Seismic events miss important kinematically governed grain scale mechanisms during shear failure of porous rock

Catastrophic failure in brittle, porous materials initiates when smaller-scale fractures localise along an emergent fault zone in a transition from stable crack growth to dynamic rupture. Due to the rapid nature of this critical transition, the precise micro-mechanisms involved are poorly understood and difficult to image directly. Here, we observe these micro-mechanisms directly by controlling the microcracking rate to slow down the transition in a unique rock deformation experiment that combines acoustic monitoring (sound) with contemporaneous in-situ x-ray imaging (vision) of the microstructure. We find seismic amplitude is not always correlated with local imaged strain; large local strain often occurs with small acoustic emissions, and vice versa. Local strain is predominantly aseismic, explained in part by grain/crack rotation along an emergent shear zone, and the shear fracture energy calculated from local dilation and shear strain on the fault is half of that inferred from the bulk deformation

Prospectus, April 26, 1977

VOTE TODAY-TOMORROW: FOUR VIE FOR PRES. IN STU-GO ELECTION; Remus, Mayeda run for V.P.; Albert Dodson unopposed; Activities Day May 3; Letters to the editor: Pres. Praises carnival, Mayeda warns of lies, Cartoon good…but, Stu-Go made many contributions: Onley; Editorial: Trouble for athletics; Hackett vs. Slack for convo., Cox opposes Stoeber for IOC; Unopposed: Propeck runs alone for secretary; Thursday set for wheel chair awareness; State provides funding for food sanitation course; Law Enforcement Club sponsors Mk\u27t Place fair; Markland: bigger not better for Twin City police force; Energy saving tips: Ripple effect causes waste; Police Chief Dye: \u27Recruitment-lifeline of police dep\u27t.\u27; Bike race today; Blooming Idiots come out of woodwork for IOC Carnival; Workshop set for Saturday: Puppetmaster Schmidt displays at PC; Afro American Theatre Workshop starts at PC; \u27Alcohol, sophisticated, sexy?\u27; Bike tour Sunday, May 1; Classifieds; Bat girls provide needed help for baseball team; Cobras expand record with 3rd no-hitter; Lincolnland doubleheader tomorrow: Women\u27s softball season nears end; June 7-10: Mudrock headed to JC golf nationalshttps://spark.parkland.edu/prospectus_1977/1018/thumbnail.jp

A convenient method for electron tomography sample preparation using a focused ion beam

Here we report a new sample preparation method for three-dimensional electron tomography. The method uses the standard film deposition and focused ion beam (FIB) methods to significantly reduce the problems arising from the projected sample thickness at high tilt angles. The method can be used to prepare tomography samples that can be imaged up to a \ub175\ub0 tilt range which is sufficient for many practical applications. The method can minimize the problem of Ga+ contamination, as compared to the case of FIB preparation of rod-shaped samples, and provides extended thin regions for standard 2D projection analyses.Peer reviewed: YesNRC publication: Ye

Microfracture evolution leading to catastrophic failure observed by hearing and seeing

&amp;lt;p&amp;gt;Catastrophic failure is a critical phenomenon present in Earth systems on a variety of scales, and is associated with the evolution of damage leading to system-size failure. Laboratory testing of rock failure permits characterization of fracture network evolution at the micro-scale to understand the interaction of cracks, pores and grain boundaries to an applied stress field, and the relationship between deformation and seismic response. Previous studies have relied on acoustic emissions (hearing) or X-ray imaging (seeing) to study the process of localization, which involves spontaneous self-organization of smaller cracks along faults and fractures on localised zones of deformation. To combine hearing and seeing of the microscopic processes and their control of system-sized failure, a novel x-ray transparent cell was used for deformation experiments of rock samples, which permits integration of acoustic monitoring with fast synchrotron x-ray imaging. To increase temporal characterization of damage beyond the temporal resolution of the fast 3D synchrotron system, acoustic emission (AE) feedback control was used to regulate the applied stress and slow down the deformation processes. As a result, there is increased temporal resolution of the incremental deformation between successive x-ray scanned states allowing synchronized comparison of acoustic emissions to x-ray scans. Here, we present the seismic analysis used to characterize the velocity evolution of the rock samples, and the location and characteristics of individual AE events in relation to microscopic deformation processes. Time-lapse velocity measurements are linked to internal stress changes and structural damage corresponding to seismic and aseismic deformation processes, while acoustic emissions are a direct indication of local cracking.&amp;amp;#160; We show that we can successfully locate AE events in 3D using only two sensors on either end of the sample, based on ellipsoid mapping, and x-ray image to event correlation. We explore temporal and spatial statistics of AE signatures and how those are linked to the strain field in the samples measured with incremental digital volume correlation between pairs of recorded x-ray tomograms. The direct observation of AE and X-ray images enables quantification of relevant seismic (local cracking leading to AE) to aseismic (elastic loading and silent irreversible damage) processes, with information extracted over fine temporal resolution throughout the deformation process through the AE-feedback control.&amp;lt;/p&amp;gt;</jats:p