Improving TC drill bit\u27s efficiency and resistance to wear by graphene coating

Displaying a two-dimensional pure crystal carbon structure, Graphene is the strongest, yet thinnest substance discovered by scientists. Coating tungsten carbide (TC) drill bits with graphene to evaluate the effect of graphene on the wear, as well as the rate of penetration of the drilling bit was examined in this research. Two evaluation approaches were employed: one with employing ANSYS Software and the second by employing atomic pressure chemical vapor deposition (APCVD synthesis) in the laboratory to produce a monolayer graphene coating. The simultaneous software-based and lab-based testing were performed to increase the credibility of the results and minimize the potential errors. Conducting the simulation using ANSYS, the maximum shear elastic strain, equivalent elastic strain, equivalent (von mises) stress, total deformation and maximum shear stress were investigated prior and after the graphene coating was applied on TC simulated bit. Total deformation was only slightly increased, while the maximum shear elastic strain was almost doubled, reflecting that the bit\u27s wear was significantly reduced after the coating. Lab-based APCVD synthesis results showed 34 % increase in compressive strength of the coated bit, in comparison to the uncoated one. The failure occurred for uncoated bit at 35 MPa, where the coated bit experienced failure at 46.9 MPa. The Von Mises stress test conducted on the coated and uncoated samples also indicated that this stress was 41 % less for the coated bit, in comparison to the uncoated one. Finally, two small-scale drilling operations, one using a 1inch graphene-coated TC bit and the other using a 1inch non-coated TC bit, were performed on a granite block, to evaluate the performance of the graphene-coated bit in practice. In a chosen 120-min time frame, 27 consecutive holes could be drilled by the graphene-coated TC bit, while 19 consecutive holes could be drilled by the uncoated TC bit, in identical drilling conditions. This implies a 42 % increase in ROP

Strain measurement with multiplexed FBG sensor arrays: An experimental investigation

In conventional rock mechanics testing, radial strain measuring devices are usually attached to the sample\u27s surface at its mid-height. Although this procedure provides a realistic picture of the lateral deformation undergone by homogeneous samples, however, this assumption may not be accurate if the tested rock has significant heterogeneity. Fibre Bragg Grating (FBG) sensors have recently been introduced to various rock testing applications due to their versatility over conventional strain gauges and radial cantilevers. FBG sensors have small size, multiplexing capability, and immunity to magnetic interference. The main objective of this study is to explore and understand the capabilities of FBG sensing for strain measurement during rock mechanics testing, including under confining. To do so, two limestone plugs (Savonnières limestone) and one acrylic Poly Methyl Methacrylate (PMMA) plug, all of 38 mm diameter, were prepared. The acrylic plug and one of the Savonnières samples plugs were subjected to Unconfined Compressive Strength (UCS) tests. The second Savonnières plug was subjected to a hydrostatic test up to 20 MPa confining at room temperature. FBG sensors of 125 μm cladding diameter with ceramics (Ormocer) coating were glued on the surface of each sample, spreading across the entire sample\u27s height. Strain gauges and cantilever-type radial gauges were used on the samples submitted to UCS for comparison. Results show that radial strain measurements and calculated elastic properties derived from the FBG readings for samples are comparable to readings from the conventional strain gauges and cantilever-type devices. Apparent bulk moduli based on volumetric strain computed from FBG radial strain readings during the hydrostatic test on the Savonnières sample was consistent with benchtop measurements conducted on the Savonnières sample and another plug extracted from the same parental block, as well as published literature data. Moreover, variations in the calculated elastic properties are interpreted as evidence that the FBG sensors detected heterogeneities in the samples\u27 inner structure, which can be seen in the density profiles computed from x-ray CT images. Such observation confirms the potential of the presented FBG sensors configuration for 3D strain mapping in rock mechanics tests