J. Jansons

Mechanical properties of polyester polymer-concrete

The properties of a polymer-concrete composed of polyester matrix and locally available rock aggregate are investigated. The formula of the concrete is found by an experimental-calculation approach in such a way as to attain a closer packing of the aggregate particles on the one hand, and to ensure the needed processing characteristics (placeability) of the mix on the other. It is shown experimentally that the material obtained has a rather high compression strength. Under prolonged compression loads, the polymer-concrete exhibits a noticeable creep behavior with a linear relation between the creep strains and stresses. After the action of half the ultimate load over 3000 h, the total strains exceed the instantaneous ones by 2.0 to 2.2 times. The accumulation of irreversible strains is also observed; however, their contribution to the total strain is small. It is found that the stress-strain relation can be represented by the equation of linear hereditary creep theory.

Creep and damage accumulation in orthotropic composites under cyclic loading

Experimental results and theoretical prediction of the response of glassfiber-reinforced polyester under quasi-static, static (creep), and cyclic (fatigue) loading are presented. The nonlinear strain component at static loading and the strain amplitude rate at cyclic off-axis loading of an orthotropic composite are shown to follow the associated flow rule with a single-parameter quadratic potential function. The influence of fatigue damage on deformation is considerable due to the reduction in the elastic modulus of the composite and is apparently negligible with respect to its effect on the parameters of the creep kernel.

Effect of Water Absoption, Elevated Temperatures and Fatigue on the Mechanical Properties of Carbon-Fiber-Reinforced Epoxy Composites for Flexible Risers

The influence of water absorption, under different temperatures and thermal aging in an oven, on the elastic and strength characteristics of carbon-fiber-reinforced epoxy composites is investigated by comparative tests in three-point bending. The tension-tension fatigue behavior of the composites is also studied.

Water Resistance of Polyester Polymer Concrete

The results of experimental investigation of polyester resin and polymer concrete at a long-term (four-year) exposure to water and air with 98% RH are presented. The polymer concrete was composed of a polyester resin as a binder, lime flour, quartz sand, and granite chips. The resin content in concrete was 20 wt.%. The features of sorption properties of the materials investigated are discussed. Data on the water effect on the compressive strength in short-term loading are reported. The creep tests of virgin polymer-concrete specimens were carried out for five years at different stress levels from 0.11 to 0.44 of the short-term prismatic strength. The effect of moisture on the creep behavior was also studied.

Analysis of reversible and irreversible strains in the creep of a nonlinear viscoelastic polymer

The results of an experimental investigation and analytical description of creep of a nonlinear viscoelasticplastic material (a Upilex-S polyimide film) in tension are presented. The elastic modulus, yield stress, and ultimate strength were found from quasi-static tests with a constant deformation rate. The total strain of the material was assumed to be the sum of elastic, viscoelastic, and irreversible strains. The reversible elastic and viscoelastic and the irreversible deformation of the material were investigated in experiments on creep with the subsequent recovery of deformations (creep recovery). The nonlinearity of its viscoelastic behavior was taken into account using the principle of stress-time superposition. The results obtained allow one to describe the creep behavior of a material at various stages of loading and unloading.

DEFORMATIONAL PROPERTIES OF POLYMER CONCRETE DURING LONG-TERM EXPOSURE TO WATER

Changes in the elastic and viscoelastic (creep) characteristics of polymer concrete and its structural components (polyester resin, unfilled or filled with diabase flour) during a long-term exposure to water at 20°C were studied. Modeling the structural changes in polymer concrete with time showed an increase in the relative volume content of pores filled with water and a decrease in that of unfilled pores. Based on the free-volume concept and the data on swelling due to moistening and shrinkage due to physical aging of the binder, a rather accurate estimate of the time-moisture reduction function for polymer concrete was obtained. The function was found to be nonmonotonic: the interval of increase was followed by an interval of decrease.

Creep of polymer concrete in the nonlinear region

Two polyester-based polymer concretes with various volume content of diabase as an extender and aggregate are tested in creep under compression at different stress levels. The phenomenological and structural approaches are both used to analyze the experimental data. Common features of changes in the instantaneous and creep compliances are clarified, and a phenomenological creep model which accounts for the changes in the instantaneous compliance and in the retardation spectrum depending on the stress level is developed. It is shown that the model can be used to describe the experimental results of stress relaxation and creep under repeated loading. Modeling of the composite structure and subsequent solution of the optimization problem confirm the possibility of the existence of an interphase layer more compliant than the binder. A direct correlation between the interphase volume content and the instantaneous compliance of the composite is revealed. It is found that the distinction in nonlinearity of the viscoelastic behavior of the two polymer concretes under investigation can be due to the difference in their porosity.

SORPTION CHARACTERISTICS OF POLYMER CONCRETE DURING LONG-TERM EXPOSURE TO WATER

The moisture sorption characteristics of polymer concrete and its components (polyester resin, unfilled and filled with diabase flour) on long-term (up to 15-year) exposure to water at different temperatures are studied. It is established that, during the long-term sorption and subsequent desorption at 20°C, the ratio of diffusion coefficients of the polymer concrete and the corresponding resin is equal to the value of time-moisture reduction function, which characterizes changes in the creep compliance of the materials. The evaluation of the diffusion coefficient of the composite from the properties of its components, by using various known heat-and-mass-transfer models, shows that most acceptable is the Kerner model. With account of volume content of pores, an estimate for the limiting moisture content in the composite is proposed. An analysis of sorption curves of the composite and the corresponding resin reveals that Ficks law does not describe the experimental results in the range of large times and/or elevated temperatures. In the case of polyester resin filled with diabase flour, the “composite effect” is expressed in a linear increase in the specimen mass (the rate of the increase is temperature-dependent. In the case of polymer concrete, the “composite effect” is expressed in mass losses, which can be described by Ficks law with a diffusion coefficient and a limiting moisture content both depending on temperature.

Modification of polyester resins during molding of glass-fiber-reinforced plastics

The effect of addition of two new urethane prepolymers on the mechanical properties of unsaturated polyester resins and glass-fiber-reinforced plastics based on them is investigated. The effect of concentration of these additives on the elastic modulus, elongation at break, and flexural strength of hardened orthophthalic resins is evaluated. A significant increase in the strength of the binders and glass-fiber-reinforced plastics (GFRPs) based on them is observed upon adding urethane prepolymers to the resins. The properties of laminated and randomly reinforced glass-fiber plastics with the modified orthophthalic resins are compared with those of similar GFRPs based on popular brands of industrial resins.

Creep prediction of a layered fiberglass plastic

The results of short-term creep tests of a layered glass fiber/polyester resin plastic in tension at angles of 90, 70, and 45° to the direction of the principal fiber orientation are presented. The applicability of the principle of time-temperature analogy for the prediction of long-term creep of the composite and its structural components is revealed. The possibility of evaluating the viscoelastic properties of the composite from the properties of structural components is shown.