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  • 1
    Online Resource
    Online Resource
    The Tension-Twist Coupling Mechanism in Flexible Composites: A Systematic Study Based on Tailored Laminate Structures Using a Novel Test Device
    MDPI AG ; 2020
    In:  Polymers Vol. 12, No. 12 ( 2020-11-24), p. 2780-
    Details
    In: Polymers, MDPI AG, Vol. 12, No. 12 ( 2020-11-24), p. 2780-
    Abstract: The focus of this research is to quantify the effect of load-coupling mechanisms in anisotropic composites with distinct flexibility. In this context, the study aims to realize a novel testing device to investigate tension-twist coupling effects. This test setup includes a modified gripping system to handle composites with stiff fibers but hyperelastic elastomeric matrices. The verification was done with a special test plan considering a glass textile as reinforcing with different lay-ups to analyze the number of layers and the influence of various fiber orientations onto the load-coupled properties. The results demonstrated that the tension-twist coupling effect strongly depends on both the fiber orientation and the considered reinforcing structure. This enables twisting angles up to 25° with corresponding torque of about 82.3 Nmm, which is even achievable for small lay-ups with 30°/60° oriented composites with distinct asymmetric deformation. For lay-ups with ±45° oriented composites revealing a symmetric deformation lead, as expected, no tension-twist coupling effect was seen. Overall, these findings reveal that the described novel test device provides the basis for an adequate and reliable determination of the load-coupled material properties between stiff fibers and hyperelastic matrices.
    Type of Medium: Online Resource
    ISSN: 2073-4360
    URL: Article
    DOI: 10.3390/polym12122780
    Language: English
    Publisher: MDPI AG
    Publication Date: 2020
    detail.hit.zdb_id: 2527146-5
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  • 2
    Online Resource
    Online Resource
    Low-Temperature Fibre Direct Compounding of Cellulose Fibres into PA6
    MDPI AG ; 2022
    In:  Materials Vol. 15, No. 19 ( 2022-09-23), p. 6600-
    Details
    In: Materials, MDPI AG, Vol. 15, No. 19 ( 2022-09-23), p. 6600-
    Abstract: This study reports on the development of a novel polymer processing approach that combines low-temperature (LT) processing and fibre direct compounding (FDC) to reduce the thermal stress on thermosensitive components that occurs during compounding and subsequent injection moulding (IM). Composites based on polyamide 6 (PA6) and cellulose fibres (CeF) were prepared using an LT-FDC process and in parallel with a conventional approach using a twin-screw extruder and IM. The morphological, optical, thermal, and mechanical properties of the prepared samples were investigated using optical microscopy (OM), differential scanning calorimetry (DSC), colorimetry, dynamic mechanical analysis (DMA) and tensile tests. Composites prepared using LT-FDC exhibited worse fibre dispersion but lower fibre degradation. In comparison to neat PA6, the LT-FDC composites had increased tensile modulus (Et) and storage modulus (E′) at 120 °C by up to 32% and 50%, respectively, while the tensile strength (σm) decreased by 20%.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma15196600
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2487261-1
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  • 3
    Online Resource
    Online Resource
    Comparison and Impact of Different Fiber Debond Techniques on Fiber Reinforced Flexible Composites
    MDPI AG ; 2020
    In:  Polymers Vol. 12, No. 2 ( 2020-02-18), p. 472-
    Details
    In: Polymers, MDPI AG, Vol. 12, No. 2 ( 2020-02-18), p. 472-
    Abstract: The focus of this paper is the realization and verification of a modified fiber bundle pull-out test setup to estimate the adhesion properties between threads and elastic matrix materials with a more realistic failure mode than single fiber debond techniques. This testing device including a modified specimen holder provides the basis for an adequate estimation of the interlaminar adhesion of fiber bundles including the opportunity of a faster, easier, and more economic handling compared to single fiber tests. The verification was done with the single-fiber and microbond test. Overall, the modified test setup showed the typical pull-out behavior, and the relative comparability between different test scales is given.
    Type of Medium: Online Resource
    ISSN: 2073-4360
    URL: Article
    DOI: 10.3390/polym12020472
    Language: English
    Publisher: MDPI AG
    Publication Date: 2020
    detail.hit.zdb_id: 2527146-5
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  • 4
    Online Resource
    Online Resource
    Relationships between the Decomposition Behaviour of Renewable Fibres and Their Reinforcing Effect in Composites Processed at High Temperatures
    MDPI AG ; 2021
    In:  Polymers Vol. 13, No. 24 ( 2021-12-18), p. 4448-
    Details
    In: Polymers, MDPI AG, Vol. 13, No. 24 ( 2021-12-18), p. 4448-
    Abstract: Engineering polymers reinforced with renewable fibres (RF) are an attractive class of materials, due to their excellent mechanical performance and low environmental impact. However, the successful preparation of such composites has proven to be challenging due to the low thermal stability of RF. The aim of the present study was to investigate how different RF behaves under increased processing temperatures and correlate the thermal properties of the fibres to the mechanical properties of composites. For this purpose, hemp, flax and Lyocell fibres were compounded into polypropylene (PP) using a co-rotating twin screw extruder and test specimens were injection moulded at temperatures ranging from 180 °C to 260 °C, with 20 K steps. The decomposition behaviour of fibres was characterised using non-isothermal and isothermal simultaneous thermogravimetric analysis/differential scanning calorimetry (TGA/DSC). The prepared composites were investigated using optical microscopy (OM), colorimetry, tensile test, Charpy impact test, dynamic mechanical analysis (DMA) and melt flow rate (MFR). Composites exhibited a decrease in mechanical performance at processing temperatures above 200 °C, with a steep decrease observed at 240 °C. Lyocell fibres exhibited the best reinforcement effect, especially at elevated processing temperatures, followed by flax and hemp fibres. It was found that the retention of the fibre reinforcement effect at elevated temperatures can be well predicted using isothermal TGA measurements.
    Type of Medium: Online Resource
    ISSN: 2073-4360
    URL: Article
    DOI: 10.3390/polym13244448
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2527146-5
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  • 5
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    Online Resource
    Precise Correlation of Contact Area and Forces in the Unstable Friction between a Rough Fluoroelastomer Surface and Borosilicate Glass
    MDPI AG ; 2020
    In:  Materials Vol. 13, No. 20 ( 2020-10-16), p. 4615-
    Details
    In: Materials, MDPI AG, Vol. 13, No. 20 ( 2020-10-16), p. 4615-
    Abstract: Stick-slip friction of elastomers arises due to adhesion, high local strains, surface features, and viscous dissipation. In situ techniques connecting the real contact area to interfacial forces can reveal the contact evolution of a rough elastomer surface leading up to gross slip, as well as provide high-resolution dynamic contact areas for improving current slip models. Samples with rough surfaces were produced by the same manufacturing processes as machined seals. In this work, a machined fluoroelastomer (FKM) hemisphere was slid against glass, and the stick-slip behavior was captured optically in situ. The influence of sliding velocity on sliding behavior was studied over a range of speeds from 1 µm/s to 100 µm/s. The real contact area was measured from image sequences thresholded using Otsu’s method. The motion of the pinned region was delineated with a machine learning scheme. The first result is that, within the macroscale sticking, or pinned phase, local pinned and partial slip regions were observed and modeled as a combined contact with contributions to friction by both regions. As a second result, we identified a critical velocity below which the stick-slip motion converted from high frequency with low amplitude to low frequency with high amplitude. This study on the sliding behavior of a viscoelastic machined elastomer demonstrates a multi-technique approach which reveals precise changes in contact area before and during pinning and slip.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma13204615
    Language: English
    Publisher: MDPI AG
    Publication Date: 2020
    detail.hit.zdb_id: 2487261-1
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  • 6
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    Online Resource
    Correlation of Tribological Behavior and Fatigue Properties of Filled and Unfilled TPUs
    MDPI AG ; 2019
    In:  Lubricants Vol. 7, No. 7 ( 2019-07-20), p. 60-
    Details
    In: Lubricants, MDPI AG, Vol. 7, No. 7 ( 2019-07-20), p. 60-
    Abstract: For a long service time, fatigue has been a typical problem that mechanical sealing materials face. How does it relate to tribological performance? In this study, filled and unfilled thermoplastic polyurethanes (TPUs) were investigated. Dumbbell and faint wait pure shear (FWPS) specimens were used to characterize the fatigue properties and crack growth rate of TPUs, respectively. Additionally, to identify the impact of temperature on fatigue tests, the tests were conducted at room temperature and 80 °C. Different tribological tests were conducted to investigate their tribological properties. Fracture surfaces from fatigue tests and worn surfaces from tribological tests were analyzed using a scanning electron microscope (SEM). Two wear models were verified to correlate between fatigue and tribological properties; one of the models is better for rough counter surfaces, while the other is advantageous if the counter surface is smooth.
    Type of Medium: Online Resource
    ISSN: 2075-4442
    URL: Article
    DOI: 10.3390/lubricants7070060
    Language: English
    Publisher: MDPI AG
    Publication Date: 2019
    detail.hit.zdb_id: 2704327-7
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  • 7
    Online Resource
    Online Resource
    Fretting Behavior of Thermoplastic Polyurethanes
    MDPI AG ; 2019
    In:  Lubricants Vol. 7, No. 9 ( 2019-08-23), p. 73-
    Details
    In: Lubricants, MDPI AG, Vol. 7, No. 9 ( 2019-08-23), p. 73-
    Abstract: Fretting tests were conducted with five different thermoplastic polyurethanes against a steel ball. Their fretting behaviors were investigated under various test parameters, such as normal load and displacement amplitude. In order to test the sliding performances, tribological tests were conducted using a ring-on-disc setup. The results show that their fretting behaviors can be related to the dynamic mechanical properties, which were characterized by dynamic mechanical analysis (DMA). The three fretting regimes were identified by means of hysteresis and wear scar analysis. In addition, investigations were carried out until the transition regimes occurred. Different wear processes were revealed for each of the three regimes. Differences were identified using dissipated energy. The profiles of wear scars and the counterparts were analyzed using a microscope. The coefficient of friction was calculated separately for the partial slip and gross slip regimes. In the mixed fretting regime, the coefficient of friction is almost at the same level among the five materials. In the partial slip regime, however, it can be distinguished. Temperature measurements were conducted on the counterparts during the tests. Overall, the material that showed the best tribological properties also performed the best in the fretting tests.
    Type of Medium: Online Resource
    ISSN: 2075-4442
    URL: Article
    DOI: 10.3390/lubricants7090073
    Language: English
    Publisher: MDPI AG
    Publication Date: 2019
    detail.hit.zdb_id: 2704327-7
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  • 8
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    Online Resource
    Influence of Viscose Fibre Geometry on the Structure–Property Relationships of High-Density Polyethylene Composites
    MDPI AG ; 2022
    In:  Polymers Vol. 14, No. 20 ( 2022-10-18), p. 4389-
    Details
    In: Polymers, MDPI AG, Vol. 14, No. 20 ( 2022-10-18), p. 4389-
    Abstract: This study investigated the influence of viscose fibre (VF) geometry on the microstructures and resulting properties of high-density polyethylene (HDPE) composites. Seven types of viscose fibres varying in cross-section shape, linear density, and length were pelletised, compounded into HDPE with a twin-screw extruder, and injection moulded. The microstructures of the composites were characterised by investigating their cross-sections and by extracting the fibres and measuring their lengths using optical microscopy (OM). The mechanical and thermal properties of the composites were characterised using differential scanning calorimetry (DSC), tensile tests, Charpy impact tests, and dynamic mechanical analysis (DMA). The composites prepared using cylindrical fibres with a linear density of 1.7 dtex exhibited the best fibre dispersion, highest orientation, and lowest fibre–fibre contact area. The decrease in the linear density of the cylindrical fibres resulted in increasingly worse dispersion and orientation, while composites containing non-cylindrical fibres exhibited a comparably larger fibre–fibre contact area. The initial fibre length of about 3 to 10 mm decreased to the mean values of 0.29 mm to 0.41 mm during processing, depending on the initial geometry. In general, cylindrical fibres exhibited a superior reinforcing effect in comparison to non-cylindrical fibres. The composites containing cylindrical fibres with a linear density of 1.7 dtex and a length of 5 mm exhibited the best reinforcing effect with an increase in tensile modulus and strength of 323% and 141%, respectively.
    Type of Medium: Online Resource
    ISSN: 2073-4360
    URL: Article
    DOI: 10.3390/polym14204389
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2527146-5
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  • 9
    Online Resource
    Online Resource
    Tribological Behavior of HNBR in Oil and Gas Field Applications
    MDPI AG ; 2018
    In:  Lubricants Vol. 6, No. 1 ( 2018-02-13), p. 20-
    Details
    In: Lubricants, MDPI AG, Vol. 6, No. 1 ( 2018-02-13), p. 20-
    Type of Medium: Online Resource
    ISSN: 2075-4442
    URL: Article
    DOI: 10.3390/lubricants6010020
    Language: English
    Publisher: MDPI AG
    Publication Date: 2018
    detail.hit.zdb_id: 2704327-7
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  • 10
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    Online Resource
    Peeling of Flexible Laminates—Determination of Interlayer Adhesion of Backsheet Laminates Used for Photovoltaic Modules
    MDPI AG ; 2022
    In:  Materials Vol. 15, No. 9 ( 2022-05-04), p. 3294-
    Details
    In: Materials, MDPI AG, Vol. 15, No. 9 ( 2022-05-04), p. 3294-
    Abstract: Delamination is one of the most critical failure modes of a PV module during service lifetime. Delamination within a backsheet primarily imposes a safety risk, but may also accelerate various other PV module degradation modes. The main aim of this paper is to present a peel test set-up, which is more practical in sample preparation and execution than the width-tapered cantilever beam test and overcomes some issues of standard peel tests like the influence of sample geometry and energy dissipation through deformation on the peel test results. The best results with respect to accuracy and effort were achieved by using a 180° peel geometry where an additional adhesive tape is applied to the peel arm in order to avoid plastic deformation or breakage. The additional support of the adhesive tape leads to comparable peel strength values without any influence of the plastic deformation behavior of the peel arms with different thickness.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma15093294
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2487261-1
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