2,769 research outputs found

    Development of configurational forces during the injection of an elastic rod

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    When an inextensible elastic rod is 'injected' through a sliding sleeve against a fixed constraint, configurational forces are developed, deeply influencing the mechanical response. This effect, which is a consequence of the change in length of the portion of the rod included between the sliding sleeve and the fixed constraint, is theoretically demonstrated (via integration of the elastica) and experimentally validated on a proof-of-concept structure (displaying an interesting force reversal in the load/deflection diagram), to provide conclusive evidence to mechanical phenomena relevant in several technologies, including guide wire for artery catheterization, or wellbore insertion of a steel pipe.Comment: 10 pages, 4 figures, Extreme Mechanics Letters (2015

    Experimental investigation of the elastoplastic response of aluminum silicate spray dried powder during cold compaction

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    Mechanical experiments have been designed and performed to investigate the elasto-plastic behaviour of green bodies formed from an aluminum silicate spray dried powder used for tiles production. Experiments have been executed on samples obtained from cold compaction into a cylindrical mould and include: uniaxial strain, equi-biaxial flexure and high-pressure triaxial compression/extension tests. Two types of powders have been used to realize the green body samples, differing in the values of water content, which have been taken equal to those usually employed in the industrial forming of traditional ceramics. Yielding of the green body during compaction has been characterized in terms of yield surface shape, failure envelope, and evolution of cohesion and void ratio with the forming pressure, confirming the validity of previously proposed constitutive models for dense materials obtained through cold compaction of granulates.Comment: 17 pages; Journal of the European Ceramic Society, 201

    Finite strain elastoplastic bulging of circular diaphragms

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    The inflation of planar thin films represents a phenomenon widely employed by engineering and biological systems, with applications ranging from pressure sensors and material characterization to growing skins in the human body. In this paper, the bulging of plane circular membranes composed of isotropic elastoplastic materials is analytically, computationally and experimentally studied. An analytical finite strain formulation is developed and implemented to model the deformation response of inflated thin films. The solution accurately predicts the elastic and plastic phases of bilinear and nonlinear elastoplastic materials, for both small and large plastic strains. It shows that a sudden change in the full-field strain distribution during diaphragm inflation is associated with the plastic strain localization that first develops at the membrane apex. The results are compared with finite element simulations for a wide range of material parameters, showing an excellent agreement. The mathematical formulation is also validated by bulge tests performed on ETFE membranes, representative of a bilinear elastoplastic response, and aluminium foils that show a nonlinear plastic behaviour. The comparison between theoretical predictions and experimental measures proves the validity of the proposed model at small and large plastic strains, which promises to find applications in the modelling of the finite strain inflation of thin films, especially for the determination of elastoplastic material parameters through bulge testing

    Nanographitic coating enables hydrophobicity in lightweight and strong microarchitected carbon

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    Metamaterials that are lightweight, stiff, strong, scalable and hydrophobic have been achieved separately through different materials and approaches, but achieving them in one material is an outstanding challenge. Here, stereolithography and pyrolysis are employed to create carbon microlattices with cubic topology and a strut width of 60–70 µm, with specific strength and stiffness of up to 468.62 MPa cm3 g−1 and 14.39 GPa cm3 g−1 at a density of 0.55 g cm−3, higher than existing microarchitected materials and approaching those of the strongest truss nanolattices. Subsequent fast Joule-heating then introduces a hierarchical nanographitic skin that enables hydrophobicity, with a water contact angle of 135 ± 2°, improving the hydrophilic response of pyrolytic carbon. As the Joule heating induced sp2-hybridization and nano-texturing predominantly affect the strut sheath, the effect on mechanical response is limited to a reduction in the distribution of compressive strength of as-pyrolyzed architectures by ~80% and the increase of the mean effective stiffness by ~15%. These findings demonstrate a technique to fabricate high strength, low density, and hydrophobic nanographite-coated carbon microlattices

    Deployment and surface accuracy of regularly creased membranes

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    Creases are highly localized regions ubiquitous across different length scales in low-dimensional natural and engineering systems. Their presence strongly influences the mechanical response and surface accuracy of creased membrane materials and structures. In this paper, we study the deployment of folded sheets composed of an arbitrary number of non-interacting and parallel creases. We develop a mathematical formulation that describes the nonlinear mechanics of systematically creased membranes composed of a single or multiple folds, and predicts their surface accuracy during unfolding. The proposed solution shows the contribution of membrane bending and crease energies during deployment, and reveals the presence of two dimensionless parameters that govern the unfolding behaviour. Sensitivity analyses are also performed to assess the influence of the crease geometry and constitutive behaviour. The analytical predictions are validated through finite element analyses and deployment tests performed on thin films with one, two and three fold lines, where imaging techniques are employed to quantify deformation. The excellent agreement between theoretical and experimental results testifies that the developed formulation represents a precise tool to assess the tensioning of creased membranes, with applications ranging from origami metamaterials to lightweight space structures where precise shape control is paramount

    Mangani-pargasite, NaCa2(Mg4Mn3+)(Si6Al2)O22(OH)2, a new mineral species of the amphibole supergroup

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    Mangani-pargasite, ideally NaCa2(Mg4Mn3+)(Si6Al2)O22(OH)2, is a new mineral species of the calcium amphibole subgroup of the amphibole supergroup. The type specimen was found on the mine dump of the Långban Fe-Mn-(Ba-As-Pb-Sb) deposit in Värmland, Sweden. Crystal chemical analyses resulted in the empirical chemical formula: A(Na0.90Pb0.07K0.03)Σ1.00B(Ca1.93Mn2+0.07)Σ2.00C(Mg4.25Mn3+0.39Al0.26 Fe3+0.10)Σ5.00T(Si6.35Al1.65)Σ8.00O22W(OH)2. In order to complete the description of this newly approved (IMA 2018-151) mineral we report here additional data to those published in papers by Jonsson and Hålenius (2010) and Hålenius and Bosi (2012). Mangani-pargasite is biaxial positive, with a=1.635(5), b=1.645(5), g=1.660(5) and the measured optic angle 2V is 85(5)°. The dispersion is weak (r>v), and the optic orientation is: Y||b; Z^c=25(3)°. Mangani-pargasite is red to brownish red with weak pleochroism; X=pale reddish brown, Y=pale reddish brown and Z=pale brownish red; X≈Y>Z. The unit-cell parameters are a=9.9448(5), b=18.0171(9), c=5.2829(3) Å, b=105.445(3)°, V=912.39(9) Å3, Z=2, space group C2/m. The ten strongest reflections in the X-ray powder diffraction pattern [d-values in Å, I, (h k l)] are: 8.420, 29, (110); 3.368, 17, (131), 3.279, 49, (240); 3.141, 100, (310); 2.817, 44, (33 0); 2.698, 21, (151); 2.389, 18, (350); 1.904, 29, (510); 1.650, 22, (461) and 1.448, 46, (661)

    Rotational sensitivity of the "G-Pisa" gyrolaser

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    G-Pisa is an experiment investigating the possibility to operate a high sensitivity laser gyroscope with area less than 1m21 \rm m^2 for improving the performances of the mirrors suspensions of the gravitational wave antenna Virgo. The experimental set-up consists in a He-Ne ring laser with a 4 mirrors square cavity. The laser is pumped by an RF discharge where the RF oscillator includes the laser plasma in order to reach a better stability. The contrast of the Sagnac fringes is typically above 50% and a stable regime has been reached with the laser operating both single mode or multimode. The effect of hydrogen contamination on the laser was also checked. A low-frequency sensitivity, below 1Hz1 \rm Hz, in the range of 10−8(rad/s)/Hz10^{-8} \rm {(rad / s)/ \sqrt{Hz}} has been measured.Comment: 6 pages, 6 figures, presented at the EFTF-IFCS joint conference 200
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