Hole Wall Research Articles

Experimental study on the static performance of arched aluminium alloy gusset joints

A gusset joint with 7° arch angle comprised of two upper and lower aluminium alloy joint plates and four H-shaped aluminium alloy members connected by Huck bolts is first designed and the static performance experiment is carried out to address the research gap regarding the static performance of arched aluminium alloy gusset joints. The failure modes of the joint are summarized in terms of the collapse phenomena, namely the local buckling of the web and the bending and torsion failure of the member, and the stress distribution is discussed based on the measured strain. Subsequently, the ultimate bearing capacity and the stiffness in different stages of the load–displacement curve are obtained. The analysis is then developed via finite element (FE) models implemented in the non-linear code ABAQUS. First, via comparison with the experimental results, the validity of the FE model is verified. Furthermore, according to the simulation, it reveals that with the plasticity development of bolt hole walls, the joint gradually reaches the ultimate bearing capacity and undergoes the obvious deformation utill it can not bear the load. To develop further understanding, the effects of different arch angles on the bearing capacity, stiffness, and failure modes of joints are investigated, and the results indicates that arch angles cannot be ignored.

Improved hole wall roughness and corrosion resistance of U-shaped hole prepared by casting

The corrosion resistance of the cooling channel in the water-cooled mold has an important impact on the application of the mold. In this paper, the influence of experimental temperature on roughness and corrosion resistance of U-shaped cooling channels prepared by casting is analyzed in detail. The results show that the experimental temperature increased from 998 to 1048K; the hole wall roughness of the U-shaped hole decreased from 83.264 to 76.287. However, the hole wall roughness increased with a further increase in temperature. Because the low experimental temperature will promote the formation of micro bulges and river ripples on the hole wall. However, with the temperature gradually increased, it will promote the aluminum matrix to react with the carbon fiber, which will increase the roughness. The corrosion performance analysis results show that a reasonable experimental temperature is beneficial to reduce the roughness of the hole wall and improve the corrosion resistance of the cooling channel. When the roughness is large, the ravines on the rough surface are easy to be the starting point of corrosion. At the same time, it is easy to cause the aggregation of Si elements to the hole wall at high experimental temperature, which will also cause corrosion. As a result, reasonable experimental temperature plays an important role in improving the corrosion resistance of the U-shaped cooling channel.

Experimental study on evaluation of underground coal gasification with a horizontal hole using two different coals

Underground coal gasification (UCG) is a technique to extract coal energy with heat energy and combustible gases through chemical reactions in the underground gasifier. In this study, an application of a coaxial UCG system with a horizontal hole is discussed by means of the model UCG experiments with a large-scale simulated coal seam having dimensions of 550 × 600 × 2740 mm. The two types of coal having 30.18 MJ/kg of calorific value with 7.9% of ash (type 1) and 22.66 MJ/kg of calorific value with 28.3% of ash (type 2) were used for the experiments to evaluate the effect of coal quality on temperature distribution of the gasification area and product gas quality. The oxygen-enriched air was used. The injection rate of the gasification agents was elevated during the experiments to analyze the effect on the product gas. The results show that the gasification area is expanded along the wall of a coaxial hole, not upwards for the type 2 coal with high ash content. The average calorific value of product gas for types 1 and 2 is 8.05 MJ/m3 and 6.91 MJ/m3 respectively, while an increase of injection flow rate produces an improvement of the calorific value for both types of coal. Additionally, it is suggested that the reacted carbon and the product gas volume can be estimated with the volume of oxygen injected regardless of the coal quality if the gasification efficiency and the reaction temperature are similar. These results help to estimate several important parameters, e.g. reacted coal amount, recovered gas volume, and recovered energy from the coal when the actual field implementation is designed.

Effect of lead angle of hole expansion mandrel on surface integrity and fatigue performance of TC17 titanium alloy hole structure

For the TC17 titanium alloy, the influence of the leading end angle of the mandrel on the expansion strengthening effect of the hole structure was studied, the surface integrity of the hole expansion strengthened under different process parameters was characterized, the high temperature and low cycle of the original and strengthened samples were tested. Fatigue life and the morphological characteristics of fatigue fracture are analyzed. The results show that the lead angle of the mandrel has a significant effect on the surface roughness after expansion. The uneven plastic flow of the metal on the surface of the hole wall during the expansion process leads to uneven residual stress distribution on the hole wall after expansion, and the residual stress amplitude at the exit end of the expansion is the largest, and the hole wall has a certain depth of residual compressive stress gradient field after expansion. When the interference of the core rod is constant, the fatigue life increases with the increase of the rear lead end angle of the mandrel. When the rear lead end angle is 8°, the median fatigue life gain after strengthening can reach 1.74 times, and the strengthening effect is the best, its minimum cycle life is 16331 times, which is higher than the longest cycle life of the original sample (13965 cycles). After strengthening, the origin of the cracks is changed from the multi-source type in the middle of the hole wall to the single-source crack initiation at the inlet end of the expansion.

Mechanism and feasibility study of low frequency vibration assisted drilling of a newly developed CFRP/Al co-cured material

CFRP/metal co-cured structure has been increasingly applied in the aerospace industry due to its outstanding mechanical properties of high specific strength and high stiffness. Compared with the stack structure, the co-cured material of which the metal was heavily wrapped by the CFRP prepregs has better interface performance due to the absence of interface gap, being helpful to improve the bonding strength with other parts. Hole making is an inevitable manufacturing process for the assembly of co-cured material while there still exists several challenges during the drilling operation. To be specific, the hole size with low accuracy and hole morphology with severe defects are the main concerns for the manufacturers, which can be mainly attributed to the tangled chips and high cutting temperatures. To solve the aforementioned problems, the low frequency vibration assisted drilling (LFVAD) operation was performed for the newly developed CFRP/Al co-cured material in the present work. The mechanism and feasibility of controlling the machining defects via LFVAD were theoretically and experimentally explored and the influence of vibration amplitude (VA) on the cutting responses was specially studied. The results show that LFVAD can reduce the average thrust forces and drilling temperatures compared to conventional drilling while the maximum thrust force shows larger magnitude with the elevation of VA, in which the VA of ∼30 μm presents the best one. Meanwhile, LFVAD can on the one hand reduce the scratch traces on the hole wall surface owing to its superior chip breakage effect and thereby improve the drilled hole accuracy, and on the other hand shrink the lower interface damage area due to the reduction of cutting temperatures. The obtained findings of the present work indicate that the proposed LFVAD method presents great superiority for the CFRP/Al co-cured material concerning the machining responses of higher hole accuracy and lower interface damage.

Effect of composite orders of graphene oxide on thermal properties of Na2HPO4•12H2O/expanded vermiculite composite phase change materials

The leakage of Na2HPO4•12H2O phase-change materials (PCMs) in the liquid state can be prevented by encapsulating them into porous expanded vermiculite (EV) to prepare composite PCMs. The main issues of EV-based composite PCMs are the low thermal conductivity and the crystal water loss of inorganic hydrated salt. Graphene oxide (GO) can help enhance the thermal conductivity of composite PCMs and firmly adsorb water molecules through oxygen groups. The composite orders of GO play an important role in adjusting the thermal properties of composite PCMs because the suitable positions of GO in the stratified structure of EVs would positively influence the PCMs. The Na2HPO4•12H2O/EV composite with GO was prepared in three different orders. Compared with the common method that involves compositing GO in Na2HPO4•12H2O, compositing GO on the hole wall of the EV exhibited a higher thermal conductivity of 0.54 W/m•K and compositing GO out of Na2HPO4•12H2O/EV exhibited better thermal stability, which incurred a weight loss of 4.14% at a high temperature. A thermal energy storage behaviour analysis indicated that GO-modified PCMs show a large heat storage capacity (melting process: 98–126 J/g; solidification process: 56–91 J/g). Two new composite orders positively affected the heat storage of the composite PCMs.

Shear Behavior of Lapped Connections Bolted by thread-fixed one-side bolts at elevated temperatures

The Thread-fixed One-side Bolt (TOB) is the bolt that can be installed from outside of a steel tube column, which is anchored by the threads on the bolt hole wall instead of the nuts. A series of tests were carried out to investigate the shear behavior of the lapped connection bolted by TOBs using both the steady state fire tests and the transient state fire tests. The two observed failure modes of TOB connected lapped connections were the bolt hole bearing failure (failure mode 1) and the bolt shank fracture (failure mode 2). The high temperature might cause the change of failure mode from failure mode 1 to failure mode 2. Lapped connections using Standard High Strength Bolt (SHSB) were also tested. The comparison results showed that the ultimate shear resistance of lapped connections using TOBs at different temperatures was about 90% of that using SHSBs with the same configuration at steady state fire test. Applicability of the design equations provided by Eurocode 3 was validated by the steady state fire test results. A Finite Element Model (FEM) was built and validated by the test results and the FEM was used to further study more derailed parameter studies including the influence of bolt strength, the bolt pretension force and the high temperature to the shear behavior of TOB connected lap connections.

Experimental study of nickel-based superalloy IN792 with femtosecond laser drilling method

The improvement of aircraft engine performance resulted in the highly demand of drilling micron-sized holes (<1 mm) into the blades. A two-step approach with an axial feed method for nickel-based superalloy IN792 femtosecond laser drilling was studied. The effects of different processing path parameters on the hole quality are described and discussed in detail. The drilling strategy containing a drilling through phase and an enlargement phase, which was able to produce cylindrical holes with diameters of 600 μm on 680 μm and 1300 μm thick plate without modification and reconstruction of the processing platform. According to the different material thickness, the corresponding drilling optimization strategy was proposed. The experiments showed that the hole quality processed using the two-step method improved obviously compared with the one-step method, including that the outlet circularity can be increased by 7.4% and the taper angle can be reduced by 4°. Moreover, there is no obvious heat-affected zone (HAZ), recast layer or micro-cracks on the hole surface and wall. In conclusion, the two-step approach is an effective hole processing method that provides the possibility of high-efficiency and high-quality machining of film cooling holes.

Elimination of Hole Mouth Burr in Multilayer PCB Micro-Hole by Using Micro-EDM.

The micro-hole is a key structure in multilayer printed circuit board (PCB), as it enables the effective transmission of electrical signals. At present, the most common way to machine PCB micro-holes is mechanical drilling using micro-bit. However, in the mechanical drilling of micro-holes, these holes are prone to burring at the hole mouth due to the micro-bit failing to cleanly cut through the first layer of copper foil on the PCB. Hole mouth burr can seriously affect the performance of the PCB, resulting in potential short circuiting or even ruining the PCB. To solve the above problems, this paper proposed to machine the first layer of copper foil on the PCB via micro electro-discharge machining (micro-EDM) to eliminate hole mouth burr. Compared with the mechanical drilling, micro-EDM is a form of non-contact machining, and the high temperature generated from the electric spark discharge can erode the first layer of copper foil, thus fully eliminating hole mouth burr. This paper performed a detailed study of the influence of spindle speed, machining voltage, pulse width, and pulse interval on hole mouth quality. After that, the technological parameters for eliminating hole mouth burr were obtained. Finally, under the effects of 20,000 rpm spindle speed, 26 V machining voltage, 4 μs pulse width, and 8 μs pulse interval, a micro-bit with a diameter of 200 μm was used to perform micro-EDM of the first layer of copper foil. From the machining results, it can be known that the PCB micro-hole was possessed of overall good quality, with good hole wall surface quality and almost no visible hole mouth burr.

Comparative study on cutting performance of conventional and ultrasonic-assisted bi-directional helical milling of CFRP

Compared with the conventional drilling, the helical milling has obvious advantages in making holes of carbon fiber-reinforced plastic (CFRP). Nevertheless, the rapid wear of cutting edges readily causes some defects in the outlet holes, such as burrs and tearing. In order to improve the hole-making quality of CFRP, a comparative experimental study on conventional and ultrasonic-assisted bi-directional helical milling of CFRP was carried out. The wear mechanism of the forward and reverse cutting edges was analyzed in the two types of machining, and the change laws of cutting forces and hole wall quality were obtained by different machining means. The experimental results indicated that the flank face of forward and reverse cutting edges was dominated by the abrasive wear mechanism in the ultrasonic-assisted milling. With aggravation of the tool wear, no obvious coating peeled off the forward cutting edge, the reverse cutting edge remained relatively intact, and the wear form of neither cutting edge changed. Furthermore, in the ultrasonic-assisted reverse milling, the axial force and hole diameter deviation were restrained better than in the conventional milling, and especially when the tool wear occurred, the cutting force fluctuation varied slowly. In the ultrasonic-assisted milling, the shear fracture predominated over bending fracture. Meanwhile, the time variation of effective rake angles improved the chip breaking and removing performance of cutters, and thus, the machining quality of hole wall was enhanced obviously.

Removal of recast layer in the laser drilled film cooling holes by a two-step inner streaming electrochemical technique

High-power millisecond laser is an efficient tool to manufacture micro holes, but the laser induced thermal defects, such as recast layer (RL), micro cracks and heat affected zone, are difficult to avoid. However, some important components, like turbine blades, are very sensitive to these defects, therefore, they must be eliminated in the manufacturing process of film cooling holes. We propose a combined processing method which includes high-power laser pre-drilling and electrochemical post-processing. One novelty of this study is that we applied a special back-bonded material (silicate mixture) under the Inconel 718 substrate, which functions as barricade to protect the opposite inner surface of the hollow blade in laser drilling, while in the electrochemical process, it functions as bottom support to form electrolyte back flow. A novel two-step inner streaming electrochemical post-processing technique was designed according to the characteristics of RL distribution in the laser pre-drilled holes. The processing strategy was optimized by a series of experiments. Finally, recast-layer free holes with clear and straight hole walls could be drilled in less than 30 s each, which is much faster than ultrafast laser drilling.

Study on the energy transfer efficiency of explosive blasting with different coupling medium

Decoupled charge blasting can effectively reduce the peak pressure of hole wall and improve the blasting effect. Aiming at the issues associated with the explosive energy transferred into rock mass with different coupling medium, the deformation and failure characteristics of rock mass under explosion were analyzed theoretically with the consideration of strain rate effect of the rock mass, and the theoretical energy transfer efficiency of blasting with different coupling medium was obtained. Combined with the numerical simulations, the effects of rock mass properties, explosive categories and decoupled charge coefficient on the energy transfer efficiency of blasting with different coupling medium were studied. The results show that the energy transferred into rock mass from explosive of decoupling charge blasting is related to the coupling medium, the energy transfer efficiency of water coupling blasting is higher than that of air coupling blasting for the same charge structure and same blasting medium. When the charge structure and blasting rock mass are the same but the coupling medium is different, the energy transferred into the rock mass from explosive will be different, depending on blasting rock mass, explosive categories and decoupling charge coefficient. When blasting with the same decoupling charge coefficient but different coupling medium, the higher the rock mass strength, the greater the difference of energy transfer efficiency between different coupling medium. For blasting with the same rock mass properties and same charge structure, the difference of energy transfer efficiency between air coupling blasting and water coupling blasting increases with the increase of decoupling charge coefficient. For emulsion explosive exploding in siltstone, when the decoupling charge coefficient increases from 1.28 to 3.44, the energy transferred from water coupling blasting to surrounding rock mass increases from 1.45 to 6.52 times of air coupling blasting. The research results are of great reference significance for optimizing blasting design, improving explosion energy distribution and increasing the explosion energy utilization rate.

The Helical Anchor Type with Application as a Horizontal Drainage Equipment for Slope Protection

Helical anchors, sometimes referred to as screw anchors, screw piles, and helical piles, are a steel screw-in piling and ground anchoring system used for building deep foundations. Screw piles are manufactured using varying sizes of tubular hollow sections for the pile or anchor shaft. This paper presents an innovation of the helical anchor for horizontal drains, a form of subsurface drainage systems for slope protection. To address the adverse effect of groundwater, an expansion of the application of the helical anchor structure in civil engineering is needed, and new drainage solutions are being considered. The features of the helical anchor type for horizontal drainage equipment, analyses of some of its advantages, and conditions of application are presented. Generally, a helical anchor for horizontal drainage is convenient for installation, maintenance, or removal, and is effective for both horizontal drainage and for anchoring the revetment. It is also a typical construction in drainage works, generally performed by a cranking handle or a rotary-percussion-type drilling machine. The helical anchor pipe for horizontal drainage has many segments with joints using a cranking hand for installation and is quite effective where the installation space is narrow or there is no machine. In particular, the installation of this equipment differs significantly from other drilling methods because it can be driven into a sand layer without a hole wall.

Novel micro-deep-hole drill with variable web thickness and flute width

This study proposes a novel micro-deep-hole drill with variable web thickness and flute width to effectively improve the problem of tool breakage and chip clogging during micro-deep-hole drilling. Firstly, the failure form and failure mechanism of micro-drill are explored by performing drilling experiments, and it is found that the torsion fracture and bending fracture are the main premature failure modes of micro-deep-hole drilling tools. The static simulation analysis of micro-drill is further conducted to investigate the influence of geometric parameters on the stiffness and strength of high-aspect-ratio micro-drill, and the results indicate that the web thickness ratio and flute width have significant effects on drill tip stiffness and spiral groove root strength. To balance the rigidity, strength and chip evacuation capability of micro-deep-hole drilling tools, the new micro-drill with variable web thickness and flute width is developed, supplemented by comparative experiments. The results confirm that the new micro-drill has better chip removal ability, greatly reduces the drilling force, torque, drill tip wear and material peeling phenomenon, and significantly enhances the machining quality of hole wall.

Study on the drilling performances of a newly developed CFRP/invar co-cured material

The CFRP/metal co-cured material which possesses the outstanding properties of both lightweight and high strength has become one of the commonly used materials in the design and manufacture of attitude control flywheel. However, few studies are reported concerning the mechanical drilling operation of this newly developed structural material. To cover the gap and enrich the scientific field of this topic, the present work was performed to specially evaluate the drilling performances of a co-cured material composed of carbon fiber reinforced plastic (CFRP) and invar alloy. The significance of the present work aims to on the one hand, reveal the evolution of vital cutting phenomena including thrust forces, cutting temperatures and surface quality of drilling holes as function of cutting parameters, and on the other hand address the mechanism of controlling the interfacial drilling response. The results indicate that both the thrust forces and cutting temperatures during drilling of the invar phase are relatively higher compared to that of the CFRP phases while it presents elevation for the lower CFRP phase than the upper one due to the effect of chip ejection. The evolution of thrust forces and drilling temperatures present common regularity, in which the feed rate and cutting speed play an essential role, respectively. It is worth noting that the hole size indicates disparities for all the involved layers regardless of the machining parameters, of which the hole size exceeds the nominal diameter for the upper CFRP phase while it presents lower magnitudes for the lower CFRP phase and close gap between the invar phase and expected value. Surface cavity and fiber pullout dominate the hole surface morphology for the upper CFRP phase, matrix degradation and micro-cracks appear on the hole wall of the lower CFRP phase, and chip adhesion and oxidation are the cases for the invar layer. The mechanical effect induces the notch and the thermal effect causes the matrix degradation, which controls the cutting response for the upper and lower interface, respectively.

Effects of heat accumulation on the characteristics of hole wall temperature and damages in drilling of UD CFRP

Application of carbon fiber reinforced plastic (CFRP) in aircraft load-carrying structure makes the component become thicker and damage tolerance get stricter. The heat accumulation highly increases the hole wall temperature along feeding direction during thicker CFRP component drilling due to the low thermal conductivity, which highly deteriorates the hole quality. Therefore, this paper proposed a hole wall temperature measurement experiment at various fiber cutting angles with different measuring distances to investigate the effects of heat accumulation on the cutting temperature and damages. Results show hole wall temperature in the vicinity of hole-exit increases by almost 20⁓40 °C and 30⁓65 °C separately for S=3000 rpm and S=5000 rpm. The fiber shearing and bending when against fiber cutting seriously increases temperature near the hole wall by increasing the fiber-rich regions and contact time between workpiece and cutting lip. Moreover, the maximum temperature distribution maps along feeding direction and radial direction were separately drawn for the first time to analyze the heat accumulation and overheating areas. The hole wall along the hole edge and feeding direction were detected, and severe matrix cracking, fiber bending, and fiber-matrix debonding occurred at the position where maximum temperature was located. In the future, the findings of borehole temperature characteristics can be used to refine the existing temperature model of CFRP drilling.

Amphiphilic ionic liquid assembly route for the synthesis of polymer/Ag spheres and Ag-decorated bimodal porous silica

The multifunctional assembly of amphiphilic ionic liquids (AILs) can play an important role in the synthesis of various composite nanomaterials. In this work, we developed a novel strategy to steer the generation of polymer/AIL16/Ag spheres by using amphiphilic ionic liquid, 1-hexadecyl-3-methylimidazolium chloride (AIL16) as a “bridge”. Two kinds of polymer spheres (poly(methyl methacrylate), PMMA or polystyrene, PS) were used to assemble of the PMMA/AIL16/Ag (or PS/AIL16/Ag) microspheres. Subsequently, the PMMA/AIL16/Ag (or PS/AIL16/Ag) microspheres and AIL16 were used as templating agents of macropores and mesoporores respectively to prepare Ag-decorated bimodal porous silica. The effects of mass ratios of m(Ag)/m(PMMA, or PS) and amount of AIL16 on the formation of the PMMA (or PS)/AIL16/Ag microspheres and the Ag-decorated bimodal porous silica structure were investigated in detail. It was found that the dispersity and loading capacity of Ag nanoparticles onto the polymer spheres and the structures of the bimodal porous silica can be easily manipulated by changing the mass ratios of m(Ag)/m(PMMA, or PS) and the amount of adding AIL16. The obtained Ag-decorated bimodal porous silica exhibited three dimensional ordered spherical macroporous array with an ordered mesoporous silica walls, in which Ag-NPs with good dispersibility were immobilized onto the inner walls of the macroporous holes. Furthermore, the synthesized Ag-decorated bimodal porous silica displayed a better catalytic activity for the reduction reaction of 4-nitrophenol by using NaBH4 as reducer.

Heat Modeling and Experiment of Micro-drilling with Multi-parameter Influence

Cutting temperature is essential to improve machining technology in micro drilling of hard material. As the unreasonable temperature distribution will increase the complexity of tool-workpiece surface contact, affect the machining quality of tool and the surface integrity of hole wall. In this paper, the cutting process model is combined with the analytical temperature rise model based on time to study the change rule of surface contact conditions. The 40Cr sample was used to carry out drilling experiments. The results show that the high feed micro drill tool is prone to structural differences at high temperature, large area size effect. It makes the contact conditions change significantly, and the heat distribution of system changes, which affects the stability of cutting.

Study on Interference Connection Based on Shape Recovery of NiTiNb Shape Memory Alloy.

Interference connection is an effective method for improving the fatigue life of bolt connections. In this paper, a new method of interference connection was designed based on the shape memory effect of shape memory alloy. Using the method of numerical simulation, a finite element model was established to analyze the stress–strain rule of the bolt and the hole wall under different interference fit sizes. The results show that the stress concentration is formed at the orifice of the connecting plate. When the interference fit size is less than 1%, the connection hole has elastic deformation. When the interference fit size is 1.5%, the hole wall has plastic deformation. When the interference fit size is 2.5%, the maximum stress on the connecting plate is close to the tensile limit of the material. If the interference fit size continues to increase, the strength of the connection structure will be damaged. The connection experiments with different interference fit size were designed, and the interference force was calculated by the pull-out force. The experimental results were compared with the numerical simulation results. The change trend of the interference force with the interference fit size is consistent, which verifies the rationality of the finite element simulation.

Erosion Process of a Core Clay in Earth and Rockfill Dams: Laboratory Experiments and Numerical Modelling

Internal erosion of dam’s embankments is a complex process and considered as the main cause of hydraulic works failure. Laboratory experiments provide a potential insight into the processes involved. Particles detachment from a core of earth and rock fill dams within a crack submitted to water seepage may lead to backward erosion which gradually progresses till forming a pipe. Clay of designed core must provide a quite good resistance against erosion, which depends on material and flow characteristics. The present study reports the results from hole erosion tests (HET) aiming to assess the erodibility of a clayey soil collected from a deposit by Tipaza (Algeria) and used in the core confection of an earthen dam. For this purpose, tests were performed under successive hydraulic loads and the pressure drop was measured as close as possible to the pipe edges. Hydrodynamic parameters effect on erosion rate of tested soil was investigated and the susceptibility of tested soil to erosion was addressed. A numerical simulation of turbulent flow in hole pipe using FEM was carried out to approach the hydrodynamic process occurring inside the hole and to compute shear stress acting along the wall. Numerical values of local shear stress were matched with analytical values and used to describe the area impacted by erosion and the hole radius evolve. Numerical results showed that the usual analytical evaluation of shear stress along the hole overestimates strongly the effect of seepage on the hole wall. Attempts are also made to assess the erodibility classification of tested soil from analytical and numerical results to estimate the deviation usually affecting the interpretation of HET.