Finite Strain Constitutive Modelling of Shape Memory Alloys Considering Partial Phase Transformation with Transformation-Induced Plasticity

This paper presents a unified modelling effort to describe partial phase transformation during cyclic thermo-mechanical loading in Shape Memory Alloys (SMA). To this purpose, a three-dimensional (3D) finite strain constitutive model considering TRansformation-Induced Plasticity (TRIP) is combined with a modified hardening function to enable the accurate and efficient prediction of partial transformations during cyclic thermo-mechanical loading. The capabilities of the proposed model are demonstrated by predicting the behavior of the material under pseudoelastic and actuation operation using finite element analysis. Numerical results of the modified model are presented and compared with the original model without considering the partial transformation feature as well as with uniaxial actuation experimental data. Various aspects of cyclic material behavior under partial transformation are analyzed and discussed for different SMA systems

Disaster Risk Management of Cultural Heritage Sites in Albania.

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

Stakes sensitivity and credit rating: a new challenge for regulators

The ethical practices of credit rating agencies (CRAs), particularly following the 2008 financial crisis, have been subject to extensive analysis by economists, ethicists, and policymakers. We raise a novel issue facing CRAs that has to do with a problem concerning the transmission of epistemic status of ratings from CRAs to the beneficiaries of the ratings (investors, etc.), and use it to provide a new challenge for regulators. Building on recent work in philosophy, we argue that since CRAs have different stakes than the beneficiaries of the ratings in the ratings being accurate, what counts as knowledge (and as having ‘epistemic status’) concerning credit risk for a CRA may not count as knowledge (as having epistemic status) for the beneficiary. Further, as it stands, many institutional investors (pension funds, insurance companies, etc.) are bound by law to make some of their investment decisions dependent on the ratings of officially recognized CRAs. We argue that the observation that the epistemic status of ratings does not transmit from CRAs to beneficiaries makes salient a new challenge for those who think current regulation regarding the CRAs is prudentially justified, namely, to show that the harm caused by acting on a rating that does not have epistemic status for beneficiaries is compensated by the benefit from them acting on a CRA rating that does have epistemic status for the CRA. Unlike most other commentators, therefore, we offer a defeasible reason to drop references to CRAs in prudential regulation of the financial industry

Shape memory response and hierarchical motion capabilities of 4D printed auxetic structures

4D printing refers to a novel trend in the field of active materials, regarding the employment of additive manufacturing to obtain structures presenting inherent complex shapes and shape evolutions under the application of proper stimuli. Such a technique is a powerful tool to realize auxetic structures with customized architectures and programmable/controllable shape change. The present paper proposes 4D printed shape memory polymer-based systems with auxetic structure, capable of hierarchical motion. The systems were prepared starting from a commercial photopolymer by means of stereolithography. The mechanical behavior of the systems was characterized in uniaxial tensile tests, measuring the strains parallel/perpendicular to the load direction. Thanks to a broad glass transition region, the photopolymer displays the so-called “Temperature-Memory Effect” (TME), i.e. the possibility to tailor the thermal trigger of the Shape-Memory Effect (SME) through the deformation temperature. Thermo-mechanical histories were applied to a single unit cell to investigate both the overall shape memory response and the possibility to undergo multiple combined out-of-plane and in-plane motions on the basis of the TME. Obtained results allow discussing the effect of deformation temperatures on the thermal region triggering the SME and show the possibility to exploit the TME to achieve sequential self-deployment of auxetic structures

Experimental investigation and modeling of the temperature memory effect in a 4D-printed auxetic structure

4D printing is an innovative manufacturing approach that combines 3D printing and stimuli- responsive abilities to produce objects with complex geometry and capable of shapeshifting over time (the fourth dimension). To pursue such an approach this paper proposes to develop re-entrant honeycomb auxetic grids with tunable shape reconfigurable behavior. Particularly, the work combines 3D printing and a photopolymer exhibiting the so-called temperature memory effect (TME), a peculiar shape memory behavior expressing the capability of the material to remember not only the original shape but also the deformation temperature. A thorough experimental activity was carried out on single auxetic unit cells, chosen as representative of the whole auxetic grid, to properly highlight and assess their response upon heating after single-step and multiple-step deformation histories and to describe the recovery process as a function of time and temperature. Results demonstrate the possibility to achieve an easily controlled TME and to successfully exploit it for autonomous, complex hierarchical transformations over a large range of temperatures. As a proof-of-concept, the study of the sequential recovery of an entire auxetic grid subjected to double-step programming allowed highlighting a decoupled in-plane elongation and out-of-plane bending. The behavior of the 4D-printed auxetic structures was simulated by means of finite element (FE) analysis, using a thermoviscoelastic model of the photopolymer and viscoelastic experimental data obtained by time-temperature superposition analysis applied to multifrequency dynamic mechanical tests and to isothermal recovery tests. A good correspondence between experiments and simulations was obtained for all shape memory tests, demonstrating that the proposed FE approach is a suitable tool to support the design of these structures. The combination of 3D printing and TME opens new perspectives to achieve dynamic tunability in mechanical metamaterials, that is a key ingredient in several application fields

An experimental, theoretical and numerical investigation of shape memory polymers

The present paper deals with the experimental analysis, constitutive modeling and numerical simulation of a class of polymers, exhibiting shape memory effects. We first present and discuss the results of an experimental traction-shrinkage campaign on semi-crystalline shape memory polymers, particularly, on low-density and high-density polyethylene-based polymers. Then, we develop a new one-dimensional phenomenological constitutive model, based on the so-called phase transition approach and formulated in a finite strain framework, in order to reproduce experimental observations. The model is treated through a numerical procedure, consisting in the replacement of the classical set of Kuhn-Tucker inequality conditions by the Fischer-Burmeister complementarity function. Numerical predictions reveal that the model is able to describe qualitative aspects of material behavior, involving both orientation and thermal retraction, as well as to predict experimental orientation processes for semi-crystalline polyethylene-based polymers with different densities