Numerical calculations of effective elastic properties of two cellular structures

Young's moduli of regular two-dimensional truss-like and eye-shape-like structures are simulated by using the finite element method. The structures are the idealizations of soft polymeric materials used in the electret applications. In the simulations size of the representative smallest units are varied, which changes the dimensions of the cell-walls in the structures. A power-law expression with a quadratic as the exponential term is proposed for the effective Young's moduli of the systems as a function of the solid volume fraction. The data is divided into three regions with respect to the volume fraction; low, intermediate and high concentrations. The parameters of the proposed power-law expression in each region are later represented as a function of the structural parameters, unit-cell dimensions. The presented expression can be used to predict structure/property relationship in materials with similar cellular structures. It is observed that the structures with volume fractions of solid higher than 0.15 exhibit the importance of the cell-wall thickness contribution in the elastic properties. The cell-wall thickness is the most significant factor to predict the effective Young's modulus of regular cellular structures at high volume fractions of solid. At lower concentrations of solid, eye-like structure yields lower Young's modulus than the truss-like structure with the similar anisotropy. Comparison of the numerical results with those of experimental data of poly(propylene) show good aggreement regarding the influence of cell-wall thickness on elastic properties of thin cellular films.Comment: 7 figures and 2 table

Mosty z samo-ataptującym się torem kolejowym

The concept of an adaptive railway track, consisting of sleepers initially elevated (with the curvature tailored according to the detected, coming train) and then yielding in a controlled way under the moving vehicle is discussed. The problem formulated as a shape control requiring the minimum integral measure of the track deflection gives, as a side effect, a significant reduction of the corresponding integral measure of the dynamic contact forces between the track and wheels.Omówiona koncepcja samo-adaptującego się toru kolejowego opiera się na zastosowaniu inteligentnych podkładów. Podkłady, których wysokość może być zmieniana dzięki wyposażeniu ich w siłowniki, zastępują podkłady (mostownice) na moście. Idea adaptacyjnego toru polega na wstępnym uniesieniu toru, którego krzywizna dopasowana jest do zidentyfikowanego, nadjeżdżającego pociągu i następnie w kontrolowany sposób opuszczaniu pod przejeżdżającym pociągiem. Zdanie zstało sformułowane jako sterowanie kształtem toru przy założeniu minimalizacji całkowitej miary uogólnionego przemieszczenia toru. Jako efekt uboczny można spodziewać się znacznej redukcji skojarzonej całkowitej miary dynamicznego przyrostu obciążenia powstającego pomiędzy torem a kołami pociągu

Pyro-adaptive impact energy absorber

The paper contains a proposal of energy dissipation density controlling in lightweight thin walled structures by reducing their crushing stiffness during an impact process. For small scale laboratory experiments, low-energy-dissipation absorber was developed. Prismatic absorber made of thin lead sheets can dissipate the impact energy at two energy density levels. Moving the concept to the real steel or aluminum structures can lead to satisfying value of the Specific Energy Absorption indicator with possible control of the energy dissipation. Experimental and FE explicit simulation results showing controllable impact process of a thinwalled prismatic absorber with rectangular crossection are presented. The control of crushing forces proved to be possible and efficient. Adaptivity ratio achieved in the presented example was 35%. The idea of the presented absorber was based on automotive front rail shape. The experimental tests have to be re-conducted. Geometry of the tested absorber should be modified to facilitate the detachment process of the stiffening members

Strategies for reduction of energy consumption during ascending and descending process of modern telescopic HAPS aerostats

In this article, the authors propose and investigate a new concept of HAPS aerostat design in a modular form, which allows for sequential increasing or decreasing of the total volume, up to the desired size. In its initial form, the aerostat has relatively small dimensions but its central cylindrical part is multi-segmented and can be easily extended. The application of controllable construction couplings enables precise control of the aerostat expansion process and significantly improves its vertical mobility. The paper describes details of telescopic aerostat construction, presents a mathematical model of its vertical motion and investigates numerically two volume control strategies aimed at maximization of operation efficiency and minimization of operation cost. The results obtained reveal the main problems that have to be addressed and the factors that play a key role in design of such telescopic aerostats and control of their vertical mobility