Intermetallics

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Intermetallics 10 (2002) 361–369 www.elsevier.com/locate/intermet

A new method for fabricating SMA/CFRP smart hybrid composites
Ya Xua, K. Otsukaa,*, H. Yoshidaa, H. Nagaia, R. Oishia, H. Horikawab, T. Kishic
a

Smart Structure Research Center, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan b Furukawa Techno MaterialCo., Ltd, 5-1-8 Higashi-Yawata, Hiratsuka, Kanagawa 254-0016, Japan c National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan Received 19 November 2001; received in revised form 25 December 2001; accepted 10 January 2002

Abstract In order to suppress the microscopic mechanical damages in composite system, and thus to increase the reliability of carbon fiberreinforced plastics (CFRP), a smart composite SMA/CFRP is attracting much attention. In this application, the shape memory alloy (SMA) is expected to exert compressive stress to CFRP by reverse transformation upon heating after fabrication. However, one big problem in the fabrication process is that the curing temperature of the composite (130  C) far exceeds the reverse transformation temperaturesof Ti–Ni alloys ( 70  C). This paper presents a new method to overcome this difficulty. The method consists of using heavily cold-worked wires to increase the reverse transformation temperatures, and of using flash electrical heating of the wires after fabrication in order to avoid damaging of the matrix around wires. By choosing the reduction of cold drawing and composition of TiNi alloys properly,it will be shown that the method is actually applicable without using special fixture jigs, which are necessary otherwise, to the fabrication of such smart composite as SMA/CFRP. # 2002 Elsevier Science Ltd. All rights reserved.
Keywords: A. Composites; B. Martensitic transformation; B. Shape-memory effects; C. Thermomechanical treatment

1. Introduction SMA smart hybrid composites, in which SMAwires or plates (hereafter we use only the term ‘‘wires’’ for brevity unless the term ‘‘plates’’ is specifically needed in the context) are embedded in composites, are attracting much attention recently to strengthen polymer matrix composites (PMCs), such as CFRP and GFRP (glass fiber reinforced plastics) and to control vibrations in an active control mode [1–8]. Among these SMA/CFRP is especiallyimportant, since CFRP is widely used for airplanes and aerospace technologies. The application of SMA to SMA/CFRP smart composite was first introduced by Rogers [1], and then investigated by

* Corresponding author. Tel.: +81-298-61-3129; fax: +81-298-613126. E-mail address: kotsuka@ni.aist.go.jp (K. Otsuka).

several researchers [6–8]. The principle of the application is the same as ‘‘theprestressed concrete principle’’. In the application, TiNi wires as SMA are expected to provide compressive stress to the surrounding CFRP, and thus to avoid the microscopic damages as an initiation to the final failure, which leads to the increase of reliability and to the reduction of maintenance cost of airplanes etc. However, there is a big problem in the fabrication process of such smart compositeSMA/ CFRP as explained below. In order for ‘‘the prestressed concrete principle’’ to work, TiNi wires must be fabricated in the martensitic state [i.e. below As (reverse transformation start temperature)], and then the TiNi wires are heated to a temperature above Af (reverse transformation finish temperature) after the fabrication, so that TiNi wires shrink (in virtue of the shape memory effect[9]) and to provide compressive stress to the surrounding CFRP. The fabrication temperature, which is called the curing temperature, is usually either 130 or

0966-9795/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0966-9795(02)00011-0

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Y. Xu et al. / Intermetallics 10 (2002) 361–369

180  C depending upon the kind of matrix resin. On the contrary,...
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