Project 4

Evaluation of hypervelocity impact-induced damage of rocks using elastic waves

Project director:

Christian Grosse, Centre for Building Materials at the Technical University of Munich (TUM)

Research staff:

Dorothee Moser (PhD student, TUM)

Summary

According to the overall goals of the MEMIN program there is need for a detailed investigation of the dynamic rock failure due to hypervelocity impact. This project is devoted to trace the damage and fracture zones beneath the experimentally produced craters three-dimensionally and in a non-destructive way at high spatial resolution. Methods based on ultrasound and acoustic emission techniques will be developed and applied to detect inhomogeneities and cracks as well as to locate zones of fluids in a target before, during, and after impact. Additionally, information about petrophysical parameters should be obtained.

The project allows, for the first time, to record the dynamic fracture growth during impact (acoustic emission). This method will essentially contribute to a better understanding of the formation of the zone of damaged rocks underneath crater structures in terms of the degree of fragmentation as a function of distance and time. Moreover acoustic sounding methods will be applied after the impact experiment, which will provide a detailed image of the fracture zone that can be directly compared with cross sections after dissecting the blocks of rock. In-situ inspection of the change in acoustic properties due to impact induced fracturing will provide important information for the interpretation of geophysical (seismic) signatures of natural impact structures with regard to the zone of fractured rocks underneath natural impact craters.

Three different techniques (i)-(iii) as well as novel emitter/sensor systems (iv) will be applied. The methods range from more or less traditional techniques (with low risk with regard to feasibility) to not yet fully developed techniques with high potential and additional benefit for the project goals.

Through-transmission ultrasound techniques are a popular tool to characterize structures within rocks. Usually, the target is evaluated by interpreting transient waves after transmission in terms of signal amplitude, frequency content, travel time and wave velocity. To enable more sophisticated analysis techniques and to enhance the sectorwise resolution of the object scanning methods, as well as computerized tomography (e.g. diffraction tomography) are applied. Generally, these techniques are addressed as ultrasound pulse spectroscopy. The goal is to apply these traditional techniques in the environment described in the proposal and to deduce from the observed change in acoustic properties of the impact-damaged rocks in the experiment to the fragmentation-state of rocks at natural impact craters.

Results

You can find the results here.