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Ropers S.,Volkswagen AG | Sachs U.,Thermoplastic Composites Research Center | Kardos M.,Volkswagen AG | Osswald T.A.,University of Wisconsin - Madison
Composites Part A: Applied Science and Manufacturing | Year: 2017

A proper description of the bending behavior is crucial to obtain accurate forming simulations, especially for continuous fiber-reinforced thermoplastic composites. These materials exhibit a highly temperature and bending-curvature dependent bending stiffness. These dependencies make the property challenging to characterize with conventional characterization methods, and therefore require novel techniques. The first part of the study has shown how Dynamic Mechanical Analysis and a rheometer-based method can be used to examine viscoelastic bending behavior. This subsequent part focuses on combining their advantages in a universal characterization method, which provides an accurate description of the bending behavior over a broad temperature range, including the phase transition of recrystallization. Dynamic isothermal experiments as well as dynamic experiments over defined temperature ranges were conducted. The aforementioned experiments were reconstructed in simulations, employing the non-linear viscoelastic material model from the first part of the study, to evaluate the characterization method and to further validate the model. © 2017 Elsevier Ltd


Wolthuizen D.J.,University of Twente | Wolthuizen D.J.,ThermoPlastic Composites Research Center | Schuurman J.,ThermoPlastic Composites Research Center | Schuurman J.,Saxion University | And 2 more authors.
Key Engineering Materials | Year: 2014

Defects and shape distortions can arise during thermoforming of thermoplastic composites. Design guidelines for thermoplastic composites can help to prevent such defects. The material selection and geometry definition are part of the design guidelines. A test to check the formability of a material is developed as an aid for the material selection. Strips of varying widths are thermoformed inducing double curvature, in order to find the width at which the material starts to wrinkle. The thermoformed strips of quasi-isotropic UD carbon/PEEK and quasi-isotropic 8HS glass/PPS show a clear difference in formability. The UD carbon and the 8HS glass strips develop wrinkles through-the-thickness of the laminate at a width of m and m m respectively. The test shows good potential to be used as part of the design guidelines.. © 2014 Trans Tech Publications, Switzerland.


Abdul Rasheed M.I.,ThermoPlastic Composites Research Center | Abdul Rasheed M.I.,University of Twente | Van Hattum F.W.J.,ThermoPlastic Composites Research Center | Van Hattum F.W.J.,Saxion University | And 4 more authors.
CAMX 2015 - Composites and Advanced Materials Expo | Year: 2015

The in-plane mechanical properties of laminates with two dimensional planar reinforcing elements (flakes in this case) are investigated. A woven structure for the flakes is considered in this study, comprising of fiber bundles in both warp and weft direction. Failure of the flake or the interface was considered as primary failure mechanisms of such a discontinuous material system. Tortuosity is used as a measure for the combined effect of distribution of overlaps between adjacent layers of flakes and the local meso-structure. Model composite specimens with defined overlaps were manufactured with the use of slit prepreg layers. The results are translated to randomly oriented flakes with respect to tortuosity estimates. Comparison between experimental values for flake systems, tortuosity based estimates and analytical solutions from existing theories are presented and give valuable insight on the predictability of the observed scatter. Copyright 2015 by M.I. Abdul Rasheed. Published by CAMX - The Composites and Advanced Materials Expo with permission.


Wolthuizen D.J.,University of Twente | Wolthuizen D.J.,ThermoPlastic Composites Research Center | Ten Thije R.H.W.,AniForm Virtual Forming | Akkerman R.,University of Twente | Akkerman R.,ThermoPlastic Composites Research Center
Key Engineering Materials | Year: 2013

Standard finite elements can exhibit the numerical artifact of intra-ply shear locking during forming simulations. The displacement fields of elements are piecewise continuous and cannot correctly capture discontinuities in the shear field. This shear locking is illustrated in simulations of bias-extension experiments with an unaligned mesh. Two simple tests were developed as a critical indicator of intra-ply shear locking in triangular elements. A single-elementtest shows the origin of the locking and a pull-out test indicates locking caused by small misalignments of the elements. Copyright © 2013 Trans Tech Publications Ltd.


Su Y.,Materials Innovation Institute M2i | Su Y.,University of Twente | De Rooij M.,Materials Innovation Institute M2i | De Rooij M.,University of Twente | And 2 more authors.
Composites Part B: Engineering | Year: 2016

Fastener free metal-carbon fibre reinforced thermoplastic composite hybrid joints show potential for application in aerospace structures. The strength of the metal-thermoplastic composite interface is crucial for the performance of the entire hybrid joint. Optimisation of the interface requires an evaluation method for these hybrid structures. This work demonstrates the applicability of a mandrel peel test method for this purpose. The suitability of the mandrel peel test for certain hybrid joints is evaluated. Furthermore, a series of parameters in mandrel peel test are assessed in order to optimise the evaluation of the performance of metal-thermoplastic interface. © 2016 Elsevier Ltd. All rights reserved.


Haanappel S.P.,ThermoPlastic Composites Research Center | Akkerman R.,ThermoPlastic Composites Research Center | Akkerman R.,University of Twente
Composites Part A: Applied Science and Manufacturing | Year: 2014

Intra-ply shear appears during the forming process of hot thermoplastic laminates with a uni-directional fibre reinforcement. This paper proposes a torsion bar test to characterise the longitudinal shear mechanism, which can be performed with a standard rheometer. Sensitivity analyses showed that most reliable shear property measurements can be obtained by using torsion bar specimens with a close to square cross section. The method is implemented in practise and critically evaluated. Storage and loss moduli were determined for carbon UD/PEEK specimens at high temperatures. Non-linear material behaviour was found for relatively small shear strains. The linear regime was focussed on subsequently, where the characteristics were found to be similar to that of a visco-elastic solid or weak gel, confirmed by a dominant storage modulus and a weak frequency dependency. Future work is recommended to be focussed on the large strain regime, for which this paper provides a found basis. © 2013 Elsevier Ltd. All rights reserved.


Haanappel S.P.,ThermoPlastic Composites Research Center | Ten Thije R.H.W.,AniForm Virtual Forming | Sachs U.,ThermoPlastic Composites Research Center | Rietman B.,ThermoPlastic Composites Research Center | And 3 more authors.
Composites Part A: Applied Science and Manufacturing | Year: 2014

The formability of two different composite materials used in aerospace industry has been investigated for a representative product geometry. The deformations during forming of carbon UD/PEEK and glass 8HS/PPS blanks with a quasi-isotropic lay-up were analysed. The UD/PEEK product showed severe wrinkling in doubly curved areas, whereas the 8HS/PPS product showed better formability in those areas. This can be explained by the relatively high resistance against intra-ply shear for the UD/PEEK material. Moreover, the predictive capability of a finite element based simulation tool was shown. For both materials, the prediction of intra-ply shear and large wrinkles showed good agreement with those observed in the actual product. The smaller wrinkles in the products cannot be accurately represented with the element size used. However, predicted waviness at the corresponding locations could indicate critical areas in the product. The presented modelling approach shows great potential for application in the composite product design process. © 2013 Elsevier Ltd. All rights reserved.


Sachs U.,Thermoplastic Composites Research Center | Akkerman R.,Thermoplastic Composites Research Center | Akkerman R.,University of Twente | Fetfatsidis K.,University of Massachusetts Lowell | And 8 more authors.
Composites Part A: Applied Science and Manufacturing | Year: 2014

A benchmark exercise was conducted to compare various friction test set-ups with respect to the measured coefficients of friction. The friction was determined between Twintex®PP, a fabric of commingled yarns of glass and polypropylene filaments, and a metal surface. The same material was supplied to all benchmark participants and the test conditions were prescribed, making the used set-up the most important variable among the laboratories. Tests at ambient temperature as well as tests above the melting point of polypropylene are part of the benchmark, in order to determine both the dry and hydrodynamic friction characteristics. The dependency on sliding velocity, average pressure and temperature was investigated. Systematic differences are observed between the measurements obtained by the different set-ups, which are discussed and related to design characteristics of the devices. The values obtained in this benchmark are comparable and may serve as a reference to evaluate other friction set-ups. The paper concludes with guidelines for the design of a friction tester. © 2014 Elsevier Ltd.


News Article | April 5, 2016
Site: www.materialstoday.com

Web Industries, Inc, a provider of prepreg composite formatting technologies and services, has joined the ThermoPlastic Composites Research Center (TPRC) based in Enschede, The Netherlands. As a member company, Web will use its experience formatting thermoplastic composites for compression molding and tape placement in ongoing and future joint development projects. According to the company, it helped define the industry standards for precision slitting, spooling and winding of aerospace-grade thermoset composite slit tape, and is a qualified prepreg slit tape provider for nearly all major automated fiber placement lines. Web Industries has a knowledge base focused on bridging the gap between composite material producers, manufacturing machine companies, and end-product fabricators. ‘We believe that our deep technical expertise formatting thermoplastic composites for use in manufacturing will be of great benefit to our fellow corporate and research members and to the greater thermoplastic composites community,’ said Grand Hou, Web's technical manager for advanced composites. The TPRC is an innovation research and development center focused on advancing the use of thermoplastic composites in industrial and commercial manufacturing. Its member companies and multidisciplinary teams conduct joint development projects researching new thermoplastic composite technologies and applications. This story uses material from Web Industries, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.

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