Frequency response analysis of laminated composite beams

Conclusions The modeling of laminated composite beams has been derived systematically from the three-dimensional elasticity relations. The correctness of the solution found by using the present finite element model is verified by comparison with the results obtained by analytical solutions and other results presented in the literature. Numerical results indicate that the present technique can given accurate results for frequency response analysis for laminated composite beams. Loss factors of structures obtained by the method of complex eigenvalues and the direct frequency response method exhibit very good agreement. Optimum design of a laminated composite beam by the finite element method and the method of experiment planning has been successfully presented.Published in Mekhanika Kompozitnykh Materialov, Vol. 30, No. 5, pp. 664–674, September–October, 1994.     

The accumulated dissipated energy of composites under cyclic-dynamic stress

This paper presents a method for the estimation of the vibratory fatigue strength of composite materials, which is based on the accumulated dissipated energy. The accumulated dissipated energy was measured with a special measuring technique that is able to catch quasi-continuously the mechanical properties of the tested samples. The samples were made of glass-fiber epoxy foams reinforced with pretreated woven fabrics. The curves of the accumulated dissipated energy were approximated by an equation that includes several parameters. These parameters were identified for experiments with different types of load and for samples with different contents of micropores. In the equation for samples that reach more than 10⁶ load cycles, the accumulated dissipated energy in one load stage tests turns out to be a linear function. With this function the fatigue limit of the samples can be predicted.     

Synthesis of 1-(pyridin-4-yl)-3,6-diazahomoadamantane and its derivatives

Condensation of 1-(pyridin-4-yl)propan-2-one with 1,3,6,8-tetraazatricyclo[4.4.1.1^3,8]dodecane gave 1-( pyridin-4-yl)-3,6-diazahomoadamantan-9-one as intermediate product in the synthesis of 1-(pyridin-4-yl)-3,6-diazahomoadamantane and its derivatives having functional substituents at the bridging carbon atom in the homoadamantane skeleton.     

Algorithm for solving the equation of radiative transfer in the frequency domain

We present an algorithm that provides a frequency-domain solution of the equation of radiative transfer (ERT) for heterogeneous media of arbitrary shape. Although an ERT is more accurate than a diffusion equation, no ERT code for the widely employed frequency-domain case has been developed to date. In this work the ERT is discretized by a combination of discrete-ordinate and finite-volume methods. Two numerical simulations are presented.     

Heteroadamantanes and their derivatives

1-p-nitrophenyl-3,6-diazahomoadamantane and 1-p-nitrophenyl-3,6-diazahomoadamantan-9-one were obtained by nitration of 1-phenyl-3,6-diazahomoadamantane and 1-phenyl-3,6-diazahomoadamantan-9-one with a mixture of potassium nitrate and sulfuric acid; 1-p-nitrophenyl-3,6-diazahomoadamantan-9-one was reduced with sodium borohydride to 1-p-nitrophenyl-3,6-diazahomoadamantan-9-ol. It was found that the nitro groups of these nitrophenyldiazahomoadamantanes were reduced to amino groups by heating with hydrazine hydrate without a catalyst. 1-p-Aminophenyl-3,6-diazahomoadamantan-9-one was obtained by reduction of nitrophenyl-azahomoadamantanone with tin in sulfuric acid, and 9-amino-1-p-aminophenyl-3,6-diazahomo-adamantane was obtained by reduction of its oxime with a nickel—aluminum alloy in water—base medium.See [1] for 17.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1257–1261, September, 1992.     

Mass-spectral Study of 9-[α(β,γ)-Picolylidene]-1(4)-azafluorenes

A mass-spectral study was carried out on the behavior of the Z- and E-isomers of 9-picolylideneazafluorenes. A possible mechanism for the elimination of a hydrogen atom from the M⁺ ion of the Z- and E-isomers of 1(4)-azafluorene derivatives was examined. Mass spectrometry permitted a distinction between compounds isomeric relative to the position of the nitrogen atom in the azafluorene fragments and also the Z- and E-isomers of picolylidene derivatives of 1- and 4-azafluorenes possessing - and -pyridyl substituents.     

Synthesis of 1-methyl-8-(pyridin-2-yl)-3,6-diazahomoadamantane and its derivatives

Condensation of 1-(pyridin-2-yl)butan-2-one with 1,3,6,8-tetraazatricyclo[4.4.1.13, 8]dodecane gave 1-methyl-8-(pyridin-2-yl)-3,6-diazahomoadamantan-9-one as intermediate product in the synthesis of 1-methyl-8-(pyridin-2-yl)-3,6-diazahomoadamantane and its derivatives with various functional groups at the bridging carbon atom.     

Optimality parameter of Korobov parallelepipedal grids for cubature formulas

When multiple integrals are approximately evaluated using Korobov cubature formulas, it is necessary to introduce a parameter characterizing the uniform distribution of the grid nodes. A new parameter for Korobov parallelepipedal grids is proposed, and an algorithm for its computation is described.     

Influence of fiber structure modification on the mechanical properties of flax fiber-epoxy composites

The mechanical characteristics of flax fibers were optimized by using the NaOH treatment process to improve the properties of composite materials. Shrinkage of the fibers during this treatment had a significant effect on the structure and, as a result, on the mechanical properties of the fibers and the composites based on them. Due to the higher mechanical strength and stiffness of flax fibers after NaOH treatment under isometric conditions, the strength and stiffness of composites in general increase. Further, NaOH treatment leads to a rougher surface morphology, as shown, e.g., for jute fibers, compared with the surface of untreated fibers without improved fiber/matrix adhesion.     

Wood-filled thermoplastic composites

Different physical properties of wood-filled thermoplastic materials produced by a special mixing and extrusion process are examined. The results show that the wood content and the kind of plastics are the main parameters that control the physical properties of composites. In general, wood-filled thermoplastic materials exhibit mechanical properties comparable to those of customary wood fiber products, i.e., medium density fiberboard (MDF); however, they show distinctly better behavior than the MDF and natural wood after exposure to moisture.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Universität Kassel, Institut für Werkstofftechnik, Kunstoff-und Recyclingtechnik, Mönchebergstraße 3, 34109 Kassel, Germany. Published in Mekhanika Kompozitnykh Materialov, Vol. 34, No. 6, pp. 795–802, November–December, 1998.