Hole Wall Research Articles

Effect of cooling strategy on the bearing capacity of CF/PEEK composite hole

Currently, carbon fibre-reinforced polyetheretherketone (CF/PEEK) hole-making process employs the same fast cooling strategy as in a traditional thermosetting composite to avoid hole wall burns. However, owing to the characteristics of thermoplastic resins, excessive cooling adversely affects the recrystallisation process of PEEK resins in the high-temperature region. This poses questions against the conventional perception that “cooling is beneficial.” To address this issue, mechanical parameters of the samples treated at different cooling rates were measured. The mechanical response and material damage of the holes under load were analysed, and the relationship between material cooling rate, crystallinity, and mechanical properties was established. A retarded cooling strategy was proposed to actively control the temperature after the hole-making. The effects of fast cooling, natural cooling, and retarded cooling on the quality of CF/PEEK holes were analysed by differential scanning calorimetry (DSC), tensile, and fatigue tests, and the detrimental effect of fast cooling on the quality of the hole structure was confirmed. The results reveal that compared with fast cooling, the ultimate tensile strength of the retarded cooling components is increased by 23.64%, and the fatigue life is increased by more than 10 times at 65% σult. The retarded cooling strategy improved the quality of CF/PEEK holes.

Relationship between local strain energy density and fatigue life of riveted Al-Li alloy plate

As an important assembly technology in aviation manufacturing, the riveting process has significant effects on the fatigue performance of aircraft skin, especially on Al-Li alloy plates. A finite element model was established by ABAQUS to simulate the riveting process of 2060-T8 Al-Li alloy plates. The distribution of strain energy in Al-Li alloy riveted plates under different riveting forces was analysed by finite element model. The local energy density within the range of 0.4 mm radial thickness along the hole wall of the lower plate was suggested as the key area to affect the fatigue life of the riveted structure. Finally, a fatigue life prediction model for 2060-T8 Al-Li alloy riveted panel was proposed based on the local energy density method. The life prediction model is verified, and all predicted results are distributed within a factor of 2-scatter band. This work provides support for the application of 2060-T8 Al-Li alloy in aviation manufacturing process.

Theoretical studies on the nature and conditions of interaction of heel and peripheral nose cones of offset roller cone bits with a bottom hole

An offset of roller cone rotation centerlines is used to increase the mechanical penetration rate while drilling in soft rocks. This enables increasing the area of a cutting structure teeth contact with a bottom hole. The analysis of offset cone drill bit (cutting structure) teeth wear showed that particularly significant wear is characteristic of the transition zone from the heel cone to the nose cone; which leads to significant reduction in the mechanical rate of penetration and a rapid decrease in the hole diameter. The purpose of this paper is to conduct a theoretical research on the nature and conditions of interaction between heel and peripheral nose cones of offset roller cone bits with a bottom hole; which is aimed at improving the efficiency of rock cutting by offset roller cone bits. To achieve the purpose; the authors analyzed data on the nature and causes of wear of existing offset roller cone bit cutting structure (teeth); developed a mathematical model in a cylindrical coordinate system allowing to determine the location and geometric parameters of the gage cone contact area with the hole wall for different roller cone bits sizes; developed a computer solid model for checking the adequacy of the mathematical model by comparing these two models; prepared recommendations for further improvement of the design of existing offset roller cone bit cutting structure (teeth). The research was carried out by the method of mathematical simulation of geometric figures and bodies corresponding to roller cones and a hole. The research has revealed that significant adjustments need to be made to the geometry of the roller cone teeth (currently being patented). This would allow decreasing the areas of cone heel blunting by 15–20 % as well as providing more prolonged contact of base and gage cones with bottom hole and wall surfaces. This allows to reduce wear of teeth in the transition zone of the generatrix from the peripheral nose cone to the gage (heel) cone of the roller cone and to maintain the required specific pressure on the cut rock for a longer period of time and; as a result; to increase both the mechanical penetration rate and the service life of the drilling tools.

Study on shear performance of multiple-bolt joints of Bamboo curtain plywood

In this paper, five sets of multi-bolted joint shear tests are designed to study the effect of bolt middle distance on the bearing performance of multi-bolted joints, and analyze the failure modes of the specimens. The main conclusions are as follows: For M10 bolts (grade 8.8) and bamboo curtain plywood connections. When the spacing increases to 50mm, the ultimate bearing capacity of the nodes increases and tends to be stable; For the initial stiffness of the joint, the distance has no obvious effect on the initial stiffness of the joint. However, the increase in the number of bolts significantly increases the initial stiffness of the joint; For the nodal yield load, the yield load increases with the increase of the distance, and the yield load is 67%~73% of the ultimate bearing capacity; The main failure mode of the multiple-bolt joint double shear specimen is that the middle of the test piece first reaches its pin groove bearing strength and fails, and the failure modes of bamboo curtain plywood mainly include shear breakout failure and hole wall bearing failure.

Experimental Study on Damage Fracture Law of Coal from Solid-Propellant Blasting

The low permeability of coal seams has always been the main bottleneck restricting coalbed methane drainage. In this paper, a coal seam anti-reflection technology with solid-propellant blasting was proposed, and the composition and proportion of the solid propellants were determined based on the principle of oxygen balance. The authors designed a solid-propellant blasting damage fracture experiment of simulation coal, tested the impact pressure on a blast hole wall, measured the ultrasonic wave velocity, explosive strain and crack propagation velocity, and then revealed the blasting damage fracture process and mechanism of coal based on the experimental results and damage fracture mechanics theory. The history curve of impact pressure time can be divided into three processes including the slow pressurization process, dramatic increase process, and nonlinear pressure relief process. The pressure distribution along the whole blasting hole was uneven, and the peak pressure was relatively small, but the pressure action time was long. The damage and fracture process of coal solid-propellant blasting can be divided into two stages including the rapid damage fracture development stage and the stable slow damage fracture development stage. Firstly, the explosion stress wave produced and rapidly accelerated the radial cracks extension; secondly, the cracks slowly expanded over a large area by the combined effects of the high-pressure gases, the gas, and the original rock stress.

Study on the Weak Interlayer Identification Method Based on Borehole Photo-Acoustic Combined Measurement: Application to a Landslide Case Study

A weak interlayer is the key factor in controlling slope stability. It is of great significance to effectively identify the weak interlayer in the study of spatial and temporal distribution law and the internal structure characteristics of a landslide. Considering the limitations of traditional optical imaging and wave speed test methods, this paper presents a weak interlayer identification method based on borehole photo-acoustic combination measurement. By using the combination of optical imaging and acoustic wave scanning, the multi-source data collection of borehole rock wall and borehole surrounding rock is realized, which effectively captures the comprehensive response characteristics of the weak interlayer. This paper first constructs a multi-source data acquisition technology based on the borehole photo-acoustic combination measurement to realize the visualization of the image information and acoustic data of the target area on the borehole rock wall. Subsequently, the optical image features and the acoustic response characteristics of the weak interlayer are clarified based on the optical image and the acoustic scanning data. The hole wall texture characteristic response function, hole wall integrity characteristic response function, hole wall acoustic characteristic response function and hole wall contour characteristic response function are constructed. Finally, the landslide weak interlayer identification method considering the texture characteristics, complete characteristics, acoustic response characteristics and contour characteristics of the borehole rock wall is proposed, which effectively distinguishes the types of rock mass structural surface and realizes the automatic identification of the weak interlayer. Combined with the case analysis, the correctness and reliability of the present method are verified. The results show that the method can identify the weak interlayer and provide scientific basis for landslide management, which can provide a feasible and effective new way to identify the landslide weak interlayer in practical engineering, with a good application prospect and promotion value.

Discrete Element Simulation of Fracture Evolution around a Borehole for Gas Extraction in Coal Seams.

The stability analysis of underground caverns, tunnels, and boreholes is of great significance to underground engineering. In order to study the stress change of the coal around a hole and the evolution law of fractures during the coal seam drilling process, the discrete element simulation of the coal seam drilling process was carried out by using the particle flow code (PFC2D). The results show that during the drilling process, under the influence of confining pressure and drilling disturbance, the coal stress field around the hole and the development of fractures around the hole have the characteristics of zoning and dynamic evolution. In the axial direction of the borehole, it is divided into front and rear areas, and in the vertical axial direction, it is divided into the drilling disturbance zone and the confining pressure main control zone. During the drilling process, the direction of the maximum principal stress in the front zone gradually changes from the vertical hole axis to the direction parallel to the hole axis, and tension fractures are mainly developed along the drilling direction. In the rear zone, the principal stress direction tends to be stable and the principal stress value undergoes dynamic changes, and a large number of vertical hole axis tension fractures are developed. The drilling disturbance zone appears near the hole wall and has an important influence on the stability of the hole wall, while the confining pressure main control zone determines the antireflection effect around the hole and the influence radius of the hole. This work helps the understanding of the damage range and failure characteristics of the surrounding rock during the drilling process and has great significance for the guidance of drilling design.

Mechanism and Application of Roof Cutting by Directional Energy-Cumulative Blasting along Gob-Side Entry

In this paper, roof-cutting technology of directional energy-cumulative presplitting blasting is taken as the research object. Through the numerical simulation software Ansys/Ls-dyna3D, the process of energy-cumulative blasting and non-cumulative blasting is simulated and analyzed by using the ALE algorithm. Moreover, the evolution processes of tensile strain energy, detonation stress wave of explosives, stress state of rock mass, and rock crack damage cumulative are compared in two conditions. In the energy cumulative state, the detonation wave acts centrally on the hole wall in the energy cumulative direction to form an initial crack, and then under the action of the jet of energy cumulative, the crack continues to propagate until it runs through. In the non-energy cumulative state, the crack propagates uniformly around the hole wall, forming irregular short cracks. The simulation is verified by the field test, and the law of crack propagation is the same with the simulation. Therefore, directional energy-concentrated presplitting blasting has good practicability in a roof presplitting operation.

Experimental study of drilling behaviors and damage issues for woven GFRP composites using special drills

Glass fiber reinforced polymer (GFRP) composites are becoming more attractive in modern engineering fields due to their outstanding mechanical/physical properties. However, a thorough understanding of their drilling machinability is seriously lacking in the research community. The present work aims to address the drilling behavior of woven GFRP composites under varying cutting speeds and feed rates. Machining studies were conducted using two different diamond-coated special tools involving a double point angle drill and a dagger drill. The drilling machinability of GFRPs was comprehensively analyzed in terms of cutting forces, machining temperatures, drilling-induced damages, dimensional accuracy, and hole wall morphologies. Theoretical analyses and experimental characterizations of delamination damage were conducted for both special drills. A special attempt was made to clarify the impact of different drill shapes on the damage formation and extension of cut GFRP materials. The results obtained can supplement the expertise of composites machining and guide the damage-free drilling of GFRP laminates for academia and industry.

Hole Wall Stability Analysis of Long-Distance Pipeline Horizontal Directional Crossing

Trenchless technology is a new technique for laying, repairing, and replacing underground pipelines in recent years, but various field accidents are often caused by the failure of hole wall in the process of trenchless construction, which leads to trenchless engineering accidents. Stress and deformation around hole are calculated by theoretical calculation. The numerical calculation method is also used to research the stability of hole wall with different diameters, buried depth, and soil parameters, and the curves of stress and deformation are fitted. The results show that stress and deformation of hole wall increase with the increase of the diameter. Under the condition of shallow burial depth, stress and deformation increase with the increase of burial depth of hole. The stress and deformation are different with different Poisson’s ratio and elastic modulus. This research has a new understanding for the instability of hole wall caused by variations of external parameters, which has important guiding significance for the selection of construction parameters and trenchless path.

Design and flow field analysis of impregnated diamond bit for seafloor drill in soft-hard interlaced strata

According to the seafloor drill working conditions and the complex formation characteristics of the seafloor, this paper aims to improve the adaptability of the diamond bit to the formation and the coring quality. The cutter tooth design scheme of the impregnated diamond bit is proposed, and Fluent analyzes the flow field of drilling fluid at the bottom hole. The results show that the cone cutting tooth bit with the primary and assistant nozzles can directly avoid 85.33% drilling fluid flushing core and reduce the disturbance of drilling fluid to the core samples. The water passage structure of the bit is reasonable, and the upward return velocity of the drilling fluid can be stabilized between 0.7 and 1.8 m/s, which meets the requirements of the upward return of cuttings in seabed strata, and has a good hole wall protection performance. Based on the bottom-jet diamond bit, the assistant nozzles are added. The drilling fluid of the assistant nozzles can better cover the bit crown, conductive to cooling the bit crown. The drilling fluid of the main nozzles can timely up-return along the outer annulus hole wall, conducive to the up-return of the cuttings with drilling fluid. This study can extend existing designs of a seafloor coring bits and bottom hole flow field analysis methods.

A gold film coated dual-core photonic crystal fiber for refractive index and temperature sensing with high isolation

• When measuring RI of an analyte, the measurement is often affected by temperature. the simultaneous measurement of RI and temperature has important significance. • In this paper, a gold film coated dual-core photonic crystal fiber (DC-PCF) was proposed and numerically investigated for both RI and temperature sensing. • The maximum sensitivity of the RI reached 8100 nm/RIU, while the maximum sensitivity of temperature reached 1.3 nm/°C. • The design of dual independent cores in DC-PCF not only avoids the problem of cross-sensitivity; but also improves the isolation of the sensor. When measuring the refractive index (RI) of an analyte, the measurement is often affected by temperature. Therefore, the simultaneous measurement of RI and temperature has important research significance. In this paper, a gold film coated dual-core photonic crystal fiber (DC-PCF) was proposed and numerically investigated for both RI and temperature sensing. In order to stimulate the surface plasmon resonance (SPR) with high sensitivity to the surrounding, two gold films were coated on the polished surface and inner wall of a cladding air hole in the DC-PCF, respectively. Numerical results showed that the measurement sensitivities of RI and temperature reached 8100 nm/RIU based on Core I and 1.3 nm/°C based on Core II, respectively. It should also be noted that the designed sensor showed a high isolation. This designed sensor can be used where the RI of analyte should be detected at a high temperature accuracy.

Drill string’s axial force transfer law in slide directional drilling in underground coal mine

During the slide directional drilling with long directional near-horizontal drilling technology, the weight on bit (WOB) at the bottom of the hole is exerted by pushing the drill pipe with the power head of the orifice drill. With the increase of drilling depth, the friction resistance between drill string and hole wall also goes up, resulting in problems including insufficient WOB, low drilling efficiency, and surge of feeding pressure. If the orifice feeding pressure continues to rise, the drill string will buckle or fracture. In our study, the field test method is adopted to explore the drilling string’s axial pressure transfer law. By comparatively analyzing different stratigraphic characteristics of five directional boreholes with an average radius of deflection, the deep-hole drill string transmitting pressure model with nine curvature radiuses is set up for simulating the relationships between drill string friction, hole depth, and strata characteristics under different working conditions. The results show that when the hole is relatively shallow, the relationship between the friction resistance and the hole depth is basically linear, which gradually develops into an exponential one with the increase in the hole depth. For the borehole with a curvature radius less than 200 m, the friction resistance is greatly affected. The softer the formation is, the greater the linear range of friction resistance becomes with the increase in the hole depth, the latter the hole depth with an exponential growth occurs, and the longer the limit depth is. The findings reveal the axial pressure transfer law of the drill string, which will facilitate future design of the drilling hole, optimize the control of drilling trajectory, and matter a lot to engineering practices.

Damage to Rocks by Eccentric Uncoupled Charge Explosion Loads

In the process of tunnel excavation, the blasting technology is one of the commonly used tunnel excavation methods. The blasting technology is mainly divided into smooth blasting and presplitting blasting. In the process of blasting, in order to prevent excessive damage caused by explosive blasting, the blasting is often carried out by means of uncoupled charging. In the previous studies, the explosive and the blast hole were mainly placed concentrically, while in the actual engineering, the charge often exists in the form of eccentricity. In this study, LS-DYNA is used to establish three-dimensional models of concentric charge and eccentric charge respectively for numerical simulation of blasting, and the whole process of uncoupled charge blasting is reproduced. Based on the damage cloud diagram, hole wall pressure and hole wall vibration velocity obtained by simulation, the damage caused by blasting under two different charging conditions is analyzed and compared.

Coupled thermo-hydro-mechanical analysis of perforated cement sheath integrity during hydraulic fracturing

The wall of perforation hole was directly pressed by the high-pressure fracturing fluid, making cement integrity more challenged in fracturing process. However, the current calculation of perforated cement sheath stress neglects the influence of transient temperature variation during fracturing process. In this work, a fully coupled thermo-hydro-mechanical (THM) model incorporating the transient heat transfer process of fracturing fluid was set up to describe the transient stress variation of cement sheath during fracturing. The maximum tension stress criterion and Mohr-Coulomb criterion were chosen as the criterions for the cement failure. The proposed model was successfully verified through its excellent agreement with experimental observations. In addition, based on the proposed model, the influence of fracturing parameters and cement mechanical parameters on cement integrity was analyzed. The results illustrate that a spindle-shaped tensile-shear failure area is formed near the cement hole. The casing pressure and the cement mechanical parameters are the main controlling factors for the failure of the perforated cement sheath. The extremely low casing pressure are beneficial for maintaining cement sheath integrity. Besides that, only optimizing the Poisson's ratio or elastic modulus of cement cannot maintain the perforated cement integrity unless improving both simultaneously.

In situ stress measurement method of deep borehole based on multi-array ultrasonic scanning technology

In order to improve the accuracy and efficiency of deep in-situ stress measurement, based on the wall collapse in deep borehole, a deep borehole in-situ stress measurement method based on multi-array ultrasonic scanning technology is proposed in this paper. The solution idea of using the combination of multiple elements for borehole contour scanning is put forward, and a multi-array ultrasonic scanning technology suitable for fine horizontal section scanning of deep geological borehole contour is formed. Through the analysis of the calculation principle of hole wall caving method and the derivation of multi-array element ultrasonic scanning solution algorithm, a multi-array ultrasonic scanning device is developed by using the effective fusion of multi-array ultrasonic full waveform scanning signals and the reconstruction of horizontal section contour. The measurement method of in-situ stress in deep borehole combined with hole wall caving method is studied. Finally, the feasibility and accuracy of this method are verified by physical experiments. The results show that: the effective fusion of multi-array ultrasonic full waveform scanning signals and horizontal section contour reconstruction can break through the limitations of conventional in borehole probe placement and in borehole medium sound velocity calibration, and improve the fine reconstruction and accurate measurement of 360° wall shape. The multi-array ultrasonic scanning technology can obtain the borehole shape data at any borehole depth, and then obtain the three-dimensional shape measurement of borehole wall, which can provide a new technical means for the three-dimensional detection of borehole wall and in-situ stress measurement.

Mechanical properties and instability analysis of concrete specimens with horizontal holes of different diameters

Uniaxial compression tests were carried on 12 concrete specimens with six different diameter holes using a rigid test machine, and the stress–strain relationship was analyzed in different hole diameter specimens. The effects of different hole diameters on specimen compression strength, elastic modulus, and Poisson’s ratio were studied, and the failure form and instability mode of concrete specimens with holes of different diameters were evaluated. The results show that the larger the compression strength of the specimen, the larger the axial and horizontal strains. As the hole diameter increased from 0 to 50 mm, the compression strength and elastic modulus reduced. The decreasing trend slowed down, and the relationships between the hole diameter and compression strength, and elastic modulus could be represented by negative liner functions. The Poisson ratio of the specimen increased in waves with the increase in hole diameter from 0 to 50 mm. A crack in the concrete specimen with 0–20 mm diameter hole started at the upper and lower diagonal angles of the hole wall; a crack in the concrete specimen with 30–50 mm diameter hole started at the left and right parts of the hole wall. The instability mode of concrete specimens with horizontal holes of different diameters was divided into shear dislocation instability and planar splitting instability.

Coupling Mechanism of Coal Body Stress–Seepage around a Water Injection Borehole

In China, coal seam water injection technology is widely used in the prevention and control of mine gas and dust disasters. The evolution law of stress–seepage field in the range of hydraulic influence in the process of coal seam water injection is the most basic theoretical problem in coal seam water injection technology. Therefore, this paper first uses the radial seepage experimental system to test the permeability of raw coal samples, and then numerically inverts the stress–seepage evolution law of the coal body around the water injection hole. The results show that the coal seam permeability decreases exponentially with the increase in the experimental overburden pressure. The dynamic water intrusion causes the pressure relief area and the stress concentration area to transfer to the deep part of the coal body, and abnormal stress occurs near the water injection hole wall. The composite stress area formed by the superposition of stress and pore water pressure reduces the permeability of the hole wall. During the radial development of water injection, the pore water pressure dropped sharply and eventually tended to zero, while Darcy’s velocity decreased significantly (within the pressure relief zone, it rapidly decreased from 7.26 × 10−3 m s−1 to 2.5 × 10−3 m s−1 (by 65.56%)). Near the initiation point, the maximum step-down height of Darcy’s velocity decreased from 6.73 × 10−3 m s−1 to 5.27 × 10−3 m s−1 (by 22.73%). This can make it clear that the seepage velocity presents a non-Darcy seepage phenomenon under the influence of pore pressure.

Analytical Model of Hole Diameter and Self-Guiding Machining Mechanism of BTA Deep Hole Drilling

The goal of this study was to explore the self-guided machining mechanism of boring and trepanning association (BTA) deep hole drilling and realize precise control of the machining quality. The motion analysis method was used to analyze the center motion trajectory of the drill during the entrance, and the self-guiding mechanism and hole-forming mechanism of BTA deep hole drilling were revealed. Considering the bending deformation of the drilling tube and the tool structure parameters, according to the elastic-plastic deformation theory and Hertzian contact theory, a novel analytical model of the extrusion contact between the guide pads and the hole wall of the BTA deep hole drilling was established for the theoretical prediction of the extrusion deformation and the machining hole diameter. Combined with the finite element method (FEM) simulation model, the variation law of the contact inclination angle, contact stress, and extrusion deformation of the guide pads and the hole wall with the drilling conditions were studied. The total extrusion deformation between the guide pad and the hole wall was between 10 and 50 μm. The maximum error between the FEM simulation results and the test results was 18.1%, and the maximum error between the analytical model results and the test results was 23.6%. The simulation and experimental results showed that the established extrusion contact model could accurately predict the extrusion deformation of the hole wall and the machining hole diameter.

Effects of liquid properties on atomization and spray characteristics studied by planar two-photon fluorescence

In this work, planar two-photon laser-induced fluorescence (2p-LIF) is applied for the first time to analyze the fluid dependent spray structure and atomization behavior of water and ethanol in a quantitative way. A commercial six-hole DISI (Direct-Injection Spark-Ignition) injector was studied at different injection pressures, operated with liquids containing the LIF dye fluorescein. Specifically for DISI-injectors, the fluid-dependent atomization is very complex and not fully understood due to the cavitating, turbulent nozzle flow that dominates the spray formation. Optical access and analysis of the near-nozzle spray are often challenging due to multiple light scattering in dense regions which is reduced by 2p-LIF measurements using a femtosecond laser. This allows high-contrast spray imaging close to the nozzle, resulting in an improved identification of single liquid structures of the spray. Thus, a higher accuracy of sizing is possible. Compared to water, the ethanol spray shape shows increased cone angles in the nozzle near-field of about 6%, which cannot be explained by classical atomization theory based on aerodynamic breakup. The larger cone angle of ethanol was attributed to its larger viscosity, which could decelerate the flow at the wall of the injection hole, affecting the velocity profile of the emerging jet. The atomization shows a main jet breakup distance of 7–10 mm in which the structure sizes decreased drastically, specifically for water. For the size of the liquid structures in the near-nozzle region, which show dimensions of about 80–130 μm, ethanol exhibited about 2% smaller Feret's diameters than water for the tested time steps at 20 MPa. This effect is even more distinct for other injection pressures and positions at a further distance to the injector. For all investigated conditions and measurement positions downstream of the nozzle, ethanol showed on average about 24% smaller structures compared to the water spray. Although this trend is in accordance with the classical atomization theory based on the aerodynamic breakup mechanism, other effects, such as cavitation and nozzle-flow induced breakup, contribute to this behavior.