Dexing Li

The Time-Space Joint Response Characteristics of AE-UT under Step Loading and Its Application

The acoustic emission (AE) and ultrasonic (UT) simultaneous monitoring program is designed using concrete samples under step loading. The time-varying response characteristics of AE-UT are studied and the cross-correlation analysis between AE-UT parameters is obtained. Moreover, the joint response of UT-AE spatial distribution field is analyzed, and an AE-UT joint monitoring method to detect early-warning signals of a rockburst disaster in a coal seam is proposed. The results show the following. During the loading process, the AE pulses/energy and UT attenuation coefficient first slowly decrease and then increase steadily and finally rapidly increase, while the UT velocity shows a trend of first gradually increasing and then slowly decreasing and finally a sharp decline. AE pulses and energy are significantly or highly correlated with the UT velocity and attenuation coefficient. The AE energy and UT attenuation coefficient can better characterize the damage evolution of concrete under step loading. The UT field evolves ahead of the rupture on the surface, and the long/narrow strip distribution region of UT parameters is consistent with the future failure zone; meanwhile, the AE events can visually reflect the evolution path of internal damage as well as the dynamic migration mechanism of UT field.

Characteristics Analysis of Post-Explosion Coal Dust Samples by X-ray Diffraction

ABSTRACT Coal dust explosion tests were performed in a 20-L spherical vessel and the post-explosion dust samples were collected for analysis. Various characteristic parameters of each explosion trial were recorded, including maximum pressure, maximum rate of pressure rise, ignition time, and deflagration index. In addition, as a new analytical technique, X-ray diffraction (XRD) was used to analyze the coal dust samples before and after each explosion, and assessments of microcrystalline structures and mineral phases were also performed. The diffraction peaks of post-explosion dust samples were shifted to larger angles and were also sharper and narrower compared to the peaks generated by the original coal dusts. Variations in microcrystalline structural parameters (d002 and L002) indicated that the post-explosion specimens had a higher degree of crystallinity and a more ordered crystal structure. Differences in mineral components between the pre-explosion and post-explosion samples were also evident, suggesting phase transformations during the explosions. The above results indicate that XRD analysis can be regarded as a reliable tool to study post-explosion coal dust and provide a new insight on further understanding of coal dust explosion characteristics.