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This study aims in understanding the rock cutting performance and optimizing the cutting parameters through DEAR-Taguchi optimization technique. The rock cutting experiments were performed by using uncoated, AlTiN-coated, and TiAlSiN-coated conical WC-Co bits. The micro-hardness, presence of coated elements, and morphological characterization were determined. The general outcomes are resultant cutting forces, specific energy, wear rate, quantity of material removed, and angle of resultant reaction forces. The input varies as cutting speed from 100 to 200 mm/sec and cutting depth from 2 to 6 mm. Designs of experiments were conducted and the optimized parameters were identified through ANOVA. The single-response optimization for each individual input parameters and MRPI were calculated to study their impacts on rock cutting parameters. The optimum combination of input parameters for better rock cutting performance is A3B3C3. The outcome of the present study extends its application in excavating hard rocks with optimized parameters for better efficiency.

Rock cutting efficiency is the most common parameter used to evaluate the performance of polycrystalline diamond compact (PDC) bits. Many studies have shown that cuttings size might be used to evaluate rock breaking efficiency; however, there are few quantitative studies of the relationship between rock cutting efficiency and cuttings size in rock cutting when a PDC bit is used. Several linear cutting tests were conducted to explore the relationship between the mechanical specific energy (MSE) and cuttings size to solve this problem. The cuttings size distributions were also discussed. Then, the coarseness index (CI) was selected as the most appropriate indicator of cuttings size and its relationship with the MSE was investigated. In addition, rock cutting tests based on the Taguchi method were conducted to analyze cutting parameters such as the depth of cut (DOC), the back rake angle (θ) and the cutting speed (v) effects on the CI and MSE. The contribution of each parameter to the response was obtained. The results show that the distribution of cuttings size conforms to the Rosin–Rammler equation, and there is a significant relationship between the MSE and cuttings size. The MSE decreases with increased cuttings size, furthermore, the relationship between the MSE and the CI could be described by an exponent function. The Taguchi experiment results show that DOC and θ have significant impacts: the CI value increases with increased DOC, and the CI increases slightly with increased θ. The most influential factor on the CI is the DOC, followed by θ. However, within the range of experiments, the cutting speed has an insignificant effect on the CI value. This work is highly pertinent to better understanding of the relationship between rock cutting efficiency and cuttings size in rock cutting using a PDC cutter.

In mechanical excavation, the response of the tool forces on the cutterhead is important when the excavation begins in actual cutting conditions because the reliability and efficiency of the cutting machine are influenced directly by the pick performance. The magnitude of the cutting force is utilized to estimate the specific energy, which is calculated from experimental tests to predict the performance of a mechanical excavation machine. However, the magnitude of normal force is also the other key parameter that used to calculate the load of the work unit of excavation machine. Therefore, based on linear rock cutting experiments performed on the low and high strength sandstones, the variation of the normal force and the variation of ratio of normal force to cutting force have been investigated under different cutting angles. The influence of related cutting angles, which have some direct or indirect effects on the normal force, has been discussed in detail. In this context, the attack angles lower than 80°, preferably between 50 and 60°, the clearance angle lower than 10°, resulted in a decrease on the normal forces. Besides, the positive values of rake angles led to more efficient cutting. Furthermore, it was suggested to employ the conical picks having the tip angles lower than 80° in order to obtain optimum cutting conditions. The certain ranges of the relevant angles exhibited the same characteristic both on low and high strength sandstones. As a result, the empirical models, which were found to be statistically significant, were put forward. These results would be essential for the design of the pick and cutterhead.

Polycrystalline diamond compact (PDC) bits are increasingly favored in the drilling field due to their high efficiency in rock breaking together with their longevity. To investigate the rock failure mechanism and further improve the performance of PDC bits, innovative experimental equipment is proposed in this paper. With its assistance, we can study the characteristics of rock-breaking using a PDC cutter under different conditions, e.g., high pressure and high temperature (HPHT), confining pressure, and jet impingement. The setup can be grouped into three parts: a rock cutting system, high-pressure jet generation system, and controlling system. A series of experiments was conducted to demonstrate the reliability of the setup. The results demonstrate the improvement in performance of PDC bits in the exploration of HPHT formations.

The creation of modern machines and improvement of existing designs of rock cutting bodies of combines is constrained by the lack of experimental studies of the process of separation of successive elementary cleavages during the potash ore cutting with cutters of winning machines. The potential of the cross cutting pattern of potash ore is shown, since the formation of zones of localization of weakening and induced fractures on the surface of layer-by-layer cutting face determines the separation of the elementary cleavages with stable geometric parameters. The verification of the conclusions obtained theoretically was carried out during laboratory tastings on a specially designed bench. The research procedure provided for comparative tests of the potash block ore cutting, staggered and cross cuttings. It has been proven that the use of the cross pattern for set cutting parameters makes it possible to reduce the specific energy costs of the cutting of potash mass, to reduce the average load on the cutter, to reduce the root-mean-square deviation, and to reduce the number of fractions that are hard to enrich in the crushing products, compared to the traditional staggered cutting pattern.

An extensive research program has been undertaken to exploit the physical and mechanical properties of thermally stable diamond composites (TSDC) for rock cutting and drilling operations in the exploration, mining, manufacturing and civil construction industries. Having previously demonstrated the superior abrasive wear resistance of TSDC as well as discovering a viable bonding process for the insertion of TSDC as cutting elements into steel tooling, the most outstanding issues to be further investigated are the tensile, transverse rupture and impact strengths of TSDC. By combining the results of these mechanical property measurements of a series of TSDC samples, some important factors that influence strength properties, including microstructural design and careful attention to chemical and phase composition of TSDC material, are discussed.

Argillization is a process in which clay-bearing rocks disintegrate into the clay under the action of high temperature, pressure, and water. When tunnel boring machines (TBMs) excavate in the mudstone, argillization takes place, causing the clogging of the TBM cutterhead. As a result, the penetration rate drops gradually. Abnormal wear might occur. To investigate the evolution of argillization of mudstone and cutter wear during the TBM tunnelling, a series of rotary indentation tests were carried out on the self-designed experimental bench for different loading times. During the test, the temperature and penetration depth of disc cutters were measured in real time. After loading, microstructures of cutting grooves, slacking mudstone, and worn cutter ring were observed by stereomicroscope. Consequently, the evolution of argillization in mudstone and cutter wear were investigated. Experimental results indicate that the argillization process of mudstone by disc cutter can be divided into three stages: mechanical cutting stage, deterioration of mudstone and the formation of slacking mudstone stage, and adherence of slacking mudstone stage. Specifically, at mechanical cutting stage, the rock was cut by cutter directly, causing high frictional heat. Then the microstructure of mudstone was deteriorated due to the water-weakening mechanisms, temperature effect, and mechanical activation effect. Finally, the slacking mudstone was adhered to the disc cutter. Correspondingly, due to the argillization of mudstone, the disc cutter wear goes through the mechanical wear stage, argillization wear stage, and secondary wear stage in sequence. This investigation reveals the rock cutting mechanism of TBM considering the argillization of mudstone. Furthermore, it provides some references for design and operation of the TBM.

The single polycrystalline diamond compact (PDC) cutter’s performance is affected by temperature during rock cutting process. The study towards understanding the factors and its interaction affecting the cutter’s temperature is essential prior to cutting process optimization. Thus, this study aims to investigate the effect of various cutting parameters and its interaction on the temperature of a single PDC cutter. A series of test was conducted in a lathe machine which utilized facing operation to cut the rock samples at 0.5 to 1.5 mm depth of cut and back rake angle of 5° to 15°. Two types of rock being tested in this study were Indiana limestone and Carthage marble. The analysis of variance (ANOVA) output indicated that cutting parameters and rock properties and its interaction have a significant effect on cutter’s temperature except for interaction between back rake angle and rock properties. Increasing the depth of cut and decreasing back rake angle has resulted in increasing temperature. The temperature of the single PDC cutter is higher when cutting Carthage marble than Indiana limestone. Combination of low back rake angle and high depth of cut producing maximum temperature. It is also validated that the data developed from the mathematical model having a difference of 5% as compared to the experimental data obtained using similar parameters which indicates that the results are reliable and can be forwarded in the future study.

Current experimental methods of assessing rock fracture toughness require a large sample size (i.e., Brazillian test, semi-circular bending, three-point bending), which cannot be extracted at greater depths and along horizontal well. Alternatively, fracture toughness can be evaluated at a finer scale using scratch testing. This study investigates the rock failure mechanism using micro-scratch testing and phase field modeling on rock fragments.The phase field approach models the crack growth and initiation based on energy minimization principles and by portraying the crack surface as a diffused entity. The method has been known for its robustness in preventing numerical singularities due to sharp crack discontinuities in complex crack topologies. In the phase-field scheme, a regularization scalar order parameter is used to indicate the material’s state (from undamaged to damage) during fracture formation. The associated loss of stiffness in rock during fracture formations is captured by the coupling of selected energy degradation function with embedded scalar order parameter and partial differential equations defining the deformation, history, and phase-field evolutions. In doing so, information on stress strain development is needed to evaluate the change in free energy during cracks formation. In this study, scratch testing is used to obtain load-displacement data related to stress strain history. During the test, an indenter scratches the surface of the rock under increasing load. The critical loads where the crack initiates and the chipping spallation occurs are identified based on the microscopic observations, acoustic emission signals, recorded tangential force and recorded depth. The critical loads are used to determine the crack length associated with chipping formation, while the recorded force displacement data are used to obtain the dimensionless stress-strain curve. Both the crack lengths and the dimensionless stress strain curve are then used as the input to the phase field model developed to approximate the fracture toughness of the rock tested.Scratch tests are performed on samples obtained from Eagle Ford formation. The experiments are conducted in short transverse and divider orientations. The crack formations are studied under the progressive load application. The critical loads where crack initiates and chips form are identified mainly based on the panoramic picture obtained after the test and the spikes seen on the Acoustic Emission signals. Preliminary results show that the fracture toughness is lower for samples tested in parallel to the bedding orientation (i.e., divider).Fracture toughness of rocks has attracted wide attention in the last few years in the design and analysis of hydraulic fracturing for hydrocarbon and geothermal recovery. The currently proposed methodology allows for a quicker and more reliable way of approximating rock fracture toughness from small rock samples. The incorporation of the phase field model allows better prediction of rock fracture toughness as the method is capable of overcoming classical model limitations of quantifying crack initiation and crack propagation in the complex fracture networks.

Cutter suction dredgers are important pieces of rock excavation equipment in port and waterway construction. It is valuable but difficult to properly estimate the cutting force on the chisel pick of the cutter suction dredger. In this paper, an analytical model, called the crushed zone expansion induced tensile failure model (CEIT model), is proposed for rock cutting with a chisel pick in order to predict the peak cutting force (Fc) more accurately. First, a review of the existing models for rock cutting with a chisel pick is presented. Next, based on the tensile breakage theory, cavity expansion theory and some hypotheses, the mathematical formula of the CEIT model is obtained. Different from that in the previous models, the effect of the rock on both sides of the chisel pick on Fc, defined as the sidewall effect is considered in the CEIT model. Then, the predicted Fc by the CEIT model is compared with the predicted Fc by existing theoretical models and experimental results to check the validity of the CEIT model. The results show that the CEIT model can well capture the relationships of Fc to the cutting parameters, including cutting width, cutting depth, and rake angle, and can predict the experimental results much better than the existing models. Finally, the sidewall effect and its influence factors according to the CEIT model are discussed.

Real-time and accurate measurement of the uniaxial compressive strength of rock on-site is the foundation of the design optimization and digital construction of the support structure in an underground project. Currently, effective methods to obtain the rock uniaxial compressive strength Rc in real-time on-site are scarce. Digital drilling test technology provides a new opportunity to solve this problem; however, the lack of a universal relational model for the drilling parameters versus Rc constrains further development of this technology. In this study, based on developed PDC bit for probing, the Sc parameters of rock cutting strength are proposed, and the relational equation between Sc and drilling parameters is deduced. Using an in-house-developed rock drilling test system, laboratory digital drilling tests for sandstone and mortar specimens with various strengths are performed. Based on the test results, a relational equation between Rc and Sc is developed. Subsequently, a relational model for drilling parameters versus Rc (the DP-Rc model) is developed, and its effectiveness is verified. The results show that the average difference in the uniaxial compressive strength predicted by the DP-Rc model versus the Rc measured in the uniaxial test is less than 10%, which proves the effectiveness of this model. On this basis, we propose a digital drilling test–based rock uniaxial compressive strength real-time measurement method that provides the foundation for the real-time and accurate measurement of the uniaxial compressive strength of the surrounding rock in underground projects.

Equipping of TBMs with rock cutting tools in the modern foreign practice of tunneling is based on the usage of CCS-type disc cutters. But there is also another type of tool for rock destruction when tunneling. It is a V-type disc cutter. As practice shows, in some situations it can provide greater work efficiency than a standard tool. Domestic research in this direction is mainly limited to the study of V-type tools of relatively small diameter for equipping roadheaders. Thus, this experience cannot be applied, if necessary, to the tunneling operations with TBM. Therefore, the studying of foreign experience on this issue is advisable. The paper analyzes studies conducted by foreign experts in the process of tunneling for various purposes in Turkey in the first decade of this century. These studies include the determination of a wide range of physical and technical properties of rocks, laboratory and field tests to determine the strength characteristics of the rock destruction process, comparison of laboratory, field and theoretical values of forces and energy performance of TBMs. As a result of the tests, it was found that the effectiveness of rock destruction is determined not only by their strength, but also by struc-tural and texture features. Differences were also observed when comparing laboratory experiments with field data, and comparing laboratory and full-scale force values on disc cutters in the process of rock destruction with theoretical values. In addition, the prospective areas of application of V-type disk cutters include the destruction of viscous non-abrasive rocks with a small amount of mineral inclusions or, with some reservations, the destruction of very hard and abrasive rocks. Not all conclusions made on the basis of the analysis performed coincide with the opinions of the authors of the initial studies, therefore, for a more complete understanding of the topic, it is recommended to read the literature (especially foreign literature) from the list of quoted sources.

Polycrystalline Diamond Compact (PDC) bit is extensively used in oil & gas drilling, the rock cutting efficiency of PDC cutter directly determines the drilling efficiency and costs. Hence, it is crucial to evaluate the rock cutting efficiency of PDC cutters. The Mechanical Specific Energy (MSE) is used as an index for long periods of time to evaluate the rock cutting efficiency, however, the energy dissipation in rock breaking cannot be further calculated in details, leading to inaccuracy. To address this problem, the new concept of Plastic Energy Dissipation Ratio (PEDR) and its model are presented, a new approach for rock cutting efficiency evaluation by using PEDR is also put forward. Compared with MSE, the PEDR can determine the Optimum Depth of Cut (DOC) under various conditions. The theoretical analysis shows that the critical DOC, governing the transition of ductile to brittle failure mode, is the optimal cutting depth, having the smallest PEDR and highest rock cutting efficiency. The test and simulation of rock cutting are carried out to verify the PEDR model, and the PEDR under different DOC, cutting velocities and rake angles are depicted and discussed. The results can provide a theoretical basis for the design of PDC cutter and optimization of drilling parameters.

It is generally accepted that drilling with drag bits (Polycrystalline Diamond Compact bits) simultaneously consists of “pure cutting” and “frictional contact” processes. To date, the mechanics of rock cutting have been mostly based on the assumption that these two processes are fully independent as the influence of wear flat inclination angle (β) with respect to the cutter velocity vector ( v ) on the frictional contact force is often not accounted for. The specific aim of this study is to determine the effect of wear flat inclination angle on the frictional force acting on the wear flat surface of a single blunt cutter over a wide range of depths of cut (d). For this purpose, an extensive and comprehensive set of cutting experiments was performed on two sedimentary rock samples (a limestone and a sandstone) using a state-of-the-art rock cutting equipment and a unique cutter holder. The results show that the normal contact stress (σ) at the wear flat-rock interface (and therefore the normal frictional force acting on the wear flat) is dependent on the depth of cut within the elastoplastic and particularly plastic regimes of frictional contact; however, the contact stress is invariant with depth of cut within the elastic regime. Further investigations indicate that the assumption that the force acting on the wear flat surface of a blunt cutter is independent of the cutting process taking place ahead of the cutter is not valid in particular, for the large values of inclination angles.

The main purpose of this paper is to predict the rock cuttability by considering the peak cutting forces and analyze the shear behavior of chisel picks by numerical simulations on the basis of theoretical and numerical studies. Numerical modeling studies were carried out as two main parts using PFC3D. In the first part, triaxial compression test was modeled on soft and hard rocks at various confining stresses. In part two, a chisel pick was numerically simulated and advanced on artificially generated soft and hard rocks depending on different cutting parameters. Then, the variation of peak cutting forces with the rake angle and cutting depth was monitored by modeling unrelieved rock cutting tests. The simulation results were compared with the results of theoretical cutting mechanisms. In conclusion, it is found that reasonable relationships exist between two predictive methods. In addition, the effects of rake angles on the shear strength were analyzed using Nishimatsu’s cutting model. The variation of shear angle during rock cutting was also examined. As a result of numerical studies, it is found that the theoretical formula proposed by Nishimatsu for the estimation of peak cutting forces and shear strength is mainly suitable in negative rake angles of chisel picks and in hard rocks. Furthermore, the shear planes of the microcracks in PFC3D were monitored and the shear angle was found to be ranging between 20° and 35°. These results were also verified by modeling of triaxial tests at different confining pressures. © 2018, Springer-Verlag GmbH Austria, part of Springer Nature.

This paper investigates the disc cutter behaviors in full-scale linear cutting tests. The experimental results obtained from different rocks varying from relatively soft rock (σc=27.6 MPa) to extremely hard rock (σc=355.54 MPa) are compared to the results of the semi-theoretical prediction model (Rostami & Ozdemir, 1993; Rostami, Ozdemir, & Nilsen, 1996). Compared to the semi-theoretical results, higher experimental normal and rolling forces and lower experimental cutting coefficients and normalized resultant forces are obtained when cutting low strength rocks. Opposite results are found when cutting extremely hard rocks. An empirical disc cutter cutting force prediction model is suggested in which the input parameters are cutter diameter, cutter spacing, cutter penetration depth and rock uniaxial compressive strength. Furthermore, based on the semi-theoretical model and the new empirical model, reverse estimation of rock strengths from disc cutter cutting forces are undertaken. The results show t...

Tungsten carbide tipped pointed attack picks is widely used in mechanical machinerysuch as roadheaders, continuous miners and longwall shearers. Great efforts have been made toinvestigate the interaction between point attack pick and rock. However, the research on theinvestigation of pick profile on the cutting performance is still a subject little investigated by thescientific community. In this study, the rock fragmentation process is simulated using a 2D discreteelement code, PFC2D. In the simulations, four types of pick tip geometries (mushroom insert, bulletinsert, conical insert, and cap) were employed to investigate the effect of pick profile on the cuttingperformance of point attack picks. The forces acting on the pick and crack propagation process werecontinuously monitored during the simulations. The preliminary results of cutting performance ofthe picks under different cutting scenarios were analyzed.

Thermally Stable Diamond Composite (TSDC) tips have attracted a great attention of rock cutting industry due to the higher thermal stability and high wear resistance of TSDC. To make the TSDC tipped picks practical for real application, it is important to understand the failure behavior of the TSDC tips for rock cutting. One of the failure characters of TSDC tips is random failures. In this paper, a method is proposed to calculate the failure probability of TSDC tips for cutting individual rock segments. This method enables to link the segment length to the failure probability of the tip for cutting the segment. A numerical case study is presented to validate the method. The method can effectively reduce the impact of the number of segments on failure probability estimation accuracy.

This paper aims at reporting the results of a number of drag pick cutting tests on selected igneous rock samples to compare the experimentally determined maximum cutting force (FC′) values with theoretically estimated ones. First, a review on theoretical rock cutting models proposed for both chisel and conical picks was presented in detail. Experimental study consists of both chisel and conical pick cutting tests in unrelieved (single-pick) cutting mode with varying cutting depths. FC′ values were determined from experimental results, and theoretical models were utilized to compute FC′ for all cutting conditions. Computed and experimentally determined FC′ data were then compared for a referenced cutting depth. It is shown that the theoretical models might overestimate or underestimate FC ′ and cannot give reliable results. Finally, explanations for these mismatches were presented. Keywords: Rock cutting mechanics, Rock cutting tests, Vertical rock cutting rig (VRCR), Cutting force, Rock cutting theories

The objective of this paper is to investigate the influence of the rake angle on the magnitude of the intrinsic specific energy and the inclination of the force acting on the cutting face of a Polycrystalline Diamond Compact (PDC) sharp cutter while tracing a groove on the surface of a rock sample. An extensive and comprehensive set of cutting experiments was performed on a wide range of quarry rock samples using a state of the art rock cutting equipment (Wombat). The results conform with the previous studies by other researchers; the intrinsic specific energy is in good agreement with the uni-axial compressive strength of the rock samples when the cutter is positioned at back rake angles between 5° to 20°. New results on a few rock samples were also obtained by performing novel experimental tests at very large rake angles ( θ > 70 ° ) as well as negative rake angles, showing that the intrinsic specific energy increases dramatically once the back rake angle exceeds 75°. Results also indicate that the decrease of the apparent interfacial friction angle with increasing back rake angle seems to follow a “universal trend” weakly dependent on the rock sample.

A special thermocouple configuration was developed to measure the temperature upon the contact surface between a point-attack pick and the rock material. The transient temperature at the hot spot was successfully measured when the rock advanced against the pick. The effects of the cutting parameters including depth of cut (DOC), spacing and cutting speed on pick temperature were investigated. It was found that the pick tip temperature increased significantly with the increased DOC and cutting speed. The effect of spacing on the pick tip temperature was smaller than that of the DOC and cutting speed, particularly when the spacing was greater than that required to change from unrelieved to relieved cutting. For all cutting conditions used, the pick tip temperature varied from 313 °C to 1100 °C. The highest temperature was obtained as about 1100 °C with cutting speed of 2.5 m/s, DOC of 10 mm and spacing of 50 mm. Reddish and black discontinuous banding chips were found in the cutting grooves under this cutting condition.