Structure Analysis of Natural Wangdaodeite—LiNbO3-Type FeTiO3

This paper reports the first structure refinement of natural wangdaodeite, LiNbO3-type FeTiO3 from the Ries impact structure. Wangdaodeite occurs together with recrystallized ilmenite clasts in shock melt veins which have experienced peak shock pressures of between 17 and 22 GPa. Comparison of natural and synthetic wangdaodeite points toward a correlation between the distortion of ferrate- and titanate-polyhedra and the c/a ratio of the unit cell. The Raman spectrum of wangdaodeite is calculated based on the refined structure. Comparison to the reported spectrum of the type-material shows that the Raman peak at 738–740 cm−1 is indicative for this phase, whereas other features in type-wangdaodeite are tentatively assigned to disordered ilmenite.

Откол в сапфире при ударном сжатии в различных кристаллографических направлениях

Shock wave profiles of sapphire with eight crystallographic orientations с m, a, s, r, g, n and d -cut were measured at shock stresses in the range 15–20 GPa. Measured values of spall strength depend on direction of shock compression and peak shock stress. The largest spall strength values ~12–13 GPa were recorded for peak shock stress 16 GPa along the a-axis and the m-direction.

Experimental study of the coherent vorticity in slightly under-expanded supersonic screeching jets

The noise generation mechanism of screech tone by shock leakage in underexpended round jets is experimentally investigated by means of phase-averaged velocity fields. Two jet flows at Mach numbers 1.10 and 1.15 are measured by a particle image velocimetry apparatus simultaneously with their near acoustic fields and sorted according to their phase with respect to a screech period. The coherent vorticity fields are then computed and analyzed. They depict two distinct regions of high level of vorticity fluctuations. Thanks to the knowledge about shock leakage gathered in previous studies, the role of both regions in the acoustic generation process is identified and a region of the flow is recognized as suitable for emitting acoustic waves. Phase-averaged schlieren visualizations are also computed and used to determine the motion of the first five shocks over a screech period. For both jets, the peak shock motion is found at the fourth shock tip. This shock is also located in the region recognized as favorable for the shock leakage to be observed.

Discovery of bridgmanite, the most abundant mineral in Earth, in a shocked meteorite

Meteorites exposed to high pressures and temperatures during impact-induced shock often contain minerals whose occurrence and stability normally confine them to the deeper portions of Earth’s mantle. One exception has been MgSiO3 in the perovskite structure, which is the most abundant solid phase in Earth. Here we report the discovery of this important phase as a mineral in the Tenham L6 chondrite and approved by the International Mineralogical Association (specimen IMA 2014-017). MgSiO3-perovskite is now called bridgmanite. The associated phase assemblage constrains peak shock conditions to ~ 24 gigapascals and 2300 kelvin. The discovery concludes a half century of efforts to find, identify, and characterize a natural specimen of this important mineral.

Impact of Peak Shock Stress on the Microstructure and Reloaded Mechanical Behavior of AZ31 Magnesium Alloy

Magnesium alloys can be utilized as potential aerospace materials due to their low density, high specific strength, good vibration and shock absorption ability. This paper deals with the mechanical behavior of hot-rolled AZ31 alloy that was shock-deformed to 2.3 and 3.3 GPa. The post shock microstructure and mechanical response have been determined via full one-dimensional recovery techniques. The microstructure of deformed sample was characterized by the transmission electron microscopy (TEM) and electron back scattered diffraction (EBSD) techniques. All the shock-deformed materials showed shock-strengthening effect that was greater at higher shock pressure. The reload yield stress of the shock-deformed 2.3 GPa sample was determined to be 238 MPa while 264 MPa for the sample which shock-deformed at 3.3 GPa. It was postulated that the shock-strengthening is ascribed to a greater dislocation density and the formation of deformation twins.

Passive Flexible-Substrate Blast Sensor Array

We have developed a design for a wearable passive blast sensor array to detect the peak shock experienced by personnel exposed to high energy events. The sensor is fabricated on a flexible substrate using a MEMS process. The design includes an array of sensors, each element of which is triggered at a different pressure level and which records the peak pressure by means of a permanently deformed diaphragm. The elements can be integrated with a flexible electrophoretic display or can be interrogated externally with an electronic reader. A key application is in predicting the exent of traumatic brain injury for military peronnel exposed to explosions in a battlefield environment. Peak blast information can assist in prioritizing and determining the appropriate battlefield treatment. The flexible substrate allows integration into personal armor or clothing and the passive nature of the sensor ensures a very long shelf life and reduces cost and maintenance. Details of the sensor designs and process flows for their fabrication are described. Prototype sensors have been fabricated and the fabrication characterized. Also included are simulation results for the preforamnce of the arrays. Finally, preliminary pressure blast test data for indivdual sensor elements are presented.