Study of the Interfacial Bond Behavior between CFRP Grid–PCM Reinforcing Layer and Concrete via a Simplified Mechanical Model

This paper presents the results of pull-out tests conducted to investigate the interfacial bond behavior between a carbon-fiber-reinforced polymer (CFRP) grid–polymer cement mortar (PCM) reinforcing layer and existing concrete, and proposes a simplified mechanical model to further study the interface bond mechanism. Four specimens composed of a CFRP grid, PCM, and concrete were tested. The influence of the type of CFRP grid and the grid interval on the interface bond behavior was discussed. The failure patterns, maximum tensile loads, and CFRP grid strains were obtained. The change process of interface bond stress was investigated based on the grid strain analysis. In addition, the simplified mechanical model and finite element model (FEM) were emphatically established, and the adaptability of the simplified mechanical model was validated through the comparative analysis between the FEM results and the test results. The research results indicate that a CFRP grid with a larger cross-sectional area and smaller grid interval could effectively improve the interface bond behavior. The tensile stress was gradually transferred from the loaded edge to the free edge in the CFRP grid. The interface bond behavior was mainly dependent on the anchorage action of the CFRP grid in the PCM, and the bond action between the PCM and the concrete. The FEM results were consistent with the test results, and the simplified mechanical model with nonlinear springs could well describe the interface bond mechanism between the CFRP grid–PCM reinforcing layer and concrete.

Geo-Composite Drainage Material for Hydro-Technical and Civil Engineering

The article deals with the «GP» geo-composite drainage material, which is used in hydro-technical, civil, as well as environmental, industrial and landscape construction. This material is intended for complex application, as a separating, filtering and reinforcing layer in the structures of protective dams on rivers, reservoirs, channels, an earth work of linear transport constructions (automobile and railway facilities) and other hydraulic engineering constructions. It is a combined geo-synthetic material, including a rigid geo-grid of the lattice structure and a filtering geotextile element. As a result of the carried out researches, its basic physical and mechanical characteristics have been established: tensile strength, surface density of geotextile and the material, relative elongation at maximum load, filtration coefficient normal to the material level.

Mechanical and Environmental Proprieties of UHP-FRCC Panels Bonded to Existing Concrete Beams

Among the techniques used to retrofit existing reinforced concrete structures, methods involving Ultra High Performance Fiber Reinforced Cementitious Composites (UHP-FRCC) are widely regarded. However, current practices make the use of this material for in-situ application expensive and complicated to perform. Accordingly, a new method to strengthen existing concrete beams by applying a precast UHP-FRCC layer on the bottom side are introduced and described herein. Two test campaigns are performed with the aim of defining the best conditions at the interface between the reinforcing layer and the existing beam and to reducing the environmental impact of UHP-FRCC mixtures. As a result, the eco-mechanical analysis reveals that the best performances are attained when the adhesion at interface is enhanced by means of steel nails on the upper surface of the UHP-FRCC layer, in which 20% of the cement is replaced by fly ash.

Modeling a Dynamic Response at Resonant Vibrations of an Elongated Plate with an Integral Damping Coating

Classical methods of surface damping using free and constraining damping layers are discussed. The structure of a perspective integrated version of a damping coating is presented. This integral damping coating consists of two layers of a material with pronounced viscoelastic properties, between which there is a thin reinforcing layer of a high modulus material. A generalization of the Thompson-Kelvin-Voigt model is given for the description of viscoelastic properties of the material under tension-compression in the case of a complex stress state. A finite-element method was developed to determine the dynamic response of an elongated plate with the integral damping coating. This method is based on a four-layer finite element with 14 degrees of freedom: the main material is within the Kirchhoff-Love's model, the damping layers are in a flat stress state, the reinforcing layer perceives tension and compression. This model allows us to take into account the effect of transverse compression of the damping layers of the plate, which significantly increases its damping properties at high vibration frequencies. The stiffness matrices, the damping matrices, and the mass matrices of the constituent layers aim at obtaining similar complete matrices of a finite element. A system of resolving equations was obtained on the basis of the Lagrange equations of the second kind with respect to the vector of nodal displacements of the finite element model of the plate with an arbitrary dynamic load. In the case of a harmonic load with a frequency that coincides with one of the frequencies of free vibrations of the plate, a transition to a modal equation with respect to the normal coordinate corresponding to the given frequency is possible. Numerical experiments were carried out to test the developed finite element method using the example of a hingedly supported elongated plate with an integral damping coating. The numerical experiments showed a qualitative change in the composition of stresses in the damping layers of the plate at high vibration frequencies, which significantly affects its damping properties.

To the issue of application of thermoplastic reinforced pipes for the construction of oil and gas pipelines in the Arctic

Ensuring the safety of oil and gas facilities and increasing their facility life are today one of the most important tasks. Emergencies related to rupture and damage of steel pipelines because of their wear and tear and external factors are still the most frequent cases of emergencies during the transportation of hydrocarbons. To expand the fuel and energy complex in the north, in the direction of the Arctic, alternative types of pipelines are needed that solve the problems of reducing energy and labor costs in oil and gas companies, reducing the risk of environmental disasters and depressurization of pipelines during hydrocarbon production. Fiber-reinforced thermoplastic pipes can be such an alternative. This article is devoted to a comparative analysis of the materials of a composite system consisting of a thermoplastic pipe (inner layer) and reinforcing fibers (outer layer); we are discussing the design of the structural system consisting of polyethylene (inner layer) and aramid fibers (outer reinforcing layer).

A method for evaluating the edge strength of soil-cutting parts of forestry machines

One of the main factors that determine the resistance of blade working bodies against damage under dynamic loads is their resistance to plastic crumpling, brittle or fatigue failure. Hard alloys that strengthen the blades of tillage parts are more brittle materials than steel, so the blunting of their edges is caused by the formation of cracks, their gradual growth or microchipping, even from a possible single impact of a solid inclusion in the soil. In addition to the usual brittle fracture of hard alloys, fatigue failure occurs under cyclic impact conditions. (Research purpose) The research purpose is in identifying the pattern of destruction of the blade edge of soil-cutting parts of forestry machines and theoretically justifying the algorithm for assessing the strength to determine the rational thickness of the wear-resistant coating during hardening. (Materials and methods) The article presents the main regularities of the influence of material properties and geometric parameters of the blade on the radius of rounding. (Results and discussion) The process of breaking the edge of the blade of hardened working bodies of forestry machines has been studied. The claim that the blunting of the blades is mainly due to its destruction and not to wear has been proved. The article presents a method for evaluating the strength of bimetallic blades of soil-cutting parts of forestry machines. It was found that the blunting of the blade occurs as a result of edge destruction in the process of multiple impacts of solid soil inclusions along the edge of the blade. (Conclusions) The article shows that the destruction of the edge of the blade leads to blunting of soil-cutting parts, which affects their performance. It was found that the sharpness of a self-sharpening hardened blade is determined by the thickness of the reinforcing layer and its ability to resist destruction under impact.

Self-equilibrated stresses in the system composed of a covering layer + spatially locally curved reinforcing layer + half-space

The system composed of a face covering layer + spatially locally curved substrate reinforcing layer + half-space is taken into consideration. It is presumed that this framework is compressed at infinity by uniformly distributed normal forces and it is required to establish the self-equilibrated normal stresses in that, caused by locally curved of the substrate reinforcing layer. The matching boundary and contact value problem is defined within the scope of 3-D geometrically non-linear exact equations. Formulated problem?s solution is introduced with the series form of small parameter which represents the degree of the aforesaid locally curving. These series? zeroth and first approximation are ascertained with the utilization of double Fourier transform. The original of values that are searching is ascertained numerically. Corresponding numerical outcomes about the self-equilibrated normal stress caused by this spatially local curving are presented and discussed.