The Experts below are selected from a list of 1767 Experts worldwide ranked by ideXlab platform

Janis Varna - One of the best experts on this subject based on the ideXlab platform.

  • Master curve approach to axial stiffness calculation for non-Crimp Fabric biaxial composites with out-of-plane waviness
    Composites Part B: Engineering, 2014
    Co-Authors: Hana Zrida, Erik Marklund, Z. Ayadi, Janis Varna
    Abstract:

    The effect of 0 degrees-tow out-of-plane waviness on the biaxial non-Crimp-Fabric (NCF) composite axial stiffness is investigated. Homogenizing, the bundle mesostructure of the NCF composite is replaced by layers. Then the composite is represented by a laminate with flat layers with effective stiffness properties representing the curved 0 degrees-layer and the 90 degrees-layer with varying thickness. It is shown that the NCF composite knock-down factor characterizing the stiffness degradation has almost the same dependence on wave parameters as the knock-down factor for the curved 0 degrees-layer. Numerical analysis showed that 90 degrees-layer knock-down factor versus amplitude curves for different wavelength can be reduced to one master curve which can be described by a one-parameter expression with the parameter dependent on the used material. This observation is used to obtain high accuracy for analytical predictions for knock-down factors for cases with different wavelength and amplitudes based on two FE calculations only.

  • Effective stiffness of curved 0 degrees-layers for stiffness determination of cross-ply non-Crimp Fabric composites
    Journal of Reinforced Plastics and Composites, 2014
    Co-Authors: Hana Zrida, Erik Marklund, Zoubir Ayadi, Janis Varna
    Abstract:

    The effect of the 0 degrees-tow waviness on axial stiffness of cross-ply non-Crimp Fabric composites is analysed using multiscale approach. The curved 0 degrees- and 90 degrees-layers are represented by flat layers with effective stiffness properties and classical laminate theory is used to calculate the macroscopic stiffness. The effective 0 degrees-layer stiffness is calculated analysing isolated curved 0 degrees-layers subjected not only to end loading, but also to surface loads. The surface loads are identified in a detailed finite element analysis and approximated by a sinus shaped function with amplitude depending on the waves parameters. The sinus shaped surface loads are then applied to an isolated curved 0 degrees-layer finite element model together with end loading to calculate the effective stiffness of the layer. Finally, the effective 0 degrees-layer stiffness was successfully used to calculate the macroscopic stiffness of the composite proving validity of the approach being used and showing that, without losing accuracy, elastic properties in the 90 degrees-layers with bundle structure can be replaced by the transverse stiffness of the homogenised 90 degrees-layer material.

  • effective stiffness of curved 0 layers for stiffness determination of cross ply non Crimp Fabric composites
    Journal of Reinforced Plastics and Composites, 2014
    Co-Authors: Hana Zrida, Erik Marklund, Z. Ayadi, Janis Varna
    Abstract:

    The effect of the 0°-tow waviness on axial stiffness of cross-ply non-Crimp Fabric composites is analysed using multiscale approach. The curved 0°- and 90°-layers are represented by flat layers with effective stiffness properties and classical laminate theory is used to calculate the macroscopic stiffness. The effective 0°-layer stiffness is calculated analysing isolated curved 0°-layers subjected not only to end loading, but also to surface loads. The surface loads are identified in a detailed finite element analysis and approximated by a sinus shaped function with amplitude depending on the waves parameters. The sinus shaped surface loads are then applied to an isolated curved 0°-layer finite element model together with end loading to calculate the effective stiffness of the layer. Finally, the effective 0°-layer stiffness was successfully used to calculate the macroscopic stiffness of the composite proving validity of the approach being used and showing that, without losing accuracy, elastic properties...

  • Master curve approach to axial stiffness calculation for non-Crimp Fabric biaxial composites with out-of-plane waviness
    Composites Part B: Engineering, 2014
    Co-Authors: Hana Zrida, Erik Marklund, Z. Ayadi, Janis Varna
    Abstract:

    Abstract The effect of 0°-tow out-of-plane waviness on the biaxial non-Crimp-Fabric (NCF) composite axial stiffness is investigated. Homogenizing, the bundle mesostructure of the NCF composite is replaced by layers. Then the composite is represented by a laminate with flat layers with effective stiffness properties representing the curved 0°-layer and the 90°-layer with varying thickness. It is shown that the NCF composite knock-down factor characterizing the stiffness degradation has almost the same dependence on wave parameters as the knock-down factor for the curved 0°-layer. Numerical analysis showed that 90°-layer knock-down factor versus amplitude curves for different wavelength can be reduced to one master curve which can be described by a one-parameter expression with the parameter dependent on the used material. This observation is used to obtain high accuracy for analytical predictions for knock-down factors for cases with different wavelength and amplitudes based on two FE calculations only.

  • damage progression in non Crimp Fabric composites
    Non-Crimp Fabric Composites#R##N#Manufacturing Properties and Applications, 2011
    Co-Authors: L E Aap, Janis Varna, Erik Marklund
    Abstract:

    Abstract: In this chapter, prevailing damage mechanisms in in-plane loaded non-Crimp Fabric (NCF) composites, as well as out-of-plane impact-loaded and subsequent in-plane compression-loaded NCF composite structures, are presented and discussed in detail. Particular emphasis is on the identification of differences and similarities in failure mechanisms for NCF composites to those in traditional tape-based composites.

F Paris - One of the best experts on this subject based on the ideXlab platform.

  • predicting failure load of a non Crimp Fabric composite by means of a 3d finite element model including progressive damage
    Composite Structures, 2019
    Co-Authors: Enrique Graciani, Luis Miguel Ferreira, F Paris
    Abstract:

    Abstract A mesoscopic scale 3D finite element model of its representative unit cell is used to study the progressive damage of a [0,90]n non-Crimp Fabric laminate under compressive loading. The tows of the unit cell have been generated with a straight finite element mesh, and the out-of-plane fibre Crimp has been incorporated into the model by defining the mechanical properties of each element according to the actual direction of the fibres. The material properties degradation (MPDG) method has been used to study the damage evolution. Non-interactive criteria (Maximum Stress and Maximum Strain), and interactive criteria (Hashin and Puck), associated with failure modes, have been employed to determine the onset of the material degradation at the fibre tows. The progressive damage throughout the mesoscopic unit cell, from the load at which damage is initiated, until the load at which the failure of the laminate is predicted, has been analysed. The mechanism responsible for the failure of the laminate has also been identified. The numerical predictions of the failure stress and failure strain, for the considered failure criteria, are discussed and compared with experimental data obtained from direct compression tests on biaxial cross-ply NCF laminates. A satisfactory agreement between the numerical and experimental failure stress, failure strain as well as the compressive stress-strain curves has been obtained for the MPDG method when using Maximum Stress, Hashin’s or Puck’s failure criteria.

  • three dimensional finite element study of the behaviour and failure mechanism of non Crimp Fabric composites under in plane compression
    Composite Structures, 2016
    Co-Authors: Luis Miguel Ferreira, Enrique Graciani, F Paris
    Abstract:

    The compressive behaviour and the mechanism responsible for failure of a [0,90]n non-Crimp Fabric (NCF) laminate are studied using a 3D finite element (FE) model of the representative unit cell at the mesoscopic scale. The tows of the unit cell were generated using a straight FE mesh taking into account the waviness of the fibres with the definition of the mechanical properties of each element according to the actual direction of the fibres. A parametric study has been carried out to evaluate the influence of the non-linear behaviour of the tows and of the fibre Crimp on the compressive failure mechanism of the laminate. The numerical predictions are discussed and compared with experimental data. The results lead to think that the mechanism of failure of a [0,90]n NCF laminate under a pure compressive load is controlled by the shear strains that appear in the Crimp part of the 0° tows. It is also found that the non-linear behaviour of the tows and the fibre Crimp substantially contribute to the development of the potential failure initiation mechanism. A satisfactory agreement between the numerical and experimental compressive stress–strain curves is obtained for the highest fibre Crimp angles considered.

  • modelling the waviness of the fibres in non Crimp Fabric composites using 3d finite element models with straight tows
    Composite Structures, 2014
    Co-Authors: Luis Miguel Ferreira, Enrique Graciani, F Paris
    Abstract:

    Abstract A new approach to efficiently model the waviness of the fibres in non-Crimp Fabric (NCF) composites using mesoscale 3D finite element (FE) models with straight tows is presented. This approach omits the geometric curvature of the tows allowing the use of a straight 3D FE mesh, the waviness of the fibres being taken into account with the definition of the mechanical properties of each element according to the actual direction of the fibres. A representative unit cell (RUC) of a single NCF lamina with fibre Crimp has been developed following this approach. The RUC has been used to predict the stiffness properties and to study the stresses/strains that develop along the length of the tows. To ensure the validity of the new modelling approach, the results obtained with its use have been compared with the results obtained from an equivalent RUC in which the FE mesh follows the actual curvature of the tows, in accordance with the classical modelling approach. The results show that the new approach is a valid alternative to model the waviness of the fibres, both in terms of simplicity in modelling and accuracy of the results, opening up the possibility of studying damage mechanisms more efficiently.

  • prediction of in plane stiffness properties of non Crimp Fabric laminates by means of 3d finite element analysis
    Composites Science and Technology, 2008
    Co-Authors: Amparo Gonzalez, Enrique Graciani, F Paris
    Abstract:

    Non-Crimp Fabric (NCF) composites are constituted by differently oriented layers of ideally unidirectional fibre tows. However, a slight waviness always appears in the tows. The applicability of the general laminate theory (GLT) to obtain the stiffness properties of NCF laminates is elucidated in this paper. For this purpose, a 3D finite element (FE) model of the representative unit cell (RUC) of a single NCF lamina has been carried out to obtain its apparent stiffness properties, which are employed, along with the GLT, to determine the stiffness properties of the laminate. These properties are compared with those obtained from the FE model of the RUC of the whole laminate for several configurations with different stacking sequences, fibre contents and Crimp angles. Finally, predictions are compared with existing experimental results. The numerical results achieved validate the use of the GLT in NCF composites, once the lamina properties have been calculated taking into account the internal structure of these materials.

Ignace Verpoest - One of the best experts on this subject based on the ideXlab platform.

  • the influence of the stitching pattern on the internal geometry quasi static and fatigue mechanical properties of glass fibre non Crimp Fabric composites
    Composites Part A-applied Science and Manufacturing, 2014
    Co-Authors: Katleen Vallons, Stepan Vladimirovitch Lomov, Georg Adolphs, Paul Lucas, Ignace Verpoest
    Abstract:

    Abstract This paper discusses the experimental results of a study comparing several aspects of the mechanical behaviour of two quasi-unidirectional non-Crimp Fabric composites based on non-Crimp Fabrics that differ only in stitching pattern. A NEW stitching pattern was compared to an industry common type (ICT). The properties studied include Fabric and laminate thickness, fibre volume fraction, static tensile modulus and strength in longitudinal and transverse direction, high-speed tensile strength and tension–tension fatigue life. Statistically significant differences were observed for Fabric and composite thickness, which was found to be higher for the ICT type composite. A higher fibre volume fraction was observed for the NEW stitching pattern material, as well as a higher longitudinal tensile strength at high and low speeds and a slightly higher fatigue life.

  • Mechanical properties of non-Crimp Fabric (NCF) based composites: stiffness and strength
    Non-Crimp Fabric Composites, 2011
    Co-Authors: Stepan Vladimirovitch Lomov, T. Truong Chi, Ignace Verpoest
    Abstract:

    Abstract: This chapter explores the behaviour of multiaxial multi-ply warp-knitted carbon/epoxy composites in tension, short beam shear test and in-plane shear test. The mechanical properties are reported and the damage initiation and development is investigated using acoustic emission and X-ray observations. The latter makes clear a sequence of damage progression in non-Crimp Fabric (NCF) composites under static loading. The behaviour of composites produced from sheared reinforcements is studied next, providing data for assessment of change of NCF composite properties over a three-dimensional (3D) shaped preform with local shear of the reinforcement.

  • impact and post impact properties of a carbon fibre non Crimp Fabric and a twill weave composite
    Composites Part A-applied Science and Manufacturing, 2010
    Co-Authors: Katleen Vallons, Stepan Vladimirovitch Lomov, Alex Behaeghe, Ignace Verpoest
    Abstract:

    Abstract The impact and post-impact static and fatigue tensile properties of a carbon fibre/epoxy NCF composite were determined and compared to those of a carbon fibre/epoxy woven Fabric composite, for two impact energies (3.5 and 7 J). The projected damage area after impact was larger for the NCF composite than that for the woven Fabric composite for both impact energies. Impacted samples were subjected to static tensile tests and tensile–tensile fatigue tests. It was found that even a relatively low energy impact has already a significant negative influence on the residual properties in both static and fatigue tests, in the fibre direction as well as in the matrix dominated direction. In the matrix dominated directions the post-impact behaviour of the two materials is very similar. In the fibre direction, however, the properties of the non-Crimp Fabric composite are degraded more by an impact than those of the woven Fabric composite.

  • fatigue and post fatigue behaviour of carbon epoxy non Crimp Fabric composites
    Composites Part A-applied Science and Manufacturing, 2009
    Co-Authors: Katleen Vallons, Stepan Vladimirovitch Lomov, Ignace Verpoest
    Abstract:

    Abstract This paper focuses on the static, fatigue and post-fatigue tensile properties of a biaxial carbon/epoxy non-Crimp Fabric composite. In a series of quasi-static tensile tests, the stress–strain level where damage initiates was determined. This stress level was then used as the maximum stress level in tensile–tensile fatigue tests in the fibre direction. It was found that in fibre direction, this load level can be considered safe for fatigue up to very high cycle numbers. The damage evolution during the tests was monitored at certain cycle times with X-ray radiography. The post-fatigue residual static tensile properties were determined after different numbers of cycles. A series of tensile–tensile fatigue tests at various higher stress levels allowed for the fatigue life curves to be constructed in each of the four testing directions. This revealed that the damage initiation load level is well below the practical fatigue limit of the material.

Luis Miguel Ferreira - One of the best experts on this subject based on the ideXlab platform.

  • predicting failure load of a non Crimp Fabric composite by means of a 3d finite element model including progressive damage
    Composite Structures, 2019
    Co-Authors: Enrique Graciani, Luis Miguel Ferreira, F Paris
    Abstract:

    Abstract A mesoscopic scale 3D finite element model of its representative unit cell is used to study the progressive damage of a [0,90]n non-Crimp Fabric laminate under compressive loading. The tows of the unit cell have been generated with a straight finite element mesh, and the out-of-plane fibre Crimp has been incorporated into the model by defining the mechanical properties of each element according to the actual direction of the fibres. The material properties degradation (MPDG) method has been used to study the damage evolution. Non-interactive criteria (Maximum Stress and Maximum Strain), and interactive criteria (Hashin and Puck), associated with failure modes, have been employed to determine the onset of the material degradation at the fibre tows. The progressive damage throughout the mesoscopic unit cell, from the load at which damage is initiated, until the load at which the failure of the laminate is predicted, has been analysed. The mechanism responsible for the failure of the laminate has also been identified. The numerical predictions of the failure stress and failure strain, for the considered failure criteria, are discussed and compared with experimental data obtained from direct compression tests on biaxial cross-ply NCF laminates. A satisfactory agreement between the numerical and experimental failure stress, failure strain as well as the compressive stress-strain curves has been obtained for the MPDG method when using Maximum Stress, Hashin’s or Puck’s failure criteria.

  • three dimensional finite element study of the behaviour and failure mechanism of non Crimp Fabric composites under in plane compression
    Composite Structures, 2016
    Co-Authors: Luis Miguel Ferreira, Enrique Graciani, F Paris
    Abstract:

    The compressive behaviour and the mechanism responsible for failure of a [0,90]n non-Crimp Fabric (NCF) laminate are studied using a 3D finite element (FE) model of the representative unit cell at the mesoscopic scale. The tows of the unit cell were generated using a straight FE mesh taking into account the waviness of the fibres with the definition of the mechanical properties of each element according to the actual direction of the fibres. A parametric study has been carried out to evaluate the influence of the non-linear behaviour of the tows and of the fibre Crimp on the compressive failure mechanism of the laminate. The numerical predictions are discussed and compared with experimental data. The results lead to think that the mechanism of failure of a [0,90]n NCF laminate under a pure compressive load is controlled by the shear strains that appear in the Crimp part of the 0° tows. It is also found that the non-linear behaviour of the tows and the fibre Crimp substantially contribute to the development of the potential failure initiation mechanism. A satisfactory agreement between the numerical and experimental compressive stress–strain curves is obtained for the highest fibre Crimp angles considered.

  • modelling the waviness of the fibres in non Crimp Fabric composites using 3d finite element models with straight tows
    Composite Structures, 2014
    Co-Authors: Luis Miguel Ferreira, Enrique Graciani, F Paris
    Abstract:

    Abstract A new approach to efficiently model the waviness of the fibres in non-Crimp Fabric (NCF) composites using mesoscale 3D finite element (FE) models with straight tows is presented. This approach omits the geometric curvature of the tows allowing the use of a straight 3D FE mesh, the waviness of the fibres being taken into account with the definition of the mechanical properties of each element according to the actual direction of the fibres. A representative unit cell (RUC) of a single NCF lamina with fibre Crimp has been developed following this approach. The RUC has been used to predict the stiffness properties and to study the stresses/strains that develop along the length of the tows. To ensure the validity of the new modelling approach, the results obtained with its use have been compared with the results obtained from an equivalent RUC in which the FE mesh follows the actual curvature of the tows, in accordance with the classical modelling approach. The results show that the new approach is a valid alternative to model the waviness of the fibres, both in terms of simplicity in modelling and accuracy of the results, opening up the possibility of studying damage mechanisms more efficiently.

Erik Marklund - One of the best experts on this subject based on the ideXlab platform.

  • Master curve approach to axial stiffness calculation for non-Crimp Fabric biaxial composites with out-of-plane waviness
    Composites Part B: Engineering, 2014
    Co-Authors: Hana Zrida, Erik Marklund, Z. Ayadi, Janis Varna
    Abstract:

    The effect of 0 degrees-tow out-of-plane waviness on the biaxial non-Crimp-Fabric (NCF) composite axial stiffness is investigated. Homogenizing, the bundle mesostructure of the NCF composite is replaced by layers. Then the composite is represented by a laminate with flat layers with effective stiffness properties representing the curved 0 degrees-layer and the 90 degrees-layer with varying thickness. It is shown that the NCF composite knock-down factor characterizing the stiffness degradation has almost the same dependence on wave parameters as the knock-down factor for the curved 0 degrees-layer. Numerical analysis showed that 90 degrees-layer knock-down factor versus amplitude curves for different wavelength can be reduced to one master curve which can be described by a one-parameter expression with the parameter dependent on the used material. This observation is used to obtain high accuracy for analytical predictions for knock-down factors for cases with different wavelength and amplitudes based on two FE calculations only.

  • Effective stiffness of curved 0 degrees-layers for stiffness determination of cross-ply non-Crimp Fabric composites
    Journal of Reinforced Plastics and Composites, 2014
    Co-Authors: Hana Zrida, Erik Marklund, Zoubir Ayadi, Janis Varna
    Abstract:

    The effect of the 0 degrees-tow waviness on axial stiffness of cross-ply non-Crimp Fabric composites is analysed using multiscale approach. The curved 0 degrees- and 90 degrees-layers are represented by flat layers with effective stiffness properties and classical laminate theory is used to calculate the macroscopic stiffness. The effective 0 degrees-layer stiffness is calculated analysing isolated curved 0 degrees-layers subjected not only to end loading, but also to surface loads. The surface loads are identified in a detailed finite element analysis and approximated by a sinus shaped function with amplitude depending on the waves parameters. The sinus shaped surface loads are then applied to an isolated curved 0 degrees-layer finite element model together with end loading to calculate the effective stiffness of the layer. Finally, the effective 0 degrees-layer stiffness was successfully used to calculate the macroscopic stiffness of the composite proving validity of the approach being used and showing that, without losing accuracy, elastic properties in the 90 degrees-layers with bundle structure can be replaced by the transverse stiffness of the homogenised 90 degrees-layer material.

  • effective stiffness of curved 0 layers for stiffness determination of cross ply non Crimp Fabric composites
    Journal of Reinforced Plastics and Composites, 2014
    Co-Authors: Hana Zrida, Erik Marklund, Z. Ayadi, Janis Varna
    Abstract:

    The effect of the 0°-tow waviness on axial stiffness of cross-ply non-Crimp Fabric composites is analysed using multiscale approach. The curved 0°- and 90°-layers are represented by flat layers with effective stiffness properties and classical laminate theory is used to calculate the macroscopic stiffness. The effective 0°-layer stiffness is calculated analysing isolated curved 0°-layers subjected not only to end loading, but also to surface loads. The surface loads are identified in a detailed finite element analysis and approximated by a sinus shaped function with amplitude depending on the waves parameters. The sinus shaped surface loads are then applied to an isolated curved 0°-layer finite element model together with end loading to calculate the effective stiffness of the layer. Finally, the effective 0°-layer stiffness was successfully used to calculate the macroscopic stiffness of the composite proving validity of the approach being used and showing that, without losing accuracy, elastic properties...

  • Master curve approach to axial stiffness calculation for non-Crimp Fabric biaxial composites with out-of-plane waviness
    Composites Part B: Engineering, 2014
    Co-Authors: Hana Zrida, Erik Marklund, Z. Ayadi, Janis Varna
    Abstract:

    Abstract The effect of 0°-tow out-of-plane waviness on the biaxial non-Crimp-Fabric (NCF) composite axial stiffness is investigated. Homogenizing, the bundle mesostructure of the NCF composite is replaced by layers. Then the composite is represented by a laminate with flat layers with effective stiffness properties representing the curved 0°-layer and the 90°-layer with varying thickness. It is shown that the NCF composite knock-down factor characterizing the stiffness degradation has almost the same dependence on wave parameters as the knock-down factor for the curved 0°-layer. Numerical analysis showed that 90°-layer knock-down factor versus amplitude curves for different wavelength can be reduced to one master curve which can be described by a one-parameter expression with the parameter dependent on the used material. This observation is used to obtain high accuracy for analytical predictions for knock-down factors for cases with different wavelength and amplitudes based on two FE calculations only.

  • Transverse strength of unidirectional non-Crimp Fabric composites: Multiscale modelling
    Composites Part B: Engineering, 2014
    Co-Authors: Erik Marklund, Leif Asp, Robin Olsson
    Abstract:

    A multiscale approach is used to predict transverse tensile and transverse compressive strength of unidirectional non-Crimp Fabric (NCF) composites. Numerical analysis on fibre/matrix scale is performed to obtain the transverse strength of the fibre bundle to be further used in an analytical mesoscale model to predict the strength of the unidirectional NCF composite. Design of unidirectional layer composites with the same fibres, interface, matrix and volume fractions as in the bundle is suggested as an alternative method for bundle strength determination. Good agreement of both methods for bundle transverse strength determination is demonstrated. The simple analytical model used on mesoscale gives accurate predictions of the tensile transverse strength whereas the compressive strength is underestimated. The necessity of including bundle waviness in models when bidirectional NCF composites are analysed is demonstrated by FEM stress analysis and by experimental data showing differences in transverse cracking pattern due to bundle waviness.