Use of ultrasonic surface waves for studying the properties of the human tibia

A method of determining the ultrasonic surface-wave velocity by means of exponential concentrators is proposed for determining the properties of human tibia in vitro. The effect of the radiation frequency and the thickness of the surface layer of bone tissue on the surface-wave propagation velocity is studied. For measurement purposes the tibia is divided into 24–28 vertical levels and six to seven horizontal zones. The variation of the surface-wave velocity with the measuring point is investigated. Relations are established between the distribution of surface-wave velocities and the statistical parameters characterizing the dispersion of the results, on the one hand, and biological age and the source of the bone (right or left leg), on the other.     

Effective equations for photonic-crystal waveguides and circuits

We suggest a novel conceptual approach to describing the properties of waveguides and circuits in photonic crystals, based on effective discrete equations that include long-range interaction effects. We demonstrate, through the example of sharp waveguide bends, that our approach is very effective and accurate for the study of bound states and transmission spectra of photonic-crystal circuits and disclose the importance of evanescent modes in these phenomena.     

Effect of parameters of the distribution of the length and orientation of short fibers on characteristics of the dynamic viscoelasticity of a polymer composite

Conclusion An algorithm for calculating the dynamic viscoelastic characteristics of a composite reinforced with short fibers was developed and realized in the form of a computer program. An analysis was made of the dependence of the characteristics of the composite on the volume content and length of its fibers, as well as on statistical distributions of fiber length and orientation in the material. It was shown that a change in the parameters of the statistical distributions has a significant effect on both the elastic and the dissi-pative properties of the composite. It was found that ignoring the statistical fiber-length distribution might lead to overestimation of the real component of the complex modulus and underestimation of the mechanical loss tangent.Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 13–17, January–February, 1990.     

Closed-form solution for a mode-III interfacial edge crack between two bonded dissimilar elastic strips

A closed-form solution is obtained for the problem of a mode-III interfacial edge crack between two bonded semi-infinite dissimilar elastic strips. A general out-of-plane displacement potential for the crack interacting with a screw dislocation or a line force is constructed using conformal mapping technique and existing dislocation solutions. Based on this displacement potential, the stress intensity factor (SIF, K_III) and the energy release rate (ERR, G_III) for the interfacial edge crack are obtained explicitly. It is shown that, in the limiting special cases, the obtained results coincide with the results available in the literature. The present solution can be used as the Green’s function to analyze interfacial edge cracks subjected to arbitrary anti-plane loadings. As an example, a formula is derived correcting the beam theory used in evaluation of SIF (K_III) and ERR (G_III) of bimaterials in the double cantilever beam (DCB) test configuration.     

Dynamic mechanical spectroscopy of polyethylenes with aggregating disperse and hybrid granular-fibrous fillers

Conclusion Based on the results of dynamic experimental studies, it was shown that addition of mineral fillers to polyethylenes does not result in a significant change in the relaxation properties of the polymer matrix of CM. It was found that aggregation of the particles of the granular filler causes a significant increase in the real part of the modulus and a decrease in the mechanical loss tangent of the CM. The possibility of using a modified elastic solution for predicting the effective characteristics of the dynamic viscoelasticity of composites was demonstrated.Translated from Mekhanika Kompozitnykh Materialov, No. 4. pp. 579–586, July–August, 1989.     

Prediction of the deformation properties of a polymeric composite with a granular-fibrous filler

Conclusion A variant of calculation of the characteristics of the deformation properties of a hybrid composite containing a complex disperse filler in the form of granular particles and short fibers was proposed. The effect of aggregation of the granular filler, the statistical distributions of the fibers by lengths and orientation in the material, and the anisotropy of the fibers are taken into consideration in the calculation. The statistical distribution of the orientation of the fibers is given by a function proportional to the distance from the center to the surface of a triaxial ellipsoid in the corresponding direction. The uniform random distribution of the fibers in bulk and in the plane is a special case of this distribution. The results of the analysis of the effect of the parameters of the statistical distributions of the length and orientation of short fibers on the elasticity characteristics of a composite are reported. The dependence of the creep of the composite on the ratio of the concentration of the components of the complex filler was determined, and the efficiency of partial replacement of a granular filler by a short-fiber filler to inhibit creep of the composite was demonstrated. The possibilities of predicting the long-term creep were experimentally confirmed on the example of LDPE filled with ground limestone and short glass fibers.Presented at the Sixth All-Union Conference on the Mechanics of Polymer and Composite Materials (Riga, November, 1986).Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 898–909, September–October, 1987.     

Thermal expansion of a composite with a hybrid granular-fibrous filler

Conclusion The thermal deformation of LDPE with a granular-fibrous filler was studied experimentally within a broad temperature range. We analyzed the effect of fillers on characteristics of relaxational transitions in LDPE as determined from dilatometric tests. A method was proposed for calculating the effective CLE of a composite with allowance for aggregation of a powdered filler and the statistical distributions of the length and orientation of the anisotropic fibers. The method was substantiated experimentally. Results were also presented of a theoretical analysis of the effect of the parameters of the fiber distributions f(l.) and (, ) and the relative volume contents of granular and fibrous fillers on _ij for the composite. It was established that aggregation of the granular filler may produce a hybrid effect consisting of maximum suppression of thermal expansion of the binder by the combination filler relative to a two-component composite.Translated from Mekhanika Kompozitnykh Materialov, No. 2, pp. 237–246, March–April, 1989.