A method for making a ductile and porous shape memory alloy (SMA) using spark plasma sintering, and an energy absorbing structure including a ductile and porous SMA are disclosed. In an exemplary structure, an SMA spring encompasses a generally cylindrical energy absorbing material. The function of
A method for making a ductile and porous shape memory alloy (SMA) using spark plasma sintering, and an energy absorbing structure including a ductile and porous SMA are disclosed. In an exemplary structure, an SMA spring encompasses a generally cylindrical energy absorbing material. The function of the SMA spring is to resist the bulging of the cylinder under large compressive loading, thereby increasing a buckling load that the cylindrical energy absorbing material can accommodate. The SMA spring also contributes to the resistance of the energy absorbing structure to an initial compressive loading. Preferably, the cylinder is formed of ductile, porous and super elastic SMA. A working prototype includes a NiTi spring, and a porous NiTi cylinder or rod.
대표청구항▼
The invention in which an exclusive right is claimed is defined by the following: 1. An energy absorbing structure comprising a first shape memory alloy (SMA) member and a second SMA member, wherein the first SMA member is disposed externally of the second SMA member, spaced apart by a gap from the
The invention in which an exclusive right is claimed is defined by the following: 1. An energy absorbing structure comprising a first shape memory alloy (SMA) member and a second SMA member, wherein the first SMA member is disposed externally of the second SMA member, spaced apart by a gap from the second SMA member when the energy absorbing structure is not subjected to any stress, and configured to constrain the second SMA member so as to increase a buckling load that the second SMA member can accommodate, the second SMA member comprising a super elastic and ductile sintered SMA exhibiting a porous microstructure, in which interstitial spaces separate adjacent SMA particles, the porous second SMA member exhibiting a trapezoidal stress-strain curve response characteristic of an equivalent SMA exhibiting a dense microstructure under compressive testing performed above an austenite finishing temperature, a performance of the energy absorbing structure being enhanced due to a super elastic deformation of the second SMA member as the second SMA member is stressed about at least two substantially orthogonal axes sufficiently to close the gap, so that the second SMA member contacts and is constrained by the first SMA member. 2. The energy absorbing structure of claim 1, wherein the first SMA member and the second SMA member are coaxially aligned. 3. The energy absorbing structure of claim 1, wherein the first SMA member comprises a spring. 4. The energy absorbing structure of claim 1, wherein an initial load applied to the energy absorbing structure is borne by the first SMA member. 5. The energy absorbing structure of claim 1, wherein deformation of the first SMA member under a load exposes the second SMA member to the load. 6. The energy absorbing structure of claim 1, wherein deformation of the second SMA member under a load causes the second SMA member to contact the first SMA member. 7. The energy absorbing structure of claim 1, wherein the first SMA member is configured to elastically deform under relatively smaller loads, and to constrain the second SMA member only under relatively larger loads. 8. The energy absorbing structure of claim 1, wherein the first SMA member is super elastic. 9. The energy absorbing structure of claim 1, wherein the first and second SMA members comprise an alloy that includes nickel and titanium. 10. An energy absorbing structure comprising a plurality of first members and a second member, wherein the plurality of first members are configured to constrain the second member, to increase a buckling load that the second member can accommodate, wherein the second member comprises a ductile and porous shape memory alloy (SMA), and wherein the plurality of first members comprise helical coils that are distributed about a periphery of the second member, such that the plurality of first members do not share a common central axis and are disposed externally of the second member. 11. The energy absorbing structure of claim 10, wherein the second member comprises a super elastic alloy that includes nickel and titanium. 12. An energy absorbing structure comprising: (a) a porous shape memory alloy (SMA) member; and (b) a constraining member configured to selectively constrain the porous SMA member so as to increase a buckling load that the porous SMA member can accommodate, wherein the constraining member is configured to elastically deform under relatively smaller loads, and to constrain the porous SMA member under relatively larger loads, a positional relationship between the constraining member and the porous SMA member having been selected such that: (i) a gap exists between the constraining member and the porous SMA member when the porous SMA member is unloaded, so that the porous SMA member is not in contact with the constraining member and is thus not constrained when the porous SMA member is unloaded; and (ii) no gap exists when the porous SMA member is experiencing a load sufficient to cause the porous SMA member to elastically deform to a degree sufficient to cause the porous SMA member to physically contact the constraining member, but insufficient to cause an irreversible deformation of the porous SMA member.
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