Use of Giant Superelasticity Effect for Improving Interface Performance

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The much promoted promise of advancing mechanical design by using such "smart materials" as shape memory and superelastic alloys (SMA and SEA) did not materialize to a significant degree. The main applications of such materials are in medicine (arterial stents, bone reconstruction, etc.) and consumer products such as women's bras and "non-destructible" eyeglass frames. This project will extend application of the smart materials, especially of SEA, to structures of high productivity precision machines machine tools. SMA and SEA materials are largely produced as wires, tubing, or strips. Up to now, they were used in tensile or bending modes of load accommodation, wherein relatively small loads cause relatively large deformations. Structural applications are usually associated with high loads and relatively small deformations. A limited scale preliminary (non-funded) study demonstrated that very high forces can be accommodated while causing small deformations if the off-the-shelf wires or tubing made from SEA are loaded radially. Moreover, it was discovered that such loading mode is associated with extremely large elastic limits. The radially loaded SEA wire exhibit elastic limit 20-24 percent, similar to rubber-like materials, while having elastic modulus at least one thousand times greater than rubber ("giant superelasticity effect"). This unique and until recently not known property opens large areas for beneficial applications. Detailed experimental and analytical (finite element modeling) studies of properties of various SEA and SMA materials (wires and tubing) under radial loading will be performed in the course of this project, to accumulate data necessary for using the "giant superelasticity effect" in structural design applications. Application of this effect for toolholders will be explored, together with Command Tooling Systems Co. (one of the largest US manufacturers of toolholders for CNC machine tools).It is anticipated, based on the previous results, that application of structural dimensional compensators utilizing the unique elastic properties of the radially-loaded SEA wires and tubing will result in a significant enhancement of stiffness and accuracy of many thousands machine tools in the U.S., thus in increasing their machining quality and productivity. These effects will be achieved in a very cost-effective way, with minimum modifications of the existing toolholders. Assessment of other design applications of the giant superelasticity effect will be performed , such as for modular tooling systems and for reconfigurable machining systems.