Hole Wall Research Articles

Real-time dynamic damage monitoring of ultra-thin-ply composite bonded/bolted joint interference-fit installation based on evolutionary affinity propagation

This research introduced ultra-thin prepregs for designing equal-thickness laminates and conducted experimental tests on interference-fit. The uncertainty of damage, attributed to the bearing and friction exerted by the shank against the hole wall during installation, posed a significant challenge. Moreover, the absence of real-time damage monitoring methods in existing literature. In this paper, we proposed the utilization of acoustic emission (AE) technology in conjunction with the evolutionary affinity propagation (EAP) algorithm to facilitate dynamic, real-time monitoring and classification of damage. The findings indicated that employing ultra-thin in composite interference-fit installations substantially reduced damage to the hole walls. Furthermore, the EAP algorithm surpassed traditional methods in its ability to accurately and efficiently monitor and analyze damage dynamically throughout the interference-fit installation.

Investigation of ultrasonic-assisted drilling temperature of SiCp/Al composites

ABSTRACT Due to their excellent properties and low manufacturing costs, SiC particle-reinforced Al matrix composites (SiCp/Al) find extensive application in automobile manufacturing and aerospace. However, SiCp/Al is less machinable. The ultrasonic-assisted drilling (UAD) decreases tool wear and enhances the quality of drilled holes when compared to conventional machining techniques. This paper investigates the effect of drilling temperature variations induced by processing conditions on the degree of softening of the base material during UAD of SiCp/Al. It also analyses the mechanism of how drilling temperature affects the quality of the holes made from the perspective of matrix softening. The study demonstrates a regularity in the impact of spindle speed, ultrasonic supply voltage(ultrasonic vibration amplitude), and feed rate as a function of drilling temperature. The effects of temperature changes caused by each of these factors on import/export edge defects, surface scratches on the hole wall, and tool machinability vary.

Effect of electromagnetic force installation method on critically reinforced interference sizes and fatigue behavior of CFRP bolted joints

AbstractThe electromagnetic force dynamic installation (DI) method of interference fit fasteners has significant advantages in improving the quality of the assembly interface of composite structure. This study aims to investigate how improving assembly interface quality may help in achieving high‐precision interference‐fit joints in composites. Single‐lap joint specimens were prepared using electromagnetic installation technique, the fatigue life and failure behaviors of the joints under different bolt‐hole clearances were measured and analyzed experimentally. In addition, a three‐dimensional finite element model was developed to predict the radial pre‐compression stresses around the hole and the progressive failure behavior of various typical damage modes in carbon fiber‐reinforced polymer induced by the interference. The results show that the critical interference range for the DI‐composite bolted structure is 1.0%–1.2%. The fatigue life of the best interference (1.0%) and the worst interference (0%, neat fit) have a difference of 36 times in amplitude. The residual stress with uniform distribution and high amplitude reduces the stress concentration of the hole wall and improves the failure evolution of the loaded hole. The contribution of this study provides vital guidance for improving the fatigue performance of CFRP bolted structures using a novel DI method.Highlights I = 1.0% is the critical damage‐enhancing interference size for dynamically installation interference fit bolts with electromagnetic forces. The residual stress amplitude introduced by the interference does not increase uniformly as the interference size increases. Excessive interference significantly reduces the uniformity and magnitude of residual stresses. Under subsequent cyclic loading, the fifth layer near the inlet and outlet of the extruded lower laminate appears to be the critical ply of extrusion deformation, and severe damage is concentrated in the critical ply of deformation. The decrease of stress amplitude and the variation of mean stress are the mechanisms of fatigue life enhancement in interference fit joints under external cyclic loading.

Experimental evaluation and optimization of parameters affecting delamination, geometrical tolerance and surface roughness in ultrasonic drilling of 3D-Printed PLA thermoplastic

Ultrasonic drilling is a suitable process to enhance the generated surfaces by additive manufacturing. In this study, polylactic acid was selected as the workpiece. The examination parameters were thrust force, delamination, geometrical tolerance, chip adhesion, hole wall morphology and surface roughness. It was explained that the harmonic movement of drill bit in ultrasonic drilling reduced thrust force, delamination, circularity, cylindricality and surface roughness up to 14.5%, 3.7%, 44%, 38%, 20% respectively and removed chip adhesion. Furthermore, number of end-mill flutes was examined and observed that 4-flutes compared to 2-flutes induced reduction in thrust force, delamination, circularity, cylindricality and surface roughness up to 15.2%, 2%, 7.5%, 18.9%, 12.5% respectively. Besides, analysis of variance was established to determine the significant parameters. Finally, non-dominated sorting genetic algorithm-II technique was implemented in order to carry out multi-response optimization.

PECVD technology deposition of high hardness a-C:H films on micro-drill surfaces: Substrate bias voltage effects

The plasma enhanced chemical vapor deposition (PECVD) technique was utilized to produce hydrogenated amorphous carbon (a-C:H) films. The overall structure of the films consists of a Cr/WC transition layer, a WC/a-C:H transition layer, and an a-C:H functional layer. The study investigated the effects of substrate bias voltages (SBVs) of −580 V, −660 V, −740 V, −820 V, and −900 V on the microstructure, mechanical, and tribological properties of a-C:H films. The findings indicate that different SBVs influence the ionic energy during the deposition of a-C:H films, consequently affecting the film growth. In this case, when the SBV is -820 V, C+ with sufficient energy will penetrate beneath the initial layer in the form of shallow injection. Therefore, compared to other experimental groups, the a-C:H films prepared under this condition have the lowest Ra value (0.42 nm), the highest sp3 CC bond content (39.88 %), the maximum hardness (31.6 GPa), the lowest friction coefficient (0.052), and the smallest wear rate (7.48 × 10−8 mm3/(N·m)), demonstrating significantly better mechanical and tribological properties. The a-C:H films, prepared at different SBVs, are deposited on micro-drill surfaces for hole drilling tests. The experimental results indicate that a-C:H films prepared at SBV of −820 V exhibit the satisfactory drilling performance due to the better mechanical and tribological properties. This is evident not only in the minimal surface wear of the film micro-drill after different drilling quantities but also by the satisfactory quality of the corresponding machined holes. The a-C:H film micro-drill prepared at SBV of −820 V exhibited larger process capability index (CPK) values for the machined holes at 500, 1000, and 2000 hole numbers of 5.449, 3.693, and 3.263 respectively. During the 2000th drill on the printed circuit board (PCB) surface, the hole wall roughness (Rz) and nail head values of the machined hole were measured to be 10.6 μm and 1.3, respectively.

Optimization of the Laser Drilling Processing Parameters for Carbon Steel Based on Multi-Physics Simulation

The laser drilling of carbon steel is always suffered from the formation of slag, the presence of cutting burrs, the generation of a significant quantity of spatter, and the incomplete penetration of the substrate. In order to avoid these defects formed during the laser drilling of carbon steel, the COMSOL multi-physics simulation method was used to model and optimize the laser drilling process. Considering the splash evolution of the material during the complex drilling process, the transient evolution of the temperature field, the flow of the molten fluid, the geometrical changes, and the absorption of the laser energy during the laser drilling process were investigated. The simulated borehole dimensions are consistent with the experimental results. The process parameters have a great influence on the fluid flow pattern and material slag splashing. The laser power has a significant effect on the laser processing compared with the process parameters. With the increase in laser power and the decrease in laser heat source radius, the time required for perforation is reduced, the flow of melt is accelerated, the perforation efficiency is increased, and the hole wall is smoother, but the degree of spattering is greater. The optimized process parameters were obtained: laser heat source radius of 0.3 mm, laser power of 3000 W. These findings can help reduce the machining defects in carbon steel with excellent mechanical properties by optimizing the laser drilling processing parameters.

The Effect of Deposition Temperature on TiN Thin Films for the Electrode Layer of 3D Capacitors Prepared by Atomic Layer Deposition

The TiN thin film is considered a promising electrode layer for 3D capacitors. In this study, TiN thin films were prepared on Si substrates using atomic layer deposition (ALD) at various temperatures from 375 °C to 475 °C. The crystallization behavior, microstructure, and conductance properties of those TiN thin films were investigated. The resistivity of TiN thin films deposited on Si wafers can reach as low as 128 μΩ·cm. TiN thin films showed lower resistivity and worse uniformity with the deposition temperature increasing. In addition, the aging of TiN thin films may weaken the device performance. Optimized deposition parameters were found and full-coverage deposition of thin films on the wall of deep holes with an aspect ratio of approximately 14 has been successfully achieved. The results would be a good reference for the development of 3D capacitors and other microelectronics components.

Preparation and application method of CNTs dispersion solution for direct electroplating on circuit board holes

Abstract The utilization of carbon black dispersion solutions for the black hole method is common in the electronics industry due to their cost-effectiveness and stable performance. However, the slow electroplating speed caused by carbon black’s poor conductivity can impact industrial processes and time. This paper introduces a water-based dispersion solution of carbon nanotubes (CNTs) for the direct copper electroplating process on circuit board holes and its application method. The dispersion solution comprises “shortened” CNTs with a small aspect ratio, a dispersant, a pH adjuster, and other optimization agents. This black hole liquid functions as a conductive fluid with “shortened” CNTs as the conductive medium, exhibiting high dispersibility, strong through-hole capability, low resistance, and excellent adhesion. Its performance surpasses that of black hole liquids using single-carbon black as the conductive medium. The key advantage lies in avoiding the entanglement associated with conventional long aspect ratio CNTs, thereby enhancing the conductivity of the water-based dispersion solution. This facilitates the formation of a uniform conductive film through the electrostatic self-adsorption method, which is suitable for preparing a conductive film on circuit board hole walls before copper electroplating.

Study on explosion impact pressure and damage distribution law of rock powder segmented charge

The charge structure is the critical to determine the bench blasting effect of rock slope. Through theoretical calculation, model testing, and numerical simulation, a formula for calculating the stress attenuation of the axial hole wall of the segmented charging structure is proposed. Moreover, the influence mechanism of the explosive ratio and interval packing length on the internal damage distribution of the concrete of concrete specimens under a segmented charging structure of the cuttings is described. Finally, the research results are applied to the mining of a rock slope in southwest China. The research results reveal the following: 1) The pressure at the charge section is highest when the rock debris interval charge is used, and with the increase in the charge section distance, the pressure markedly decreases—sharply first before stabilizing. In the upper filling interval charge section, the minimum pressure corresponded to approximately the midway point of the filling section, and the stress distribution on the axial hole wall is concave: high at both ends and low in the middle. 2) The ratio of the upper and lower sections of the explosive column determines the form of blasting damage, and the range of blasting damage increases first and then decreases with the increase in the length of the rock debris in the interval section. 3) The field test shows that compared with the traditional blasting charge structure, the optimized segmented charge structure can reduce the blasting block rate by 13.1%. 4) Using the optimized charge structure, the explosive unit consumption can be decreased from 0.27 kg/m3 to 0.24 kg/m3, which improves the economic benefits of mining and construction of related mines.

Enhanced electrochemical ozone production via sp2 carbon content optimization in boron doped diamond electrodes using laser micromachining

The role and bonding arrangement of deliberately added sp2 carbon in maximising the current efficiency, output and longevity of boron doped diamond (BDD) electrodes for electrochemical dissolved ozone generation is elucidated. We show, using a zero-gap cell (ZGC) arrangement, how systematically increasing sp2 carbon results in increased ozone concentration and current efficiency. sp2 carbon addition is made using nanosecond pulse laser micromachining which converts BDD to sp2 carbon. Two ZGC geometries are investigated which both incorporate a Nafion membrane sandwiched between two BDD electrodes. Through-holes (perforations) are integrated into either the membrane or the BDD, the latter using laser micromachining which also converts the hole walls to sp2 carbon. Increasing the number of through-holes (or changing hole geometry), in the perforated BDD, increases the sp2 carbon content of the electrode (from 5 to 100 %). For the perforated Nafion membrane in contact with a planar BDD electrode, patterned laser micromachining of the BDD surface is used to control the sp2 carbon content of the electrode (from 4 to 100 %). For both electrodes, sp2 carbon content is significantly higher than is possible using diamond growth. sp2 carbon contents >40 % and >60 % for the planar and perforated BDD electrodes, respectively, are found to be particularly effective, allowing electrode designs to be proposed for optimised ZGC ozone generation. Notably, the sp2 carbon introduced via laser micromachining is shown to be extremely stable over 20 h (anode potential ∼ 10 V) in contrast to glassy carbon, which corrodes within 10 min. Whilst both are 100 % sp2 carbon, the laser-machined surface (after ozonolysis) is amorphous whereas the glassy carbon contains disorganized graphitic layers. This work also highlights the intriguing stability of amorphous sp2 carbon towards high oxidative potentials.

Damage prediction and improvement method based on cutting mode of circular empty hole

Based on the theory of empty hole effect of cutting blasting, the Hopkinson effect and Saint–Venant principle are integrated to establish a two-dimensional calculation model of dynamic stress evolution of the holes wall, and then the dynamic fracture mechanism and damage distribution mode of the rock mass in the cutting area under the action of longitudinal waves are predicted. The results of the calculation and numerical simulation are verified by experiments, and the results show that: The time-varying stress function of the circular cavity wall conforms to the periodic dynamic evolution of the trigonometric function, and the theoretical calculation is consistent with the simulation results. Through the calculation of the round holes cut model and the square empty hole cut model, the change of the shape of the holes in the cut area changes the failure form of the surrounding rock mass. The circular empty hole wall is affected by the stress wave to produce "interval ring" destruction, and the effect of the reflected stretch wave is inhibited. The large range of rock mass in the square empty hole wall produces tensile and shear failure, and the rock mass collapses inward under the influence of the second stage stress. Among them, the empty space utilization rate of the square empty hole model is about 8.5 times that of the circular holes model. Vibration monitoring in the center of the cutting area shows that the vibration effect of the circular empty hole is larger than that of the square empty hole, and the proportion of rock breaking energy is lower.

Ultra-high sensitive dual-parameter sensor based on double-hole fiber for simultaneous detection of magnetic field and temperature

An ultra-high sensitive dual-parameter sensor based on double-hole fiber (DHF) is proposed for simultaneous detection of magnetic fields and temperatures. The sensor utilizes the DHF containing a Ge-doped core with two large air holes symmetrically arranged at its two sides. To enhance the sensitivity to both a magnetic field and temperature, Al wires with different diameters are embedded on the inner walls of the air holes in the DHF, creating a magnetic field sensing channel filled with magnetic fluid and a temperature sensing channel filled with thermo-sensitive liquid. Structural parameters and metal materials of the sensor are optimized by using the finite element method. Numerical results demonstrate that this DHF-based dual-parameter sensor can detect magnetic fields ranging from 40 Oe to 130 Oe and temperatures ranging from 24.3 °C to 49.3 °C simultaneously. The maximum magnetic field sensitivity reaches up to 64000 pm/mT, while the maximum temperature sensitivity is approximately 44.6 nm/°C, both exceeding current reports by more than one order of magnitude for simultaneous detection of magnetic field and temperature. With its high sensitivity, low fabrication difficulty, and simple structure, this DHF-based dual-parameter sensor has potential applications in the fields of material characterization analysis, geological environmental monitoring, and aeronautical engineering.

Photonic quasi-crystal fiber electro-optical modulator

The integration of graphene with optical fiber is considered to be a new interdisciplinary research hotspot for functional fiber. In this paper, an electro-optical modulator based on a six-fold Stampfli-type photonic quasi-crystal fiber (PQF) is theoretically proposed with a sandwiched graphene/hexagonal boron nitride/graphene (Gr/hBN/Gr) film covering all the hole walls. This design exhibits a strong light-graphene interaction with an excellent modulation depth of ∼64 dB mm−1 at 1550 nm by applying an external bias voltage (below 30 V) on both graphene layers. As the Fermi level of the graphene changes with voltage, the fiber shows ‘On’ and ‘Off’ states, serving well as a light-switch. For the modulator performance, the dependence of modulation depth on multiple factors is studied in terms of the layer numbers of graphene and hBN films, the incident wavelength, and the structure parameters. Interestingly, an attenuation peak occurs due to the epsilon-near-zero effect in graphene and shows a linear relationship between the wavelength and the Fermi level. This design provides a guidance for the integration of PQF and graphene, and holds great promise for future all-fiber systems.

Influence of clean cooling medium on the hard drilling performance and machined surface integrity of 42CrMo steel

42CrMo ultra-high strength steel has high strength and fracture toughness, which is widely used in key components, such as gears, connecting rods and molds. This type of workpiece material, especially after quenching and hardening treatment, still has prominent issues with hole machining. In this work, the clean cutting media, including dry, cold air and liquid nitrogen (LN2), are selected to investigate the hard drilling performance and machined surface integrity of 42CrMo steel. The feasibility of extending tool life and improving hole machining quality is explored through clean cooling medium. The cutting force and cutting temperature are lower under cold air and LN2 conditions than that under dry cutting conditions. The tool life is extended under cold air and LN2 conditions. The low temperature brought by LN2 promotes the transformation from folded to lamellar for chip free surface. The degree of chip curling becomes larger and easier to break and discharge, which reduces the unfavorable effects of chip clogging. The thermal damage phenomenon on the hole wall surface is disappeared. The surface roughness is reduced by 37.3%, and the maximum microhardness is increased by 6.6%, which significantly improves the machined surface integrity of holes. This work demonstrates the feasibility of improving the machinability of harnessed ultra-high strength steel by LN2 cooling.

Analysis of hole wall stability in saturated clay using undrained solution for cylindrical cavity contraction

To investigate the stress state of soil during the instability of the hole wall (hole shrinkage) in saturated clay, the theory of cylindrical cavity contraction in an infinite medium is applied, utilizing the modified Cam-Clay (MCC) model. By employing intermediate variables, the issue of cylindrical cavity contraction is reformulated into a first-order ordinary differential equation in Lagrangian form, with three effective stress components and pore pressure as the unknowns. In MATLAB, the stress conditions at the elastoplastic boundary serve as the initial values for solving the initial value problem of the differential equation system. After determining the correlation between the stress distribution around the cavity and the diameter reduction ratio, the analysis proceeds to evaluate the internal support pressure required for stabilizing the hole wall according to various stability criteria. This pressure is then integrated into the hole wall stability coefficient formula within the soil pressure model, facilitating the evaluation of hole wall stability. The effectiveness and accuracy of the proposed semi-analytical elastic–plastic solutions were subsequently confirmed through comparison with finite element analysis results, underscoring its relevance for addressing hole wall stability challenges.

Soft coal drilling technology and application based on air directional drilling

In China, there are many layers and a wide distribution of crushed soft coal seams, which are commonly characterized by complex structural stress, high gas pressure, and low mechanical strength of coal bodies. In response to the problems of hole collapse and spray during the drilling process of such coal seams, such as hole wall instability, drilling difficulties, and the existence of blind spots for extraction, a dual tube and dual action air directional drilling method was proposed for coal mine soft and fractured coal seams. The grading of protective casing and inner tube directional drilling tools was studied, the parameters of spiral casing blades were optimized, and air supply parameters such as air volume and pressure were studied. Numerical simulation and on-site testing methods were used to study the law of powder discharge and the optimal drilling process parameters. Research and field experiments have shown that the construction depth of dual pipe and dual action drilling can reach over 300 meters, effectively improving the hole formation rate and drilling construction accuracy and providing a new process method for precise drilling of deep holes while drilling in fragmented soft coal seams.

Damage characteristics of rock induced by unloading in hole under true triaxial boundary stresses: Experimental study

In order to study the effect of unloading of underground rock excavation on the stability of surrounding rock, the true triaxial compression (TTC) and coupled true triaxial compression and in-hole loading-unloading tests (TTC-HU) were conducted on hollow cubic rock (100mm × 100mm × 100mm). The experimental results indicate that the compressive strengths of the specimens increase as confining pressure increases in the equal biaxial stressand increase with increasing intermediate principal stresses in the unequal biaxial stress. At low confining pressure (σ < 30 MPa), the internal stress at unloading damage in the hole of hollow cubic specimen increases with the increase of the three-directional boundary stresses. At high confining pressure (σ ⩾ 30 MPa), the specimen will not be damaged during the entire unloading process in the hole. The damage mode of the specimen is dominated by tensile damage. The shape of the holes in the specimens did not significant change, and hole wall of specimen have layered destruction along the circumference in low confining pressure. In high confining pressure, the hole area of the specimen undergoes significant deformation damage, forming a V-groove along the direction of the minimum principal stress, and the wall of the hole is completely peeled off. This study can reasonably predict the actual engineering damage patterns and guide the optimization of surrounding rock support.

A prediction model for drilling temperature of CFRP/Ti stacks and green cooling strategy considering chip ejection process

Drilling temperature has always been a hot issue in the drilling process of CFRP/Ti stacks. Accurately predicting drilling temperature is necessary for reliable optimization of drilling parameters. However, since the drilling process involves two materials and may affect each other, the prediction of temperature during drilling is still a challenge. In this paper, a novel drilling temperature model is established to predict the temperature distribution in CFRP workpiece during the drilling process of CFRP/Ti stacks, considering the minor cutting edge and titanium alloy chip ejection process. Specifically, according to different drilling phases, in addition to considering the heat source of the cutting zone of different materials, the heat source generated by the interaction of minor cutting edge and rebound hole wall of CFRP and the heat source formed by the thermal-mechanical effect of Ti chip ejection process are also considered. The results show that the prediction errors of peak temperature in CFRP entrance and stack interface region during drilling are within 15.8 % and 10.9 %, respectively, which indicates the validity of the model. Finally, the green cooling strategy (High and low frequency compound vibration-assisted drilling) is adopted to significantly reduce the peak temperature in the drilling process by controlling the chip morphology and ejection process, which further proves that the thermo-mechanical action of Ti chips on CFRP cannot be ignored, and provides reference for temperature modeling and low-damage processing of CFRP/metal stacks.

A Study on the Borehole Wall Stability Analysis and Slurry Ratio Optimization for Construction of Pile in Complex Marine Strata.

In order to address the issue of hole collapse, which frequently arises when boring piles are being constructed in intricate marine strata, this paper discusses the influence of the slurry ratio on the slurry performance as well as the mechanism of slurry wall protection. It performs this by means of theoretical analysis, laboratory ratio testing, engineering analogies, numerical simulation, and field testing. Our findings demonstrate that adding sodium polyacrylate and sodium carboxymethyl cellulose can enhance mud's viscosity, contribute to flocculation, and improve the connection between mud and soil layers. Refering similar engineering cases, three optimization schemes are proposed for achieving a mud ratio that offers wall protection in complex marine strata. Furthermore, the particle flow model of slurry viscous fluid is established. The collapse of holes in the sand layer is reflected in the uneven radial displacement of hole walls and the invasion of mud particles. Increasing the viscosity of mud gradually transforms the uneven radial deformation of pore walls in the sand layer into a uniform radial deformation, whereas increasing the proportion of mud significantly decreases the radial displacement of hole walls. Additionally, when the mud pressure in the hole is 300 kPa and 600 kPa, the wall protection effect is better, and there is no particle penetration by substances such as sand. It is found that a high mud pressure can promote the diffusion of mud particles into the sand layer, while low mud pressure cannot balance the pressure on deep soil. The results of the field tests show that the ratio of water-clay-bentonite-CMC-Na-sodium carbonate = 700:110:90:1.5:0.5 used (where the mass percentage of each material is 77.8% water, 12.2% clay, 10% bentonite, 0.16% CMC-Na, and 0.05% sodium carbonate) can effectively prevent hole collapse and reduce the thickness of the sand layer at the bottom of the hole by 50%.

Analysis of failure characteristics of screen plates of ring hammer crusher used in coal handling applications

The screen plate, a critical component within a ring hammer crusher (also known as a ring granulator or rolling ring crusher), plays a vital role in the secondary crushing of coal. Functioning both as a platform for coal crushing and as a sieve to achieve the desired coal size, it is essential to understand and examine its failure characteristics to enhance its mechanical and wear resistance properties in coal handling applications. This study thoroughly explored the failure modes, mechanisms, and underlying causes of screen plate failures. Microscopic techniques such as optical microscopy (OM), scanning electron microscopy (SEM), Vickers microhardness test and spectrochemical analysis were utilised to identify the failure mechanism. Failure modes identified from the macroscopic analysis were discharged hole widening, hole wall break-off, plate edge crack, plate fracture, one-sided edge slimming, and general surface wear of the screen plate. The fractographic and wear track analysis identified the principal failure mechanisms of three-body abrasive wear, two-body sliding abrasion wear, shear-induced fatigue fracture and brittle shear fracture. The root causes of the failures are the rotor’s direct impact, defects in the parent material, the presence of hard materials in the coal and the use of unsuitable steel grade in the screen plate manufacturing. The service life of the screen plate can be improved through proper material selection, uniform crusher feeding, surface modification of the surface of the “as purchase” screen plate with appropriate wear-resistant materials, and adherence to good maintenance practices.