Stress Evaluation Technique-Cum-Physical Model for Intelligent Helical SMA Spring

In this physical proposed technique-cum-model that enables the stability of intelligent helical SMA spring by defining the various working parameters before its practical implementing as an actuator. Spring-load values which have been also calculated by scale-value. The presented illustration of intelligent helical spring (originally made SMA wire) and parameters included as average load-cell strain values, values of average currents, obtained values of average temperatures, atmospheric temperature changed values and applied voltage values. The various relationships as the minimum value to maximum value relationship for applied voltages and springload values, the maximum value to minimum value relationship for applied voltages and spring-load values, the minimum value to median value relationship for applied voltages and spring-load values, the maximum value to median value relationship for applied voltages and spring load values mentioned with the help of correlations. Then, two model equations are obtained based on minimum value to maximum value & vice-versa. The working parameters resulted as correlations and minimum value to maximum value & vice-versa resulted as model equations during the experimentation of intelligent helical spring.


INTRODUCTION
NiTi alloys are very famous in recently few years due to large strain setup (8%) into the internal structure in which temperature or heat used as working parameter [5]. They also are applicable in aerospace and biomedical sciences so researchers consistently focusing on bulk production with minimize costing. The actuation is mainly depends upon the set of control conditions of temperature and applied pressure with the quality of materials used. So, synthesis of NiTi vary from alloy thickness to thickness and applied different methods such as vacuum induction melting electrical are melting, HIP (Hot Isostatic Pressing), elementary power sintering, and mechanical alloying [4]. Segregation, gas absorption and crucible contamination absorption methods were old & had conventional problems [1]. In recently years, mechanical alloying (MA) technical have been used to reduce the need of precursor materials, control of chemical composition and higher level of porosities. The NiTi compound commonly exhibits two stable phases i.e. 'B2' austenite phase of high-temperature structure and 'B19' martensite phase of low-temperature structure. 'B2' is cubical crystalline structure but 'B19' is monoclinic crystalline structure. The shape memory behavior were firstly observed in 1932 by Olander in his study of "rubber life effect" in the samples of gold-cadmium and in 1938 by Greninger & Mooradian in their of brass alloys (copper-zinc). Many years later in 1951 Chang & Read first reported the term shape recovery. They were also working on gold-cadmium alloys. In 1962 William-J-Buebler and his co-workers at naval ordinance laboratory discovered shape memory effect in an alloy of nickel & titanium. Nowadays, these alloys are becoming the point of interest due to the special characteristics such as shape memory effect, super-elasticity, high tensile strength, wear & corrosion resistance etc [2,3]. Ahmed Frikha, Patrice Cartraud, Fabien Treyssède investigated the static behavior of helical structures under axial loads by taking into account their translational invariance and the homogenization theory [6]. Fabien Treyssède, Ahmed Frikha, Patrice Cartraud again focused on mechanical modeling of helical structures accounting for translational invariance in his part two study. The static behavior had been addressed using a helical homogenization approach which provides the stress state corresponding to axial loads [7]. G.Machado, H.Louche, T.Alonso, D.Favier discussed the mechanical super-elastic behavior of NiTi architecture tube-based NiTi materials subjected to quasistatic compression was studied using two simple cellular samples. They assumed that modeling is very useful for designing and optimizing architectured materials. The super-elastic behavior of two simple architecture materials based on identical tubes [8] Amir Sadjadpour and Kaushik Bhattachary suggested constitutive model for shape-memory alloys that builds on ideas generated from the micromechanical studies of the underlying microstructure as a rate-dependant one-dimensional thermodynamically consistent constitutive framework for the dynamic behavior of polycrystalline SMA's [9]. Ferdinando, Auricchio and Davide performed experimental tests on superelastic shape-memory alloys (SMAs) show a significant dependence of the stress-strain relationship on the loading-unloading rate, coupled with a not negligible oscillation of the material temperature [10].
In present work we has used the NiTi wire with a preset conditions as prescribed by the seller and investigation objective to established physical model based on smart helical spring by using the basic electronic components such as registers, capacitors', P-N diodes, transistors, rectifier and also using the electrical components such as sockets, DC supply power, transformers, cables, connectors. This work model can be measure the any helical SMA spring at any predefined condition.

MODEL PREPARATION
The proposed model comprised of the following main subparts included as: 2.1 Iron-Stand: Iron Stand has been used because it is made of ordinary Iron and easily availability of Iron-pieces in any shape in market or marking college workshop. Further it included following parts:-Base plate with vertical column: The base plate has dimensions = 18.2X9.5X0.6 (0.6 cm represents the thickness of plate, 9.5cm represents width, whereas 18.2 cm represent length at which vertical column is welded along length). The hole represents in base plate as M7.9X0.375 (dimensions in mm). So it is obvious that width of plate = 9.5, the vertical column dimension = 24.4cmX0.5cm whereas 24.5cm represent vertical height of column, 2.4cm represent the width of vertical column and 0.5 cm represent the thickness of vertical column respectively. The base plate also has the threaded hole within itself which is 1.2 cm far away from width side and vertical column is welded near to the edge of plate as possible as by the tungsten arc welding m/c 400Amp. The tolerance of ±0.1 mm might be possible, but have no effect of such error. Adjustable lower plate with locking: It consists of cylindrical hollow part. The dimensions of cylindrical hollow part as: length = 2.7cm, thickness = 0.7 cm, Inner diameter (ɸi) = 1.2 cm, Outer diameter (ɸo) = 1.2+2X0.7 = 2.6 cm. Now for rectangular thick part, the dimensions= 11.5X2.5X0.3 (all dimension in cm), the hole dimension of this part include ɸh = 1.2 cm. The tightened hexagonal nut also used with 0.8cm each side and having centralized hole (ɸ) = 7.9mm such that M7.9x0.375. The allowance of all meshing parts varies from 0.02 to 0.04 for reading taken in mm.
And the dimensions of locking plate= 3.5cmX1.9cmX3mm whereas 3 mm represent the  The straight bar load cell has been applied here; range from 0-20 kg of pressure (force) and it is single point HT sensor. Specification as-received: The LM35 has an advantage over linear temperature sensors calibrated in °K, as the user is not required to subtract a large constant voltage from its output to obtain convenient centigrade scaling. The LM-35 does not require any external calibration.

Amplifier Circuit (Operational):
The load cell had the attachment with strain gauge measuring kit which is basically amplifier circuit and this kit had setup in the work. It includes the IC7107 in which 0-2000 V digital panel meter using seven-segments display driver circuit as seven light emitting diodes.
IC 7107: A high performance and low power consuming integrated circuit (IC) 7107 that consists of seven segments decodes, reference voltage source, comparator and display drives as its internal circuiting [12].  fig.5. The sets of diodes here referred to bride type rectifiers [11,12]. 6. MATERIAL & MANUFACTURING OF SMA HELICAL SPRING The material of spring wire is flexinol (trade name of NiTi alloy) which behave as smart material. The one way SMA was purchased from the thing bits electronics Pvt. Ltd. as in drawn condition. As-received informing about SMA in composition as 49% Nickel and 51% Titanium with one way metallic material, also produced by vacuum induction melting. The flexinol wire of dia 1.0 mm, the manufacturing of SMA helical spring used the threaded screw, end restraints and mild steel fixture with copper clamping wire. The muffle furnace is utilized for the tolerance of ±5°C and muffle voltage regulator is set at 530°C for 45 minutes to made typical helical spring with mean coil dia. of 7.4 mm & '8' no. of turns. The annealing process was firstly applied by just switch off the muffle furnace and removing the helical spring after 24 hours and then normalized for 6 hours.

RESULTS AND DISCUSSION
The main data obtained in table 3, firstly the combined relationship of V, I, T, Wt and Ls were described as shown in fig.9 and corresponding table 5 showing the data. The minimum value to maximum value relationship for average wire temperatures and average load cell strains corresponding to applied voltages is shown graphically as in fig.9. It can be seen from the fig.9, red colour indicate the variation of WT (Avg. wire temperature) corresponding to the value against applied voltage and also blue colour indicates the variation of LS (avg. load cell strain) corresponding to the value against applied voltage in the above mention graph.

The minimum value to maximum value relationship
for Avg. current in SMA wire which is measured in ampere and avg. load cell value in mm. The seven readings have been considered as shown in table 7 above.  The seven readings also have been taken again from table 3 as shown in table 8 above. The correlations obtained as: Y= 0.749x+0.028, R 2 =0.933……. (iv) The same correlation was obtained due to no change of data but used to the find the avg. load model equation in case of maximum value to minimum value relationship for applied voltage (V) and spring-load value (WT). Four readings had considered as median in 7 values must be 4 th.  Here again four readings had considered as median must be 4 reading.

Resultant Stress (τrs) calculation:
We know that experimental helical spring behave like as an compression spring as at applied voltages the currents passes throughout wire and try to became full helical spring so forced imparted direction towards the each other or we can say lower end of wire try to move in upper direction and upper end of wire try to move in downward direction. Imaginary resultant stress equations (τirs) have been calculated from data mentioned in experimental work based on voltages & spring-loads values of intelligent helical spring SMA. From the given Table 3 = ∫ (−k. δ). = -1k/2[(δinitial) 2 -(δfinal) 2 ] Work done by two springs (one-dimensional loading) Ws1 = ∫ −(k1 + k2).dδ (for II rl condition) Ws1 = ∫ −(1/k1 + 1/k2).dδ (for series) For New design of helical spring necessary parameters are d(wire dai.), D(mean coil dia.) and P(load simply knowing k and calculated load (P)= YAl= ZAL. The resultant shear stress also calculated with or without considering the stress concentration in inside fibre of coil. Above three equations also help to find P.E of falling load(P), K.E of falling load(P) and also which types of damping of load (P) required during falling (all in one-dimensional loading only). CONCLUSIONS This Physical model enables the stability of intelligent helical SMA spring by defining the various working parameters before its practical implementing as an actuator. It also enables to the design of single spring or no. of springs based on the SMA. It includes 1. The various relationships with the help of correlations for the minimum value to maximum value relationship for applied voltages and spring- This prescribed work will be helpful to researchers as an alternative to evaluate SMA helical spring working parameters or SMA running condition helical spring/wire before implementing in the form of actuator in any system.