[CCoE Notice] Thesis Defense: Analysis of Damage Accumulated in Multi-Stage Triaxial Tests Using Acoustic Emissions Data

[Grayson, Audrey A]

Analysis of Damage Accumulated in Multi-Stage Triaxial Tests Using Acoustic Emissions Data
Sabyasachi Prakash
Defense Date: Thursday, August 3rd,2017 Time: 12.00 pm Location Room: 125, ERP 9
Committee Members: Dr. Michael Myers, Dr. Lori Hathon, Dr. Steven Glaser and Dr. Robert Stewart
The purpose of this research is to develop a technique to quantify damage and support the assertion that a Poisson’s Ratio of 0.5 is an appropriate point of unloading for Multi-Stage Triaxial tests (MST). Acoustic Emissions (AE) were measured on five different samples undergoing Multi-stage Triaxial Tests. Two different behaviors were observed. For the cemented quartz rich samples (Weeks Island, Wilcox and Burhan), the number of AE events did not show a strong dependence on confining stress. They did have an exponential increase of AE events with increasing load at each stage. The total axial strain for fine-grained samples is significantly larger than the quartz dominated samples indicating a more ductile and diffused failure mechanism.
The choice of PR of 0.5 was validated using AE data as the point of unloading for quartz dominated samples in the MST. The number of AE events for quartz dominated samples showed a sharp increase as Poisson’s Ratio (PR) approached 0.5. In contrast, the fine-grained samples (Niobrara Marl and Niobrara Chalk) followed a different behavior. Plots of PR versus axial strain however do show a change in slope before a PR of 0.5 and then sharply increase further along the stress path for all samples. Even though the correction between maximum compressive strength and the point of positive dilation is about 1.2 for these samples, the simple connection between AE events is not observed. This would be investigated in future work.
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