Browse Articles

In this paper is presented an analytical model, which makes the similitude between the DTMM theory of composite multilayer bars and the FSDT theory used in the study of composite bars and plates in a dynamic regime. The authors proposed a numerical application of the model, for two different bars made from glass-epoxy reinforced composite. The experimental validation of theoretical results was made on a composite bar as a component of a quadrilateral mechanism, whereon the leading element describes a rotation motion with the constant angular speed. Keywords: composite materials, vibrations, movement in a plane

The behaviour of some microstructured polymers obtained in dynamic conditions using a mixture (1:1) of EPDM (ethylene-propylene-dien monomer) rubber and high-density polyethylene (in the presence of sulphur as reticulating agent) was studied. The experiments consisted in determination of swelling by maintaining the polymeric composite materials in three organic solvents (benzene, p-xylene, carbon tetrachloride) and also in recording their IR spectra. The results are useful for selection of operating conditions during preparation and for choosing the appropriate utilization of polymeric products. Keywords: microstructural polymer, EPDM (ethylene-propylene-dien monomer) rubber, polyethylene, swelling, IR spectroscopy

The paper deals with the shrinkage and warpage phenomenon briefly presenting the most important influence factors and their interaction involved in dimensional changes of injected plastic parts. The predictable tolerances, design strategy and the main required action are debated for one final purpose: maximum and yet realistic accuracy of dimensional precision, in a cheapest, easy manufacturability and easy operating injection tool. Finally, there are presented some useful considerations for minimizing the effect of shrinkage and warpage in dimensional variance of injected plastic parts. Keywords: injection moulding, tolerance, shrinkage, warpage

In this work we have applied a Hays –Kendall mathematical model to the Vickers microhardness values to eliminate the troublesome indentation size effect (load dependence of hardness) and obtain a unique value representing the true hardness for each coating. Examination of the unique hardness values has been possible in conditions of heat treatment at 190 0C and 420 0C. Key words: Hays –Kendall model, Ni-P/SiC coatings, hardness, ISE effect, heat treatment

Degenerative disc disease in the lumbar spine is marked by a dehydration of the intervertebral disc and loss of biomechanical function of the spinal unit. Since the current surgical procedures are ineffective in restoring natural biomechanical function back to the diseased disc, researchers have looked to replace the intervertebral disc. These designs are flawed in that they either don’t restore natural movement back to the spinal unit, require surgeries that are highly invasive, or they further promote disc degeneration of adjacent spinal levels. Recently, researchers have sought to only replace the central portion of the disc called the nucleus pulpous. A potential nucleus replacement could mimic a healthy nucleus pulpous in restoring healthy biomechanical function to the spinal unit. A hydrogel, poly (vinyl alcohol) (PVA), has been investigated to serve as a nucleus replacement. However, semi crystalline PVA suffers dissolution under physiological conditions and for this reasons are tested others hydrogels (HEMA) which are biocompatible, maintain the liquid transport function, the shape and the size of intervertebral disc and are very good shock-absorbent. Keywords: prosthesis, hydrogel, HEMA, intervertebral disc

Poly-(vinyl alcohol) (PVA) films, colored with pyridinium ylids and dried by water evaporation, become stretched under the heating influence. The visible electronic spectra of the stretched films were measured for linearly polarized visible radiations having their electric field intensity parallel and perpendicular on the stretching direction. The dichroism of the colored PVA films depends on the stretching degree. The birefringence of each film was estimated by using a polarizing microscope with compensatory wedge. Keywords: stretched PVA films, pyridinium ylids, dichroism, birefringence

A mathematical model of the heat transport in nanofluids using the fractal theories (the scale relativity theory in the topological dimension DT = 2) is established. Through a scale covariance form of the Newton’s equation, a Navier-Stokes type equation with an imaginary viscosity coefficient and particularly a Schrödinger’s type equation are obtained. Some applications of the model are given like the heat transport through an effective thermal conductivity, by Brownian motion or by liquid layering at liquid-nanoparticle interface. It results that the heat transport in nanofluids is performed through an unique mechanism, the above standard sequences mentioned being imposed by the interaction scales. Moreover, the quantum thermal conductance of electrons in an one-dimensional wire is obtained. Keywords: nanofluid, heat transfer, fractal, thermal conductance

The paper proposes an analysis on the influence of the elastic rubber elements as component parts of the elastic tram wheels, as well of the railroad, on the stress state, on the wear and the loss in time of the mechanical properties under dynamic conditions. It is noticed the importance of the proping of the rubber elastic element (all degrees of freedom or vulcanized on a metallic support) going to a „brick” element shape proposal, which is absolutely „covered” for practical applications. This approximation leads to new correction coefficients, as well as to the validation of the simplified „brick” shape of specimens for a future experimental test standartization. Keywords: elastic wheel, stress, mechanical testing, finite element analysis

A degradation mathematical model based on the dependence of the carbonyl index by the degradation time to measure the polyolefins degradability was proposed. The mathematical model was verified with good results with own and literature degradation data. It was demonstrated that the three aging parameters of the mathematical model that can be calculated by fitted method, reflect the degradation behaviour of primary and secondary polyolefins and can be used for quantitative estimation of the polyolefins degradability. The possibility of using the mathematical model for estimation the opportunity of using the mechanical recycling as recycling method is the practical importance of the obtained results. There is also, a mathematical demonstration of the reason for which the polymers can not be infinitely recycled as other materials like metals, glass e.g. Keywords: mechanical recycling, ageing parameters, contamination

The frictional factor of new hip endoprosthesis was measured using one hip testing device designed in Biomechanics Laboratory of Medical Bioengineering Faculty. Hip simulator respect physiological condition (variable load, variable motion). The friction factor value for fluid film regime through the gait cycle was founded variable like a consequence of UHMWPE visco-elasto-plastic behaviour. Keywords: friction factor, gait cycle, visco-elasto-plastic behaviour