A working prototype of a non-explosive, static rock splitter for space exploration using shape memory alloys (SMAs) as the driving member also has terrestrial applications. The static, compact, non-explosive shape memory alloy rock splitter (SMARS) was designed for sampling geological deposits, including planetary bodies such as the Moon, Mars, and near-Earth asteroids (Figure 1). The splitter employs high-temperature SMAs that generate extremely large forces in response to thermal loads, while providing a compact and cost-effective method for fracturing rocklike materials and minerals when compared to hydraulic or explosive-based alternatives. The active elements, in the form of pre-shaped cylindrical pellets, are used in conjunction with custom-built DC voltage heaters placed in boreholes.
SMARS is inserted into a pre-drilled hole in a rock or pre-existing cracks. At this state, the material exists in its compressed state with an effective diameter equal to that of the drilled hole. Once inserted, current is supplied to the heaters until the critical transformation temperature of the SMA is reached. At this point, the material expands, but since it is constrained by the rock walls within the hole, the SMA exerts forces in excess of l GPa, causing the rock to break (Figure 2).
High-strength and stable SMAs based on NiTi-X compositions containing a secondary, nanometer-size precipitate phase are produced through compositional control and aging heat treatments, and are used as the expanding element of the non-explosive rock splitter device. These new materials are fully resettable for future use without any wasted consumables. It will allow for the return of rock or other geologic samples to Earth for more detailed studies and investigations in a reasonably undistorted condition. The use of explosives, on the other hand, can badly damage samples or result in the loss of samples in low-gravity environments.
These devices would also be useful for terrestrial applications; for example, breaking rock in a well-controlled manner that does not involve damaging a structure is a common practice in fossil hunting, collecting, and recovery, and in the sampling of other fragile geologic samples. These rock breakers would be instrumental in such applications both in the field and in the laboratory where fracture of large samples is required, but where explosive or impact techniques are not acceptable because of the damage they may do to the underlying sample.