Phase morphology of nanofibre interlayers: Critical factor for toughening carbon/epoxy composites (original) (raw)
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Composites Science and Technology, 2015
Electrospun thermoplastic nanofibres have a large potential for the interlaminar toughening of composite laminates. They can easily be placed in resin rich interlayers between reinforcing plies prior to laminate production and require no dispersion into the matrix resin. Although there are many expected benefits, the research on composite laminates enhanced with electrospun thermoplastic nanofibres is still very limited and a thorough understanding of the toughening mechanism is still missing. This article provides thorough insights into the micromechanisms that lead to the interlaminar toughening of carbon/epoxy composite laminates interleaved with electrospun polyamide nanofibrous veils. The main mechanism leading to a higher interlaminar fracture toughness, both under Mode I and Mode II loading conditions, was the bridging of (micro)cracks by PA nanofibres. The effectiveness of the nanofibre bridging toughening mechanism is dependent on a good load transfer to the nanofibres. Crack propagation under Mode II loading conditions resulted in much higher improvements than under Mode I loading due to an optimal loading of the nanofibres along their fibre direction in the plane of the nanofibrous veil. In Mode I crack propagation, however, the loading of the nanofibres is less optimal and was shown to be dependent on both the primary reinforcement fabric architecture, as well as on the presence of a carbon fibre bridging zone.
Advanced Composites Letters
In this study, the effects of modifying interlaminar region of unidirectional carbon fibre/epoxy composites by the incorporation of electrospun polyvinyl alcohol (PVA) nanofibres were investigated. PVA nanofibres were directly deposited onto the carbon fabrics by electrospinning method to improve mechanical performance of those composites. The features of the electrospun nanofibres were characterized by microscopy techniques. The unidirectional carbon fibre/epoxy composite laminates with/without PVA nanofibre interlayers were manufactured by vacuum-infusion technique in a [0] 4 configuration. Tensile, three-point bending, compression, Charpy-impact and Mode-I fracture toughness tests (Double Cantilever Beam (DCB)) were carried out in accordance with ASTM standards to evaluate mechanical performance of the composites. Scanning electron microscopy (SEM) observations were made on the specimens to evaluate microstructural features. It was observed that the carbon fabrics were successfully coated with a thin layer of PVA nanofibres by electrospinning technique. The results showed that PVA nanofibres improve the mechanical properties of unidirectional carbon/epoxy composite laminates when subjected to in-plane loading. On the other hand, PVA nanofibres slightly reduced the mode-I fracture toughness values although they led to more stable crack propagation.
Delivering interlaminar reinforcement in composites through electrospun nanofibres
Advanced Manufacturing: Polymer & Composites Science, 2019
Electrospun nonwoven veils comprising thermoplastic fibres (average diameter 400-600 nm) based on polysulfone (PSU), polyamide (PA-6,6), and polyetherimide (PEI) have been fabricated and used as interlaminar reinforcements in carbon fibre composites containing a commercial epoxy resin (8552/IM7). Samples were tested for their interlaminar properties and improvements were observed in the initial mode I interlaminar toughness of 30% (PA-6,6), 36% (PEI), and 44% (PSU), while improvements of 7% (PSU) and 8% (PEI) were observed in the propagation of the mode I interlaminar toughness. A reduction of 11% was observed for the propagation of the mode I interlaminar toughness for PA-6,6. Post-testing analysis of the cross-section and the fracture surface revealed that the crack front avoids the reinforcement significantly for PA-6,6. For mode II, however, this failure mechanism leads to improvements of 30% in interlaminar toughness for the PA-6,6, whereas the other reinforcements display negligible (PEI) and 31% reduction (PSU) interlaminar toughness.
Journal of Applied Polymer Science, 2013
This article reports a novel hybrid multiscale carbon-fiber/epoxy composite reinforced with self-healing core-shell nanofibers at interfaces. The ultrathin self-healing fibers were fabricated by means of coelectrospinning, in which liquid dicyclopentadiene (DCPD) as the healing agent was enwrapped into polyacrylonitrile (PAN) to form core-shell DCPD/PAN nanofibers. These core-shell nanofibers were incorporated at interfaces of neighboring carbon-fiber fabrics prior to resin infusion and formed into ultrathin selfhealing interlayers after resin infusion and curing. The core-shell DCPD/PAN fibers are expected to function to self-repair the interfacial damages in composite laminates, e.g., delamination. Wet layup, followed by vacuum-assisted resin transfer molding (VARTM) technique, was used to process the proof-of-concept hybrid multiscale self-healing composite. Three-point bending test was utilized to evaluate the self-healing effect of the core-shell nanofibers on the flexural stiffness of the composite laminate after predamage failure. Experimental results indicate that the flexural stiffness of such novel self-healing composite after predamage failure can be completely recovered by the self-healing nanofiber interlayers. Scanning electron microscope (SEM) was utilized for fractographical analysis of the failed samples. SEM micrographs clearly evidenced the release of healing agent at laminate interfaces and the toughening and self-healing mechanisms of the core-shell nanofibers. This study expects a family of novel high-strength, lightweight structural polymer composites with self-healing function for potential use in aerospace and aeronautical structures, sports utilities, etc. V C 2012
Toughening Behavior of Carbon/Epoxy Laminates Interleaved by PSF/PVDF Composite Nanofibers
Applied Sciences
This paper presents an investigation on fracture behavior of carbon/epoxy composite laminates interleaved with electrospun nanofibers. Three different mats were manufactured and interleaved, using only polyvinylidene fluoride (PVDF), only polysulfone (PSF), and their combination. Mode-I and Mode-II fracture mechanics tests were conducted on virgin and nanomodified samples, and the results showed that PVDF and PSF nanofibers enhance the Mode-I critical energy release rate (GIC) by 66% and 51%, respectively, while using a combination of the two registered a 78% increment. The same phenomenon occurred under Mode-II loading. SEM micrographs were taken, to investigate the toughening mechanisms provided by the nanofibers.
Composite Structures, 2014
The necessity to produce modern composites with an acceptable impact resistance is an essential task in automobile and aerospace industry that needs to be satisfied. This capability is addressed by noteworthy energy absorption augmentation which is the most vital characteristic of such composite materials. In this paper, nanofibers are applied as interleaves to modify the delamination strength with a minimum rise in weight and thickness of the high-modulus polypropylene/epoxy composites. Nylon 6,6 nanofibers are produced by the electrospinning method. The distribution of nanofibers across the mats is examined by SEM. Innegra fabrics have been applied in composite layers production. The proper hand lay-up manufacturing of the laminates has been assured by the assistance of a hydraulic press. The energy absorption capacity at the onset of breakdown and impact resistance of the nanomodified and non-modified laminates were determined by quasistatic three-point flexural for the former and low-velocity impact tests for the latter. The obtained results were compared. The results showed a 6.2 and 16.9% increase in the energy absorption capacity of nanomodified laminates in quasi-static three-point flexural test and low-velocity impact tests, respectively. In addition, low-velocity impact tests revealed 16 and 26% improvement in maximum load capacity.
Interlaminar toughening of glass epoxy composites by electrospun nanofibers
2016
List of publications xiii Publications directly presented in this PhD xiii Other publications xiv 1 Introduction 1.1 Fiber reinforced composites 1.2 Composite laminates and delamination 1.3 Toughening methods for FRP composites 1.3.1 Z-binders 1.3.2 Rigid nanoparticle toughened epoxies 1.3.3 Rubber and thermoplastic toughened epoxies 1.4 Nanofiber toughened composites 1.4.1 Nanofibers and their applications 1.4.2 Production of nanofibers by electrospinning 1.4.3 Nanofibers in composite materials 1.5 Objectives and outline 2 Materials and methods 2.1 Materials 2.1.1 Materials used for the production and postmodification of electrospun fibers 2.1.2 Materials used for the production of glass epoxy laminates 2.2 Electrospinning 2.2.1 Electrospinning equipment 2.2.2 Electrospun membranes 2.3 Production of glass epoxy laminates using vacuum assisted resin transfer molding 2.4 Characterization of electrospinning solutions and electrospun nanofibrous veils 2.4.1 Viscosity 2.4.2 Conductivity 2.4.3 Scanning electron microscopy 2.4.4 Tensile properties 2.4.5 Dynamic mechanical analysis 2.4.6 Infrared spectroscopy 2.5 Characterization of the composite laminates 2.5.1 Mode I interlaminar fracture toughness 2.5.2 Mode II interlaminar fracture toughness 2.5.3 Tensile properties 2.5.4 Open hole strength 2.5.5 Low velocity impact 2.5.6 Dynamic mechanical analysis 2.5.7 Optical microscopy 3 Interlaminar toughening using electrospun nanofibers: general toughening mechanisms 3.1 Introduction: a multi-level approach for analyzing nanofiber reinforced composites 3.2 Level 1: The nanotoughened epoxy 3.3 Level 2: Nanotoughened interlaminar region 3.4 Level 3: Nanotoughened laminate 3.5 Conclusions 4 Effect of electrospun morphology on the interlaminar toughness of PCL toughened laminates 4.1 Introduction: importance of toughening morphology and interlaminar crack path 4.2 Production of different electrospun morphologies and their laminates 4.3 Morphology and tensile properties of electrospun structures 4.4 Effect of the electrospun PCL morphology on the Mode I interlaminar fracture toughness 4.5 Effect of electrospun PCL morphology on the Mode II interlaminar fracture toughness 4.6 Conclusions 5 How different interleaving methods can affect the interlaminar fracture toughness 5.1 Sample preparation using different interleaving methods 5.2 Effect of the interleaving method on Mode I interlaminar fracture toughness 5.3 Position of the delamination initiation film in the DCB specimen iii 5.4 Effect of nanofiber veil areal density for SLD and DLD configuration 5.5 Effect of PCL nanofibers on the in-plane laminate properties and open hole strength 5.6 Conclusions 6 The use of triazolinedione click chemistry for tuning the mechanical properties of electrospun SBS fibers 6.1 Introduction: tunable electrospun SBS fibers 6.2 Development of an SBS electrospinning system in butyl acetate 6.3 TAD post-treatment of electrospun SBS membranes 6.4 Effect of a TAD post-treatment on the thermomechanical properties of electrospun SBS membranes 6.5 Effect of a TAD post-treatment on the tensile properties of electrospun SBS membranes 6.6 Conclusions 7 The influence of the mechanical properties of electrospun nanofibers on the interlaminar fracture toughness of nanofiber toughened laminates. 7.1 Introduction: linking the mechanical properties of tunable SBS fibers to the fracture toughness of composite laminates 7.2 Effect of MDI-TAD cross-linker on tensile properties of SBS fibers 7.3 Effect of the mechanical properties of the SBS fibers on the mechanism of electrospun fiber bridging 7.4 Effect of the mechanical properties of the SBS fibers on the Mode II interlaminar fracture toughness 7.5 Effect of the mechanical properties of the SBS fibers on the Mode I interlaminar fracture toughness 7.6 Conclusion 8 Concluding remarks and outlook References xiii
2018
Carbon fibre-reinforced polymer (CFRP) composites are extensively used in high performance transport and renewable energy structures. However, composite laminates face the recurrent problem of being prone to damage in dynamic and impact events due to extensive interlaminar delamination. Therefore, interlaminar tougheners such as thermoplastic veils are introduced between pre-impregnated composite plies or through-thickness reinforcement techniques such as tufting are employed. However, these reinforcements are additional steps in the process which will add a degree of complexity and time in preparing composite lay-ups. A novel material and laying-up process is proposed in this paper that uses highly stretched electrospun thermoplastic nanofibers (TNF) that can enhance structural integrity with almost zero weight penalty (having 0.2gsm compared to the 300gsm CFRP plies), ensuring a smooth stress transfer through different layers, and serves directional property tailoring, with no int...