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Garcia-Moreno O.,University of Oviedo | Borrell A.,University of Oviedo | Bittmann B.,Fundacion ITMA | Fernandez A.,Kaiserslautern Institute for Composite Materials | Torrecillas R.,University of Oviedo
Journal of the European Ceramic Society | Year: 2011

Composite materials formed by a LAS matrix reinforced with second phases are promising materials in many applications where better mechanical properties than those corresponding to conventional low thermal expansion coefficient materials are required. In this study we will show the capability of the design of a LAS-alumina submicron composite. The main scope of this work is to test the sinterability of the composites and to design a composition for a very low thermal expansion submicron composite. For this purpose, Taimei alumina (TM-DAR) powders and an ad hoc synthesized β-eucryptite phase were used to fabricate the composite. XRD phase compositions and microstructures are discussed together with data from dilatometries in a wide temperature range. The results obtained show the possibility of designing a submicron composite with a very low thermal expansion coefficient and improved mechanical properties that can be used in oxidizing conditions. © 2011 Elsevier Ltd.

Hess H.,BASF | Himmel N.,Kaiserslautern Institute for Composite Materials
Composites Science and Technology | Year: 2011

Based on experimental investigations on structurally stitched non-crimp fabric (NCF) carbon fiber/epoxy laminates under in-plane tension, compression and shear loading [1], a finite element based unit cell model was developed to estimate the in-plane strength of NCF laminates taking into consideration the yarn diameter, the stitching pattern and direction as well as the load type. Depending on these parameters, regions with undisturbed and disturbed fiber orientations leading to resin pockets as well as local changes of the fiber volume fraction are taken into account in the model. The comparison of experimental and numerical results showed that the strength of structurally stitched NCF laminates under in-plane tension, compression or shear loading can be predicted with an acceptable accuracy. The overall mean deviation between simulation and experiment observed was between 8% and 13%. © 2010 Elsevier Ltd.

Fejos M.,Budapest University of Technology and Economics | Karger-Kocsis J.,Budapest University of Technology and Economics | Grishchuk S.,Kaiserslautern Institute for Composite Materials
Journal of Reinforced Plastics and Composites | Year: 2013

Biocomposites were prepared using epoxidized linseed oil and flax fibre reinforcements in different assemblies. Epoxidized linseed oil was cured by two different anhydrides to check how its thermomechanical properties can be influenced. As reinforcements, nonwoven mat, twill weave and quasi-unidirectional textile fabrics with two different yarn finenesses were used. Their reinforcing effect was determined using dynamic mechanical analysis in flexure. Dynamic mechanical analysis served to determine the glass transition temperature (Tg) also. Shape-memory properties were derived from quasi-unconstrained flexural tests performed near to the Tg of the epoxidized linseed oil and its biocomposites. Flax reinforcement reduced the Tg that was attributed to off-stoichiometry owing to chemical reaction between the hydroxyl groups of flax and anhydride hardener. The shape-memory parameters were moderate or low. They were affected by both textile content and type. © The Author(s) 2013.

Sharma M.,Indian Institute of Technology Delhi | Bijwe J.,Indian Institute of Technology Delhi | Mitschang P.,Kaiserslautern Institute for Composite Materials
Tribology International | Year: 2011

Carbon fabric (CF) being inert towards the matrix, the quality of its adhesion with the matrix is poor and hence, needs treatment to enhance fibermatrix bonding. In this paper, cold remote nitrogen oxygen plasma (CRNOP) treatment to CF was employed to improve fibermatrix adhesion. Composites were developed using CF with polyethersulphone (PES) and polyetheretherketone (PEEK) matrices. Performance enhancement due to CF treatment was quantified by improvement in mechanical and wear resistance (WR) properties. A fairly good linearity was observed for specific wear rate (K0× ILSS) as a function of a factor (μP/E). © 2010 Elsevier Ltd.

Kasperovich G.,German Aerospace Center | Hausmann J.,Kaiserslautern Institute for Composite Materials
Journal of Materials Processing Technology | Year: 2015

Generative processes or additive layer manufacturing like selective laser melting (SLM) enable the fabrication of highly precise and complex component geometries that are otherwise difficult, costly, or even impossible to realize using conventional techniques. Titanium alloys and in particular TiAl6V4 are suited well for processing by SLM. However, a careful optimization procedure of the process parameters is necessary to obtain a high quality material: firstly, the optimization of the initial process parameters for the minimization of inherent defects, and secondly, the optimization of the further thermomechanical treatment to minimize internal stresses and adjust the microstructure. These two stages of optimization are represented here. For the initial program more than 40 small TiAl6V4 cuboids were produced with the variable scan parameters and two- and three dimensionally analyzed. The reducing of the porosity by 6-10 times is shown. The optimized process parameters were used for further manufacturing of the test specimen, some of them were then thermomechanically treated: annealed or hot-isostatically pressed. The hardness, tensile properties and high cycle fatigue resistance of all samples were tested and the similar tests were also conducted for the reference material: wrought TiAl6V4 alloy. The microstructure, porosity and the received mechanical properties were analyzed and compared, and the influence of thermomechanical treatment was evaluated. As a result of this double optimization, a significant improvement of ductility (ε = 19.4%) and fatigue resistance compatible to the wrought TiAl6V4 for the SLM produced material was achieved. Furthermore, since some surfaces in complex components such as the channels in the turbine blade cannot be machined or polished, both treated ('machined') and untreated ('as built') surface conditions were considered and discussed. © 2015 Elsevier B.V. All rights reserved.

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