Initial Mechanical Properties Research Articles

Impact response of hybrid composites under varying environmental conditions: A comparative study

AbstractComposite materials are widely preferred in the aviation, automotive, construction and maritime industries due to their many superior properties. As a result of this widespread use, composite structures are inevitably subjected to various environmental conditions. Various environmental conditions may negatively affect the mechanical performance of the structure, and the structure may become unable to maintain its initial mechanical properties, especially in the face of critical loading, such as low‐velocity impacts. This research investigated the influence of various environmental conditions on the low‐velocity impact strength of composite materials. 12‐layer plate samples with epoxy matrix reinforced with woven glass fabric (GF), woven carbon fabric (CF), and hybrid fabric (HF), where the two fabrics are used together, were produced. Low‐velocity impact tests were conducted to these specimens at 20 and 40 J energy levels. Damages occurring in the material as a result of the low‐velocity impact test were interpreted using high‐resolution camera and optical microscope images. Force‐time and force‐ displacement curves were drawn and interpreted. It was concluded that as the impact energy values increased, the maximum force and displacement values also increased.Highlights The influence of various environmental conditions to which composite materials may be exposed on the dynamic response of the structure has been investigated. Various environmental conditions significantly affected the composite structure's impact behavior. While glass fabric (GF) composite samples were more affected by the seawater environment, carbon fabric (CF) composite samples were more affected by the HCl environment. Hybrid (HF) composite samples were affected by seawater and HCl in approximately equal amounts.

Influence of Heat Treatment on Microstructure Evolution and Yield Surfaces of Ni/PU Hybrid Foams

Metal foams are characterized by low weight, high resource efficiency, high relative stiffness, and exceptional energy absorption capacity under compressive load. Nickel/polyurethane (Ni/PU) hybrid foams consist of an open‐cell polyurethane foam coated with a layer of nickel produced by electrochemical deposition. The coating of the PU foams takes place in a flow reactor, in which the electrolyte is pumped through the foam at a defined flow velocity. The macromechanical properties of foam‐like structures depend on the structure of the skeleton, the inherent material properties and, in the case of Ni/PU hybrid foams, the properties of the electrochemically generated nickel layer. To influence their mechanical properties, the Ni/PU hybrid foams are subjected to heat treatment. In the given experimental setup, the parameters flow velocity, temperature, and duration of the heat treatment are each investigated at two different levels. Thus, interactions between the initial microstructure and the type of heat treatment are evaluated by means of X‐ray diffraction (XRD) and electron backscatter diffraction (EBSD) measurements. Interactions between initial mechanical properties and heat treatment are investigated by uniaxial compression tests and superimposed compression‐torsion tests. The knowledge gained is used to control the macromechanical properties of the hybrid foam.

Effect of Carbon Nanofiber Distribution on Mechanical Properties of Injection-Molded Aramid-Fiber-Reinforced Polypropylene.

The mechanical recycling of discarded plastic products as resources for environmental preservation has recently gained research attention. In this context, it is necessary to use waste materials for fiber-reinforced thermoplastics (FRTP). Glass and carbon fibers are often damaged by shear and compression during melt-forming processes. To achieve a sustainable society, it is necessary for thermal recycling to produce minimal to no residue and for mechanical recycling to maintain the length of fibers used in FRTP to preserve their performance as a reinforcing agent. Aramid fibers (AFs) do not shorten during the melt-molding process, and their composites have excellent impact strength. On the other hand, plastics reinforced with glass or carbon fibers are reported to have a superior strength and modulus of elasticity compared to aramid fibers. This study investigates the dispersion of a carbon nanofiber (CNF), a whisker, as the third component in aramid-fiber-reinforced polypropylene (PP/AF). The results and discussion sections demonstrate how the dispersion of CNF in PP/AF can enhance the mechanical properties of injection-molded products without compromising their impact resistance. The proposed composition will have excellent material recyclability and initial mechanical properties compared to glass-fiber-reinforced thermoplastics.

Study on the interfacial bonding properties between alkali-treated bamboo fibers and high-performance seawater sea-sand concrete

In this paper, the interfacial bonding properties between alkali-treated bamboo fibers and the matrix in fiber-reinforced high-performance seawater sea-sand concrete (HPSSC) materials were investigated. The natural bamboo fibers were modified with NaOH solution, and the cellulose crystallinity, chemical composition, and microstructure of the bamboo fibers before and after modification were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). The impact of alkali treatment on the water absorption and mechanical properties of bamboo fibers were evaluated by water absorption test and single fiber tensile test. In addition, the influences of NaOH concentration, treatment time, and embedded length on the interfacial bonding properties were analyzed by pull-out test. Subsequently, the bonding mechanism between the fibers and the matrix was revealed based on the SEM scans of the extracted fiber surfaces. The experimental results indicate that appropriate alkali treatment could significantly eliminate the non-structural substances on the surface of bamboo fibers, reduce the water absorption, and increase the cellulose crystallinity. This process made the bamboo fibers exhibit better stability and bonding performance while ensuring the initial mechanical properties. Moreover, various fiber embedded lengths have a significant impact on the pull-out behavior of bamboo fibers. The maximum pull-out force of bamboo fibers increased with the increase of embedded length, while the fiber-matrix interfacial shear strength decreased. Based on the experimental results, a theoretical model for the pull-out behavior of bamboo fibers was proposed, and the predicted results showed a strong correlation with the experimental results.

Effect of production angle on low cycle fatigue performance of 3D printed auxetic Re-entrant sandwich panels

This study explores the static and fatigue behavior of re-entrant sandwich structures fabricated via 3D printing to assess their energy dissipation capability and durability. Various core structures of sandwich panels with different angles are considered for analysis. The shells, cores, and the entire sandwich structures are manufactured using polylactic acid (PLA) material. A combination of numerical simulations and experimental tests were employed to evaluate the energy absorption capacity and stiffness of re-entrant sandwich structures. Initial mechanical properties of the core structures were obtained through static tensile testing and the experimental fatigue analysis was carried out by using an Instron 8871 servo hydraulic test device, following the principles of the three-point bending test. The results of both static and fatigue analyses evaluated and the energy absorption capacity of the structures increases with increase in production angles. FEM and experimental results are compared and both results are in good agreement with eachother. Additionally, affect of changes in the geometry of re-entrant sandwich panels evaluated in terms of Young's Modulus and Poisson's ratio. The improved structures characterized by a negative Poisson's ratio hold significant innovation potential, especially in the defense and automotive industries, through the integration of various topological research findings.

Accelerated aging procedure of epoxy structural adhesive for marine offshore applications

Knowledge of the long-term performance of adhesive connections is undoubtedly of paramount importance to enable their deployment in civil, mechanical, and other engineering applications. Over time, adverse environmental conditions can strongly influence the performance of adhesive joints leading to a progressive deterioration of their initial mechanical properties. The use of adhesive connections for secondary structures in offshore applications is a technology that allows for the rapid creation of structural members that, however, cannot ignore the influence of hydrothermal effects on mechanical performance due to environmental conditions. In this context, the investigation of the hygrothermal durability of adhesive connections was undertaken through an extensive experimental programme. More specifically, 130 cylindrical steel joints bonded with a commercially epoxy resin for structural applications were tested in Mode I using an Arcan-modified device. Prior to test, the specimens were placed in climatic ovens capable of combining the effects of temperature and humidity for approximately 320 days. In addition, the glass transition temperature, Tg, was assessed by employing the differential scanning calorimeter (DSC) technique to correctly define the experimental ageing conditions. The experimental results show how ageing conditions influence the mechanical properties of the epoxy resin investigated. Finally, some predictive formulations are proposed to calculate the loss of strength of adhesive joints over time.

Synthesis of C-S-H accelerating admixture and its effect on mechanical and hydration properties of engineering cementious composites

Due to the advantageous tensile ductility and multi-slit cracking characteristics, ECC material has attracted great from scholars. It has demonstrated promising potential in various fields including spray construction, additive manufacturing, building repair, and structural reinforcement. However, it is of note that ECC materials typically contain a substantial amount of low-activity mineral admixtures, which can cause lower initial mechanical properties. To address the existing issue, a hydrated calcium silicate (CSH) suspension was synthesized and added to the ECC material as an accelerating admixture. In this study, mechanical properties and hydration products of the ECC material were explored. The results suggest that CSH effectively enhances the early compressive, flexural, and tensile strength of ECC materials, and makes a positive impact on the later mechanical properties. However, it is of importance to note that CSH increases the fracture toughness of the ECC matrix, which may generate a negative effect on the tensile ductility of ECC. Microscopic analysis indicated that CSH promotes the formation of hydration products such as hydrated calcium silicate, ettringite, and Ca(OH)2, leading to improved hydration of cement clinker. In addition, CSH enhances the bond between the fiber and ECC matrix. In general, the research findings indicate that CSH can serve as a promising accelerating admixture for preparing early-strength ECC materials. The current research is highly significant for the advancement of early-strength ECC materials and expanding the range of applications for CSH accelerating admixture.

Sustainability through Optimal Compositional and Thermomechanical Design for the Al-7XXX Alloys: An ANOVA Case Study

The quest for lightweight, high-performance structural materials for demanding applications such as in the fields of automotive, aerospace, and other high-tech and military industries pushes the boundaries of material science. The present work aims to draw attention to a novel, sustainable manufacturing approach for the development of next-generation 7xxx series aluminum alloys that have higher strength by rejuvenating a sustainable compositional and thermomechanical processing strategy. Our innovative strategy integrates two key synergies: trace hafnium (Hf) addition for microstructural refinement, unique thermomechanical treatment involving cryorolling, and a short annealing method. Experimental results revealed that our base alloy exhibited a 33 µm grain size and impressive initial mechanical properties (334 MPa UTS, 150 HV). Adding 0.6 wt.% Hf and employing 50% cryorolling with short annealing led to a remarkable 10 µm grain size reduction and significant mechanical property leaps. The resulting alloy boasts a 452 MPa UTS and 174 HV, showcasing the synergistic advantageous effect of Hf and cryorolling plus annealing treatment. The developed alloys were compositional- and work hardening-dependent, leading to a rich mix of strengthening mechanisms. Optical and scanning electron microscopy reveal several intermetallic phases within the fcc matrix, wherein the Al3Hf phase plays a key role in strengthening by impeding dislocation movement. In addition to experimental results, a 12-full-factorial design experiment via ANOVA analysis was also utilized to validate the significant influence of Hf and cryorolling on properties with (p-values < 0.05). Among the different parameters, cryorolling plus annealing appeared as the most noteworthy factor, followed by the composition. Using the regression model, the ultimate tensile strength and hardness were predicted to be 626 MPa UTS and 192 HV for an alloy with 0.6 wt.% Hf and 85% cryorolling, which opens a new avenue for ultra-high-strength Al7xxx alloys.

Effect of high humidity on the initial mechanical properties and failure modes of thin spray-on liners (TSLs)

Thin Spray-on Liners (TSLs) are a novel rock support technology used in underground projects, which often encounter harsh environments such as high humidity. The mechanical properties of TSLs are affected by the high humidity environment. This study aims to summarize the support mechanisms of TSLs and evaluate the effects of humidity on their performance. Two cement-based TSLs were prepared. They used vinyl acetate-ethylene copolymer emulsion (VAE emulsion) and polyacrylate emulsion as modifying materials, respectively. Specimens were subjected to four different humidity environments for 7 days. The mechanical properties of the specimens were evaluated through compressive, flexural and pull-out tests. The impermeability test was utilized to test the sealing of TSLs. Microscopic observation was conducted using a Lecia microscope. The study also analyzed the interfacial failure modes observed in the pull-out test. The results indicated that increasing humidity hindered the film formation reaction of TSLs, preventing the formation of a continuous three-dimensional spatial polymer mesh structure. Instead, cohesive large particles were formed, negatively impacting the mechanical properties. Additionally, increasing humidity led to the formation of large pores and crack lines within TSLs, further decreasing their mechanical and sealing properties. The increase in humidity also weakened the dry shrinkage effect of TSLs, resulting in increased bond strength. Therefore, analyzing the initial mechanical properties of TSLs under high humidity conditions is crucial for guiding their application in underground projects.

Improving the comprehensive mechanical property of the AlSi10Mg alloy via parameter adaptation of selective laser melting and heat treatment

In this work, the AlSi10Mg alloys with distinct molten pool structures, namely fish-scale and lamellar, were fabricated by using selective laser melting (SLM) technology. The effects of solid solution temperature on the microstructural evolution and mechanical properties of the two types of alloys were systematically investigated. The relationship among initial structure, heat treatment and mechanical properties was revealed. The experimental results showed that for the alloy with fish-scale structure, Si diffused more easily after solid solution treatment due to the finer eutectic network, resulting in a larger Si particle size. At 510 °C, the nano Si particles in the fish-scale sample basically disappeared, but a small amount of nano Si particles still existed in the lamellar sample, leading to a bimodal distribution in the Si particle size. Different sizes and distributions of Si particles present different strengthening mechanisms and affect the nucleation and growth of recrystallized grains in the α-Al matrix, leading to significant differences in mechanical properties. The strength of the lamellar sample decreased with increasing the temperature, and the abnormally growth of grains could be found after being treated at 510 °C, resulting in a poor mechanical property. The strength of fish-scale sample first decreased and then increased with the increase of solid solution temperature. When the alloy with fish-scale structure was solid solution treated at 510 °C, Si particles could promote the nucleation of recrystallized grains but hinder their growth, and the ultimate tensile strength decreased from 478.8 MPa of SLMed state to 393.4 MPa, a reduction of 17.8%, while the elongation increased from 7% to 21%, an increase of 300%, showing an excellent overall mechanical property. Therefore, the present study demonstrates that adjusting the SLMed molten pool structure and heat treatment parameters is necessary to obtain a good combination of microstructure and mechanical property.

Effect of N and aging treatment on precipitation behavior, mechanical properties and wear resistance of Ti–V–Nb alloyed high manganese steel

To address the limited wear resistance attributed to the insufficient initial mechanical properties observed in high manganese steel (HM) wear behavior, we introduced nitrogen (N) to modulate precipitation behavior, thereby elevating material mechanical properties and wear resistance, and this was further enhanced through aging treatments. Due to the nitrogen addition, the precipitates transformed from MC to M(C, N), concurrently triggering a substantial increase and refinement in precipitates. As a result, nitrogenous high manganese steel (NHM) exhibited improved strength, toughness, and work-hardening capacity. The enhancements amounted to 67–77 MPa in yield strength and 5.3–9.3 % in elongation, with these improvements becoming more pronounced after extending the aging treatment. Under impact abrasive wear conditions, the NHM demonstrated the development of a stable work-hardened layer. The NHM hardened layer rapidly reached a depth of 4–6 mm, effectively resisting abrasive embedding and suppressing matrix abrasion. This transitioned the primary wear mechanisms from cutting and plowing to plastic deformation and micro-spalling. Additionally, NHM's great uniformity and toughness-plasticity played a crucial role in preventing the initiation and propagation of fatigue cracks and fatigue sheds.

A gelatin-based ionogel with anti-swelling properties for underwater human physiological signal detection.

A hydrogel is an ideal matrix material for flexible electronic devices, electronic skin and health detection devices due to its outstanding flexibility and stretchability. However, hydrogel-based flexible electronic devices swell once they are placed in a high humidity or underwater environment. The swelling behavior could damage the internal structure of hydrogels, ultimately leading to the reduction or complete loss of mechanical properties, electrical conductivity and sensing function. In order to resolve the above problems, a double network ionogel with remarkable anti-swelling behavior, stretchability and conductive properties was prepared. The ionogel consisted of gelatin (G) and copolymerization of acrylic acid (AA), 2-hydroxyethyl methacrylate (HEMA), butyl acrylate (BA), dimethylaminoethyl methacrylate maleate (D) and N,N'-methylene-bis-acrylamide (MBAA). Due to the dense crosslinking network and hydrophobic interaction, the ionogel exhibited remarkable anti-swelling properties (7.64% of the 30-day equilibrium swelling ratio in deionized water). D and MBAA were simultaneously introduced into the ionogel system as cross-linking agents to provide a large number of cross-linking points, improving the cross-linking density of the ionogel. Importantly, the introduction of D avoided ionic leakage by free radical copolymerization. Furthermore, the ionogel maintained stable mechanical properties and conductivity after being submerged in deionized water owing to remarkable anti-swelling performance. The mechanical properties of the ionogel retained 89.75% of the initial mechanical properties after a 5-day immersion in deionized water. Therefore, this ionogel could be employed as an underwater flexible wearable sensor for high humidity or underwater motion monitoring.

Automatic enhancement of vascular configuration for self-healing concrete through reinforcement learning approach

Vascular self-healing concrete (SHC) has great potential to mitigate the environmental impact of the construction industry by increasing the durability of structures. Designing concrete with high initial mechanical properties by searching a specific arrangement of vascular structure is of great importance. Herein, an automatic optimization method is proposed to arrange vascular configuration for minimizing the adverse influence of vascular system through a reinforcement learning (RL) approach. A case study is carried out to optimize a concrete beam with 3 pores (representing a vascular network) positioned in the beam midspan within a design space of 40 possibilities. The optimization is performed by the interaction between RL agent and Abaqus simulation environment with the change of target properties as a reward signal. The results illustrates that the RL approach is able to automatically enhance the vascular arrangement of SHC given the fact that the 3-pore structures that have the maximum target mechanical property (i.e., peak load or fracture energy) are accessed for all of the independent runs. The RL optimization method is capable of identifying the structure with high fracture energy in the new optimization task for 4-pore concrete structure.

Assessment of Existing Masonry Resistance Using Partial Factors Approaches and Field Measurements

The vast majority of existing structures in Croatia, as well as in other European countries, are made of unreinforced masonry. The seemingly ideal building material presents a great challenge for engineers in earthquake-prone zones. Given that structural failure can have significant consequences in terms of loss of human lives as well as financial losses, a comprehensive structural reliability assessment is needed. Old existing masonry structures often do not have design documentation, and even when they do, the initial mechanical properties have almost certainly degraded over time. That is why in situ testing is of great importance, but masonry is also characterized by a large scattering of results. After recent severe earthquakes in Croatia, more than ever, there is a need for a more reliable assessment of existing masonry structures. This paper presents reliability approaches for resistance evaluation of existing masonry in a real case study where basic failure modes of the masonry were observed. First, the data recommended in standards were used, followed by the updated data obtained from the flat-jack test. Finally, the design value method (DVM) and the adjusted partial factor method (APFM) were used. These methods align with Eurocode standards for new structures but are also adaptable for the assessment of existing structures. Differences in the results between the existing and the new version of the standard were observed, as well as an increase in the obtained resistances with an increase in the complexity of the methods used. Also, the influence of in situ testing proved to be an important factor in the analysis.

Study on the structure and properties of non-water reacted polyurethane grouting materials

In this study, non-water reacted polyurethane grouting materials were prepared using three different molecular chain lengths of polyether polyols. The influence of polyols and -NCO/-OH index (Rx) on the initial viscosity, mechanical properties, and concrete adhesion performance was investigated. Additionally, the damping performance of the cured materials was evaluated using dynamic mechanical analysis (DMA). The research results showed that with an increase in the molecular chain length of the polyether polyols, the strength of the cured material significantly decreased, while the elongation at break increased noticeably. Compared to the molecular chain length of the polyether polyols, the effect of the Rx on the mechanical properties of the cured material was not significant, especially in the low molecular weight polyether polyol system with shorter molecular chains (G3). The adhesion strength of the non-water reacted polyurethane grouting materials to concrete was highly correlated with the gelation time, and a slow gelation time could result in the formation of foam-like structures and reduce the adhesion strength. Grouting materials with shorter molecular chain lengths combined with low Rx (G3-1.0) or medium molecular chain lengths combined with moderate Rx (G5-1.4) exhibited excellent mechanical and damping properties.

Quasi-static tensile failure mechanism analysis of CFRP/Al countersunk electromagnetic riveted joints with different rivet-hole clearances

CFRP/Al countersunk riveting can meet the requirements of aircraft aerodynamic shape and lightweight joining. This paper reports an experimental study on the forming mechanism and quasi-static tensile failure of single-lap electromagnetic riveted joints with varying rivet-hole clearances. The aim is to quantitatively evaluate their deformation characteristics and mechanical properties. The failure process and fracture mechanism are revealed through the use of digital image correlation (DIC) and scanning electron microscope (SEM). The results demonstrate that the rivet-hole clearance has a significant impact on the initial damage and mechanical properties of riveted joints. The interference is not uniformly distributed in the Al sheet and the CFRP sheet. Increasing the clearance can delay the occurrence of damage of the laminate under external load. As the clearance increases, the riveted joint failure mode changes from rivet sheared off to manufactured head fracture and rivet pull-off, and the rivet fracture shows a brittle- ductile mixed fracture mode. Additionally, the initial riveting damage of the joint does not determine the final extent of damage to the laminate after failure, and the bearing damage of CFRP laminates increases with the increase in the load-carrying capacity of the joint.

Evaluation on Early Strength Development of Concrete Mixed with Non-Sintered Hwangto Using Ultrasonic Pulse Velocity.

Currently, in order to reduce the greenhouse gases of global warming, research on alternative cement materials is being actively conducted in the construction industry to reduce cement use, and it is judged to be important to evaluate the timing of form removal for the initial age. Therefore, in this study, we evaluated the initial mechanical properties of concrete in which cement was partially replaced with non-sintered hwangto (NHT). Specimens without NHT (namely, normal mortar (NM) and normal concrete (NC)) and specimens with NHT (namely, non-sintered hwangto mortar (HTM) and non-sintered hwangto concrete (HTC)) were prepared. NHT was substituted for 15% and 30% of cement. Two water-to-binder (W/B) ratios, 41% and 33%, were used to analyze the variation in the mechanical properties according to the cement and NHT content per unit volume of concrete. The compressive strength and ultrasonic pulse velocity (UPV) were measured. Experimental results indicated that compressive strength decreased with an increase in NHT content. The mortar with NHT substitution rates of 15% and 30% exhibited higher UPV than NM at a W/B ratio of 41%, in contrast to the behavior observed for concrete. The UPVs of most specimens were similar regardless of the NHT substitution rate. The correlation between the compressive strength and UPV of HTC was analyzed, and therefrom, exponential equations with a high correlation coefficient (R2) were proposed for strength prediction; the resulting predictions were compared with the results of previous compressive strength prediction models.

Parameter calibration method of clustered-particle logic concrete DEM model using BP neural network-particle swarm optimisation algorithm (BP-PSO) inversion method

A high precision back propagation neural network-particle swarm optimization (BP-PSO) algorithm inversion method is proposed to calibrate the microparameters of the clustered-particle logic concrete discrete element method model. The calibration targets include initial damage, failure mode, and mechanical properties of the material. The research utilise 243 training datasets generated through orthogonal experimental design and conducted simulations to train the BP neural network. In addition, a parameter sensitivity analysis is employed on the trained BP neural network to quantify the impact level of each microparameter and guide future macroparameter fine-tuning. The results indicate that the mean absolute percentage error of the BP-PSO inversion method is only 3.79%. This research also study on the concrete failure mechanism by using a mesoscale model based on clustered-particle logic, which considered concrete as a three-phase composite composed of mortar matrix, aggregates, and interfacial transition zone. The crack initiation, propagation and coalescence of DEM model show a good agreement with the experimental results.

Hydrolytic degradation of polylactide/polybutylene succinate blends with bioactive glass

Polylactides (PLAs) have been vastly studied for biomedical engineering applications, but their rigidness limits their use. Blending them with more flexible polymers, such as polybutylene succinate (PBSu), results in softer materials, expanding the range of possible applications. However, the biopolymers lack bioactivity, which can be overcome by adding bioactive glass. Combining the inorganic phase with the organic phase (especially with blends) results in a complex material. Therefore, understanding the hydrolytic degradation of each component is crucial. In this context, we report on processing polylactide and polybutylene succinate (PLA/PBSu) blends and their composites (30 wt% of bioactive glass 13‐93, BaG). The impact of blending and compounding with BaG on the final product's molecular weight and mechanical properties and the BaG dispersion in the polymer matrices was assessed. In addition, in vitro degradation in PBS was studied. While the degradation of the polymer was assessed by GPC, the BaG dissolution was quantified by ICP-OES. Blending decreased the initial mechanical properties and molecular weight, and compounding with BaG further decreased the initial mechanical properties. During the immersion in PBS, blending accelerated the loss of mechanical properties and molecular weight, while BaG accelerated the degradation of PLA-containing materials but had little effect on PBSu. Blending and compounding with BaG enabled us to produce materials with a wide range of mechanical properties: bending strength of 34–125 MPa, shear strength of 22–47 MPa and bending modulus of 1.1–3.9 GPa. The selection of tailorable properties of these polymer/BaG composites enables their application for tissue engineering of bone to soft tissue.

In-situ damage self-sensing and strength recovery activated by self-electricity in carbon fibrous composites embedded with multi-functional interleaves

It is challenging to simultaneously in-situ monitor and then repair the delamination crack of carbon fiber reinforced plastics (CFRPs) without sacrificing the initial mechanical properties. Herein, two sandwich interleaves are prepared by using healable poly (ethylene-co-methacrylic acid), reinforced and conductive carbon nanotubes (CNTs), and shear-resistant epoxy columns, to achieve self-sensing and self-healing functionalities. The results reveal that both interleaves show significant self-resistance changes to damage initiation and tensile strength of the interleaves themselves can be restored to 67.9–69.1%. Also, the interleaved CFRP exhibits obvious resistance change features during the progressive damage process after multiple healings. Moreover, a self-healing efficiency of more than 90% to interlaminar shear strength after two damage-healing cycles can be obtained. Furthermore, the interleaf with more CNTs possesses higher initial and healed strength. Therefore, the proposed interleaves can be used to prepare CFRP structure with self-sensing and self-healing functions, thereby with improved service reliability and service life.