Yu. P. Zezin

Effect of hydrostatic pressure on the viscosity of failure of polymeric materials

ConclusionsA setup and method were developed for studying the effect of hydrostatic pressure on the characteristics of the crack resistance of polymeric materials. The viscosity of failure of material K-4I based on butyl rubber was determined in a wide range of rates of crack propagation and hydrostatic pressures. It was found that an increase in the hydrostatic pressure increases the resistance to crack propagation in a polymeric material. The pressure-time analogy method, where the dependences of the viscosity of failure on the rate of crack growth are parallelly shifted to the value of the pressure-time shift and a generalized curve is formed, can be used for taking the effect of the pressure into consideration.

Thermovisco-hyperelastic behavior of elastomeric materials modified by filler nanoparticles

We present the results of experimental studies of hyperelastic and relaxation properties of polymer composites with elastomeric matrix made of hydrogenated nitrile butadiene rubber filled with nanoparticles of technical carbon in the temperature range 19–150° C. We present typical experimental diagrams of deformation of the material with constant strain rate and the stress relaxation curves at different strain levels under tension and compression conditions. We consider a possible version of constitutive relations for describing some singularities of the behavior of the material under study. We developed a method for determining all the parameters of the accepted relations on the basis of the results of uniaxial tests. We found a nonmonotone dependence of the relaxation modulus on the temperature and proposed a formula for describing this dependence in the temperature range under study. To justify the possible use of the considered constitutive relations to perform calculations under conditions of arbitrary compound stress state, we performed numerical modeling of the compression experiment for cylindrical samples. A rather satisfactory agreement between the computational results and experimental data was obtained.

Damage accumulation and strength of adhesion bonds in filled polymeric systems

ConclusionWe have proposed a model for the mathematical description of the kinetics of FPS debonding during deformation, based on use of the tension curves and the dependences of the volume strain on the longitudinal strain. For the evaluation of the strength of the bonding of the filler particles with the polymeric matrix, we have used the concepts on reduction of the resistance to deformation of the FPS as a result of debonding. This approach makes it possible to determine the distribution of the debonded filler particles as a function of the tensile strain, the critical value of the strain corresponding to transition from the adhesive type of damage accumulation in the FPS to the cohesive type, and the distribution of the filler particles with respect to the adhesion bond strength.

Effect of Hydrostatic Pressure on the Rate Dependence of the Fracture Toughness of High-Filled Polymeric Materials

The paper presents results of an experimental investigation of the effect of hydrostatic pressure on the fracture toughness of high-filled polymeric materials. It has been shown that the critical value of the stress intensity factor and hence the crack propagation rate increase with increasing hydrostatic pressure of the medium. To take into account the effect of pressure on the fracture toughness characteristics of the materials under investigation, it is proposed to employ the pressure-time analogy method. The method makes it possible to represent experimental plots of fracture toughness against crack propagation rate, obtained at various levels of hydrostatic pressure, as a generalized pressure-time plot that defines the influence of loading conditions on fracture characteristics of the material. Simple empirical relations are proposed for the approximation of the experimental data obtained.

Nonlinear effects in deformation of filled elastomers with nanodimensional fillers

Various nonlinear effects manifesting themselves in the deformation of filled elastomers are analyzed, and the advantages and restrictions in the use of several constitutive relations proposed to describe the nonlinear viscoelastic behavior of the materials under study are discussed. We also note that further development of models of nonlinear deformation of filled elastomers under finite strains, which would permit describing their deformation properties more completely, is highly desirable.

Study of viscoelastic properties of elastomers reinforced by nanoparticles

The results of experimental studies of hyperelastic and relaxation properties of polymer composites with elastomer matrix based on hydrogenated nitrile-butadiene rubber filled with technical carbon particles in the temperature range 20–125°C are presented. The characteristic experimental strain curves of materials in extension at a constant strain rate and the stress relaxation curves in materials at various tensile strain levels are given. A possible version of constitutive relations for describing some specific features of mechanical behavior of the considered materials under finite strains is considered. The obtained experimental data are used to verify the proposed constitutive relations experimentally. It is shown that the temperature-time analogy permits one to use the obtained constitutive relations to analyze nonmonotone variations in the relaxation properties of the considered materials as the temperature increases in the range under study.

The effect of hydrostatic pressure on the crack resistance of particulate reinforced composite materials

The effect of hydrostatic pressure on the fracture toughness of disperse-reinforced composite materials is investigated. It is shown that increased hydrostatic pressure leads to an increase in the critical value of the stress intensity factor and, as a consequence, to an increase in the crack propagation rate. In this case, the pressure-time analogy method can be used to describe the effect of hydrostatic pressure on the characteristics of the crack resistance. This method enables us to represent the experimental data obtained in the form of a generalized dependence of the fracture toughness on the reduced loading rate.

Cracking resistance and long-term strength of dispersion-hardened composites

ConclusionsThe previously proposed relationships were used to develop a method of predicting the endurance of dispersion-hardened composites on the basis of results of tensile tests on the material at a constant strain rate. It is shown that stress raisers in the form of cut out or defects which weaken the working cross section, greatly reduce the endurance of the material. The proposed method of evaluating the effect of stress raisers on the endurance of polymer materials is based on the assumption on the initiation of a crack-like defect and its propagation in accordance with the loss of linear fracture mechanics.

Conditions of the ductile-brittle transition in failure of polymer materials

ConclusionsThe polymer materials are characterized by the transition from ductile to brittle fracture with increasing loading rate and decreasing temperature. The brittle fracture susceptibility of the material can be determined on the basis of the critical size of the defect/ crack. The measure of the cracking resistance of plastics can often be represented by the material scale of the crack length. The quality of the critical size of the defect/crack to the material scale of the crack length can be used as a criterion determining the conditions of transition from ductile to brittle fracture.