TY - JOUR A1 - Hummel, Sabine A1 - Obermeier, Katharina A1 - Zier, Katja A1 - Krommes, Sandra A1 - Schemme, Michael A1 - Karlinger, Peter T1 - Analysis of Mechanical Properties Related to Fiber Length of Closed-Loop-Recycled Offcuts of a Thermoplastic Fiber Composites (Organo Sheets) JF - Materials N2 - Increasing demand for energy-efficient means of transport has steadily intensified the trend towards lightweight components. Thermoplastic glass fiber composites (organo sheets) play a major role in the production of functional automotive components. Organo sheets are cut, shaped and functionalized by injection molding to produce hybrid components, such as those used in car door modules. The cutting process produces a considerable amount of production waste, which has thus far been thermally recycled. This study develops a closed mechanical recycling process and analyzes the different steps of the process. The offcuts were shredded using two shredding methods and implemented directly in the injection-molding process. Using tensile tests and impact bending tests, the material properties of the recycled materials were compared with the virgin material. In addition, fiber length degradation via the injection-molding process and the influence of the waterjet-cutting process on the mechanical properties are investigated. Recycled offcuts are both comparable to new material in terms of mechanical properties and usability, and are also economically and ecologically advantageous. Recycling polypropylene waste with glass fiber reinforcement in a closed loop is an effective way to reduce industrial waste in a sustainable and economical production process. KW - sustainability KW - fiber composites KW - recycling KW - renewable materials KW - manufacturing process KW - resource efficiency KW - emissions KW - degradation KW - characterization Y1 - 2022 UR - https://doi.org/10.3390/ma15113872 VL - 15 IS - 11 SP - 3872 ER - TY - JOUR A1 - Obermeier, Frederik A1 - Karlinger, Peter A1 - Schemme, Michael A1 - Altstädt, Volker T1 - Thermoplastic Hybrid Composites with Wood Fibers: Bond Strength of Back-Injected Structures JF - Materials N2 - Due to their lightweight potential and good eco-balance, thermoplastic hybrid composites with natural fiber reinforcement have long been used in the automotive industry. A good alternative to natural fibers is wood fibers, which have similar properties but are also a single-material solution using domestic raw materials. However, there has been hardly any research into wood fibers in thermoplastic back-injected hybrid composites. This article compares the bond strength of an injection molded rib from polypropylene (PP) and wood fibers to different non-wovens. The non-wovens consisted of wood fibers (spruce) or alternatively natural fibers (kenaf, hemp), both with a polypropylene matrix. Pull-off and instrumented puncture impact tests show that, given similar parameters, the natural and wood-fiber-hybrid composites exhibit very similar trends in bond strength. Further tests using viscosity measurements, microscopy, and computed tomography confirm the results. Wood-fiber-reinforced thermoplastic hybrid composites can thus compete with the natural fiber composites in terms of their mechanical behavior and therefore present a good alternative in technical semi-structural applications. KW - biocomposites KW - wood fibers KW - polypropylene KW - back-injection molding KW - bond strength Y1 - 2022 UR - https://doi.org/10.3390/ma15072473 VL - 15 IS - 7 SP - 2473 ER - TY - JOUR A1 - Schmitz, Regine A1 - Haupert, Frank A1 - Rüthing, Justus A1 - Sigrüner, Michael A1 - Strübbe, Nicole T1 - Tribologische Charakterisierung von Polymerfasern unter Trockenreibung, Mischreibung und Hydrodynamik mittels einer optimierten Pin-on-Disc-Prüfmethode JF - Tribologie und Schmierungstechnik N2 - Ausgehend von der herkömmlichen Pin-on-Disc-Prüfmethodik wurde ein Tribologieprüfstand hinsichtlich seiner Leistungsfähigkeit zur Fasercharakterisierung optimiert und angepasst. Die Methodik wird erläutert und erste Anwendungen im Bereich der tribologischen Charakterisierung von Einzelfasern werden vorgestellt. Der Prüfungsablauf zur Untersuchung der Polymerfasern, deren Durchmesser nur einige 100 µm betragen, ist so generiert, dass eine Erfassung der Daten als Funktion der Zeit im Bereich von einigen 10 µm bis zu einigen 100 µm Faserverschleiß kontinuierlich während der Messung bereits in den ersten Minuten erfolgen kann. Der Prüfmodus startet hierbei mit Linienlast und entwickelt sich dynamisch zur Flächenlast durch Änderung der Auflagefläche der Faser während der Messung. Es wird gezeigt, dass Einzelfasern hinsichtlich ihrer Reibungs- und Verschleißeigenschaften in unterschiedlichen tribologischen Systemen charakterisiert werden können. Die Abhängigkeit der Verschleißraten von Fasermaterial, Oberflächenrauheit der Gegenkörper und Schmiermittelraten wird dargestellt. N2 - Based on the conventional pin-on-disc test method, a tribology test rig was adapted and optimized regarding its ability to characterize polymer fibers. The method is explained and first applications in the field of tribological characterization of single fibers are presented. The test sequence to investigate the polymer fibers (diameters of only a few 100 µm) is generated in such a way that data can be recorded continuously as a function of time in the wear range from a few 10 µm to several 100 µm even during the first few minutes. The test mode starts by applying line load and dynamically progresses to area load by changing the contact area during the measurement. It is shown that single fibers can be characterized with respect to their friction and wear properties in different tribological systems. The dependence of the wear rates of fiber material, surface roughness of the counter bodies and lubrication rates is presented. KW - Polymerfasern KW - Pin-on-Disc KW - abrasiver Verschleiß KW - Reibung KW - Wasserschmierung KW - Oberflächenrauheit KW - polymer fibers KW - abrasive wear KW - friction KW - water lubrication KW - surface roughness Y1 - 2021 UR - https://doi.org/10.24053/TuS-2021-0015 VL - 68 IS - 3-4 SP - 13 EP - 21 ER - TY - JOUR A1 - Sigrüner, Michael A1 - Muscat, Dirk A1 - Strübbe, Nicole T1 - Investigation on pull‐out behavior and interface critical parameters of polymer fibers embedded in concrete and their correlation with particular fiber properties JF - Journal of Applied Polymer Science N2 - A crucial problem in concrete engineering is the corrosion of steel reinforcements. Polymer fibers as alternative reinforcement material can prevent corrosion; however, high adhesion to concrete and good fiber mechanics are necessary for polymers to be considered as an alternative reinforcement. This study tested different thermoplastic polymer materials to evaluate their level of adhesion to concrete. The adhesion properties of different self‐drawn polymer fibers were analyzed by extracting the fibers from concrete using single fiber pull‐out test (SFPT). To determine the adhesion mechanism, different polymer properties were analyzed and correlated to SFPT. Strong evidence was found that the fibers mechanical properties correlate with SFPT. Roughening the fiber surface increases the SFPT results significantly. While highly polar materials can support the adhesion process, a clear correlation could not be found. This study identifies high stiffness and roughness as the crucial properties of polymer fibers used in concrete engineering. If these factors can be engineered into the fiber, polymer fibers can present an alternative to steel in concrete reinforcement. KW - extrusion KW - fibers KW - mechanical properties KW - surfaces and interfaces KW - thermoplastics Y1 - 2021 UR - https://doi.org/10.1002/app.50745 VL - 138 IS - 28 SP - 50745 ER - TY - JOUR A1 - Obermeier, Frederik A1 - Schumacher, Mara A1 - Barth, Simon A1 - Karlinger, Peter A1 - Schemme, Michael A1 - Altstädt, Volker T1 - Verstärkung von Polypropylen mit Holzfasern durch Direkt-Compoundierung JF - Zeitschrift Kunststofftechnik N2 - Ergänzend zum bisherigen Stand der Wissenschaft und Technik wurden in dieser Veröffentlichung Fichtefasern aus einem thermo-mechanischen Aufschlussprozess über einen Spritzgusscompounder mit Polypropylen und Haftvermittler direkt compoundiert. Bei der direkten einstufigen Verarbeitung wurde ein steigender Holzfaseranteil bis 30 Gew.-% untersucht. Die Charakterisierung der Materialkombinationen erfolgte durch Zugversuche, Melt-Flow-Rate Messungen, Dichtebestimmung, Mikroskopie und Kerbschlagbiegeversuche. Bei steigendem Holzfaseranteil wird eine Steigerung der Zugeigenschaften, der Viskosität und der Dichte festgestellt. Die Kerbschlagzähigkeit bleibt bei steigendem Holzfaseranteil im Rahmen der Standardabweichung konstant, ist jedoch im Vergleich zum unveränderten Grundpolymer geringer. KW - Direkt-Compoundierung KW - Spritzgusscompounder KW - Holz KW - Holzfaser KW - Polypropylen Y1 - 2021 VL - 2021 IS - 2 SP - 87 EP - 111 PB - Carl Hanser Verlag CY - München ER - TY - JOUR A1 - Versen, Martin A1 - Ernst, W. T1 - Row hammer avoidance analysis of DDR3 SDRAM JF - Microelectronics Reliability N2 - A DDR3 SDRAM test setup implemented on the Griffin III test system from HILEVEL Technologies is used to analyse the row hammer bug. Row hammer pattern experiments are compared to standard retention tests for different manufacturing technologies. The row hammer effect is depending on the number of stress activation cycles. The analysis is extended to an avoidance scheme with refreshes similar to the Target Row Refresh scheme for the DDR4 SDRAM technology. KW - DDR4 SDRAM technology Y1 - 2020 UR - https://doi.org/10.1016/j.microrel.2020.113744 SP - 113744 ER - TY - JOUR A1 - Wohlschläger, Maximilian A1 - Versen, Martin T1 - Detection of plastics in water based on their fluorescence behavior JF - Journal of Sensors and Sensor Systems N2 - Plastic waste is one of the biggest growing factors contributing to environmental pollution. So far there has been no established method to detect and identify plastics in environmental matrices. Thus, a method based on their characteristic fluorescence behavior is used to investigate whether plastics can be detected and identified in tap water under laboratory conditions. The experiments show that the identification of plastics as a function of water depth is possible. As the identification becomes more difficult with higher water depths, investigations with a highly sensitive imaging method were carried out to obtain an areal integration of the fluorescent light and thus better results. KW - identification of plastics Y1 - 2020 UR - https://doi.org/10.5194/jsss-9-337-2020 VL - 9 IS - 2 SP - 337 EP - 343 ER - TY - JOUR A1 - Dechant, Eduard A1 - Seliger, Norbert A1 - Kennel, Ralph T1 - Power cycling and temperature endurance test of a GaN switching cell with substrate integrated chips JF - Microelectronics Reliability N2 - We present a reliability study of a half-bridge switching cell with substrate integrated 650 V GaN HEMTs. Power Cycling Testing with a ΔTj of 100 K has revealed thermo-mechanically induced failures of contact vias after more than 220 kcycles. The via failure mode of contact opening is confirmed by reverse-bias pulsed IV-measurements to be primarily triggered by a ΔTj imposed thermal gradient and not by a high Tj. The chip electrical characteristics, however, remained unaffected during Power Cycling. Furthermore, a High Temperature Storage test at 125 °C for 5000 h has shown no changes in the electrical performance of substrate integrated GaN HEMTs. KW - switching cell Y1 - 2019 UR - https://doi.org/10.1016/j.microrel.2019.06.064 VL - 100-101 SP - 113372 ER - TY - JOUR A1 - Lazar, Markus A1 - Jarre, F. T1 - Calibration by Optimization Without Using Derivatives JF - Optimization and Engineering N2 - Applications in engineering frequently require the adjustment of certain parameters. While the mathematical laws that determine these parameters often are well understood, due to time limitations in every day industrial life, it is typically not feasible to derive an explicit computational procedure for adjusting the parameters based on some given measurement data. This paper aims at showing that in such situations, direct optimization offers a very simple approach that can be of great help. More precisely, we present a numerical implementation for the local minimization of a smooth function f:Rn→R subject to upper and lower bounds without relying on the knowledge of the derivative of f. In contrast to other direct optimization approaches the algorithm assumes that the function evaluations are fairly cheap and that the rounding errors associated with the function evaluations are small. As an illustration, this algorithm is applied to approximate the solution of a calibration problem arising from an engineering application. The algorithm uses a Quasi-Newton trust region approach adjusting the trust region radius with a line search. The line search is based on a spline function which minimizes a weighted least squares sum of the jumps in its third derivative. The approximate gradients used in the Quasi-Newton approach are computed by central finite differences. A new randomized basis approach is considered to generate finite difference approximations of the gradient which also allow for a curvature correction of the Hessian in addition to the Quasi-Newton update. These concepts are combined with an active set strategy. The implementation is public domain; numerical experiments indicate that the algorithm is well suitable for the calibration problem of measuring instruments that prompted this research. Further preliminary numerical results suggest that an approximate local minimizer of a smooth non-convex function f depending on n≤300 variables can be computed with a number of iterations that grows moderately with n. KW - Engineering KW - Mathematical optimization Y1 - 2016 VL - 2016 IS - 17/4 SP - 833 EP - 860 PB - Springer ER - TY - JOUR A1 - Versen, Martin A1 - Ernst, W. A1 - Gulati, P. T1 - A row hammer pattern analysis of DDR2 SDRAM JF - Microelectronics Reliability N2 - A DDR2 SDRAM test setup implemented on the Griffin III ATE test system from HILEVEL Technologies is used to analyse the row hammer bug. Row hammer pattern experiments are compared to standard retention tests. The analysis confirms that the row hammer effect is caused by a charge excitation process depending on the number of stress activation cycles. The stress has to occur in the local neighborhood of the cells under test. Shallow impurity levels support the responsible charge carrier transport process in the used DDR2 SDRAM technology KW - Microelectronics KW - pattern analysis Y1 - 2018 UR - https://doi.org/10.1016/j.microrel.2017.07.022 VL - 76-77 SP - 64 EP - 67 ER -