This work reports the development and testing of a magnetic polymer (Polyamide 6, PA6) nanocomposite capable of melting when exposed to an external magnetic field. Addition of high concentrations of iron oxide nanoparticles (NPs) can induce quick melting but is detrimental to the mechanical properties of the polymer. To reduce the amount of NPs required for achieving efficient melting, they should be well dispersed in the polymer. In this study, the oleic acid loading on the surfaces of the NPs was varied to study the effect of variations in coatings on the dispersion in the polymer and on the polymer melting time. The NPs functionalized with oleic acid were added to melted monomer e-caprolactam and polymerized using ring-opening polymerization. The resulting PA6 nanocomposite was characterized by Fourier-transform infrared spectroscopy, differential scanning calorimetry, x-ray diffraction and transmission electron microscopy. The results confirmed that the PA6 nanocomposite showed a decrease of 8-10% in its glass-transition temperature compared to commercial PA6. The crystallinity of the synthesized samples were found to vary between 42% and 57%. The 55 wt.% oleic acid-loaded NPs were found to disperse most efficiently in the PA6 matrix; however, some large agglomerates were formed due to excessive oleic acid. Therefore, the 22 wt.% oleic acid coating showed overall superior dispersion. Additionally, the magnetic induction response was tested by observing a melt-characteristic of the magnetic polymer composite using a model setup. Oleic acid concentration is found to affect the dispersion, melting time and crystallinity of the nanocomposite.

Continuous fibre reinforced thermoplastic composites are increasingly finding their use as engineering materials in many industries due to the excellent fire, smoke and toxicity performance. However, the composite component produced using automated continuous fibre reinforced thermoplastic tapes laying machine are susceptible to sudden failure emanating from microscale cracks. This study demonstrates the healing potential of a layered Glass Fibre Reinforced Polymer (GFRP) composite consisting of alternative layers of GFRP and a magnetic polyamide-6 (PA-6) nanocomposite (PNC) film. The self-healing process is presented in three steps, viz. (i) polymer nanocomposite synthesis, (ii) preparation of the layered GFRP layered composite sample and (iii) selfhealing and testing of GFRP layered composite sample. Firstly, the multilayer dog bone sample consisting of a magnetic polymer nanocomposite (PNC) film sandwiched between thermoplastic unidirectional GFRP tapes are prepared. Healing is triggered by exposing the damaged multilayer sample to microwave causing selective heating of nanocomposite film and its subsequent melting. The healing process completes when liquid polymer fills the micro-crack in the multilayer tape through capillary action and solidifies upon cooling. The healing yields 84% of the undamaged tensile strength recovery. Results demonstrate the potential application of an autonomous self-healing method for thermoplastic composite used in the offshore environment.

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A polymer−metal oxide nanocomposite is a key in developing a high-temperature insulation material for power electronics and high-voltage direct current (HVDC) and medium-voltage direct current (MVDC) subsea cables having the capability of transmitting offshore renewable energy with lower losses and higher reliability. To achieve a higher operation voltage level and larger power capacity at a reduced cable size, weight, and volume, the lighter material offering improved electrical insulation at a high operating temperature is required. Addition of metal oxide ceramics in the polymer is shown to improve the insulating properties of the polymer used in the cable and power electronic applications; however, their performance deteriorates at elevated temperatures as thermal energy facilitates the electron injection to the bulk material by following conduction according to the Schottky emission. In this work, the heat insulating Al 2 O 3 nanoparticles are added to the MgO−polyethylene nanocomposite to observe the effect of the interface between mix oxide nanoparticles on current density and breakdown strength of the nanocomposite compared to the MgO−polyethylene nanocomposite at room and elevated temperatures (90 °C). The concentrations of the MgO and MgO + Al 2 O 3 mixture were varied from 1 to 12 wt % to find out that the nanocomposite containing MgO showed the best response than MgO + Al 2 O 3 at elevated and room temperatures. There was no unified trend observed in the leakage current density and breakdown strength results for the MgO + Al 2 O 3 nanocomposite, indicating the absence of the interface formation between MgO and Al 2 O 3 . The decrease in the interaction radius, calculated using numerical simulation of the nanoparticle dispersion state, resulted in the high breakdown strength. Addition of 12 wt % MgO helped achieving the highest breakdown strength, but overall breakdown strength for the MgO + Al 2 O 3 nanocomposite improved at elevated temperatures. All nanocomposites showed improved electrical insulating properties compared to virgin low-density polyethylene (Pure LDPE) .

The growing demand and diversity in the application of industrial composites and the current inability of present non-destructive evaluation (NDE) methods to perform detailed inspection of these composites has motivated this comprehensive review of sensing technologies. NDE has the potential to be a versatile tool for maintaining composite structures deployed in hazardous and inaccessible areas, such as offshore wind farms and nuclear power plants. Therefore, the future composite solutions need to take into consideration the niche requirements of these high-value/critical applications. Composite materials are intrinsically complex due to their anisotropic and non-homogeneous characteristics. This presents a significant challenge for evaluation and the associated data analysis for NDEs. For example, the quality assurance, certification of composite structures, and early detection of the failure is complex due to the variability and tolerances involved in the composite manufacturing. Adapting existing NDE methods to detect and locate the defects at multiple length scales in the complex materials represents a significant challenge, resulting in a delayed and incorrect diagnosis of the structural health. This paper presents a comprehensive review of the NDE techniques, that includes a detailed discussion of their working principles, setup, advantages, limitations, and usage level for the structural composites. A comparison between these techniques is also presented, providing an insight into the future trends for composites’ prognostic and health management (PHM). Current research trends show the emergence of the non-contact-type NDE (including digital image correlation, infrared tomography, as well as disruptive frequency-modulated continuous wave techniques) for structural composites, and the reasons for their choice over the most popular contact-type (ultrasonic, acoustic, and piezoelectric testing) NDE methods is also discussed. The analysis of this new sensing modality for composites’ is presented within the context of the state-of-the-art and projected future requirements.