Crack Pinning Research Articles

Toughening effect and mechanisms of AlN whiskers on a low‐temperature sintered AlNw/AlN ceramics

AbstractConventional aluminum nitride (AlN) ceramics exhibited insufficient mechanical properties expected from their potential applications in the presence of dynamic loads and intensive stresses caused by thermal shock. In this study, the mechanical properties of AlN ceramics were enhanced by toughening them using AlN whiskers (AlNw) via gel casting followed by low‐temperature sintering at 1650°C. The addition of AlNw simultaneously increased the bending strength, toughness and thermal conductivity of the AlN ceramics. The maximum values of the bending strength, toughness, and thermal conductivity of 9.0 wt% AlNw/AlN were 303.92 MPa, 3.92 MPa·m1/2 and 186.53 W·m−1·K−1, respectively, which were higher than those of the AlN ceramics by 39.93%, 61.31% and, 15.61%, respectively. The AlNw in AlNw/AlN ceramics tightly bonded with the ceramic matrix, leading to two characteristic toughening mechanisms in the ceramics: crack pinning and deflection at irregular grain boundaries caused by doped whiskers, as well as bridging and stress relaxation caused by whiskers incorporated with the grains. Moreover, the one‐dimensional morphology of AlNw can provide a channel for quick photon transport, thereby enhancing the thermal conductivity of AlNw/AlN.

Synergic effects of silica aerogel (SA) particles on tensile behavior of cryo-conditioned epoxy: The role of particle morphology and mixing sequence

Cryogenic conditions are of crucial importance for gas storage tanks to provide increased storage density, reduced pressure requirements and minimized energy losses. Incorporation of silica aerogel (SA) particles as a nanostructured material with extremely low density and exceptional thermal insulating properties into epoxy matrices has the potential to facilitate the progress of high performance nanocomposite coatings for advanced cryogenic applications. The objective of this study is therefore to investigate the impacts of particle size, particle content, milling method and mixing sequence on toughness of the cryo-conditioned epoxy coatings. SA particles of varying size (50 μm to 300 μm) were prepared using two different techniques (planetary ball milling vs. 2-blade grinding). Nanocomposite samples were prepared using two distinct mixing sequences, i.e., adding particles (in 0, 0.5, 1 and 1.5%wt.) to epoxy followed by mixing with hardener or adding particles to epoxy/hardener (with 3 or 15 min delay). The nanocomposite samples were subjected to different cryogenic conditions (single 3-h immersion in liquid nitrogen vs. three consecutive 1-h immersions). Mechanical properties of the samples were evaluated by conducting fractography, dynamic mechanical thermal analysis (DMTA) and tensile tests. Large SA particles settled towards the bottom of nanocomposite and resulted in loss of mechanical properties at cryo-conditions. Mixing 1 wt% of optimized SA particles with epoxy/hardener system led to an enhanced tensile strength (26 %), stiffness (3 %) and toughness (71 %) by providing uniform cross-linking reactions and mitigating thermal shock effects at cryo-conditions. Toughening mechanisms included crack deflection, crack pinning, crack arrest and crack branching.

Soft, Tough, Antifatigue Fracture Elastomer Composites with Low Thermal Resistance through Synergistic Crack Pinning and Interfacial Slippage.

Soft elastomer composites are promising functional materials for engineer interfaces, where the miniaturized electronic devices have triggered increasing demand for effective heat dissipation, high fracture energy, and antifatigue fracture. However, such a combination of these properties can be rarely met in the same elastomer composites simultaneously. Here a strategy is presented to fabricate a soft, extreme fracture tough (3316J m-2) and antifatigue fracture (1052.56J m⁻2) polydimethylsiloxane/aluminum elastomer composite. These outstanding properties are achieved by optimizing the dangling chains and spherical aluminum fillers, resulting in the combined effects of crack pinning and interfacial slippage. The dangling chains that lengthen the polymer chains between cross-linked points pin the cracks and the rigid fillers obstruct the cracks, enhancing the energy per unit area needed for fatigue failure. The dangling chains also promote polymer/filler interfacial slippage, enabling effective deflection and blunting of an advancing crack tip, thus enhancing mechanical energy dissipation. Moreover, the elastomer composite exhibits low thermal resistance (≈0.12K cm2 W-1), due to the formation of a thermally conductive network. These remarkable characteristics render this elastomer composite promising for application as a thermal interface material in electronic devices.

In Situ Processing to Achieve High-Performance Epoxy Nanocomposites with Low Graphene Oxide Loading

Modifying the polymer matrix by nanoparticles can be a promising approach to improve the performance of fiber-reinforced polymer (FRP) composites. Organic solvents are usually used for dispersing graphene oxide (GO) well in the polymer matrix. In this study, a green, facile, and efficient approach was developed to prepare epoxy/GO nanocomposites. In situ polymerization is used for synthesizing nanocomposites, eliminating the need for organic solvents and surfactants. By loading just 0.6 wt% of GO into the epoxy resin, Young’s modulus, tensile strength, and toughness improved by 38%, 46%, and 143%, respectively. Fractography analysis indicates smooth fracture surfaces of pure resin that changed to highly toughened fracture surfaces in this nanocomposite. Plastic deformation, crack pinning, and deflection contributed to improving the toughness of the nanocomposites. FTIR investigations show that amide bonding was created by the reaction of the carboxylic acid groups in GO with some amine groups in the curing agent during the dispersion processes.

Effect of molybdenum disulfide functionalized multiwalled carbon nanotubes based hybrid on morphology, mechanical and thermal properties of epoxy nanocomposites

AbstractThree‐dimensional molybdenum disulfide (MoS2) functionalized MWCNTs hybrid nanoparticles were synthesized using in‐situ hydrothermal reaction. Two types of hybrids, MoS2/MWCNTs‐1 and MoS2/MWCNTs‐2 with MWCNTs to MoS2 precursor weight ratios 1:2 and 1:1 respectively were prepared with varying degrees of hybridization and the effects of their incorporation on tensile strength and fracture toughness properties of epoxies were investigated. Epoxy/MoS2/MWCNTs‐2 nanocomposites showed exceptional mechanical properties due to their improved dispersion, constrained chain mobility and excellent interfacial interactions. MoS2/MWCNTs‐2 nanocomposites showed maximum improvement of tensile strength by 28.52% at 0.5 wt% nanofiller concentration and the highest improvements in fracture toughness by 172% at 0.2 wt% nanofiller concentration. The excellent enhancement of fracture toughness properties was due to the synergic effect of MoS2/MWCNTs hybrid nanoparticles due to the crack pinning and bifurcation properties of MoS2 nanoparticles along with the pull‐out and crack bridging mechanisms of MWCNTs as observed in morphological analysis of fractures nanocomposites. The incorporation of 0.2 wt% of MoS2/MWCNTs‐2 increased the degradation temperatures of epoxy from 591 to 796°C at 95% weight loss due to the improved physical barrier effect.Highlights MoS2/MWCNTs nanoparticles were synthesized using in‐situ hydrothermal reaction 0.5 wt% MoS2/MWCNTs‐2 incorporated epoxies showed highest tensile strength 0.2 wt% MoS2/MWCNTs‐2 incorporated epoxy composites show improved K1c value Incorporation of MoS2/MWCNTs improved the thermal stability of epoxy Synergistic effect of nanocomposite due to crack pinning, bifurcation & bridging

Construction of multileveled and oriented micro/nano channels in Mg doped hydroxyapitite bioceramics and their effect on mimicking mechanical property of cortical bone and biological performance of cancellous bone

Drawing on the structure and components of natural bone, this study developed Mg-doped hydroxyapatite (Mg-HA) bioceramics, characterized by multileveled and oriented micro/nano channels. These channels play a critical role in ensuring both mechanical and biological properties, making bioceramics suitable for various bone defects, particularly those bearing loads. Bioceramics feature uniformly distributed nanogrooves along the microchannels. The compressive strength or fracture toughness of the Mg-HA bioceramics with micro/nano channels formed by single carbon nanotube/carbon fiber (CNT/CF) (Mg-HA(05-CNT/CF)) are comparable to those of cortical bone, attributed to a combination of strengthened compact walls and microchannels, along with a toughening mechanism involving crack pinning and deflection at nanogroove intersections. The introduction of uniform nanogrooves also enhanced the porosity by 35.4 %, while maintaining high permeability owing to the capillary action in the oriented channels. This leads to superior degradation properties, protein adsorption, and in vivo osteogenesis compared with bioceramics with only microchannels. Mg-HA(05-CNT/CF) exhibited not only high strength and toughness comparable to cortical bone, but also permeability similar to cancellous bone, enhanced cell activity, and excellent osteogenic properties. This study presents a novel approach to address the global challenge of applying HA-based bioceramics to load-bearing bone defects, potentially revolutionizing their application in tissue engineering.

A new platform for designing high‐performance epoxy film adhesive with poly (butyl acrylate‐block‐styrene) block copolymer and alumina nano particles in aluminum–aluminum bonded joints: Preparation and analysis of the mechanical, adhesion, and thermal properties

AbstractEpoxy film adhesives are typically used in different industries. However, these adhesives suffer from brittleness, low flexibility, and thermal stability problems. In this research, phenolic resin (Novolac) and poly (butyl acrylate‐block‐styrene) were used in the formulation of epoxy film adhesive (Diglycidyl ether bisphenol A) to increase thermal stability and adhesion strength and as the toughening agent, respectively. Alumina nanoparticles were also employed to enhance the mechanical properties. The influence of block copolymer and alumina nano particles was also assessed on the mechanical and thermal properties of epoxy‐based film adhesives. The investigation of the mechanical properties of dumbbell‐shaped samples and adhesion strength of the Al‐Al bonded joints were evaluated by tensile, lap shear, and T‐peel tests. The thermal stability of the optimal samples was assessed by thermogravimetry analysis (TGA). SEM analysis was also utilized to study the toughening mechanism. Tensile test of the dumbbell‐shaped samples indicated that the incorporation of 2.5 phr block copolymer and 2 phr alumina nanoparticles enhanced the toughness to 250%. The shear and peel strengths of this sample also exhibited 51% and 76% increase, respectively, showing a remarkable synergistic effect. On the other hand, TGA results revealed that the incorporation of block copolymer improved the thermal stability of the adhesive matrix. The copresence of these two materials also showed a considerable synergistic effect on the thermal stability. The SEM results were also in line with the results of mechanical tests as the crack deviation, crack pinning, and debonding were the most important mechanisms of toughening.Highlights A new platform was developed for designing epoxy films adhesives with high mechanical, adhesion, and thermal properties. The hybrid of butyl acrylate block styrene copolymer, phenolic resin, and alumina nanoparticles showed synergistic effects on the lap shear and T‐peel strength. The greatest improvement in toughness was related to the epoxy adhesive containing 2.5 phr block copolymer and 2 phr alumina nanoparticles. Analysis of the fracture surface showed that by using hybrid of nanoparticles and block copolymers in the epoxy film adhesive formulation, the cohesive failure occurred. The use of hybrid additives in film adhesive formulations enlightened manufacture of adhesives for future studies on adhesive formulations.

Polydopamine chelating strontium on graphene oxide enhances the mechanical and osteogenic induction properties of PLLA/PGA bone scaffold

Poly (lactic acid)/poly (glycolic acid) (LG) bone scaffold exhibits good biocompatibility for bone defect regeneration but lacks satisfactory mechanical and osteogenic induction properties. Here, graphene oxide (GO) was encapsulated by polydopamine (PDA) via self-polymerization of dopamine, and strontium (Sr) was loaded onto GO by the chelation of PDA. The modified GO was added to the LG scaffold prepared via selective laser sintering as a reinforcing phase to improve the mechanical properties and osteogenic induction properties. The results indicated that the tensile and compressive strengths of the scaffold with 1.5 wt% modified GO were 9.49 MPa and 19.22 MPa, respectively, representing 67.08% and 95.33% improvement compared to the LG scaffold. The enhancement mechanisms of the modified GO in the scaffold included crack branching, crack deflection, crack pinning, crack bridging, and pulling out. More importantly, the scaffold with modified GO exhibited superior bioactivity and osteogenic induction properties compared to the LG scaffold, because PDA could chelate calcium ions derived from the surrounding physiological environment, and the calcium ions attracted phosphate ions through electrostatic interactions to promote the apatite layer deposition. Additionally, the presence of Sr in the scaffold promoted the proliferation and differentiation of osteoblasts, thereby improving osteogenic induction properties.

Influence of miscibility of PEG-B-PPG-B-PEG/EPOXY systems on thermal, mechanical and fracture properties

Epoxy matrix blends with poly (ethylene glycol)-block-poly (propylene glycol)-block-poly (ethylene glycol) triblock copolymer (PEG-b-PPG-b-PEG) with 30% PEG blocks were elaborated and investigated. The systems were prepared by the casting method with cure at 100 °C, with different amounts of copolymer in the epoxy matrix, and with the aim of evaluating the influence of the modifier on the properties of the blends. By DSC it was verified that the glass transition temperature relating to the matrix phase decreased in systems with copolymer in relation to neat epoxy, thus the blends formed partially miscible systems. On the other hand, phases separation or microdomains of the block copolymer within the epoxy matrix were not discernible by scanning electron microscopy. In general, the addition of the block copolymer impaired the mechanical properties evaluated in the tensile test. However, the fracture mechanisms observed on the fracture surface of the blends indicate that an improvement in the toughness of the systems may have occurred due to the crack pinning and crack deflection mechanisms.

Pinning cracks by microstructure design in brittle materials

In this work, we explore the possibility of controlling toughening mechanisms in brittle materials through microstructure design to enhance their resistance to crack growth. First, a computational framework is established using the distinct element method (DEM) with J integral implemented to simulate complex crack propagation and characterize the effective fracture energy of brittle materials. The fracture behavior of a soda-lime glass plate containing pre-existing voids under tensile loading is simulated, and toughening mechanisms associated with the existence of voids, including blunting-induced pinning and deflection-induced pinning, are identified in brittle materials. Then we seek to modulate the fracture toughness of brittle materials by introducing either randomly distributed voids or sinusoidally distributed voids and controlling the pinning events. Our findings reveal that randomly distributed voids with different volume fractions induce only modest toughening in brittle materials. Sinusoidally distributed voids with specific amplitude and wavelength trigger both crack blunting and deflection in the vicinity of voids, increasing the probability of crack pinning and leading to a significant increase in crack growth resistance. Moreover, we identify the critical conditions for the “embrittlement-toughening transition” and “maximized toughening”. Finally, we discuss the difference between void toughening for brittle materials and ductile materials due to distinct toughening mechanisms activated, and also extend the toughening strategy to nacre-like materials. The stairwise herringbone structure is demonstrated to be a promising candidate for structure optimization due to unique stiffness, strength, and toughness.

Carburization and tensile behavior of Alloy 617 in impure helium containing a part-per-million level of CH4 at 950 °C

The carburization and tensile behavior of Alloy 617 corroded at 950 °C for 100 h in the impure helium containing methane were investigated. In helium containing 20 ppm CH4, Alloy 617 exhibited slight carburization and held its plasticity. However, in helium containing 200 ppm CH4, Alloy 617 was carburized to a depth of over 20 % and lost plasticity. In addition, the stress-strain curves in the plastic phase at room temperature exhibited a serrated flow phenomenon in both two environments, primarily caused by dynamic interactions between carbide-induced crack pinning and stress-concentration-induced crack unpinning.

EPOXY-SILICA NANOCOMPOSITE: CREEP RESISTANCE AND TOUGHENING MECHANISMS

In this article, the effect of modified nanosilica (m-nanosilica) on the mechanical and creep performance of epoxy resin were investigated. At the same time, the toughnening mechanisms of epoxy resin with m-nanosilica were also considered. The results show that the crack pinning and crack deflection mechanism contributes only a small part to nanocomposite, this due to the size of the nanosilica particles is such smaller than crack-opening displacement. The FE-SEM surface fracture shows evidence of the debonding of the nanoparticles from the polymer matrix and the expansion of the holes around the nanoparticles as well as the existence of the plastic deformation zone. Plastic deformation and plastic void growth are the main toughening mechanism in nanocomposite material.

Introducing a new approach for designing advanced epoxy film adhesives with high mechanical, adhesion, and thermal properties by adding hybrid additives for structural bonding

BackgroundEpoxy-based adhesives are widely used in different industries in various forms. Among them, epoxy film adhesives are particularly applicable in constructing honeycomb structures in aerospace systems. However, these adhesives suffer from brittleness, low flexibility, and thermal stability. In the current paper, the effect of pure and functionalized SiO2 and ZrO2 nanoparticles (NPs), the addition of a block copolymer (butyl acrylate-block-styrene), and Novolac resin on the mechanical, thermal, and adhesive properties of the epoxy film adhesive were thoroughly studied. MethodsThe mechanical properties, thermal stability, and surface morphology of the epoxy adhesive samples were evaluated using tensile, thermogravimetric analysis (TGA), and field emission scanning electron microscopy (FE-SEM) images, respectively. More importantly, the Lap shear and Peel tests were utilized to investigate the adhesive properties. Significant findingsPure and functionalized NPs were added to the prepared epoxy adhesive samples. Intriguingly, compared to the non-functionalized NPs, by only adding 1 phr of each functionalized NPs to the formulation, the tensile modulus, tensile strength, and toughness increased to 66 %, 197 %, and 553 %, respectively. More importantly, the single lab shear and T-peel strength were increased as high as 121 % and 101 %, respectively, indicating a synergistic effect. After optimizing the parameters effective on the properties, FE-SEM images of the fractured surface of optimized samples were used to study the possible fracture mechanisms, including crack deflection, crack pinning, nanoparticle debonding, and shear band formation. Also, this synergistic effect was observed in the thermal stability where the only addition of 1 phr of functionalized NPs increased the decomposition onset temperature up to 40 ℃ higher than the neat one. This simple and applicable method can pave the way for using functionalized NPs in modifying epoxy adhesives.

R-Curve Behavior of Polyhedral Oligomeric Silsesquioxane (POSS)–Epoxy Nanocomposites

Polyhedral oligomeric silsesquioxane (POSS) is a suitable nanoscale reinforcement for thermosetting polymers, such as epoxy resin systems in order to modify its mechanical, thermal and chemical properties. The inclusion of POSS in the epoxy resin at higher loading (greater than 1 wt.%); however, it introduces the ductility during the fracture behavior of these nanocomposites. Consequently, the J-integral is used to quantify the fracture behavior of these materials and characterize the crack growth resistance curve against stable crack growth. A range of nanocomposites is prepared by adding 0.5, 1, 3, 5, and 8 wt.% of glycidyl POSS into DGEBF epoxy resin cured with an amine-based curing agent. From fracture toughness experiments, the load-displacement result confirms that when the POSS reinforcement is greater than 1 wt.%, the fracture behavior of the nanocomposite changes from brittle to ductile. For both brittle and ductile nanocomposites, the addition of POSS molecules improves the crack initiation toughness. The development of POSS–POSS compliant domains, reported previously, is responsible for this change in the failure behavior. The fractured images of POSS–epoxy nanocomposites, obtained by using scanning electron microscopy, show that the increase in fracture resistance at higher values of POSS loading occurs due to the extensive shear yielding. Meanwhile, the increased fracture toughness at lower values of POSS loading occurs due to crack pinning and crack deflection.

Ballistic behaviour of nanosilica and rubber reinforced kevlar/epoxy composite targets

The ballistic performance of Kevlar/Epoxy composites reinforced with nanosilica and liquid rubber has been investigated. The individual and synergistic effects of these reinforcements on the ballistic performance of the composite target were determined. Surface hardened 10 mm diameter conical nosed projectiles with 125 m/sec velocity were used for the initial ballistic test. Three mm thick specimens with six different combinations were tested. Nine mm FMJ projectiles at 430 ± 15 m/sec were used for the ballistic testing at a higher velocity with four different target thicknesses. The mechanical properties of the nanofillers intruded composite showed the highest improvement. The lower velocity ballistic impact experiments also indicated a higher ballistic resistance for the stacked composite. The conjoint matrix toughening actions of nano-silica and rubber particles through crack pinning, crack deflection and rubber cavitation provided the necessary resistance. The target thickness of 10 mm of this optimum combination was able to prevent the projectile’s penetration.

Vertical and uniform growth of MoS2 nanosheets on GO nanosheets for efficient mechanical reinforcement in polymer scaffold

ABSTRACT Graphene oxide (GO) and molybdenum disulphide (MoS2), have drawn more and more attention as reinforcement in polymer. However, their large specific surface area and strong van der Waals forces result in serious aggregations in polymer matrix, which restrains the reinforcement effect. In this study, MoS2 nanosheets were in situ synthesised vertically and uniformly on the surface of GO nanosheets with the help of a hexadecyl trimethyl ammonium bromide (CTAB) assisted hydrothermal process to facilitate their dispersion in polylactic acid (PLLA) scaffold manufactured via selective laser sintering (SLS). The experimental results revealed that the 1.5 wt% GO/MoS2 nanocomposite exhibited better dispersion state compared with the 1.5 wt% GO and 1.5 wt% MoS2 in PLLA matrix. Therefore, the PLLA scaffold loading 1.5 wt% GO/MoS2 presented 10.2 and 1461 MPa of tensile strength and modulus with enhancement of 61% and 58%, respectively, compared with the pure PLLA scaffold. The reinforcement mechanisms mainly included crack deflection, crack bridging, crack pinning and pulling out of GO/MoS2. What’s more, the GO/MoS2-PLLA scaffold possessed benign cytocompatibility for cell behaviour, suggesting hopeful applications in bone defect repair.

MWCNT and nano-silica hybrids effect on mechanical and fracture characterization of single lap joints of GFRP plates

The current study aimed to explore the effects of nanoparticle hybridization on the shear and flexural performance of single lap joints (SLJs) of glass fiber reinforced polymer (GFRP) substrates. To this end, the hybridizations of multi-walled carbon nanotubes (MWCNT) and silica nanoparticles at various concentration rates were incorporated into the epoxy adhesive. Three-point bending tests and single-lap shear tests were performed to analyze in detail the effects of hybrid nanoparticle inclusions on adhesion performance under different loads. The maximum values for both shear and flexural strengths were achieved from the samples containing the combination of 0.5 wt.% MWCNT and 0.25 wt.% Nano-silica particles. The enhancements in shear strength and flexural strength were 45.4% and 63.2%, respectively, compared to pure samples. Furthermore, damage surfaces were examined via scanning electron microscopy (SEM) to investigate fracture mechanisms and failure modes. The findings demonstrated that almost all nanoparticle-doped samples, regardless of hybrid or single nanoparticle, exhibited higher load-bearing capability by increasing the adhesion ability of the additive and the adhesive. It was observed that the failure mechanisms such as crack deviation, crack pinning, pull out, bridging, etc. occurred in the nanoparticle doped adhesive joints as seen in SEM images.

Simultaneously stiffening and toughening epoxy by urea treated hydroxylated halloysite nanotubes

Epoxy and its composites have been extensively applied in widespread applications, such as encapsulation of electronics, automobile parts, aircraft components, and so on. The stiffening and toughening of epoxy via the incorporation of nanofillers, such as halloysite nanotubes (HNTs), a naturally occurring and low-cost aluminosilicate, have attracted increasing research attention. Herein, we introduce an effective and facile method that substantially enhances the interface of hydroxylated HNTs (h-HNTs) and epoxy matrix by the introduction of urea molecules. As confirmed by the characterization results, urea formed hydrogen bonds with the external surface of the h-HNTs and covalent bonds with the epoxy matrix. The resultant epoxy/h-HNT-urea nanocomposites exhibited significant enhancements simultaneously in tensile strength, Young's modulus, and fracture toughness by 23.4%, 31.4%, and 61.4%, respectively, as compared with the neat epoxy. Through systematic investigation, it was determined that micro-cracking, nanotube bridging, and crack pinning were responsible for the toughening of the epoxy/h-HNT-urea nanocomposites.

Simultaneously improved corrosion/wear resistances of epoxy coating on Mg alloy via the coupled hybridization of GO and nano-SiO2

The extensive application of Mg alloys is restricted by their poor corrosion, wear resistances and long-term service performance. Although the low-cost epoxy (EP) coating has excellent corrosion resistance, many pores and cracks are easily formed during the curing process, leading to the deterioration of barrier capacity. This study reports an epoxy-based nanocomposite coating, fabricated through the hybridization of γ-(2, 3-epoxypropoxy) propytrimethoxy silane modified silica nanoparticles and graphene oxide (mSiO2/GO). The insulating SiO2 particles can isolate the direct contact between Mg alloy substrate and GO sheets, avoiding the formation of micro-cells and preventing the galvanic corrosion. The SiO2/GO in EP coating with “crack pinning and bridge” structure has reduced porosity and enhanced consistency, which effectively prevents crack propagation and electrolyte penetration. The corrosion rate of SiO2/GO/EP coating is 374 and 10 times lower than that of pure EP coating and individual GO/EP coating, respectively. The wear rate of GO/EP and SiO2/GO/EP coating specimens is 81.2 % and 70.4 % less than that of the pure EP coating, which is related to the favorable lubricating performance and high hardness of GO nanosheets. The results show that the embedding of well-distributed mSiO2-GO hybrids can remarkably improve the barrier effect and anti-corrosion of EP coating.

Self-healing of matrix cracking and delamination damage assessment in microcapsules reinforced carbon fibre epoxy composite under flexural loading

Structural integrity of micro cracked CFRP composite structures can be re-established by incorporating the microcapsules based self-healing system into the composite. In the current study, in order to fabricate capsules reinforced CFRP composite, 0.54: 0.39: 0.07 vol fractions of matrix, carbon fibre and separately encapsulated epoxy, hardener microcapsules were employed. Effect of microcapsules addition and induced damage on the flexural strength of the composite were investigated. It was noticed that flexural strength decreases with the increase in capsules concentration and for 5 wt% capsules reinforced composite flexural strength reduced by 21.73%, 29.32% due to induce of matrix cracking and delamination damage respectively. In order to assess self-healing performance of the composite, different damage events were induced in the composite and healing efficiency was evaluated based on the recovery in flexural strength. Effect of capsules wt%, healing temperature and pressure on the healing efficiency were assessed and noticed higher healing efficiencies at elevated temperature and pressure healing conditions. Healing efficiencies of 71.30%, 54.21% were obtained at optimal healing conditions for matrix cracking, delamination damage recovery respectively. Crack path deflection, crack pinning and capsules rupture mechanisms were observed in the microstructural investigation of fracture surface of capsule reinforced composite.