Abstract
The research presented starts with a focus on Smart Materials, or rather materials with properties that react to external stimuli (temperature, electric or magnetic field, pH or mechanical stress, for example) related to the environmental changes, modifying one or some of their own properties (mechanical, electrical, appearance, etc.). Afterward, one category of Smart Materials, Shape Memory Alloys (SMAs), has been investigated with the aim to develop an industrial application. In particular, a smart and active shadow system for thermal comfort of urban or indoor environments, based on the valorization of the unique property of SMAs to change their shape depending on the temperature (SME, Shape Memory Effect). Without the need to use expensive and complex mechanical system composed of many parts to assemble and characterized by higher cost of energy required for its functioning and its manufacturing. In order to develop the system, SMAs like Nitinol (Ni-Ti) wires with a diameter of 0,75 mm (Austenite finish 85°C) have been studied. Particularly, DSC (Differential Scanning Calorimetry) thermal analysis, aimed to investigate a characteristic range of temperature for martensitic and austenitic transformations and get data to plan more suitable and optimized procedures, conditions and parameters for heat treatments needed for Nitinol training have been carried out. In parallel, CAD models have been developed to simulate and better understand forces needed for a proper functioning of the smart shadow system, to predict its behavior, to have a support for a correct choice of SMA wires (selecting wires with a diameter suitable to produce a force high enough to produce strains), to decide wires positioning and quantity. Finally, for “as-drawn” Nitinol wires, using the data experimentally collected with DSC thermal analysis, SME training procedures have experimented. With the wires, programmed to have a two-way memory effect, using milling and additive technologies, prototypes where the wires are embedded in casted polymers (rubber silicone or polyurethane) or assembled to parts manufactured with additive technologies have been built, in order to test and enhance product functioning and manufacturability. The results obtained for the application, although the Smart Shadow System is not completely engineered and other evolutionary steps for it are possible, show that the use of SMAs gives the possibility to have an active system able to be weather responsive, ensuring a significant shape memory effect depending on the temperature. This advanced property, in fact, gives the possibility, optimizing functioning parameters (temperatures, thicknesses, geometry, structure), to have a sensitive, adaptive and smart system that can ensure the best thermal condition for any meteorological situation.
Highlights
The research presented starts with a focus on Smart Materials, or rather materials with properties that react to external stimuli related to the environmental changes, modifying one or some of their own properties.Afterward, one category of Smart Materials, SMAs (Shape Memory Alloys), has been investigated with the aim to develop an industrial application.In particular, a smart and active shadow system for thermal comfort of urban or indoor environments, based on the valorization of the unique property of SMAs to change their shape depending on the temperature (SME, Shape Memory Effect)
Among the main categories there are Piezoelectric materials, that are Smart Materials able to produce a voltage when a stress is applied or to produce a deformation when a voltage is applied, for this characteristic they are used as sensors or actuators; Shape Memory Alloys, that are characterized by Shape Memory Effect and pseudoelasticity, they can “remember” different shapes for different temperatures, Magnetostrictive materials, that exhibit change in shape under the influence of magnetic field; temperatureresponsive materials, that undergo under change upon temperature; Halochromic materials that change their color upon acidity changes; Photomechanical materials, that change shape under exposure to light (Fig. 1)
In addition to low solidification rate, amorphous metals have a surface roughness of fewer than 0.05 μm. This is a significant benefit compared with other processes that require post-processing to meet a good quality surface, while Metal Injection Molding (MIM) components, instead, typically have surface roughness values included between 0.8-1.6 μm
Summary
One category of Smart Materials, SMAs (Shape Memory Alloys), has been investigated with the aim to develop an industrial application. A smart and active shadow system for thermal comfort of urban or indoor environments, based on the valorization of the unique property of SMAs to change their shape depending on the temperature (SME, Shape Memory Effect). In order to develop the system, SMAs like Nitinol (Ni-Ti) wires with a diameter of 0,75 mm (Austenite finish 85°C) have been studied. DSC (Differential Scanning Calorimetry) thermal analysis, aimed to investigate a characteristic range of temperature for martensitic and austenitic transformations and get data to plan more suitable and optimized procedures, conditions and parameters for heat treatments needed for Nitinol training have been carried out
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