Composites with aligned carbon nano-reinforcements: synergistically improving the damage tolerance and detection

Advanced fibre-reinforced polymer composites offer numerous advantages over metallic alloys, including higher specific strength and stiffness, resistance to corrosion damage and fatigue cracking. However, in the absence of through-thickness reinforcement, laminated composite materials are susceptible to interlaminar and intralaminar delamination damage due to accidental impact from bird strikes, hailstones, and tools dropped during maintenance. In addition, the low through-thickness conductivity of composites and its bonded structure presents challenges in protecting of aircraft against lightning strikes and detection of damage using traditional electrical based non-destructive techniques. In light of these challenges this PhD project investigated the effects of carbon nano-reinforcements alignment on the fracture and electrical properties of epoxy composites. The alignment of the nano-reinforcements was investigated using two different external field based techniques, namely electric-field and magnetic-field. The carbon nano-reinforcements used for the investigations include one-dimensional carbon nanofibres (CNFs) and two-dimensional graphene nanoplatelets (GNPs). The project explores key parameters for reinforcing the epoxy composites with carbon nano-reinforcements, including their weight content, shape (one-dimensional and two-dimensional), orientation (random and aligned), and alignment techniques (electric- and magnetic-field). The PhD also investigates the influence of the alignment of CNFs on the damage detection ability of the CNF-reinforced epoxy adhesive bonded composite joints. The study showed that the addition of just 1.0 wt% of aligned CNFs and GNPs increase the fracture energy of their epoxy nanocomposites by about eleven and seven fold, respectively. A mechanistic model is presented to quantify the contributions from the different toughening mechanisms induced by CNF and GNP nano-reinforcements which lead to the dramatic improvements in fracture toughness of the nanocomposites. The CNF-reinforced epoxy composites also showed a greater resistance to fatigue cracking when subjected to cyclic loading. The improved fatigue resistance of CNF-epoxy nanocomposites was due to a combination of intrinsic and extrinsic toughening mechanisms induced by the CNFs. In addition, the alignment of the nano-reinforcements also increased the electrical conductivity and simultaneously lowered the percolation threshold necessary to form a conductive network in the nanocomposites. Compared to the unmodified epoxy, the improvements in electrical conductivity of the nanocomposites with aligned CNFs and GNPs were increased by about ten and seven orders of magnitude, respectively. The improved electrical conductivity of the CNF-reinforced epoxy enabled real-time in-situ detection of fatigue cracking using a DC potential drop technique. A further study investigated the effects of using through-thickness nano-scale (CNFs) and micro-scale (z-pin) carbon reinforcements on the delamination resistance of carbon fibre-epoxy laminates. The delamination toughness of the composite laminate reinforced concurrently with CNFs and z-pins increased (by about 400%) in comparison to the control laminate, suggesting a synergistic toughening mechanism. The new class of fibre composites with multi-scale through-thickness reinforcements offers a unique opportunity to greatly enhance the damage tolerance and its detection in advanced fibre composite materials

Formulation, evaluation and optimization of stomach specific in situ gel of clarithromycin and metronidazole benzoate

The present investigation deals with the formulation, optimization and evaluation of sodium alginate based In situ gel of Clarithromycin and Metronidazole Benzoate. Sodium alginate used as a polymer and CaCO3 was used as a cross-linking agent. The In situ formulation exhibited well, viscosity, drug content and sustained drug release; this study reports that oral administration of aqueous solutions containing sodium alginate results in formation of In situ gel, such formulations are homogenous liquid when administered orally and become gel at the contact site. The results of a 32 full factorial design revealed that the concentration of sodium alginate and concentration of CaCO3 significantly affected the dependent variables Q1, Q12 and T80. These In situ gels are, thus, suitable for oral sustained release of Clarithromycin and Metronidazole Benzoate.Keywords: In situ gel; Stomach specific; Gastric residence time

Formulation, evaluation and optimization of stomach specific in situ gel of clarithromycin and metronidazole benzoate

The present investigation deals with the formulation, optimization and evaluation of sodium alginate based In situ gel of Clarithromycin and Metronidazole Benzoate. Sodium alginate used as a polymer and CaCO3 was used as a cross-linking agent. The In situ formulation exhibited well, viscosity, drug content and sustained drug release; this study reports that oral administration of aqueous solutions containing sodium alginate results in formation of In situ gel, such formulations are homogenous liquid when administered orally and become gel at the contact site. The results of a 32 full factorial design revealed that the concentration of sodium alginate and concentration of CaCO3 significantly affected the dependent variables Q1, Q12 and T80. These In situ gels are, thus, suitable for oral sustained release of Clarithromycin and Metronidazole Benzoate.Keywords: In situ gel; Stomach specific; Gastric residence time

Clinicoepidemiological study of fixed drug eruption in tertiary care hospital

Background: Adverse cutaneous drug reactions pose diagnostic difficulties due to a varied clinical manifestations and broad categories of causative agents. Fixed drug eruptions (FDE) are one of them. Present study aims i) to record various clinical features of FDE, their causative agents and ii) to study the pattern of morbidity in patients with FDE in a tertiary care hospital, Rajkot, Gujarat, India.Methods: The 88 patients with FDEs attending department of dermatology, venereology and leprosy at PDU govt. medical college and hospital, Rajkot, Gujarat from September 2018 to September 2020 were included after informed consent. After taking thorough history, complete blood count and biochemical tests were done. HIV testing was done in severe reactions with generalised involvement. Appropriate treatment was given with counselling regarding the offending drug for prevention of reaction in future.Results: The male patients were more affected than female patients with M: F ratio of 1.3:1. The most common age group affected was 21-30 years (22.7%). Antimicrobials were the most common offending drugs (43.2%). None of the patients were HIV reactive in our study. No mortality was reported in our study.Conclusions: The patterns of FDE and the causative drugs are remarkably different in our study. Knowledge of patterns and the causative agents helps in prevention of same reactions in future in patients

A novel route for tethering graphene with iron oxide and its magnetic field alignment in polymer nanocomposites

We present a new route for tethering graphene nanoplatelets (GNPs) with Fe3O4 nanoparticles to enable their alignment in an epoxy using a weak magnetic field. The GNPs are first stabilised in water using poly(vinylpyrrolidone) (PVP) and Fe3O4 nanoparticles are then attached via coprecipitation. The resultant Fe3O4/PVP-GNPs nanohybrids are superparamagnetic and can be aligned in an epoxy resin, before gelation, by applying a weak magnetic field as low as 0.009 T. A theoretical model describing the alignment process is presented. The resulting nanocomposites exhibit anisotropic properties with significantly improved electrical conductivities (three orders of magnitude) in the alignment direction and dramatically increased fracture energy (about 530%) when the nanohybrids are aligned transverse to the crack growth direction, compared with the unmodified epoxy. Compared with the randomly-oriented nanocomposites, these aligned nanocomposites show approximately 50% increase in toughness transverse to the alignment direction and a seven-fold increase in electrical conductivity in the alignment direction

On the recent cyclone lashed across Gujarat coast and its effect on marine flsheries sector

A heavy cyclonic wind crossed the coastal Gujarat on 9-6-'98 resulting in the destruction of life and property besides total disruptions of communication, electricity and water supply systems. The present report summarises the effect of this cyclone on the marine fishery sector of coastal Gujarat

Epoxy nanocomposites containing magnetite-carbon nanofibers aligned using a weak magnetic field

Novel magnetite-carbon nanofiber hybrids (denoted by "Fe3O4@CNFs") have been developed by coating carbon nanofibers (CNFs) with magnetite nanoparticles in order to align CNFs in epoxy using a relatively weak magnetic field. Experimental results have shown that a weak magnetic field (∼50 mT) can align these newly-developed nanofiber hybrids to form a chain-like structure in the epoxy resin. Upon curing, the epoxy nanocomposites containing the aligned Fe3O4@CNFs show (i) greatly improved electrical conductivity in the alignment direction and (ii) significantly higher fracture toughness when the Fe3O4@CNFs are aligned normal to the crack surface, compared to the nanocomposites containing randomly-oriented Fe3O4@CNFs. The mechanisms underpinning the significant improvements in the fracture toughness have been identified, including interfacial debonding, pull-out, crack bridging and rupture of the Fe3O4@CNFs, and plastic void growth in the polymer matrix

Sudden emergence of fishery and some aspects of biology and population dynamics of Aluterus monoceros (Linnaeus, 1758) at Veraval

The sudden emergence of a fishery and selected aspects of biology and population dynamics of Aluterus monoceros landed by trawlers at Veraval was studied from January 2008 to December 2009. Total catch of 475 t recorded in September 2009, which increased to 7042 t in October dominated in the trawl landings with a contribution of 29.5%. However, in November and December, the catch decreased sharply to 1374 t and 94 t, respectively. The combined length-weight relationship was log W = -1.50 + 2.694 log L (r = 0.86) (n = 222) indicating allometric growth. Sex ratio was 1:1.05 (n = 129). Females attained sexual maturity at 50.2 cm total length. Zoobenthos, dominated by benthic invertebrates, cnidarians and worms, zooplankton dominated by copepods and nekton dominated by Acetes spp. and clupeid juveniles were the major food items of A. monoceros. The von Bertalanffy growth equation was Lt = 63.53 [1 – e - 0.22 (t + 0.077)]. Natural mortality, fishing mortality and exploitation ratio were 0.53, 0.58 and 0.52 respectivel

Improving the toughness and electrical conductivity of epoxy nanocomposites by using aligned carbon nanofibres

There is an increasing demand for high performance composites with enhanced mechanical and electrical properties. Carbon nanofibres offer a promising solution but their effectiveness has been limited by difficulty in achieving directional alignment. Here we report the use of an alternating current (AC) electric field to align carbon nanofibres in an epoxy. During the cure process of an epoxy resin, carbon nanofibres (CNFs) are observed to rotate and align with the applied electric field, forming a chain-like structure. The fracture energies of the resultant epoxy nanocomposites containing different concentrations of CNFs (up to 1.6wt%) are measured using double cantilever beam specimens. The results show that the addition of 1.6wt% of aligned CNFs increases the electrical conductivity of such nanocomposites by about seven orders of magnitudes to 10-2S/m and increases the fracture energy, GIc, by about 1600% from 134 to 2345J/m2. A modelling technique is presented to quantify this major increase in the fracture energy with aligned CNFs. The results of this research open up new opportunities to create multi-scale composites with greatly enhanced multifunctional properties

Using carbon nanofibre sensors for in-situ detection and monitoring of disbonds in bonded composite joints

This paper focuses on the ability of carbon nanofibre (CNF) networks to in situ monitor fatigue induced disbond damage in adhesive bonded composite joints. The inclusion of CNFs in the epoxy adhesive increases its conductivity by five orders of magnitude. The improved electrical conductivity is utilized to evaluate the ability of the CNF network to monitor and detect the fatigue induced disbond damage by measuring the in-situ resistance changes using a four probe setup. The changes in total resistance was a function of the bulk electrical resistivity of the adhesive and the bond dimensions, which were related to the disbond length to model and determine the size of the disbond. The simple resistivity model was in good agreement with the resistance measured during fatigue testing. Good agreement was found between the optical disbond observations and the disbond length calculated using the proposed model. Finite element simulations were performed to ascertain the range of applicability of the proposed model. The simplicity of the disbond detection technique via direct current potential drop technique enables real time monitoring of crack growth in the composite structure