Shape Memory Alloy Rock Splitters Project

A static rock splitter device based on high temperature shape memory alloys (HTSMAs) will be developed for space related applications requiring controlled geologic excavation. The device, referred to as the shape memory alloy rock splitter (SMARS), is intended for sampling geological deposits in extra-terrestrial environments including planetary bodies such as the moon, Mars, and near-Earth asteroids. SMARS will consist of active elements made of NiTiHf alloys that generate extremely large forces in response to thermal input, while providing a dense and cost-effective method for fracturing rocklike materials when compared to hydraulic or explosive-based alternatives. The fractured rocks can be analyzed by onboard instruments on rovers or spacecrafts, or the rock masses can be returned to Earth for more detailed studies and investigations. The active elements will be used in conjunction with custom built, DC voltage heaters that are placed in borehole(s). The active elements can be recovered and are fully resettable for future use without any wasted consumables. Various rock types including igneous rocks (e.g., basalt, quartz, granite) and sedimentary rocks (e.g., sandstone, limestone) will be tested. The shape memory alloy rock splitter (SMARS) is ideal for critical planetary rock drilling/sampling operations, where flying debris from blasting methods can destroy the rock formation of interest, pose safety concerns to the astronauts, or cause damage to the costly nearby equipment (e.g., rover mirrors and sensors). In addition, static SMARS requires little setup and activation time compared to other static methods such as chemical agents that can take up to a few days to react with some hard and unknown rock formations. Mission reliability is another benefiting factor since SMARS operates based on a material response and only requires heat input to activate without the need for complex valve systems or hydraulic fluids, making it extremely simple and essentially fool proof to operate. The small volume and extremely low weight of the SMARS reduces payload launch costs and transportation hazards when compared to heavy hydraulic wedges and dangerous explosive materials and chemicals. Thus, the goal of this work was to explore high temperature SMAs, referred to as HTSMAs, for use as a static rock breaker where higher activation temperatures and higher force generations can be achieved. SMARS developed as part of this work employed Ni-rich NiTiHf alloys that have shown promising results regarding actuation and stability [9] as the expanding members. Along with custom heaters and transportable controller, SMARS key components and performance parameters were evaluated using new material conditioning methods, also known as training, using several rock types.