Viscoelastic properties of 3D fabric reinforced Vinyl Ester composites were studied in different
directions using Dynamic Mechanical Thermal Analysis (DMTA). Such materials filled by
nanoparticles (silicon carbide) with different concentrations were also investigated. The increases of
storage and loss moduli with addition of nanoparticles and with increase of their concentrations
were observed. The maximal tangent of the angle of mechanical losses was especially compared at
below and over glass transition temperature. Below glass transition temperature the presence of
nanoparticles increases storage and loss moduli and loss tangent. These effects achieved maximum
at glass transition temperature. Over glass transition, the loss modulus and loss tangent are
decreased with increase of the concentration of nanoparticles.
The problem of buckling of a vertical rod loaded by dead weight and tensile force to its top end was examined. Four variants for attachment of the top end of the rod upon clampingIn light of the partial depletion of off-shore petroleum deposits, work has begun on exploiting deposits at deeper sites. Floating platforms have been developed for this purpose, which are connected to the bottom by vertical oil pipelines and held over the well by a system of mooring lines [1][2][3]. The use of composites in various structural elements of the platforms, pipelines, and mooring lines appears more promising with increasing sea depth above the site.Let us examine vertical oil pipelines (risers). One of the major loads acting on this structure is its dead weight (there is no extrusion force for a vertical rod buried into the bottom and rising above the water surface, Fig. I). The mechanical behavior of a pipeline may be described satisfactorily by a model for a flexible rod or model of an absolutely flexible thread (depending on the ratio of the length of the pipeline to its diameter). The strength of a vertically suspended thread is a function of the specific tensile strength of the material in the longitudinal direction (the specific strength for composites is much higher than for traditional materials). The tension of the upper end of the suspended thread is equal to its weight. We should note that the weight of a pipeline increases nonlinearly relative to the depth of the deposit since not only its length but also the wall thickness is augmented to resist the acting pressure. The required tension for a flexible rod capable of accepting some compressive load is less than the weight, and its magnitude is a function of the strength depending on the specific rigidity of the material.It follows from the formula for a critical distributed longitudinal load [4] EI qcr = kb--p-,where I is the moment of inertia, E is Young's modulus, k b is a numerical coefficient dependent on the nature of fixation of the upper end of the rod (Table 1) loaded by dead weight q = pgS (,o is the density, g is the acceleration of gravity, and S is the area of the cross section) that there is an interrelationship between the radius r and length l in the case of a round tubular rod. One of these parameters may be given and the other may be considered as a critical value, for example rot "-4~ riot= l 3/2 ~Og/(Ekb),where rcr is the critical value of the mean radius of a thin-walled tube and rio r is the critical value of the inertial radius. The wall thickness does not enter Eq. (2) since both the moment of inertia of the cross section I and the cross-sectional area S, Institute of Polymer Mechanics, Latvian Academy of Sciences, LV-1006, Riga, Latvia.
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