Search

Das Ziel des Forschungsprojekts „ProSize“ war es, die Einflüsse der Hybridgarneigenschaften wie die Schneidbarkeit und die elektrostatische Aufladung auf die Verarbeitbarkeit im Faserspritzprozess zu identifizieren und zu quantifizieren, um basierend auf diesen Erkenntnissen simultan gesponnene Glasfaser / Polyamid-6.6(GF / PA 6.6)-Hybridgarne mit angepassten Schlichterezepturen zu entwickeln. Durch die Zusammenarbeit des IPF und des IKV konnten Hybridgarne entwickelt werden, die speziell für die Verarbeitung im Faserspritzprozess ausgelegt sind, um Inhomo­genitäten des lokalen Flächengewichts und der Faserorientierung im Preform auf ein zulässiges Maß zu reduzieren.

Polymers 15(3), 721 (2023). doi:10.3390/polym15030721, Polylactic acid (PLA) is one of the most promising bioplastic representatives that finds application in many different areas, e.g., as single-use products in the packaging industry, in the form of mulch film for agriculture, or in medical devices. For the development of new areas, especially in terms of long-term applications and the production of recyclable products, the material properties controlled by processing must be known. The state of the art is investigations at the global scale (integral values) without consideration of local structure inhomogeneities and their influence on the material properties. In this work, morphological, thermal, and mechanical properties of injection-molded PLA tensile bars are investigated at different length scales (global and local) as a function of processing parameters. In addition to the processing parameters, such as melt temperature, mold temperature, and cooling time in the mold, the influence of the D-isomer content on the crystallization behavior and the resulting material properties are investigated. The material was found to form crystalline structures only when cooled in a mold tempered above Tg. In addition, PLA with a lower content of D-isomer was found to have a higher degree of crystallinity. Since the mechanical properties obtained by tensile tests could not be correlated with the degree of crystallinity, detailed analysis were performed showing a characteristic inhomogeneous morphology within the tensile bars. By means of micromechanical investigations on samples with different microstructure ranges, the relationship between local morphology and failure behavior could be explained., Published by MDPI, Basel

Most concepts to characterize crack propagation were developed for elastic materials. When applying these methods to elastomers, the question is how the inherent energy dissipation of the material affects the cracking behavior. This contribution presents a numerical analysis of crack growth in natural rubber taking energy dissipation due to the visco-elastic material behavior into account. For this purpose, experimental tests were first carried out under different load conditions to parameterize a Prony series as well as a Bergström–Boyce model with the results. The parameterized Prony series was then used to perform numerical investigations with respect to the cracking behavior. Using the FE-software system ANSYS and the concept of material forces, the influence and proportion of the dissipative components were discussed.

Bei BTA-Tiefbohrprozessen kommt es aufgrund der großen Werkzeuglängen häufig zu Torsionsschwingungen des Werkzeugsystems aus Bohrkopf und Bohrrohr. Im Vergleich zu konventionellen Stahl-Bohrrohren reduzieren Bohrrohre aus faserverstärktem Kunststoff diese Schwingungen durch ihr materialspezifisches Dämpfungspotenzial und erhöhen damit die Prozesssicherheit und verringern den Werkzeugverschleiß. Die Einbindung von Sensorfasern direkt in das Laminat erlaubt zudem eine Prozessüberwachung. In BTA deep hole drilling, torsional vibrations of the tool system consisting of a drill head and a drill tube often occur due to the long tool lengths. Compared to conventional steel drill tubes, drill tubes made of fiber-reinforced plastic reduce these vibrations through their material-specific damping behavior and thus increase the process reliability and reduce the tool wear. The integration of sensor fibers directly into the laminate also allows a monitoring of the drilling process.

The large tool length in BTA deep hole drilling often leads to strong torsional vibrations of the tool system, leading to a reduced bore hole quality failures. When substituting steel drill tubes with tubes from composite material, the laminate structure dampens these vibrations. Secondly, the integration of sensors allow to monitor process vibrations. This contribution introduces a new sensor platform to measure process vibrations, feed force and drilling torque using Fibre-Bragg Grating Sensors. The presented experimental results focus on characteristic frequency spectra with natural torsional and compression frequencies of the CFRP drill tube, which show variations due to changed feed.

Although powder coating systems offer many environmental, ecological and energy related benefits over liquid based coatings, in the case of uretdione based polyurethane systems, high curing temperature is still an issue. On the other hand, powder coating systems make it possible to reduce the costs and enhance the process of forming complex 3D structures using the deep drawing method by pre-coated metal substrates. During this processing method, there is a probability of micro crack formation in the coated film due to strain impact on the coating layer. A powder coating with self-healing ability is an ultimate solution to face not only this kind of fraction but also any other possible ones (such as defects caused by any impact on film surface during processing, transporting or even service). Here, a single molecule that is prepared via Diels–Alder cycloaddition reaction and retro Diels–Alder cleavage reaction was utilized as a self-healing additive to achieve self-healing ability in the powder coating system that is based on a commercially available uretdione cross-linker and OH-polyester resin. Coatings were prepared through melt mixing of components in a lab mixer, milling, sieving, and then application on the metal substrate through the electrostatic spraying method. To illustrate the role of self-healing additive, various concentrations (4 and 9% wt.) in combination with different curing temperatures (80 °C to 200 °C) were investigated. Both samples containing HA showed self-healing ability at elevated temperature around 120 °C for about 30 min with acceptable roughness and surface properties. Hardness measurement of cured film as well as thermal investigation indicate the chemical reaction of HA in a cross-linked network of cross-linker and resin. In addition, using HA leads to a 40 K drop in curing temperature of the system without using any catalyst. A 2.58% improvement in hardness values at a lower curing temperature and healing time of around 12.5 min at 120 °C to recover 100% of initial scratch (more than 10 cycles) in the sample containing 9% wt. HA was observed.

Polyamide 6 (PA6) is able to absorb water from the surrounding air and bond to it by forming hydrogen bonds between the carbonamide groups of its molecular chains. Diffusion processes cause locally different water concentrations in the (component) cross-section during the sorption process, resulting in locally different mechanical properties due to the water-induced plasticisation effect. However, the water content of PA6 is usually specified as an integral value, so no information about a local water distribution within a component is provided. This paper shows a method to characterise moisture distributions within PA6 samples using low-energy computer tomography (CT) techniques and comparing the reconstructed results with a developed finite elements (FE) modelling method based on Fick’s diffusion laws with concentration-dependent diffusion coefficients. For this purpose, the ageing of the samples at two different water bath temperatures as well as at different integral water contents are considered. The results obtained by CT reconstruction and FE modelling are in very good agreement, so that the concentration distributions by water sorption of PA6 calculated by FEM can be regarded as validated.

Polyamides are known to absorb and desorb water to establish an equilibrium with their environment. Water uptake by diffusion leads to a drastic reduction in the strength and stiffness of the material, which is referred as the water-induced plasticizing effect. This effect leads to a shift of the glass transition region towards lower temperatures what can be determined by differential scanning calorimetry (DSC). However, a determination of the glass transition temperature T g is not accurate in samples with inhomogeneous moisture distribution before an equilibrium is reached by diffusion and T g is superimposed by water-specific effects. It is shown that the glass transition can be measured by StepScan DSC even with inhomogeneous moisture distribution within the sample. In addition, a method is developed and validated which uses the low thermal conductivity and the shift of T g to detect a water-saturated sample boundary layer in inhomogeneously conditioned PA 6 samples.

Polyamide 6 (PA6) is known to absorb water from its environment due to its chemical structure. This water absorption leads to a change in the mechanical properties as well as an increase in volume (swelling) of the polyamide. In the present work, the sorption and swelling behaviour of polyamide 6 in different conditioning environments was experimentally investigated on different part geometries to develop a finite element (FE) method on the basis of the measured data that numerically calculates the sorption and swelling behaviour. The developed method includes two analyses using the Abaqus software. Both the concentration-dependent implementation of the simulation parameters and the calculation of swelling-induced stresses are performed. This enables the modelling of the sorption curves until maximum saturation is reached and the simulation of the characteristic S-shaped swelling curves. Therefore, the developed methodology represents an efficient method for predicting the sorption and swelling behaviour of polyamide 6 parts during conditioning in a water bath. The determined properties provide the basis for the development of an FE-based simulation environment to take moisture absorption into account during the part design. This enables the calculation of moisture-induced swelling processes and the resulting initial stresses in a given part.

Schalenformige Bauteile zeichnen sich durch ein sehr groses Verhaltnis von Breite oder Lange zur Wanddicke aus. Durch die geringe Wandstarke kommt der Einleitung von Lasten in derartige Strukturen eine besondere Bedeutung zu. Hierfur werden haufig spezielle Lasteinleitungselemente (Inserts) in die Struktur eingebracht, die als Anbindungspunkte dienen. Die Kombination von metallischem Lasteinleitungselement und CFK-Struktur wird anhand drei verschiedener Teilprojekte untersucht. Im Projekt „Multilayer-Inserts – Intrinsische Hybridverbunde zur Krafteinleitung in dunnwandige Hochleistungs-CFK-Strukturen“ wurde ein Lasteinleitungselement fur automatisiert gefertigte Faserverbundstrukturen entwickelt. Das Projekt „Grundlagenuntersuchungen intrinsisch gefertigter FVK/Metall-Verbunde – vom eingebetteten Insert zur lasttragenden Hybridstruktur“ untersucht die faserschonende, intrinsische Herstellung von FVK/Metall-Verbunden im RTM-Prozess anhand verschiedener Hybridisierungsansatze. Im Projekt „Einfluss, Detektion und Vorhersage von Defekten in grosserientauglichen Hybridverbunden fur Metall/CFK-Leichtbautragstrukturen“ wurde ein neuartiges Anbindungskonzept fur Metall-CFK-Hybridstrukturen mit thermoplastischer Zwischenkomponente entwickelt. Im Rahmen dieses Kapitels werden die Ergebnisse der Teilprojekte detailliert vorgestellt und erortert.

In light weight construction, the concept of multi-material design allows to benefit from the advantageous properties of different materials. Thereby the joining technique for dissimilar materials must always be taken into account. The joining of carbon fibre reinforced polymers and metals is an example where innovative approaches complement or replace the usual joining technology. A special approach is a metal insert overmoulded with a multifunctional polymer, whereby the surface structures improve the intrinsic properties of the compound. These inserts are produced in an injection moulding process.

In this contribution, the influence of the reaction injection moulding process on the thermomechanical material behaviour of aliphatic hexamethylene diisocyanate (HDI) based fast curing polyurethane is demonstrated. Uniaxial tensile tests, temperature-frequency dependent dynamic mechanical thermal analysis (DMTA) and Differential Scanning Calorimetry (DSC) are used to show the differences in properties for ten different sets of process parameters. The mould and resin components temperature, the mass flow during the filling process and the residence time during the reaction process of the polyurethane are varied in several stages. Further experiments to determine the molar mass of the molecular chain between two crosslinking points of the polyurethane are used to explain the process influences on the thermomechanical properties. Thus, a direct correlation between manufacturing and material properties is shown. In addition, the mutual effect of the different parameters and their overall influence on the material behaviour is presented.

The quality of the fiber orientation of injection molding simulations and the transferred fiber orientation content, due to the process–structure coupling, influence the material modeling and thus the prediction of subsequently performed structural dynamics simulations of short-fiber reinforced, thermoplastic components. Existing investigations assume a reliable prediction of the fiber orientation in the injection molding simulation. The influence of the fiber orientation models and used boundary conditions of the process–structure coupling is mainly not investigated. In this research, the influence of the fiber orientation from injection molding simulations on the resulting structural dynamics simulation of short-fiber reinforced thermoplastic components is investigated. The Advani–Tucker Equation with phenomenological coefficient tensor is used in a 3- and 2.5-dimensional modeling approach for calculating the fiber orientation. The prediction quality of the simulative fiber orientations is evaluated in comparison to experiments. Depending on the material modeling and validation level, the prediction of the simulated fiber orientation differs in the range between 7.3 and 347.2% averaged deviation significantly. Furthermore, depending on the process–structure coupling and the number of layers over the thickness of the model, the Kullback–Leibner divergence differs in a range between 0.1 and 4.9%. In this context, more layers lead to higher fiber orientation content in the model and improved prediction of the structural dynamics simulation. This is significant for local and slightly for global structural dynamics phenomena regarding the mode shapes and frequency response behavior of simulative and experimental investigations. The investigations prove that the influence of the fiber orientation on the structural dynamics simulation is lower than the influence of the material modeling. With a relative average deviation of 2.8% in the frequency and 38.0% in the amplitude of the frequency response function, it can be proven that high deviations between experimental and simulative fiber orientations can lead to a sufficient prediction of the structural dynamics simulation.

Funding Information: The authors are grateful to CNPq (Universal projects 424426/2016-1 and 310649/2017-0 ), FAPERGS (PqG project 17/2551-0001 ), CAPES/DAAD (PROBRAL project 88881.198774/2018-01 and 57447163 ), and FAPESP/FAPERGS (project 19/2551-0002279-4 ) for their financial support. J.H.S. Almeida Jr. is supported by the Royal Academy of Engineering under the Research Fellowship scheme [Grant No. RF/201920/19/150 ]. Publisher Copyright: © 2022 The Author(s) This work aims at developing a strategy to obtain damage evolution parameters of wound cylinders to verify the influence of the winding pattern on them. First, a detailed description of the pattern generation is presented. Then, a finite element (FE) model is developed, in which the cylinders are constructed with winding patterns (WP) of 1/1, 2/1, and 3/1 and subjected to radial compressive loading. Since the cylinder-to-plate contact is considered, the variation of radial stiffness with respect to the parallel plate position is also analyzed. In addition, a damage model is used to predict the progressive failure of those cylinders. A finite element model updating (FEMU) routine is then developed to find the damage input parameters that best simulate experimental force–displacement curves. Key results show that the FEMU algorithm is strongly dependent on the initial guesses producing, however, an excellent correlation with experimental data. The predicted force versus displacement curves for all winding patterns are within the experimental standard deviation, except for the cases in which the winding pattern is not taken into consideration. The computational framework proposed is validated both quantitatively and qualitatively through post-mortem analysis of the specimens. The winding pattern affects the failure and damage mechanisms of the cylinders and, consequently conventional FE models that disregard the pattern cannot capture these mechanisms.

PEN is an industrial polyester plastic which has become interesting for the physics community as a new type of plastic scintillator. PEN scintillates in the blue regime, which is ideal for most photosensor devices. In addition, PEN has excellent mechanical properties and very good radiopurity has been achieved. Thus, it is an ideal candidate for active structural components in low-background experiments. One possible application are holders for germanium detectors operating in cryogenic liquids (LAr, LN2). Such structures can help to reject surface and external backgrounds, boosting the sensitivity of experiments. In this contribution, the R\&D on PEN is outlined and an evaluation of the first production of PEN structures for the LEGEND-200 experiment is reported., Conference ICHEP2020

A highly ordered, hexagonal, nacre-like composite stiffness is investigated using experiments, simulations, and analytical models. Polystyrene and polyurethane are selected as materials for the manufactured specimens using laser cutting and hand lamination. A simulation geometry is made by digital microscope measurements of the specimens, and a simulation is conducted using material data based on component material characterization. Available analytical models are compared to the experimental results, and a more accurate model is derived specifically for highly ordered hexagonal tablets with relatively large in-plane gaps. The influence of hexagonal width, cut width, and interface thickness are analyzed using the hexagonal nacre-like composite stiffness model. The proposed analytical model converges within 1% with the simulation and experimental results., J. Compos. Sci.;4(3)

The applicability and the influence of pin structures in dependence on the adhesive properties in hybrid joints are investigated in the course of this paper. First, single lap joint experiments are performed and a Finite Element model is used to obtain force-displacement curves, and thus the specific simulation parameters. The comparison of different models with a pin a semi-spherical pin, and without a pin show that the pin has a positive influence, especially on low adhesive strengths. In contrast, the pin has a lesser effect for adhesive joints with high strength. In the following study, different pin geometries, pin sizes and adhesive bonding parameters are tested. It is shown that the negative influence of a pin for high adhesive strength can be compensated by the specific design of a pin. Furthermore, small pins ensure the best force transmission performance. Finally, the alignment of elliptical pins depends on the bonding properties, as for high strength parameters, the pin should be oriented in load direction, and for low strength parameters, it is ideal to orient the pin transversely to the load direction.

The collaboration with domain experts concentrates always on an application domain where the experts work. Usually, they provide the data and directions of research that require visualization support. This chapter presents seven successful cases of such collaborations. The domain varies from biology and medicine to mechanical engineering. There are examples of long time cooperation as well as smaller short-term projects. The description concentrates on the process, output, and especially on the lessons learnt from these cooperations. The scientific work is described to understand the context and goals of the cooperation, but many details can only be found in the references. The reason for this unusual writing is the wish on the one hand to describe various aspects of collaboration with domain experts which is an important part of the foundations of data visualization. On the other hand, the text should not become lengthy and filled with too many details of individual cases that can be found elsewhere.