Bundeswehr Research Institute for Materials

Erding, Germany

Bundeswehr Research Institute for Materials

Erding, Germany
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Forster T.,Bundeswehr Research Institute for Materials
Advanced Structured Materials | Year: 2017

Compatibility tests of elastomers with unpolar liquids usually afford long time intervals to simulate applications and high experimental effort to determine mechanical properties. This paper describes the influence of short term storage in mineral oil on the composition of in-service acrylonitrile butadiene elastomer (NBR) and correlates it to its mechanical strength. Hardness and tensile strength at break are related to the fraction of volatile components determined by thermogravimetry coupled with IR spectroscopy (TG-IR). It is shown that the change of mechanical properties predominantly depends on the fraction of soluble/volatile components and barely on their detailed composition, as long as elastomers do not undergo chemical aging. TG-IR offers a new method of predicting mechanical performance based on chemical analysis applicable for in-service NBR independent of the acrylonitrile content. © Springer Science+Business Media Singapore 2017.

Wolfrum J.,Bundeswehr Research Institute for Materials | Whitney E.,Bundeswehr Research Institute for Materials | Eibl S.,Bundeswehr Research Institute for Materials
Journal of Composite Materials | Year: 2017

This study focuses on understanding and prediction of short-term thermal degradation of polymer matrix composites. One sided irradiation of two commercial composites (HexPly® 8552/IM7 and M18-1/G939) is carried out on specimens of various thickness (2, 4, 6 mm) at different heat fluxes (50 and 80 kW/m2) for various exposure times prior to ignition. The aim is to correlate the amount of the applied thermal energy with the heat damage and the residual mechanical strength. Among the two primary components of each matrix the epoxy resin is observed to degrade faster than the thermoplastic under thermal load, as measured by IR spectroscopy. A correlation is achieved between the interlaminar shear strengths and the relative amount of the residual matrix components. The interlaminar shear strengths and degradation processes are assessed in dependence of the applied energy per volume. The derived relationships and a chemometric analysis of IR spectra, can be used to rapidly estimate mechanical properties, as well as other properties of specimens with unknown thermal preload. Degradation processes are discussed in detail. © 2016, © The Author(s) 2016.

Holtmannspotter J.,Bundeswehr Research Institute for Materials | Czarnecki J.V.,Bundeswehr Research Institute for Materials | Wetzel M.,Bundeswehr Research Institute for Materials | Dolderer D.,Aalen University of Applied Sciences | Eisenschink C.,Bundeswehr Research Institute for Materials
Journal of Adhesion | Year: 2013

In the fabrication of fiber-reinforced plastics materials peel plies are commonly used as an additional layer on top of the laminates to sponge up the surplus resin and to create an activated surface for adhesive bonding or coating by peel ply removal. In theory, the peel ply removal results in a new and uncontaminated fracture surface that is activated by polymer chain scission. The peel ply method is often presented as being a good surface treatment for structural bonding. In this study carbon fiber-reinforced plastics (Hexcel® 8552/ IM7) were produced by the use of five different peel plies and a release foil made of polytetrafluorethylene (PTFE). The peel plies themselves and the surfaces on the CFRP created by peeling were examined by scanning electron microscopy (SEM), x-ray photo electron spectroscopy (XPS), energy-dispersive x-ray spectroscopy (EDX), infrared (IR) spectroscopy, atomic force microscopy (AFM), and contact angle measurements to characterize the surfaces produced. Furthermore, the bond strength of lap shear and floating roller peel samples was determined with and without additional plasma treatment. For bonding, a room temperature-curing two-component-epoxy adhesive (Hysol® 9395) was used to prove the applicability of different peel plies for structural adhesive bonding under repair conditions. © 2013 Copyright Taylor and Francis Group, LLC.

Schneider S.,Bundeswehr Research Institute for Materials
International Journal of Modern Physics B | Year: 2012

In this work, a new method to determine the wall shear stress was developed step by step. To determine the wall shear stress, methods of the suspension rheology are being used for the first time to characterize ER fluids. This work focuses on investigations of the flow behavior of electrorheological suspensions in flow channels with different geometries at different electrical field strengths. Careful interpretation of the results with respect to different gap geometries has shown that the measured flow curves should undergo a combination of corrections. As a result it can be shown that wall slip effects can be measured under application like conditions on a hydraulic test bench. © 2012 World Scientific Publishing Company.

Scheuermann S.S.,Bundeswehr Research Institute for Materials | Eibl S.,Bundeswehr Research Institute for Materials | Bartl P.,Bundeswehr Research Institute for Materials
Lubrication Science | Year: 2011

This study has been conducted with the aim to gain detailed insight into the chemical nature of polyalphaolefin dimer (PAO dimer, C20H 42). By using gas chromatography/mass spectrometry, a large number of isomers the complex mixture consists of has been identified; the variety of structural motifs ranges from a homologous series of almost linear vicinal dimethyloctadecanes to highly branched isomers such as 6,7-dibutyldodecane. However, the mixture is characterised by the presence of isomers, which exhibit an intermediate degree of branching. Furthermore, a generally applicable protocol has been established to determine the relative content of these isomers. This protocol has then been applied to analyse samples from different PAO dimer batches, and a correlation between isomeric distribution and bulk properties, namely the viscosity-temperature behaviour, has been found. It turns out that the viscosity of PAO dimer depends less on temperature if the amount of weakly branched and almost linear isomers increases. © 2011 John Wiley & Sons, Ltd.

Eibl S.,Bundeswehr Research Institute for Materials
Fire and Materials | Year: 2014

SUMMARY: The integration of an intumescent barrier between the plies of prepreg based polymer matrix composite and sandwich panels is investigated in detail with regard to reaction-to-fire properties. Incident heat flux, panel thickness and insertion depth within the panel were varied systematically. Fire retarding effects are compared to the application of an intumescent and top coating on the surface. All tests were carried out with a commercial material: HexPly® 8552/IM7 by Hexcel. Design rules for an effective improvement of reaction-to-fire properties are derived. Two practical applications were identified not interfering with mechanical properties: A metal mesh as support for the intumescent material underneath a single top ply and the one-sided integration in a sandwich with the possibility to expand into the honeycomb. Degradation mechanisms are characterized by cone calorimetry and temperature development throughout the specimens. © 2014 John Wiley & Sons, Ltd.

Eibl S.,Bundeswehr Research Institute for Materials | Reiner D.,Bundeswehr Research Institute for Materials
Materials and Corrosion | Year: 2011

Two representative types of commercial volatile corrosion inhibitor (VCI) packaging materials without a potential for health hazards according to TRGS 615 were investigated: a paper containing ethanol amine and a polyethylene foil containing sodium nitrite as main VCI ingredients. For a variation of VCI concentration the packaging material was thermally treated at 60-100 °C and the amount of VCI remaining was determined after this accelerated desorption. Additionally a nitrite-free polyethylene foil was impregnated with various amounts of sodium nitrite. Correlations of VCI content - of both the amine and nitrite - with corrosion protection of mild steel were observed. For ethanol amine a color change reaction is proposed to indicate the remaining potential of corrosion protection. This work is aimed at regaining trust in VCI technology. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Heimbs S.,Airbus | Nogueira A.C.,Airbus | Hombergsmeier E.,Airbus | May M.,Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut | Wolfrum J.,Bundeswehr Research Institute for Materials
Composite Structures | Year: 2014

An experimental and numerical study of the failure behaviour of composite T-joints under quasi-static and high-rate dynamic loading is presented, focusing on the investigation of a novel reinforcement technique in the through-thickness direction using metallic arrow-pins to increase failure resistance and damage tolerance. Specimen manufacturing and testing are described in detail. The test campaigns covering 0° T-pull and 30° T-bending tests were conducted under quasi-static and high-rate dynamic conditions in order to assess potential loading rate effects. The novel concept with the arrow-pin reinforcement showed significantly increased post-damage load levels and energy absorption capability with the pins being pulled out of the laminate under large global deformations. In addition to the experimental test campaign, numerical simulations with the explicit finite element code LS-Dyna were conducted on local, global and macro-modelling level. The models were validated against the test results and applied to ballistic impact simulations of an exemplary composite fuel tank structure under hydrodynamic ram loading, where the novel joint design led to significantly higher damage resistance. © 2013 Elsevier Ltd.

Holtmannspotter J.,Bundeswehr Research Institute for Materials | Czarnecki J.v.,Bundeswehr Research Institute for Materials | Gudladt H.-J.,University of Federal Defense Munich
International Journal of Adhesion and Adhesives | Year: 2010

A reliable performance is what the engineers need to take advantage of for the weight-saving potential of adhesive bonded structures. The present paper presents a new approach to ensure improved and quality assured adhesive bonds by using power ultrasound in combination with the adhesive application to support interface formation. In contrast to various known publications in this paper ultrasound is not used at low power-level as for inspection by nondestructive testing (NDT) but to influence interface cleaning and to improve contamination tolerance of the adhesive bonding process. Power ultrasound with an intensity of 10-100 W/cm2 is used to transfer energy for a short time into the liquid adhesive. The general idea and various advantages for adhesive bonding by supplying energy for the developing adhesive/substrate interface are presented and discussed. Power ultrasound can be used: to remove surface contaminations, to obtain contamination tolerance for the bonding process, to improve substrate wetting, to mix adhesives, to outgas adhesives and the substrate surface or to establish chemical reactions at the interface. Results from adhesive bonded lap shear and roller peel tests with contaminated samples, rheological measurements and pictures from high speed videos demonstrate the effectiveness of the approach. © 2009 Elsevier Ltd. All rights reserved.

Eibl S.,Bundeswehr Research Institute for Materials
Fire and Materials | Year: 2012

The influence of the orientation of carbon fibres on the reaction-to-fire characteristics of a layered composite has been investigated in detail. 8552/IM7 prepregs were laid up to give unidirectional and quasi-isotropic laminates. Specimen thickness (0.25 to 8.0 mm) and heat flux (15 to 80 kW/m 2) were varied for irradiation. Fundamental reaction-to-fire properties of this composite are interpreted on the basis of the matrix components: epoxy resin and polyethersulfone. Cone calorimetry and temperature distributions through the laminate showed that the velocity and degree of combustion are dominated by fibre orientation for a given resin. In general, a quasi-isotropic fibre orientation leads to faster ignition, because of preferred delaminations, but retards combustion processes more effectively than a unidirectional lay-up. Migration velocities of the pyrolysis zone were measured. Copyright © 2011 John Wiley & Sons, Ltd. Copyright © 2011 John Wiley & Sons, Ltd.

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