MODELING OF CONNECTING STRUCTURE FOR PIPE JOINING WITH APPLICATION TO Fe- Mn-Si SHAPE MEMORY ALLOYS SLEEVES

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1 MODELING OF CONNECTING STRUCTURE FOR PIPE JOINING WITH APPLICATION TO Fe- Mn-Si SHAPE MEMORY ALLOYS SLEEVES Ion MITELEA a,, Dieter Schinle a, Corneliu Marius Craciunescu a, Ion-Dragos UTU a a POLITEHNICA UNIVERSITY OF TIMISOARA, Pta Victoriei,no. 1, Timisoara,Romania, ion.mitelea@mec.upt.ro, dschinle@r-world.de, craciunescucm@yahoo.com, utu.dragos@mec.upt.ro Abstract Fe-Mn-Si shape memory alloys can be used to substitute other materials for joining pipes, with important economical benefits. The increase in the applicative potential of shape memory alloys has amplified the activities concerning the modeling of the response to thermomechanical behavior. The current paper details the modeling of a FeMnSi shape memory alloy undergoing the martensitic phase transformation responsible for the shape memory effect. The shape memory alloy connecting sleeve is modeled based on specific thermomechanical conditions. Keywords: shape memory alloys, Fe-Mn-Si system, joining tubes, modeling 1. INTRODUCTION Shape memory alloys can be used in various intelligent solutions to replace simple or complex systems with only one substituting component [1-4]. They are based on the shape recovery that occurs on heating the material that has been previously deformed at low temperature. The key element in shape memory alloys behavior is the martensitic transformation that develops between a softer low temperature phase and a harder high temperature one. Pipe joining is an interesting solution that can benefit out of shape memory effect. The process related to joining pipes using a shape memory alloy ring is schematically detailed below in figure 1. Fig. 1. Principle of joining using SMA rings and sleeves A shape memory alloy has been manufactured and characterized and a model for connecting sleeve based on such a materials has been developed.

2 2. EXPERIMENTAL DETAILS FOR FABRICATING FE-MN-SI SHAPE MEMORY ALLOYS The materials used for the purpose of analyzing the the joining are Fe-based shape memory alloys belonging to the Fe-Mn-Si family [5,6]. They are much cheaper than the Ni-Ti ones, are not difficult to process and provide high austenite yield strength as a result of the presence of Si which acts as solid solution hardening and prevents the permanent deformation by slip. Such alloys also show good recovery strain % 2.5~4.5 and stress 150~200MPa [7]. The alloys in this family are characterized by a phase transition between a high temperature face centered cubic (FCC) γ phase and a corresponding martensite (ε phase) with a hexagonal close packed (HCP) structure. Among the advantages of Fe-Mn-Si alloys is the large hysteresis range which is about 100 o C, thus allowing enough time for additional processing phases, when practical applications are considered. In addition, a magnetic ordering transition from paramagnetic to antiferromagnetic ordering is observed [8]. The relative position of magnetic and martensitic transformation temperatures can also play a role in the transformation behavior and the shape memory effect [9]. For the purpose of this work, a Fe-Mn-Si alloy was prepared using an induction melting furnace. The high purity materials have been melted under protective argon atmosphere and the casting was made in a copper mold. Hot working has been performed on the materials using a conventional rolling system, down to a thickness of about 10 mm. The sheets were subsequently annealed at 1050 o C, for 10 minutes, followed by water quenching. Samples cut from the hot rolled ingot have been investigated using scanning electron microscopy (SEM), for microstructure, as well as energy dispersive spectrometry (EDS), for composition. The results are shown in fig.2. Elmt Spect. Element Atomic Type % % Si K ED Mn K ED Fe K ED Total a. SEM image of the sample b. EDS results Fig. 2. Structural and compositional details for the Fe-Mn-Si alloys

3 3. A MODEL FOR JOINING TUBES APPLICABLE IN THE FE-MN-SI SYSTEM Several models have been developed for modeling the shape memory alloy behavior (e.g. for superelastic behavior [10, 11]. For the modeling, the pipes were designed using the Solid Works 2011 program (fig. 3a). In order to simulate the joining of two steel pipes with a shape memory alloy sleeve, the following dimensions have been used: 90 mm diameter for the pipes, and 91 mm diameter for the Fe-32Mn-6Si sleeve. The properties for the pipe material were extracted from the program database, while the data for the shape memory alloy have been taken from the literature [12]. A solid type discretization with elements detailed in Table 1, resulting in the mesh shown in figure 3b has been realized for the steel end pipes and the shape memory alloy sleeve with 9400 nods and 4625 elements. Table 1. Details about the discretization used in the simulation Mesh type Solid Mesh Total Nodes 9432 Mesher Used: Curvature based mesh Total Elements 4625 Jacobian points 4 Points Maximum Aspect Ratio Maximum element size mm Total Nodes 9432 Minimum element size mm Total Elements 4625 Mesh Quality High Maximum Aspect Ratio Remesh failed parts with incompatible mesh Off % of elements with Aspect Ratio < a

4 b Fig. 3. Details about the constraints and the discretization used in the simulation The next step is to put constraints for the pipe and sleeve. These movement constraints are shown by arrows on the of the pipe and sleeve ends (Fig. 3a, b). Also in this stage one inputs the temperature variation in the shape memory effect sleeve. In our case its cooling from 350 to 0 Celsius degrees. After entering all the physical parameters and constraints of the pipes and of the shape memory alloy sleeve one runs the simulation by clicking RUN from the menu bar (Fig. 4). Fig.4. The simulation results for a joint made with Fe-Mn-Si sleeve

5 After running the simulation process the obtained results can be viewed and interpreted by the postprocessor, making possible the creation of a report generated directly from Solid Works. In the postprocessor one can choose the units of measurement and other parameters that can be viewed and interpreted. One can see a variety of results depending on the need of analysis and one can create animations to view the deformation or forces variation and also the material stresses (fig. 5). 4. CONCLUSIONS Fig. 5. List of parameters which can be varied during the simulation Fe-Mn-Si alloys are important materials for applications involving the shape memory effect in joining pipes. They can be easily manufactured, compared to NiTi alloys and show better properties, compared to Cubased alloys, thus are better suited for joining applications of massive products. Modeling activities for joining elements made out of Fe-Mn-Si components can be useful for the development of novel practical applications and a better identification of the parameters to be controlled during the technological phases in view of possible applications in industrial conditions. ACKNOWLEDGEMENTS The work presented in this paper has been supported by Romanian National Research Grants code 1005/2009 Modelarea fenomenologica a sudabilitatii prin frecare a materialelor cu gradient functional. The work was also partially supported by the grant POSDRU 107/1.5/G/13798, inside POSDRU Romania co-financed by the European Social Fund Investing in People. REFERENCES [1]. Lipscomb, I.P, Nokes L.D.M.: The Applications of Shape Memory Alloys in Medicine, Paston Press, [2]. Kohl, M.: Shape Memory Actuators, Springer Verlag, [3]. Humbeeck, J.V. Introduction to shape memory alloys, Proc. S(3)T2010 Smart Structural System Technologies, Aveiro, Portugal, [4]. Fu, Y., Du, H., Huang, W., Zhang, S., Hu, M, TiNi-based thin films in MEMS applications: a review Sensors and Actuators A: Physical, 2004, Volume 112, Issue 2-3, Pages [5]. Sato A., Chishima, E., Soma K. and Mori, T. Acta Metall., No. 34, 1986, 287.

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