Initial stress and heterogeneity effects on torsional waves in dry sand half-space between reinforced half-space and poroelastic medium

PurposeThe purpose of this paper is to investigate the effect of initial stress and heterogeneity on the propagation of torsional waves in dissipative medium. The problem consists of dry sand poroelastic half-space embedded between heterogeneous self-reinforced half-space and poroelastic medium. The frequency equation is derived in the framework of Biot's theory with some variants.Design/methodology/approachTorsional wave propagation in dry sand poroelastic half-space embedded between self-reinforced half-space and poroelastic medium. All the constituents here are assumed to be dissipative, heterogeneous and initial stressed.FindingsPhase velocity and attenuation are computed against wavenumber for various values of self-reinforcement parameter, inhomogeneity parameter and initial stress. Particular cases are discussed in absence of dissipation. The numerical results are presented graphically.Originality/valueInitial stress and heterogeneity effects on torsional waves in dry sand half-space between reinforced half-space and poroelastic medium are investigated. The frequency equation is derived, and which intern gives the phase velocity and attenuation coefficient for various values of initial stress, self-reinforcement parameter and heterogeneity parameter. From the numerical results, it is clear that as wavenumber varies phase velocity and attenuation are periodic in nature for all the cases. Particular cases are discussed in absence of dissipation. This kind of analysis can be extended to any elastic solid by taking magnetic, thermo and piezoelectric effects into account.

Reinforcement Parameter Effect on Properties of Three-Phase Composites

In this study, a micromechanics model has been proposed for predicting the effects of particle size and aggregation on elastic properties of nanocomposites, and the interphase between the particle and matrix is also taken into account. Inherent characteristics of nanoparticle, such as small size and high surface area ratio, make nanoparticle in a state of unstable energy and easy to agglomerate in matrix. The analytical expressions for the effective elastic modulus of nanocomposites are derived, which can consider the effect of particle agglomeration. The dispersion state or degree of agglomeration of nanoparticle and the thickness and stiffness of interphase are known to have a significant influence on nanocomposites. The results show that the increase of particle radius and agglomeration volume fractions reduces the elastic stiffness of nanocomposites. Moreover, the composite reinforcement can be improved by increases of interphase thickness and stiffness.

Antnet Routing Algorithm with Link Evaporation and Multiple Ant Colonies to Overcome Stagnation Problem

Antnet is a software agent-based routing algorithm that is influenced by the unsophisticated and individual ant’s emergent behaviour. The aim of this chapter is twofold, firstly to introduce improvements to the antnet routing algorithm and then to critically review the work that is done around antnet and reinforcement learning in routing applications. In this chapter a modified antnet algorithm for packet-based networks has been proposed, which offers improvement in the throughput and the average delay by detecting and dropping packets routed through the non-optimal routes. The effect of traffic fluctuations has been limited by applying boundaries to the reinforcement parameter. The round trip feedback information supplied by the software agents is reinforced by updated probability entries in the distance vector table. In addition, link usage information is also used to prevent stagnation problems. Also discussed is antnet with multiple ant colonies applied to packet switched networks. Simulation results show that the average delay experienced by data packets is reduced for evaporation for all cases when non-uniform traffic model traffic is used. However, there is no performance gain on the uniform traffic models. In addition, multiple ant colonies are applied to the packet switched networks, and results are compared with the other approaches. Results show that the throughput could be increased when compared to other schemes, but with no gain in the average packet delay time.

OVERCOMING INCOMPATIBILITY PROBLEMS IN ELASTOMER BLENDS BY TAILORED SURFACE PROPERTIES OF RUBBER ADDITIVES

ABSTRACT Rubber is a challenging composite material, whose functionality strongly depends on the affinity of the different materials in the composite and its morphology. One way to tailor polarity and chemistry of the filler surface is plasma coating. When using acetylene, thiophene, or pyrrole as monomers, the coating results in a reduced polarity of the filler compared with untreated silica, and unsaturated C–C bonds are formed on the surface. This improves the compatibility of the filler–polymer blends. In a SBR/EPDM blend, the filler–polymer compatibility is improved for all plasma-coated fillers compared with untreated silica. The best dispersion is achieved by plasma–pyrrole coating, as measured by the Payne effect and reinforcement parameter. The rubber–filler interaction is also highest for this blend, as measured by the bound rubber content. As expected, this results in improved tensile properties. In NBR/EPDM, the filler–filler interaction is significantly reduced by the plasma–pyrrole coating, which indicates a balanced compatibility of the pyrrole-treated silica in both polymers. The properties of the vulcanizate show the combinatorial effect of dispersion, filler–polymer interaction, polymer entanglements, and cross-link density. All plasma-treated, silica-filled NBR/EPDM materials show a considerable increase in tensile strength compared with untreated silica, with polyacetylene-treated silica resulting in the best properties. When plasma-coated curatives are used in SBR/EPDM blends, the scorch safety of the compounds is increased and the rupture energy is enhanced. In NBR/EPDM blends, all packages of the modified curatives provide an increased maximum torque compared with the control. Mechanical properties of the NBR/EPDM blend are improved even more than they are with SBR/EPDM. This indicates a more-balanced distribution of cross-links, along with a more-homogeneous carbon black dispersion over the different rubber phases. A better polarity match between additives and polymers usually results in improved material properties. The wide variety of monomers for the plasma polymerization allows researchers to tailor the surface properties of the additives.

Simplied Calculation Method for Reinforcement of Rectangular Sectional Flexural Members Considering Crack Width

Based on maximum crack width checking of flexural member with rectangular section, the limited maximum crack width value of code was substituted into checking formula. In this paper, according to the different value scope of non-uniformly distributed strain of coefficient longitudinal tensile reinforcement, controlling equations expressed with the diameter and numbers of steel bars are derived, thus reinforcement meeting the requirement of crack width can be calculated directly according to known value. The example indicates that this method can avoid the repeated reinforcement adjustment and crack checking calculation process, and the reinforcement parameter can meet the requirements well. It may be a reference for the designers.

Comparative Study of Plasma-Thiophene and -Acetylene Coated Silica in SBR and EPDM Reinforcement

The surface characteristics of silica were modified by plasma-thiophene and -acetylene film deposition. The plasma-coated fillers were blended with S-SBR and EPDM, and their influence on the final vulcanizate properties was compared with untreated silica and silanized silica. The change in the surface energy of plasma-acetylene (PA) and thiophene- (PTh) coated silica was characterized by immersion tests in liquids of various surface tension, water penetration measurements, Thermo Gravimetric Analysis (TGA) and Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS). All techniques gave evidence of a polymeric PA- and PTh-film deposition on the surface of silica. The properties of S-SBR and EPDM, filled with untreated, PA-, PTh- and silane-treated silica, were investigated by measurement of the Payne effect, bound rubber content and weight loss related to bound rubber, the reinforcement parameter, relative ranking of cross-link density and mechanical properties. The results show a lower degree of flocculation for PTh-silica filled EPDM due to a better match of the surface energies compared to untreated and PA-treated silica. EPDM filled with plasma-thiophene coated silica shows the lowest reinforcement parameter value, thus improved dispersion compared to untreated, silane-treated and plasma-acetylene silica. However, PA-silica filled EPDM shows better mechanical properties compared to untreated and plasma-thiophene coated silica. The PTh-silica filled S-SBR shows a higher bound rubber content, which results in better mechanical properties of the S-SBR compound compared to the one with PA-coated silica. The overall results show that the compatibility and interaction of silica with different rubbers can be controlled by tailoring the surface energy of the filler by plasma-polymerization. The different functionalities on the silica surface result in different levels of compatibility and interaction, as well as final vulcanizates properties.

Effect of Plasma Polymerization on the Performance of Silica in NBR, EPDM and NBR/EPDM Blends

The surface modification of precipitated silica powders by plasma-polymerization with acetylene monomer in order to improve their performance in NBR, EPDM and NBR/EPDM rubber blends, by matching the surface energies of the silica fillers of the rubbers, is the subject of this study. Silica, used as reinforcing filler for elastomers, is coated with a polyacetylene (PA) film and characterized by water penetration measurements, Cetyltrimethyl Ammonium Bromide (CTAB) area, Thermo Gravimetric Analysis (TGA), Time of Flight-Secondary Ion Mass Spectroscopy (ToF-SIMS) and Scanning Electron Microscopy with elemental analysis by Energy Dispersive X-ray spectroscopy (SEM/EDX). All techniques show the evidence of a PA-film deposition on the surface of silica. The properties of NBR, EPDM and blends based on NBR and EPDM, filled with untreated, PA- and silane-treated silica, are investigated by measurement of the Payne effect, the bound rubber content and weight loss related to bound rubber, the reinforcement parameter and mechanical properties. The PA-silica filled samples show a lower Payne effect for EPDM and NBR/EPDM compared to the rubbers filled with unmodified silica. However, PA-silica filled NBR shows a higher Payne effect. This indicates an improved filler dispersion in the EPDM and NBR/EPDM, and a poorer dispersion in the NBR. The reduction of the reinforcement parameter as found for NBR, EPDM and NBR/EPDM indicates a lower degree of agglomeration in comparison with untreated and silane-treated silica. The PA-silica filled samples show the highest bound rubber contents and “in-rubber structure” for both rubbers as well as for the blend, compared to both other silica samples. The mechanical properties of untreated silica filled blend of NBR/EPDM are worse compared to the pure rubbers, but acetylene polymerization onto silica results in a significant improvement relative to the unmodified silica. The combined effects all point in the direction of improved compatibility of the PA-silica with the apolar EPDM. This results in better dispersion and stronger interaction with the EPDM, particularly in the blend with NBR, so as to significantly improve the mechanical properties of the blend relative to the use of untreated or silane-treated silica.

An Integrated Mechanics-of-Materials Model for the Elastic Stiffness of Composites

An integrated mechanics-of-materials model is developed herein for three classes of composites, namely continuous unidirectional fibre composites, particulate reinforced composites and periodically bilaminate composites. Through a judicious choice of expressing the model, a new parameter, which describes the effect of reinforcing geometry on the composite stiffness in the direction of interest, was extracted. The reinforcement parameter ranges from zero (for the lowest possible reinforcing efficiency) to unity (for the highest possible reinforcing efficiency). The reinforcement parametric values for all the three classes of composites, both parallel and transverse to the reinforcement axis-of-symmetry, are presented. Finally the possible reinforcement parameter range for unidirectional short fibre composites and aligned flake composites are suggested based upon the reinforcement parameter of the three presently considered special cases.