Fretting occurs when two bodies in contact undergo small-amplitude oscillations, which is related to two complex degradation phenomena of structure integrity, namely fretting wear and fretting fatigue due to steep stress gradients. Many mechanical components have the potential to experience fretting damage, such as aero-engine spline couplings, blade-disk attachments in turbines and hip joint implants, etc. A large number of parameters are responsible for fretting crack initation and wear such as normal load, tangential force, coefficient of friction, surface roughness and micromechanical properties. In this project, a multiscale approach is employed to accomplish the contact homogenisation and formulate a macroscopic law of fretting wear based on microscale information such as the topography and properties of the contacting surface. In addition, an embedded cell model is used in the micromechanical simulation to etablish the relationship between the accumulated inelastic deformation at microcale and marcoscale deformations. A phenomenlogical constitutive model is developed in the framework of continuum damage mechanics to predict the life of fretting crack initation. A damage evolution law based on the critical plane concept is proposed to decribe the fatigue crack initiation process under proportional and nonproportional loadings. The multiscale simulation incorpatating the interaction of fretting wear and damage provides an efficient tool to estimate the structural integrity of the service components subjected to fretting loadings.
Next generation of lithium ion batteries in electric vehicles and other portable devices are anticipated to meet the rapidly growing demand for high energy density and chemomechanical integrity over long-term cycles. Silicon stands as a very promising candidate for the anode material due to its enormous capacity, which is theoretically one order of magnitude higher than the traditional graphite anodes. However, Li insertion/extraction induces large inelastic deformations and stresses inside silicon-anodes, leading to a rapid degradation in chemomechanical properties and failures of battery systems. In this project, we aim to develop a nonlocal chemomechanical model within the framework of finite strain for studying main degradation mechanisms and the relationship between the nanostructures and chemomechanical properties of the silicon electrodes. The proposed model incorporates the lithiation-inelastic deformation interaction, the formulation of the solid electrolyte interphase and inhomogeneous growth of lithiated phases observed in experiments. By employing the developed chemomechanical model, computational simulations are conducted to tailor and optimise the nanostructure of the silicon electrodes in order to improve the chemomechanical integrity of the next generation of lithium ion batteries.
Biological hard composites with hierarchical structures are designed from the nano- to the macroscale in order to fulfil multifunctions of hard tissues. The unique highly-mineralised microstructures are often correlated with their improved wear-fatigue properties and damage-tolerance under cyclic mechanical and environmental loadings. For developing engineering composite and surface coating with excellent wear-fatigue resistance and damage-tolerance, mimicking these hard tissues that have evolved to fulfil multifunctions may lead to the innovative design of novel wear‐resistant materials. In this project, the dental enamel, which is daily subjected to friction and wear during a large number of mastication cycles, is selected to study the building principle of the hierarchical structure for achieving exceptional mechanical properties and functionalities. For this purpose, experimental studies are conducted to characterise the wear-fatigue behaviour of the dental enamel. Based on the experimental results, the micromechanical simulations are performed to identify relationship between the multiscale structure and exceptional wear-fatigue resistance and damage-tolerance. In addition, macroscopic model incorporating multiple degradation mechanisms of structure integrity is developed to describe the damage behaviour under cyclic loadings and predict the wear-fatigue life. These lessons from nature can be utilised as inspiration for the development of engineering materials with the desired wear-fatigue properties.
Contact persons: Dr.-Ing. S. Ma
Biodegradable magnesium alloys are regarded as promising candidates for the material of orthopaedic implants due to the desired properties: 1) similar mechanical properties compared to nature bone to avoid stress shielding, 2) the good biosafety and biocompatibility (280–300 mg daily intake), 3) the ability to biodegrade due to corrosion (second surgery not required). The extensive application of biodegradable magnesium implants is still limited by the uncontrollable corrosion rate in the physiological conditions. The development of biodegradable implants with sufficient strength in the healing phase of bone requires understanding the degradation behaviour, quantifying the degradation process of mechanical integrity. In the project, we focus on the experimental investigation of corrosion-fatigue behaviour in the physiological environment and multiscale modelling of the degradation process of biodegradable implants. The phase field approach is employed for studying corrosion mechanism at microscale and establishing the map between the corrosion behaviour and the surface topography of coating. The phenomenological damage model based on the experimental observation is proposed to describe the corrosion-fatigue behaviour of implants at macroscale. The computational simulations are performed for evaluating and optimising the structure design of biodegradable implants for orthopaedic applications.
Contact persons: Dr.-Ing. S. Ma
This research topic focuses on the gas detonation forming technique, which has the potential to form complex geometries, including sharp angles and undercuts, in a very short process time. Currently, finite element method simulations of the cup forming process are performed. The simulations on 3D computational models are carried out with the explicit dynamic analysis using the Johnson-Cook material model. The results obtained in the simulations are in good agreement with the experimental observations, e. g., deformed shape and thickness distribution. Moreover, the proposed computational model is capable of predicting the damage initiation and evolution correctly, which is mainly due to the high-pressure magnitude or an initial offset of the workpiece in the experiments.
Contact persons: Dr.-Ing. S. P. Patil, Kaushik Prajapati
Silica aerogels are nanostructured, highly porous solids, which have, compared to other soft materials, special mechanical properties, such as extremely low densities. In this project, the mechanical properties of silica aerogels have been studied with molecular dynamics (MD) simulations. The silica aerogel model was created by direct expansion of beta-cristobalite, along with a series of thermal treatments. The mechanical properties of the silica aerogel MD model in uniaxial tension and compression were studied. Moreover, cyclic loading simulations, under compression, were carried out on the silica models of the different densities. Under larger strains, nearly no recovery of the collapsed structural network was observed. The response is characterised by inelastic phenomena like residual deformation, hysteresis, and Mullins effect.
Contact persons: Dr.-Ing. S. P. Patil
In high speed forming like detonation forming method, a plate made of wide range of metals is deformed plastically by means of high kinetic energy. Shock waves are propagated from high pressure chamber of shock tube to low pressure chamber by membrane burst, thus they deform the specimen and then reflect. By applying short time measurement techniques, some parameters such as pressure and deflection are measured during the impulse. The aim of this project is to investigate the deformation behaviour and vibration of specimen during the experiment, and developing an empirical method in order to deform structures especially composite plates inelastically. Moreover, using a fixed or flexible die in experiment in order to achieve different shapes can be evaluated. Because of considerable high strain rates during inelastic deformation, a visco-plastic model will be used and numerical simulation regarding different structural and constitutive equations and damage effect will be done. Therefore, a comparison with our experimental results can be achieved.
Funded by: Institute of General Mechanics (IAM)
Contact person: M.Sc. N. Shirafkan
This project compares cement-free and cemented Rotationstable Screw Anchors that are used to treat femoral neck fractures. Therefore, both implantation techniques are applied to pairwise cadaveric femura and loaded with a defined time dependent cyclic force history to evaluate different medically relevant parameters. The motion of the three segments, i.e. screw, femur head and femur shaft, are measured by an optical infrared tracking system. The load applied by a material testing machine (Mini Bionix, MTS) imitates 10 000 gait cycles with different body weights until structural failure of the implant.
Funded by: University Hospital RWTH Aachen, Department of Orthopedic Trauma and Reconstructive Surgery
Contact person: M.Sc. M. Mundt
This project aims to develop an inertial sensor based system that is able to detect pathologies in motion and specifically gait in daily life. Unfortunately, most systems available on the market for gait analysis are limited to measurements in the laboratory. During the last years the availability of low-cost inertial measurement units has been rising. The application of these sensors in combination with smart phones for the detection of motion pathologies and the notification of the user will be a valuable tool not only to improve people’s gait but also to evaluate post-OP changes or to support people in learning gait strategies, e.g. to avoid further damage of the knee joint.
Contact person: M.Sc. M. Mundt
The implantation of cell-free scaffolds is a promising therapeutic approach in regenerative medicine. Therefore, the project aims to investigate the in-vivo remodeling effects of regenerative tissue using in-vitro systems. The predominant impact factors are the scaffold's colonization potential, the immigration and migration behaviour of the cells, the cellular molecule synthesis performance and the mechanical stimulation. Based on experimental characterization, numerical simulations of the mechanobiological processes are performed to simulate varying cultivation and loading conditions.
Breast cancer is the most common type of cancer in women worldwide and its incidence is continuously increasing. As early detection significantly improves survival rates, a widely available, reliable detection method is needed . The current gold standard for breast cancer screening, mammography, has recently engendered controversy . Hence, the underlying research project aims to improve cancer detection by means of infrared imaging of the skin which is economical and non-hazardous. The significant hyper-perfusion of cancerous tissue is known to lead to a local increase in temperature. While the application of infrared thermal imaging has recently shown promising results in skin cancer diagnosis , the application to breast cancer detection has not yet led to satisfying results. The difficulty mainly lies in the complexity of the breast structure consisting of different tissue types and vessels with varying diameters resulting in complex heat transfer. The cancerous heat source can have a detectable influence on the surface temperature field of the breast depending on its location, size and heat generation e.g.. The challenge lies in solving the inverse problem and determining the location and intensity of the source from measured infrared radiation of the breast surface. While most research in this field concentrates on image processing, the approach of this project is to subsequently develop a thermo-mechanical porous media model for the female breast. Based on data generated by this model, we will be able to train a neural network to assist cancer detection.
Contact person: M.Sc. A. Niedermeyer
Ultrasonic welding is a joining technique applied in various industries, such as automotive, food, medical and electronics. Ultrasonic welding (USW) of metals is counted as a rapid manufacturing process to create solid state joints between same or different materials as mating parts. Energy consumption in this process is low compared to other common welding processes, such as oxy-fuel welding and arc welding. The present research investigates the USW of aluminum on brass and focuses mainly on the influence of some of the USW parameters, such as applied pressure and vibrational amplitude on the quality of the joint.
Contact person: M.Sc. S. Mostafavi
The aim of the project is the numerical modelling of hydraulic fracture in fluid-saturated porous materials, which can be carried out using multiphase continuum mechanics theories. This way of treatment considers the crack initiation and propagation, deformation of the solid skeleton and changing the flow of the interstitial fluid. In particular, a fluid-saturated porous material represents a volume coupled solid-fluid problem. By use of e.g. the Theory of Porous Media (TPM), the motion of the pore fluid and the deformation of the solid matrix can be described. The hydraulic- or stress-induced fracture occurs in the solid body and is simulated by means of the phase-field modelling approach.
Contact person: Dr.-Ing. Y. Heider
Structural damage detection using time domain vibration response has advantages such as simplicity in calculation and no requirement of a finite element model, which is appealing in recent years. In this project, several vibration-response-based damage detection methods that suitable for online structural health monitoring have been proposed and validated using numerical simulation and different kinds of experiment.
Contact person: M.Sc. M. Zhang
In order to cool turbine blades, laser drilled holes can be distributed over the structure. However, they can have significant influence on the mechanical behavior of the blade. Therefore, it is the aim of the sub-project about the quantitative analysis of local loading parameters to understand the damage initiation and its evolution around the holes under cyclic thermo-mechanical loading, followed by a proposed model. This project is carried out with two university and three industrial partners.
In this study, the influence of spine instrumentations on the range of motion of functional spinal units is tested on lumbar spines. To this end, a 6 DOF spine testing rig with a bioreactor of a former study has been developed to test under physiological conditions . The use of a bioreactor impedes mechanical and optical measurement approaches, which is accomplished by use of a special magnetic tracking system with implantable microreceivers. Further the effects of instrumentations on the spinal kinematics are assessed via FE simulations.
- Department of Orthopedic Trauma and Reconstructive Surgery (UCH RWTH)
- RWTH Start Nachwuchsförderprogramm
- Department of Orthopedic Trauma and Reconstructive Surgery University Hospital Cologne
- Department of Orthopedic Trauma and Trauma Surgery Medical Centre CR Aachen GmbH
Contact person: M.Sc. A. Beckmann
The main objective of the research project is a development of a powerful simulation tool for modelling of the essential effects characterizing the behaviour of IVD. The study focuses on the development of a new anisotropic viscoelastic material model which not only takes the mechanical behaviour of solid part into account but also the flow behaviour of the fluid. Secondly, the damage mechanism has to be realized. This is based on a phase field model (PFM) which captures realistic features of IVD herniation and the interactions of the solid and fluid phases based on continuum porous media theories. The third aim of this research is to develop of a new experimental technique for the realistic investigation of human IVDs by means of a bioreactor. Therefore, a bioreactor has to be
developed in order to appropriately investigate the cellular activities and solute diffusion rates in different stages of the damage process. This enables the study of the degeneration of healthy and injured IVDs.
contact person: M.Sc. M. Azarnoosh
The behaviour of cells under mechanical stimulation is of great interest for the development of novel therapies, e. g. for the cultivation of autologous donor cells. The purpose of this project is the development of a novel cultivation environment for cells simulating the most important biological boundary conditions, such as proper temperature and nutrient supply as well as the mechanical boundary conditions, and documenting the measured data. Important aspects are a reproducible working clamp device and the load cell interface as well as a new-developed electric control device driven by a GUI application, also developed at the IAM. Beside the online monitoring during the cultivation period, the numerical analysis of the cell carrier material is an additional feasibility getting more information about the cultivated cells.
contact person: Dipl.-Ing. W. Willenberg
The objective of this research project is the numerical modelling of ductile fracture typical from different steel grades, Aluminum and Superalloys, which could also be extended into advanced continuum mechanics and thermodynamics. This project focuses on the computation of crack initiation and propagation as well as the material deformation and changes in the material properties and behaviour. The crack initiation and propagation, as well as the potential branching, is computed with help of a Phase-field Modell (PFM). Damage, hardening and plastic deformations are calculated using a conventional model for cristal plasticity
Contact person: M.Sc. C. Hernández
The objective of this project is the numerical modelling as well as the experimental validation of forming and surface treatment of metal components through different detonation methods. This research focuses on the estimation of damage, fracture, deformation and changes in the material properties of the components. The material behaviour will be described with help of molecular dynamics as well as superplasticity theories. Experimental trials could determine the feasibility to implement such technologies on the industrial production.
Contact person: M.Sc. C. Hernández
Parameter selection of the Finite Element Method (FEM) in particular in the field of fracture mechanics of composites is governed by large uncertainties.
The goal of ciFEM is the development of finite elements exactly describing the non-linear mechanical behaviour of structural components over their entire life cycle with the use of computational intelligence.
The intelligent finite element independently and adaptively develops the material model, material parameters and integration method based on experiments. Uncertainties and constraints, such as thermodynamic consistency of the material model and numeric stability of the solution, are also taken into account.
Contact person: Dipl.-Ing. A. Koeppe
More detailed Description: Structural Health Monitoring (SHM) of structures has a wide variety of applications for example structural monitoring of bridges and offshore-wind parks. The project “Smart-SHM” concerns with the analysis of smart structures with respect to optimization and extension of Online-SHM-systems. Questions regarding data acquisition and data interpretation should be answered and validated experimentally. Additionally with the context of “Smart-SHM” a demonstrator will be set up in order to illustrate the results of this research field.
Contact person: M.Sc. D. Hesser
Spider dragline silk has the unusual combination of high strength, extensibility and toughness, which outperforms some of the best man-made materials in terms of its mechanical performance. Dragline silk has a semi-crystalline structure consisting of crystalline region of short polyalanine segments that form stiff β-sheet nano-crystals surrounded by amorphous glycine-rich domains, which provides extensibility of the fiber. A 3D finite element model of silk fiber is proposed, which is based on the secondary structure of the Araneus diadematus silk fiber, which takes into account the plasticity of β-sheet crystals as well as the viscous behavior of the amorphous matrix. The silk fiber model shows the predicted mechanical properties are in excellent agreement with available experimental evidence. Initial randomly distributed crystals in the fiber silk rearrange themselves during deformation, and form lamellar-like arrangement of the phases, which results initial stiffness from initial random arrangement, and high toughness due to lamellar-like arrangement. The proposed continuum mechanics based macro-scopic silk fiber model, not requiring any empirical parameters, and contribute towards an improved understanding of silk fiber mechanics during deformation and the source of the toughness of this extraordinary fiber. Hence, it is an efficient model for the design of artificial silk fiber as well as applicable to other composite materials.
Contact person: Dr.-Ing. S. P. Patil
Nacre, also known as the Mother of Pearl is an organic-inorganic composite material produced by some mollusks as an inner shell layer. In the last three decades, the structure and the toughening mechanism of nacre have been the subject of intensive research. This interest originates from nacre's excellent combination of strength, stiffness and toughness. It is composed of hexagonal platelets of aragonite arranged in a continuous parallel lamina. The layers are separated by sheets of organic matrix composed of elastic biopolymers. This mixture of brittle platelets and the thin layers of elastic biopolymers make the material strong and resilient.
Contact person: Dr.-Ing. S. P. Patil
A test bench with a rotating brake disk and a coupling is setup. The dissipated energy is realised from the mechanical inertia and electric engine of the brake disk. In addition to the classical rotation speed and torque measurements, an infrared camera is located in front to the disk A part from surface disk measurements, thermocouples are inserted in the disk and in the friction pad, giving local information of temperature in the materials. In addition, the sensory measurements are recorded. In the present case, the disk is composed of 28CrMoV5-08 steel. The inner and outer diameters are respectively 380 and 640 mm with a thickness of 45 mm without internal ventilation (full disk). The brake pads were made of organic resin bonded composite material. The general test procedure is to define the inertia (mechanical and electrical) to simulate the required energy, to bring the brake rotor to the chosen speed, and finally to apply the brake pressure corresponding to the required braking maximal power (decreases linearly with time). After each braking, the disc is cooled down to a given temperature before the next run. Data from infrared camera will be monitored and recorded continuously during the tests. The environmental conditions such as the room temperature and humidity are kept constant. The aim of this work is to engineer a brake test bench with all its components. The control of the electro engine and the hydraulic brake system is also necessary.
Contact person: Dipl.-Ing. A. Lamjahdy