This article highlights the effects from composite manufacturing parameters on fiber-reinforced composite laminates modified with layers of piezoelectric thermoplastic nanofibers and a conductive electrode layer. Such modifications have been used for enabling in situ deformation measurement in high-performance aerospace and renewable energy composites. Procedures for manufacturing high-performance composites are well-known and standardized. However, this does not imply that modifications via addition of functional layers (e.g., piezoelectric nanofibers) while following the same manufacturing procedures can lead to a successful multifunctional composite structure (e.g., for enabling in situ measurement). This article challenges success of internal embedment of piezoelectric nanofibers in standard manufacturing of high-performance composites via relying on composite process specifications and parameters only. It highlights that the process parameters must be revised for manufacturing of multifunctional composites. Several methods have been used to lay up and manufacture composites such as electrospinning the thermoplastic nanofibers, processing an inter digital electrode (IDE) made by conductive epoxy–graphene resin, and prepreg autoclave manufacturing aerospace grade laminates. The purpose of fabrication of IDE was to use a resin type (HexFlow RTM6) for the conductive layer similar to that used for the composite. Thereby, material mismatch is avoided and the structural integrity is sustained via mitigation of downgrading effects on the interlaminar properties. X-ray diffraction, Fourier transform infrared spectroscopy, energy dispersive X-ray spectroscopy, and scanning electron microscopy analyses have been carried out in the material characterization phase. Pulsed thermography and ultrasonic C-scanning were used for the localization of conductive resin embedded within the composite laminates. This study also provides recommendations for enabling internally embedded piezoelectricity (and thus health-monitoring capabilities) in high-performance composite laminates.

The present article overcomes existing challenges ahead of inter-laminar toughening of novel multifunctional fibre-reinforced polymer composites via development and embedment of highly stretched, ultra-thin electrospun thermoplastic nanofibers made of polyamide 6.6. The nanofibers have exhibited significant enhancement of the composite laminate's structural integrity with almost zero weight penalty via ensuring a smooth stress transfer throughout the plies and serving tailoring mechanical properties in desired directions, with no interference with geometric features e.g. thickness. The findings for 1.5 grams per square meter (gsm) electrospun nanofibers have demonstrated, on test coupons specimens, improvements up to 85% and 43% in peak load and crack opening displacement, respectively, with significant improvement (> 25%) and no sacrifice of fracture toughness at both initiation and propagation phases. The initial stiffness for the modified specimens was improved by nearly 150%. The enhancement is mainly due to nano-fibres contributing to the stiffness of the resin rich area at the crack tip adjacent to the Polytetrafluoroethylene (PTFE) film. Glass fibre-reinforced woven phenolic preimpregnated composite plies have been modified with the nano-fibres (each layer having an average thickness of <1 micron) at 0.5, 1.0, 1.5, 2.0 and 4.0 gsm, electrospun at room temperature on each ply, and manufactured via autoclave vacuum bagging process. Inter-laminar fracture toughness specimens were manufactured for Mode I (double cantilever beam, DCB) fracture tests. It was found that there is threshold for electrospun nanofibers density, at which an optimum performance is reached in modified composite Manuscript File

Electrospinning generates nanofibres at speeds that often surpass those of conventional man-made fibre production. This makes control and manipulation of these nanofibres that much more difficult and challenging. However, to take full advantage of the superior properties of electrospun nanofibres, their production process must be clearly understood and all possible means of fibre formation and hence fibre control explored. This article attempts to explain electrospun fibre production from first principles and uses schematics to follow the electrospinning process from inception, i.e. in the nozzle, to collection with respect to electrostatic behaviours. The complex interrelationship between the charged species in the moving solution and their subsequent polarization and the induced internal field by the applied external electric field are systematically explored and explained.

A new test method is presented that is considered suitable for measuring the long term mechanical properties of composites loaded in shear. The test method is assessed for its reproducibility and accuracy and compared to conventional Iosipescu tests for short term test results. Some initial test data for long term shear creep are also presented