Manufacture and Processing of Large Nitinol Rings for Application in Seismic Dampers

This paper discusses the methods used to manufacture and process large-scale Shape Memory Alloy (SMA) rings (> 200 mm O.D.) for the use as energy absorbing and re-centering elements in the so-called SMA-based multi-ring seismic damping devices. The results of several cyclic tests on SMA rods used to identify optimal heat treatment processes are also presented.

Manufacture of the rings, using both superelastic Nitinol and shape-memory Nitinol, was accomplished by first hot upset forging 100-mm dia. billet at 900^oC. The forging produced disks of much larger diameter and a thickness appropriate for ring rolling to the desired final dimensions. The ring rolling was also done at 900°C by first piercing the upset forgings, then ring rolling to the appropriate dimensions. A total of 10 rings of various sizes were created. Seven rings were made from superelastic Nitinol and three rings were made from shape-memory Nitinol.

After ring rolling, the rings were given a stabilizing heat treatment followed by an aging treatment to enhance their deformation and superelastic properties. These heat treatments were determined by a range of trial treatments and fully cyclic tests on hot rolled rod stock of the same alloys as used to make the rings.