Topological design of multi-cell hexagonal tubes under axial and lateral loading cases using a modified particle swarm algorithm

Multi-cell structures have widely been studied due to their excellent energy absorption ability. However, few systematic studies have been conducted on the topological design of cross-sectional configurations of thin-walled tubes. To make full use of the material, topology optimization of multi-cell hexagonal tubes was conducted under both axial compression and lateral bending loadings. A binary particle swarm optimization (PSO) was enhanced by introducing the mass constraint factor to guide the movement of particles, which could improve the success rate of obtaining the global optimum. It was found that the optimum designs under the axial load placed the material outward to strengthen the interaction between the outer and inner walls and created more partitions between the inside rib walls. While under the lateral load, all the optimum designs have diagonally-connected elements to resist local deformation, and the material was also placed outward to increase the moment of inertia and thus to resist the global deformation. For the multiple loading cases, the final optimal designs are similar to the compression designs or combined designs from the two loading cases.     

Effect of fiber orientation on the structure of shock waves in carbon fiber-epoxy composites

Using an analytical relation between the Hugoniot (anisotropic and isotropic) states and other thermodynamic (anisotropic and isotropic) states at high pressures, the effect of fiber orientation on the structure of shock waves in carbon fiber-epoxy composites of various symmetry is investigated. A correct nonlinear model of propagation of shock waves in anisotropic materials is proposed, which employs the conception of total generalized pressure and the pressure corresponding to the thermodynamic response, i.e., to the equation of state. The equation generalizes the nonlinear Hugoniot equation to anisotropic materials and is reduced to the classical variant in the case of isotropy. Invoking the relations of nonlinear anisotropic solids and the generalized decomposition of stress tensor, the double structure of shock waves, consisting of nonlinear anisotropic and isotropic elastic parts, is examined. The numerical calculations of Hugoniot levels of stress agree well with experimental data for a carbon fiber-epoxy composite selected.     

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.     

Effect of the size of the specimen cross section on the long-term strength of polyethylene

The scale effect has been investigated in relation to the long-term strength of specimens of high-density polyethylene. Time dependences of the tensile strength at ordinary temperatures have been obtained. It is shown that the long-term strength depends on the dimensions of the specimen cross section. The deformation of the specimens depends on their size and the shape of the gage cross section.Higher Chemical Technology Institute, Sofia. Translated from Mekhanika Polimerov, No. 4, pp. 741–743, July–August, 1973.     

Moisture absorption and mechanical and acoustic responses in shear of a glass fiber fabric/epoxy resin composite

An analysis of the mechanical and acoustic responses of a laminate composed of 12 layers of glass fiber fabric/epoxy resin and conditioned in environments with relative humidities of 0, 60, and 96% RH at 60°C is presented. The first part of the study consists in following the weight gain according to the duration of hygrothermal conditioning, and the second part—in test ing 45°-oriented specimens in uniaxial tension up to failure at constant imposed displacement rates, with registrating the acoustic emission to track the damage process. The influence of moisture content in the material showed up as a significant decrease in its shear modulus, shear stress, and acoustic emission with growing quantity of absorbed water. An exponential function is proposed for describing the relationship between the varying shear modulus and the shear strain. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 43, No. 5, pp. 595–602, September–October, 2007.     

Effect of fiber length on the strength and fracture properties of a fiber-filled silicone composite

The mechanism by which fillers strengthen polymers is discussed, and the effect of fiber length on static and impact bending strength and on the area of the fracture surface is studied with reference to the example of a silicone composite. A correlation is established between the strength properties and the area of the fracture surface. On the basis of the data obtained it is shown that, as the fiber length increases, the fracture mechanism changes from extraction of the ends of the fibers along the fracture path to breakage of the fibers.Moscow Lomonosov Institute of Fine Chemical Technology. Ter-Gazaryan State Scientific-Research Planning Institute of Polymer Adhesives, Kirovakan. Translated from Mekhanika Polimerov, No. 3, pp. 445–449, May–June, 1971.