Influence of nanorubber toughening on the tensile deformation and tensile fatigue behaviour of a carbon fibre reinforced epoxy composite

This study investigates the effect of nanocarboxylic acrylonitrile butadiene rubber on the tensile fatigue behaviour of carbon fibre-reinforced polymer composites with dicyandiamide-cured epoxy matrix. The stress-controlled tension–tension fatigue behaviour at a stress ratio of R = 0.1 and maximum stresses between 400 MPa and 650 MPa was investigated for the case of carbon fibre-reinforced polymers with pristine and nanorubber-modified epoxy matrices with loadings of 5 phr, 10 phr, 15 phr and 20 phr. The results from the experimental tests show that the high-cycle fatigue life of the laminates with 15 phr of nanorubber-modified resin matrix was increased by a factor of two compared to the pristine matrix samples. Scanning electron microscopy images of the fracture surfaces also show an enhanced plastic deformation existing at the fibre–matrix interface and a lower extent of fibre pull-out; both contributing towards the enhancement of the fatigue performance of the carbon fibre-reinforced polymer composites. </jats:p

Enhancement of the electrical conductivity and interlaminar shear strength of CNT/GFRP hierarchical composite using an electrophoretic deposition technique

In this work, an electrophoretic deposition (EPD) technique has been used for deposition of carbon nanotubes (CNTs) on the surface of glass fiber textures (GTs) to increase the volume conductivity and the interlaminar shear strength (ILSS) of CNT/glass fiber-reinforced polymers (GFRPs) composites. Comprehensive experimental studies have been conducted to establish the influence of electric field strength, CNT concentration in EPD suspension, surface quality of GTs, and process duration on the quality of deposited CNT layers. CNT deposition increased remarkably when the surface of glass fibers was treated with coupling agents. Deposition of CNTs was optimized by measuring CNT’s deposition mass and process current density diagrams. The effect of optimum field strength on CNT deposition mass is around 8.5 times, and the effect of optimum suspension concentration on deposition rate is around 5.5 times. In the optimum experimental setting, the current density values of EPD were bounded between 0.5 and 1 mA/cm2. Based on the cumulative deposition diagram, it was found that the first three minutes of EPD is the effective deposition time. Applying optimized EPD in composite fabrication of treated GTs caused a drastic improvement on the order of 108 times in the volume conductivity of the nanocomposite laminate in comparison with simple GTs specimens. Optimized CNT deposition also enhanced the ILSS of hierarchical nanocomposites by 42%

Enhancement of fracture toughness of epoxy nanocomposites by combining nanotubes and nanosheets as fillers

In this work the fracture toughness of epoxy resin has been improved through the addition of low loading of single part and hybrid nanofiller materials. Functionalised multi-walled carbon nanotubes (f-MWCNTs) was used as single filler, increased the critical strain energy release rate, GIC, by 57% compared to the neat epoxy, at only 0.1 wt% filler content. Importantly, no degradation in the tensile or thermal properties of the nanocomposite was observed compared to the neat epoxy. When two-dimensional boron nitride nanosheets (BNNS) were added along with the one-dimensional f-MWCNTs, the fracture toughness increased further to 71.6% higher than that of the neat epoxy. Interestingly, when functionalised graphene nanoplatelets (f-GNPs) and boron nitride nanotubes (BNNTs) were used as hybrid filler, the fracture toughness of neat epoxy is improved by 91.9%. In neither of these hybrid filler systems the tensile properties were degraded, but the thermal properties of the nanocomposites containing boron nitride materials deteriorated slightly

Full-scale fatigue testing of a wind turbine blade in flapwise direction and examining the effect of crack propagation on the blade performance

In this paper, the sensitivity of the structural integrity of wind turbine blades to debonding of the shear web from the spar cap was investigated. In this regard, modal analysis, static and fatigue testing were performed on a 45.7 m blade for three states of the blade: (i) as received blade (ii) when a crack of 200 mm was introduced between the web and the spar cap and (iii) when the crack was extended to 1000 mm. Calibration pull-tests for all three states of the blade were performed to obtain the strain-bending moment relationship of the blade according to the estimated target bending moment (BM) which the blade is expected to experience in its service life. The resultant data was used to apply appropriate load in the fatigue tests. The blade natural frequencies in flapwise and edgewise directions over a range of frequency domain were found by modal testing for all three states of the blade. The blade first natural frequency for each state was used for the flapwise fatigue tests. These were performed in accordance with technical specification IEC TS 61400-23. The fatigue results showed that, for a 200 mm crack between the web and spar cap at 9 m from the blade root, the crack did not propagate at 50% of the target BM up to 62,110 cycles. However, when the load was increased to 70% of target BM, some damages were detected on the pressure side of the blade. When the 200 mm crack was extended to 1000 mm, the crack began to propagate when the applied load exceeded 100% of target BM and the blade experienced delaminations, adhesive joint failure, compression failure and sandwich core failure

Improving the fracture toughness properties of epoxy using graphene nanoplatelets at low filler content

This paper reports improvement in the fracture properties of epoxy nanocomposites using plasma functionalized graphene nanoplatelets (f-GNP) at low filler content. Various mechanical tests were performed on a series of f-GNP/epoxy at low nanofiller loading to assess the effect of the nanofiller on mechanical properties. Most importantly, a significant enhancement in fracture toughness is achieved without compromising the tensile and thermal properties of the nanocomposites. The fracture toughness of neat epoxy resin was increased by over 50% with the incorporation of 0.25 wt% f-GNP loading, obtaining a value of 245 J m−2, while the neat epoxy indicated a value of 162 J m−2. The glass transition temperature (Tg) and coefficient of thermal expansion (CTE) both showed a slight increase of 3% and 2%, respectively, both at 1 wt% f-GNP loading. These enhancements are competitive with current literature results on nanocomposites, but at significantly lower filler content. We therefore demonstrate that f-GNPs are capable of providing effective toughening of epoxy resins, while maintaining other tensile and thermal properties

Ballistic impact behaviour of glass fibre reinforced polymer composite with 1D/2D nanomodified epoxy matrices

In this paper, experimental studies on the ballistic impact behaviour of nanomodified glass fibre-reinforced polymer (GFRP) are reported. The epoxy matrix of the GFRP was modified by the addition of graphene platelets (GNPs), carbon nanotubes (CNTs), combined hybrid hexagonal boron nitride nanosheets (BNNS)/CNT, and combined boron nitride nanotubes (BNNTs)/GNPs nanoparticles. Ballistic impact tests were carried out on GFRP laminates at two projectile velocities of 76 ± 1 m s−1 for full-field deformation measurements and 134.3 ± 1.7 m s−1 for perforation tests. The behaviour of the plates during impact was recorded using digital image correlation (DIC), in order to monitor strain and out-of-plane deformation in panels with nanoreinforced matrices. Following penetrative impact tests, pulse thermography was used to characterise the delamination of impacted plates. The results of full-field deformation, exit velocity and energy absorption measurements from the ballistic tests show significant improvements in impact resistance for the panels made from nanomodified epoxies relative to laminates with the unmodified epoxy matrix. The highest absolute absorbed energy was observed for the GFRP panels fabricated using the epoxy matrix loaded with BNNT/GNP at 255.7 J, 16.8% higher than the unmodified epoxy matrix

CFD modeling of wind turbine blades with eroded leading edge

The present work compares 2D and 3D CFD modeling of wind turbine blades to define reduced-order models of eroded leading edge arrangements. In particular, following an extensive validation campaign of the adopted numerical models, an initially qualitative comparison is carried out on the 2D and 3D flow fields by looking at turbulent kinetic energy color maps. Promising similarities push the analysis to consequent quantitative comparisons. Thus, the differences and shared points between pressure, friction coefficients, and polar diagrams of the 3D blade and the simplified eroded 2D setup are highlighted. The analysis revealed that the inviscid characteristics of the system (i.e., pressure field and lift coefficients) are precisely described by the reduced-order 2D setup. On the other hand, discrepancies in the wall friction and the drag coefficients are systematically observed with the 2D model consistently underestimating the drag contribution by around 17% and triggering flow separation over different streamwise locations. Nevertheless, the proposed 2D model is very accurate in dealing with the more significant aerodynamics performance of the blade and 30 times faster than the 3D assessment in providing the same information. Therefore the proposed 2D CFD setup is of fundamental importance for use in a digital twin of any physical wind turbine with the aim of carefully and accurately planning maintenance, also accounting for leading edge erosion

On the extent of fracture toughness transfer from 1D/2D nanomodified epoxy matrices to glass fibre composites

Abstract: In this study, the effects of adding nanofillers to an epoxy resin (EP) used as a matrix in glass fibre-reinforced plastic (GFRP) composites have been investigated. Both 1D and 2D nanofillers were used, specifically (1) carbon nanotubes (CNTs), (2) few-layer graphene nanoplatelets (GNPs), as well as hybrid combinations of (3) CNTs and boron nitride nanosheets, and (4) GNPs and boron nitride nanotubes (BNNTs). Tensile tests have shown improvements in the transverse stiffness normal to the fibre direction of up to about 25% for the GFRPs using the ‘EP + CNT’ and the ‘EP + BNNT + GNP’ matrices, compared to the composites with the unmodified epoxy (‘EP’). Mode I and mode II fracture toughness tests were conducted using double cantilever beam (DCB) and end-notched flexure (ENF) tests, respectively. In the quasi-static mode I tests, the values of the initiation interlaminar fracture toughness, GICC, of the GFRP composites showed that the transfer of matrix toughness to the corresponding GFRP composite is greatest for the GFRP composite with the GNPs in the matrix. Here, a coefficient of toughness transfer (CTT), defined as the ratio of mode I initiation interlaminar toughness for the composite to the bulk polymer matrix toughness, of 0.68 was recorded. The highest absolute values of the mode I interlaminar fracture toughness at crack initiation were achieved for the GFRP composites with the epoxy matrix modified with the hybrid combinations of nanofillers. The highest value of the CTT during steady-state crack propagation was ~ 2 for all the different types of GFRPs. Fractographic analysis of the composite surfaces from the DCB and ENF specimens showed that failure was by a combination of cohesive (through the matrix) and interfacial (along the fibre/matrix interface) modes, depending on the type of nanofillers used