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In this paper it is presented a creep model in the theory of viscoelasticity for polymeric materials.

This work brings to the forefront local nonlinear problems that appear in junctions of beam structures made of plastics, subjected to heavy loads. We also revealed the notions of local problems and heavy loads. These theoretical aspects are explained with the help of two beam structures of various complexity, made of plastic, with local problem. The results are presented as stress maps, maps of mechanical strains, charts with the evolution of the states reached in the structure with the loading steps. We mentioned the situations that require local study; nonlinear problems classification is presented and the methodology for nonlinear calculus is described. Keywords: local problem, beam structure, heavy loads, nonlinearity

This paper deals with synthesis and characterization of some copolyamides 6/12 obtained by rotational molding via activated anionic ring–opening copolymerization of e–caprolactam with laurolactam. Sodium bis[(2–metoxyetoxy)e–caprolactam] aluminate, as initiator and N,N’–[methylene–di(1,4–phenylene)bis–carbamoyl]–bis–e–caprolactam, as activator were used. The initial mold temperature (initial polymerization temperature) was kept constant at 160oC. The incorporation of laurolactam into nylon 6 chain depresses both in the degree of crystallinity and the melting temperature of nylon 6/12 copolymers. The notched Izod impact strength of the copolymers increased as the laurolactam content was increased, while the flexural modulus and the water absorption decreased.

The main purposes of this article are: 1) the minimization of an objective multi-criterial function which implies the reaction time, the polidispersion coefficient and the monomer conversion; 2) the obtaining of reaction conditions (temperature and initiator concentration) which determine the realisation of some final imposed values for conversion and polymerization degree. Within the optimization algorythm there were successively considered as decision variables: 1) a single value of temperature (the isothermal case) and the initiator concentration; 2) two temperature levels and the initiator concentration; 3) thee temperature levels. Of the three optimization strategies, the right one was proved to be the temperature trajectory constituted of two values. The obtained optimal politics essentially depend on the objectively chosen function and on the weight factors attached to each interest measure.

The ortocresol, the p-aminophenol and the formaldehyde were taken in different molar ratios and condensed in the presence of hydrocloric acid as catalyst and of toluene) N-methyl pyrolidone mixture as extraction agent of the reaction water. The condensing products are polymers with a low molecular mass, friable solid substances soluble in polar organic solvents which show colors from transparent pink for the ortocresolformaldehidic resin, to dark brown for the p-amino-phenolformaldehidic one. The obtained formaldehidic resins were structurally characterized using IR and 1H-RMN spectroscopy. The thermal properties were also investigated.

This paper presents the performance of two aminic antioxidants (TMQ and PBN) and a phenolic antioxidant (SPH) in formulations based on diene rubbers, typical for tyre treads. An imidazoline was used as secondary accelerator and the influence of antioxidant nature was investigated following its influence on scorch safety, curing behaviour, tensile strength, fatigue behaviour, abrasion performance, and thermo-oxidative degradation.

The work presents a study on a possible solution of metal replacement for pneumatic drives rods working in dry friction condition. If the total absence of lubricant and others contaminating agents is required, due to specific working environment, the pneumatic drives use is recommended. The rod sealing system is elastomeric lip seal based and works, in this case, in linear sliding dry condition. The authors tried to establish the way that polymeric material replacing the metallic rod behaves, taking into account the working conditions. Considering that the sealing system failure is due to wear, a closer investigation is performed at surfaces level by optical and 3D reconstruction methods. The observations allowed an optimization of polymeric rod rubber lip seal system in dry sliding conditions from the materials choosing point of view. Keywords: dry friction, elastomer-plastomer couple, linear sliding motion

Working on high structures is one of the jobs in the cities vertically developed. The abilities of climbing workers are used for the purpose of mounting publicity banners, cleaning building face, mounting objects on buildings etc. The use of fall arrester equipment is made under strict surveillance and training of the workers because of imminence of the accidents. Before sailing, the fall arrester equipment is tested and certified. Keywords: polyethylene, shock absorber, fall arrester, climbing, HBM MGC

Conventional methods for processing and shaping plastics parts (mold injection, thermoforming, extrusion etc) require heating (melting) process in which plastics material is soften or liquefied firstly and then imparted by using different dies and techniques. However, plastics material could be formed without any heating and for that purpose a few non-conventional procedures have been developed. An alternative to conventional shaping of plastic parts offers metal forming processes and cold forming technique.In this paper results of theoretical, numerical and experimental investigation of cold forming of plastics are present. Traditional metal forming processes such as upsetting and backward extrusion were applied for shaping billets made from HDPE and PA. Both processes are simulated by FEM and Simufact.Forging 8.1 program package. Numerically predicted load-stroke diagrams are compared to those experimentally recorded. All necessary material data and process parameters were determined according to the methodology which is used in metal forming processes. Keywords: thermoplastics, cold forming, FEM

The main characteristics of pressure sensitive adhesives are: peel resistance, shear and tensile strength. This work presents the tensile tests and related phenomena of pressure sensitive adhesives based on polychloroprene rubber with wood and steel substrates. The tensile breaking mechanism for the adhesive assembly is proposed and discussed within this article. Keywords: pressure sensitive adhesives, elastomers, tensile strength, wood, steel