Shear Strength Research Articles

Identification of interfacial strength between carbon fiber and epoxy matrix in CFRP laminates using pulse laser spallation method

Carbon fiber reinforced plastics (CFRP) have high specific strength and specific stiffness and are used in various fields such as aircraft, space structures, automobiles, and other transportation equipment. Since the internal structure of CFRP is very complex, it is very difficult to define failure criteria when external loads are applied. Various methods have been proposed to evaluate the interfacial shear strength between carbon fiber and resin matrix, such as microbond test, rupture test, and pull-out test, but currently no effective method has been proposed to evaluate the tensile strength of the CF/resin interface. In this study, we applied the pulsed laser spallation method, which has been confirmed to be effective for evaluating the adhesion strength of thin films and coating films on substrates, to the evaluation of CFRP. A finite element method based on the Laplace transform was used for the numerical analysis of the unsteady elastodynamic problem. The macroscopic stresses generated by ultrasonic waves excited by pulsed laser irradiation were calculated by inverse analysis using a transfer function with the displacement history of the back surface of the CFRP specimen as supplementary information. Microscopic stresses at the fiber/resin interface were evaluated by the homogenization method, taking into account the effects of fiber arrangement, distance between fibers, and molding residual stress in unidirectionally reinforced CFRP laminates. As a result, this series of investigations revealed that the vertical interfacial stress is dominant with respect to the strength of the fiber/resin interface with the strength of about 54MPa.

Assessing the strength of deep-sea surface ultrasoft sediments with T-bar penetration: A machine learning approach

With the expansion of marine resource utilization, geological disaster prediction, and ecological protection in deep-sea regions, accurate identification of deep-sea engineering geological environments has become paramount, highlighting the significance of understanding the mechanical characteristics of deep-sea surface ultrasoft sediments (DSUSs). However, DSUSs typically exhibit low strength, high compressibility, and significant fluidity, making sampling for indoor strength testing a challenging task. On-site testing employing a T-bar penetrometer has become increasingly prominent for assessing DSUS strength, but the complexity of influencing parameters limits the application of this valuable method. This study utilizes a validated computational fluid dynamics (CFD) approach to model the complete process of T-bar penetration into a DSUS. The aim is to understand the quantitative effects and corresponding mechanisms of various significant complex parameters, including the undrained shear strength, dimensionless penetration depth, rate effect, and interface contact condition, on the dimensionless penetration resistance coefficient. Additionally, a machine learning model based on the random forest algorithm is introduced to establish a multiparameter evaluation method for the dimensionless penetration resistance coefficient. The findings illuminate the intricate interactions and effective evaluation of these factors when evaluating DSUS strength using a T-bar penetrometer, addressing the above challenges in marine engineering geology and the environment.

Influence of argon plasma treatment on interfacial performance of CFRP at high temperature

ABSTRACT This study introduces a novel approach to significantly enhance the interfacial properties of carbon fiber reinforced composites at elevated temperatures. Utilizing argon plasma treatment significantly boosted the interlaminar shear strength (ILSS) of the CF/PI composite when subjected to high temperatures. An optimal treatment condition, utilizing a power setting of 200 W, facilitated a 33.37% enhancement in ILSS over the untreated CF/PI composite at 300 °C, demonstrated an 89.39% retention of ILSS at the same temperature, and preserved ILSS at 77.90 MPa at 350 °C. At an optimal plasma treatment power, the fiber surface exhibited protrusions; surface roughness augmented to 181.90 nm, and the AD/AG ratio (the ratio of integral intensity between the Raman’s D-peak and G-peak) increased to 2.692. These modifications are identified as crucial factors in the improvement of the ILSS of the CF/PI composite at elevated temperatures.

HYDRAULIC BARRIER PROPERTIES OF SOIL BENEATH EGBEDI ACTIVE MUNICIPAL SOLID WASTE DUMPSITE

This study researches the potential of soil underlying an active municipal solid waste dumpsite as compacted clay liner in municipal solid waste repository structure. Identification of soil samples and their chemical constituents was conducted. Ex-situ tests were conducted in the laboratory to obtain three important hydraulic barrier parameters: coefficient of hydraulic permeability (k), volumetric shrinkage strain (VSS) and shear strength (UCS) of the natural soil samples employing three compaction techniques namely; British Standard Light (BSL), West African Standard (WAS) and British Standard Heavy (BSH). Soil specimens were also prepared with varying moulding moisture contents −2%, +2 and + 4 % of optimum moisture content (OMC). The microstructure of the natural specimen was investigated via scanning electron microscopy. The natural samples were identified as; A-2-7(0), A-2-7(2) and A-7-5(5) for sample A, B and C respectively according to AASHTO classification while all samples are classified as SC (Clayey Sand) according to USCS classification. The moulding moisture content that satisfy the k and VSS conditions of k ≤ 1.0 × 10−7 cm/s and VSS ≤ 4 % falls between 9.63 – 17.68 % and 9.63–12.75 % respectively, but the tested specimens fall short of strength condition. This study revealed that the natural soil samples fail to fulfil the design parameter requirements for strength in its application as liner/cover in the active waste dumpsite, therefore further investigation to ameliorate the strength property of the soil samples using additives or microbial induced calcite precipitation (MICP) technique is recommended.

Hydraulic barrier properties of soil beneath Egbedi active municipal solid waste dumpsite

This study researches the potential of soil underlying an active municipal solid waste dumpsite as compacted clay liner in municipal solid waste repository structure. Identification of soil samples and their chemical constituents was conducted. Ex-situ tests were conducted in the laboratory to obtain three important hydraulic barrier parameters: coefficient of hydraulic permeability (k), volumetric shrinkage strain (VSS) and shear strength (UCS) of the natural soil samples employing three compaction techniques namely; British Standard Light (BSL), West African Standard (WAS) and British Standard Heavy (BSH). Soil specimens were also prepared with varying moulding moisture contents −2%, +2 and + 4 % of optimum moisture content (OMC). The microstructure of the natural specimen was investigated via scanning electron microscopy. The natural samples were identified as; A-2-7(0), A-2-7(2) and A-7-5(5) for sample A, B and C respectively according to AASHTO classification while all samples are classified as SC (Clayey Sand) according to USCS classification. The moulding moisture content that satisfy the k and VSS conditions of k ≤ 1.0 × 10−7 cm/s and VSS ≤ 4 % falls between 9.63 – 17.68 % and 9.63–12.75 % respectively, but the tested specimens fall short of strength condition. This study revealed that the natural soil samples fail to fulfil the design parameter requirements for strength in its application as liner/cover in the active waste dumpsite, therefore further investigation to ameliorate the strength property of the soil samples using additives or microbial induced calcite precipitation (MICP) technique is recommended.

Discussion on ‘engineering properties of clay soil stabilised with glass powder and rubber particles – a comparative study’ [geomechanics and geoengineering (2023), 1–25, DOI: 10.1080/17486025.2023.2288927]

ABSTRACT We read with great interest the recent article by Anglaaere et al. (2023). In this article, clay soil with various contents of glass powder (GP) and tyre shred particles (TSP) were subjected to direct shear and California Bearing Ratio (CBR) test, and shear strength (τ) parameters and bearing capacity were reported, respectively. Furthermore, Anglaaere et al. (2023) have performed a correlation analysis and proposed a relationship between the CBR values and τ of the samples. The results presented by Anglaaere et al. (2023) might have been useful, but there are various issues associated with this article, which we want to bring to the attention of the authors, readers, and researchers. We further emphasise that this discussion article would eliminate the dissemination of errors in the scientific knowledge presented by Anglaaere et al. (2023), and will also open new perspectives to the readers and the research fraternity.

Microstructure and properties of Zircaloy-4 alloy under low-temperature diffusion bonding with a Ni-plated surface

Zircaloy-4, which is used as a structural material for nuclear cladding, requires precise bonding at low temperature in nuclear power applications. We achieved this using diffusion bonding with Ni plating on the surface of Zircaloy-4. We evaluated the performance of joints at temperatures between 650 and 780 °C. At 650 °C, the joint was successfully bonded. The joint exhibited a maximum shear strength of 207 MPa at 780 °C, which was twice as high as that produced by direct diffusion bonding at 700 °C under the same parameters. The interface was analyzed by using a combination of SEM and TEM to identify the presence of multilayered intermetallic compound layers in the joints. We investigated the mechanism of interface generation and determined the sequence of phase formation by Gibbs free energy calculations to be NiZr, Ni10Zr7, NiZr2, Ni7Zr2, and Ni3Zr. Through X-ray diffraction and cross-section elemental analysis of the fractures, we observed that, at lower temperatures, the joint fracture tended to occur in the Ni layer, whereas at higher temperatures, it occurred between Ni7Zr2 and Ni3Zr. The utilization of diffusion welding with Ni plating applied to the surface of Zircaloy-4 reduces the joining temperature and enhances the properties of the joint.

Outstanding interlaminar strength of carbon fiber reinforced epoxy resin via graphene oxide chemical bridge bonding

Carbon fiber reinforced polymers (CFRPs) are susceptible to interlaminar failure under high shear stress, which reduces their service life. Herein, we report a strategy to address the interlaminar damage problem of CFRPs by utilizing graphene oxide (GO) as a bridge to chemically bond carbon fibers and epoxy resin. Amino groups were grafted on the surface of carbon fibers to react with GO, then active amino functional groups were introduced onto GO, enabling crosslink with the epoxy resin. The chemical bonding force and mechanical interlocking effect of GO tightly integrated the carbon fibers with the epoxy resin, greatly reducing relative slip under high shear stress. This flexible and robust connection resulted in a significant improvement in the interfacial adhesion strength of CFRPs. The GO content and type of amino reactants were optimized to fabricate CFRPs, and the interlaminar shear strength and transverse fiber bundle tensile strength were increased to 76.36 MPa and 34.2 MPa, which were 46.2 % and 77.2 % higher than those of pre-modification materials, respectively. This research demonstrates that the chemical bonding provided by grafting graphene oxide significantly enhances interlaminar bond strength, thereby extending the service life of CFRPs and offering a promising path for manufacturing high-strength composites.

Bond Shear Tests to Evaluate Different CFRP Shear Strengthening Strategies for I-Shaped Concrete Cross-Sections.

I-shaped concrete girders are widely used in precast bridge and roof construction, making them a common structural component in existing infrastructure. Despite well-established strengthening techniques using various innovative materials, such as externally bonded carbon fibre reinforced polymer (CFRP) reinforcement, the shear strengthening of an I-shaped concrete girder is not straightforward. Several research studies have shown that externally bonded CFRP reinforcement might exhibit early debonding at the concave corners of the I-shape, resulting in a marginal increase in shear capacity. This research study aims to assess the performance of two different CFRP shear strengthening strategies for I-shaped concrete cross-sections. In the first strategy, CFRP was bonded along the I-shape of the cross-section with the provision of additional anchorage. In the second strategy, the I-shape was transformed into a rectangular shape by using in-fill blocks over which the CFRP was bonded in a U-configuration. In addition to the strengthening strategies, the investigated parameters included two different materials for the in-fill blocks (conventional and aerated concrete) and two different anchoring schemes (bolted steel plate anchor and CFRP spike anchor). To avoid testing on large-scale girders, a new test methodology has been implemented on concrete I-sections. The test results demonstrate the feasibility of comparing different shear strengthening configurations dedicated to I-sections. Among other findings, the results showed that the local transformation of the I-shape to an equivalent rectangular shape could be a viable solution, resulting in shear strength enhancement of 12% to 53% without and with the anchorages, respectively.

Bond Shear Tests to Evaluate Different CFRP Shear Strengthening Strategies for I-Shaped Concrete Cross-Sections

I-shaped concrete girders are widely used in precast bridge and roof construction, making them a common structural component in existing infrastructure. Despite well-established strengthening techniques using various innovative materials, such as externally bonded carbon fibre reinforced polymer (CFRP) reinforcement, the shear strengthening of an I-shaped concrete girder is not straightforward. Several research studies have shown that externally bonded CFRP reinforcement might exhibit early debonding at the concave corners of the I-shape, resulting in a marginal increase in shear capacity. This research study aims to assess the performance of two different CFRP shear strengthening strategies for I-shaped concrete cross-sections. In the first strategy, CFRP was bonded along the I-shape of the cross-section with the provision of additional anchorage. In the second strategy, the I-shape was transformed into a rectangular shape by using in-fill blocks over which the CFRP was bonded in a U-configuration. In addition to the strengthening strategies, the investigated parameters included two different materials for the in-fill blocks (conventional and aerated concrete) and two different anchoring schemes (bolted steel plate anchor and CFRP spike anchor). To avoid testing on large-scale girders, a new test methodology has been implemented on concrete I-sections. The test results demonstrate the feasibility of comparing different shear strengthening configurations dedicated to I-sections. Among other findings, the results showed that the local transformation of the I-shape to an equivalent rectangular shape could be a viable solution, resulting in shear strength enhancement of 12% to 53% without and with the anchorages, respectively.

Study on dynamic shear properties of sulfate saline soil- geotextile interface with different salt content

Using geotextiles to improve saline soil roadbeds has become increasingly widespread. However, salt unavoidably enriches at the saline soil-geotextile interface. Under complex external forces, the mechanical properties of the saline soil geotextile interface are not yet clear. Therefore, this study systematically studied the dynamic shear performance of saline soil geotextile interface under dynamic load under different salt content conditions using three shear forms: cyclic direct shear, monotonic direct shear, and post-cycle direct shear. The main research focuses on the influence of salt content, vertical stress and shear displacement amplitude on interface shear strength, stiffness, damping ratio, vertical displacement and other indicators. The results show that after cyclic shear, the strength of the interface of saline soil decreases, and the phenomenon of plastic softening is obvious. The interface shear strength and stiffness exhibit a non-linear relationship with the increase of salt content. When the salt content is 3 %, the interface shear performance reaches its optimum. Excessive salt content can cause crystalline slippage and weaken interface mechanical properties. Increasing vertical stress or reducing shear displacement amplitude is beneficial for improving interface shear strength and stiffness. The amplitude of shear displacement has the greatest impact on the interface damping ratio. The higher the salt content, the more severe the stress damage to the geotextile, and the more significant the accumulation of interface crystallization. The study revealed the mechanical response law of saline soil geotextile interface under dynamic load.

Hygrothermal effect and statistical analysis of the interfacial performance of nano and microscale polymer composites

ABSTRACT Hygrothermal exposure significantly impacts polymer composite (PMC) performance, affecting various industries. This study evaluated the short-term hygrothermal effects on PMCs by examining interfacial shear strength (IFSS), water uptake, glass transition temperature (Tg), and morphology. Data-driven techniques minimized experimental time while analyzing multiple factors. Specimens were immersed in water at 25°C and 70°C for 3, 7, and 14 days. The IFSS between carbon nanotube yarns and carbon fiber with epoxy (EPON™ 862) was measured before and after exposure. Statistical analysis indicated that fiber type significantly influenced IFSS, while time had a marginal effect and temperature had no impact. The IFSS decreased by 4.14% for CF/epoxy and 14.9% for CNT/epoxy. Water uptake analysis revealed weight gains of 0.465% and 1.566% for epoxy after 14 days at 25°C and 70°C, respectively. Morphological studies showed moisture penetration between 7 and 14 days. Thermomechanical analysis (TMA) indicated that pristine epoxy expanded by 0.318% of its original height. After 14 days, the Tg of epoxy decreased by 6.4% at 25°C and 9.7% at 70°C. Dynamic mechanical analysis (DMA) on dried epoxy samples showed similar Tg but varied tan delta curves due to plasticization. Short-term hygrothermal evaluation revealed degradation in interface quality and viscoelastic properties.

Enhancing the Mechanical Properties of Transient-Liquid-Phase Bonded Inconel 617 to Stainless Steel 310 through Altering Process Parameters and Homogenisation

This study investigated the impact of temperature, time, and homogenisation on the transient liquid phase bonding of Inconel 617 to stainless steel 310, employing AWS BNI2 foil as an interlayer. Nine test series were conducted at temperatures of 1050 °C and 1100 °C, with bonding durations ranging from 10 to 60 min. The homogenisation process was carried out on specimens that underwent full isothermal solidification at a temperature of 1170 °C for 180 min. The microscopic analysis indicated that extending the time and raising the bonding temperature resulted in the extension of the isothermal solidified zone, accompanied by a reduction in the quantity of eutectic phases. Complete isothermal solidification was seen exclusively in samples bonded at temperatures of 1050 °C for 60 min and 1100 °C for a duration of 50 min. The size of the diffusion-affected zone expanded as the bonding temperature and duration rose, but the presence of brittle intermetallic phases diminished. The microstructure of the homogenised sample indicated that the diffusion-affected zone had been almost completely eliminated. Hardness variations indicated heightened hardness in the diffusion-affected zone (DAZ) and athermal solidified zone (ASZ). Shear strength is maximised in homogenised specimens with minimised ASZ.

Effect of seawater corrosion on the mechanical properties of basalt fiber reinforced polymer composites modified by silane coupling agent KH560 and carboxylated carbon nanotubes

Basalt fiber reinforced composite (BFRP) has been widely used in various engineering fields, while the corrosion resistance of BFRP in harsh environments needs to be improved. In this work, the effects of seawater corrosion on mechanical properties of silane coupling agent (KH560) and carboxylated carbon nanotubes (CNTs) modified basalt fiber reinforced epoxy resin composites (BF/EP) were studied by simulating seawater corrosion under different conditions. The results showed that with the increase in corrosion time and temperature, the flexural performance and interlaminar shear strength (ILSS) of the composite material significantly decreased. Under the same corrosion conditions, the modified basalt fiber composite has better corrosion resistance to seawater than the untreated one due to an enhanced "soft-rigid" multi-scale stress transfer region between the BF and resin matrix. The flexural strength, flexural modulus and ILSS of modified basalt fiber composites decreased by 17.7 %, 12.2 % and 11.3 %, respectively, after 7 weeks of seawater corrosion at 60 °C, while that of untreated basalt fiber composites decreased by 28.2 %, 20.4 % and 19.7 %, respectively. In addition, the corrosion of distilled water on basalt fiber composites was also studied. Similarly, the modified basalt fiber composites showed better corrosion resistance to distilled water compared to the untreated basalt fiber composites. The research shows that the synergistic modification of KH560 and CNTs can effectively improve the corrosion resistance of BF/EP. This work is significant for promoting the development of BFRP and its application in marine environment.

Waste sawdust as a raw material: Synthesis, modification and characterization of novel bio-based phenol-formaldehyde wood adhesives

Lignocellulosic biomass is a sustainable alternative to petroleum-derived chemicals for the development of bio-based wood adhesives. However, limited by the complexity and reactivity of biomass, bio-based adhesives are not competitive in terms of physicochemical properties. In this study, a novel bio-based phenol-formaldehyde resin was prepared directly using phenol to liquefy waste sawdust without removing the residue, and modified with a small amount of melamine. The results demonstrated that the melamine-modified bio-based phenol-formaldehyde resin (MBPF) exhibited better physicochemical qualities. Particularly, the free phenol content was 0.36 %, 57.6 % less than in common phenol-formaldehyde resin. Various characterizations of resins showed that liquefied sawdust could successfully substitute phenol in the resin system. Ortho hydroxymethylphenol was produced by an addition reaction between the liquefied sawdust or phenol and formaldehyde during the resin production process. A reticulated cross-linking structure was then formed between the hydroxymethylate liquefied sawdust and polyhydroxymethylphenol through the dehydrated condensation reaction. The degraded sawdust chain segments were successfully embedded in the resin, increased the molecular weight of the resin prepolymer and improved the initial thermal stability. After a tiny amount of melamine was added, the resin produced a denser cross-linked network, which improved resin condensation activity, decreased the curing time, and successfully increased the bonding force between the liquefied sawdust and resin molecules. The wet shear strength of MBPF resin could reach 1.43 MPa, which was equivalent to PF resin.

Effect of the percentage of MUF adhesive coverage on shear strength when bonding different wood species

Due to climate changes, it is necessary to consider the use of other wood species to replace currently used woods. This work deals with the determination of the shear strength of bonded veneers (eight European wood species: spruce, larch, pine, beech, oak, poplar, birch, and alder) with Silekol® 311 melamine-urea-formaldehyde adhesive (MUF) with a variable coverage on the surface of the samples: 10, 15, 20, 25, 30, 50, 75, and 100%. The Automated Bonding Evaluation System (ABES) was used to evaluate and compare adhesive bond strengths. The larch, beech, and oak samples exhibited greater single-lap shear strength than the control samples from spruce. There was no statistically significant difference in shear strength regarding the adhesive coverage from 100% to 20% on the surface of the samples, for almost all wood species. The results of the project provide basic information about the bonding strengths with different coverage in the adhesive layer, comparing non-commonly used wood species in wood-based composites such as oriented strand board and particleboard.

Brazing of Porous Nickel to Copper and Stainless Steel: Microstructure and Mechanical Properties

A porous nickel (Ni) was brazed to copper (Cu) and stainless steel 304 (SS304) using VZ2250 and MBF67 brazing filler metal with a composition of 77.4Cu-9.3Sn-7.0Ni-6.3P and 64.5Ni-25Cr-6P-1.5Si (Cu: Copper, Sn: Tin, Ni: Nickel, P: Phosphorus, Cr: Chromium, Si: Silicon), respectively for joint microstructure and mechanical properties analysis. Porous Ni with a pore density of 15 pores per inch (PPI) was sandwiched between Cu/VZ2250 and MBF67/SS304. A brazed joint of Cu/Porous Ni/SS304 with VZ2250 and MBF67 brazing filler metal was prepared in a high vacuum furnace at different brazing times of 5, 10, and 15 minutes for 1015 °C with a heating and cooling rate of 10 °C/min, respectively for comparison purpose. The microstructure and mechanical properties of the brazed joint were investigated to identify the joint ability after the brazing process. Scanning Electron Microscope (SEM) equipped with Energy Dispersive X-Ray Spectroscopy (EDS) confirmed the interfacial microstructure by the formation of the diffusion filler metal (dark grey colour) for the Cu/Porous Ni/SS304 with VZ2250 and MBF67 brazing filler metal. For shear strength tests, the value decreases with an increase in the brazing time. The shear strength tests for the brazed joint of Cu/Porous Ni/SS304 with VZ2250 and MBF67 brazing filler metal show the maximum shear strength test value can be achieved for the brazing time of 5 minutes. The decreasing shear strength value was observed with differences in structural data of porous Ni due to the softening after the brazing process. Keywords: Brazing, Microstructure, Porous Nickel, Shear Strength.

Experimental investigation on mechanical behavior of natural soft clay by true triaxial tests

Laboratory tests on undisturbed and remolded Shanghai clay were conducted with a novel mixed boundary true triaxial apparatus. The strength and deformation behaviors of the structured soft clay at different Lode angles were carefully investigated. The relationship between the shear stress ratio and the dilatancy ratio of the clay in three different stress spaces, that is p–q space, TS stress space and tij modified stress space, are discussed in detail. In particular, the influences of the stress path and the structure of non–disturbed clay on the strength, deformation and failure criterion of Shanghai clay were quantitatively evaluated. The shear strength and dilatancy of undisturbed /remolded clay decreases with the increase of the Lode angle. It is also found that the shear strength and dilatancy of the undisturbed clay are larger than those of the remolded clay; while the influence of the structure on the dilatancy decreases with an increase in the Lode angle. In the π–plane, the maximum strength of Shanghai clay under different stress paths generally obeys the SMP failure criterion. The coincidence of the stress–dilatancy relationship given by the TS and tij stress spaces with the test results is much better than that given by p–q stress space. Furthermore, the linearity of the plastic potential curves of the undisturbed/remolded clay is more evident in tij stress space.

Self‐emulsifying anionic polyester sizing agents for enhancing the interfacial and mechanical properties of carbon fiber/vinyl ester resin composites

AbstractWith the increasing emphasis on environmental protection, there is a growing focus on the synthesis of water‐solvent self‐emulsifying sizing agents. In this study, five types of anionic polyester sizing agents with varying molecular weights were synthesized to explore the effect of molecular weight on the interfacial bonding strength of carbon fiber (CF) reinforced vinyl resin composites. The results demonstrated that the molecular weights of the synthesized sizing agents were precise; the particles in the sizing agents were nanometer‐sized, monodisperse, and exhibited high thermal stability. When the molecular weight was 8000, it exhibited optimal wettability for CF, leading to a substantial improvement in the interlaminar shear strength, reaching 71.8 MPa, which represents a significant increase of 22.7% compared with commercial CFs (CFF). Additionally, the interfacial shear strength was maximized at 13.23 MPa, which was significantly increased by 14.2% compared with CCF. These significant improvements in surface properties and mechanical performance were attributed to the excellent wettability of the CF surface, effective spreading performance of the sizing agent, the presence of double bonds in the sizing agent facilitating reactions with free radicals on the CF surface, and the residual double bonds further undergoing curing with the vinyl resin, promoting the reinforcement of interface bonding.

Bonding and fracture properties of SPI-CNTs/epoxy adhesive on SPI-CNTs deposited CFRP composites

Adhesive bonding is frequently used to connect CFRP structures due to its lightweight, easy implementation and high production efficiency. However, the bonding performance of adhesive is far from satisfactory as dimension and complexity of CFRP structures increase. In this paper, a new bonding strategy for CFRP structures via introducing soy protein isolate modified carbon nanotubes (SPI-CNTs) both in the epoxy resin adhesive and on the bonding parts' surface is proposed. Results showed that SPI can effectively improve CNTs' dispersion on the two areas, notably enhancing the bonding performance of the adhesive. When 0.3 wt% SPI-CNTs was added in the adhesive, its adhesive shear strength increased to 12.76 MPa, which was 72 % higher than the unmodified CNTs/epoxy adhesive. Based on this concentration, the SPI-CNTs was deposited uniformly on the surface of the CFRP adherends via bath sonication and resulted in a maximum shear strength of 15.59 MPa, which was 22.2 % greater than the untreated ones. Based on the above condition, the Mode I fracture toughness G1c and the Mixed-Mode I/II fracture toughness Gc could reach a maximum of 0.31 and 0.44 N/mm respectively, which were 117 % and 97 % higher than the pure epoxy adhesive. The present work shows a new pathway for the effective bonding of CFRP structural components used in the aerospace industry.