On the subject of analyzing the post-buckling behavior of composite sandwich panels with thin skins of variable stiffness under longitudinal compression

The use of variable stiffness panels can be considered as one of the measures to improve the weight efficiency of aircraft structures. The object of research in this work is three-layer panels of variable stiffness loaded with longitudinal compressive forces. The purpose of the work is to evaluate the overcritical behavior of the specified panels when geometrically nonlinear relations are used. The variable parameter of three-layered panels in the case under consideration is the height of the rigid filler, which varies linearly. An analytical solution of the problem of determining the stress-strain state by the Bubnov-Galerkin method is given. The deflection of a panel is represented by two terms, and the problem is reduced to the solution of a nonlinear system of two unknown equations with respect to the values of the deflection amplitudes. Analytical expressions for calculating membrane stresses are given. The practical significance of the work lies in the possibility of estimating the overcritical behavior of a three-layer panel of variable stiffness under compression and the possibility of constructing an algorithm for the optimal design of the panels.

Pseudo-Ductility, Morphology and Fractography Resulting from the Synergistic Effect of CaCO3 and Bentonite in HDPE Polymer Nano Composite

Polymeric materials such as High density polyethylene(HDPE) are ductile in nature, having very low strength. In order to improve strength by non-treated rigid fillers, polymeric materials become extremely brittle. Therefore, this work focuses on achieving pseudo-ductility (high strength and ductility) by using a combination of rigid filler particles (CaCO3 and bentonite) instead of a single non-treated rigid filler particle. The results of all tensile-tested (D638 type i) samples signify that the microstructural features and surface properties of rigid nano fillers can render the required pseudo-ductility. The maximum value of tensile strength achieved is 120% of the virgin HDPE, and the value of elongation is retained by 100%. Furthermore, the morphological and fractographic analysis revealed that surfactants are not always going to obtain polymer–filler bonding, but the synergistic effect of filler particles can carry out sufficient bonding for stress transfer. Moreover, pseudo-ductility was achieved by a combination of rigid fillers (bentonite and CaCO3) when the content of bentonite dominated as compared to CaCO3. Thus, the achievement of pseudo-ductility by the synergistic effect of rigid particles is the significance of this study. Secondly, this combination of filler particles acted as an alternative for the application of surfactant and compatibilizer so that adverse effect on mechanical properties can be avoided.

Strengthened, recyclable shape memory rubber films with a rigid filler nano-capillary network

Water-soluble CMCS nano-capillary network endowed XSBR films with improved mechanical properties, recyclability and shape memory effects.

EFFECTS OF INTERFACIAL ADHESION ON DEFORMATION AND FRACTURE BEHAVIOUR OF COMPOSITES BASED ON POLYPROPYLENE AND GLASS BEADS

In this study, the isotactic polypropylene, a semicrystalline polymer, was used as a matrix for composites containing 20% and 40% (by weight) of glass bead filler. Selected surface treatment was applied to obtain different adhesion between particles and polymer matrix. In addition to non-treated filler, filler treated with i) a release agent (labelled as NO adhesion) and ii) an adhesion promoter (labelled as GOOD adhesion) were incorporated into the matrix. The morphology, tensile mechanical and fracture behaviour (J-integral) were investigated. Morphology observation revealed a poor interfacial adhesion in the case of non-treated and “NO adhesion” samples represented with debonding of particles. In contrast, strong particle-matrix interactions were confirmed in “GOOD adhesion” samples. The presence of rigid filler particles increased the stiffness, while strain at break was decreased with the lowest value for the composites with strong interfacial adhesion. On the other hand, the higher rigidity and lower deformability decreased in fracture toughness.

MODIFIED GUTH–GOLD EQUATION FOR CARBON BLACK–FILLED RUBBERS

ABSTRACT The modulus increase in rubbers filled with solid particles is investigated in detail here using an approach known widely as the Guth–Gold equation. The Guth–Gold equation for the modulus increase at small strains was reexamined using six different species of carbon black (Printex, super abrasion furnace, intermediate SAF, high abrasion furnace, fine thermal, and medium thermal carbon blacks) together with model experiments using steel rods and carbon nanotubes. The Guth–Gold equation is only applicable to such systems where the mutual interaction between particles is very weak and thus they behave independently of each other. In real carbon black–filled rubbers, however, carbon particles or aggregates are connected to each other to form network structures, which can even conduct electricity when the filler volume fraction exceeds the percolation threshold. In the real systems, the modulus increase due to the rigid filler deviates from the Guth–Gold equation even at a small volume fraction of the filler of 0.05–0.1, the deviation being significantly greater at higher volume fractions. The authors propose a modified Guth–Gold equation for carbon black–filled rubbers by adding a third power of the volume fraction of the blacks to the equation, which shows a good agreement with the experimental modulus increase (G/G0) for six species of carbon black–filled rubbers, where G and G0 are the modulus of the filled and unfilled rubbers, respectively; ϕeff is the effective volume fraction; and S is the Brunauer, Emmett, Teller surface area of the blacks. The modified Guth–Gold equation indicates that the specific surface volume ()3 closely relates to the bound rubber surrounding the carbon particles, and therefore this governs the reinforcing structures and the level of the reinforcement in carbon black–filled rubbers.