Optimization of energy input for underwater rock fracture

Deep-sea mining is carried out by a special machine traveling on a seafloor and providing a possibility for fracture and grinding of the seafloor material for the future transportation to the mining support vessel. Fracture of rocks entails large energy input being responsible for the considerable part of the process costs. It was suggested that high-frequency oscillations being imposed on the mining tool can result in significant reduction of the energy input needed in order to maintain the fracture process. Incubation time approach developed by RCD formed the basis for a model that was used to predict and explain the reduction of a force on the fracturing tool appearing as a result of the high-frequency oscillations imposed on the static force on the tool.

A number of experiments were performed in collaboration with the Mechanics of Materials Laboratory (Nizhny Novgorod State University). These experiments were aimed for the fracture incubation time measurement for dry and water saturated limestone. In addition to this, other values for parameters needed for the performed simulations were evaluated. Simulation results displayed a possibility to receive significant reduction of the fracturing force on the tool for certain frquencies of oscillations imposed on the fracturing tool. Latest investigations in this field are supported by FP7 EU MARIE CURIE Project TAMER No. 610547.

Left: An example of calculations of average fracture force as a function of frequency of the imposed oscillations 

Right: Impact and quasi-static tests of dry and water-saturated limestone specimens