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This paper presents a numerical investigation into the effects of pre-induced cracks on polycrystalline diamond compact (PDC) rock drilling processes under varying pressure conditions. A 3-D finite element model was created using a linear Drucker–Prager yield criterion in conjunction with a damage criterion to model element erosion. The model used a single PDC linear cutting configuration to highlight the differences between uncracked and cracked rock cutting in terms of cutting forces and cutting mechanism. The objective is to address the change in the effectiveness of pre-induced cracks under high-pressure conditions, similar to those in actual deep-drilling operations. The results show that the pre-induced cracks reduce the cutting force under the tested pressure range (0–100 MPa). The overall effectiveness decreases as the confining pressure increases because the pressure compacts the rock, restricting fracturing ahead of the cutter surface. Additionally, the rock cutting mechanism changes from a continuous removal of material at the atmosphere to a more intermittent form at higher pressures. Highlights: Finite element simulations reveal the impact of confining pressure and pre-existing cracks on single cutter rock cutting dynamics Calibration of granite rock behavior utilizing a pressure dependent Linear Drucker–Prager Yield criteria Integration of pre-existing cracks in the simulation through a node-separation algorithm Analysis of the interaction between confining pressure and pre-existing cracks on rock cutting efficiency Simulation results showed changes in cutting mechanisms and force responses due to varying confining pressures and crack presence [ABSTRACT FROM AUTHOR]

Drilling into deep formation characterized by high formation and hydrostatic pressures often brings great challenges to oil and gas industry and the phenomena, such as bit slip, balling and cutter wear, are easy to be exposed. Therefore, it is very important to conduct rock-breaking experiments under high confining and hydrostatic pressures and understand the cutter–rock interaction behaviour for revealing the rock-breaking mechanism of Polycrystalline Diamond Compact (PDC) cutter. In this paper, granite, sandstone and shale were used to carry out PDC cutter cutting experiments under confining and hydrostatic pressures. Cutting force, mechanical specific energy (MSE), cuttings, cutting grooves and energy change were comprehensively analyzed when rock suffers different failure modes under different cutting conditions. The results show that hydrostatic pressure significantly increases the cutting force and MSE compared with cutting results under atmospheric pressure. In addition, different lithology of rocks leads to the different changing trends of cutting force with hydrostatic pressure and affects the pore pressure and differential pressure under hydrostatic pressures. Besides, the smoother cutting grooves and fragmentary cuttings are obtained with increased hydrostatic pressure during cutting and the mud phenomenon of cuttings is witnessed. Furthermore, the fluctuation of cutting force curve and the number of peaks and valleys in cutting force curve reveal the failure behaviour and energy change of rock during cutting. In general, the distance between peaks or valleys is small and more peaks and valleys are obtained when rock suffers ductile failure. Meanwhile, the energy absorption time of rock is shorter and the small-sized cuttings are obtained. Conversely, the distance between peaks or valleys is large and less peaks and valleys are produced when rock suffers brittle failure and the energy absorption time of rock is longer and large-sized cuttings are obtained. Although hydrostatic pressure tends to change the failure mode of rock from brittle to ductile, the number of peaks and valleys in the cutting force curves obtained under hydrostatic pressures is less. The experimental results provide a new understanding of the failure behaviour of rocks and cutter–rock interaction under different cutting conditions. Highlights: Rocks cutting experiments with three kinds of rocks under confining and hydrostatic pressures were conducted to truly simulate the rock-breaking process of bit at the bottom of the well. The rock-breaking performance of PDC single cutter under hydrostatic pressures was analyzed from the aspects of mechanical specific energy, cuttings, cuttings morphology and cutting groove. The rock failure behaviour and the cutter–rock interaction under hydrostatic pressures were studied from the perspectives of fluctuation of cutting force curve, cuttings formation process and energy change during cutting process. The influence of lithology on failure process and pore pressure of rock was initially investigated through rock soaking experiments. [ABSTRACT FROM AUTHOR]

This study introduces a simplified method for predicting the optimal cutting conditions to maximize excavation efficiency based on tool forces. A laboratory-scale linear rock-cutting test was conducted using a conical pick on Finike limestone. The tool forces and their ratios were analyzed in relation to cutting parameters such as penetration depth and spacing. While the cutting force (FC) and normal force (FN) increased with the penetration depth and spacing, this relationship could not predict the optimal cutting conditions. The ratio of the mean normal force to the mean cutting force (FNm/FCm) increased with the penetration depth and the ratio of spacing to penetration depth (s/d). However, even while including this relationship, predicting optimal cutting conditions remained challenging. The ratio of the peak cutting force to the mean cutting force (FCp/FCm) reached a maximum value at a specific s/d, which is similar to the relationship between the specific energy (SE) and s/d. The optimal s/d obtained through the SE methodology was found to be between 3 and 5, and FCp/FCm reached a maximum at s/d. The error between the optimal s/d and the s/d in which FCp/FCm was maximized was less than 5%. Therefore, it was confirmed that the optimal cutting conditions could be predicted through the relationship between FCp/FCm and s/d. Additionally, by using the results from previous studies, the optimal cutting conditions obtained from the SE methodology and the proposed methodology were found to agree within a margin of error of 20%. The proposed methodology can be beneficial for the design of cutter heads and the operation of excavation machines. [ABSTRACT FROM AUTHOR]

Preconditioning of rock for drilling operations is a potential method to facilitate the mechanical breakage and mitigate the tool wear. This paper numerically investigates one such preconditioning technique, namely, the thermal jet assisted rock cutting. For this end, a numerical method for solving the governing thermo‐mechanical problem is developed and validated. The continuum approach is chosen to describe the rock failure, being based on a damage‐viscoplasticity model with the Drucker–Prager yield surface and the modified Rankine surface as the tensile cut‐off. In the damage part, separate scalar damage variables are employed for tension and compression. The cutters are modelled as rigid bodies and their interaction with the rock is modelled by imposing contact constraints by the forward increment Lagrange multiplier method, which is compatible with the chosen explicit time integration scheme. A damage‐based erosion criterion is applied to remove the contact nodes surrounded by heavily damaged elements. The thermal jets are modelled with a moving external heat flux boundary condition. The global thermo‐mechanical problem is solved with a staggered approach explicitly in time while applying mass scaling to increase the critical time step. The novel 3D numerical simulations involving two cutters demonstrate the capabilities of the method with a special emphasis on cutter‐thermal jet configurations. Therefore, the present method provides a potential tool for the bit design in thermal jet assisted drilling. [ABSTRACT FROM AUTHOR]

Rock abrasivity influences wear of cutting tools and consequently, performance of mechanized tunneling machines. Several methods have been proposed to evaluate rock abrasivity in recent decades, each one has its own advantages. In this paper, a new method is introduced to estimate wear of disc cutters based on rock cutting tests using scaled down discs (i.e. 54 and 72 mm diameter). The discs are made of H13 steel, which is a common steel type in producing real-scale discs, with hardness of 32 and 54 HRC. The small-scale linear rock cutting machine and a new abrasion test apparatus, namely University of Tehran abrasivity test machine, are utilized to perform the tests. Tip width of the worn discs is monitored and presented as the function of the accumulated test run to classify the rock abrasion. Abrasivity tests show that by increasing the uniaxial compressive strength (UCS) of the rock samples, wear rate is doubled gradually that reveals the sensitivity of the test procedure to the main parameters affecting the abrasivity of hard rocks. For the rocks with the highest UCS, the normal wear stops after performing 5 to 10 rounds of the tests, and then, deformation of the disc tip is detectable. Two abrasivity indices are defined based on the abrasivity tests results and their correlations with Cerchar Abrasivity Index (CAI) and UCS are established. Comparison of the established correlations in this study with previous investigations demonstrates the sensitivity of the indices to the parameters affecting wear of the disc cutters and repeatability of the outputs obtained from abrasivity tests using scaled down discs. Findings of this study can be used to enhance the accuracy of rock abrasivity classifications. [ABSTRACT FROM AUTHOR]

Rock abrasivity influences wear of cutting tools and consequently, performance of mechanized tunneling machines. Several methods have been proposed to evaluate rock abrasivity in recent decades, each one has its own advantages. In this paper, a new method is introduced to estimate wear of disc cutters based on rock cutting tests using scaled down discs (i.e. 54 and 72 ​mm diameter). The discs are made of H13 steel, which is a common steel type in producing real-scale discs, with hardness of 32 and 54 HRC. The small-scale linear rock cutting machine and a new abrasion test apparatus, namely University of Tehran abrasivity test machine, are utilized to perform the tests. Tip width of the worn discs is monitored and presented as the function of the accumulated test run to classify the rock abrasion. Abrasivity tests show that by increasing the uniaxial compressive strength (UCS) of the rock samples, wear rate is doubled gradually that reveals the sensitivity of the test procedure to the main parameters affecting the abrasivity of hard rocks. For the rocks with the highest UCS, the normal wear stops after performing 5 to 10 rounds of the tests, and then, deformation of the disc tip is detectable. Two abrasivity indices are defined based on the abrasivity tests results and their correlations with Cerchar Abrasivity Index (CAI) and UCS are established. Comparison of the established correlations in this study with previous investigations demonstrates the sensitivity of the indices to the parameters affecting wear of the disc cutters and repeatability of the outputs obtained from abrasivity tests using scaled down discs. Findings of this study can be used to enhance the accuracy of rock abrasivity classifications.

The cutting tools in mining industry are especially prone to rapid wear, since most of the rocks exhibit aggressive abrasion attributes. A typical representative of fast wearing mining end-tools is a conical pick (also known as tangential-rotary cutter). In order to decrease the premature deterioration, the manufacturers and users tend to enhance the lifespan of the tool by wide range of approaches, namely heat treatment, chemical treatment, burnishing, hardfacing etc. In order to estimate the wear rate of a given pick one has to select appropriate procedure and method of evaluation. By this time, most commonly applied method is to estimate the wear rate basing on mass loss measurements of the tools being exploited with constant cutting parameters and fixed conditions. The Authors proposed also a new method of volumetric wear assessment, basing of three-dimensional photogrammetric scanning and compared the results with the outcome of traditional mass wear evaluation of the same sets of tools. Additionally, this paper contains recommendations regarding both approaches (volumetric and mass), especially focusing on the possibilities of the new method concerning measurements of the manufactured tool.

This study introduces a simplified method for predicting the optimal cutting conditions to maximize excavation efficiency based on tool forces. A laboratory-scale linear rock-cutting test was conducted using a conical pick on Finike limestone. The tool forces and their ratios were analyzed in relation to cutting parameters such as penetration depth and spacing. While the cutting force (FC) and normal force (FN) increased with the penetration depth and spacing, this relationship could not predict the optimal cutting conditions. The ratio of the mean normal force to the mean cutting force (FNm/FCm) increased with the penetration depth and the ratio of spacing to penetration depth (s/d). However, even while including this relationship, predicting optimal cutting conditions remained challenging. The ratio of the peak cutting force to the mean cutting force (FCp/FCm) reached a maximum value at a specific s/d, which is similar to the relationship between the specific energy (SE) and s/d. The optimal s/d obtained through the SE methodology was found to be between 3 and 5, and FCp/FCm reached a maximum at s/d. The error between the optimal s/d and the s/d in which FCp/FCm was maximized was less than 5%. Therefore, it was confirmed that the optimal cutting conditions could be predicted through the relationship between FCp/FCm and s/d. Additionally, by using the results from previous studies, the optimal cutting conditions obtained from the SE methodology and the proposed methodology were found to agree within a margin of error of 20%. The proposed methodology can be beneficial for the design of cutter heads and the operation of excavation machines.

In order to study the mechanism of crack propagation in rock cutting, experiments and discrete element numerical simulation of rock cutting at different depths were adopted in this paper. The rock fragmentation can be divided into mini-size fragmentation and normal-size fragmentation from a size viewpoint. The discrete element method (DEM) is used to further investigate the mechanism of normal size fragmentation at different depths and record the process of crack initiation and propagation. Additionally, the paper characterizes the process of crack initiation and examines the representative rock fragmentation. According to the mechanism of crack development, rock fragmentation can be divided into three categories: conventional failure, fracture failure, and damage failure. The fragmentation of three kinds of failure has one common point. To form semi-dislodged rock fragmentation, the macroscopic shear cracks are first formed. Subsequently, the tensile failure at weak places causes fragmentation ejection. Therefore, the mechanism of fragmentation generation in rock cutting is investigated in terms of crack initiation and extension. In this study, the fracture phenomenon of previous rock cutting experiments is reproduced by an experiment, and the failure process is analyzed in detail by the discrete element method, which reveals the essence of producing fragment phenomena and summarizes the fracture phenomenon and damage crack propagation mechanism in rock cutting. [ABSTRACT FROM AUTHOR]

In this study, actual laboratory rock cutting tests on sandstone specimens that were performed at NTUA's Laboratory of Excavation Engineering were simulated numerically with the use of a 3D bonded particle DEM model implemented in Yade. The numerical assembly was calibrated to closely match the macroscopic strength, Young's modulus, and brittleness of the real material, by controlling the grain interlocking through careful selection of the appropriate value for the interaction range coefficient. The calibrated model was then used to examine the effect of the microparameters' values on the cutting force history and the failure mechanism. The Fast Fourier Transformation was used to compare the characteristics of the simulated cutting force data with those from the actual cutting tests. It was found that for high values of the interaction range coefficient the numerical model showed a more brittle behaviour, while for low values the simulation behaved more realistically for the specific type of rock. It is concluded that the use of the interaction range coefficient can substantially provide more realistic simulations of the cutting process by capturing both the rock-cutting tool interaction and the failure mechanism. [ABSTRACT FROM AUTHOR]

As a cost-effective method for formation evaluation, analysis of rock cuttings provides essential information on petrophysical rock properties that help reservoir engineers to understand the reservoir's behavior. Gradually, researchers have started paying greater attention to utilizing rock cuttings for formation evaluation, as it is a cost-effective substitute for collecting subsurface core samples. This work focuses on porosity measurement from rock cuttings. The proposed objective of obtaining representative porosity values from rock cuttings was achieved by comparing porosity data from different sizes of cuttings to reference porosity values measured from core samples. Seven different sandstone core samples were considered for the study, and reference porosities were measured. Additionally, rock permeability values were determined for the core samples to investigate the effect of permeability on porosity derived from rock cuttings. The cuttings were then classified according to their permeability and sieve sizes. The cuttings' porosity was measured using their grain and pore volumes, which, in turn, were estimated using grain density and gravimetric method, respectively. A systematic comparison of cutting-derived porosity and reference porosity values with desaturation time was made in the end, using the sieve size of cuttings as a sensitivity parameter. The results were also analyzed for rock permeability sensitivity, using permeability values from initial data. The results demonstrate that the method utilized for estimating porosity using rock cuttings in this study yields practically acceptable values that are in close agreement with reference porosities from core samples. However, the size of cuttings significantly affects porosity determination, with deviation from reference values increasing as the size of cuttings decreases. Also, the interstitial saturation fluid is responsible for greater deviations as smaller cuttings have a greater surface area-to-volume ratio. The study results show that rock permeability affects porosity determination from cuttings and should be considered during such analyses. [ABSTRACT FROM AUTHOR]

Highlights: Effect of the spring on the conical pick rotation was investigated experimentally for the first time. The combination of spring and conical picks resulted in higher amounts of rotation especially for 5 mm cutting depth. A precise conclusion was not drawn about the effect of the skew angle on rotation. 4% of permanent deformation was observed on the spring as a result of 124 cutting tests. [ABSTRACT FROM AUTHOR]

The abrasive and rock properties have a significant impact on the performance and profitability of abrasive water jet (AWJ) cutting. In the relevant literature, there is no comprehensive study that investigates the effects of abrasive type on the AWJ cutting of rocks. As a result, in the current study, various abrasives (garnet, white fused alumina, brown fused alumina, glass beads, emery powder, olivine, steel shot, and plastic granule) were used in tests where workpieces prepared from various rock types (igneous, metamorphic, and sedimentary) were cut with AWJ. The cutting parameters were kept constant during the cutting operations. The cutting depth was taken into account when evaluating the AWJ performance. It was revealed that garnet, steel shot, and fused alumina (brown and white) have higher cutting abilities (cutting depth: 39.23–125.94 mm by the rock type). Compared to them, olivine, emery powder, and glass bead produced shallower cuts (21.11–80.00 mm by the rock type). Despite this, effective cutting did not occur with plastic granules. It was demonstrated that there are strong correlations between the cutting depth-abrasive hardness (up to r: 0.82 by rock type) and cutting depth-abrasive density (up to r: 0.87 by rock type). It was determined that the cutting depth increases as the Bohme abrasion loss, effective porosity, and water absorption capacity of the rocks increase. It was also found that the cutting depth decreases as the strength, Schmidt hardness, unit volume weight, and ultrasonic wave velocity of the rocks increase. The most essential rock properties influencing cutting depth were determined as the Bohme abrasion loss, uniaxial compressive strength, and point load strength. [ABSTRACT FROM AUTHOR]

In this paper, acoustic emission (AE) method was used to differentiate three concretes having different strengths in laboratory. Cutting tests under different conditions in full-scale cutting testing rig coupled with AE measurements were realised. AE measurements were evaluated by means of magnitude. Afterwards, moving maximum algorithm was utilised to process AE signals, and processed plots were employed to create surface contour plots. It was clearly seen that AE measurements can be used to differentiate materials being cut in terms of strength differences, such that higher strength concrete yielded higher magnitudes of AE signals where lower strength concrete showed lower magnitudes. [ABSTRACT FROM AUTHOR]

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Featured Application: The presented method can be used to estimate the energy consumption of hydraulic drills and chain saw machines in the extraction of natural stone. A method based on extensive laboratory and field measurements was developed to determine the dependence of specific rock cutting energy (SEc) on specific drilling energy (SEd) for machines with different operating and design characteristics and similar breaking mechanics. Laboratory measurements were performed on a linear rock cutting device and a laboratory drill, using a measurement system to measure electrical power and cutting forces using force/torque transducers. Field power consumption measurements were performed on a chainsaw cutting machine and a hydraulic rotary drill under real working conditions in the dimension stone quarries. The analysis of the measured results confirmed the strong dependence of the specific rock cutting energy on the specific drilling energy and confirmed that laboratory devices can be used to simulate actual rock cutting and drilling process. In addition, the results are applicable in the dimension stone exploration and exploitation phase in order to assess and reduce energy consumption by optimizing the operating parameters of the chain cutter and/or the hydraulic rotary drill. [ABSTRACT FROM AUTHOR]

The relevance of the work is justified by the need to study interaction of cutting elements of modern PDC (Polycrystalline Diamond Compact) bits with rock, and, as a result, the presence of various approaches in the world scientific centers to assess the mechanism of dynamic penetration of PDC cutters into rocks during well drilling. The purpose: detailed analysis of the current state and prospects for the development of scientific research for a comprehensive assessment of the dynamic processes of rock cutting with PDC bits. Methods: theoretical analysis of the problems of the efficiency of rock destruction by cutters and modern PDC bits; application of mathematical and physical modeling of rock cutting processes, fluctuation theory of solid strength to describe the patterns of rock behavior during the operation of PDC cutters; comparative assessments of the study of processes and mechanisms of static and dynamic embedding when cutting rock with single elements and PDC bits, based on research conducted by the world's leading scientific schools in this field. Results. The paper introduces the results of research conducted by the world's leading schools on various fundamental aspects of the interaction of the executive bodies of PDC bits with destructible rocks. It is revealed that many research results give a complete qualitative picture of the work of PDC drill bits. However, there are not many most important and accurate quantitative characteristics of rock cutting processes with modern PDC chisels in the scientific literature. The ways of development of new methods of increasing the efficiency of rock cutting based on more accurate methods of assessing their behavior during cutting by PDC bits are considered. One of the considered promising techniques allows us to experimentally obtain a characteristic of the «dynamic hardness of rocks», which can be successfully used for the design of drilling modes and the design of PDC bits.

• A DEM-based model for rock indentation testing using a conical pick is established. • The mechanisms of rock breakage under conical pick indentation are elucidated. • The effects of three cutting parameters (cone angle, attack angle and cutting depth) on rock breakage are analyzed. • The optimal cutting parameters for achieving the optimal rock breakage performance with a conical pick are proposed. To comprehensively understand the effects of roadheader cutting parameters on rock breakage, this paper conducts a numerical investigation of rock vertical indentation tests using a conical pick, utilizing the discrete element method (DEM). Three crucial cutting parameters, including cone angle, attack angle, and cutting depth, are analyzed as independent variables to elucidate their impact on rock breakage characteristics, such as peak cutting force and specific energy. The research results indicate that the ultimate failure of rock is primarily caused by the accumulation of microcracks from each local fracture, predominantly governed by tensile failure. As the cone angle increases, both the peak cutting force and specific energy exhibit a monotonic upward trend, while the maximum stress at the tip of the conical pick shows a fluctuating pattern. To achieve a balance between cost effectiveness and efficient rock breakage, an optimal cone angle range of 55° to 100° is recommended. The peak cutting force and specific energy decease exponentially as the attack angle increases, with an optimal range of 70° to 90°. Under continuous cutting conditions with a fixed total length of 60 mm, the average peak cutting force increases with cutting depth, while the average specific energy initially decreases and then increases, identifying an optimal cutting depth of 20 mm. These findings have significant engineering implications for optimizing the cutting parameters of roadheader to enhance the efficiency of mechanized excavation. [ABSTRACT FROM AUTHOR]

The mining sector seeks innovation to enhance operational efficiency and prolong cutting tool life. This research investigates the impact of cryogenic treatment (CT) for 12, 24, and 36 h on tungsten carbide cutting bits used in mine machineries, focusing on its effects on cutting force, energy consumption, and tool wear during lab-scale linear rock cutting. Microstructural analysis and hardness testing follow CT, revealing improvements in hardness, the formation of new compounds, and the presence of eta carbides. Analysis of linear rock cutting experiments shows that longer holding periods under CT lead to reduced cutting force, energy consumption, and tool wear. Comparing CT 24 to untreated bit at a cutting speed of 200 m/s, CT 24 demonstrates reduction in specific energy by 39.35 %, 41.13 %, and 29.39 % at depth of cut (DoC) of 2 mm, 4 mm, and 6 mm, respectively. Additionally, CT 24 exhibits significantly lower wear rates (79.24 %, 85.44 %, and 85.01 %) compared to UT bits at the same cutting speed. Microstructural analysis identifies multiple wear mechanisms in both treated and untreated worn tools. To optimize the cutting process for mining efficiency, grey relational analysis and Python-based non-dominant sorting are employed. Grey relational analysis identifies 24-h CT, a cutting speed of 200 m/s, and a 2 mm depth of cut as optimal. Non-dominant sorting suggests 24-h CT, a cutting speed of 200 m/s, and 2–4 mm cut depth for optimal results. Pareto solutions indicate specific energy ranging from 14.96 to 9.20 kWh/m3 and wear rates ranging from 0.33 to 0.39 × 10−4 cm3/cm. Insights from this study offer valuable guidance for the mining industry to enhance cutting tool efficiency and promote environmentally sustainable mining practices. • Cryogenic treatment resulted in reduced specific energy and wear rate during lab-scale rock cutting • Primary drivers behind the enhanced performance were microstructural modifications and improvements in hardness. • A 24 h holding duration of cryogenic treatment demonstrated superior performance across various cutting parameters. [ABSTRACT FROM AUTHOR]

The linear cutting process in rock poses challenges for verification in field experiments, laboratory investigations, or numerical simulations. This study aims to analyze the rock cutting process and disc cutter force estimation when using linear cutting mode. Three-dimensional numerical simulations using the explicit dynamic finite element method (LS-DYNA software) are conducted to characterize the cutting process. In this regard, two computational algorithms (Lagrangian and Smoothed Particle Hydrodynamics (SPH)) and two material models (Johnson-Holmquist Concrete (JHC) and Riedel-Hiermaier-Thoma (RHT)) are compared, with SPH and RHT identified as more suitable for rock cutting simulation. The results of comparative analyses show that the Lagrangian computational algorithm is highly dependent on the erosion value, hence this method is not suitable for the simulation of the rock-cutting process. Comparing to the RHT material constitutive model, the Johnson-Holmquist model does not well model the post-failure softening strain behavior, which leads to a reduction in the width of the failure area. The comparative analyses also show that the normal and rolling forces predicted by the JHC model are well over 30% higher than the actual experimental results, while the RHT model shows a good agreement between the predictions and the actual results. Overall, the RHT material model with the use of the SPH computational algorithm shows a very good combination in rock cutting process simulation. [ABSTRACT FROM AUTHOR]

In order to study the mechanism of crack propagation in rock cutting, experiments and discrete element numerical simulation of rock cutting at different depths were adopted in this paper. The rock fragmentation can be divided into mini-size fragmentation and normal-size fragmentation from a size viewpoint. The discrete element method (DEM) is used to further investigate the mechanism of normal size fragmentation at different depths and record the process of crack initiation and propagation. Additionally, the paper characterizes the process of crack initiation and examines the representative rock fragmentation. According to the mechanism of crack development, rock fragmentation can be divided into three categories: conventional failure, fracture failure, and damage failure. The fragmentation of three kinds of failure has one common point. To form semi-dislodged rock fragmentation, the macroscopic shear cracks are first formed. Subsequently, the tensile failure at weak places causes fragmentation ejection. Therefore, the mechanism of fragmentation generation in rock cutting is investigated in terms of crack initiation and extension. In this study, the fracture phenomenon of previous rock cutting experiments is reproduced by an experiment, and the failure process is analyzed in detail by the discrete element method, which reveals the essence of producing fragment phenomena and summarizes the fracture phenomenon and damage crack propagation mechanism in rock cutting.

Conical picks are widely used as cutting tools in shearers and roadheaders, and the mean cutting force (MCF) is one of the important parameters affecting conical pick performance. As MCF depends on a number of parameters and due to that the existing empirical and theoretical formulas and numerical modelling are not sufficient enough and reliable to predict MCF in a proficient manner. So, in this research, a novel intelligent model based on a random forest algorithm (RF) and a heuristic algorithm called the salp swarm algorithm (SSA) have been applied to determine the optimal hyper-parameters in RF, and root mean square error is used as a fitness function. A total of 188 data samples including 50 rock types and seven parameters (tensile strength of the rock σt, compressive strength of the rock σc, cone angle θ, cutting depth d, attack angle γ, rake angle α and back-clearance angle β) were collected to develop an SSA-RF model for mean cutting force prediction. The prediction results of the SSA-RF model were compared with seven influential formulas and four classical models, such as random forest, extreme learning machine, support vector machine and radial basis function neural network. The mean absolute error (MAE), root mean square error (RMSE), mean absolute percentage error (MAPE) and Pearson correlation coefficient (R2) were employed as evaluation indexes to compare the capability of different predicting models. The MAE (0.509 and 0.996), RMSE (0.882 and 1.165), MAPE (0.146 and 0.402) and R2 (0.975 and 0.910) values between measured and predicted MCF for training and testing phases of the SSA-RF model clearly demonstrate the superiority in prediction compared to the other tools. A sensitivity analysis has also been performed to understand the influence of each input parameter on MCF, which indicates that σc, d and σt are the most important variables for MCF prediction.

The current paper is prepared with the objective of providing experimental evidence that the internal friction angle of rocks can be assessed using a scratch test with a blunt polycrystalline diamond compact (PDC) cutter. For this purpose, a comprehensive set of cutting experiments was carried out to determine the wear flat-rock friction coefficient in two limestones and one coarse-grained sandstone using state-of-the-art scratch based rock cutting equipment. Additional triaxial compression (TC) experiments were conducted on specimens of these rock formations, and a Coulomb failure analysis was conducted to independently estimate the internal friction coefficient of each specimen. The experimental results indicate that the value of internal friction angle (intrinsic rock property) derived from TC experiments is related to the apparent friction angle at the wear flat-rock interface of the blunt PDC cutter when the wear flat surface is inclined at inclination angles ranging between 0 ∘ to 1 ∘ . Further, new results on one rock specimen were obtained by performing novel scratch tests with blunt PDC cutters with different wear flat properties, showing that the apparent friction angle at the wear flat-rock interface of a blunt cutting tool is significantly affected by the wear flat roughness and the wear flat material properties. Highlights: A new method was introduced to measure the internal friction angle of rock samples using rock cutting/drilling data. An extensive set of cutting experiments was conducted using different PDC blunt/worn cutters. The internal friction angle of rock specimens were obtained using triaxial compressrion (TC) tests. The internal friction angles of rock specimens were related to the apparent friction angles at the wear flat-rock interface when the wear flat surface is parallel to the rock free surafce. The wear flat properties of the PDC cutters have a significant effect on the apparent friction angle. [ABSTRACT FROM AUTHOR]

The poor drill-ability of rock in deep hard formation leads to the problems of low rate of penetration (ROP) and high drilling cost. A detailed understanding of the rock-tool interaction is of great significance for improving the rock breaking efficiency and optimizing the cutting parameters. For this purpose, this paper establishes a numerical model of heterogeneous granite which considers the influence of mineral distribution and real grain structure. The fracture behaviors of granite under tool cutting and indentation are investigated subsequently. It is found that there are always four kinds of microcracks in granite, intragranular tensile crack, intragranular shear crack, intergranular tensile crack and intergranular shear crack, among those four crack types, the intergranular tensile crack and intragranular shear crack are dominated, almost no intergranular shear cracks occur. Lateral pressure has no great influence on the volume of cutting chips in rock cutting, but is the direct factor that affects the rock-breaking efficiency in rock indentation. The initiation and propagation of radial cracks will be obviously inhibited in large lateral pressure, and the number of radial cracks will decrease sharply, resulting in low rock-breaking efficiency. Lateral pressure seems to have little effect on the indentation force, the possible reason for this lateral pressure insensitivity is because the far-field lateral pressure has less influence on the indenter tip around field than the existence of free surface. The research results can provide the basis for improving granite rock-breaking efficiency and optimizing rock-breaking tools to a certain extent. [ABSTRACT FROM AUTHOR]

A rock sample was obtained from an underground lignite mine for the investigation of the cutting characteristics of a ductile rock where the heading is achieved with a roadheader. The rock sample (metasiltstone) was classified according to a pertinent brittleness classification by means of its compressive strength to tensile strength ratio. Two types of drag picks are used for the execution of the experimental campaign on core and block samples of the metasiltstone. The cutting force, the specific energy and the breakout angle variables were investigated. The cutting force-distance histories of cutting trials were compared with the present literature. It was seen that even an extremely ductile rock sample exhibited the characteristics of brittle cutting regime.

The usage of polycrystalline diamond compact (PDC) drill bit has significantly increased in the petroleum industry due to its high rate of penetration and long life. However, it is becoming increasingly difficult to ignore the temperature effect to PDC bit, specifically its cutter during the drilling operation. Temperature causes the degradation of the PDC cutter by reducing its lifespan. A thorough understanding of factors that affect the temperature of the PDC cutter is crucial in predicting the optimum cutting parameters. Hence, it is the objective of this study to evaluate the effect of cutting parameters on the temperature of the single PDC cutter in rock cutting. In this study, a rock cutting experiment was conducted by using a lathe machine tested on single PDC cutter. The parameters involve were rotational speed and depth of cut. The temperature was captured using an infrared thermographic camera, FLIR T640 and the spot measurement was used to pinpoint the temperature readings at the tooltip of PDC cutter. It was found that the depth of cut had the greater influence on temperature when measured over a range of 16 levels as the temperature increase in linear trend with increasing depth of cut as well as the high correlation of the plot (R2=0.98). However, tests for rotational speed showed less significant influence on temperature when measured over a range of four levels where the percentage error of the temperature for each rotational speed was less than 10%. It can be concluded that only the depth of cut has a significant effect on the temperature of a single PDC cutter.

A method based on extensive laboratory and field measurements was developed to determine the dependence of specific rock cutting energy (SEc) on specific drilling energy (SEd) for machines with different operating and design characteristics and similar breaking mechanics. Laboratory measurements were performed on a linear rock cutting device and a laboratory drill, using a measurement system to measure electrical power and cutting forces using force/torque transducers. Field power consumption measurements were performed on a chainsaw cutting machine and a hydraulic rotary drill under real working conditions in the dimension stone quarries. The analysis of the measured results confirmed the strong dependence of the specific rock cutting energy on the specific drilling energy and confirmed that laboratory devices can be used to simulate actual rock cutting and drilling process. In addition, the results are applicable in the dimension stone exploration and exploitation phase in order to assess and reduce energy consumption by optimizing the operating parameters of the chain cutter and/or the hydraulic rotary drill.

Hot dry rock (HDR) is an important renewable energy resource within the overall energy mix. However, its popularization is restricted by drilling costs due to the high hardness and abrasiveness of the rock. As a type of cryogenic fluid, liquid nitrogen (LN2) could aggravate the damage of high-temperature rocks and provide a novel insight in improving the drilling efficiency of HDR. To investigate the rock failure process under the joint action of cutting and jet impingement, a series of experiments were conducted in the present paper. The cutting force was monitored in real-time to evaluate the characteristics of rock-breaking. Then, the 3D topography of cutting grooves was analyzed to determine the rock failure modes (brittle failure or ductile failure). Finally, the rock failure mechanism was investigated by observing micro-structures of cutting grooves including cracks on surfaces and inside the rock. Results indicate that rock strength degrades obviously during the heating process, resulting in a 31.13% decrease in normalized cutting force (F). Meanwhile, the brittle failure of rocks is enhanced at elevated temperatures. This phenomenon can be validated by the fluctuation of cutting force and roughness of cutting grooves. The jet impact can induce thermal stress, thereby, further intensifying the volumetric breakage of rocks. Compared with the water jet, the LN2 shows better performance in improving the rock-breaking efficiency due to its cryogenic feature and lower viscosity. The F reduces by 43.96 and 52.53% with the assistance of water jet and LN2 jet, respectively. Besides, micro-cracks generate with the increasing temperature. The fluid penetrates the rock along these cracks, which rises the width of subsurface cracks and facilitates the subsequent rock cutting. [ABSTRACT FROM AUTHOR]

Rock excavation is a dynamic process where rock is dynamically loaded by mechanical cutting tools. Previous researches have shown that rock strength in dynamic loading is greater than that in static loading. However, existing prediction models for mechanical excavation of rock do not take into account the dynamic features of the rock. This issue has the potential to deliver misleading outcomes when estimating cutting performance and assigning an equipment for excavation work. The mechanical cutting issue was explored from a dynamic standpoint in this paper. To begin, the dynamic level of mechanical cutting was studied with multiple attempts and was shown to be at intermediate strain rate (ISR). Then, experiments were designed to determine dynamic mechanical properties via a loading device powered by a non-explosive powder reaction capable of creating dynamic loading in the ISR range. Furthermore, numerical simulation of pick cutting using the finite element technique was carried out, incorporating dynamic and quasi-static parameter settings. Also, a laboratory linear cutting test was conducted under various cutting configurations to validate the numerical results. The numerical simulation with quasi-static inputs was shown to be less accurate than the modeling with dynamic inputs. The simulation with dynamic inputs matches the laboratory findings closer by exhibiting a narrower margin. Thus, this study offers a unique view of evaluating mechanical excavation issues from a rock dynamic perspective. [ABSTRACT FROM AUTHOR]

In recent years, the use of natural stone, especially in the construction sector, has increased as a result of rapid economic development. One of the most important cost parameters in natural stone cutting processes is energy costs. Generally, cut granites with block cutters differ from other rocks in terms of both the cutting machines used and the energy consumed. Increases in energy prices and emission reduction requirements require cutting processes to work most efficiently. This article describes the energy consumption process in a stone processing plant, and makes recommendations to decision-makers for the more efficient use of energy. A total of 456 real cutting tests were conducted at three different cutting depths and at three different feed rates using a multi-blade block cutter with 10 saw blades at a plant with a monthly production capacity of over 4000 square meters. Real time energy consumption values were recorded with the help of a power analyzer installed on the control panel of the block cutter. The obtained data were used to calculate specific cutting energy values, and the energy consumed throughout the entire process was analyzed. The energy consumption values as the saw blade moves back and forth were examined in eight different regions, starting with the first phase in which the saw blade approaches the granite block. From the obtained power consumption values and calculated specific cutting energy values, an approach has been introduced in terms of cutting efficiency to the specific cutting energy values and energy consumption characteristics in rock cutting processes using circular saw blade. [ABSTRACT FROM AUTHOR]

High-energy laser beams have a powerful ability to induce rock fragmentation, but there is still a lack of suitable calculation methods to quantitatively predict the laser-induced rock cutting slit depth. This work aims to provide a new predictive model for the quantitative determination of the laser rock cutting slit depth. In this paper, based on the energy consumption model of laser-induced rock breaking, the prediction model of laser cutting slit depth is creatively established by comprehensively considering the factors affecting laser cutting slit depth, such as laser power, moving speed, and spot radius. Then, relying on the three kinds of rocks exposed in the second phase of the Xinjiang water supply project, which is the longest water conservancy tunnel in the world, the prediction model is verified by laboratory tests, and the variation rules of slit depth, width and specific energy with laser parameters are explored. The results show that the slit depth of laser rock cutting is directly proportional to the laser power and inversely proportional to the moving speed and the defocusing amount. The prediction error for cutting slit depth of the model is less than 10% for palimpsest alkali feldspar granite, and less than 15% for granitic shallow granulite and siliceous schist. Under the same laser condition, the cutting slit depth of siliceous schist is about 25% larger than that of the other two kinds of rocks for its high content of plagioclase. The prediction model and experimental rules proposed in this paper are expected to further promote the application of laser cutting technology in the field of auxiliary TBM rock breaking. [ABSTRACT FROM AUTHOR]

Steel shots are suitable for abrasive waterjet rock cutting and recycling because of the high hardness and magnetic properties of steel. This study evaluated the rock-cutting performance and recycling characteristics of steel shot waterjet. The rock-cutting responses of steel shot and garnet were compared at the same waterjet conditions. The used steel shot was collected and the particle-size changes were evaluated before reuse, and its cutting performance was re-evaluated. Overall, the steel shot waterjet yielded improvements in performance in the range of 30–50% compared with the garnet waterjet. Moreover, the recycled steel shot yielded a 50% reduction in cutting performance. Rust was observed on the surface of the used steel shot, the used steel shots were partially destroyed, and the debris on the abrasive surface needed to be removed by drying. The reusable steel shot left on the 80th sieve converged to 60% in each recycling run. The results of this study can be used to reduce the cost of abrasive waterjet and industrial waste. [ABSTRACT FROM AUTHOR]

The abrasive mixing variables, such as the abrasive and water flow rates and the focus geometry parameters, determine the profitability of an abrasive waterjet system. In this study, the mixing efficiency characteristics in abrasive waterjet rock cutting were investigated. To demonstrate comprehensively the efficiency reduction due to collision during abrasive mixing, the chance of collision was expressed as the distance between the abrasive particles in the focus. The mixing efficiency was then assessed by utilizing the empirical relationship between the experimental results and the developed model. Based on the particle density and the velocity, the closer particles showed higher chances of collision, thus yielding a reduced cutting performance. Using the distance between particles model, the optimum abrasive flow rate and the cutting performance of abrasive waterjet systems can be estimated. This developed model can be used for the design selection of abrasive flow rate and systems for the cost-effective use of abrasive waterjets. [ABSTRACT FROM AUTHOR]

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 that rock uniaxial compressive strength can be reliably evaluated from disc cutter cutting forces, but the estimation results for rock Brazilian tensile strength are not so good. This study is pertinent to the better understanding of the disc cutter behaviors in cutting rocks of different strengths and can improve the geological information acquisition and operation control during TBM tunneling. [ABSTRACT FROM AUTHOR]

Various numerical methods have been used to simulate the rock cutting process. Numerical simulation is a useful tool for estimating the performance of a cutting tool and for understanding the mechanism of rock cutting and interaction between a cutting tool and the rock. These methods supplement the rock cutting test, which is commonly referred to as the linear cutting machine (LCM) test. Mechanical excavators, such as roadheaders, longwall shearers, and trenchers, generally use pick cutters as the cutting tool. In this study, a rock cutting simulation with a pick cutter was developed using the smooth particle hydrodynamics (SPH) technique, which is a mesh-free Lagrangian method. The Drucker–Prager (DP) strength model was used to simulate the brittle behavior of rock. The cumulative damage (CD) model was used to simulate the degraded fragmentation process of rock and the distinctive behavior of rock in the compression and tensile stress regions. In this study, an attempt was made to simulate sequential cutting by multiple pick cutters. The results showed that the numerical simulation matched the experimental results closely in terms of cutter forces, specific energy, and the fragmentation phenomenon. These results confirmed the applicability of the SPH technique in simulating the rock cutting process. [ABSTRACT FROM AUTHOR]

Aiming at the problem of rock cutting fragmentation, large-scale cutting model test was carried out with sandstone, cutting fragment information was captured by high-power digital camera, and the fractal distribution characteristics of cutting fragments were analyzed by image analysis technology combined with fractal theory. The influence of cutting angle and cutting depth on fractal of cutting fragments was studied. The experimental results show that the fragment-size distribution of fragments has fractal characteristics, when using the perimeter -area method to calculate, the fractal dimension of test fragments is concentrated in 1.07-1.25. The fractal dimension has a good linear relationship with cutting depth and decreases with the increase of cutting depth. The relationship between fractal dimension and cutting angle can be fitted by quadratic function, with the increase of the cutting depth, the quadratic coefficient of the fitting function increases, and it changes from negative value to positive value at a certain cutting depth. [ABSTRACT FROM AUTHOR]

Theoretical explanation of rock cutting mechanism with a conical pick is a very difficult task due to inherent complexities in the cutting action. Furthermore, previous studies evidently showed that theoretical models have difficulties on estimating the cutting force accurately. The empiricism seems as the only option for proposing a general force estimation equation with considering the strength of rock, the geometry of tool and the geometry of cutting action. Based on this context, a detailed analysis of conical pick cutting mechanism was performed to demonstrate challenges of the theoretical explanation. Afterwards, present conical pick cutting data, which have been published so far, were compiled including 165 cutting test results of 47 different materials including rocks, ores, coals and artificial rocks with considering the brittleness (σc/σt) of the materials. As an initial step, a general trend between the cutting force and the rock strength was explored. Afterwards, a theoretical rake angle function which had been, formerly, proposed for chisel picks was assigned to explain the trend between the cutting force and the rake angle. Furthermore, a back-clearance angle correction function was assigned to the model to reflect the actual cutting conditions. Besides, a universal ratio of maximum cutting force to mean cutting force (k) was investigated through the entire data by considering the probability distribution of experimental results. As a result of this effort, it was discovered that k = 2.45 for conical picks and k is independent of tool geometry and rock properties. The final versions of the proposed models were utilized to compare the estimated and the experimental cutting force. The results from these comparisons have led to a conclusion that the models successfully estimate the cutting force and capture the overall trend between the cutting force and the cutting depth. From a practical standpoint, proposed models might be used for computation of the torque and the power requirements of partial-face excavation machines such as roadheaders which are widely employed in mining and tunnelling practices. [ABSTRACT FROM AUTHOR]

This study is to investigate the change in resultant force, cutting coefficient and normalized resultant force of the TBM (tunnel boring machine) disc cutter when using different cutting conditions and different linear cutting machines. Full-scale linear cutting tests on three rocks of different compressive strengths were conducted. The experimental results, combined with other previously published data, were compared to the prediction results of the semi-theoretical CSM (Colorado School of Mines) prediction model. The influences of rock compressive strength, disc cutter diameter and machine frame stiffness on the comparison results were analysed. From the general view, experimental resultant forces tend to be underestimated while experimental cutting coefficients and normalized resultant forces both tend to be overestimated when using the semi-theoretical CSM prediction model, and the underestimation or overestimation degrees are different when the above three influencing factors are different. The reason responsible for these phenomena can be mainly attributed to the lower actual cutter penetration depth compared to the pre-set one during the rock–machine interaction process. The results of this study can offer more accurate understanding of the full-scale linear cutting tests using different cutting conditions and different linear cutting machines, and thus it can contribute to the more reliable and accurate prediction on disc cutter cutting forces. [ABSTRACT FROM AUTHOR]

• This paper presents a new method for evaluating rock excavation efficiency. • The new method uses the excavated surface to obtain the optimal cutting geometry. • Volumes of underbreaks and overbreaks vs s-p ratio yield a unique turning point. • The turning point represents the optimal cutting geometry of the tested geology. Efficient rock excavation requires an optimal s-p ratio, where adjacent cuts interact to completely plane the rock surface. Traditionally, the specific energy (SE) methodology has been used to determine this ratio, but its U-shaped curve is sometimes incomplete or absent, making it difficult to find the optimal s-p ratio. In this research, an alternative methodology is proposed. This methodology relies on the morphology of the excavated rock surface, specifically, the amounts of overbreaks. To evaluate the proposed methodology, full-scale rock cutting experiments were conducted in the laboratory. Numerical simulations were also conducted in 3D particle flow code (PFC3D) and the results were validated by the full-scale laboratory rock cutting experimental data. The study also involved conducting sensitivity analyses to evaluate the effectiveness of downscaling and upscaling the PFC3D-based model to obtain results for full-scale applications. Following the excavation, laser profilometry was employed to characterize the excavated rock surfaces, and the resulting profiles were used to calculate the volume of overbreaks. Plots of these volumes against the s-p ratio were generated to identify the optimal s-p ratio. The findings indicated the presence of a noticeable optimal s-p ratio in both the PFC3D-based simulations and full-scale laboratory experiments. This optimal s-p ratio was not evident when the specific energy methodology was employed. This proposed methodology exhibits considerable potential and can prove beneficial in determining cutting geometry that is optimal for site-specific and TBM-specific, as well as in the design and production of tunnel boring machines. [ABSTRACT FROM AUTHOR]

Deep coal cutting is a hot research topic at present. In this paper, the cutting technology of three-drum shearer was proposed based on previous studies. Besides, the influence of confining pressure on coal cutting performance was studied by using the discrete element method, and the induction effect of central cutting on coal cutting performance was discussed. Moreover, coal cutting with different boundary conditions was simulated with the aid of PFC2D software. The results show that as the confining pressure increases, the model dominated by tensile failure does not change, but the crack gradually develops from the vertical direction to the free surface of coal. The cutting debris first increases and then decreases; so does the cutting force. Under the effect of central cutting, the crack tends to develop towards the free surface of coal more, and both the peak cutting force and the specific energy consumption increase with the increase of confining pressure. Induced by central cutting, with the increase of confining pressure, the reduction value of peak cutting force increases first and then decreases while the reduction value of cutting specific energy consumption increases.

Rock damage is one of the key factors in the design and model choice of mining machinery. In this paper, the influence of rock damage on rock fragmentation and cutting performance was studied using PFC2D. In PFC2D software, it is feasible to get rock models with different damage factors by reducing the effective modulus, tensile and shear strength of bond by using the proportional factors. A linear relationship was obtained between the proportion factor and damage factor. Furthermore, numerical simulations of rock cutting with different damage factors were carried out. The results show that with the increase of damage factor, the rock cutting failure mode changes from tensile failure to brittle failure, accompanied by the propagation of macro cracks, the formation of large debris and a notable decrease in the peak cutting force. The mean cutting force is negatively correlated with the damage factor. Besides this, the instability of cutting force was evaluated by the fluctuation index and the pulse number of unit displacement. It was found that the cutting force was quite stable when the damage factor was 0.3, which improves the reliability of cutting machines. Finally, the cutting energy consumption of rock cutting with different damage factors was analysed. The results reveal that an increase of damage factor can raise the rock cutting efficiency. The aforementioned findings play a significant role in the development of assisted rock-breaking technologies and the design of cutting head layout of mining machinery.