Materials Science Forum Vol. 1016

Abstract: Revisiting a spiral design for X-ray pole figure measurementsand a symbolic definition of a cumulative crystallographic orientation distributiona one-dimensional deterministic approximately uniform sequential design is appliedto evaluate and cumulate a given orientation density function resulting in a properly definedcumulative crystallographic orientation distribution.It provides a complementary means to compare distributionsin terms of graphs and the Kolomogorov-Smirnov distance.

Abstract: Conductive polymers are promising for application in the medical and sport sectors, e.g. for thin wearable health monitoring systems. While many today’s electrodes contain either carbon or metals as electrically conductive filler materials, product design manufacturing has an increasing interest in the development of metal free and carbon free, purely polymer based electrode materials. While conducting polymers have generally rather low electrical conductivities compared to metals or carbon, they offer broad options for industrial processing, as well as for dedicated adjustments of final product properties and design aspect, such as colour, water repellence, or mechanical flexibility in addition to their electrical properties. The development of electrically conducting polymer blends, based on conductive polymers is thus timely and of high importance for the design of new attractive flexible electrodes. We have developed material formulation and processing techniques for the fabrication of self-supporting thin film electrodes based on polyaniline (PANI) and polyvinylidene fluoride (PVDF) blends. Electrical four-point probing was used to evaluate the electrode conductivity for different processing and fabrication techniques. Optical microscopy and atomic force microscopy measurements corroborate the observed electrical conductivity obtained even at low PANI concentrations revealing the nanoscale material distribution within the blends. Our self-supporting thin film electrodes are flexible, smooth, and water repellent and were furthermore successfully tested under bending and upon storage over a period of several months. This opens new perspectives for the design of metal free and carbon free flexible electrodes for medical, health, and sports applications.

Abstract: Flexible electrodes play an increasing role for medical applications, such as ECG (electrocardiography) or TENS (Transcutaneous electrical nerve stimulation) due to comfort in use and thus their suitability for health monitoring under movement and during sport. Polymers, such as polyvinylidene fluoride (PVDF), are promising for the development of fabrication methods and materials for such application cases, as stable flexible thin polymer membranes can be produced at large scale. We have compared different up-scalable fabrication techniques of thin electrode membranes based on PVDF as a function of silver nanowire concentration, using electrospinning, spincoating, and drop-casting techniques. The produced thin films and membranes and thin films were investigated by electrical four-point probing, optical microscopy, atomic force microscopy, as well as by stability tests under bending, and water exposure. We show, that a combination of electrospinning and spin-coating presents a reliable method for the fabrication of AgNW-PVDF based flexible nanofiber membrane electrodes (NMEs). Our nanofiber membrane electrodes (NMEs) exhibit a 10 times lower sheet resistance than AgNW-PVDF thin film electrodes (TFEs) produced for comparisons by a combination of spincoating and drop-casting using the same amounts of AgNWs. Upon immersion in water for up to 48 hours, we do not detect any nanowire release or decomposition of the fabricated electrodes, which is promising in view of application of the AgNW-PVDF composite electrodes in humid environment.

Abstract: Blood sampling as well as sample preparation are time consuming and requires a strict procedure, which is generally performed by medical trained personal. Not carrying out the procedure correctly could result in an infection of the patient or contamination of the sample itself. These limitations should be especially considered in case of pandemic outbreaks. In order to handle such a high number of patients a novel sample preparation system paired with modern blood sampling procedure is necessary. For this reason, a new device for blood sampling and preparation is designed containing an integrated microfluidic system. The fabrication is carried out by utilizing micro moulding of PDMS as well as micro milling. A first set of initial experiments as part of a first-generation study shows promising results. However, further steps of optimisation considering flow time and preparation cycle are part of a second-generation study.

Abstract: The current state of technology for 3D printing with biomaterials is based on the extrusion of viscous materials. Mostly, extrusion heads utilize pneumatic pressure systems or stepper motors to force the substrate onto a surface. These methods are well developed for high viscouse materials. However, processing low viscous liquids may cause leakages in the system. This could be solved by applying continuous extrusion. Additionally, in order to process gelable substrates, such as gelatine and agar, tempered print heads in combination with a multi stage tempering system are required to prevent the system from clogging. The ongoing work presented in this paper focuses on the development of an extrusion system, which should be able to process multiple viscosities of gelatine sequentially. In order to achieve this, several measurements to examine the properties, as well as the material parameters of different biomaterials are performed. In this process gel point, force resistance and elasticity are the factors of particularly interest. Due to their ability to gel and their availability, the most relevant biomaterials are gelatine and agar. Using this data, an extrusion system involving a peristaltic pump, a heated tube and a nozzle, has been developed. The next step envisaged is to calibrate the extruder based on the obtained data and finally to validate the printing process by printing simple geometric structures. Assuming that a positive evaluation is obtained, the printing system will be tested for printing first organic test structures from patient data using the examined biomaterials.

Abstract: Residual stress is one of the main reasons for failure of automotive cylinder blocks and engine heads. These failures are typically associated with in-service distortion or cracking occurring in engines during operation cycles. The problem becomes more pronounced for engines that are running at elevated operating pressures and temperatures, limiting R&D options in developing and implementing higher-efficiency engines. New aluminum alloys and manufacturing methods have been introduced with varying degree of success, in many cases affected by the stress magnitudes and stress distribution in the component. Therefore, active research is ongoing internationally on finding the most reliable methods of stress analysis as a basis for developing efficient methods for stress mitigation. The current study presents a comparison between two experimental strain measurements techniques: a destructive method that is based on application of strain gauge sensors, and a non-destructive method using neutron diffraction. The results indicate that although the strain gauge method provides an indication of the nature (i.e. compression or tension) of strain within a component, this method should primarily be used for surface measurements and qualitative analyses only. Neutron diffraction remains the superior technique for strain analysis, particularly for engineering components with complex geometries. The results from this study provide the transportation industry with a more comprehensive understanding of the efficacy of utilizing strain gauge sensors, neutron diffraction or finite element modelling for measuring the residual strain in cast components. The results will help manufacturers to develop the next generation of powertrain systems with increased efficiency and improved performance.

Abstract: The microstructure and magnetization of SmCo₅ micro-particles may be used as feedstock for 3D printing to make miniature strong magnets. Thus, the magnetic response and microstructures of commercially available SmCo₅ micro-particles were studied under various heat treatments using a high wattage laser. The magnetization of laser heat treated powders at 50-watt showed an increase in magnetization, while the 75-watt melt showed a little to no change. Unfortunately, the coercivity of both laser heat treated samples decreased significantly. Oxidation during the heat treatment is suspected to result in low coercivity. Purging with argon-gas prior to laser heating showed improved coercivity. To further minimize the oxidation problem a set of SmCo₅ powder was reduced prior to laser heat treatment using a constant flow of hydrogen gas while being heated at various temperatures from 100 oC to 400 oC for a period of ~4 hours. The results show that the magnetization generally increases with the temperature, while the coercivity decreases significantly. Another set of SmCo₅ was annealed in a vacuum furnace for one hour at temperatures between 200 oC and 400 oC in order to confirm that no hydride phases were formed during reduction. The magnetization and coercivity showed similar variations with annealing temperature to those for the reduced powders confirming that these variations may be due to change in crystal structure rather than formation of hydrides. X-ray Diffraction (XRD) studies were performed to identify the changes in crystal phases.

Abstract: This paper aims to study the peculiarities of a modified layer in the surface of ultrafine-grained (UFG) Ti-6Al-4V alloy after high energy ion nitrogen implantation. The UFG structure in the alloy was produced by equal channel angular pressing. X-ray diffraction analysis and scratch-testing were applied for the investigation. The influence of low-temperature annealing (400°C during 1 hour) on the substructure parameters and phase composition of the surface layer depending on a number of cycles of ion implantation with annealing was shown in the research. The effect of the UFG structure on mechanisms and strengthening degree of the surface after ion implantation is discussed.

Abstract: Roughing has been simulated with the Finite element software Abaqus^TM to replicate an industrial-scale process. The model has been made to be as close as possible to its real counterpart. For this purpose, an automated controlling logic has been created to simulate the multiple passes as well as inter-pass times for roughing. Simulating multiple passes with FEM is computationally very demanding, so new methods to reduce computing times are worth considering. During a roll pass an explicit solver is necessary due to high deformation amounts and rates. An explicit solver is tied to a very small time increment, so it takes a long time. On the other hand, inter-pass periods do not include any deformation or roller contact, so an implicit solver is quite capable of computing this portion of the simulation. An implicit solver can speed up the time increment considerably when compared to the explicit solver, so using it potentially saves a significant amount of computing time. Unfortunately, Abaqus does not include any methods to change the solver during a single simulation. Instead it is possible to communicate between the two solver types by manually importing data from a completed simulation to a new simulation model. A new method to change solvers automatically using a self-made Python code is proposed in this paper.

Abstract: Spinning is a type of plastic forming in which a tool such as a roller is pressed against a rotating plate or tube to gradually deform the shape and obtain a product with the same shape as the forming die. This processing method has the advantage that it can be processed seamlessly but has the drawback of causing internal defects due to deformation. In this study, the purpose is to obtain basic knowledge about the internal defect generation mechanism in spinning, and to perform cold and hot spinning with high diameter reduction under various conditions on Al-Mg-Si alloy tube. From the experimental results, it was confirmed that the inner defects increased as the diameter reduction ratio increased. It was considered that the main cause of the occurrence of inner defects was that, at a high diameter reduction ratio, the amount of processing was large, so that the increase of material flow led to increase of wall pressure.