Shape Memory Alloy Cables for Structural Applications

Shape memory alloys (SMAs) have attracted a great deal of attention as a smart material that can be used in various civil engineering applications. In contrast to the use of SMAs in the biomedical, mechanical, and aerospace applications, which requires mostly a small diameter of material, the larger size bars are usually needed in a structural application. It is well known that properties of large-section SMA bars are generally poorer than those of wires because of difficulties in material processing, which also increases the cost. SMA cables have been recently developed as an alternative and new structural element. This study explores the performance of large-diameter nickel-titanium (NiTi) SMA cables and their potential use in civil engineering. The SMA cable, which has a diameter of 8mm, is composed of 7 strands and each strand has 7 wires with a diameter of 0.885mm. The uniaxial tensile tests are conducted at various loading rates and strain amplitudes to characterize the superelastic properties of the SMA cable. An optical digital image correlation (DIC) measurement system and an infrared thermal imaging camera are employed to obtain the full-field strain and temperature fields. The cyclic tests are performed to evaluate the low-cycle fatigue characteristics of the SMA cables. Results show that large-diameter SMA cables exhibit very good superelastic properties and can be used in various real-world structural applications.