NiTi Springs Exhibiting Pseudoelastic behavior from negative 130 degrees to 90 degrees celsius

The Mars Spring Tire Project at NASA Glenn Research Center is considering procuring NiTi springs (wire formed in a helical shape) that meet specific material, geometric, and environmental requirements. The following is a list of specifications that are required in the finished springs. 1. Springs shall be made from a binary NiTi alloy that is processed to achieve pseudoelastic (otherwise known as superelastic) stress-induced martensite transformation over temperature ranges from 90° down to -130°C. All springs shall have finished properties such that pseudoelastic performance is achievable through this entire temperature range in both tension and bending. 2. At all temperatures (-130° to 90°C), the material used to manufacture the springs shall have a fully reversible, strain potential of at least ε tran = 6% in tension (where ε tran is the transformation strain of the material). 3. The material used for spring production shall have an onset-stress plateau, stress/temperature sensitivity less than or equal to 2 MPa/°C. (i.e. the slope of the stress plateau shift as a function of temperature shall not exceed 2 MPa/°C). 4. The material shall have a fully stabilized stress-induced response having a stress required to achieve 2% strain at 90°C of at least 550 MPa and a stress required to achieve 5% strain at 90°C of at least 850 MPa, regardless of final wire diameter sought. This is required to ensure both adequate strength properties as well as the proper non-linear deformation behavior that is required for achieving the correct force/deflection characteristic for the application. 5. The vendor shall be capable of manufacturing springs with the above properties using wire diameters from 0.010” – 0.100” for coil diameters ranging from 0.090” – 0.500” with pitches ranging from 0.200” – 0.500”. 6. Springs within the ranges listed above shall be manufacturable in lengths ranging from 8” – 24”. 7. Pitch in the delivered springs shall be controlled to within +/- 0.002” in order to ensure that the delivered springs can be woven to form a cylindrical mesh. 8. Vendor must be able to supply quantities between 500 – 1000 springs per batch, within two months from time of order. Vendor must also be able to demonstrate capability to deliver 40 batches of 500 – 1000 springs over a 4-year period. 9. Vendor shall meet the following requirements of NASA-STD-6016A: a. Section 4.1.2a,d,e,f (M&P Controls) b. Section 4.1.7 (Materials Certification and Traceability) 10. Vendor shall be AS9100 compliant or equivalent.