CRG is also using these materials to develop morphing truss structures for aircraft. Cornerstone Research Group (CRG) is developing shape memory polymers, foams and dynamic composites for morphing aircraft with funding from NASA and DARPA ( Cornerstone Research Group, 2011). Research is also being conducted on a family of new polymers that exhibit behavior similar to the shape memory alloys. A simplified thermo-mechanical model for the SMA inclusion, able to reproduce the super-elastic as well as the shape memory effect, is proposed ( Auricchio and Sacco, 2001). Sacco from the University of Cassino in Italy is developing a micro-mechanical model for the evaluation of overall constitutive behavior of a composite material obtained by embedding SMA wires into an elastic matrix. They have constructed SMA-controlled airfoil camber, winglets and motors ( Mueller et al., 2005). The Technical University of Berlin has been conducting research into the use of embedded SMA wires in aircraft structures. SMA use in smart composites is fairly new and is currently being studied by many research groups. Composites incorporating SMA are often referred to as smart composites. SMA can be used alone as an actuator or incorporated into the matrix of a composite structure. When the voltage is removed, the heat dissipates and the material returns to its original shape. Passing a voltage through the SMA wire or sheet generates the temperature change needed to produce a shape change. SMA can be produced as both wire and sheet (Auricchio and Sacco, 2000). These changes can be interpreted as reversible martensitic transformations between a crystallographic more-ordered parent phase, the austenite (A), to a crystallographic less-ordered product phase, the martensite (M). The behavior of SMA is due to their native capability to undergo reversible changes of the crystallographic structure, depending on temperature and state of stress. Shape memory alloys (SMA) are metallic alloys that are able to undergo large reversible deformations under loading/thermal cycles and are able to generate high thermal–mechanical driving forces. Guiler, in Innovation in Aeronautics, 2012 3.5.4 Shape memory materials The SMA presents good durability and corrosion resistance, while it has low sensitivity (i.e., gauge factor) ranging from 3.8 to 6.2 and high cost. The embedded SMA wire will monitor strain and deformation of concrete structures. The rate of change of SMA resistance has a good linear relationship with the mid-span deflection of the beam. He also investigated the sensing behavior of concrete beams reinforced with SMA wires. The tested results show that the fracture in electric resistance changes almost linearly with the strain, and the relationship between fracture of electric resistance and stress is similar to the relationship between the stress and strain. Liu studied the sensing property of SMA wires.
#PARACOSM LUMEN 1.0.3 CRACK CRACK#
It was found that the electrical resistance value of the SMA cable experienced large and repeatable changes with the opening and closing of the crack, indicating that electrical resistance can be used to monitor crack width. conducted bending tests on concrete beams reinforced with SMA cables. SMA can be used to monitor the strain (or deformation) of concrete and to estimate the crack width in concrete. SMAs can work as sensors because their electrical resistance is dependent on their strain (the electric resistance is increased with applied tension strain). Jinping Ou, in Self-Sensing Concrete in Smart Structures, 2014 11.3.4 Concrete Integrated with SMA
Due to these drawbacks, an input current of 2.5 A is applied to both the 100 and 150 µm wire diameter SMA spring in the SMAHV, to determine the displacement of the SMA spring-based SMAHV.īaoguo Han. Applying an input current of 3.0 A and above to both 100 and 150 µm wire diameter SMA spring in the SMAHV, required longer cooling time for the SMA spring and the SMAHV was unable to return to its initial position in the 3 seconds relaxation period. Applying an input current of 1.0–2.0 A to both 100 and 150 µm wire diameter SMA spring in the SMAHV produced a displacement of 0.1–0.4 mm, which is very low and renders the valve unsuitable for CBI process due to its negligible change in the lumen area.
Each cycle of the SMAHV is actuated for a period of 8 seconds, with an actuation phase of 5 seconds and a relaxation phase of 3 seconds. An input current of 1.0–3.0 A was applied to the SMA wire in the SMAHV, and the displacement while decreasing the area of the lumen is video-recorded and analyzed using Tracker 5.0 (Douglas Brown©). The SMA springs in the SMAHV are actuated by applying current using an external DC supply through copper wires. Hongliang Ren, in Flexible Robotics in Medicine, 2020 20.3.2.2 Shape memory alloy spring-based shape memory alloy–actuated hydrogel valve
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