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Graf Matthias - One of the best experts on this subject based on the ideXlab platform.

  • Entwicklung und Validierung einer neuen Methode zur Charakterisierung des Scherverhaltens von Carbonfasergewebe mit Binderauftrag unter Normalkraft und viskoser Reibung bei hohen Prozesstemperaturen
    KIT Scientific Publishing, 2018
    Co-Authors: Graf Matthias
    Abstract:

    In this work the influence of normal force on the shear behavior of carbon fiber fabric during the draping process at different temperatures is investigated. For this purpose an extended Test method based on the Picture Frame Test is developed and its suitability Tested. The normal force and the visco-elastic friction of the binder particles applied to the fabric show a significant increase in shear resistance

  • Entwicklung und Validierung einer neuen Methode zur Charakterisierung des Scherverhaltens von Carbonfasergewebe mit Binderauftrag unter Normalkraft und viskoser Reibung bei hohen Prozesstemperaturen
    KIT-Bibliothek Karlsruhe, 2018
    Co-Authors: Graf Matthias
    Abstract:

    Die Formgebung von Carbonfasergewebe in komplexe dreidimensionale Bauteilgeometrien erfordert eine Drapierung des zweidimensionalen Zuschnitts. Aufgrund der hohen Steifigkeit und der vernachlässigbar kleinen Bruchdehnung erfolgt die Formgebung hauptsächlich über den Mechanismus der Scherdeformation. Eine Vorhersage der Formbarkeit, Faltenbildung und des Faserverlaufs kann über die Durchführung einer Drapiersimulation erreicht werden. Zur Erzielung einer realitätsnahen Übereinstimmung sind die Materialkennwerte des Gewebes erforderlich. Einer der wichtigsten Kennwerte ist das charakteristische Scherverhalten über den Verlauf des Scherwinkels. Nach dem Stand der Forschung wird diese Kenngröße beispielsweise über einen Picture Frame Test, unidirektionalen Bias Extension Test oder unter Berücksichtigung der Zugspannungsversteifung, einen Biaxialer Bias Extension Test ermittelt. Bei nahezu allen Drapiermethoden entstehen bei der Formgebung Zugkräfte in Faserrichtung sowie Normalkräfte, die senkrecht auf das Gewebe wirken. Die Scherversteifung durch die Zugkräfte wurde in zahlreichen Arbeiten erforscht und beruht indirekt auf Normalkräfte, die durch die Ondulation der Faserbündel an den Kreuzungspunkten des Gewebes entstehen. Der Einfluss der direkt auf das Gewebe einwirkenden Normalkräfte auf das Scherverhalten wurde bisher nur wenig erforscht. In der Arbeit wird zunächst eine neue Prüfeinrichtung entwickelt, mit der die Scherkennlinie unter Normaldruck und bei verschiedenen Temperaturen zur Prüfung von einseitig mit Binder versehenem Gewebe ermittelt werden kann. Die Prüfeinrichtung wird auf der Basis der gängigen Prüfmethode des unidirektionalen Bias Extension Tests und des Picture Frame Tests aufgebaut und anhand eines Carbonfaser-Leinwandgewebes auf seine Eignung geTestet. Es zeigt sich hierbei, dass der modifizierte Picture Frame Test die zuverlässigere Methode zur Messung des Scherverhaltens unter Normalkraft und Temperaturen im Schmelzbereich des Binders ist. Unter Normalkraft entstehen reibungsbehaftete Relativbewegungen zwischen dem Gewebe und den Druckplatten, an den Kreuzungspunkten innerhalb des Gewebes (intralaminiar) und zwischen benachbarten Lagen eines Mehrschichtstapels (interlaminar). Die Reibkräfte werden in umfangreichen Messreihen unter Variation der Normalkraft, der Reibgeschwindigkeit, der Temperatur, mit und ohne Binderauftrag und die Art der Schichtung des Mehrschichtstapels untersucht. Auf Basis der Ergebnisse der Reibwertuntersuchung wird eine Berechnungsgleichung aufgestellt, mit der die viskos-elastische Reibung in Abhängigkeit von der Viskosität, dem Normaldruck und der Reibgeschwindigkeit ermittelt werden kann. Anhand von Mikrographieaufnahmen wird das Tragbildung an den Kreuzungspunkten des Gewebes aufzeigt und lässt Rückschlüsse auf das viskos-elastische Verhalten des Binders bei der Scherung zu. Mit der entwickelten Prüfeinrichtung auf Basis des Picture Frame Tests unter Normaldruck und Temperatur werden mit einem Leinwandgewebe mit T700SC 12K 50C Fasern und einseitig aufgetragenem Reaktivbindersystem des Herstellers Toray unter Variation des Normaldrucks, der Temperatur, mit und ohne Binder und Art der Stapelbildung zahlreiche Messreihen durchgeführt. Hierbei bestätigt sich der signifikante Einfluss der Normalkraft auf die Scherkennlinie des verwendeten Gewebes. Die Verifizierung der Ergebnisse erfolgt über die Durchführung von Simulationen der Schercharakterisierung der wesentlichen Messreihen. Um eine Verifizierung erreichen zu können wird ein mathematischer Ansatz aufgestellt, der die Wirkzusammenhänge für die Reibung des Gewebes zu den Druckplatten, des intralaminaren Scherwiderstandes und des interlaminaren Scherwiderstandes beschreibt. Für alle Varianten wird somit ein durchgehend gleicher Rechenansatz gewählt, der auf physikalische Größen, wie Reibungskoeffizient, Normalkraft und Übersetzungsverhältnis (Proportionalitätskonstante) beruht. Die abstrahierten Scherkennlinien werden hierbei in drei charakteristische Bereiche eingeteilt, dem Anfangshaftreibungsbereich, dem Plateau Bereich und dem Scherversteigungsbereich. Die Untersuchung zeigt, dass die intralaminare Scherversteifung zu einem großen Teil durch die Querkompression der Faserbündel entsteht und stark von der Normalkraft abhängt. Hierbei zeigt sich auch, dass die Querkompression unter Normaldruck bereits vor dem Schließen der Lücken zwischen benachbarten Faserbündeln eintritt. Der Grenzwinkel (Locking Angle) ab dem die Scherversteifung einen progressiven Anstieg verzeichnet, setzt bei steigender Normalkraft bereits bei einem geringeren Scherwinkel ein. Dieses Phänomen wird auf den reduzierten Mikroporengehalt der Faserbündel durch den Normaldruck zurückgeführt

James A Sherwood - One of the best experts on this subject based on the ideXlab platform.

  • investigation of sample geometry and strain rate dependence in shear characterization of a uhmwpe unidirectional cross ply for finite element simulation of composite processing
    Proceedings of the American Society for Composites — Thirty-fourth Technical Conference, 2019
    Co-Authors: Kari D. White, James A Sherwood
    Abstract:

    In-plane shearing is the dominant mode of deformation in many composite forming processes, including thermoforming. The shear-Frame, or Picture-Frame, Test is a widely accepted method to characterize the shear behavior of a material system to find the properties to use in forming simulations, and this Test has been shown to be applicable for providing shear stiffness as a function of the state of shear for a variety of woven-fabrics based material systems. The current research explores the use of shear-Frame Testing of a non-woven material system made of Ultra High Molecular Weight Polyethylene (UHMWPE), specifically DSM Dyneema® HB210 unidirectional fiber cross-ply. The material system was characterized at an elevated temperature for processing applications. The effects of sample size and sample geometry were investigated. The load contribution from the sample arms is of particular interest for these types of materials, so an investigation of appropriate gage area and normalization methods was performed. Finite element simulations of the shear-Frame Test were completed to validate the characterization methodology. Also, during the processing of UHMWPE material systems into complex shapes, the rate of shear in different sections of the part will differ. Therefore, the effects of strain rate on shear characterization were explored by performing constant strain-rate shear Frame Testing over a range of shear rates. In a typical shear-Frame Test, the crosshead rate remains constant which leads to an increasing shear strain rate. The decreasing crosshead rate required to maintain a constant shear rate was obtained and implemented into the Testing software. Representative shear curves were examined to determine if rate-dependence is required in a finite element simulation of the thermoforming process.

  • Picture-Frame Testing of woven prepreg fabric: An investigation of sample geometry and shear angle acquisition
    International Journal of Material Forming, 2019
    Co-Authors: Christian Krogh, Alessandro Sabato, Kari D. White, James A Sherwood
    Abstract:

    This paper examines different concepts in relation to the Picture-Frame Test for shear characterization of a woven prepreg fabric. The influence of the sample arms is investigated by means of cut slits as well as removed transverse tows. Shear angles are obtained using Digital Image Correlation (DIC) and also from images taken during the Test which are processed for fiber angles directly from the weave texture. The image processing relies on the Hough transform in MATLAB. The concept of constant shear strain rate is discussed and implemented in the Test software by a multi-linear crosshead velocity profile. Finally, bias-extension data are obtained and used for comparison. It is found that the sample arm modifications have a pronounced effect on the measured shear load whereas the uniformness of the shear strain field in the samples is not improved considerably.

  • 256 shades of gray: Application of image processing to evaluate the effect of sample geometry and constant shear strain rates in the Picture-Frame Test
    PROCEEDINGS OF THE 22ND INTERNATIONAL ESAFORM CONFERENCE ON MATERIAL FORMING: ESAFORM 2019, 2019
    Co-Authors: Christian Krogh, Lisa M. Dangora, Kari D. White, Johnny Jakobsen, James A Sherwood
    Abstract:

    Shearing or trellising is recognized as the primary deformation mechanism in textile-reinforced composite forming processes. A popular method for characterization of the shear properties of a ply is the Picture-Frame Test. The Test setup involves the clamping of a cruciform shaped specimen in a Frame hinged at its corners. During the processing of the Test results, it is often assumed that the shear distribution in the central square of the sample is uniform, such that a shear force vs. shear angle relation can be calculated based on kinematics. One thing to note is that a constant displacement rate of the Frame yields a nonlinear shear-strain rate throughout the Test. Relying on Digital Image Correlation (DIC), this study considers two concepts in relation to the Picture-Frame Test: First, the effect of sample geometry is Tested, i.e. whether modifications of the standard cruciform shape influence the uniformness of the shear-strain field. Two different materials are considered: a woven carbon-fiber prepreg and a thermoplastic cross-ply sheet. Second, methods of obtaining constant shear rate data are explored. The methods involve programming of a universal Testing machine with a multi-linear approximation of a nonlinear crosshead displacement rate and post-processing data obtained with a constant crosshead rate.Shearing or trellising is recognized as the primary deformation mechanism in textile-reinforced composite forming processes. A popular method for characterization of the shear properties of a ply is the Picture-Frame Test. The Test setup involves the clamping of a cruciform shaped specimen in a Frame hinged at its corners. During the processing of the Test results, it is often assumed that the shear distribution in the central square of the sample is uniform, such that a shear force vs. shear angle relation can be calculated based on kinematics. One thing to note is that a constant displacement rate of the Frame yields a nonlinear shear-strain rate throughout the Test. Relying on Digital Image Correlation (DIC), this study considers two concepts in relation to the Picture-Frame Test: First, the effect of sample geometry is Tested, i.e. whether modifications of the standard cruciform shape influence the uniformness of the shear-strain field. Two different materials are considered: a woven carbon-fiber prep...

  • investigation of shear characterization of a uhmwpe unidirectional cross ply for finite element simulation of composite processing
    Proceedings of the 22nd International ESAFORM Conference on Material Forming: ESAFORM 2019, 2019
    Co-Authors: Kari D. White, Christian Krogh, James A Sherwood
    Abstract:

    In-plane shearing is the dominant mode of deformation in many composite forming processes, including thermoforming. The shear-Frame, or Picture-Frame, Test is a widely accepted method to characterize the shear behavior of a material system to find the properties to use in forming simulations, and this Test has been shown to be applicable for providing shear stiffness as a function of the state of shear for a variety of woven-fabrics based material systems. The current research explores the use of shear-Frame Testing of a non-woven material system made of Ultra High Molecular Weight Polyethylene (UHMWPE), specifically DSM Dyneema® HB210 unidirectional fiber cross-ply. The material system was characterized at an elevated temperature for processing applications. The effects of sample size and sample geometry were investigated. The load contribution from the sample arms is of particular interest for these types of materials, so an investigation of appropriate gage area and normalization methods is performed. Finite element simulations of the shear-Frame Test are completed to validate the characterization methodology.

  • analytical model of shear of 4 harness satin weave fabrics
    MATERIALS PROCESSING AND DESIGN: Modeling Simulation and Applications - NUMIFORM 2004 - Proceedings of the 8th International Conference on Numerical M, 2004
    Co-Authors: Lu Liu, Julie Che, James A Sherwood
    Abstract:

    Trellis shear is the main deformation mode in the thermo‐stamping process of woven fabric composites. To model the shear properties of woven fabrics analytically, the equilibrium equation of the unit cell of a 4‐harness satin weave glass/polypropylene woven fabric is studied. Frictional resistance moment and lateral compaction resistance moment are then predicted by studying the geometry of the unit cell. Then the model is used to predict the load versus shear angle curves in the Picture Frame Test to reduce or eliminate the Test itself. A parametric study is carried out to determine the sensitivity of the friction coefficient. To validate the model, Picture‐Frame experimental results are presented. A very close correlation is observed between the model predictions and the experimental results. Results of plain weave fabrics are included to show the analytical model’s ability to predict the effect of weave pattern. Results from an international benchmark Testing are also presented to help establish the te...

Abbas S Milani - One of the best experts on this subject based on the ideXlab platform.

  • a Frameless Picture Frame Test with embedded sensor mitigation of imperfections in shear characterization of woven fabrics
    Composite Structures, 2019
    Co-Authors: H Montazerian, Armin Rashidi, Mina Hoorfar, Abbas S Milani
    Abstract:

    Abstract Picture Frame Test (PFT) is frequently employed for characterizing the shear behavior of woven fabrics. In the present study, the main sources of possible imperfections in the PFT, arising from the operator error during sample installation, to the fixture misalignment and the inherent non-uniformities within the fabric, are reviewed and modeled using the kinematic as well as continuum-based approaches. Upon new understandings from these models, a new Test methodology was designed where the shearing Frame boundary condition is inscribed on the fabric sample itself during sample preparation; in lieu of fabricating and installing a metallic Picture Frame. The new Frameless Picture Frame (FPF) Test was proven to effectively mitigate the imperfections and provide a simple operation and better control and uniformity of the fabric installation and deformation. Contrary to the conventional PFT, the wrinkling behavior and normalized force response in the FPF was in agreement with the conventional bias extension Test, with no close-to-arm fiber bending, while showing a superior Test repeatability at both loading and unloading stages. Finally, a mechanically compatible, stretchable sensor was developed and integrated into the fabric samples to monitor and verify the induced local deformation along the yarns under different Test methods.

  • identifying the distinct shear wrinkling behavior of woven composite preforms under bias extension and Picture Frame Tests
    Composite Structures, 2018
    Co-Authors: A Hosseini, Masoud Haghi Kashani, Farrokh Sassani, Abbas S Milani
    Abstract:

    Abstract An analytical-experimental study of the shear wrinkling behavior of plain woven composite preforms under bias extension Test (BET) and Picture Frame Test (PFT) is presented. The intentionally induced tension in the PFT has been regarded in a large portion of the literature as the source of delay in fabric wrinkling initiation as compared to the BET. Through this study, however, it is demonstrated that shear within yarns – known as intra-yarn shear – could be another cause of the delayed wrinkling in the PFT, even when the tension level in yarns is kept at zero. To better explain this hypothesis, an analytical model has been developed and the meso-level nature of wrinkle formation in the BET and PFT is compared. Analytical equations are provided to predict both the fabric locking and wrinkling onsets under these characterization Tests, and verified experimentally on a carbon fiber plain woven fabric.

  • a method for the approximation of non uniform fiber misalignment in textile composites using Picture Frame Test
    Composites Part A-applied Science and Manufacturing, 2007
    Co-Authors: Abbas S Milani, J A Nemes, R C Abeyaratne, Gerhard A Holzapfel
    Abstract:

    Due to the complexity of woven structures, the assumption of perfectly aligned fibers for some textile composites is unrealistic. In more sophisticated material models, therefore, possible fiber misalignment is accounted for. On the other hand, non-uniformity of the misalignment distribution in a fabric may become a second but important problem. This paper presents an inverse methodology from which a reliable approximation of the non-uniform misalignment state in a woven fabric may be made. Basically, the approximation requires a representative constitutive model and a set of Picture Frame Tests where fiber misalignment plays a key role. Uniaxial and bias-extension Tests are also used to identify the constitutive model parameters independently. The detail procedure is shown for a typical 2 x 2 twill weave fabric as an illustrative example. Results are discussed and compared to other approaches to reveal the benefits and limitations of the proposed method.

Stepan Vladimirovitch Lomov - One of the best experts on this subject based on the ideXlab platform.

  • deformability of textile performs in the manufacture of non crimp fabric composites
    Non-Crimp Fabric Composites#R##N#Manufacturing Properties and Applications, 2011
    Co-Authors: Stepan Vladimirovitch Lomov
    Abstract:

    Abstract: Deformability of multiaxial multi-ply stitched preforms is studied in biaxial tension, shearing and compression. Biaxial tension Tests reveal a strong interrelation between the two directions of tension in the case of tension in bias direction. The Picture Frame Test is combined with full-field optical measurements of the shear strain, allowing true registration of the fabric shear angle. The difference between the shear behaviour in different directions relative to the stitching is shown. Thickness is measured for one of the sheared fabrics. Compression Tests reveal a high compressibility of the preforms and a limited nesting effect in laminates.

  • Picture Frame Test of woven composite reinforcements with a full field strain registration
    Textile Research Journal, 2006
    Co-Authors: Stepan Vladimirovitch Lomov, Ignace Verpoest, Marcin Barburski, An Willems, Y Zhu, Tzvetelina Stoilova
    Abstract:

    Results of Picture Frame shear Tests with optical registration of the strain fields are presented for glass (plain and twill, three types) and glass/PP woven (plain and twill) fabric reinforcements for composite materials. Four problems were investigated. (1) How does the shear diagram vary with differences in Test conditions? The major factor is the sample pretension, which is influenced by its gripping, removing/preserving yarns near the grips and “conditioning” in the shear cycles. (2) Does the shear of the fabric differ from the pure shear prescribed by the Frame? The differences are normally negligible. (3) How large are the variations of the local fabric shear? The scatter of the local fabric shear does not exceed 2°. (4) How is shear of the fabric translated into deformations of the yarns on the micro-scale? Different stages of the fabric deformation are identified: rotation of the yarns followed by their lateral compression.

  • carbon composites based on multiaxial multiply stitched preforms part 3 biaxial tension Picture Frame and compression Tests of the preforms
    Composites Part A-applied Science and Manufacturing, 2005
    Co-Authors: Stepan Vladimirovitch Lomov, Ignace Verpoest, Marcin Barburski, Tzvetelina Stoilova, Remko Akkerman, Richard Loendersloot, R Ten H W Thije
    Abstract:

    Deformability of bi- and quadri-axial multi-axial multiply stitched preforms is studied in biaxial tension, shear (Picture Frame Test) and compression. The results complement KES-F measurements in the low load range, reported in the Part 2 of the series (Compos A, 34, 2003, 359–70). The biaxial tension Tests reveal a strong interrelation between the two directions of tension in the case of tension in bias direction (relative to the fibres) and independence of deformation in two directions for tension in fibre direction. Non-linearity of the initial part of the tensile diagram due to fibre misalignment is demonstrated. The Picture Frame Test is combined with full-field optical measurements of the shear strain field, allowing true registration of the fabric shear angle (which differs from the shear angle of the Frame). Difference between the shear behaviour in different directions relative to the stitching is shown. Thickness is measured for one of the sheared fabrics. Compression Tests reveal a high compressibility of the preforms (up to 60%) and a limited nesting effect for compression of the laminates. The compression Tests are done also on sheared fabrics.

M P F Sutcliffe - One of the best experts on this subject based on the ideXlab platform.

  • microscopic investigation of tow geometry of a dry satin weave fabric during deformation
    Composites Science and Technology, 2003
    Co-Authors: Seunghwa Chang, M P F Sutcliffe
    Abstract:

    Abstract In this paper the changes in tow geometry during deformation of dry woven carbon-fibre satin-weave fabric are measured and correlated with the in-plane forces applied. The evolution of geometric tow parameters such as tow spacing, crimp angle, tow amplitude and wavelength is investigated. To observe the change in the fabric architecture, specimens from bias extension, biaxial and Picture Frame Tests are sectioned and observed under the microscope. It is found that the different loading conditions cause differences in the evolution of tow architecture during deformation, in particular affecting the onset of ‘lock-up’. (At lock-up interactions between tows prevent further significant shear deformation.) In one Picture Frame Test the fabric is deliberately misaligned with respect to the sides of the Frame so that, during subsequent deformation, one set of tows is under tension, while the other is compressed. There is a significant difference in behaviour between the two sets of tows. The variation in deformed tow geometry with shear angle is fitted using a simple parametric model.