Hole Wall Research Articles

The effect of cutting tool coating on the form and dimensional errors of machined holes in GLARE\xae fibre metal laminates

Fibre metal laminates (FMLs) are multilayered metal composite materials currently used in aeronautical structures, especially where fatigue and impact resistance are required. FMLs are produced in large panels and often require assembly using the drilling process for riveting purposes. Hole making is a critical machining process in the joining and assembly of aeronautical components, which has to meet stringent tolerance requirements. This paper reports a systematic analysis of hole integrity when drilling an FML known as GLARE®. In particular, the primary objective is to investigate the impact of three different drill coatings (TiAlN, TiN and AlTiN/TiAlN), against several important hole parameters: thrust force, hole size, circularity, cylindricity and perpendicularity. The results show that TiAlN-coated drills produced the highest thrust force, while TiN-coated drills produced holes with the lowest deviation between the hole diameter measured at the entry and the exit and that the drill coating was the most influential parameter for the resulting hole size. TiAlN-coated drills resulted in the highest circularity at the upper part of the hole, while hole cylindricity tended to be best when using AlTiN/TiAlN- and TiN-coated drills. The ANOVA analysis shows that the drill coating and the spindle speed had a significant influence on hole size and circularity, while drill coating was the only influential parameter on hole cylindricity, and spindle speed was the only contributing parameter on hole perpendicularity. Finally, scanning electron microscopy analyses showed two distinct hole wall surface damage phenomenon due to broken fibres and evacuated metallic chips.

Micro-drilling characteristics of sequential glass fiber-reinforced resin-based/copper foil multi-layer sheets

High frequency printed circuit board (HFPCB), a sequential glass fiber-reinforced resin-based/copper foil multi-layer sheet, is widely used as printed circuit boards in next-generation 5G communication base stations, radar antenna, smart cars, etc. Micro-holes are key components that enable the interconnections of different layers, fixed electronic components, and high-density wiring. However, hole wall debris and micro-drill breakage during the micro-drilling of sequential glass fiber-reinforced resin-based/copper foil multi-layer sheet negatively affect the quality and reliability of signal transmission. Herein, chip removal, chip morphology, drilling temperature, thrust force characteristics, and hole wall morphology of HFPCB micro-drilling are investigated. The effect of chip morphology on chip removal is analyzed. Additionally, the effects of thrust force and micro-drill breakage are analyzed. The formation mechanism of hole wall debris is proposed. Compared with traditional FR4, the fracture mechanism and control method of micro-drill breakage are proposed by analyzing the characteristics and cause of typical thrust force variations. Results show that the drilling temperature and chip removal of HFPCB are primary factors causing hole wall debris. The morphology of HFPCB chips primarily includes the chips of copper foil, agglomerate chips of resin layer, and mixed copper-foil–resin chips. The increase in prepreg, resin content, and number of multi-layers causes a large amount of cutting heat during HFPCB micro-drilling. Meanwhile, the large thickness, large depth ratio, and diameter resulted in poor chip removal. Subsequently, the constant accumulation of heat in the hole resulted in resin melting, followed by adhering to the hole wall, thus generating hole wall debris through a thermo-mechanical coupling extrusion. The long-term fluctuation of thrust force is the main reason for micro-drill breakage during micro-drilling.

Hole Formation in a Diamond Substrate of Hybrid-Monolithic Integral SHF Schemes

In this paper, we study the technological process of separating a heteroplate from a polycrystalline diamond film (PDF-Si), separating a whole plate from sacrificial silicon. The hole formation in a diamond substrate from PDF via laser milling and plasma-chemical etching is studied. Plasma-chemical etching provided batch hole fabrication based on planar technology and precision lithography. The technological modes of hole etching through an aluminum mask via reactive ion etching with an inductively coupled plasma source (RIE-ICP) were optimized. The hole etching rate in the PDF was ~ 1.1 μm/min. A mathematical model of the technological process is developed. Etching is shown to occur mainly in oxygen. The technological process is adapted for the plasma-chemical etching setup “Plasma TM5”. The possibility of etching in a PDF holes 100 μm in diameter and more than 300 μm deep was studied. The etching rate was shown to depend on the hole depth and is nonlinear in nature, with etching of the hole walls and the aluminum mask.

Experimental Research on Hole Wall Integrity of TiBw/TC4 Based on Ultrasonic Vibration Assisted Drilling

Titanium Matrix Composites (TMCs) are widely used in aerospace because of their excellent mechanical properties, but it is accompanied by the difficulty of machining. Ultrasonic Vibration Assisted Drilling (UVAD) can effectively reduce the axial force in the drilling process and improve the integrity of machined surface. In this paper, the discontinuous titanium matrix composite TiBw/TC4 was developed by preparation method of in situ. In order to obtain the machining parameters of TiBw/TC4 and guide the application of UVAD in TiBw/TC4, the contrast experiments between conventional drilling (CD) and UVAD were carried out to analyze the variation law of axial force. In this experiment, the frequency and amplitude of ultrasonic vibration were set as 35 kHz and 2.5 μm respectively, and the drilling conditions were that the spindle speed was (1500/1600/1700/1800/1900) r/min and the feed speed was (6/7/8/9/10) mm/min. The surface integrity of hole wall such as roughness, residual stress and white layer was discussed. The experimental results show that the yield strength of TiBw/TC4 developed by in situ is 51% higher than that of pure TC4. Compared with CD, the axial force of TiBw/TC4 in UVAD is significantly reduced, and the formation of continuous chips and winding cutters is effectively reduced. Besides, the wear rate of the cutters is reduced. The number and size of hole wall defects, such as scratches, delamination and tearing, are obviously reduced. As well as the residual stress, white layer thickness and hole wall roughness are reduced by 4.67–16.31%, 42.48% and 5.98–29.27% respectively. Within the limits of the experiment, when the spindle speed is 1700 r/min and the feed speed is 8 mm/min, UVAD can obtain better hole wall surface integrity parameters.

Real-time spectral response guided smart femtosecond laser bone drilling

Bone drilling is a common surgical procedure of knee arthroplasty, craniotomy, stapedotomy, dental treatment, and laminotomy. Although femtosecond laser processing provides a promising method for precision bone drilling, it is still challenging to achieve thermal accumulation suppression and damage protection for large-scale hole drilling. In this paper, we propose a real-time spectral response guided femtosecond laser bone drilling method with the second-harmonic-generation (SHG) signals for positioning and monitoring. SHG green signal centered at 513.5 nm is generated below laser ablation threshold of bone, which can provide as a label-free detection for initial positioning. Results show that the spectral intensity ratio of green and white signal gradually decreases due to the accelerated removal of hydroxyapatite with the increased laser fluence, while the spectral intensity ratio of red signal and other visible signal can be used to indicate the thermal damage due to the abnormal enhancement of the red signal ranging from 700 to 800 nm when carbonization occurs. Based on the real-time spectral response at different laser fluence, the key laser processing parameters including defocus distance, flow rate of cooling water, and laser fluence are successfully optimized. Finally, a damage-free hole with the average diameter of 3 mm and the depth of 3.6 mm is successfully drilled within 5 min, while the temperature of surrounding hole wall is 37.1 °C. The proposed method provides a direct-viewing, damage-free and high-efficiency way of laser bone drilling with real-time positioning and monitoring.

Microstructural evolution of soft magnetic 49Fe-49Co-2V alloy induced by drilling

Mechanical drilling can change the microstructure of the regions near the hole wall, remarkably affecting the working performance of precision parts. The present work investigated the microstructural evolution in the regions from the drilled hole wall to the inner matrix of the soft magnetic 49Fe-49Co-2V alloy after the common drilling experiments were carried out. The microstructures and microhardness in different regions near the hole wall along the radial direction were characterized with OM, SEM, TEM, EBSD and Vickers Microhardness tester. The experimental results show that the nearest region to the hole wall is constituted of nano-sized refined grains. It exhibits a disordered BCC phase due to the rapid cooling from the high temperature during the drilling, different from the dual-phase of BCC and B2 of the matrix. The second-nearest region to the hole wall is distributed by a huge number of dislocations, leading to a maximum in microhardness. The microstructural evolution contributes to the variation of the microhardness, which increases firstly, reaches a maximum, and then decreases to the level of the matrix with the distance increasing from the hole wall. This variation tendency is discussed in light of both refined grain-boundary strengthening and dislocation strengthening mechanisms.

Mechanical and seismic anisotropy of rocks from the ONKALO underground rock characterization facility

Olkiluoto is an island that was selected as the site for a final nuclear waste disposal facility in Finland. ONKALO underground research facility was constructed for the purpose of rock characterization. A hybrid stress path, incorporating the uncertainties of the near-field stress state estimated for the different Posiva Olkiluoto Spalling Experiment (POSE) phases, was developed as the basis for boundary conditions for a series of true-triaxial tests. Evolution of each principal stress component as a result of excavations and heating of the experimental holes to understand the phenomenon of excavation damage zone (EDZ) development was evaluated. The analysis of the temporal and spatial acoustic emission (AE) activity, construction of 3D damage fracture network images from X-ray CT, and thin section studies performed on tested specimens are presented here. AE events are used to evaluate the chronological occurrence of the damage fracture networks within the induced fractures preferably initiating and propagating within the foliation zones characterized by mica grains, and predominantly avoiding quartz and feldspar grains. Veined gneiss (VGN) samples with a 30° foliation angle relative to the maximum loading direction, and the minimum loading direction perpendicular to the strike of foliation, exhibited the lowest strength, showing shear type fracture initiating parallel to the foliation planes at 55 MPa of axial stress. This value corresponds to the stress state at the POSE experiment hole wall when the first shear type damage was observed to be parallel to the foliation planes. Comparison of the evolution of AE events and seismic velocity measured at the field site for granitic pegmatite (PGR) with its counterpart laboratory specimen was found to be in good agreement. PGR is the strongest member of the rock mass and shows significant AE activity for specimens subjected to the simulated in situ loading without development of macroscale fractures.

Water-based helical laser hole-cutting in nickel super-alloy GH4049 assisted by longitudinal and transverse magnetic fields with/without ultrasonic assistance

A novel helical laser hole-cutting (HLHC) technology based on coupled assistance of water-based ultrasonic vibrations and external longitudinal/transverse magnetic fields is reported for cutting holes in nickel super-alloy GH4049 sheets. Effects of external unidirectional transverse and longitudinal magnetic fields on HLHC performance were correspondingly analyzed and compared with and without water-based ultrasonic assistance. The influence of the loading direction of an external magnetic field and the magnetic field intensity of an external longitudinal/transverse magnetic field on HLHC performance is first reported based on systematic corresponding comparisons with and without water-based ultrasonic assistance. The effects of external longitudinal/transverse magnetic fields and beam expanding ratios on actual laser focal spot sizes were analyzed and discussed. It was demonstrated that the latest reported HLHC technology assisted by water-based ultrasonic vibrations and external longitudinal magnetic fields could generate deeper holes with relatively high cutting efficiency, smaller hole taper, higher hole aspect ratio, smaller hole circularity deviation, better hole wall quality, much better performance for relieving residual stress, thinner recast layer, more uniform refinement of grains, and better performance for improving micro hardness. Generally, a stronger external longitudinal magnetic field coupled by water-based ultrasonic vibrations was more helpful for cutting deeper and higher-quality holes. It was shown that the change of loading direction of an external magnetic field with/without ultrasonic assistance did not greatly alter recast layer formation and micro hardness performance for the workpiece helically cut. Compared to the transverse magnetic assistance, a corresponding longitudinal magnetic field coupled with water-based ultrasonic vibrations was more effective for micro hardness improvement for this reported HLHC technology. When using the same water-based ultrasonic vibration assistance, a stronger longitudinal magnetic field was more effective for relieving residual stress for the workpiece helically cut (a stress reduction percentage of around 96.5% was reported in this work). The average laser focal spot size obviously decreased with laser beam expanding ratio, but the external longitudinal/transverse magnetic assistance did not greatly alter the actual laser focal spot size.

Rigid-flexible coupled multi-body dynamics analysis of horizontal directional drilling rig system

To reduce the failure probability of gas drainage drilling holes in coal mines, a new modeling method of gas drainage drilling machine is presented. Firstly, each drill pipe is regarded as a flexible body, and the Lagrange’s equation of second kind is used to model it. Secondly, the joint of drill bit, hole wall and drill pipe are regarded as rigid bodies, and the Newton-Euler method is used to model it. Thirdly, the rigid-flexible coupling multi-body dynamic model of drilling rig-drill pipe-hole wall system in medium and short horizontal section of soft coal seam is established by using relative node coordinate method, and the time complexity and operation complexity of modeling are reduced by using ADAMS macro program. Finally, the finite element method is used to discretize the model, and the virtual prototyping technology is used to solve the mathematical model. The simulation results show that the coupling of friction and vibration does not necessarily increase the probability of drilling failure, but sometimes reduces the amplitude of vibration. Compared with the length of each drill pipe, the influence of drilling depth on the system is greater, and the bit-bounce behaviours is more likely to occur in the deep hole. The operating frequency range of the drilling rig is 6.9E-3 to 2.1E+4Hz. When the length of the drill pipe is constant, the natural frequency of the system increases with the increase of the order, while the natural frequency of the deep hole section is almost unaffected by the order. In practical engineering, the vibration excitation of the actuator should be controlled to avoid the natural frequency. Meanwhile, the modal frequency should be avoided as far as possible to reduce the vibration and the failure probability of drilling holes. The model can simulate a series of dynamic responses of drilling rig system in drilling process, and provide theoretical support for subsequent multi-factor coupling modeling.

Sandwiched graphene/hBN/graphene photonic crystal fibers with high electro-optical modulation depth and speed.

Graphene-photonic crystal fibers (PCFs) are obtained by integrating the broadband optical response and electro-optic tunability of graphene with the high-quality waveguide capacity and easy-integrability of the PCF, and this has been proven to be an important step towards multimaterial multifunctional fiber and all-fiber integrated circuits. However, the reported electro-optic modulator based on directly-grown graphene-PCF suffers from very low response speed (below 100 Hz) due to the slow response of ionic liquid. Here, we propose new functional PCFs with a sandwiched graphene/hBN/graphene (Gr/hBN/Gr) film attached to the hole walls of the fibers, and theoretically demonstrate that the in-line modulator based on it can achieve simultaneous single-mode transmission ranging from 1260 nm to 1700 nm (covering all optical communication bands), significant modulation depth (e.g. ∼42 dB mm-1 at 1550 nm) and high modulation speed (up to ∼0.1 GHz). Furthermore, various device functions can be designed by changing the structure of the fiber, including the length, the hole diameter and the layer numbers of graphene and hBN films. This proposed approach directs a viable path to obtain high-performance all-fiber devices based on hybrid two-dimensional material optical fibers.

Numerical Study on Shear Performance of a New Perfobond Connector with Controllable Stiffness

To improve the shear behavior and design applicability of rubber ring perfobond connectors (RPBLs), a new rubber ring that aims to make the shear stiffness of RPBLs controllable was proposed. Firstly, the conceptual design and configuration of the new rubber rings were presented and discussed. Subsequently, finite element (FE) models for modified push‐out tests of new RPBLs were established based on the validated modeling method. The initial shear stiffness is dominated by the horizontal projected contact area between hole walls and concrete dowels. γ is defined as the ratio of the horizontal projected length of hollows to the diameter of holes. The shear stiffness of new RPBLs is about 35%, 60%, and 82% of the shear stiffness of PBLs when γ equals 0.25, 0.5, and 0.75, respectively. Employing the new rubber rings with varying central angles on conventional PBLs is feasible to obtain the required stiffness for RPBLs. Further, the effects of the number of sectors, the size of side wings, the central angle of hollows, the offset angle, and the thickness of rubber rings were analysed. Based on the numerical results, the proper thickness of side wings is no larger than 2 mm. The thicker side wing could reduce the confinement effects provided by surrounding concrete on concrete dowels, resulting in a drop of the yield load of new RPBLs. The number of sectors is suggested to be no less than 6 so that the shear behavior of new RPBLs is irrelevant to the offset angle. Besides, the shear stiffness is not related to the thickness of rubber rings. To improve the yield load of RPBLs and obtain the moderate recovered stiffness, the thickness of rubber rings is recommended as 2 mm. Finally, the expression for the shear stiffness of new RPBLs was proposed.

Thermal Conductivity of Silica-aerogel (SA) and Autoclave Aerated Concrete (AAC) Composites

Improving the thermal insulating performance of porous building materials is of great practical significance for building energy conservation. In this work, silica aerogels (SA) with ultralow thermal conductivity were proposed as an appropriate candidate to be integrated with autoclaved aerated concrete (AAC) to produce novel SA-AAC composites with higher thermal insulating performance by physical solution impregnation method. The pore-structures, mechanical and thermal properties of the SA-AAC composites were probed by various experimental tests. According to the microscopy and porosimetry results, SA were observed to adhere to the surface walls of the AAC holes, thus reducing the amount of macro-sized pores. In addition, the improved thermal insulating performance of AAC was successfully achieved with the relative improvement depending on the porosity of the pristine AAC. At the mass fraction of SA of ~7%, the highest relative improvement was found to be ~30% The results of this work exhibited a great potential of this novel SA-AAC composite in engineering applications.

Synthesis of photonic crystal fiber based on graphene directly grown on air-hole by chemical vapor deposition

The integration of fiber with graphene has greatly expanded the two-dimensional functional materials in the field of photonics research. However, the growth method by using chemical vapor deposition with metal catalytic substrateis limited to the fabrication of a graphene-fiber composite due to inevitably transferring graphene flakes onto the optical fiber surface. In order to fully achieve the interaction between light and graphene material, optical fibers have to be treated with special structure, which greatly damages the fiber structure, resulting in inefficient and harmful manufacturing strategy for the mass production. In this paper, a graphene-photonic crystal fiber (G-PCF) composite is prepared by atmospheric chemical vapor deposition (APCVD), which can directly grow monolayer and multi-layer graphene into the air-hole of photonic crystal fiber. Furthermore, we randomly break a G-PCF and then conduct an electron microscope (SEM) test at the fractured section. It is obvious that a tube-like graphene protruding out of one hole in the fractured area of the G-PCF is observed, thus further demonstrating that a monolayer graphene is grown on the inner hole walls of the PCF as shown in <xref ref-type="fig" rid="Figure2">Fig. 2</xref>. By changing the process parameters such as growth temperature, duration and gas flow rate of carbon source, the law of the influence of different parameters on the graphene layers is explored. In addition, the uniformity of graphene and defects in the graphene-photonic crystal fiber(G-PCF) are experimentally analyzed. As illustrated in <xref ref-type="fig" rid="Figure7">Fig. 7</xref>, a 4-cm-long uniform graphene-photonic crystal fiber sample is achieved by controlling the gas flow rate, growth time and the growth temperature. The APCVD method of directly growing graphene onto the inner hole walls of the PCF is simple and effective. The flexible structure and optical control enable the G-PCF to have great potential applications in all-optical devices and photonics. The development of high-quality graphene synthesis and opto-electronics technology ensures its compatibility with the integrated electronics platform and existing optical fiber systems. Moreover, our results will pave the way for 2<i>D</i> materials and optical fiber applications, providing a new idea for the application of graphene to the integration of all-optical fibers.

Effects of Different Cooling Methods on the Specific Energy Consumption when Drilling CFRP/Ti6Al4V Stacks

As the current trend in the manufacturing industry is moving toward cleaner production and sustainable manufacturing, selecting a proper cooling method is of vital importance to reduce the environmental and economical impacts of machining processes. Thus, one of the biggest challenges a manufacturer faces when machining titanium-composite stacks is whether or not to use coolant, and, if so, how to apply it effectively. Therefore, it is important to know how the application of coolants to machined composite stack surfaces affects the kinetics of cutting and how the cut surfaces interact with the coolant. The aim of this paper is to study the cutting energy distribution in drilling CFRP/Ti6Al4V stacks under different cooling conditions and to optimize the machining process in order to reduce the energy consumption. A series of drilling tests using TiAlN-coated drill bits under dry and MQL conditions were conducted to quantify the specific cutting energy consumption of each stacked phase. The results indicate that the use of vegetable-based lubricating oil can effectively reduce the energy consumed on the the friction work between the drill bit and the machined hole wall, which leads to a decrease in drilling torque and specific cutting energy. To achieve better hole quality and energy efficiency, large feed rates under MQL conditions are recommended.

Experimental Investigation of the Formation of Rockburst Pits in Circular Tunnel Based on CT Scanning

The rockburst simulation experiments of granite samples with a circular hole under biaxial loading were conducted, and the samples were scanned by computed tomography (CT) at the end of experiment. Through a series of CT images, the failure characteristics of the circular hole wall were analysed to determine the types of rockburst pits, and the detailed formation process of different types of rockburst pits was studied in combination with the crack characteristics around them. The experimental results indicate that there are mainly two types of rockburst pits, namely, pan‐shaped and V‐shaped, which can occur symmetrically or asymmetrically on the left and right sidewall of the circular hole. The formation of rockburst pits is related to the cracks parallel and perpendicular to the principal stress. Cracks parallel to the principal stress can determine the depth of the rockburst pit and affect the type of the rockburst pit, and cracks perpendicular to the principal stress determine the width of the rockburst pit. There is a correlation between the formation process of pan and V‐shaped rockburst pits. During the formation of a V‐shaped rockburst pit, several rockbursts occur, and each rockburst forms a pan‐shaped rockburst pit. In the process of developing from the tunnel wall to the deep rock, the width of the pan‐shaped rockburst pit gradually decreases and a V‐shaped rockburst with a stepped upper and lower boundary is formed.

Development of a laser-guiding-type deep small-sized hole-measurement system: Measurement accuracy

In this study, a system for measuring small-sized holes with a 17–21 mm diameter and 1000 mm length was constructed. The system comprises a laser interferometer to detect hole accuracy, a probe connected to a measurement bar, and an optical apparatus for detecting the probe attitude (position and inclination). The probe was supported by supporting pads. A steel workpiece with 18 -mm diameter and 800 mm length was used for the performance test. During the experiment, errors were found in terms of hole deviation and roundness profile. Further experiments, using new experimental apparatus and analysis, revealed the causes of errors: electrical noise that increased with time, two periodic stylus swings in the longitudinal direction of the hole per rotation of the measurement unit, and the excessive spring force pushing the tip of the stylus, causing a large frictional force with the hole wall, etc. If these errors are corrected, high accuracy in the measurement of hole deviation and roundness can be achieved.

Anchoring Mechanism and Bearing Characteristics of the Inflatable Controlled Anchor

The support technology of temporary slope engineering such as building foundation pit, has the problems of small anchorage force, non-recyclable and excessive length of anchor. Focusing on these issues, this study puts forward a new support structure system named as inflatable controlled anchor. This new type of anchor was designed and manufactured for field test. To investigate the performance of the proposed anchor, a series of full-scale field model tests were carried out with the variables of inflation pressure, anchorage length, embedment depth, and steel strip thickness. The results show that the bearing capacity of inflatable controlled anchor mainly depends on the friction resistance between the steel strips and the hole wall. The rubber membrane as an independent part only provides the compressive pressing to steel strips, and the bearing capacity can be greatly improved by increasing the inflation pressure. The bearing capacity of the anchor is also improved by the increasing of anchorage length and embedment depth. If the thickness of the steel strips is too thin, the steel strip has obvious bending deformation under inflation pressure, which affects the anchoring effect, so the thickness of steel strip has a critical value of 5 mm. According to the experimental results, the working mechanism of inflatable controlled anchor is discussed, and the calculation method for the bearing capacity is proposed. The calculated values of the proposed formula are basically consistent with the experimental results, which verifies the correctness of the formula for forecasting the bearing capacity of inflatable controlled anchor.

Fracture Analysis of the Main Valve Stem in the Steam Turbine

The failure analysis of the main valve stem in the steam turbine made of 2Cr12NiMo1W1Vis presented.The failure of the main valve stem in the steam turbine occurred at 11 operating years.Several examinations were carried out to identify the main valve stem failure’s root cause: macroscopic inspection, chemical composition analysis, hardness test, metallographic analysis, mechanical properties analysis.It is found that there are multiple cracks in the fracture of the valve stem. From the lines, it can be seen that the cracks develop from the inner wall of axial and radial holes to the outer diameter of the valve stem, and finally break in the outer wall of the four quadrals.The material performance of the valve stem is lower than the reference standard GB/T 8732-2014 and the manufacturer’s requirements, which is the internal factors of the valve stem fracture. The axial cross opening of the valve stem and the center of the axial inner hole do not coincide with the valve stem center. Local stress concentration and additional stress are the external (mechanical) factors of the valve stem fracture.It is suggested to contact steam turbine manufacturers to optimize the valve stem structure, to avoid the influence of axial cross orifice stress concentration, and to avoid the factor that may produce additional stress; Check and accept valve stem in strict accordance with manufacturer’s standard, including but not limited to valve stem material quality certificate, geometric dimension review, spectrum, etc.

Comparative tool wear and hole quality investigation in drilling of aerospace grade T800 CFRP using different external cooling lubricants

The T800 Carbon fiber reinforced polymer/plastic (CFRP) has been increasingly used for its considerable specific strength/modules to manufacture the primary load-carrying structures in aerospace industry. The abrasive carbon fibers can cause rapid tool wear in CFRP drilling, which deteriorate the quality of hole wall and result in unpredictable decrease of bearing capacity. In order to effectively reduce the tool wear, a cooling method namely external cooling lubrication (ECL) is applied in this study by using two different lubricants (Boelube 70104 and Castrol Syntilo 9828). The results show that Boelube 70104 lubricant exhibits the maximum flank wear (VB) reduction (34.5%) as compared to dry drilling after drilling 30 holes. And, the maximum CER reduction (57.4%) is obtained by using Castrol Syntilo 9828 lubricant. Different from previous researches, the maximum thrust force of drilling process using ECL presents obvious decrease as compared to dry drilling. And, the value of surface roughness (Ra) exhibits an obvious decrease when using Boelube 70104 lubricant. Two main different mechanisms for Ra decrease namely reducing surface cavity at FCA of 90° < θ < 180° and reducing saw-tooth surfaces at FCA of 0° < θ < 90° are separately observed for Boelube 70104 and Castrol Syntilo 9828 separately.

Effects of preform aperture/hole wall ratio on the microstructure and properties of ZTAp/HCCI matrix honeycomb structure composites

Zirconia toughened alumina particles (ZTAp)/high chromium cast iron (HCCI) matrix honeycomb structure composites were successfully prepared by the non-pressure infiltration casting process. The transformations of ZTA ceramic particles and high chromium cast iron during the compound process were analyzed by using x-ray diffraction (XRD) and Electron probe microanalysis (EPMA). The maximum stress and average value of the maximum stress simulated by COMSOL Multiphysics software shows a trend of decreasing first and then increasing with decreasing preform aperture/hole wall ratios. The maximum stress and average value of the maximum stress are minimal among the six comparison groups and the stress range is 0.8 ∼ 1.8 GPa with preform aperture/wall ratio of 1.25. Owing to the change in the main impregnation resistances influenced by the hole wall value, the dispersion uniformity of ZTA ceramic particles in the composites becomes better with preform aperture/wall ratio of 1.43, 1.25 or 1.11. When the preform aperture/hole ratio is 1.25, the compressive strength of the samples reaches a maximum value of 1240 MPa. And the trend of the compressive mechanical properties is consistent with the results of the stress simulation. The wear volume loss of the composites reaches the smallest with preform aperture/hole wall ratio of 1.25, because the protective effect of ZTA ceramic particles and the supporting effect of high chromium cast iron achieve the best synergistic cooperation at this ratio.