143 research outputs found

    Explicit finite element implementation of a shape memory alloy constitutive model and associated analyses

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    Shape memory alloys (SMA) represent an important class of smart metallic materials employed in various innovative applications thanks to their unique thermomechanical behavior. Since the 1980s, several SMA constitutive models have been proposed and implemented into both commercial and academic finite element analysis software tools. Such models have demonstrated their reliability and robustness in the design and optimization of a wide variety of SMA-based components. However, most models are implemented using implicit integration schemes, thus limiting their applicability in highly nonlinear analyses. The objective of this work is to present a novel explicit integration scheme for the numerical implementation of the three-dimensional Souza-Auricchio model, a phenomenological model able to reproduce the primary SMA responses (i.e., pseudoelasticity and shape memory effect). The model constitutive equations are formulated by adopting the continuum thermodynamic theory with internal variables, following a plasticity-like approach. An elastic predictor-inelastic corrector scheme is here used to solve the time-discrete non-linear constitutive equations in the explicit framework. The proposed algorithm is investigated through several benchmark boundary-value problems of increasing complexity, considering both pseudoelastic and shape memory response in quasi-static conditions; a comparison with an implicit integration scheme is also performed. Such numerical tests demonstrate the ability of the algorithm to reproduce key material behaviors with effectiveness and robustness. Particularly, the analysis of SMA cables demonstrates the effectiveness of the explicit algorithm to solve complex problems involving widespread nonlinear contact, which prevent the convergence of the implicit scheme. Details such as mass-scaling options are also discussed

    Valorisation of vine-shoots: ultrasound-assisted extraction of proanthocyanidins

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    Vine-shoots are agricultural wastes of vineyards. About 1.4-2.0 tons of shoots can be obtained per hectare of vine per year. The world area under vines is about 7.5 million ha, and then an estimated total of 10.5-15 million tons of vine-shoots are produced each year. The studies conducted on the phenolic composition of vine-shoots generally focused on the stilbenes because of the interest in their health-promoting. However, to the best of our knowledge, there has been no work, thus far, on the proanthocyanidins (PAs) from vine-shoots. Proanthocyanidins exist as oligomers (OPCs), containing two to ten or more \u2018catechin\u2019 units, and polymers (PPCs). This study aims at performing optimisation of ultrasound-assisted extraction (UAE) of OPCs and PPCs from vine\u2013shoots using response surface methodolog

    Disaster Risk Management of Cultural Heritage Sites in Albania.

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    UNESCO has a vital role to play in constructing a global culture of disaster preparedness and mitigation, building in the minds of people a Disaster Risk Management of Cultural Heritage Sites in Albania culture of resilience to risk, promoting awareness, education and capacity and foremost a different way to approach the domain of Disaster Risk Reduction (DRR) and preparedness. UNESCO is also the secretariat of the 1972 World Heritage Convention, of which the properties have recently been the focus of substantial advancement in securing better capacity in risk management and reduction. Since UNESCO is engaged in important actions for the protection of cultural heritage it implements several projects in post disaster scenarios. This book has been elaborated as a final outcome of the project \u201cNatural Risk Preparedness and Mitigation - Building capacity in the field of risk mitigation for Cultural Heritage properties in Albania\u201d during the period 2011-2013. The project aimed to streamline disaster risk management in the Country, using its World Heritage properties as demonstration sites. The project was conceived to assist the country in order to enhance its capacity for Disasters Risk Management (DRM) and advancement in seismological and geological vulnerability of Cultural Heritage properties

    Stress-Free Two-Way Shape Memory Effect of Poly(ethylene glycol)/ Poly(epsilon-caprolactone) Semicrystalline Networks

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    In this work, poly(ethylene glycol) (PEG)/poly(epsilon- caprolactone) (PCL) semicrystalline networks were prepared by photo-cross-linking of methacrylated macromonomers with different molecular weights and in different proportions to obtain amphiphilic materials capable of displaying properly designed shape memory effects. Networks based on PCL 10 kDa and PEG 3 kDa showed suitable thermal and mechanical properties with well-separated crystallization and melting regions to achieve a self-standing two-way shape memory effect. Particularly, after the application of a specific thermomechanical history, these materials are capable of cyclically changing their shape between two configurations upon cooling-heating cycles in the absence of any external load applied. The effect of the composition of the networks and of the employed thermomechanical parameters, such as the applied strain and the actuation temperature, was investigated to shed light on the shape memory mechanism for this class of materials, which are considered promising for applications in the biomedical field and as reversible actuators for soft robotics

    Computable R\'enyi mutual information: Area laws and correlations

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    Mutual information is a measure of classical and quantum correlations of great interest in quantum information. It is also relevant in quantum many-body physics, by virtue of satisfying an area law for thermal states and bounding all correlation functions. However, calculating it exactly or approximately is often challenging in practice. Here, we consider alternative definitions based on R\'enyi divergences. Their main advantage over their von Neumann counterpart is that they can be expressed as a variational problem whose cost function can be efficiently evaluated for families of states like matrix product operators while preserving all desirable properties of a measure of correlations. In particular, we show that they obey a thermal area law in great generality, and that they upper bound all correlation functions. We also investigate their behavior on certain tensor network states and on classical thermal distributions.Comment: 15 pages, 2 figures, comments welcom

    Enhanced Mechanical Properties by Ionomeric Complexation in Interpenetrating Network Hydrogels of Hydrolyzed Poly (N-vinyl Formamide) and Polyacrylamide

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    Tough hydrogels were made by hydrolysis of a neutral interpenetrating network (IPN) of poly (N-vinyl formamide) PNVF and polyacrylamide (PAAm) networks to form an IPN of polyvinylamine (PVAm) and poly (acrylic acid) (PAAc) capable of intermolecular ionic complexation. Single network (SN) PAAm and SN PNVF have similar chemical structures, parameters and physical properties. The hypothesis was that starting with neutral IPN networks of isomeric monomers that hydrolyze to comparable extents under similar conditions would lead to formation of networks with minimal phase separation and maximize potential for charge–charge interactions of the networks. Sequential IPNs of both PNVF/PAAm and PAAm/PNVF were synthesized and were optically transparent, an indication of homogeneity at submicron length scales. Both IPNs were hydrolyzed in base to form PVAm/PAAc and PAAc/PVAm IPNs. These underwent ~5-fold or greater decrease in swelling at intermediate pH values (3–6), consistent with the hypothesis of intermolecular charge complexation, and as hypothesized, the globally neutral, charge-complexed gel states showed substantial increases in failure properties upon compression, including an order of magnitude increases in toughness when compared to their unhydrolyzed states or the swollen states at high or low pH values. There was no loss of mechanical performance upon repeated compression over 95% strain

    Reversible Stress-Driven and Stress-Free Two-Way Shape Memory Effect in a Sol-Gel Crosslinked Polycaprolactone

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    The two-way shape memory effect is the ability of a material to change its shape between two configurations upon application and removal of a stimulus, and, among shape memory polymers, it is featured only by few systems, such as semicrystalline networks. When studied under tensile conditions, it consists of elongation-contraction cycles along cooling and heating across the crystallization and melting region, typically under the application of a constant load. However, recent studies on crosslinked semicrystalline co-polymers demonstrate that also a completely stress-free, or self-sustained, two-way effect may be achieved through specific thermomechanical cycles. This effect is currently regarded with interest for the development of intrinsically reversible sensors and actuators, and it may also be displayed by simpler materials, as homopolymer-based semicrystalline networks. Only seldom articles investigate this possibility, therefore in this work the two-way shape memory behavior is studied on a poly(e-caprolactone) system, crosslinked by means of a sol-gel approach. The effect is studied both under stress-driven and stress-free condition, by applying properly set-up thermo-mechanical histories. The results allow to describe the effect as a function of temperature, to reveal the dependence on specific testing parameters and to compare the extent of the reversible strain variation under these two conditions

    Multi-material 3D printed shape memory polymer with tunable melting and glass transition temperature activated by heat or light

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    Shape memory polymers are attractive smart materials that have many practical applications and academic interest. Three-dimensional (3D) printable shape memory polymers are of great importance for the fabrication of soft robotic devices due to their ability to build complex 3D structures with desired shapes. We present a 3D printable shape memory polymer, with controlled melting and transition temperature, composed of methacrylated polycaprolactone monomers and N-Vinylcaprolactam reactive diluent. Tuning the ratio between the monomers and the diluents resulted in changes in melting and transition temperatures by 20, and 6 °C, respectively. The effect of the diluent addition on the shape memory behavior and mechanical properties was studied, showing above 85% recovery ratio, and above 90% fixity, when the concentration of the diluent was up to 40 wt %. Finally, we demonstrated multi-material printing of a 3D structure that can be activated locally, at two different temperatures, by two different stimuli; direct heating and light irradiation. The remote light activation was enabled by utilizing a coating of Carbon Nano Tubes (CNTs) as an absorbing material, onto sections of the printed objects
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