Search

Legume proteins are increasingly used in structuring various foods under the influence of heating and stirring energy. Based on available studies, this structuring potential is not yet fully understood. This raises the question of the suitability of legume isolates and concentrates for structuring in emulsion gels and the effect of heat and oil on the gel properties. In this study, soy- and pea-based suspensions and emulsions were prepared with the least gelling concentration using different oil concentrations (0%, 7.5%, 15%, 22.5%, and 30%). The viscoelastic properties were measured before and after heating cycles (65 °C and 95 °C). Scanning electron microscopy images complemented the results. All gels measured showed viscoelastic solid behavior. Thermal treatment showed a positive effect on the gel properties for most samples, especially for concentrates (reduction in the loss factor and networking factor > 1). The concentrates showed much higher networking factors and tighter cross-linking than the isolates. The rheological and microstructural properties of the emulsion gels are influenced by a number of factors, such as carbohydrate content, protein chemistry, the protein purification method, and initial viscosity. Moreover, the influence of oil on the rheological properties depends on the material used and whether oil droplets act as an active or inactive filler. [ABSTRACT FROM AUTHOR]

Ultrasonic vibration superimposed milling (UVSM) with an oscillating movement of the specimen in the direction of the tool axis is an efficient method for the generation of microstructured functional surfaces. The application of end milling cutters with a diameter smaller than the length and the width of the surface to be structured generally results in recuts and path overlaps. In order to avoid surface recutting, a small lead angle was realized by slightly tilting the ultrasonic system with the specimen. The overlapping area of two adjacent paths was kinematically simulated for different widths of cut (from 70% to 90% of the tool diameter). Cutting experiments were carried out by UVSM of X46Cr13 and X40CrMoV5-1 steel specimens to investigate the influence of the width of cut on the surface generated in the overlapping area and also the adherence of a subsequently deposited CVD diamond layer. For this purpose, 3-D laser scanning microscopy and SEM analysis were applied. The knowledge gained allows for designing UVSM processes, especially regarding 3-D freeform surfaces with defined microstructures subjected to CVD diamond coating. [ABSTRACT FROM AUTHOR]

Ultrasonic vibration superimposed face milling enables the generation of predefined surface microstructures by an appropriate setting of the process parameters. The geometrical reproducibility of the surface characteristics depends strongly on the plastic material deformation. Thus, the precise prediction of the emerging surface microstructures using kinematic simulation models is limited, because they ignore the influence of material flow. Consequently, the effects of plastic as well as elastic deformation are investigated in depth by finite element analysis. Microstructured surfaces resulting from these numerical models are characterized quantitatively by areal surface parameters and compared to those from a kinematical simulation and a real machined surface. A high degree of conformity between the values of the simulated surfaces and the measured values is achieved, particularly with regard to material distribution. Deficits in predictability exist primarily due to deviations in plastic deformation. Future research can address this, either by implementing a temperature consideration or adapting specific modeling aspects like an adjusted depth of cut or experimental validated material parameters. [ABSTRACT FROM AUTHOR]

The coefficient of friction (COF) is an important parameter for mechanical engineers to consider when designing frictional connections. Previous work has shown that a surface microstructuring of the harder friction partner leads to a significant increase in the COF. However, the impact of the changes in the tribological system on the COF are not known in detail. In this study, the tribological influence factors such as the nominal surface pressure, the material pairing, lubrication, and the surface properties of the counterbody are investigated. Microstructuring is applied by turn-milling of an annular contact surface of cylindrical specimens. A torsional test bench is used to measure the torque depending on the displacement of the two specimens, thus enabling the determination of the COF. All tests with the microstructured specimens result in higher COF than the reference test with unstructured samples. The manufacturing process of the counterbody surface, the nominal surface pressure, and the materials in contact have a significant influence on the COF. While lubrication reduces friction in the case of unstructured specimens, the COF does not change significantly for microstructured samples. This proves that the deformative friction component dominates over the adhesive. Microstructuring the harder friction partner increases the transmittable torque in frictional connections and reduces the sensitivity towards possible contamination with lubricants. [ABSTRACT FROM AUTHOR]

The importance of functional surfaces is continuously growing in the context of increasing demands on the sustainability of performance, resource efficiency and manufacturing costs of technical systems. For example, microstructured substrate surfaces can contribute to enhance the adhesion of layers, which in turn ensure the wear protection of a highly loaded component. Many microstructuring processes require a system change, entailing high costs. However, the ultrasonic vibration superimposed machining (UVSM) can be implemented as a finishing process. Due to its defined cutting-edge geometry and kinematics, UVSM represents a suitable method for a reliable generation of predefined surface microstructures. In order to optimize the process regarding the tool wear behavior and thus the geometrical characteristics of the surface microstructure, experimental investigations are carried out to find the most suitable combination of heat treatment condition of the martensitic stainless-steel X46Cr13 and various cutting materials. A vibration system for workpiece-side excitation is used for the experimental cutting tests. The most promising results were obtained within the combination of cemented carbide as a cutting tool and soft annealing as a heat treatment condition. They serve as a base for extensive investigations on the effects of substrate microstructuring to the adhesion of chemical vapor deposition (CVD) diamond layers to steel. [ABSTRACT FROM AUTHOR]

Diamond coatings applied by chemical vapor deposition (CVD) provide extraordinary properties concerning hardness and wear resistance, which enables an increase of the performance or lifetime of highly stressed components. In particular, the combination of steel substrates and diamond coatings allows for numerous applications in several sectors of industry. However, there are significant challenges considering the coating adhesion strength. For example, the mismatch concerning the thermal expansion of steel and diamond commonly leads to a delamination of the coating. Thus, a suitable pre-treatment of the substrate surface is compulsory. With the aim of improving CVD diamond coating adhesion, ultrasonic vibration superimposed machining (UVSM) is applied when doing face milling on steel X46Cr13 specimens. The vibration direction is parallel to the tool axis and perpendicular to the feed direction. The tool wear and the surface microstructure are determined by 3D laser scanning microscopy. The investigations show, that predefined microstructuring of the substrate surface by UVSM contributes to an enhancement of the CVD diamond coating adhesion, especially regarding coatings with a thickness up to 10 µm. This can be referred to a better distribution or a reduction of thermally induced residual stresses in the diamond layer. However, a reliable generation of deterministic microstructures by UVSM significantly depends on the wear behavior of the tool. Uncoated cemented carbide grades exhibit considerable deficits reflecting in rapid tool wear. Therefore, adapted tool coatings are experimentally investigated, which result in an increase of the tool life and a reduction of the geometrical deviations of the microstructures. With an appropriate system of surface microstructure and coating, for example for tribological applications substantial improvements in terms of wear resistance and coefficient of friction are expected. [ABSTRACT FROM AUTHOR]

An approach for a reduction of weight and fuel consumption of passenger cars consists in a replacement of grey cast iron by aluminium alloys as base material of combustion engine blocks. Regarding the insufficient chemical resistance of these alloys to the fuels with its additives, material compounds with thermally sprayed coatings are used as cylinder linings. For machining and in service a high connection strength between the substrate and the coating is demanded. This can be gained by a predefined microstructuring of the substrate surface to attain a local form fit with the coating. But, the microstructured surface also influences the local morphology of the layer. Another possibility to improve the connection strength is the application of a primer between the substrate and the coating. For basic investigations, spiral dovetail microstructures with different pitches (200 µm – 500 µm) are machined by face turning using tools with CVD diamond tippings. The substrates consist of the aluminium alloy EN AW-5754 and their microstructured surfaces are coated with a nickel-aluminium layer. The coating with a thickness of about 200 µm is produced by high-velocity arc spraying. The material is usually used as a primer between the substrate and an iron-based coating. The substrate microstructures and the morphology of the coatings are analysed by SEM and 3D laser scanning microscopy. To determine the adhesive tensile strength of the coating tensile adhesion strength tests are performed. The results show that a higher number of structure elements per length increase the tensile adhesion strength, the hardness and the oxide proportion of the coating. Furthermore, tensile adhesion strength tests reveal failure mechanisms of the compound of substrate and coating depending on the substrate microstructure. [ABSTRACT FROM AUTHOR]

The removal of biofilms from microstructured titanium used for dental implants is a still unresolved challenge. This experimental study investigated disinfection and removal of in situ formed biofilms from microstructured titanium using cold atmospheric plasma in combination with air/water spray. Titanium discs (roughness (Ra): 1.96 μm) were exposed to human oral cavities for 24 and 72 hours (n = 149 each) to produce biofilms. Biofilm thickness was determined using confocal laser scanning microscopy (n = 5 each). Plasma treatment of biofilms was carried out ex vivo using a microwave-driven pulsed plasma source working at temperatures from 39 to 43°C. Following plasma treatment, one group was air/water spray treated before re-treatment by second plasma pulses. Vital microorganisms on the titanium surfaces were identified by contact culture (Rodac agar plates). Biofilm presence and bacterial viability were quantified by fluorescence microscopy. Morphology of titanium surfaces and attached biofilms was visualized by scanning electron microscopy (SEM). Total protein amounts of biofilms were colorimetrically quantified. Untreated and air/water treated biofilms served as controls. Cold plasma treatment of native biofilms with a mean thickness of 19 μm (24 h) to 91 μm (72 h) covering the microstructure of the titanium surface caused inactivation of biofilm bacteria and significant reduction of protein amounts. Total removal of biofilms, however, required additional application of air/water spray, and a second series of plasma treatment. Importantly, the microstructure of the titanium discs was not altered by plasma treatment. The combination of atmospheric plasma and non-abrasive air/water spray is applicable for complete elimination of oral biofilms from microstructured titanium used for dental implants and may enable new routes for the therapy of periimplant disease. [ABSTRACT FROM AUTHOR]

The functionality of surfaces, especially for thermodynamic applications, can be enhanced by help of a specific surface modification. Therefore this study investigates different selected surface structures and their influence on the heat transfer capability. Specific micro geometries are in focus of this research. A systematic design and a determination of appropriate thermodynamic micro structures by the help of FEM multiphysics simulations were executed. Afterwards the investigated structures were fabricated applying electrochemical and laser beam machining. Furthermore a systematic analysis of the exactness and the surface quality was carried out, which underlines the potential of these procedures for micro structuring of surfaces for thermodynamic applications. [ABSTRACT FROM AUTHOR]

The industrial production of technical systems is characterized by increasing demands on performance sustainability, resource efficiency and manufacturing costs. As a result, surfaces with special properties become more important. Therefore, their functionalisation is subject of many fields of research. Typical application ranges are improving haptics, the generation of optical effects or the reduction of friction in mechanical as well as fluidic systems. Furthermore, functional surfaces can contribute to an increase of the adhesive strength of coatings and coating systems, respectively. This can extend the implementation possibilities for the substrate material. Due to its defined cutting edge geometry and kinematics, the ultrasonic vibration assisted milling (UVAM) represents a suitable method for a reproducible generation of a defined micro structure. Accordingly, an ultrasonic vibration system was implemented in a high precision machining centre and initial experimental investigations were carried out. Moreover, a surface simulation tool was developed and used for the structure design and modelling, which predicts a virtual micro structure using the relevant parameters. In the first tests, a high degree of conformity with the machined surfaces could already be achieved. Thus, a possibility for economic micro structuring of components made of steel was developed. [ABSTRACT FROM AUTHOR]

Jet Electrochemical Machining (Jet-ECM) is a technology for fast creating microstructures into metallic parts without any thermal or mechanical impact and independent from the material's hardness. The processed surface is very smooth and no tool wear occurs. The Jet-ECM process depends strongly on the shape of the jet which is hardly predictable. In a previous study Hackert (2010) built a numerical model with COMSOL Multiphysics based on a predefined jet shape. In the present study a new model was created integrating fluid dynamics using the level set method for two-phase flow. According to the Jet-ECM process the simulation was divided into two steps. In the first step the jet is formed. In the second step the anodic dissolution is simulated by deforming the geometry. The dynamic behavior of the electrolyte jet could be simulated during the dissolution process. So effects became visible which affect the machining results. The results of the present study lead to a better understanding of electrochemical machining via electrolytic free jet. Especially a secondary electric contacting of the nozzle by electrolyte reflected from the work piece could be proven. [ABSTRACT FROM AUTHOR]

Abstract: Electrochemical machining (ECM) is a potential procedure for high precision micromanufacturing. Especially the machining of work pieces without any thermal or mechanical impact is a significant feature. Additionally, the electrochemical dissolution behavior of the work piece material is only defined by its electrochemical attributes. Hence, mechanical characteristics such as the material's hardness and the ductility have no influence. This makes ECM an alternative process for mechanically hard to machine materials. In this study, a special procedure for machining microgeometries in carbide metal alloys is investigated, whereat a continuous electrolytic free jet (Jet Electrochemical Machining – Jet-ECM) is applied. The special characteristic of this technology is the restriction of the electric current to a confined area by the jet, which leads to a high localization of the removals. Even complex structures can be machined by the help of continuous direct current. Hence, higher dissolution rates compared to pulsed electrochemical processes can be achieved. In the experiments the machining of step holes and grooves in tungsten carbide alloys is performed. Therefore, point erosions without nozzle movement and linear erosions by single- and multi-axis motions of the tool are conducted. In addition, three-dimensional shaping of the investigated materials is presented by overlapping linear erosions. [Copyright &y& Elsevier]