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  • MDPI AG  (5)
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  • MDPI AG  (5)
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  • 1
    Online Resource
    Online Resource
    Consolidation and Tow Spreading of Digitally Manufactured Continuous Fiber Reinforced Composites from Thermoplastic Commingled Tow Using a Five-Axis Extrusion System
    MDPI AG ; 2021
    In:  Journal of Composites Science Vol. 5, No. 3 ( 2021-03-05), p. 73-
    Details
    In: Journal of Composites Science, MDPI AG, Vol. 5, No. 3 ( 2021-03-05), p. 73-
    Abstract: During the development of digitally manufactured, commingled tow continuous fiber reinforced composites, consolidation force was controlled using a controlled spring force that yielded a repeatable tow width. However, the use of the extruder face to consolidate the material requires that the extruder remain perpendicular to the placement surface throughout the process. When considering more complex tool contours including sloped surfaces, more than three axes of motion are necessary to maintain the perpendicularity of the extruder tip to the surface. In this effort, a five-axis system is developed and used to demonstrate the ability to consolidate over complex contours. In addition, the nozzle face temperatures required for good consolidation and wetout result in poor tow path fidelity when complex paths are introduced. The implementation of an automated, computer-controlled localized cooling system enables both good wetout and consolidation while also enabling more accurate changes in tow path due to improvements in local tow tack. With the development of the five-axis system it is also shown that the tow width can be adjusted by rotating the existing placement nozzle to angles not equal to 90°. Thus, through a combination of controlled localized cooling and real-time control of the nozzle angle, a possible approach to control of tow width, independent of the tow placement angle and radius of curvature during tow steering, is described.
    Type of Medium: Online Resource
    ISSN: 2504-477X
    URL: Article
    DOI: 10.3390/jcs5030073
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2911719-7
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    Online Resource
  • 2
    Online Resource
    Online Resource
    A DMA-Based Approach to Quality Evaluation of Digitally Manufactured Continuous Fiber-Reinforced Composites from Thermoplastic Commingled Tow
    MDPI AG ; 2022
    In:  Journal of Composites Science Vol. 6, No. 2 ( 2022-02-18), p. 61-
    Details
    In: Journal of Composites Science, MDPI AG, Vol. 6, No. 2 ( 2022-02-18), p. 61-
    Abstract: Direct digital manufacturing of continuous fiber-reinforced thermoplastics exhibits the potential to relieve many of the constraints placed on the current design and manufacture of composite structures. At present, the additive manufacturing of continuous fiber-reinforced thermoplastics is demonstrated to varying extents; however, a comprehensive investigation of manufacturing defects and the quality of additively manufactured high fiber volume fraction continuous fiber-reinforced thermoplastic composites is limited. Considering the preliminary nature of the additive manufacturing of continuous fiber-reinforced thermoplastics, composites processed in this manner are typically subject to various manufacturing defects, including excessive void content in the thermoplastic matrix. Generally, quality evaluation of processed composites in the literature is limited to test methods that are largely influenced by the properties of the continuous fiber reinforcement, and as such, defects in the thermoplastic matrix are usually less impactful on the results and are often overlooked. Hardware to facilitate the direct digital manufacturing of continuous fiber-reinforced thermoplastic matrix composites was developed, and specimens were successfully processed with intentionally varied void content. The quality of the additively manufactured specimens was then evaluated in terms of the measured maximum storage modulus, maximum loss modulus, damping factor and the glass transition temperature by means of dynamic mechanical analysis (DMA). DMA allows for thermomechanical (i.e., highly matrix sensitive) evaluation of the composite specimens, specifically in terms of the measured elastic storage modulus, viscous loss modulus, damping factor and the glass transition temperature. Within the tested range of void contents from roughly 4–10%, evaluation by DMA resulted in a distinct reduction in the maximum measured storage modulus, maximum loss modulus and glass transition temperature with increasing void content, while the damping factor increased. Thus, the results of this work, which focused on the effect of void content on DMA measured properties, have demonstrated that DMA exhibits multi-faceted sensitivity to the presence of voids in the additively manufactured continuous fiber-reinforced thermoplastic specimens.
    Type of Medium: Online Resource
    ISSN: 2504-477X
    URL: Article
    DOI: 10.3390/jcs6020061
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2911719-7
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  • 3
    Online Resource
    Online Resource
    Composite Single Lap Shear Joint Integrity Monitoring via Embedded Electromechanical Impedance Sensors
    MDPI AG ; 2023
    In:  Journal of Composites Science Vol. 7, No. 2 ( 2023-02-02), p. 53-
    Details
    In: Journal of Composites Science, MDPI AG, Vol. 7, No. 2 ( 2023-02-02), p. 53-
    Abstract: Composite bonded structure is a prevalent portion of today’s aircraft structure. Adequate bond integrity is a critical aspect of fabrication and service, especially since many of today’s structural bonds are critical for flight safety. Over the last decade, non-destructive bond evaluation techniques have improved but still cannot detect a structurally weak bond that exhibits full adherend/adhesive contact. The result is that expensive and time-consuming structural proof testing continues to be required to verify bond integrity. The objective of this work is to investigate the feasibility of bondline integrity monitoring using piezoelectric sensors, embedded at different locations within the composite joint, and to assess the benefits of monitoring the thickness mode in addition to the radial mode. Experiments and analyses are performed on single lap shear composite joints, with and without embedded sensors, subjected to incrementally increasing tensile loads. The results indicate that the embedded piezoelectric sensors measure a change in the resonance in both the radial and thickness mode during incremental loading and that the thickness resonance shows enhanced sensitivity to impending failure. Thus, it is demonstrated that monitoring both modes of the piezoelectric sensor provides addition details for prognostic performance evaluation.
    Type of Medium: Online Resource
    ISSN: 2504-477X
    URL: Article
    DOI: 10.3390/jcs7020053
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2911719-7
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  • 4
    Online Resource
    Online Resource
    Digital Manufacture of a Continuous Fiber Reinforced Thermoplastic Matrix Truss Core Structural Panel Using Off-the-Tool Consolidation
    MDPI AG ; 2022
    In:  Journal of Composites Science Vol. 6, No. 11 ( 2022-11-07), p. 343-
    Details
    In: Journal of Composites Science, MDPI AG, Vol. 6, No. 11 ( 2022-11-07), p. 343-
    Abstract: Sandwich panels are commonly used as structure, based on fiber reinforced composites, with the goal of high flexural stiffness and low mass. It is most common to separate two high performance composite facesheets with a low-density core, generally in the form of a foam or honeycomb. A recent concept has been to replace these traditional core materials with fiber reinforced truss-like structures, with the goal of further reducing mass. A system is described that can radically reduce the amount of tooling required for truss core sandwich panel manufacture. This system, which is a digital manufacturing platform for the extrusion of continuous fiber reinforced commingled glass fiber/PET tow, was developed to demonstrate the rigidization of composites both on, and off, a tool surface. Navtruss core panels were successfully manufactured using this digital manufacturing platform, without conventional tooling, and the resulting through thickness compression moduli and panel shear moduli were within 14.6% and 23% of the values baseline compression molded specimens. Thus, the results suggest that, with further development, complex truss core structures with performance approaching that of compression molded panels can be manufactured with radically reduced tooling requirements from high volume fraction, continuous fiber reinforced thermoplastic matrix composites.
    Type of Medium: Online Resource
    ISSN: 2504-477X
    URL: Article
    DOI: 10.3390/jcs6110343
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2911719-7
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    Online Resource
  • 5
    Online Resource
    Online Resource
    Cost, Draping, Material and Partitioning Optimization of a Composite Rail Vehicle Structure
    MDPI AG ; 2022
    In:  Materials Vol. 15, No. 2 ( 2022-01-07), p. 449-
    Details
    In: Materials, MDPI AG, Vol. 15, No. 2 ( 2022-01-07), p. 449-
    Abstract: This study proposes a novel methodology to combine topology optimization and ply draping simulation to partition composite structures, improve structural performance, select materials, and enable more accurate representations of cost- and weight-efficient manufacturable designs. The proposed methodology is applied to a structure as a case study to verify that the methodology is effective. One design concept is created by subjecting the structure to a kinematic ply draping simulation to inform the partitioning of the structure, improve drapability and performance, and reduce structural defects. A second design concept is created that assumes that plies are draped over the entire structural geometry, forming an integral design. The two design concepts’ topologies are subsequently optimized to specify ideal material and ply geometries to minimize mass and reduce costs. The results indicate that the partitioned structure has a 19% lower mass and 15% lower material costs than the integral design. The two designs produced with the new methodology are also compared against two control designs created to emulate previously published methodologies that have not incorporated ply draping simulations. This demonstrates that neglecting the effects of ply draping produces topology optimization solutions that under-predict the mass of a structure by 26% and costs by 38%.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma15020449
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2487261-1
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