Rheological Properties of Bitumens from the Perspective their Chemical Composition

The quality of bituminous binders is commonly evaluated by the empirical tests. The functional approach to the evaluation of bitumen properties is a trend that has been applied in the last years. The dynamic shear rheometer (DSR) test has been widely used to determine the shear complex modulus of bitumen in the wide range of frequencies and temperatures. A lot of research works were focused on the effect of the chemical compounds of bitumen on the values of the shear complex modulus. The missing information related to the effect of the compound of bitumen on the elastic and plastic part of the shear complex modulus was input for the presented investigation. The significant effect on the elastic part of the complex modulus was determined only at the high temperatures (60 and 80 °C). The aromatics, resins and asphaltenes were identified as the influencing compounds. The important effect was also noted for the resins at the temperatures of 5 and 15 °C. It was also concluded that the effect of the saturates on the elastic part of the shear complex modulus is marginal. The effect of the aromatics and asphaltenes on the plastic part of the shear complex modulus was identified only at the temperature of 80 °C. The effect of these two compounds at other temperatures seems to be unimportant. The significant effect of the resins was stated for the temperatures of 15 °C and 5 °C. Their effect at other temperatures can be supposed as marginal. The negligible effect of the saturates on the plastic part of the shear complex modulus was deducted.The regression analysis of the chemical composition of the bitumen and the parts of the shear complex modulus at the temperature of 80 °C proved that the frequency of the DSR test can be a factor affecting the level of the relationship between the group composition of the bitumen and its rheological properties.

RATIONALE FOR THE USE OF DOUBLE SHOULDER THREADED CONNECTIONS OF HOLLOW SUCKER RODS

Frequent failures of standard threaded connections of hollow sucker rods are caused by their fatigue failures, self-loosening and leakages. This is mainly caused by such design flaws as unequal load on threads, insufficient shoulder area, stress concentration in the groove, low resistance to bending and torsion loads. Using iterative design, based on parametric geometric modeling and the finite element method, the feasibility of using double shoulder threaded connections for hollow sucker rods has been proved and their design has been improved. The improved connection has two shoulders, modified grooves with an elliptical profile, correction of the first turn of the nipple thread and optimal values of interferences. Due to this, the joint has greater tightness, strength at bending, torsion and compression, higher resistance to self-loosening, more equal load on the threads and greater fatigue strength compared to the standard one. The value of the fatigue safety factor in the area of the first turn of the nipple thread is increased by 13...14, in the area of the last turn of the coupling – by 2.6...4, in the area of the nipple groove by 0…0.4. The use of an elastic element on an additional shoulder allowed increasing the tolerance of the interference on it to 0.2 mm, making it unnecessary to control dimensions before screwing. Even after damage to the elastic part and loss of tension on an additional shoulder, the connection has greater strength than the standard one. In case of rod repairs, improved nipples can be easily implemented by welding them to the rod body. There is also the possibility of implementation of double shoulder cylindrical connections without modifying the standard nipple.

Cooling of a Partially Elastic Isothermal Surface by Nanofluids Jet Impingement

Numerical study of nanofluid jet impingement cooling of a partially elastic isothermal hot surface was conducted with finite element method. The impingement surface was made partially elastic, and the effects of Reynolds number (between 25 and 200), solid particle volume fraction (between 0.01 and 0.04), elastic modulus of isothermal hot surface (between 104 and 106), size of the flexible part (between 7.5 w and 25 w), and nanoparticle type (spherical, cylindrical, blade) on the fluid flow and heat transfer characteristics were analyzed. It was observed that average Nusselt number enhances for higher Reynolds number, higher values of elastic modulus of flexible wall, smaller size of elastic part, and higher nanoparticle solid volume fraction and for cylindrical shaped particles. It is possible to change the maximum Nusselt number by 50.58% and 33% by changing the elastic modulus of the hot wall and size of elastic part whereas average Nusselt number changes by only 9.33% and 6.21%. The discrepancy between various particle shapes is higher for higher particle volume fraction.

Quantization of energy and weakly turbulent profiles of solutions to some damped second-order evolution equations

We consider a second-order equation with a linear “elastic” part and a nonlinear damping term depending on a power of the norm of the velocity. We investigate the asymptotic behavior of solutions, after rescaling them suitably in order to take into account the decay rate and bound their energy away from zero. We find a rather unexpected dichotomy phenomenon. Solutions with finitely many Fourier components are asymptotic to solutions of the linearized equation without damping and exhibit some sort of equipartition of the total energy among the components. Solutions with infinitely many Fourier components tend to zero weakly but not strongly. We show also that the limit of the energy of the solutions depends only on the number of their Fourier components. The proof of our results is inspired by the analysis of a simplified model, which we devise through an averaging procedure, and whose solutions exhibit the same asymptotic properties as the solutions to the original equation.

FATIGUE CHARACTERIZATION OF A THERMOPLASTIC ELASTOMER

ABSTRACT The capacity to resist crack development in an olefinic thermoplastic elastomer (TPE) has been measured via a set of experiments that quantify (1) the fracture mechanical strength of the material under quasi-static loads, (2) the rate of growth of a crack under dynamic solicitations as a function of the energy release rate, and (3) the size of crack precursors in new material. Because the subject TPE exhibited strong inelasticity in the stress–strain response, it also was necessary to characterize the development of an inelastic set under cyclic loading as a function of the applied strain. Combined with the multiplicative kinematic split, this additional measurement yields the elastic part of the strain. It also enables engineering calculations to be made of fatigue life.

A Griffith–Euler–Bernoulli theory for thin brittle beams derived from nonlinear models in variational fracture mechanics

We study a planar thin brittle beam subject to elastic deformations and cracks described in terms of a nonlinear Griffith energy functional acting on [Formula: see text] deformations of the beam. In particular, we consider the case in which elastic bulk contributions due to finite bending of the beam are comparable to the surface energy which is necessary to completely break the beam into several large pieces. In the limit of vanishing aspect ratio we rigorously derive an effective Griffith–Euler–Bernoulli functional which acts on piecewise [Formula: see text] regular curves representing the midline of the beam. The elastic part of this functional is the classical Euler–Bernoulli functional for thin beams in the bending dominated regime in terms of the curve’s curvature. In addition there also emerges a fracture term proportional to the number of discontinuities of the curve and its first derivative.

Weak solutions for generalized stationary Oldroyd-B fluid with a diffusive stress

This paper focuses on the analysis of the stationary case of incompressible viscoelastic generalized Oldroyd-B fluids derived in [2] by Bejaoui and Majdoub. The studied model is different from the classical Oldroyd-B fluid model in having a viscosity function which is shear-rate depending, and a diffusive stress added to the equation of the elastic part of the stress tensor. Under some conditions on the viscosity stress tensor and for a large class of models, we prove the existence of weak solutions in both two-dimensional and three-dimensional bounded domains for shear-thickening flows.