Effect of surface modification of fibers with a polymer coating on the interlaminar shear strength of a composite and the translation of fiber strength in an F-12 aramid/epoxy composite vessel

The surface of aramid fibers was modified with a polymer coating — a surface treatment reagent containing epoxy resin. The resulting fibers were examined by using NOL tests, hydroburst tests, and the scanning electron microscopy. The modified fibers had a rougher surface than the untreated ones. The interlaminar shear strength of an aramid-fiber-reinforced epoxy composite was highest when the concentration of polymer coating system was 5%. The translation of fiber strength in an aramid/epoxy composite vessel was improved by 8%. The mechanism of the surface treatment of fibers in improving the mechanical properties of aramid/epoxy composites is discussed. Russian translation publeshed in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 6, pp. 729–738, November–December, 2006.     

Effects of plasma and nitric acid treatment of carbon fibers on the mechanical properties of thermoplastic polymer composites

Polyacrylonitrile-based carbon fibers were submitted to nitric acid oxidation and a dielectric barrier discharge treatment to improve the interfacial adhesion in carbon-fiber-reinforced thermoplastic polymer composites. The mechanical properties of the composites were investigated. The results obtained showed that the tensile strength of the composites improved considerably due to the treatments.     

The Effect of Adhesion Interaction on the Mechanical Properties of Thermoplastic Basalt Plastics

The effect of temperature, adhesion time, and surface treatment of a reinforcing filler on the mechanical properties of thermoplastic basalt plastics based on a high-density polyethylene and a copolymer of 1,3,5-trioxane with 1,3-dioxolan is investigated. An extreme dependence for the adhesive strength in a thermoplastic-basalt fiber system is established and its effect on the mechanical properties of basalt plastics and the influence of the adhesion contact time on the adhesive strength in the system are clarified. The surface modification of basalt fibers in acidic and alkaline media intensifies the adhesion of thermoplastics to them owing to a more developed surface of the reinforcing fibers after etching. It is found that the treatment in the acidic medium is more efficient and considerably improves the mechanical properties of basalt plastics.     

Modeling of the mechanical characteristics of chaotically reinforced GRP

Experimental results on the mechanical properties under tension and compression of composites based on a phenol-formaldehyde binder reinforced with short glass fibers are reported. Unidirectional structures, in which the reinforcing elements had different orientations with respect to the external load, were studied, as well as chaotically reinforced composites. In addition, the mechanical properties of the polymer matrix and of the reinforcing elements as well as the bond strength between them were also determined. An analysis of the results obtained in the tension experiments is presented, based on a model in which the frictional mechanism of interaction between the polymer matrix and the reinforcing elements is utilized. The quantitative relationships deduced give results agreeing with those obtained experimentally.     

Change in the Surface Properties of Carbon Fibers as a Result of Plasmochemical Modification

The influence of plasmochemical modification of carbon fibers on their surface properties and compatibility with the PTFE matrix is investigated. It is shown that the thin PTFE coating formed on the carbon fiber surface improves the wetting of the fibers by PTFE. As a result, the mechanical characteristics of PTFE-based composites are improved.     

Regulation of the mechanical properties of thermoplastic carbon fiber-reinforced plastics by changing their production conditions and surface treatment of the fibers

The effect of technological parameters of processing and surface treatment of carbon fibers on the mechanical properties of carbon fiber-reinforced plastics (CFRPs) was investigated. The copolymer of 1,3,5-trioxane with 1,3-dioxolane was used as the polymer matrix, and medium-modulus hydrated cellulose Ural LO-24 carbon fibers served as the reinforcing filler. The polymer matrix was mixed with the carbon fibers by the method of combined extrusion. The dependence of the mechanical properties of CFRPs on the technological parameters of screw-disk extrusion was studied. It was found that the properties of the composites were greatly affected by the size of the working disk gap, the disk rotation rate, and the temperature in the zone of normal stresses. The surface of the carbon fibers was activated with atmospheric oxygen in the temperature range of 450–600°C, with mass loss of the fibers no greater than 3–4%. A 30–40% increase in the mechanical properties of the CFRPs was achieved. A decrease in the melt index of the 1,3,5-trioxane copolymer with 1,3-dioxolane reinforced with oxidized carbon fibers was observed, which should be taken into account in processing the composites into products. Introduction of carbon fibers in the 1,3,5-trioxane copolymer with 1,3-dioxolane allows us to increase the wear resistance and decrease the friction coefficient, which makes it possibile to use these materials in the friction units of machines and mechanisms, such as plain bearings, gears, and flange packings.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Ukrainian State University of Chemical Technology, Dnepropetrovsk, Ukraine. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 5, pp. 673–682, September–October, 1998.     

Composites reinforced with a system of three straight mutually orthogonal fibers

The effectiveness of reinforcement in direction 3 has been estimated by investigating the mechanical characteristics of two types of three-dimensionally reinforced materials differing with respect to the arrangement of the reinforcement and the fiber content in each direction. The superior transverse stiffness, shear strength, and transverse tensile strength of three-dimensionally reinforced composites based on a system of three mutually orthogonal fibers, as compared with laminated materials, is demonstrated. The theoretical values of the elastic constants, calculated from the relations of [5], are compared with the experimental data.For communication 1 see [5].Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 1011–1018, November–December, 1973.     

Effect of combined extrusion parameters on mechanical properties of basalt fiber-reinforced plastics based on polypropylene

Basalt fibers are efficient reinforcing fillers for polypropylene because they increase both the mechanical and the tribotechnical properties of composites. Basalt fibers can compete with traditional fillers (glass and asbestos fibers) of polypropylene with respect to technological, economic, and toxic properties. The effect of technological parameters of producing polypropylene-based basalt fiber-reinforced plastics (BFRPs) by combined extrusion on their mechanical properties has been investigated. The extrusion temperature was found to be the main parameter determining the mechanical properties of the BFRPs. With temperature growth from 180 to 240°C, the residual length of the basalt fibers in the composite, as well as the adhesive strength of the polymer-fiber system, increased, while the composite defectiveness decreased. The tensile strength and elastic modulus increased from 35 to 42 MPa and 3.2 to 4.2 GPa, respectively. At the same time, the growth in composite solidity led to its higher brittleness. Thus, a higher temperature of extrusion allows us to produce materials which can be subjected to tensile and bending loads, while the materials produced at a lower temperature of extrusion are impact stable. The effect of the gap size between the extruder body and moving disks on the mechanical properties of the BFRPs is less significant than that of temperature. An increase of the gap size from 2 to 8 mm improves the impregnation quality of the fibers, but the extruder productivity diminishes. The possibility of controling the properties of reinforced polypropylene by varying the technological parameters of combined extrusion is shown. The polypropylene-based BFRPs produced by the proposed method surpass the properties of glass and asbestos fiber-reinforced plastics.Submitted to the 10th International Conference on Mechanics of Composite Materials (Riga, April 20–23, 1998).Ukrainian State University of Chemical Technology, Dnepropetrovsk, Ukraine. Translated from Mekhanika Kompozitnykh Materialov, Vol. 33, No. 6, pp. 845–850, November–December, 1997.     

Influence of Modifiers on the Physicomechanical Properties of Sawdust-Polyethylene Composites

Polymer-wood composites based on recycled polyethylene (RPE) are investigated. Dispersed alder sawdust was utilized as a filler. To improve the compatibility between the nonpolar matrix and the polar wood fibers as a reinforcement, two types of modifiers were used, which differed in their chemical nature and mechanical interaction with the constituents of the composites. The modifiers of the first type (paraffin and OP) improved the dispersibility of sawdust (SD), and those of the second type (Exxelor 1015 and OREVAC) contained groups of maleic anhydride, which interacted with the OH-groups of SD. The effect of the modifiers on the moisture sorption by SD, the dispersibility of the filler in the matrix, and the strength characteristics (ultimate strengths and moduli in tension and bending) of dry and moist RPE–SD composites and on their moisture sorption is estimated. The best results were obtained for the composites modified with paraffin, which is due to the more efficient employment of the strength and rigidity of well-dispersed SD fibers. In their strength characteristics, the RPE-based composites investigated are comparable to composites based on low-density polyethylene.     

The Effect of Surface Treatment of F-12 Aramid Fibers with Rare Earths on the Interlaminar Shear Strength of Aramid/Epoxy Composites

Solutions of a rare-earth modifier (RES) and the epoxy chloropropane (ECP) grafting modification method are used for the surface treatment of F-12 aramid fibers. The effects of RES concentration on the interlaminar shear strength (ILSS) of F-12 aramid fiber/epoxy composites are investigated in detail, and the fracture surfaces of ILSS specimens are analyzed by SEM. It is shown that the RES surface treatment is superior to the ECP grafting treatment in promoting the interfacial adhesion between aramid fibers and the epoxy matrix. However, the tensile strength of single fibers is almost unaffected by the RES treatment. The optimum ILSS is obtained at a 0.5 wt.% content of rare-earth elements.__________Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 41, No. 2, pp. 265–272, March–April, 2005.     

Strength properties of unidirectionally reinforced hybrid composites

Conclusions Experiments were carried out with several types of unidirectionally reinforced hybrid composites (organic fiberglass plastic, organic carbon-reinforced plastic, organic boron-reinforced plastic, and carbon fiberglass plastic) with various ratios of the volume content of the fibers in various modes of simple quasistatic loading. It is shown that the strength of the examined materials in the plane stress state can be described phenomenologically by the polynomial criterion of strength with the components of the tensors of the strength surface depending on the structural parameters. The result can be used to predict (carry out interpolation calculations) the strength of the above-mentioned composites within the examined ranges of the volume content of the reinforcing fibers to optimize the selection of the type and ratio of the content of various fibers in the hybrid composite taking into account specific requirements on the strength properties of the material in the structures.Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 35–41, January–February, 1984.     

Polypropylene reinforced with aramid and glass fibers

The effect of the chemical nature of the aramid fibers Phenylone, Terlon, Armos, and SVM on the mechanical, thermophysical, and antifriction properties of reinforced polypropylene was investigated. It was found that the composite filled with SVM fibers based on a stiff-chain polymer has high tensile strength and bending modulus. Reinforcement of polypropylene with Phenylone stiff-chain fibers produces a composite with a high impact viscosity. Organoplastics based on polypropylene and aramid fibers have a low density and friction coefficient and high durability. Reinforcement of polypropylene with aramid (SVM) and glass fibers increases the technological properties of the composites. The glass-filled organoplastics developed can be used in instrument making, radio engineering, and machine building as antifriction and construction materials.Ukrainian State Chemical Technological University, Dnepropetrovsk, Ukraine. Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 106–110, January–February, 1996.     

Method of investigating the stiffness and strength of composites

The use of a method of investigating the stiffness and strength of composites reinforced with fibers capable of conducting electricity, waves, or light is considered.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 1, p. 181, January–February, 1976.     

Influence of a Silica Aerogel Filler on the Mechanical,Thermal, and Physical Properties of Flax/Epoxy Composite

Mechanics of Composite Materials - The influence of Maerogel (MA) on the material properties of the flax fiber reinforced epoxy composites has been investigated. The composites were fabricated...     

Investigation of the dynamic characteristics of composites

The dynamic characteristics E and G and the damping capacity δ* of polymeric resins and composites based on glass, carbon, and boron fibers have been investigated. It is shown that the mechanical losses are correlated with the modulus of elasticity and the shear modulus of the resin and composites with different types of reinforcement. The vibrational strength of various structural materials is estimated.     

Predicting the transverse strength of unidirectional composites under combination loading

This article presents a mathematical model for predicting the transverse strength of unidirectional fiber composites subjected to combination transverse loading under different conditions. The behavior of the matrix is described by nonlinear physical equations consistent with the strain theory of plasticity for the active loading section. The fibers are assumed to be isotropic and elastic. The boundary-value problem of micromechanics that is formulated includes strength criteria for the matrix and fibers that mark the beginning of their possible failure. The modeling of the fracture process is taken farther through the use of a scheme that reduces the stiffness of the matrix and fibers in the failed regions in relation to the sign of the first invariant of the stress tensor. The method of local approximation is used together with the finite-element method to calculate the stress and strain fields in unidirectional composites with cylindrical fibers in a tetragonal layup. The model is used to study the behavior of an epoxy-based organic-fiber-reinforced plastic subjected to transverse loading in different simple paths — including simultaneous compressive and tensile loads, as well as transverse shear.Paper to be presented at the Ninth International Conference on the Mechanics of Composite Materials (Riga, October 1995).Translated from Mekhanika Kompozitnykh Materialov, Vol. 31, No. 4, pp. 473–481, July–August, 1995.     

Mechanical properties of henequen fibre/epoxy resin composites

By using surface-treated and untreated henequen fibres and an epoxy resin, composites were made by compression moulding, and their mechanical properties and failure modes were determined experimentally in tension, bending, and impact loading. The results obtained show that the treatment of fibre surface does not improve the bond between the fibres and the resin matrix, and the general mechanical properties of the composites are similar.     

Estimation of the optimal distribution of the fibers in carbon/carbon composite

Carbon/carbon (C/C) composites are widely represented in the industry and are utilized for extreme thermal and mechanical loading. Optimization of the fibers distribution allows by still high stiffness to provide reducing of the weight of the components that has crucial importance in aircraft and aerospace industry. A microstructure optimization problem for estimation of the microstructure with minimal compliance is formulated. The design variables of the posed problem are the local fibers distribution and porosity. The volume fractions of the fibers and pores in the whole microstructure are fixed. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effect of CNT modification on the mechanical properties of polyimide composites with and without MoS<Subscript>2</Subscript>

The aim of this work was to investigate the effect of surface modification of carbon nanotubes (CNTs) on the mechanical properties of polyimide (PI) composites with and without MoS₂. A three-phase system of CNT/PI/ MoS₂ laminates were fabricated with an extrusion-grade PI to produce CNT-reinforced laminates with MoS₂ volume fractions of 1–5%. The tensile and impact properties of CNT/PI composites and CNT/PI/MoS₂ laminates were also measured and compared. Results showed that the introduction of CNTs as reinforcing additives improved the tensile properties of the composites, but worsened their impact properties. Furthermore, the addition of MoS₂ increased the impact strength of the CNT/PI composites greatly. The optimum contents of CNT and MoS₂ have been found.