High-strength Composite Materials Research Articles

Fiber reinforcement of polymer hybrid sandwich composites using SNiPs: effect of silica nanoparticles on flexural and compressive strength

The increasing demand for lightweight, high-strength composite materials in aerospace, automotive, and structural applications has intensified research into polymer composites. To address the challenge of enhancing mechanical properties while maintaining weight efficiency, this study investigates the effect of silica nanoparticles (SNiPs) on the flexural and compressive strength of sandwich composites. These composites are constructed from fiber-reinforced carbon, para-aramid, glass, and polyurethane (PU) foam. Composite specimens with varying concentrations of SNiPs were produced using a hand layup process with synthetic fiber-reinforced polymer glass fibers (GFRP), carbon fibers (CFRP), para-aramid fibers (KFRP), urethane foam, and epoxy glue. Fabricated using a quasi-static stacking sequence technique, the composites feature a three-layer sandwich matrix(0 K 1 / 45° C 1 / 45° G 1/PU/ 45° G 1 / 45° C 1 /0 K 1). Flexural and compressive strength tests were conducted to assess their mechanical behavior. The results show that incorporating SNiPs into polymer hybrid sandwich composites significantly enhances both flexural and compressive strength. This improvement is attributed to the high aspect ratio and surface properties of SNiPs, which facilitate effective stress transfer between the reinforcing fibers and the polymer matrix. The flexural strengths achieved with 0, 2, 4, and 6 wt.% SNiPs were measured as 52.583, 58.713, 64.108, and 61.397 MPa, respectively. Similarly, the compressive strengths were measured as 2.207, 2.813, 3.528, and 3.182 MPa for the respective weight percentages.

Preparation and Mechanical Properties of PBAT/Silanized Cellulose Composites

Polybutylene adipate-terephthalate (PBAT) is a fully biodegradable polyester, which has been proven to be the most suitable alternative to traditional plastics. However, due to the low strength of PBAT (17.2 MPa) and high price, the use of PBAT has a degree of limitations. To obtain a cost-effective and high-performance composite material of PBAT, for this study we selected microcrystalline cellulose, which is inexpensive and easily available, as the reinforcing medium. However, due to the hydrophobicity of PBAT, the mechanical properties of PBAT when mixed with hydrophilic cellulose were low. In order to improve the compatibility of cellulose and PBAT, this study selected hexadecyltrimethoxysilane (HDTMS) containing long carbon chains to silanize microcrystalline cellulose (MCC) to obtain silanized cellulose (SG). Three types of SGs with different degrees of silanization were obtained by controlling HDTMS with different mass ratios (1:10; 3:10; 5:10) to react with MCC. Characterization of these three types of SGs was conducted using FTIR, TEM, and water absorption analysis. The results demonstrated the successful synthesis of SG. With the increase in the reaction ratio of HDTMS and MCC, the size of the nanoparticles increases, and the water absorption decreases significantly. Subsequently, PBAT/SG composites were prepared by blending three kinds of silanized cellulose with PBAT in different proportions by the sol-gel method. To study the thermal stability and compatibility, the mechanical properties of the composites were evaluated, including thermogravimetric testing, scanning analysis, and dynamic thermomechanical testing. The optimal blending ratio and the optimal type of silane cellulose were found. Analysis of the mechanical properties revealed that the tensile strength initially increased and then decreased with increasing blending ratio for all three composites tested. Among them, the PBAT/SG2 composites exhibit superior performance, with a maximum tensile strength reaching 22 MPa at an 85/15 blending ratio, nearly 30% higher than that of pure PBAT alone. The addition of SG significantly improved the strength of the PBAT, and SG2 is more suitable for preparing high-strength composite materials. In addition, after the addition of SG, the yield stress of the composite is improved while maintaining good thermal stability. Both the SEM and DMA results indicated good compatibility of the PBAT/SG composites. This study provides a new idea for the industrial-scale development of degradable polyesters with low cost and good mechanical properties.

Investigation of Thermomechanical Analysis of Carbon/Epoxy Composite for Spacecraft Structure Material

When building spacecraft structures, it is crucial to use lightweight and high-strength composite materials with the necessary characteristics. Aerospace applications benefit significantly from the exceptional properties of carbon/epoxy composite materials. As part of a study on composite materials, this work focuses on exploring the thermo-mechanical properties of carbon fiber. The matrix used in this research is LY-5052 epoxy, applied through a vacuum infusion technique. To achieve optimal composite properties, various tests are conducted to evaluate its thermo-mechanical behavior. These tests may include measuring Thermal Conductivity and performing thermogravimetric analysis (TGA). Most importantly, the composite is subjected to tensile testing at room temperature to 200 °C. This is done because most tensile tests on carbon/LY5052 composites are carried out at room temperature. The results obtained from the measurement of the thermal conductivity of the carbon/LY5052 composite were 0.419 W/mK; from the Thermogravimetric Analysis (TGA), the carbon/LY5052 composite began to decompose at a temperature of 365.63 °C and the tensile test was carried out simultaneously with variations in temperature from room temperature, 50 °C, 100 °C, 150 °C and 200 °C have tensile strengths of 553, 507, 340, 266, and 242 MPa, respectively. This trend confirms that strength decreases with higher temperature loads. Several image observations are also presented in this report to understand composite materials' failure behavior at these various temperatures.

Effects of Novel Dental Composites on Streptococcus mutans Biofilms.

With the phase-out of amalgam and the increase in minimally invasive dentistry, there is a growing need for high-strength composite materials that can kill residual bacteria and promote tooth remineralization. This study quantifies how antibacterial polylysine (PLS) and re-mineralizing monocalcium phosphate monohydrate (MCPM) affect Streptococcus mutans biofilms and the strength of dental composites. For antibacterial studies, the MCPM-PLS filler percentages were 0-0, 8-4, 12-6, and 16-8 wt% of the composite filler phase. Composite discs were immersed in 0.1% sucrose-supplemented broth containing Streptococcus mutans (UA159) and incubated in an anaerobic chamber for 48 h. Surface biomass was determined by crystal violet (CV) staining. Growth medium pH was measured at 24 and 48 h. Biofilm bacterial viability (CFU), exo-polysaccharide (water-soluble glucan (WSG) and water-insoluble glucan (WIG)), and extracellular DNA (eDNA) were quantified. This was by serial dilution plate counting, phenol-sulfuric acid microassay, and fluorometry, respectively. The biaxial flexural strengths were determined after water immersion for 1 week, 1 month, and 1 year. The MCPM-PLS wt% were 8-4, 8-8, 16-4 and 16-8. The normalized biomass, WSG, and WIG showed a linear decline of 66%, 64%, and 55%, respectively, as the PLS level increased up to 8%. The surrounding media pH (4.6) was all similar. A decrease in bacterial numbers with the 12-6 formula and a significant reduction with 16-8 compared to the 0-0 formulation was observed. The eDNA concentrations in biofilms formed on 12-6 and 16-8 formulations were significantly less than the 0-0 control and 8-4 formulations. Doubling MCPM and PLS caused a 14 and 19% reduction in strength in 1 week, respectively. Average results were lower at 1 month and 1 year but affected less upon doubling MCPM and PLS levels. Moreover, a 4% PLS may help to reduce total biomass and glucan levels in biofilms on the above composites. Higher levels are required to reduce eDNA and provide bactericidal action, but these can decrease early strength.

Bio-inspired copper ion-chelated chitosan coating modified UHMWPE fibers for enhanced interfacial properties of composites

Ultra-high molecular weight polyethylene (UHMWPE) fibers are broadly applied in lightweight and high-strength composite fiber materials. However, the development of UHMWPE fibers is limited by their smooth and chemically inert surfaces. To address the issues, a modified UHMWPE fibers material has been fabricated through the chelation reaction between Cu2+ and chitosan coatings within the surface of fibers after plasma treatment, which is inspired by the hardening mechanism, a crosslinked network between metal ions and proteins/polysaccharides of the tips and edges in arthropod-specific cuticular tools. The coatings improve the surface wettability and interfacial bonding ability, which are beneficial in extending the application range of UHMWPE fibers. More importantly, compared to the unmodified UHMWPE fiber cloths, the tensile property of the modified fiber cloths is increased by 18.89% without damaging the strength, which is infrequent in modified UHMWPE fibers. Furthermore, the interlaminar shear strength and fracture toughness of the modified fibers laminate are increased by 37.72% and 135.90%, respectively. These improvements can be attributed to the synergistic effects between the surface activity and the tiny bumps of the modified UHMWPE fibers. Hence, this work provides a more straightforward and less damaging idea of fiber modification for manufacturing desirable protective and medical materials.

On line construction of carbon nanotube/polytriazole composite films with high tensile and heat resistant properties

Carbon nanotubes (CNTs) have low densities and excellent mechanical properties due to their unique one-dimensional tubular structures, and are thus considered as an ideal reinforcement for lightweight and high-strength resin-based composites. However, it is still difficult to prepare high-performance composites with a high content of well-aligned CNTs. Besides, limited by the poor heat resistance of epoxy resin, it is still challenging to prepare composites with both high strength and heat resistance. In the present study, a simple on-line process is proposed to prepare CNT/polytriazole composite films. That is, a CNT assembly just having formed in a high temperature reactor is pulled through solution containers for shrinking and resin infiltration and subsequently winded on a drum to form a composite film. By optimizing the resin content and CNT alignment for better densification and inter-binding, the tensile strength of the composite film can reach a high level of 2.52 GPa with a decent elongation of 4.3 %. Associated with the use of the polytriazole resin, the composite could be cured at a low temperature of 80 °C but have a high glass transition temperature of 298 °C. Thus, the present technique is useful for preparing high-strength composite materials which are required to be able to be cured at low temperature but applied at high temperature.

Востановление городских памятников: ресурсный потенциал Северного Кавказа

Introduction. Repair and restoration binders and compositions based on them are necessary, first of all, for the repair, restoration and restoration of cultural heritage sites, both in the Russian Federation and abroad. They are subject to special requirements, so the conduct of related engineering and survey, research and development work is an important condition for the development of modern scientifically verified, practically tested and in demand in practice repair and restoration materials. One of the main conditions for the practical implementation of the proposed investment project is the presence of a mineral resource base in the region and the country. The resource potential of carbonate, halogen and clayey rocks is fully represented in the mountainous part of the Chechen Republic (CR). Based on the results of research and prospecting work on the territory of the Czech Republic, 6 forecast areas were identified, promising for the identification of deposits of carbonate Purpose of research. Development of compositions of binders for repair and restoration work based on the resource potential of the rocks of the mountainous part of the Czech Republic. Materials and methods. The work uses methods of analytical research and scientific generalizations, expert assessments, process modeling and system analysis. Results and discussion. The classification of inorganic binders was performed, which for the first time included organic-inorganic binders and additives in repair and restoration binders and compositions. Because of exploratory research, it was proposed to repair, restore and restore historical and cultural monuments using the ones developed at the Kh.I. Ibragimov RAS of modern technologies and materials for repair and restoration work. A concept for the development of a new scientific direction "High-strength composite materials based on lime (hydraulic and hydrate), gypsum (gypsum and anhydrite) and magnesia binders for the repair and restoration of cultural heritage sites" has been developed. Conclusions. The article presents the results of studies of repair and restoration binders and compositions based on them. It is shown that they are subject to special requirements, therefore, carrying out related engineering and survey, research and development work is an important condition for the development of modern scientifically verified, practically tested and in demand in practice repair and restoration materials. The paper shows that the new developed classification is more complete and allows more accurate determination of the compositions necessary for restoration work. According to the results of the work, it is clear that it is possible to carry out the repair, restoration and restoration of historical and cultural monuments using the proposed technology. When carrying out such work on the territory of the Chechen Republic, it is possible to do these using local raw materials. Resume. It is planned to continue work in this direction and analyze the sources of raw materials for restoration work in more regions of the North Caucasus.

Assessment of orthopedic treatment quality in patients with complete absence of teeth

Objective. To evaluate the effectiveness of dental orthopedic treatment in patients with complete absence of teeth using removable plate prostheses applying integral qualitative and evaluative indicators. The relevance of the study is dictated by the need to improve the quality of orthopedic treatment in patients with complete absence of teeth, through the introduction of new composite materials, the use of which provides high strength of prosthetic structures. For an objective assessment of the effectiveness of dental orthopedic treatment of patients using removable plate prostheses, integral approaches based on the calculation of qualitative and evaluative indicators have been modified.
 Materials and methods. In order to improve the quality of orthopedic treatment of patients with complete absence of teeth, a design of a complete removable plate prosthesis with a combined basis and a method of its manufacture based on the use of digital technologies was developed. In the course of the work, the evaluation of the effectiveness of treatment in patients with complete absence of teeth in the long-term follow-up using integral qualitative and evaluative indicators was carried out.
 Results. Clinical and laboratory stages of manufacturing a new design combining analog and digital metols were developed and tested. As a result of clinical studies, it was found that the type of construction of a complete removable plate prosthesis does not significantly affect the indicator of the integral assessment of the quality of orthopedic treatment, with the exception of the criterion of the prosthesis integrity.
 Conclusions. To conclude, it was found that the type of construction of a complete removable plate prosthesis does not significantly affect the integral assessment of the quality of orthopedic treatment, except for the criterion of the integrity of the prosthesis; the introduction of a composite material based on fiberglass into the design of a combined prosthesis allows to improve the strength properties of the prosthesis basis and increase the performance characteristics of the structure. The use of CAD / CAM technologies provides the possibility of using high-strength composite materials, gives sufficient accuracy in the manufacture of the frame of a combined full removable plate prosthesis. Due to satisfactory physical and mechanical properties, the application of the developed design contributes to the predicted increase in the durability of prostheses.

Thermal vibration analysis of functionally graded graphene platelets-reinforced porous beams using the transfer function method

Functionally graded graphene platelets-reinforced (FG-GPL) porous materials are advanced, designable, lightweight, and high-strength composite materials promising in launch vehicles, space shuttles, and hypersonic vehicles as integrated heat-protection and load-bearing structures. Thermal vibration analysis ensures service safety in environments with dynamic thermal loads. A free vibration analysis model of an FG-GPL porous beam was proposed based on the micromechanical model and Timoshenko beam theory (TBT) under a nonlinear temperature profile. First, three types of functionally graded porosity distributions and graphene-platelet dispersion patterns were assumed along the thickness direction of the beam. Material properties, including elastic modulus, Poisson’s ratio, and density, were calculated using the Gaussian random field scheme and Halpin–Tsai model. Second, a nonlinear temperature profile was established considering the influence of porosity and graphene platelets by solving a one-dimensional–heat-conduction equation. Third, the governing equations of thermal vibration of the beam were obtained using the TBT and Hamilton’s principle. The frequencies of different porosity distributions and graphene-platelet dispersion pattern combinations were calculated by solving the governing equations using the transfer function method. Finally, the results were validated, and the parameter effects of the temperature profiles, weight fraction of graphene platelets, porosity coefficient, and thermal gradient on the fundamental frequencies were analyzed. Compared to a linear temperature profile, the frequency under a nonlinear temperature profile is hardly changed for the combined symmetrically distributed porosity and GPL beams, while it is different for the asymmetric combinations.

Influence of the milling conditions on the compressive strength of Ti/TiC composite materials sintered at atmospheric pressure

High compressive strength composite materials based on commercially pure titanium were synthesized from Ti Cp grade 2 powders processed by high-energy ball milling using n-hexane as PCA and subsequent sintering in a tubular furnace under argon atmosphere at 1100 °C for 2 h, at atmospheric pressure. The study focused on two main aspects: (i) The effect of speed and milling time on the microstructure and (ii) the relationship between the microstructure and the mechanical resistance of the obtained material. It was found that the presence of TiC was related to the mechanochemical process during milling that occurs under specific conditions of speed and time when enough energy was transferred to the powder coupled with the thermal process at elevated temperature. According to the DSC peaks, the activation energy for the transformations is close to 171 kJ/mol. The microstructure of the sintered samples was characterized by SEM EDS, XRD, and TEM, and the mechanical properties by compression and hardness tests. The high compressive strength of the specimens was attributed to three aspects: (i) the distribution of particles in the sintered samples, (ii) the fine grain size derived from the milling process and (iii) the formation of titanium carbide. A maximum compressive strength of 2.8 GPa makes this material sintered by a simple and low-cost route, very competitive with other advanced Ti composites.

Characterization of the structural and mechanical properties of pinecone fish (Monocentris japonica) scales.

In this paper, the microstructure characteristics and mechanical properties (including nano-indentation, tensile, and penetration behaviors) of the scales from pinecone fish (Monocentris japonica) were investigated. The M. japonica scales display a unique hierarchical structure and consist of three layers: an outer bone layer with high mineralization, an intermediate bone layer with obvious pore structures, and an inner collagen layer composed of multiple plies of collagen fibers. The hardness and indentation modulus of the three structural layers exhibit gradient changes, and decrease gradually from the outer layer to the inner layer. Tensile tests show that the tensile response and failure modes of the scales are different under dry and hydrated conditions. The dry scales have higher tensile strength (46.35 MPa) and Young's modulus (0.74 GPa), while the hydrated scales exhibit higher ultimate strain (20.18%) and toughness (4.57 MPa). Penetration tests indicate that the scales have a significantly high resistance to penetration, and increase the penetration force by more than six times compared with the descaled skin. Furthermore, the structure-property relationship of the M. japonica scales was discussed. It is found that the hard outer layer and the porous intermediate layer help to disperse the stress, and the soft inner layer containing collagen fiber plies helps to deflect the crack propagation, which are responsible for the excellent mechanical properties of the scales. The outcome of this study can provide a valuable biomimetic design inspiration for lightweight and high-strength composite materials in engineering fields. RESEARCH HIGHLIGHTS: Microstructure characteristics and mechanical properties of the Monocentris japonica scales were investigated. The M. japonica scales can be divided into three layers rather than two layers. The M. japonica scales exhibited high tensile strength and penetration resistance.

Carbon fiber reinforced polymer and tensegrity structures in search of model architectural and engineering solutions

The current era of nanomaterials brings advancements in science and technology. This creates new solutions and possibili-ties in the creation of novel spatial structures. This study leads through the presentation of iconic architectural objects creat-ed with the use of high strength composite materials and tensegrity structure. Then presents the design process, numerical simulations of the three-way tensegrity grid prototype module. Static stress simulations were done within the simulation engine of the Fusion 360 software. Moreover, 1:1 scale prototype was developed. It could be used as a modular construction slab of a novel architectural design. One of the key characteristic features of high strength composite materials, high strength-to-weight ratio, combined with tensegrity structures allows to develop lightweight and hence very durable spatial structures. This gives tensegrity structures a very low dead load value as compared to traditional reinforced concrete struc-tures. Thanks to the application of high strength and hence lightweight materials, the dead load of the prototype is only 0,18 kN/m2.

Identification of temperature-dependent elastic and damping parameters of carbon–epoxy composite plates based on experimental modal data

High-strength composite materials are receiving increased attention within the aerospace and transportation industries. These materials, although light in weight, still impart high stiffness when compared to conventional structural materials, e.g., aluminum and steel. Fibers and matrix are the basic constituents of composite materials. During high-speed maneuvering of aircraft and high-speed trains, the composite materials are subjected to dynamic loads in changing temperatures. The dynamic behavior of composites strongly depends on the ambient thermal environment. Furthermore, during the in-situ operation, the quantification of real-time dynamic loads is a challenging task. Therefore, the experimental investigation of the dynamic behavior of several carbon-fiber epoxy laminated composite plates at different temperatures, namely 0°C, 25°C, 50°C, 75°C, 100°C, and 125°C, is carried out using operational modal analysis, to identify the modal characteristics of the structure, and the temperature-dependent modal data of the tested composite plates is given in the supplementary data. The temperature-dependent elastic and damping parameters of the carbon–epoxy laminate are estimated using a genetic algorithm-based parameter identification scheme for different sets of modal contribution. A combined experimental and numerical simulation procedure is implemented to estimate deterministic material parameters at different temperatures. To obtain the in-situ material parameters for a given operating frequency range, the modal contribution is selected such that the operating frequency of interest lies within the considered resonance modes. As an example of matrix-dominated elastic parameter, the shear modulus, has been found to degrade significantly with increasing temperature, and shown a strong correlation with temperature.

Multifunctional Carbon-Basalt hybrid composites against bird strike

A bird strike is a common occurrence during an aircraft's takeoff and landing and is classified as a high-velocity impact, which can cause severe damage, a decrease in aerodynamic efficiency, and may lead to catastrophic failure. High strength composite materials are used in the wing structure to resist the bird strike. Stealth is an important factor for military aircraft, as it reduces the detectability range of the target. The current aircraft wing structure incorporates different systems to perform various functions, so a composite wing capable of performing multiple functions of providing stealth while retaining its existing properties is required. The need for sustainable green materials has shifted the focus to natural materials, and hybridization is the way to improve the properties. The current study proposes a multifunctional hybrid carbon-basalt-polyaniline composite for aircraft wing skin that can absorb electromagnetic (EM) waves while maintaining its mechanical properties. A polyaniline with 5 % weight was found to be optimal, as the prepared sample has a dielectric loss tangent of 2.1396. The hybrid composite was simulated against a bird strike and a maximum deflection of −48.54 mm was observed for a thickness of 1.2 mm. The deflection behavior of the prepared composite was compared to several works, and a thickness of 3.6 mm was found to be optimal for a deflection of −28.97 mm. For a curved leading-edge profile, the observed deflection for 1.488 mm thickness was 580 mm. An all-composite wing model was designed and proposed having two ribs, one spar, and two stringers all modelled in carbon-basalt-PANI composite showing the maximum center point deflection of 450 mm. The prepared multifunctional hybrid composite has a high potential for use in aircraft wing skins due to its reasonable mechanical properties, good EM wave absorption, and ability to withstand bird strike.

A Building of Energy Keeping Mobile House Based on Basalt Fiber

Research relevance: recently production of basalt fiber has become widespread as the basis for various industrial products. The mobile house is effectively used in the Ministry of Emergency Situations, energy conservation, agriculture and livestock. Research objectives: to investigate the deformation properties of basalt networks and basalt composites to obtain a layered system. Creation of multilayer heat-insulating high-strength composite materials based on basalt fiber and modeling of an energy-saving mobile home based on a multilayer composite material. Research materials and methods: the deformation of the basalt mesh depending on temperature was studied in order to strengthen the structure of the composite material. Basalt grids withstood temperatures from 100°С to 400°С for 30 minutes. Research results: prototypes of mobile houses based on a new layered material were prepared. Conclusions: tested basalt-plastic rebars are characterized by brittleness during destruction, depending on the thickness and diameter of the rod.

High Strength Construction Material Based on Sulfur Binder Obtained by Physical Modification

In this work, a method for obtaining a high-strength composite material on a sulfur binder without the use of chemical modifiers was proposed. It consists in obtaining a thixotropic casting mixture in the vicinity of the yield point of the system during vibration laying. The compressive strength of the obtained composite was about 97.5–94.0 MPa. Physical and mechanical characteristics remained stable for 7 years. The samples were obtained for a model composition of sulfur/marshalite (finely ground 98% silicon dioxide). The microstructure of the synthesized material was studied by electron microscopy, the results of which showed that shrinkage cavities are characteristic of a material with a low density, and no shrinkage cavities were found for a high-strength material. The phase composition was determined by the methods of XRD analysis, according to the results of which it can be argued that sulfur is in the orthorhombic form (S8). This technique can be proposed for obtaining the high-strength stable building material.

Dynamic Simulation and Parameter Analysis of Weaved Composite Material for Unmanned Aerial Vehicle Parachute Recovery in Deployment Phase

Aiming at the parachute recovery of fixed-wing unmanned aerial vehicles, a method of parachute deployment by tractor rocket is proposed. First, the tensile tests were carried out on high-strength polyethylene and brocade silk-weaved composite materials. The dynamic property parameters of the materials were obtained, which was the input for the dynamic model of the parachute deployment phase. Second, the model was verified by the experiment results. Finally, parachute weight and rocket launch temperature during the deployment phase were studied. The results showed that the dynamic model has good accuracy; as the parachute weight increases, the maximum snatch force of the extraction line and the sling decreases as the force on the suspension lines increases and the deployment effect worsens. With the temperature rise, the maximum snatch force on the extraction line, sling, and suspension lines increases and the deployment length changes slightly.

Study on the Variation Pattern and Influencing Factors of Poisson’s Ratio of Bamboo

As a natural polymer material, bamboo is regarded as a super material with lightweight but excellent mechanical properties. With the increasing application of bamboo in structures, high-strength composite materials, bridges, musical instruments, and damping materials, the study of Poisson’s ratio is of great significance to the structural design and stability of these materials. In this work, Poisson’s ratio of bamboo for different ages, growth heights, and bamboo wall radial positions were determined by electrical measurement. The relationships between intrinsic factors (density, chemical composition, crystallinity, and microfibril angle) and Poisson’s ratio were also analyzed. The results showed that Poisson’s ratio of bamboo for different ages and locations ranged from 0.180 to 0.334, decreased with the increasing bamboo age, growth height, and the radial position from the outer layer to the inner layer. While the peak values of Poisson’s ratio were obtained at bamboo of 2 years old, lower growth height, and near the outer layer of the bamboo. Furthermore, the Poisson’s ratio had a positive correlation with the increasing density, cellulose content, and MFA, but a negative correlation with lignin content. There is no direct relationship between the crystallinity and Poisson’s ratio, but it affects the axial and transverse deformation of bamboo, which can be used as an indirect index to judge Poisson’s ratio.

High strength composites of carbon fiber sheets-veneers sandwich-structure for electromagnetic interference shielding materials

Due to the advantages of porous structure, anisotropy, and fiber composition, wood possesses great potential to be a high-strength electromagnetic interference (EMI) shielding material. This study used vacuum assisted resin transfer molding (VARTM) technology to fabricate EMI shielding composite material by combining carbon fiber sheets and wood veneers via infusion of epoxy resin. The shielding effectiveness of the composites against electromagnetic waves in the 8.2–12.4 GHz (X-band) can reach 40 dB. The flexural and tensile strength (i.e., 442.3 and 195.5 MPa, respectively) of the composite were 6-fold and 3-fold higher than natural poplar (i.e., 69.8 and 55.6 MPa, respectively), respectively. The composites possessed superior thermal conductivity (0.91 W m-1 K-1) compared to poplar, good water resistance and surface hydrophobicity. The addition of carbon fiber sheets not only improved the mechanical performance of samples, but also made samples possessing the ability to shielding electromagnetic waves. This work provides a novel technology to make a natural bio-based high-strength composite material for the EMI shielding applications.

Improving the strength of bending elements of glued wood

In the article, the behaviour of glued wood beams are studied in order to increase their strength under normal stresses by means of combined reinforcement. The design of the reinforced beam provides reinforcement of the compressed area by steel rod, and of the tensioned zone – by external tape reinforcement from high-strength composite materials. An attempt to increase the strength of wood elements at normal bending stresses using this type of reinforcement has been made. Based on the experimental research results, graphs of layer-by-layer deformation along the height of beams are constructed. Data on the bearing capacity of the tested samples are presented.