Improvement In Shear Strength Research Articles

Influence of adding nanomaterials on shear properties of epoxy resin at different temperatures

Adhesive joints play a vital role in different industries owing to their advantages and ease of application compared to other joining methods. This research focuses on enhancing the mechanical properties of epoxy adhesives by incorporating graphene nanoplatelets (G) and iron-oxide nanofillers (Fe<sub>3</sub>O<sub>4</sub>). Single-lap adhesive joints, including both G and Fe<sub>3</sub>O<sub>4</sub> nanoparticles, are fabricated at 2%, 3%, and 4% weight percentages and tested under tensile load at ambient, 45°C, and 88°C. The results reveal that adding G and Fe<sub>3</sub>O<sub>4</sub> nanofillers enhances shear strength at elevated and room temperatures without altering the epoxy glass transition temperature (Tg). Furthermore, G nanofiller performs better in improving shear strength than Fe3O4. The optimal weight percentage is identified as 3 wt% for G and Fe<sub>3</sub>O<sub>4</sub>, as higher percentages lead to decreased shear strength due to agglomerations. This study provides insight into tailoring epoxy adhesives for improved mechanical performance under varying temperature conditions.

Review of Subgrade Soil Stabilised with Natural and Synthetic Fibres

Subgrade soil is an essential component in the design of road structures as it provides lateral support to the roadway. One of the main reasons for pavement failure is subgrade settlement, which leads to a loss of subgrade strength. If the mechanical properties of subsoils are lower than required, a soil stabilisation method may be an option to improve the soil properties of the weak subsoil. Soil stabilisation is one of the techniques for improving poor subsoil, which results in significant improvement in tensile strength, shear strength and bearing capacity of subsoil. Soil stabilisation can be broadly divided into four types: thermal, electrical, mechanical, and chemical. The most common method of improving the physical and mechanical properties of soils is stabilisation with binders such as cement and lime. However, soil stabilisation with conventional methods using cement and lime has become uneconomical in recent years, so an alternative such as fibres may be sought. This review provides a comprehensive comparison of the effectiveness of natural fibres and synthetic fibres in stabilising subgrade soils.

Microstructural and mechanical characterizations of SiC–304SS joints brazed with Cu–10TiH2 filler

A high-quality brazed joint of SiC ceramic and 304 stainless steel (SiC–304SS) was achieved by Cu–10TiH2 brazing alloy. The effects of brazing temperature on the interfacial microstructure and mechanical properties of SiC–304SS were analyzed. The typical interfacial microstructure of joints brazed at 1030 °C for 10 min was 304SS/σ-phase/(Fe, Cr) Ti/Fe2Ti/Cu(s,s) + Fe2Ti + TiC/SiC ceramic. With the brazing temperature increasing, the element Fe continued diffusing into the brazing seam and reacted with the element Ti. Then the width of σ-phase and the amount of Fe2Ti phase became increasing, and Fe2Ti phase became continuous. While, due to the reaction between Fe and Si, a buffer layer formed in SiC–304SS joints brazed at 1040 °C and 1050 °C. The main component of the buffer layer was FeSi2, TiC phases and carbon particles. In addition, the buffer layer contributed to forming a good gradient transition of coefficient of thermal expansion (CTE), releasing residual stress and improving shear strength of the joints. When brazing at 1050 °C for 10 min, the maximum shear strength of the joint was 100 MPa at room temperature and 53 MPa at 600 °C.

Sustainable design framework for enhancing shear capacity in beams using recycled steel fiber-reinforced high-strength concrete

According to a recent estimate, over 1.5 billion wasted tyres which containing over 40% of vulcanised rubber and 15% of steel fibre are discarded yearly, which posing a serious threat to circular economy implementation and transition to net zero. To minimise the greenhouse gas(GHG) emission and the environmental side effect caused by burning and burying these waste tyres, recycling and reusing these materials for sustainable structural designs has become the centre of attention. This paper focuses on applying recycled bead steel fibre to improve the shear capacity of fibre-reinforced concrete beams. Moreover, the existing national standard known as Eurocode 2 and TR63 can hardly illustrate the relationship between fibre and high-strength concrete. This study is the first to investigate shear behaviours of high-strength industrial and recycled steel fibre reinforced concrete beams with consideration of different shear span ratios. Therefore, twenty real-scale beams are constructed to examine the shear capacity of high-strength industrial and recycled steel-fibre reinforced concrete beams, which aims to compare the improvement of shear strength through experiments and identify different shear strength improvements of the two categories of steel fibre. Besides, comprehensive data of 164 beams from previous studies have been collected to benchmark with the experimental results for the formula design. This study proves the feasibility of replacing industrial steel with recycled steel fibre to improve the shear capacity of fibre-reintroduced concrete beams. Moreover, there are six novel equations designed developed using Eurocode 2 and TR63 as a basis in this study. Based on the findings of the paper, the proposed formulas demonstrate remarkable accuracy, with an average value of 0.982 and standard deviation of 0.213, respectively. Following an exhaustive comparison of RSF and ISF reinforced concrete beams, with a focus on economic expenditure and GHG emissions, it can be concluded that RSF offers superior economic and environmental benefits, which reduce the emissions up to 25.39% and price up to 28.04% when replacing ISF 0.8% RSF, respectively.

Microstructural effects of copper deposits on direct bonding for 3D IC integration

Cu-to-Cu direct bonding has been regarded as an important approach to achieve three-dimensional integrated circuit integration. This study aims to investigate the effects of microstructure and Xenon flash exposure on the direct bonding of copper deposits. Copper electrodeposits, along with a sputtered deposit, with various grain sizes, preferred orientations, as well as surface hardnesses, were prepared to clarify the influence of individual factors quantitatively. Experimental results show that joint strength and grain boundary density followed a positively linear relationship regardless of other microstructural differences, suggesting the dominating role of grain boundary diffusion. Grain refinement can effectively enhance bonding strength, even only one side of the directly bonded joints possessed fine grains. Considering the portable device applications which may suffer from drop shocks, drop testing of the packages comprising sputtered copper on Si chips joined with electroplated copper on Al2O3 substrates assembled by thermal compression bonding was performed for the first time. Noticeably, a proper flash irradiaiton prior to bonding brought about not only remarkable improvement in shear strength by up to 60 % but also drop resistance for direct-copper bonds. The resistance against drop shock for directly-bonded daisy chains subjected to an appropriate light exposure prior to bonding was superior than the joints bonded using impact-resistant solders.

Slurry infiltration and sintering cycle‐dependent mechanical properties of 3D oxide/oxide ceramic matrix composites

AbstractIn this study, oxide/oxide ceramic matrix composites reinforced with three‐dimensional fiber preform were fabricated by a slurry infiltration and sintering (SIS) process. The influence of the SIS cycle on microstructures and mechanical properties of the 3D oxide/oxide composite was investigated. Results showed that the porous matrix was densified due to the SIS effect. The elastic modulus of the weak matrix and interfacial shear strength increased with the increasing SIS cycle. This led to an obvious improvement in flexural strength and interlaminar shear strength of the composite. The fracture toughness and work of fracture of the composite slightly decreased. A good balance between fracture strength and damage tolerance was achieved on the sixth SIS fabricated oxide/oxide composite, which had a high flexural strength of 295.1 ± 14.9 MPa, a high interlaminar shear strength of 18.2 ± .5 MPa, and a high fracture 11.5 ± .8 MPa m1/2. The SIS process is a promising way to fabricate the 3D oxide/oxide composite.

Shear strength evaluation of solid waste incinerator ash-derived composites

Waste product utilization for natural resource conservation in the construction and building industry is now standard practice. The study targets the behaviour of cement-stabilized fiber-reinforced Incinerated bottom ash (IBA) when tested under unconsolidated-undrained (UU) conditions. Triaxial tests were conducted on the stabilized IBA specimens with varying cement content (3–9%) and fibers (13 and 19 mm) with a variation limited from 0% to 1%. The results indicate that cement stabilization leads to the improved shear strength of bottom ash specimens, whereas the additional transformation in the performance from brittle to ductile was noted in fiber-reinforced specimens. The observed UU strength values improved with the addition of fibers and later decreased. Adding 13 mm fiber (0.5%) with 9% cement content produced the best results, with an improvement of 66.25% in strength compared to the unreinforced composites for 28 days of curing. SEM analysis of the cured specimen comments on the effect of the curing period and the experimental results. The study also aims to predict the shear strength of IBA composites using four modelling techniques: Back Propagation neural network (BP-NN), Adaptive Neuro-fuzzy systems (ANFIS), Beetle Antenna search-Random Forest (BAS-RF model), and M5P model tree. These predictions were attempted by considering fiber percentage, fiber length, cement content, and the curing period. BAS-RF and ANFIS strongly correlated to the experimental results compared to BP-NN and M5P Tree. The precision of designed models is analyzed by the Coefficient of determination, Root mean square error, and Variance accounted for.

Two-Way Slab Punching Shear Resistance: Experimental Insights into Basalt-FRP Bar as Flexural Reinforcement

This study seeks to experimentally evaluate the punching shear performance of two-way concrete slabs reinforced with conventional steel and basalt fiber-reinforced polymer (basalt-FRP) bars subjected to punching loading condition. Basalt-FRP bars offer high tensile strength and corrosion resistance but are understudied in two-way concrete slabs concerning punching shear. This study aims to fill this gap, with key implications for future structural design considerations. To achieve the objectives of the study, six large-scale square slabs were fabricated and subjected to a concentric load until failure. The parameters of the experiment included are the type of reinforcement used (either basalt-FRP or steel), the percentage of basalt-FRP used (ranging from 0.88% to 1.77%), the size of the basalt-FRP bars used (either 16 or 12 mm), and the concrete’s compressive strength (25, 30, and 35 MPa). The findings from the tests showed that incorporating basalt-FRP bars with one-quarter equivalent axial stiffness (ρ(Ef/Es)) to that of steel significantly enhanced the punching shear resistance of flat slabs, achieving approximately 65% of the capacity observed in steel-reinforced control sample. Moreover, increasing the amount of basalt-FRP bar reinforcement to half of the equivalent axial stiffness of steel had a substantial effect in improving shear strength, reaching approximately 89% of the capacity observed in the steel-reinforced specimen and concurrently reducing deflection during the failure. Additionally, the reinforcement type and concrete compressive strength played a crucial role in determining the ultimate load, failure modes, and crack propagation patterns. The study reveals discrepancies between experimental results and existing models for punching shear in FRP-reinforced slabs. Certain prevalent models prove to be conservative in their estimates, while others offer more accurate predictions, indicating the need for comprehensive model refinement. The investigation found that one model, encompassing the majority of variables affecting punching shear, exhibited the highest level of precision, with a slight adjustment recommended to enhance its accuracy further. This study suggests a sustainable, more durable way to reinforce concrete in bridges and high-rise buildings, potentially improving construction efficiency, enhanced service life, and potential updates to building codes.

Effect of the Chemical Properties of Silane Coupling Agents on Interfacial Bonding Strength with Thermoplastics in the Resizing of Recycled Carbon Fibers

Upcycling recycled carbon fibers recovered from waste carbon composites can reduce the price of carbon fibers while improving disposal-related environmental problems. This study assessed and characterized recycled carbon fibers subjected to sizing treatment using N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (APS) chemically coordinated with polyamide 6 (PA6) and polypropylene (PP) resins. Sizing treatment with 1 wt.% APS for 10 s yielded O=C-O on the surface of the carbon fiber, and the -SiOH in the APS underwent a dehydration–condensation reaction that converted O=C-O (lactone groups) into bonds of C-O (hydroxyl groups) and C=O (carbonyl groups). The effects of C-O and C=O on the interfacial bonding force increased to a maximum, resulting in an oxygen-to-carbon ratio (O/C) of 0.26. The polar/surface energy ratio showed the highest value of 32.29% at 10 s, and the interfacial bonding force showed the maximum value of 32 MPa at 10 s, which is about 15% better than that of commercial carbon fiber (PA6-based condition). In 10 s resizing treatments with 0.5 wt.% 3-methacryloxypropyltrimethoxysilane (MPS), C-O, C=O, and O=C-O underwent a dehydration–condensation reaction with -SiOH, which broke the bonds between carbon and oxygen and introduced a methacrylate group (H2C=C(CH3)CO2H), resulting in a significant increase in C-O and C=O, with an O/C of 0.51. The polar/surface free energy ratio was about 38% at 10 s, with the interfacial bonding force increasing to 27% compared to commercial carbon fiber (PP-based conditions). MPS exhibited a superior interfacial shear strength improvement, two times higher than that of APS, with excellent coordination with PP resin and commercial carbon fiber, although the interfacial bonding strength of the PP resin was significantly lower.

SHEAR STRENGTH OF SOFT CLAY REINFORCED WITH ACRYLONITRILE BUTADIENE STYRENE (ABS) COLUMN

The troublesome soil that many geotechnical engineers encounter in the sector is clay soil. It presents a major danger to the foundations of light structures. Granular columns have proved beneficial in resolving foundation stabilisation and settling issues, making soft clay more appropriate for foundation building. This study aims to determine whether adding acrylonitrile butadiene styrene (ABS) to kaolin clay increases its shear strength. The physical, mechanical, and morphological properties of the materials used in this research (i.e., kaolin and ABS) must first be identified. The soft clay kaolin was strengthened with ABS columns and tested using the unconfined compression test (UCT) and the unconsolidated undrained test (UUT). The diameter of the columns used in this study was 8, 12, and 16 mm, while the penetration depth ratio used was 0.5, 0.75, and 1.0. The highest improvement in shear strength occurred at a height penetration ratio of 0.5 with values of 102.94%, 48.56%, and 50.02%. The UCT results demonstrated a decrease in the volume of the replacement ratio, followed by an increase in the height of the column. The UUT was conducted to evaluate the soft clay's shear strength when reinforced with an ABS column. The cell pressure used was 50, 100, and 200 kPa with the same column diameter specification as the UCT. The friction angle, υ, increased significantly from 8.92% to 18.21%. Furthermore, there was an improvement in cohesiveness, c, which increased from 4.54% to 45.45%. The results show that installing ABS columns improves the strength and compressibility of clay samples.

Welding reinforcement between silica glass and stainless steel using nanosecond fiber laser with chromium interlayer

Modern manufacturing industries need high strength and stable joint between glass and steel. Laser welding is an efficient technique to meet the requirement, but strength still needs to be improved. In this work, a welding reinforcement method of Cr addition was proposed to improve shear strength. The two materials were added with Cr metal film and Cr3+ solution in the interface, and welded by an nanosecond fiber laser. A maximum shear strength of 41.4 MPa was obtained, 40 % higher than that without Cr addition. The surface morphology and elemental distribution of the welds were observed. With Cr addition, the elemental diffusion in the interface was extended. Fe-O-Si and Cr-Si bonds were greatly increased in the welds. And microcracks were significantly reduced. In addition, the Cr layer also reduced the adverse effects caused by the different thermal expansion, making it more reliable in various industrial production fields.

Optimization of CMT welding process parameters of dissimilar hot rolled E250 and polymer sandwich steel lap joints

Lap joints of 1.5 mm thin sheets of dissimilar hot rolled E250 with polymer sandwich steel (MPM) were produced by cold metal transfer (CMT) process, closer to the real application. The polymer layer polystyrene-butadiene-styrene sandwiched between two DC06 sheets of MPM was found to be intact at significantly lower heat inputs (0.16 − 0.24 kJ/mm), which otherwise had been quite challenging during TIG welding leading to huge rejections. After several iterative trials for acceptable weld quality, experiments were conducted as per L9 orthogonal array, Taguchi technique with welding speed (WS), wire feed rate (WFR) and welding torch orientation (TO) as the process parameters. The joints were investigated through optical macrograph, micrographs, hardness, tensile lap shear tests and fractography on the fractured specimen. Optimum parameters were determined for maximizing shear strength. The sample with optimized parameters exhibited 6% improvement in shear strength achieving 152.09 MPa and polymer layer retention. ANOVA analysis suggested WS to be most significant parameter with 69.85% contribution affecting shear strength. Coefficient of determination (R 2) for the shear strength was 87.26% derived from the linear regression model. Significantly, lower error 0.96% computed from the confirmatory test concluded very effective optimization. Highlights Thin sheets of polymer sandwich steel (MPM) sheets were joined successfully with hot rolled E250 sheet without thermal disengagement of the polymer layer in MPM by CMT welding. Under optimal parameters MPM/E250 joints exhibited excellent mechanical properties. Fractography analysis revealed ductile failure mode. The error between experimental and predicted results by Taguchi was significantly lower and very well within the acceptable range.

Improving interfacial shear strength of fique fibres using an acrylic coating.

Natural fibres have proven to be a potential alternative to replace synthetic fibres in some composite materials applications. However, drawbacks such as impregnation difficulties and the poor fibre-matrix interface limit the use of natural fibres in high-performance applications. This work proposes using an acrylic resin to coat the fibre surface to enhance the interfacial compatibility among fique fibres and polyester resin. Pull-out tests revealed an improvement in the interfacial shear strength of about 110% for coated fibres. Furthermore, nanoindentation test, Micro Raman spectroscopy and scanning electronic microscopy indicated that the acrylic resin eliminates the gap at the fibre/matrix interface seen in the uncoated fibres. Observed behaviour could be attributed to a better chemical bonding between the fibre and matrix and is also hypothesised that the elastic characteristic of the coating helps to transfer loads effectively from the matrix to the fibre.

Characteristics of MICP- and EICP-treated sands in simple shear conditions: a benchmarking with the critical state of untreated sand

Microbial- or enzyme-induced calcium carbonate (CaCO3) precipitation (MICP and EICP) are relatively new ground improvement techniques. In this study, the mechanical behaviour of biotreated (MICP/EICP) and untreated sands was investigated in light of the critical state soil mechanics framework using a series of direct simple shear (DSS) tests. A wide range of calcium carbonate content (CC), initial void ratio after consolidation (e0) and effective initial normal stress ([Formula: see text]) was considered. The biotreated specimens showed improved shear strength and dilative tendency compared to untreated specimens with similar initial states. The ultimate state (US) for the biotreated sand shifted towards a smaller void ratio (e) than the value of e at the critical state of untreated sand at the same σ′N in e–log σ′N space. Compared to untreated sand, a significantly larger US stress ratio was achieved for the biotreated sand, particularly at high CC and low [Formula: see text]. The characteristic features of undrained behaviour, such as instability stress ratio, stress ratio at phase transformation and flow potential showed good relationships with modified initial state parameter, void ratio after biotreatment and CC. The bonding ratio, (τ/σ′N)bond, was used to quantify the interparticle bonding. The peak value of (τ/σ′N)bond for the biotreated sand was significantly larger than zero, particularly at high CC and low [Formula: see text], while the peak (τ/σ′N)bond for the untreated sand was negligible. It was also observed that the mobilisation and degradation of calcium carbonate bonds in biotreated sand during DSS shearing are influenced by both CC and [Formula: see text].

Experimental Research on the Physical and Mechanical Properties of Remolded Fine-Grained Debris-Flow Deposits

Abstract To make better use of debris-flow deposits, this paper adopts fine-grained debris-flow deposits (< 2 mm) sampled from Jiangjia Gully to constitute 17 gradation structures and determines the shear strength of the remolded structures at different moisture contents and vertical loads. Furthermore, the role and mechanism of each grain size interval in the remolded soils is discussed in depth. Grey correlation analysis is also introduced to evaluate the degree of influence of each factor on remolded structures. The results indicate that the difference in grain size distribution causes different physical and mechanical characteristics for remolded structures under different external conditions. The correlation degree of each influencing factor on the shear strength of remolded soil is ordered as follows: vertical load > moisture content > structural gradation. At different moisture contents, fine particles exert the greatest effect on the physical and mechanical characteristics of remolded soils, especially variation in the content of fine particles of less than 0.16 mm. At low moisture content, both fine particles and coarse particles facilitate the improvement of shear strength, and the increase in particle content in the range of 0.315–0.16 mm helps to enhance the mechanical properties of remolded structures. At high moisture content, the influence of the variation in intermediate particle content should be considered, especially the increase in particle content in the size range of 0.63–0.315 mm, which helps to improve the shear strength. The change in moisture content affects the cohesion of fine particles in the structures, and the change in vertical load shifts the contact form between particles in the structures, thereby affecting the internal frictional resistance and cohesion of remolded structures. The results obtained from this research are expected to provide a good basis for the reutilization of debris-flow deposits.

Cement and fly ash-treated recycled aggregate blends for backfilling trenches in trafficable areas

The shortage of natural aggregates available for filling excavated pipeline trenches in trafficable areas has prompted the exploration of alternative resources. This study investigates the feasibility of using cement and fly ash-treated recycled aggregates as trench backfill materials subjected to traffic loadings. Blends of recycled glass (RG), plastic (RP), and tire (RT) were treated with different proportions of cement and fly ash, resulting in a total of 8 treated blends. Geotechnical tests including compaction and California Bearing Ratio (CBR) were conducted to evaluate the mixtures according to backfill specifications. Specialized pavement testing, such as repeated load triaxial testing (RLT) and quick shear, simulated real-life stress levels at trafficable areas. Scanning electron microscope (SEM) images were taken to investigate the microstructural characteristics of the cement and fly ash-treated samples. The results showed that the CBR and resilient modulus of the treated blends improved with higher cement, fly ash, and RG contents, while they decreased with increased RT content. Cement-treated blends demonstrated significant improvements in peak shear strength with increased cement and RG contents and decreased RT content. Fly ash-treated blends showed minor improvement in peak shear strength when the fly ash, RG, and RT contents varied. Only cement-treated blends exhibited properties comparable to Class 4 (CL4) crushed rock, which was the control material. Under the same stress levels, cement-treated blends demonstrated up to 1.17 and 2.62 times greater stiffness than CL4 and clay subgrades, respectively. The SEM analyses confirmed that the inclusion of cement in the recycled blends resulted in the formation of greater bonds between particles compared to fly ash, which led to higher strength. These findings highlight the potential of sustainable materials in backfilling pipeline trenches under traffic loadings, reducing the reliance on natural aggregates for this application.

Effect of MWCNTs on mechanical properties of woven angle ply GFRP laminates

Impact of MWCNTs on the mechanical behaviour of woven GFRP angle ply laminates have been studied. GFRP laminates was fabricated with eight layers of fiber orientation (45˚/-45˚) of neat epoxy, 0.5 wt% and 1.0 wt% MWCNTs filled GFRP using vacuum assisted hand layup method. With the aim to perform the mechanical testing like tensile, compression, short beam and three-point bending test, required samples were made from the manufactured laminates in accordance with respective ASTM standards. Addition of 0.5 wt% MWCNTs into GFRP laminates improved the tensile and bending strength. Woven angle ply GFRP modified with 1.0 wt% of MWCNTs enhanced only the ultimate tensile strength. Incorporation of MWCNTs into GFRP has no effect on improvement of compression and interlaminar shear strength.

Formation of ductile close-packed hexagonal solid solution on improving shear strength of Au–Ge/Cu soldering joint

The morphology, chemical composition, mechanical properties of the interface reaction products and their effects on the shear strength of the Au–Ge/Cu soldering joint were systematically investigated. The results showed that a close-packed hexagonal (HCP) structure solid solution phase was formed at the interface after soldering at 400 °C for 5–60 min. The composition of the HCP phase varied among 78–46 at.% Cu, 9–42 at.% Au and ~12 at.% Ge. The Young’s modulus and hardness of HCP phase were 105–112 GPa and 4.3–4.7 GPa, respectively. The shear strength of the 5 min soldering joint was 57 MPa; however, it increased to 68 MPa when the soldering time was prolonged to 60 min. The increasing shear strength can be ascribed to the formation of HCP ductile phase and its effect on depleting the brittle (Ge) phase. It suggested that a HCP structured solid solution formed at the interface could enhance the shear strength of the solder joint.

Biomimetic construction of 3D needle‐punched CF/PEEK composites based on ladybug forewing structure for directional reinforcement

Abstract3D needle‐punched CF/PEEK composites are a kind of composites with promising applications in multiple fields, such as implant materials, but their mechanical properties in the Z‐axis and interlaminar are still weak at present. In this study, a bio‐inspired reinforcement structure based on ladybug forewing was developed to achieve directed reinforcement of 3D needle‐punched CF/PEEK composites. Carbon fiber yarns were stitched into the 3D needle‐punched CF/PEEK preforms according to the set structure, and the bio‐inspired CF/PEEK composites were obtained after hot pressing. The interlaminar and in‐plane mechanical properties of the composites were investigated at different stitch lengths. The results showed that the addition of the bio‐inspired structure greatly improved the interlaminar shear strength of the composites, reaching 111.30 MPa, an enhancement of 95.06%. The in‐plane mechanical properties, including tensile, flexural, and compression, were also significantly improved to different degrees. The “structure‐effect” relationship in the bio‐inspired CF/PEEK composites was investigated, and the effectiveness of such a bio‐inspired reinforcement structure was demonstrated. This new reinforcement strategy provides a new idea for the improvement of the mechanical properties of multi‐stage carbon fiber‐reinforced thermoplastic resin matrix composites.Highlights The in‐plane and interlaminar mechanical properties of composites were simultaneously improved. Up to 95.06% improvement in interlaminar shear strength. A novel bionic strategy of directional reinforcement was developed. The “structure‐effect” relationship in the composites was investigated.

Enhancement of interfacial properties of HMCF composites by constructing of rigid‐flexible interphase through naphthalenediimide with different flexible chain lengths

AbstractNaphthalenediimide copolymers with long, middle and short flexible chain lengths (LN, MN and SN) were designed and used to construct rigid‐flexible interphase on high‐modulus carbon fiber (HMCF) surface, and the interfacial performance and interphase reinforcing mechanism of composites were explored. Compared with desized HMCF (HMCF‐desized), the surface activity and roughness of HMCF‐LN, HMCF‐MN and HMCF‐SN were gradually increased. In contrast to HMCF‐LN and HMCF‐MN composites, wider transit‐modulus platform and increased interphase thickness were detected in HMCF‐SN composites, the improved deformation and decreased thermal residual stress from rigid‐flexible interphase were obtained. The highest improvement of transverse fiber bundle test strength (TFBT) and interfacial shear strength (IFSS) of HMCF‐SN composites were achieved, which was ascribed to the effective relaxation of interfacial stress and stronger chemical interaction of HMCF‐SN with matrix by the reduced flexible chain lengths and the increased functionality of SN copolymers.Highlights Rigid‐flexible interphase was constructed by naphthalenediimide copolymers. Wider transit‐modulus platform was detected in HMCF‐SN composites. Improved deformation and decreased residual stress of interphase were obtained. The interfacial performance of HMCF‐SN composites were greatly improved.