Gn Dayananda

Recovery stress generation in shape memory Ti50Ni45Cu5 thin wires

Abstract The recovery stresses evolving in constrained Ti 50 Ni 45 Cu 5 (at.%) shape memory wires were investigated in thermomechanical experiments performed in combination with electric resistance measurements. The hysteretic stress–temperature responses of the wires in constrained thermal cycles were analyzed by comparing the experimental results with simulated responses using a phenomenological algorithm developed for prediction of uniaxial thermomechanical SMA behaviors. The effects of individual SMA material parameters, constraint parameters, test boundary conditions and thermomechanical history on the evolution of recovery stresses in SMA wires are predicted.

Shape Memory Alloy Based Smart Landing Gear for an Airship

The design and development of a shape memory alloy based smart landing gear for aerospace vehicles is based on a13; novel design approach. The smart landing gear comprises a landing beam, an arch, and a superelastic nickeltitanium shape memory alloy element. This design is of a generic nature and is applicable to a certain class of light13; aerospace vehicles. In this paper a specixFB01;c case of the shape memory alloy based smart landing gear design and13; development applicable to a radio controlled semirigid airship (radio controlled blimp) of 320 m3 volume is13; presented.Ajudicious combination of carbon xFB01;ber reinforced plastic for the landing beam, cane (naturally occurring13; plant product) wrapped with carbon xFB01;ber reinforced plastic for the arch, and superelastic shape memory alloy is13; used in the development. An appropriate sizing of the arch and landing beam is arrived at to meet the dual requirement of low weight and high-energy dissipation while ndergoing x201C;large elasticx201D; (large nonlinear recoverable13; elastic strain) deformations to ensure soft landings when the airship impacts the ground. The soft landing is required13; to ensure that shock and vibration are minimized (to protect the sensitive payload). The inherently large energydissipating character of the superelastic shape memory alloy element in the tensile mode of deformation and the superior elastic bounce back features of the landing gear provide the ideal solution.Anonlinear analysis based on the classical and xFB01;nite element method approach is followed to analyze the structure. Necessary experiments and tests have been conducted to check the veracity of the design. Good correlation has been found between the analyses and testing. This exercise is intended to provide an alternate method of developing an efxFB01;cient landing gear with satisfactory geometry for a x201C;certain class of light aerospace vehiclesx201D; such as airships, rotorcraft, and other light unmanned air vehicles.

Low Cycle Fatigue Evaluation of NiTi SESMA Thin Wires

AbstractThis paper presents experimental studies on low cycle fatigue (LCF) life of super-elastic shape memory alloy (SESMA) wires. The effect of frequency of the loading and amplitude of the strain on the fatigue life has been studied individually. Various loading frequencies have been considered to study the effect of frequency, by keeping the amplitude constant. From the experimental data, it was found that the LCF life of the SESMA reduces with increase in the frequency. The effect of amplitude on the LCF life of SESMA has also been studied, and it was found that the SESMA cycled at lower net strain has more fatigue life than the one cycled at higher net strain. Further, the plastic strain accumulation is also more in the samples tested at the higher net strain loadings. The modulus of austenite is found to be by and large independent of the frequency and amplitude of the loading. Further, martensitic unloading modulus is same for all the minimum strain amplitudes.

Smart Aerodynamic Surface for a Typical Military Aircraft Using Shape Memory Elements

the landing characteristics of the aircraft on the aircraft carrier. The mousche is designed and constructed out of carbon-fiber-reinforced plastic to withstand the full load and is deployed using the actuator bank containing the arrays of shape memory alloy elements. The shape memory alloy actuator bank moves a distance of 15 mm while generating a net actuator force of over 2000 kg. This force is used to deploy the additional aerodynamic surface measuring 790 215 32 mm against a simulated lift and drag load acting simultaneously, i.e., a resultant lift load of 331.6 kg and a drag load of 33.16 kg acting at the center of gravity of the mousche. The shape memory alloy bank consists of 138 wires of about 1 mm in diameter and 650 mm in length. The actuation of these 138 wires is electronicallyandmechanicallysynchronized.Themouschehasbeenanalyzedusing finiteelementmethodcodesfor the combined lift and drag load. Experimental and analysis values have matched well. The electronics circuit assembly of the smart actuator drive electronics that powers the shape memory alloy actuator bank has been designedanddevelopedintheformofmother-anddaughterboards.Eachdaughterboardhassixminiaturizeddc–dc converters, and the required power and control signals are routed to the motherboard. The smart actuator drive electronics have been integrated to carry out the full load test. The National Instruments 6009 data acquisition modulealongwithgraphicaluserinterfacesoftwareLabVIEWareusedtoconducttheexperimentsandtoeffectthe closed-loop position control of the mousche.

Development of electronic actuation system for shape-memory-alloy-based aerospace structures

Shape memory alloy (SMA) is being widely used to implement smart concepts such as shape control and vibration suppression of aerospace structures. Shape memory alloy wires while undergoing phase transformation from martensite state to austenite state produce large strains. While doing so they serve as actuators and generate large forces when constrained while recovering their pre-defined shape, imparting this force to the structural component on which they are mounted which results in its movement. While designing the electronic system to energise an aerospace structure with shape memory alloy based actuators the amount of current and time for which this current is passed through the shape memory alloy wire are important considerations. It is equally important to design very efficient and miniature power sources (constant voltage as well as constant current) and control system to achieve fine and steady positioning of the structural component. This paper discusses different issues involved, as well as design and development of the electronics and control system for actuating and controlling a typical aerospace structural component with SMA actuators.

Effect of Cross-linking Density on Creep and Recovery Behavior in Epoxy-Based Shape Memory Polymers (SMEPs) for Structural Applications

Epoxy-based shape memory polymers (SMEPs) are gaining importance in the area of aerospace structures due to their high strength and stiffness which is a primary requirement for an SMEP in structural applications. The understanding of viscoelastic behavior of SMEPs is very essential to assess their shape memory effect. In the present work, three types of SMEPs with varying cross-linking densities were developed by curing an aromatic epoxy resin with aliphatic amines. Glass transition temperature (Tg) was measured for these SMEPs using advanced rheometric expansion system, and from the Tg measurements, a range of temperatures from glassy to rubbery regimes were chosen. At selected temperatures, creep-recovery tests were performed in order to evaluate the viscoelastic behavior of SMEPs and also to investigate the effect of temperature on creep-recovery. Further, a three-parameter viscoelastic model (Zener) was used to fit the data obtained from experiments. Model parameters like moduli of the springs and viscosity of the dashpot were evaluated by curve fitting. Results revealed that Zener model was well suited to describe the viscoelastic behavior of SMEPs as a function of test temperatures.

Investigations on tensile creep of CNT-epoxy shape memory polymer nanocomposites

In this work, epoxy-based shape memory polymer nanocomposites (SMPnCs) were prepared using 0.5 wt% and 1 wt% multi walled carbon nanotubes (MWCNTs) pre-dispersed in epoxy resin. This was cured with triethylene tetraamine (TETA) curing agent. The glass transition temperatures (Tg) were determined using Advanced Rheometric Expansion System (ARES). The creep behaviour of the 0 wt% CNT SMPnC as well as the 0.5 wt% and 1 wt% MWCNT SMPnCs were studied through short term tensile creep test at different temperatures. Master curves of creep compliance were derived using a time-temperature superposition principle (TTSP) based on Williams-Landel-Ferry (WLF) equation. A Findley power-law model was used to predict the creep deformation behaviour of 0, 0.5 and 1 wt% CNT SMPnCs. Good correlations between experimental data and the predictive model were obtained for both SMPs particularly at lower temperature and above Tg.