duration: 01.10.2014 bis 31.03.2019
The modeling of phase fields and size effects in solids, such as the width of shear bands or the grain size dependence of the plastic flow in poly-crystals, need to be based on non-standard continuum approaches which incorporate length-scales.
With the ongoing trend of miniaturization and nanotechnology, the predictive modeling of these effects play an increasingly important role.
The mixed multi-field representation of gradient-type problems is a recently introduced thermomechanically consistent framework for modeling such kind of phenomena. The key idea is to extend the field of constitutive state variables by micromechanical independents and further to derive the macro and micro balance equations in a closed form.
22250_ Development of a novel stent design for targeted vessel deformation to reduce blood flow into the aneurysm
Duration: 01.09.2018 bis 31.01.2019
For several years now, the cause of death statistics in Germany have been dominated by cardiovascular diseases. According to the Federal Statistical Office, these were responsible for around 39% of all deaths in 2015. These include strokes, which can be caused by a subarachnoid hemorrhage. This is when blood enters the subarachnoid space surrounding the brain. These bleedings are mainly caused by the rupture of cerebral aneurysms. These are balloon-like dilatations of arterial blood vessels that develop in approx. 2-6% of the Western population in the course of their lives. Approximately 10 out of 100,000 people per year experience a rupture.
Various measures are intended to prevent such a rupture. Surgical (clipping) or endovascular (coiling, balloon angioplasty, stenting, placement of flow diverters or WEB devices) interventions are used to reduce the blood flow into the aneurysm. This is aimed at the formation of thrombi, which cause a natural occlusion of the vessel. These measures are neither risk-free nor necessarily successful. This motivates the development of new procedures and the continuous improvement of established ones.
The aim of the project is to develop a stent with a novel mode of action for therapeutic deformation of the carrier vessels of intracranial aneurysms. As a result of the targeted guidance of the blood flow, more favorable hemodynamics are achieved and the blood inflow into the aneurysm interior is reduced. This in turn increases the dwell time of the blood in the aneurysm and promotes natural thrombosis, which closes the aneurysm.
This is a completely new concept in a) the treatment method and b) the necessary stent design. For this reason, the simulative methods are to be developed within this framework in order to determine the expected individual effectiveness of this concept.
22578_ FE analysis of a newly designed impact protection coupling
Duration: 01.10.2018 bis 31.12.2018
FE simulations of a newly designed impact protection coupling under mechanical and thermal loads are being carried out as part of the project. This coupling consists of a modified shaft-hub connection that is to be used to transmit a constant maximum torque over several cycles.
For this purpose, validation simulations are to be implemented using the finite element method (FEM) for a simplified test setup. This axial test setup consists of two identical test specimens that are axially loaded with a contact force on a circular ring surface and then twisted against each other.
Extensive material and system characteristics as well as the practical boundary conditions are taken into account in order to enable an appropriate comparison between existing experiments and FE simulations. In addition, parameter studies are subsequently carried out in order to understand their influence on the system response. These parameters include, for example, the layer thickness and the friction coefficient. In addition to varying the contact pressure, simulations under changing temperatures are also taken into account.
Virtual simulation of the deformation behaviour of NiTi stents in minimally invasive vasular therapy
Duration: 16.09.2016 bis 15.09.2018
Cardiovascular diseases are the main cause of death in Western countries today. There are various treatment methods for such pathologies, but the trend of the future is percutaneous minimally invasive therapy. Here, high-tech endoprostheses are inserted into the pathological area via an endoluminal path. One of the best-known families of such implants are vascular stents. They are characterized by their complex geometry and non-trivial material properties. The safe use of these stents requires continuous technological improvement in terms of material, design and operating conditions in order to achieve safe implantation, efficient drug release and optimal long-term behavior. In addition, the concept of predictive medicine, i.e. the prediction of alternative treatment methods for individual patients, is becoming increasingly important, which is not possible without robust and cost-efficient simulation methods.
This project aims to contribute to the efficient simulation of the deformation behavior of carotid stents in the carotid artery. The long-term goal is the real-time simulation of stent behavior during synchronous surgery on humans, so that various processes can be tested virtually shortly before real placement and optimally performed with regard to the individual patient.
19428_ Finite element simulation of the deformation behavior of shape memory alloy structures
Duration: 01.05.2015 bis 30.04.2018
Shape memory alloys (SMA) can undergo phase transformation between a high-ordered austenite phase and a low-ordered martensite phase, as a result of changes in the temperature and the state of stress. Consequently, SMA exhibits several macroscopic phenomena not present in the traditional materials. Two significant phenomena are the shape memory effect (SME) and the pseudoelastic effect (PE). These unique features of SMA have found important fields of applications especially in medical technology. The increasing use in commercially valuable applications have motivated a vivid interest in the development of accurate constitutive models to describe the thermomechanical behavior of SMA. In this project a thermomechanical 3D model for SMA, which includes the effect of pseudoelasticity as well as the shape memory effect will be extended with regard to fatigue behavior and crack resistance.
16895_ Investigation and conceptual description of the service life of rubber materials under multiaxial loading conditions
Duration: 01.06.2013 bis 31.05.2017
In this project, an in-depth investigation of the service life of technical rubber materials under multi-axis loading conditions and, in particular, under shear with rotating axes is being carried out.
In addition to experimental investigations, a theoretical concept for predicting service life is already being developed in the early phase of the project which, based on shearing with rotating axes, can cover a much wider range than previous conventional concepts.
The concept is to be validated by means of further targeted tests for double-sided shear, shear with rotating axes and under single-sided shear and tension. The load amplitude will also be varied.
16897_ THEVE - A new physically motivated thermoviscoelastic model for filled elastomers to investigate the material response under dynamic loading conditions on rolling tires
Duration: 15.02.2013 bis 14.01.2017
The aim of the project funded by the Luxembourg Research Foundation (FNR) is the numerical investigation of the efficiency of special elastomer materials with regard to their rolling resistance properties. The so-called dynamic flocculation model (DFM) is being used and further developed for this purpose. This physically motivated material model can realistically represent the inelastic material behavior of filled elastomers under cyclic load history (e.g. Mullins effect and stress-strain hysteresis) in a large strain range. The extension of the material model to time- and temperature-dependent phenomena enables a more accurate representation of the dissipative properties of the material under dynamic loads, as they occur in rolling tires. Finally, the material model is used to establish a correlation between the dissipation that occurs and the rolling resistance, which can be used for the targeted selection of materials for tire treads.
16899_ FE simulation of high-performance adhesive tapes
Duration: 01.01.2012 bis 31.12.2016
Double-sided adhesive tapes are characterized by their viscoelastic and particularly good adhesive properties on a variety of substrates. They are either a multi-layer system consisting of a thin adhesive layer on the top and underside applied to an inner backing layer, or a single material is used that serves as both the adhesive layer and the backing material.
In this research project, a simulation tool is being developed that enables a better estimation of the application limits, taking into account the complex material characteristics, such as strong non-linearity and viscoelasticity of the material. With the help of this tool, the model parameters regarding material variation, time-dependent changes in the external boundary conditions and long-term behavior can be easily adapted and realistic predictions can be made about the complex structural behavior of single and multi-layer high-performance adhesive tapes.
16886_ ParaFit - Parameter adjustment using test specimens close to the component
Duration: 01.10.2013 bis 30.09.2016
The quality and informative value of FEM simulations of technical components is limited by the suitability of both the material laws used and the assigned material parameters.
A material model suitable for industrial application is not necessarily the most accurate and complete simulation of real material behavior. Rather, the practical suitability of a material law requires a balanced compromise between problem-specific requirements regarding the scope, accuracy and combination of properties of the material description on the one hand and economic restrictions regarding the required computer capacities and calculation times on the other.
In most cases, the corresponding material parameters are adjusted using homogeneous tests on laboratory test specimens. However, technical components and associated laboratory test specimens usually have very different geometries and are also often manufactured in different ways. In many cases, this causes serious deviations in material behavior. Component simulations with material laws that have been adapted to measurements on such test specimens are therefore prone to errors from the outset.
The core objective of the research project is the realization of a computer program suitable for industrial use for the identification of material law parameters, which enables the efficient use of measurement data from tests on test specimens close to components with inhomogeneously distributed stresses and distortions. In this way, the above-mentioned disadvantages of the restriction to homogeneous reference measurements are avoided, and the possibility is opened up to take into account specific characteristics of product groups and loading processes when adapting the material laws. The inevitable increase in computing times associated with this approach is of secondary importance given the performance of today's standard computers, provided that the potential of efficient algorithms and clever programming is fully exploited.
19899_ Finite element analysis for the assembly of an elastomer rolling lobe
Duration: 01.06.2016 bis 31.08.2016
As part of this project, a well-founded investigation of the deformation behavior of a rolling lobe bellows under realistic load conditions is being carried out. During installation and operation, the rolling lobe undergoes large deformations, which can lead to complex contact conditions, among other things. Under operating conditions, this can lead to undesired early failure of the rolling lobe. Since the rolling lobe consists of filled elastomer, an extended material model must be used that can map the inelastic properties (such as material softening, permanent elongation and loading and unloading hysteresis).
16901_ DIK-Project: Simulation of contact forces considering adhesion, compliant surface roughness and rubber materials with equilibrium hysteresis
Duration: 01.10.2012 bis 30.09.2015
This project, funded by the German Rubber Society (DKG), aims to increase the development potential of rubber components whose function is largely dependent on friction properties. To this end, the understanding of friction processes involving a rubber surface is to be improved on the basis of computer simulations. In particular, the significance of adhesive force components is to be reassessed and researched in detail in connection with compliant contact surface roughness. For the simulations, a model of a representative section of a contact pairing with realistic surface roughness will be created. Under contact pressure, the increase in the effective contact area due to deformation of the roughness is to be observed. A load tangential to the contact surface is then simulated. In both phases, the force components from elastic deformation, adhesion and dissipative effects are balanced.
16900_ DIK project: Finite element simulation of the dynamic deformation behavior of foamed elastomers
Duration: 01.10.2013 bis 30.04.2014
The institute has developed a material model to describe the mechanical behavior of foamed elastomers. This model can realistically depict the extremely complex material behavior of foamed elastomers under any mechanical stress. A functional relationship between the mechanical properties and the pore content is taken into account using a homogenization approach. The material model has so far been developed for quasi-static loading conditions, i.e. time- and frequency-dependent properties of both the elastomer matrix and the pore structure cannot yet be modeled. The aim of this project is to extend the model with regard to the time-dependent properties that can occur in particular under high-frequency loads due to the spontaneous pressure build-up within the pore structure. The model will also be implemented in a suitable finite element program so that it can be used for the FE simulation of more complex, multi-dimensional load conditions.
DIK-Projekt: Entwicklung eines Materialmodells zur thermo-mechanischen Beschreibung von thermoplastischen Elastomeren
Duration: 01.10.2010 bis 30.09.2013
In dem von der Deutschen Kautschukgesellschaft geförderten Projekt wird ein neues Materialmodell für thermoplastische Elastomere entwickelt, das die mechanischen Eigenschaften von TPEs, wie z.B. Inelastizität, Viskoelastizität und Temperaturabhängigkeit der Materialparameter, realitätsnah abbilden kann. Das Modell beruht auf einer Homogenisierungsmethode in der explizit der Volumengehalt der elastomeren und thermoplastischen Phase einfließt. Das Modell wird in die Finite-Elemente-Methode implementiert und kann somit in Zukunft für die realitätsnahe Simulation des Strukturverhaltens von TPE-Bauteilen benutzt werden.