Optimisation of a four-wheeled-walker for geriatric patientsCopyright: IAM
Due to the aging society an increasing number of people is dependent on assistive technology. The use of four-wheeled-walkers can preserve the self-reliance of older people over a long period of time. But, until now, there are no clear indications for the use of a four-wheeled-walker and there are many users that do not have sufficient knowledge on how to use such an assistive technology. To close this research gap, biomechanical parameters that differ between non-users and users of four-wheeled-walkers need to be determined. The influence of the settings of a four-wheeled-walker to gait parameters needs to be quantified. Using these findings, a concept to minimise the erroneous use of a four-wheeled-walker will be developed.
Multiscale modeling of fretting crack initiation and wear under nonproportional loadings
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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 unterstand the inelastic deformation. 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.
Cell Migration Behavior under Mechanical Loading
Cell migration is a fundamental process which plays a key role in wound healing. Enhancement of cell migration and proliferation could improve the effectiveness of cell-based therapies in wound healing. The aim in this project is to define appropriate mechanical forces in order to enhance cell migration. Therefore, we are using different carrier materials seeded with cells and they are stimulated in custom-made tensile bioreactor. Based on experimental results, we want to figure out how the stiffness of carrier materials and different mechanical loading conditions affects the cell migration.
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.
Multiscale modelling of wear-fatigue behaviour of biomimetic hierarchical structures
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.
Multiscale modelling of corrosion behaviour and mechanical integrity assessment of biodegradable magnesium implants for orthopedic applicationsCopyright: IAM
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.
Numerical modelling of the gas detonation process
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: Dr.-Ing. Sandeep Patil