A Method to Determine The Critical Depth of Cut for Various Rock Types
Open Access
- Author:
- Koc, Salih
- Graduate Program:
- Petroleum and Mineral Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 19, 2020
- Committee Members:
- Arash Dahi Taleghani, Thesis Advisor/Co-Advisor
John Wang, Committee Member
Luis F Ayala H, Committee Member
Mort D Webster, Program Head/Chair - Keywords:
- critical depth of cut
rock cutting
ductile and brittle modes
surface roughness
scratched test - Abstract:
- Knowing correctly the mechanical properties (toughness) of a rock is crucial for many applications such as hydraulic fracturing and borehole stability. It is known that rocks may have two failure modes during cutting: ductile and brittle. Besides the strength of rock samples, operational parameters such as cutting depth or the sharpness of a cutter also are deterministic criteria in the transition between these mechanisms. The failure mode continuously evolves from ductile to brittle failure mode with rising depth of cut. In the strength driven mode, rock deforms plastically, and the debris is powdered ahead of the cutting face. On the other hand, cracks are the major cutting characteristics of the brittle failure during cutting. The critical depth of cut represents the transition point of these two models, so this value helps better understand the failure mechanism of rock. In this paper, a new method is introduced for determining the threshold point of failure modes for every rock sample using the scratch test. The scratch test is a simple, and nearly non-destructive analysis, as the most common technique for obtaining the property of a rock by measuring normal, shear loads, and the cleared roughness surface of a rock sample. In this work, the correlation between the cutting force and surface roughness is analyzed throughout the cutting process, and the relationship between groove roughness difference and the average rate of height differences between every two points of the surface is found to reveal the rock breaking mechanism. Graph of surface asperity difference versus the ratio of roughness change to the time taken has a linear slope for different scratching depths. The value of this slope increases until the depth of cut reaches the threshold point, and then this number remains almost constant. The main purpose of this paper is to estimate the critical depth of cut of different rock specimens employing the new surface roughness model. The work submitted here analyzes the scratch test results of Berea sandstone, Indiana limestone, and mudstone (shale) core samples, scratched by a 5-mm-sharp cutter at several depths of cuts, as an extensive laboratory test.