On the vibration-damping properties of the prestressed polyurethane granular material

Granular materials promise opportunities for the development of high-performance, lightweight vibration-damping elements that provide a high level of safety and comfort. Presented here is an investigation of the vibration-damping properties of prestressed granular material. The material studied is thermoplastic polyurethane (TPU) in Shore 90A and 75A hardness grades. A method for preparing and testing the vibration-damping properties of tubular specimens filled with TPU granules was developed. A new combined energy parameter was introduced to evaluate the damping performance and weight-to-stiffness ratio. Experimental results show that the material in granular form provides up to 400% better vibration-damping performance as compared to the bulk material. Such improvement is possible by combining both the effect of the pressure–frequency superposition principle at the molecular scale and the effect of the physical interactions between the granules (force-chain network) at the macro scale. The two effects complement each other, with the first effect predominating at high prestress and the second at low prestress. Conditions can be further improved by varying the material of the granules and applying a lubricant that facilitates the granules to reorganize and reconfigure the force-chain network (flowability)

Raziskave lestvičastega okova poznolatenske nožnice s predrtim okrasom iz Ljubljanice pri Bevkah

The paper gives the results of our research into the technique of manufacture of the laddered chape from the sword scabbard with openwork fitment from the River Ljubljanica. In addition to characterisation of the alloys by proton-induced X-ray emission spectrometry (PIXE; cf. Šmit, Istenič, Perovšek 2010) the study included observation of fragments of bridges from the laddered chape using scanning electron microscopy (SEM), semi-quantitative chemical analysis of minute areas under an electron microscope (SEM/EDS) and metallographic research. Results of the study indicate that the laddered chape was made of forged steel and that the very thin layers (lamellae) of bronze in the front bridges acted as solders, thus giving an idea of how the laddered chape was constructed.Članek podaja izsledke raziskav lestvičastega okova nožnice z okovom okrašenim v predrti tehniki, ki je bil najden v reki Ljubljanici. Preiskovanje je vključevalo revizijo restavratorskega postopka in sondažne posege v lestvičasti okov, določanje zlitin z metodo protonsko vzbujenih rentgenskih žarkov (PIXE; glej Šmit, Istenič, Perovšek 2010), opazovanje dveh odlomkov prečk lestvičastega okova v vrstičnem elektronskem mikroskopu (SEM), semikvantitativne kemijske analize izredno majhnih površin v elektronskem mikroskopu (SEM/EDS) ter metalografske raziskave. Izsledki so pokazali, da je bil lestvičast okov iz kovanega jekla in da so zelo tanke plasti brona v sprednjih prečkah delovale kot spajke, kar tudi nakazuje, kako je bil lestvičasti okov narejen

Continuous modelling of cyclic ageing for lithium-ion batteries

The energy industry, transportation and even the smallest consumer electronics benefit from the practical applications of rechargeable batteries. Expectations of battery performance are greatly related to capacity, power output and available lifetime. However, the lifetime is affected by gradual chemical and mechanical degradation of the internal battery structure that cannot easily be predicted prior to installation. The reduction in performance is closely related to a particular usage pattern which is unique to the user and application, and is thus difficult to predict. Reliable real-time prediction of the remaining battery life therefore remains an important research topic. In this paper we show that fading battery performance under cyclic loading can be effectively and continuously followed by introducing the concept of the damage parameter derived from mechanical durability modelling approaches. The damage parameter is calculated continuously by the novel macro-scale hysteresis damage operator model. The hysteresis model is formed by a system of constitutive spring-slider modelling elements, here bridging the complex relation between the battery load and the durability data. The spring and the slider properties are individually calibrated for lithium nickel manganese cobalt oxide (NMC) batteries, however other battery structures can also be used. The durability data is obtained experimentally under controlled steady thermal and cyclic loading (constant charge/discharge current) conditions. The approach is validated on a standardised driving pattern with a complex current history. The predicted battery life is in good agreement with observed repetitions of a simulated load block until 90% of the initial battery capacitywith 589, 590 and 698 repetitions for the combined test and simulation prediction, full simulation prediction and experiment, respectively. When compared to established equivalent circuit or analytical approaches, the proposed approach requires only a small number of cyclic durability tests with constant current and temperature. In addition, the approach supports the battery design process by allowing simulations for different usage patterns, material and durability data

Mechanistic modelling of cyclic voltage-capacity response for lithium-ion batteries

One of the challenging tasks related to lithium-ion batteries (LIBs) remains a comprehensive approach for battery behaviour modelling. An approach is presented that enables modelling the voltage-capacity response of LIBs that are subjected to variable temperature and current load histories. A detailed presentation of the developed macro-scale phenomenological model embedding the mechanistic properties of the Prandtl type hysteresis operator and the concept of the force-voltage analogy is made. The necessary input data preparation for the model calibration is also presented. Accuracy of the model is confirmed with experimental observations for both nested current load history at two different temperatures and for arbitrary current load history. The same measured data is used to calibrate and to simulate response of the first order Thevenin equivalent circuit topology in order to amply compare the obtained results