Shape memory alloy rock splitters (SMARS)
View Patent ↗Shape memory alloys (SMAs) may be used for static rock splitting. The SMAs may be used as high-energy multifunctional materials, which have a unique ability to recover large deformations and generate high stresses in response to thermal loads.
1. An apparatus for splitting a rock, comprising:
a housing containing two shape memory alloy (SMA) expanding elements, wherein each SMA expanding element comprises a body, a first end cap, and a second end cap, wherein the body is constructed of nickel titanium hafnium (NiTiHf), nickel titanium zirconium (NiTiZr), or nickel titanium hafnium zirconium (NiTiHfZr);
two heaters, wherein each heater substantially surrounds a respective body of one of the two SMA expanding elements; and
a controller configured to selectively power the heaters, wherein:
when the bodies reach a predefined temperature within a predefined borehole of the rock, the first and second end caps are configured to exert force on walls of the borehole, and
the selective powering of the heaters causes the SMA expanding elements to sequentially exert force on the walls of the borehole.
2. The apparatus of claim 1 , wherein the SMA expanding elements comprise a temperature capability of at least 100 degrees Celsius.
3. The apparatus of claim 1 , wherein the SMA expanding elements comprise a stress capability of at least 800 MPa.
4. The apparatus of claim 1 , wherein the SMA expanding elements comprise a stress capability of at least 1000 MPa.
5. The apparatus of claim 1 , wherein the first and second end caps of each SMA expanding element are adjustable end tips configured to enhance cracking of the rock and compensate for irregularity in a borehole diameter.
6. The apparatus of claim 5 , wherein the adjustable end tips comprise one or more shapes depending on rock type being explored.
7. The apparatus of claim 5 , wherein the adjustable end tips are machined directly onto ends of the body.
8. The apparatus of claim 5 , wherein the adjustable end tips are attached to the bodies of the SMA expanding elements.
9. The apparatus of claim 1 , further comprising:
one or more pushers configured to provide additional displacement at a relatively lower stress after the SMA expanding elements have been activated.
10. The apparatus of claim 9 , wherein the one or more pushers comprise a specific amount of weight required to deflect the material per unit length, or spring rate, to achieve a desired final splitting.
11. The apparatus of claim 1 , wherein each heater comprises a sleeve to house a SMA expanding element.
12. The apparatus of claim 11 , wherein each heater comprises adhesive cement surrounding that heater's sleeve.
13. The apparatus of claim 11 , wherein each heater comprises conductive wires wrapped around that heater's sleeve.