Assessment of transmission of the shear stress in potted anchors for composite rods 1. Sleeve of constant thickness

The key problem facing the application of fiber-reinforced polymer (FRP) stay cables and tendons is the anchorage. Potted (bond-type) anchors have been used more extensively than anchors of any other type. The main aim in the design of anchors is to minimize the peak shear stress at the FRP rod-pottant interface. To this end, parametric analyses of the stress state in the anchors are carried out. Since parametric studies can not be easily performed by the finite-element method, an analytical model of the anchor is proposed. The model involves significant simplifying assumptions and allows one to obtain a relatively simple analytical solution for shear-stress distributions at the FRP rod-pottant interface. The use of this solution at various boundary conditions and various geometrical and mechanical parameters of anchor components enables one to search for and evaluate, at least qualitatively, different methods for decreasing the peak interfacial shear stress in the anchor. In this part of the investigation, an anchor consisting of a sleeve of constant thickness is considered. Russian tanslation published in Mekhanika Kompozitnykh Materialov, Vol. 45, No. 3, pp. 321-346, May-June, 2009.     

Assessment of transmission of the shear stress in potted anchors for composite rods. 2. Sleeve of variable thickness

The key problem facing the application of FRP stay cables and tendons is the anchor age. In the first part of the investigation, a model of a potted (bond-type) anchor was proposed, and a parametric analysis of the solution for the distribution of the interfacial shear stress in side the anchor with a sleeve of constant thickness was made. In this, second part, the solution is generalized to consider sleeves with a variable thickness (stepped and tapered), and the parametric analysis is extended. All the results obtained are compared, and the most effective means for decreasing the peak interfacial shear stress in the anchor are high lighted.     

Assessment of transmission of the shear stress in potted anchors for composite rods: 4. Nonlinear bond behavior between the FRP rod and the potting material

An analytical model for estimating the load-carrying capacity of cylindrical potted anchors with round rods made of high-strength composites is developed taking into account a partial debonding at the rod-pottant interface under tension loading. A detailed parametric analysis of the influence of propagation of the debonding on the load-carrying capacity of a potted anchor is carried out.     

Braided reinforced composite rods for the internal reinforcement of concrete

This paper reports on the development of braided reinforced composite rods as a substitute for the steel reinforcement in concrete. The research work aims at understanding the mechanical behaviour of core-reinforced braided fabrics and braided reinforced composite rods, namely concerning the influence of the braiding angle, the type of core reinforcement fibre, and preloading and postloading conditions. The core-reinforced braided fabrics were made from polyester fibres for producing braided structures, and E-glass, carbon, HT polyethylene, and sisal fibres were used for the core reinforcement. The braided reinforced composite rods were obtained by impregnating the core-reinforced braided fabric with a vinyl ester resin. The preloading of the core-reinforced braided fabrics and the postloading of the braided reinforced composite rods were performed in three and two stages, respectively. The results of tensile tests carried out on different samples of core-reinforced braided fabrics are presented and discussed. The tensile and bending properties of the braided reinforced composite rods have been evaluated, and the results obtained are presented, discussed, and compared with those of conventional materials, such as steel. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 44, No. 4, pp. 327–338, May–June, 2008.     

Errors for a shear model in studying stress concentrations

The possibility is studied of using revised theories for calculating stress concentration in transtropic and isotropic plates. It has been shown that in studying stress concentration the error for revised theory is of the same order as that for Kirchhoff theory. The first gives results with an excess, but the second gives results with a deficit. It has been noted that for transtropic plates of average thickness acceptable accuracy for engineering may be obtained by an energy-symptotic method. However, the nonlinear nature of stress distribution through the thickness obtained by three-dimensional theory cannot be revealed by the energy-asymptotic method.Translated from Teoreticheskaya i Prikladnaya Mekhanika, No. 18, pp. 20–25, 1987.     

Torsional vibrations and dispersion of torsional waves in orthotropic composite rods

The Barr’s refined theory of torsional vibrations of isotropic rods of noncircular cross section is generalized for an orthotropic material. An analysis of natural frequencies of torsional vibration of free-free orthotropic prismatic rods of rectangular cross section is carried out with the help of an exact solution of the frequency equation. For orthotropic CFRP and GFRP rods, the improved theory, which takes into account the normal stresses and inertia forces in the axial direction, in some cases, predicts a noticeable raise in the natural frequencies compared with those following from the Saint-Venant classical theory. A good agreement is obtained between the experimental and calculated values of natural frequencies of torsional vibrations of rectangular quartz and fiber glass rods. The dispersion of torsional waves in an orthotropic quasi-homogeneous rod is considered. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 44, No. 2, pp. 165–182, March–April, 2008.     

Three-dimensional model of the deformation of twisted multilayered rods of composite materials

Conclusion An analytical approach based on certain assumptions regarding the character of the kinematic relations and equilibrium conditions was developed to calculate the stress-strain state of naturally twisted rods of composite materials. A computer program for calculating the stress and strain parameters in each layer was also developed. The results of calculations performed in accordance with the linearized variant (Eq. (5)) of general relations (4) agree satisfactorily with experimental data within a broad range of acting longitudinal loads. The method that was developed has been widely used in the design and optimization of several types of structures.Translated from Mekhanika Kompozitnykh Materialov, No. 4, pp. 610–614, July–August, 1990.     

Experimental investigation of the propagation of longitudinal stress waves in optically active polymeric rods

A photoelastic technique has been used to investigate the propagation of longitudinal stress waves in free rods. The experiments have made it possible to establish the mechanism of stress wave formation under impulsive loading, explore the dynamic state of stress of the rod, and estimate the effect of the inelastic resistance of the material.B. E. Vedeneev All-Union Scientific-Research Institute of Hydroengineering, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 68–75, January–February, 1970.     

New variational-asymptotic formulations for 3-D stress analyses of laminated composite shells with a circular hole

A new approach for three-dimensional stress analyses in composite cylindrical shells is presented. The method of composite expansions along with Hellinger-Reissner variational formulation is employed to derive the interior and edge layer problems for high order approximations. Classical assumptions have been justified and new approximations have been established. These formulations are directed especially towards, new high integrity mixed-hybrid finite element schemes. The expository examples chosen are of cross-ply and angle-ply laminated shells. The circumferential location of the delamination failure initiation, for angle-ply laminates containing a circular hole, is within a sector located symmetrically around the perpendicular direction to the applied load.     

The transmission problem in bending of plates with transverse shear deformation

The existence of weak solutions is proved for contact problemsin bending of elastic plates with transverse shear deformation,and for various boundary integral equations arising from potentialrepresentations of such solutions.     

Analysis of methods of determining the interlaminar shear strength of composite materials

Conclusions The range of geometrical dimensions of a sample in which the values of the interlaminar shear strength determined by four of the five methods discussed are practically constant has been established. Good agreement is shown in the values of the characteristic being determined which are obtained by each of the four methods. It has been established that the experimental data obtained by the method of three-point deflection of short beams does not characterize their interlaminar shear strength. It is shown that the interlaminar shear strength of glass-plastic and the shear strength of the adhesive with which it is prepared are very similar in value.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 640–648, July–August, 1976.     

Optimal control of longitudinal vibrations of composite rods with the same wave propagation time in each part

We consider longitudinal elastic vibrations of a composite rod and find closedform expressions that describe optimal boundary controls bringing the rod from the quiescent state into a state with given displacement function φ(t) and velocity function ψ(t) in time T. We assume that the wave propagation time through each part of the rod is the same and T is a multiple of that time.     

Structural elastic and creep models of a UD composite in longitudinal shear

The transient creep of a UD composite with a quadratic arrangement of elastic fibers of quadratic cross section is investigated. The deformational properties of the composite are determined from the known properties of its constituents. A structural model of the UD composite is developed, whose minimal elementary cell contains four elements. The stress-strain state of the elements is assumed homogeneous. Two types of basic and resolving governing equations of transient creep are deduced, which are based on static or kinematic assumptions. In each of the cases, a formula for the longitudinal elastic shear modulus of the composite is found. The stationary solutions of creep equations allow one to obtain formulas of the steady-state creep of the composite in a form similar to Norton’s law. Numerical calculations are also performed, and a comparison of the results with data given in the literature bears witness to the efficiency of the models developed and the solutions obtained. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 43, No. 4, pp. 437–448, July–August, 2007.