Tailoring energy absorption with functional grading of a contact-aided compliant mechanism

Functional grading can be used for spatial control of local mechanical properties and control of the stiffness and energy absorption of a structure. Cellular contact-aided compliant mechanisms (C3M) are cellular structures with integrated self-contact mechanisms, i.e. the compliant segments experience self-contact during deformation. The contact changes the load path and the C3M cells can be tailored for a specific structural application, such as energy absorption. The focus of the paper is on C3M made of nickel titanium which exploit self contact, the superelastic effect, and functional grading to improve performance and increase energy absorption. Continuous and discrete functional grading models are implemented in finite element analyses of the C3M cells. It is found that there is a complex relationship among self contact, superelastic properties, and functional grading, which are tailored to improve the performance of C3M. The functionally graded cells can be realized through metal additive manufacturing of NiTi, where functional grading and superelasticity are achieved by varying the material composition locally.