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 εtran = 6% in tension (where εtran 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.
Brian M. Evans, Contract Officer, Phone 2164332407, Email brian.m.evans@nasa.gov