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  1. Article ; Online: Experimental Analysis of Matrix Cracking in Glass Fiber Reinforced Composite Off-Axis Plies under Static and Fatigue Loading.

    Just, Gordon / Koch, Ilja / Gude, Maik

    Polymers

    2022  Volume 14, Issue 11

    Abstract: The inter-fiber failure of glass fiber-reinforced epoxy specimens with four different fiber angles was analyzed. Flat specimens were subjected to static and fatigue loading considering different load levels and load ratios. Damage investigation in terms ... ...

    Abstract The inter-fiber failure of glass fiber-reinforced epoxy specimens with four different fiber angles was analyzed. Flat specimens were subjected to static and fatigue loading considering different load levels and load ratios. Damage investigation in terms of crack density measurement was performed by transmitted white light imaging using a digital camera and LED illumination from the back of the specimen on a servo-hydraulic testing machine. Static and fatigue results were examined with respect to crack initiation and crack growth, considering the special case of bonding yarns parallel to the fiber directions. The bonding yarns act as stress concentrations, influencing the early cracking behavior, and complicate the detectability of cracks growing underneath or next to the bonding yarns. In cyclic loading, the influence of load level, load ratio, mean stress, fiber orientation, and ply thickness was the focus of the experimental campaign. Cyclic cracking behavior in terms of initiation and growth was analyzed based on the applied loading conditions and laminate configurations. It was found that halving the ply thickness nearly doubled the amount of microcracks in case of high loads. For low loads, no such effect was observed up to 5×105 loading cycles. Experimental findings on individual crack growth confirmed that crack interaction started for crack spacings less than four times the ply thickness and that subsequent crack growth shifted into regions of larger local crack spacing.
    Language English
    Publishing date 2022-05-26
    Publishing country Switzerland
    Document type Journal Article
    ZDB-ID 2527146-5
    ISSN 2073-4360 ; 2073-4360
    ISSN (online) 2073-4360
    ISSN 2073-4360
    DOI 10.3390/polym14112160
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Article ; Online: Hydrogen permeability of thermoplastic composites and liner systems for future mobility applications

    Condé-Wolter, Jan / Ruf, Michael G. / Liebsch, Alexander / Lebelt, Tobias / Koch, Ilja / Drechsler, Klaus / Gude, Maik

    Composites Part A. 2023 Apr., v. 167 p.107446-

    2023  

    Abstract: High pressure hydrogen permeation tests were carried out and specific permeation rates of various thermoplastic matrix materials have been measured as well as of continuous fiber reinforced thermoplastic composites (PA6, PA12, PA410, PPA, PPS), ... ...

    Abstract High pressure hydrogen permeation tests were carried out and specific permeation rates of various thermoplastic matrix materials have been measured as well as of continuous fiber reinforced thermoplastic composites (PA6, PA12, PA410, PPA, PPS), considering non-crimp and crimp textile architectures. Furthermore, liners based on thermoplastic high barrier films made of EVOH were applied on PA6 composites and their effect on permeation rate were investigated. All samples were accompanied by pressure tightness tests and micrographs to determine manufacturing effects, microstructure, porosity and additional defects like microcracks. Experiments show that thermoplastic composites can reach low permeation rate as long as a damage-free microstructure is ensured. Furthermore, the influence of the matrix material can be assessed, whereby the influence of the textile architecture can only be roughly estimated and is considered to be small. EVOH layers show remarkable barrier properties and are easy to integrate into the composite structure.
    Keywords fabrics ; hydrogen ; microstructure ; permeability ; porosity ; thermoplastics ; Hydrogen permeation ; Thermoplastic composites ; Liner ; EVOH
    Language English
    Dates of publication 2023-04
    Publishing place Elsevier Ltd
    Document type Article ; Online
    Note Use and reproduction
    ZDB-ID 2012223-8
    ISSN 1359-835X
    ISSN 1359-835X
    DOI 10.1016/j.compositesa.2023.107446
    Database NAL-Catalogue (AGRICOLA)

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  3. Book ; Thesis: Modellierung des Ermüdungsverhaltens textilverstärkter Kunststoffe

    Koch, Ilja

    2010  

    Author's details von Ilja Koch
    Language German
    Size XIII, 94 S., Ill., graph. Darst.
    Document type Book ; Thesis
    Thesis / German Habilitation thesis Techn. Univ., Diss.--Dresden, 2010
    Database Library catalogue of the German National Library of Science and Technology (TIB), Hannover

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  4. Article: Influence of Reversed Fatigue Loading on DamageEvolution of Cross-Ply Carbon Fibre Composites.

    Just, Gordon / Koch, Ilja / Brod, Martin / Jansen, Eelco / Gude, Maik / Rolfes, Raimund

    Materials (Basel, Switzerland)

    2019  Volume 12, Issue 7

    Abstract: Microcrack formation and delamination growth are the main damage mechanisms in thefatigue of composites. They lead to significant stiffness loss, introduce stress concentrations andcan be the origin of subsequent damage events like buckling or fibre ... ...

    Abstract Microcrack formation and delamination growth are the main damage mechanisms in thefatigue of composites. They lead to significant stiffness loss, introduce stress concentrations andcan be the origin of subsequent damage events like buckling or fibre breakage, especially in case ofshear and compression stresses during load reversal. Fatigue experiments of carbon fibre reinforcedlaminates were conducted at several stress ratios and analysed in terms of crack and delaminationgrowth. These investigations were accompanied by microscopic imaging, digital image correlationand finite element modelling to take into account the effects of residual stresses and crack closure.It was found that residual stresses significantly change the local stress ratio in off-axis layers andlead to residual crack opening of inter fibre cracks. These cracks remain open and close under highcompression loadings only. Furthermore, crack formation under pulsating compression loadingturned out to be driven by residual stresses leading to perpendicular cracks as observed underpure tension loading. The experimental findings further confirm the severe detrimental effect oftension-compression loading on crack formation and delamination growth compared to pulsatingtension-tension or compression-compression loads.
    Language English
    Publishing date 2019-04-09
    Publishing country Switzerland
    Document type Journal Article
    ZDB-ID 2487261-1
    ISSN 1996-1944
    ISSN 1996-1944
    DOI 10.3390/ma12071153
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  5. Article: Evaluation and Modeling of the Fatigue Damage Behavior of Polymer Composites at Reversed Cyclic Loading.

    Koch, Ilja / Just, Gordon / Brod, Martin / Chen, Jiuheng / Doblies, Audrius / Dean, Aamir / Gude, Maik / Rolfes, Raimund / Hopmann, Christian / Fiedler, Bodo

    Materials (Basel, Switzerland)

    2019  Volume 12, Issue 11

    Abstract: Understanding the composite damage formation process and its impact on mechanical properties is a key step towards further improvement of material and higher use. For its accelerated application, furthermore, practice-related modeling strategies are to ... ...

    Abstract Understanding the composite damage formation process and its impact on mechanical properties is a key step towards further improvement of material and higher use. For its accelerated application, furthermore, practice-related modeling strategies are to be established. In this collaborative study, the damage behavior of carbon fiber-reinforced composites under cyclic loading with load reversals is analyzed experimentally and numerically. The differences of crack density evolution during constant amplitude and tension-compression block-loading is characterized with the help of fatigue tests on cross-ply laminates. For clarifying the evolving stress-strain behavior of the matrix during static and fatigue long-term loading, creep, and fatigue experiments with subsequent fracture tests on neat resin samples are applied. The local stress redistribution in the composite material is later evaluated numerically using composite representative volume element (RVE) and matrix models under consideration of viscoelasticity. The experimental and numerical work reveals the strong influence of residual stresses and the range of cyclic tension stresses to the damage behavior. On the microscopic level, stress redistribution dependent on the mean stress takes place and a tendency of the matrix towards embrittlement was found. Therefore, it is mandatory to consider stress amplitude and means stress as inseparable load characteristic for fatigue assessment, which additionally is influenced by production-related and time-dependent residual stresses. The phenomenological findings are incorporated to a numerical simulation framework on the layer level to provide an improved engineering tool for designing composite structures.
    Language English
    Publishing date 2019-05-28
    Publishing country Switzerland
    Document type Journal Article
    ZDB-ID 2487261-1
    ISSN 1996-1944
    ISSN 1996-1944
    DOI 10.3390/ma12111727
    Database MEDical Literature Analysis and Retrieval System OnLINE

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