The present paper is aimed at clarifying the dependence of the force reduction ability of sport surfaces used in athletic tracks on the material’s viscoelastic properties and on the geometry of the sample. The study is based on laboratory tests carried out with an “artificial athlete” apparatus and dynamic mechanical analysis. Seven different sport surfaces were tested; other polymeric materials were also examined in order to widen the property ranges covered. The results show a prominent effect of sample thickness on the measured value of force reduction; a method to relate it to the intrinsic properties of the material is proposed
This work deals with the production and characterization of low-density rigid foams with anisotropic cellular structures based on polypropylene filled with nanoclays, which present a high potential to be employed for structural applications. The use of nanoclays and different external pressures during foaming allowed to modify several structural parameters such as anisotropy ratio, cell size, and open cell content which had a huge impact on their mechanical behavior. Moreover, nanoparticles catalyzed the thermal decomposition reaction of the blowing agent, which involved the formation of bimodal cellular structures. The mechanical anisotropy of these foams was characterized by measuring the compressive modulus in three different directions. The results indicate that mechanical properties can be significantly improved due to the introduction of nanoclays and to the structural modifications induced by their presence, especially when it comes to the anisotropy ratio parameter. POLYM. COMPOS., 00:000-000,
Abstract. In this work, the viscoelastic behavior of open cell polyurethane foams used in noise control applications is investigated through dynamic mechanical analysis in compression. Several levels of static strains superimposed on a small dynamic one were considered in order to assess the effect of material non-linearity on the mechanical response.Further, a wide range of frequencies and temperatures was explored. For each static strain a different master curve for conservative component of complex modulus, E', could be determined. Interestingly, the loss factor was the same at all static strains, indicating that the relative contribution of energy dissipation and conservation is unaffected by the static strain. Moreover, shift factors (and thus the bulk material relaxation times) turned out to be independent on static strain level. These results suggest that the non-linearity of the foam is linked to the change in foam structure with strain rather than to a non-linear behavior of the viscoelastic constituent material. The acoustic performance of the considered materials was modelled for a case study with two approaches: i) standard simulations performed taking a single valued complex modulus, measured at 50Hz and room temperature or ii) simulations taking into account the complex modulus frequency dependence obtained from the master curves. The transmission loss prediction obtained in the second case is in better agreement with experiments, especially at high frequencies.
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