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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.


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.


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.


Tapeinos I.G.,University of Aegean | Miaris A.,Kaiserslautern Institute for Composite Materials | Mitschang P.,Kaiserslautern Institute for Composite Materials | Alexopoulos N.D.,University of Aegean
Composites Science and Technology | Year: 2012

A methodology was devised to evaluate the newly-developed carbon nanotube reinforced polymer composites by means of mechanical performance and manufacturing cost. Glass fibre reinforced-epoxy composite plates were produced having different parameters: (a) three manufacturing processes, (b) geometrical dimensions, (c) carbon nanotubes concentration in the epoxy resin and finally (d) modified resin infusion temperature. Tensile coupons were machined out of the manufactured plates and their quasi-static mechanical properties were evaluated. Three cost models were developed to assess plates and tensile coupons manufacturing cost for each different case. Optimal values were evaluated for major manufacturing parameters, driving force being the mechanical properties of interest (quality) as well as their low manufacturing cost. It is demonstrated that the added cost to manufacture such nano-reinforced composites is attributed to increase strength on the expense of ductility; the main benefit of the carbon nanotube-based polymer composites seems to be their ability to be monitored. Almost 20% added cost is paid to attain this new function of piezo-resistivity for the RTM process, while this amount further increases for the non-automated processes such as the Hand Lay-up. © 2012 Elsevier Ltd.


Rieber G.,Kaiserslautern Institute for Composite Materials | Jiang J.,Donghua University | Deter C.,Kaiserslautern Institute for Composite Materials | Chen N.,Donghua University | Mitschang P.,Kaiserslautern Institute for Composite Materials
Composites Part A: Applied Science and Manufacturing | Year: 2013

Product parameters of woven textiles like weave, linear density, yarn density, and crimp determine permeability, infiltration, and use as reinforcement textile in a polymer composite structure. Nevertheless, attempts to link these parameters to the permeability of woven textiles are rare. In this study 19 woven glass fiber textiles were selected to determine the effect of the weave, linear density, yarn density, and crimp on in-plane permeability. The measurements have been conducted on a stiff two-sided aluminum tool with eight linear capacitive sensors. The anisotropic flow behavior of isotropically built-up textiles is explained by using the crimp in the warp and weft yarns. Textiles with a higher crimp ratio (warp/weft) showed a higher anisotropy in permeability respectively. A relationship between the weaving density (defined as the product of linear density and yarn density) of a textile and the slope of the permeability-fiber volume fraction curve was found. In a comparison of three identically built- up balanced and unbalanced twill and satin weave textiles it was observed that the K2 permeability of twill weave textiles is significantly lower compared to the K1 permeability. Consequently, twill weave textiles are more anisotropic. The results of this study allow the selection and tailoring of woven textiles with specific, e.g. very low or isotropic, permeabilities. © 2013 Elsevier Ltd. All rights reserved.


Noll A.,Kaiserslautern Institute for Composite Materials | Burkhart T.,Kaiserslautern Institute for Composite Materials
Composites Science and Technology | Year: 2011

In this study, poly(p-phenylene sulfide) based nanocomposites containing multi-walled carbon nanotubes (MWNTs) were produced by dilution of a 15. wt.% MWNT/PPS masterbatch via twin screw extrusion process. The electrical conductivities of the nanocomposites were measured and percolation threshold was observed below 0.77. vol.% MWNTs. The state of dispersion and distribution quality of MWNTs was analyzed on macro- and nanoscale through transmission light and scanning electron microscopy (SEM). A good deagglomeration of primary macroagglomerates and a homogenous MWNT distribution on nanoscale was found. The dependence of conductivity on MWNT concentration was estimated using statistical percolation theory which matches the experimental data quite well. A new empirical equation was set up to fit the electrical conductivity using quantitative values of visible percolating MWNTs which were detected by charge contrast imaging in SEM. © 2011 Elsevier Ltd.


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.


Khan M.A.,Kaiserslautern Institute for Composite Materials | Mitschang P.,Kaiserslautern Institute for Composite Materials | Schledjewski R.,Kaiserslautern Institute for Composite Materials
Advances in Polymer Technology | Year: 2010

Investigations of the tape placement process are still underway to achieve the laminate quality comparable with other highly developed composite manufacturing methods, such as autoclave-based processes. The evaluation of the products and the mechanical properties of the material has revealed regions where some upgrading could bring significant enhancement in performance. This study is concerned with issues related to the characterization of material properties, interlaminar bond development, and ways of optimizing process parameters. These include heating, layup velocity, tool temperature, and consolidation force, which were studied to determine their effects on the mechanical strength of the composites produced. The bonding degree of the laminates was simulated taking into account a combination of process parameters, comparing the predictions with the actual test results. The thermal stability of the polyether ether ketone matrix, in relation to the processing conditions used in the manufacture, and their effects on the interlaminar bonding stability were also investigated and explained. © 2010 Wiley Periodicals, Inc.


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.


Rieber G.,Kaiserslautern Institute for Composite Materials | Mitschang P.,Kaiserslautern Institute for Composite Materials
Composites Part A: Applied Science and Manufacturing | Year: 2010

Textile preforming is the stitching, cutting, and assembling of reinforcement textiles to enhance mechanical properties or optimize the RTM-tool loading. The stitching of the reinforcing textile has direct influence on the permeability of the preform. In this paper the influence on permeability of two different stitching patterns with five different seam distances is described. The two-dimensional permeability has been determined continuously in a matched metal tool incorporating capacitive sensors. Beforehand, the glass twill weave textile has been thoroughly evaluated to determine the permeability behavior of the textile without stitching in dependence on the fiber volume fraction and the cavity height. The paper reveals the significant influence of the stitching seam distance and the stitching pattern on the permeability values K1 and K2, the orientation angle of the flow front ellipse, and the anisotropy of the preform for two different fiber volume contents. © 2009 Elsevier Ltd. All rights reserved.

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