Dissipative properties of composite structures. 1. Statement of problem

Object and purpose of research. The object under study is a sandwich plate with two rigid anisotropic layers and a filler of soft isotropic viscoelastic polymer. Each rigid layer is an anisotropic structure formed by a finite number of orthotropic viscoelastic composite plies of arbitrary orientation. The purpose is to develop a mathematical model of sandwich plate. Materials and methods. The mathematical model of sandwich plate decaying oscillations is based on Hamilton variational principle, Bolotin’s theory of multilayer structures, improved theory of the first order plates (Reissner-Mindlin theory), complex modulus model and principle of elastic-viscoelastic correspondence in the linear theory of viscoelasticity. In description of physical relations for rigid layers the effects of oscillation frequencies and ambient temperature are considered as negligible, while for the soft viscoelastic polymer layer the temperaturefrequency relation of elastic-dissipative characteristics are taken into account based on experimentally obtained generalized curves. Main results. Minimization of the Hamilton functional makes it possible to reduce the problem of decaying oscillations of anisotropic sandwich plate to the algebraic problem of complex eigenvalues. As a specific case of the general problem, the equations of decaying longitudinal and transversal oscillations are obtained for the globally orthotropic sandwich rod by neglecting deformations of middle surfaces of rigid layers in one of the sandwich plate rigid layer axes directions. Conclusions. The paper will be followed by description of a numerical method used to solve the problem of decaying oscillations of anisotropic sandwich plate, estimations of its convergence and reliability are given, as well as the results of numerical experiments are presented.

The Effect of Rheology of Viscoelastic Polymer on Pressure Transient Response in Near-Wellbore Regions

Viscoelastic polymer solution shows shear thinning behavior at low shear rates and shear thickening behavior at high shear rates in reservoirs. However, models that ignored shear thickening behavior were commonly employed to interpret transient pressure data derived from tested wells in viscoelastic polymer flooding systems; although, viscoelastic polymer solutions show shear thickening behavior in the near-wellbore region due to high shear rate. To better characterize the oilfield with pressure transient analysis in viscoelastic polymer flooding systems, we developed a numerical model that takes into account both shear thinning behavior and shear thickening behavior. A finite volume method was employed to discretize partially differential flow equations in a hybrid grid system including PEBI mesh and Cartesian grid, and the Newton-Raphson method was used to solve the fully implicit nonlinear system. To illustrate the significance of our model, we compared our model with a model that ignores the shear thickening behavior by graphing their solutions on log-log plots. In the flow regime of near-wellbore damage, the pressure derivative computed by our model is distinctly larger than that computed by the model ignoring shear thickening behavior. Furthermore, the effect of shear thickening behavior on pressure derivative differs from that of near-wellbore damage. We then investigated the influence of shear thickening behavior on pressure derivative with different polymer injection rates, injection rates, and permeabilities. The results can provide a benchmark to better estimate near-wellbore damage in viscoelastic polymer flooding systems. Besides, we demonstrated the applicability and accuracy of our model by interpreting transient pressure data from a field case in an oilfield with viscoelastic polymer flooding treatments.

Temperature-dependent rheological properties of viscoelastic polymer based flexible abrasive media for finishing process

The objective of the present investigation is to develop and study the thermal and rheological properties of the in-house developed flexible abrasive media. It is a mixer of viscoelastic polymer and plasticizer mixed with micro-abrasive particles, used for removing debris and irregularities present on internal and external complex surfaces used in the aerospace, automotive and medical industries. This paper presents, morphology of the developed abrasive media is captured using the Scanning Electron Microscope (SEM), thermal properties of the abrasive media are studied using Thermo Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) analysis along with tensile properties of the abrasive media ascertained using the universal testing machine. The rheological properties of the media play a major role in media flow over the intricate shapes and removing the material from the surface. To understand the media behavior, further rheological properties such as viscosity, shear stress, storage modulus, loss modulus, loss tangent, and complex viscosity are ascertained with varying shear rate and frequency at different temperature using rheometer. The TGA and DSC results shows abrasive media has good thermal stability and possibility of using the media for finishing process under lower temperature <100 °C. Rheological studies shows the shear thinning behaviour of the media and elastic solid behavior (G′ > G′′) at different temperatures which is suitable for finishing the complex internal and the external features efficiently and effectively. The developed abrasive media is used to finish the hydraulic components which are difficult to access with conventional tools and the results of finishing process are presented.

Coupled vibrations of viscoelastic three-layer composite plates. 2. Numerical experiments

Results of numerical studies of the influence of reinforcement orientation of hard layers and the relative thickness of the soft layer of an isotropic viscoelastic polymer on the values of natural frequencies and coefficients of mechanical losses are discussed. In a symmetrical three-layer plate, a bending-torsion interaction arises, generating mutual transformations of the eigenmodes of the coupled vibration modes, if at least one of its own forms in plate directions is characterized by an even number quarters of a wave, and another proper form - an odd number of quarters the waves. In an unsymmetrical asymmetric three-layer plate, bending-bending interaction arises, generating mutual transformations eigenmodes of coupled vibration modes in two mutually orthogonal planes if in the main directions of the plate both of their own forms characterized by either an even or an odd number of quarters of a wave. It was found that each mode of natural vibrations of three-layer plates corresponds to the effective relative thickness of the soft isotropic layer viscoelastic polymer.