In situ microscopic and spectroscopic studies of samples allow us to understand the mechanisms and measure kinetics of phase transformations in materials. We use a light microscope and a Raman microspectrometer to study phase transformations induced by contact loading. Many interesting phenomena occur in materials during indentation that can only be analyzed during indentation, in situ. By analyzing what occurs to ceramics and semiconductors in situ we can gain valuable insight into the mechanisms and kinetics of phase transformation. A microindentation device has been designed and fabricated to achieve these objectives. The microindentation device can provide the means to study pressure-induced phase transformations in real time. The basic design of the device is adaptable to several configurations, so that the device may be used in a wide variety of applications. The device consists of a piezoelectric actuator (piezoelectric translator), load cell, linear microscrew stage, translation stage containing the specimen mount and specimen holder, and diamond-tip indenter. For the first time, an indentation tester has been coupled with a Raman microspectrometer to conduct in situ studies of pressure-induced phase transformations. This article describes the design, operation, and experimentation of a microindentation device for the in situ analysis of pressure-induced phase transformations in materials.

Context. The current model of planet formation lacks a good understanding of the growth of dust particles inside the protoplanetary disk beyond mm sizes. A similar collisional regime exists in dense planetary rings. In order to investigate the low-velocity collisions between this type of particles, the NanoRocks experiment was flown on the International Space Station (ISS) between September 2014 and March 2016. We present the results of this experiment. Aims. The objectives of our data analysis are the quantification of the damping of energy in systems of multiple particles in the 0.1 to 1 mm size range while they are in the bouncing regime, and the study of the formation of clusters through sticking collisions between particles. Methods. We developed statistical methods for the analysis of the large quantity of collision data collected by the experiment. We measured the average motion of particles, the moment of clustering, and the cluster size formed. In addition, we ran simple numerical simulations in order to validate our measurements. Results. We computed the average coefficient of restitution (COR) of collisions and find values ranging from 0.55 for systems including a population of fine grains to 0.94 for systems of denser particles. We also measured the sticking threshold velocities and find values around 1 cm/s, consistent with the current dust collision models based on independently collected experimental data. Conclusions. Our findings have the following implications that can be useful for the simulation of particles in PPDs and planetary rings: (1) The average COR of collisions between same-sized free-floating particles at low speeds (< 2 cm/s) is not dependent on the collision velocity; (2) The simplified approach of using a constant COR value will accurately reproduce the average behavior of a particle system during collisional cooling; (3) At speeds below 5 mm/s, the influence of particle rotation becomes apparent on the collision behavior; (4) Current dust collision models predicting sticking thresholds are robust.

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We present the results of a series of laboratory low-speed impacts (< 4 m s−1) of centimeter-sized spherical projectiles into simulated dry and icy regolith samples. The target material was comprised of JSC-1 (Johnson Space Center) lunar simulant grains in the size range 100–250 μm, mixed with similar-sized water ice grains. Impacts were performed under vacuum, either at room temperature for JSC-1 samples or at cryogenic temperatures (<150 K) for icy mixtures. We measured the ejecta masses from a collection plate and impact crater dimensions from post-impact crater photographs. We find that both the ejecta masses and crater diameters followed trends predicted by established scaling laws, albeit with different fitting parameters, and we were able to fit a strength regime π scaling to our measured crater diameters. The water ice in our target material took two forms: grains mixed with the regolith grains and frost from air condensation coating regolith grains. In both cases, the presence of water ice in the sample led to lower ejected masses and smaller crater sizes. In addition, our measured crater sizes were several orders of magnitude larger than expected for impacts into solid rock or water ice. Using our measured scaling parameters, we applied our findings to a planetary context for the study of secondary craters on icy moons, as well as eroding collisions occurring in Saturn’s rings. We found that the deviation of our measurements from solid targets and from commonly used scaling parameters allowed us to reconcile our measurements with the models in both cases.