Hole Wall Research Articles

Towards understanding the hole making performance and chip formation mechanism of thermoplastic carbon fibre/polyetherketoneketone composite

Here, we report the first study on the hole making performance of thermoplastic carbon fibre/polyetherketoneketone (CF/PEKK) composite. Different hole making methods (conventional drilling vs. helical milling) have been compared and the effect of different feed rates has been investigated. The effect of thermal-mechanical interaction on the resulting hole damage has been elucidated for the first time for carbon fibre reinforced thermoplastics (CFRTPs) hole making. In the material science dimension, advanced material characterization techniques have been deployed to reveal the material removal mechanisms at microscopic scale and unveil the underlying material structural change at a molecular level. Results show that the delamination damage of CF/PEKK is a result of the thermal-mechanical interaction. For conventional drilling, the high machining temperature (at low feed rate <0.1 mm/rev) has a stronger influence on the delamination damage and the delamination starts to show stronger dependence on the thrust force at high feed rate >0.1 mm/rev. In contrast, helical milling generates a much higher machining temperature which plays a more predominant role in the associated delamination damage. Microstructural analysis shows that all the hole surfaces feature matrix smearing, as a result of combined in-plane shear stress and high machining temperature. Conventional drilling leads to more severe hole wall microstructural damage (matrix loss and surface cavity) as compared to helical milling. Finally, thermal analysis reveals that the hole making process has led to significantly increased crystallinity in the PEKK matrix as a result of the strain-induced crystallization under the combined effect of shear stress and high temperature. • Hole making performance of CF/PEKK is investigated for the first time. • A comparative study on conventional drilling and helical milling is reported. • The role of thermo-mechanical interaction is elucidated for CF/PEKK hole making. • Chip morphology and the associated material removal mechanism are revealed. • Shear-induced crystallization caused by hole making is reported for the first time.

Monitoring analysis and environmental assessment of mine subsidence based on surface displacement monitoring

Over the past several years, a metal mine by block caving method has experienced a long-term and progressive surface deformation and fracturing, and then we start our investigation based on this background. The location of surface rupture was based on a series of mapping activities and the deformation data was collected by GPS from 2013 to 2016. In this paper, emphasis was put on the analysis of the fissures, deformation and stress of surface subsidence. Results reveal the diversity magnitude and structural features of surface deformation and ground fissures. In addition, the time dependent behavior is comprehended and the subsidence zone reflects different types of time-displacement curve – regressive phase, steady phase and progressive phase, all these achievements indicate the complexity and diversity of the subsidence zone. On the other hand, stress calculation which inspired from the mechanical model of the cracking of hole wall is carried out, it is meaningful to understand the relation between fracture features, displacement vectors and horizontal stress.

Disturbance Effect of Blasting Stress Wave on Crack of Rock Mass in Water-Coupled Blasting

The disturbance of a blasting stress wave on rock crack propagation directly affects blasting efficiency. This study aimed to explore the disturbance effect of water-coupled blasting using experimental and theoretical analyses. First, a model of crack instability under a blasting stress wave was analyzed. Next, experiments were conducted to study the characteristics of the blasting stress wave disturbance loads. Finally, blasting disturbances in different coupling media were compared. Following a blasting stress wave, explosive-source-penetrating (ESP) and explosive-source-nonpenetrating (ESNP) cracks underwent tensile failure and compression-shear or tension-shear cracking, respectively. In ESP cracks, the blasting stress wave disturbance load included direct and indirect explosive loads; in ESNP cracks, only the disturbance load was transmitted through rock mass. The differences in the disturbances of blasting with different coupling media were primarily due to the peak explosion pressure of hole wall and the wave-attenuation law in coupling medium. In water-coupled blasting, the disturbance effects transmitted indirectly and directly to the ESP crack tip exceeded those in air-coupled blasting by 1.19 and 3.80 times, respectively. In ESNP cracks, the disturbance effect in water-coupled blasting was equal to or greater than 1.32 times that in air-coupled blasting. The results of this study provide a theoretical basis for improving the design of water-coupled blasting.

THE EFFECTS OF WEATHERING ON WHOLE ROCK FRACTURES BY LABORATORY TESTING

Cracked rock is an indication of instability in underground excavations due to being under high-pressure conditions that cause new cracks to appear by forming cracks in the walls of holes or tunnels. The cracking process can be influenced by environmental conditions around the rock. Therefore, this study aims to analyze the effects of weathering on cracks and other characteristics in intact rock. Petrographic observations indicate differences in the presentation of rock mineral preparation in the six samples. Changes in the preparation of primary rocks are plagioclase minerals (32% -39%) and hornblende minerals (12% -20). While the opaque mineral (3% -5%) is a change from the mineral hornblende, volcanic glass (8% -21%) has partially decayed into clay and plagioclase microlites (17%). The results of the uniaxial compressive strength test suggested that the crack initiation stress value of rock samples KA2, KA3, BT1, BE2, TS2, and TD3 are 22.55 MPa, 35.07 MPa, 20.04 MPa, 50.08 MPa, 34, 92 MPa and 105.22 MPa. The rock strength of the six rock samples is 61.92 MPa, 47.6 MPa, 86.43 MPa, 89.39 MPa, 88.54 MPa, and 120.25 MPa, respectively. The results also showed a tendency to increase fracture initial stress (crack initiation) along with the increase in uniaxial compressive strength values. the stronger the pressure of the withstanding test, the greater the initial stress of the crack (crack initiation). This is caused by weathering which can reduce the elasticity of rocks that increases surface tension. Weathering plays an important role in changing the initial stress value of fractures and the strength of intact rock. The higher the weathering the smaller the rock strength and the initial stress value of the crack. Weathering due to degradation and mineralogy changes in intact rock samples has an impact on the characteristics of intact rock. This is shown in changes in the value of the content weight, porosity, rock strength, rock fracture, Modulus Young and Poisson Ratio decreases with increasing weathering.

Fracturing mechanism and pore size distributions of rock subjected to water jets under in-situ stress: Breakage characteristics investigation

Water jet drilling is considered a possible method used during the development of underground unconventional natural gas. Meanwhile, the fracture mechanisms of rock subjected to various in-situ stresses may differ significantly. Thus, laboratory experiments are conducted in this paper using the new jet testing system for the deep reservoir to simulate the drilling process of a water jet in the deep reservoir. The breakage mechanisms of rock are examined using the three-dimensional (3D) reconstruction visualization models of damage distributions, surface morphology, and micro-structural analysis on the influenced zone. The results revealed the dependence of two typical breakage characteristics on the stress state of the tested rock. When the samples were subjected to stress in the triaxial cell, the range of the hole was considerably reduced. Besides, as the horizontal stress difference was increased by 6 MPa, the diameter and depth of the erosion holes increase by 60% and 38.6% respectively. Moreover, the results of the scanning electron microscopy (SEM) showed that the fracturing of the hole wall was mostly caused by tensile failure generated by a water wedge that was easily controlled by high in-situ stress. The in-situ stress state of the reservoir significantly affected the pore size distribution and porosity. The increase of stress inhibited the increase of porosity around the hole. The porosity reaches 6.1% when the stress difference is 6 MPa, which increases by 135%. These results were anticipated to be used as a guide for the utilization of unconventional natural gas in deep reservoirs with complex stress.

Research on interference fit of high-lock bolts based on finite element simulation

Firstly, the finite element simulation of high-lock bolt pressing into single-layer plate is carried out based on ABAQUS,and compared with the theoretical calculation results which are derived from the elastic-plastic mechanics.It illustrates that the validity of the finite element model.Finally, the life-death unit technology of ABAQUS is used to analyze and compare the stress state of hole wall, the HST10AG6 high-lock bolt hole is wrongly installed by HST110AG6 high-lock bolt. It is considered that it is appropriate to expand the hole and install the HST10AG8 high-lock bolt.

A MEMS Electrochemical Seismometer Based on the Integrated Structure of Centrosymmetric Four Electrodes.

This paper presented an electrochemical seismic micro sensor based on an integrated structure of four centrosymmetric electrodes. In this integrative structure, cathodes were not only distributed on wafer surfaces but also on the inner walls of the flow holes of the wafer, which increased the effective cathode areas and improved the sensitivity of the sensor. Numerical simulations were conducted to validate the feasibility of the integrated structure of four centrosymmetric electrodes in monitoring seismic vibrations where variations in the arrangements of the flow holes and anode width were investigated. The integrated structure of the four centrosymmetric micro electrodes was fabricated based on Micro-Electro-Mechanical Systems (MEMS) without the requirement of manual alignments. Experimental characterizations revealed that: (1) the maximum sensitivity of the electrochemical seismic sensor based on the integrated structure of four centrosymmetric electrodes was two orders of magnitude higher than that of the commercial counterpart of CME6011 and three times higher than the electrochemical seismic sensor based on the integrated structure of four planar micro electrodes; (2) the electrochemical seismic sensor based on the integrated structure of four centrosymmetric micro electrodes demonstrated comparable and even lower noise levels in comparison to CME6011. Thus, the electrochemical seismic micro sensor developed in this study may function as an enabling tool in future applications of seismic monitoring and geophysical explorations.

Design and Testing of Reverse-Rotating Soil-Taking-Type Hole-Forming Device of Pot Seedling Transplanting Machine for Rapeseed

To address the problem whereby the size of the hole formed by the existing hole-forming device of hole-punching transplanters is significantly inconsistent with the theoretical size as it is impacted by the inserting and lifting methods, a scheme for eliminating the forward speed of the whole machine by the horizontal linear velocity of reverse rotation of the hole-forming mechanism is proposed to vertically insert and lift the hole-forming device in accordance with the working characteristics of hole-punching transplanting and the agronomic requirements of rapeseed transplanting. In addition, a novel type of reverse-rotating soil-taking-type hole-forming device for the pot seedling transplanting machine for rapeseed was developed. A test bench for the hole-forming device was set and its effectiveness was verified in the soil bin. It was found, from the test results, that, when the forward speed of the hole-forming device was between 0.25 m/s and 0.45 m/s, the average qualified rates of hole forming of the device were 95.2%, 94.0% and 93.3%, respectively; the average change rates of the hole size were 2.3%, 2.9% and 5.5%, respectively; and the average error between the theoretical value of effective depth and the experimental value was between 2.0% and 5.6%. The average angle between the hole-forming stage trajectory of the hole opener and the horizontal direction at different forward speeds was higher than 88.0°; the coefficient of variation was between 0.16% and 0.64%; the perpendicularity of the hole-forming operation was high; the change rates of soil porosity of the hole wall were between 8.2% and 9.3%; and the average soil heave degrees at the hole mouth after the completion of the hole-forming operation were 3.9%, 4.1% and 4.2%, respectively. The average soil stability rates of the hole wall were 91.9%, 91.2% and 91.0%, respectively. The different performances of the hole-forming device were confirmed to meet the requirements of rapeseed pot seedling transplanting. This study can provide a reference for the structural improvement and optimization of the hole-punching transplanter for rapeseed pot seedlings.

Fractal damage and crack propagation of PMMA in multiple slit charge blasting

To study the formation mechanism and propagation characteristics of explosive cracks of slit charges with different slit numbers, the propagation law was analyzed using PMMA as the test material and a digital laser dynamic caustics explosion loading test system. The ABAQUS explicit dynamic analysis module is used to simulate the generation process of the initial crack in slotted charge blasting, and the propagation law of stress waves under the action of slotted charges with different numbers of slots is revealed. Based on fractal theory, the damage values in the slit and non-slit directions are calculated quantitatively. The results show that when the number of slits of the slit charge is two, three, and four, the directional crack along the slit direction of the charge can be controlled. The Von Mises stress along the slit direction near the blast hole wall is 9.5–15.6 times that in the non-slit direction, and it gradually tends to equalize with the increase in the distance from the center of the blast hole. In the process of crack propagation, the propagation speed and dynamic stress intensity factor of the exploded main crack of the specimen exhibit an oscillatory downward trend. The propagation law is the same for all the main cracks in the same specimen. Increasing the number of slits can increase the overall energy utilization of the specimen. When the number of slits is two, three, and four, the damage value (0.6130–0.638) of the burst crack in the cutting direction of the specimen is significantly greater than that in the non-cutting direction (0.4540–0.4885).

Research into using a fiber Bragg grating sensor group for three-dimensional in situ stress measurement

Abstract. The observation and estimation of the deep crustal stress state is a key and difficult problem for in situ stress measurement. Using a borehole wall strain gauge based on the overcoring stress-relieving method is one of the main methods of in situ stress measurement. In this paper, a strain-sensing array based on fiber Bragg grating (FBG) is designed by using the main structure of the classical hollow inclusion cell, and its layout scheme on the hollow inclusion is studied. According to the layout scheme, the in situ stress inversion algorithm of hole wall strain to stress is deduced. Following this, the triaxial loading and unloading experiment platform is built, and the calibration experiment for the FBG strain sensor is designed. Finally, Abaqus finite element software is used to simulate the in situ stress measurement process of the overcoring stress relief. The FBG strain values of each measurement direction before and after the overcoring process are extracted, and the stress inversion equation is used to carry out the stress inversion. The comparison of the inversion results proved that the FBG strain sensor group is feasible and reliable. The quasi-distributed FBG sensor module designed in this paper can invert the three-dimensional in situ stress by measuring the hole wall strain, which places a theoretical and experimental foundation for the development and application of an FBG hole wall strain gauge. It makes up for the deficiency of the existing hole wall strain gauge based on a resistance strain gauge, provides direct and accurate observations for hole wall strain measurement, and has important practical value for the development of in situ stress measurement technology.

Research on Variable Parameter Drilling Method of Ti-CFRP-Ti Laminated Stacks Based on Real-Time Sensing of Drilling Axial Force.

Ti-CFRP-Ti laminated stacks have been widely used in aviation, aerospace, shipbuilding and other industries, owing to its excellent physical and electrochemical properties. However, chip blockages occur easily when drilling into Ti-CFRP-Ti laminated stacks, resulting in a rapid rise of drilling temperature and an increase of axial drilling force, which may lead to the intensification of tool wear and a decline of drilling quality. Cutting force signals can effectively reflect the drilling process and tool condition, however, the traditional plate dynamometer is typically difficult in realizing the follow-up online measurement. Therefore, an intelligent tool holder system for real-time sensing of the cutting force is developed and constructed in this paper, and the variable parameter drilling method of Ti-CFRP-Ti laminated stacks is studied on this basis. Firstly, an intelligent tool holder system with high flexibility and adaptability is designed; Secondly, a cutting force signal processing method based on compressed sensing (CS) theory is proposed to solve the problem of high-frequency signal transmission; Lastly, the drilling experiment of Ti-CFRP-Ti laminated stacks is carried out based on the intelligent tool holder system, and the drilling parameters are optimized using a compromise programming approach and analytic hierarchy process (AHP). The comparison of results show that the optimized drilling parameters can effectively reduce the hole wall surface roughness and improve the drilling efficiency while ensuring a small axial force.

Bolt insertion damage and mechanical behaviors investigation of CFRP/CFRP interference fit bolted joints

Interference fit has advantages in improving fatigue behaviors of composite bolted joints; however, interference fit bolt insertion tends to cause damages in laminates weakening joint mechanical properties. Therefore, an experimental study was conducted to investigate bolt insertion damages of Carbon Fiber Reinforced Polymer (CFRP)/CFRP interference fit bolted joints. Mechanical behaviors of joints were also evaluated experimentally under both quasi-static loads and cyclic loads. Scanning Electron Microscope (SEM) and high-resolution X-ray micro-CT scan were used to examine micro damages in laminates. Damage and failure behaviors of joints were characterized. The results demonstrated that the hole entrance in upper laminate and the laminate boundary near the hole wall were the most critical regions for damages during bolt insertions. However, the influence of those damages on quasi-static failure loads and fatigue failure modes of joints was minimal. Delamination and matrix cracking occurred first in laminates following fiber and matrix fracture in quasi-static tensile tests. Interference fit could improve the fatigue resistance of the laminate hole; however, the bolt seemed to suffer a more critical local fatigue loading condition. This paper can contribute to composite structure designs, especially in understanding damage and failure behaviors of composite bolted joints.

Simulation and Experimental Study on Reverse Helical Milling with the Gradual-Removal Reverse Edge Milling Cutter under Ultrasonic-Assisted Condition.

As a new machining method, ultrasonic-assisted bi-direction helical milling has obvious advantages in making holes on carbon fiber-reinforced plastics (CFRP). However, cutting edges of the flat-bottomed milling cutter are easy to wear, which may cause severe defects such as burrs and tears in the outlet of the hole. In order to improve the hole-making quality of CFRP, the gradual-removal reverse edge milling cutter was proposed and designed. The finite method models of reverse helical milling CFRP with the flat-bottomed reverse edge milling cutter and the gradual-removal reverse edge milling cutter under an ultrasonic vibration were established, and the comparative cutting experiments of the two cutters were carried out. By comparing the cutting performance of the two milling cutters under the condition of ultrasonic vibration assistance, the cutting mechanism of improving the hole wall quality by the gradual-removal reverse edge milling cutter was studied. The results showed that when the reverse cumulative cutting depth reached about 60 mm, compared with the flat-bottomed reverse edge milling cutter, the gradual-removal reverse edge milling cutter transferred part of the cutting task of the peripheral edge to the end edge, and the wear of the reverse peripheral edges which directly affects the hole quality was effectively alleviated. This mechanism made the cutting state of the peripheral edge dominated by shear failure, which led to the significant improvement of the quality at the outlet of the hole.

Effect of cryogenic cooling in deep hole drilling process – a stride in the direction of green manufacturing

ABSTRACT In this study research efforts have been made to unveil the ability of Cryogenic machining as a sustainable manufacturing process for deep hole drilling of AISI 1045 and Ti6Al4V. Environmental protection is the most pressing concern for manufacturers today when it comes to adverse health effects caused by cutting fluid and its disposal after usage. For better machining results, choosing the right cutting fluid is important. Investigation on drilling performance is done in terms of tool wear, hole wall temperature (HWT), circularity, surface roughness (Ra) to study the effects of input parameters such as cutting speed, coolant used, feed rate and coolant pressure. The type of coolant employed, cutting speed, feed and coolant pressure have a significant impact in determining the hole quality. Furthermore It was found that the employment of cryogenic coolant (LCo2) was effective on Ti6Al4V in compared with AISI 1045 in many output parameters. HWT of Ti6Al4V was higher compared with AISI 1045 Surface finish was better in Ti6Al4V, tool wear was considerably low while performing deep drilling on Ti6Al4V.

Numerical Simulation of Integrated Mechanics of Drilling and Mechanical Cavitation in Coal Seam.

For coal and gas outburst and difficult extraction in soft, low-permeability, and high-gas seam, the integration technology of drilling and mechanical cavitation is put forward to relieve pressure and improve permeability of coal seam. Through the test of mechanical parameters of the coal body, the physical model of drilling and cave-making in coal seam is established, and the mechanical characteristics of drilling and mechanical cavitation are simulated numerically. The results show that the peak strength of coal increases linearly with confining pressure. When the drill bit just touches the coal, the maximum stress occurs at the center of the coal sample. With the increase in the drilling depth of the drill bit, the maximum stress point shifts to the depth. When the coal at the center of the sample is broken, the position of the maximum stress shifts to the surrounding. With the increase of drilling depth, the maximum contact number between the drill bit and coal body increases sharply. When the bit body basically enters the coal body, the maximum contact number between the drill bit and coal body remains unchanged. When the drill pipe rotates, the reaming tool collides with the hole wall at the reaming position on the axis. In general, the contact area increases with the opening of the reaming tool, but the contact between the reaming tool and the hole wall is random. As time increases, the contact force begins to increase and then basically stabilizes; at this time the reaming tool has been fully opened.

Stability Evaluation Method of Hole Wall for Bored Pile under Blasting Impact

Blasting impact load may be encountered during the construction of some pile foundation projects. Due to the effect of blasting impact, hole collapse can easily occur in the hole-forming stage of pile foundation construction. In order to prevent hole collapse, it is very necessary to evaluate the stability of a pile hole wall before pile foundation construction. The calculation of hole collapse can usually be attributed to an axisymmetric circular hole stress concentration problem. However, the existing collapse failure theory of pile hole hardly considers the effect of blasting impact load. In view of this, this paper proposes the stability evaluation method of a pile hole wall under blasting impact. Compared with the existing collapse failure theory, the proposed method fully considers the effect of blasting impact stress. Using Mohr–Coulomb strength theory and symmetry analysis, the strength condition of collapse failure is established in this work for accurate evaluation of the stability of a hole wall. The proposed stability evaluation method is demonstrated by a pile foundation construction project of a bridge. Moreover, a shaking table test on the pile hole model was performed to verify the proposed method by experimental data. The results indicate the effectiveness and usability of the proposed method. The proposed method provides a feasible way for the stability analysis of a pile hole wall under blasting impact.

Measurement method of bolt hole assembly stress based on the combination of ultrasonic longitudinal and transverse waves

Accurate measurement of the assembly stress of the aero-engine rotor bolt hole is of great significance for improving the assembly quality and safety of the aero-engine. The bolt hole is covered by the nut and the bolt's head so that the assembly stress cannot be directly and effectively measured. Aiming at this problem, this paper uses the ultrasonic method to measure the assembly stress of bolt holes based on the principle of wave mode conversion and acoustoelastic effect. On the basis of analyzing the influence of stress on the propagation velocity of longitudinal and transverse waves, an assembly stress measurement model for bolt holes based on the combination of longitudinal and transverse waves is established. The reflected signal of the bolt hole wall is analyzed by the finite element calculation software. The experimental results show that the method based on the combination of ultrasonic longitudinal and transverse waves realized the bolt hole assembly stress measurement. The average measurement error and average relative error of this method are 2.230 MPa and 5.456%, respectively. This study provides a promising method for accurately measuring the assembly stress of the aero-engine rotor bolt hole.

Study on Smoothing of Hole Wall Surface by Electron Beam Polishing under Control of Magnetic Field

A surface finishing method by large-area electron beam (EB) irradiation called EB polishing has been developed recently. Highly efficient surface smoothing of mold steels with planar shape can be performed by the EB polishing. However, it is difficult to smooth wall and bottom surfaces in hole shape by the EB polishing, since the EB tends to concentrate on entrance edge or upper inside wall of hole, and the energy density of EB on the wall and bottom surface of hole may decrease. Our previous study showed that the bottom surface could be smoothed by EB polishing under control of magnetic field around the workpiece. It is highly expected that EB can be also guided to the whole area of hole wall surface under appropriate control of magnetic field there.In this study, smoothing of hole wall surface by EB polishing under control of magnetic field around the workpiece was proposed. As a basic study for smoothing of hole wall surface, L-shaped workpiece was prepared by combining two stainless steel plates, and magnet was set under the workpiece. The electromagnetic field analysis results suggested that EB could be guided to the whole area of side surface by setting magnet under appropriate setting position, since magnetic force lines are uniformly distributed on whole area of side surface. In addition, magnetic flux destiny on the side surface more increases by setting a yoke made of steel on the magnet. The experimental results show that smoothed area with the surface roughness of less than 1.5μmRz can be obtained on the whole area of side surface. Therefore, the whole area of side surface can be uniformly smoothed by guiding the EB to the side surface under appropriate control of magnetic field.

Elastic-plastic solutions for analyzing wellbore stability

Selecting a good practical prediction method of wellbore instability has extensively become an important issue in order to overcome the resulting instability problems during drilling. Therefore, the aim of this paper is to simulate the actual stresses around wellbore using elastoplastic rock behavior in order to describe the actual cases of wellbore instability problems. Description of stress state around wellbore is presented. Common failure criteria are also presented. Selection of the most applicable equations for description of stress state using elastoplastic rock behavior. Experimental data are used to calculate the cylindrical stresses surrounding the drilling hole wall at various diameters. Furthermore, a sensitivity analysis is done to test changing the radial stress with overbalance support and wellbore radius.

Study on initial stress and damage law of hole wall in water interval blasting

Study on initial stress and damage law of hole wall in water interval blasting