A. M. Kuperman

Comparison of Fracture Energies of Epoxy-polysulfone Matrices and Unidirectional Composites Based on Them

The fracture energies of modified epoxy matrices and unidirectional glass (GFRP)-, organic (OFRP)-, and carbon (CFRP)-fiber-reinforced plastics based on them are compared. The unidirectional composites were fabricated by winding. Epoxy-polysulfone compositions were used as matrices containing from 5 to 20 wt.% of PSK-1 polysulfone. The matrices were cured with triethanolaminotitanate. It is shown that the fracture mechanisms of GFRP, OFRP, and CFRP in shear differ, which is supposedly related to the nature of fibers. The fracture energy of reinforced plastics is mainly determined by the impact strength of matrix. The delamination energy GIRcm of GFRP, OFRP, and CFRP increased monotonically with content of polysulfone in the matrix. A marked growth in GIRcm was observed at a content of polysulfone exceeding 10 wt.%. The crack resistance of the composites under investigation increased two times. The fracture toughness of GFRP and OFRP was 3-4 times higher than that of CFRP at any concentration of polysulfone. A growth in GIRm of the matrices started when the content of PSK-1 exceeded 5 wt.%, and at 15-20 wt.% of PSK-1, the values of GIRm increased four times. In all the cases investigated, a correlation between the crack resistance of reinforced plastics and that of polymeric matrices was observed.

Behavior of reinforced plastics based on polysulfone matrix under impact loading

A particular method of studying the dynamic response of fibrous composites is used. The method comprises a “stage-by-stage” investigation of oscillograms of the impact impulse for carbon, glass, and aramid fiber-reinforced plastics. The optimum combination of estimate parameters is given for the adequate description and comparison of failure processes in different reinforced plastics. It is shown that polysulfone polymer increases the energy required for the appearance of considerable delamination in the plastics, thus increasing the impact resistance of the materials. The experimental data show that the polysulfone plastics have the same strength characteristics as the epoxy plastics and are superior with regard to the absorbed energy. The carbon fiber-reinforced plastics (both polysulfone and epoxy) show lower impact resistance than the aramid and glass fiber plastics.

Organic fiber reinforced plastics based on complex hybrid matrices including polysulfone and carbon nanotubes as modifiers of epoxy resins

Organic Fiber Reinforced Plastics (OFRP) based on aramid fibers are as a rule used in constructions working under extremal conditions. In view of this, the possibility of increasing the resistance of OFRP to destruction by modifying matrices with thermoplastic polymers and carbon nanotubes (CNTs) offers much promise. In this work, we present the results obtained in a study of the properties of OFRP based on Rusar fibers and epoxy matrices containing either CNTs or a thermoplastic (PSK-1 polysulfone) or both these components simultaneously. The data obtained substantiate the possibility of using epoxypolysulfone matrices for the preparation of wound composites. This modification noticeably increases crack and impact resistance of OFRP based on aramid fibers without decreasing the glass transition temperature, as when matrices are plasticized by rubber and active diluents. The strongest effect of polysulfone introduced into an epoxy matrix is observed at a large (20 wt %) content of PSK-1. The modification of epoxypolysulfone matrices by CNTs also increases the shear strength of OFRP and almost does not change the fracture toughness and compression strength. The introduction of CNTs into epoxy matrices is less effective and can increase crack growth resistance of OFRP by approximately 30% only at a large (1%) content of CNTs. Small CNT admixtures (0.3–0.6%) do not influence the fracture toughness. Possible mechanisms of the changes observed are considered.

Stresses Arising During Cure of the Composite Wound on the Cylindrical Surface of an Element of Exhaust System

The interaction between an anisotropic composite ring and a metal mandrel with reference to the problem of repair of the exhaust system of road cars by means of composite materials is investigated. The axisymmetric problem on determination of the stress-strain state of the composite ring upon its cooling on the cylindrical mandrel is solved. Expressions describing the distribution of stresses and strains across the thickness of the ring and mandrel in the case of elastic statement of the problem are obtained. The cases of emergence of tension between the mandrel and composite ring are analyzed. It is shown that an increase in thickness of the unidirectional anisotropic composite ring can lead to the emergence of tensile stresses as a result of which the ring can separate from the mandrel. A criterion of solidity of the structure ensuring tension of the composite on the mandrel is put forward.

Shear Elastic and Strength Characteristics of Syntactics Based on Hollow Glass Microspheres

Different methods to study the elastic and strength properties of syntactics — materials based on epoxy resins filled with hollow glass microspheres (HGMs) — are presented. Measurement results for the shear modulus and strength of the materials are analyzed. The effect of microsphere volume fraction in the polymeric matrix on the characteristics is shown. Experiments are performed to investigate the failure mechanisms of syntactics under compression.

Relaxation characteristics of reinforced plastics in tension of ring specimens by split disks

The behavior of organic- and carbon-fiber-reinforced plastics based on three different binders was investigated under three test modes: stress relaxation, strain relaxation, and creep. In the theory used, the linearized generalized Maxwell–Gurevitch equation is employed. From stress relaxation diagrams, the relaxation constants of the equation are determined, which are utilized for calculating creep diagrams. The elastic and strength characteristics of the composites are also investigated.

Carbon nanotubes as modifiers in epoxypolysulfone matrices for wound organic-fiber-reinforced plastics

The effect of multiwalled carbon nanotubes (MWCNTs) on the properties of wound organic-fiber-reinforced plastics (OFRPs) based on an epoxy matrix modified with a 20% polysulfone has been investigated. It is shown that polysulfone and a polysulfone-MWCNT blend do not affect the density and porosity of the composites obtained. The use of small additions (to 0.3%) of MWCNTs increased the strength and fracture energy of OFRPs in shear. The introduction of 0.1-1.0 wt.% nanotubes into the epoxypolysulfone matrix did not increase the fracture toughness of the composites.

EPR spectroscopic and X-Ray diffraction studies of carbon fibers with different mechanical properties

The carbon fibers obtained by carbonization of polyacrylonitrile fibers were studied by electron paramagnetic resonance and X-ray diffraction analysis in the range of small and wide scattering angles. Their elastic and strength characteristics were also studied. The concentration of the paramagnetic centers was correlated with the mechanical properties of carbon fibers. The wide-angle X-ray diffraction study did not reveal essential structural differences in the carbon fiber samples with different mechanical properties. At the same time, the small-angle X-ray scattering study showed that the fiber nanostructures with different mechanical properties differ substantially.

Adhesion of modified epoxy matrices to reinforcing fibers

The adhesive strength of joints between fibers and epoxy matrices modified with three types of modifiers—active diluents, thermostable rigid-chain thermoplasts, and dispersed fillers—is studied. It is shown that the introduction of modifiers increases interface strength in several cases in a particular concentration interval. The introduction of thermostable thermoplasts into epoxides is more effective. Possible mechanisms of adhesive-strength synergism for each of the modification types are discussed.

High-strength reinforced plastics

A historical excursus is presented on the participation of the Laboratory of Reinforced Plastics of the Institute of Chemical Physics RAS in the development of scientific and technological foundations of producing and refining these materials. The main directions of research include studying the extent of realization of the fiber properties in unidirectional composites and determining the roles of the fibers, polymer matrix, and material structure. Record tensile properties of organic- and carbon-fiber reinforced plastics and compressive properties of glass-fiber reinforced plastics have been achieved. Most effective directions for application of these materials are identified.