Exit Side Research Articles

Investigation on the Influence of Multi Walled Carbon Nanotubes on Delamination in Drilling Epoxy/Glass Fabric Polymeric Nanocomposite

Abstract Nanocomposites are rapidly emerging as important engineering materials. This paper presents a study of the influence of multi walled carbon nanotubes (MWCNTs) on the drilled hole quality. The influence of MWCNTs was analyzed by comparing the drilled hole quality on epoxy/glass fabric polymeric composite fabricated with neat and MWCNTs filled epoxy matrix. Drilling tests were carried out on these materials with HSS twist drill of diameter 6 mm. Factorial design based experiments were conducted at chosen levels of cutting speeds and feed rates. Delamination factor was taken as a measure of hole quality. Image processing technique was used to measure the delamination factor at the entrance and exit sides. Analysis of variance (ANOVA) is employed to study the significance of the presence of MWCNTs and the effect of cutting parameters. Statistical analysis showed that the presence of MWCNTs has significantly improved the drilled hole quality both at the entrance and exit sides.

ISWI Remodelers Slide Nucleosomes with Coordinated Multi-Base-Pair Entry Steps and Single-Base-Pair Exit Steps

ISWI-family enzymes remodel chromatin by sliding nucleosomes along DNA, but the nucleosome translocation mechanism remains unclear. Here we use single-molecule FRET to probe nucleosome translocation by ISWI-family remodelers. Distinct ISWI-family members translocate nucleosomes with a similar stepping pattern maintained by the catalytic subunit of the enzyme. Nucleosome remodeling begins with a 7 bp step of DNA translocation followed by 3 bp subsequent steps toward the exit side of nucleosomes. These multi-bp, compound steps are comprised of 1 bp substeps. DNA movement on the entry side of the nucleosome occurs only after 7 bp of exit-side translocation, and each entry-side step draws in a 3 bp equivalent of DNA that allows three additional base pairs to be moved to the exit side. Our results suggest a remodeling mechanism with well-defined coordination at different nucleosomal sites featuring DNA translocation toward the exit side in 1 bp steps preceding multi-bp steps of DNA movement on the entry side.

Surface roughness in rotary ultrasonic machining: hypotheses and their testing via experiments and simulations

Rotary ultrasonic machining (RUM) is a non-traditional drilling process. It has been used to drill not only brittle but also ductile materials. It was observed that the surface roughness of the drilled hole near the entrance side was better than that near the exit side. However, explanations about this observation could not be found in the literature. This paper aims to provide explanations about this observation. It presents three hypotheses and their testing via experiments and simulations.

1119 開口部付き緩衝工から放射される微気圧波に関する模型実験と解析(OS11-4 流体関連振動・騒音,OS11 流体関連振動・騒音)

An impulsive pressure wave emitted from a tunnel portal, called a micro-pressure wave, is one of the important wayside environmental problems in high-speed railways. A tunnel hood with openings on its side wall installed at the portal of the train entrance side is the principal countermeasure for reducing the micro-pressure wave. However, the micro-pressure wave tends to have large peak value around openings of the hood when the micro-pressure wave is emitted from the tunnel exit portal with the hood. In this study, we carried out the model experiment focused on the effects of the tunnel hood with openings installed at the portal of the train exit side. In addition, we developed a simple theoretical model simulated the micro-pressure wave around openings of the hood.

가스메탈아크용접에서 콘택트팁의 마모에 미치는 용접재료의 영향

The contact tip is higher the wear of resistance and the longer life are demanded to GMA welding process. In this study, four different contact tips with three different compositions by two wires were evaluated their wear resistance by measuring in every one hour the area of enlarged hole at the exit side during actual wleding. Experimental results clearly showed that the Cr-containing tips strengthened by precipitation hardening have much better resistance to wear than those made by work hardening. In addition, flux cored wire is excellent abrasion resistance test results showed. Based on these results, the domestic industry, the life of the contact tip to know will be used as basic data.

Controlling the Cut in Contour Residual Stress Measurements of Electron Beam Welded Ti-6Al-4V Alloy Plates

The multiple cut contour method is applied to map longitudinal and transverse components of residual stress in two nominally identical 50 mm thick electron beam welded Ti-6Al-4V alloy plates, one in the as-welded condition and a second welded plate in a post weld heat treated (PWHT) condition. The accuracy and resolution of the contour method results are directly linked to the quality of the electro-discharge machining cut made. Two symmetric surface contour artefacts associated with cutting titanium, surface bowing and a flared edge, are identified and their influence on residual stresses calculated by the contour method is quantified. The former artefact is controlled by undertaking a series of cutting trials with reduced power settings to find optimal cutting conditions. The latter is mitigated by attaching 5 mm thick sacrificial plates to the wire exit side of the test specimen. The low level of noise in the measured stress profiles for both the as-welded and PWHT plates demonstrates the importance of controlling the quality of a contour cut and the added value of undertaking cutting trials.

Skin dose in longitudinal and transverse linac‐MRIs using Monte Carlo and realistic 3D MRI field models

The magnetic fields of linac-MR systems modify the path of contaminant electrons in photon beams, which alters patient skin dose. To accurately quantify the magnitude of changes in skin dose, the authors use Monte Carlo calculations that incorporate realistic 3D magnetic field models of longitudinal and transverse linac-MR systems. Finite element method (FEM) is used to generate complete 3D magnetic field maps for 0.56 T longitudinal and transverse linac-MR magnet assemblies, as well as for representative 0.5 and 1.0 T Helmholtz MRI systems. EGSnrc simulations implementing these 3D magnetic fields are performed. The geometry for the BEAMnrc simulations incorporates the Varian 600C 6 MV linac, magnet poles, the yoke, and the magnetic shields of the linac-MRIs. Resulting phase-space files are used to calculate the central axis percent depth-doses in a water phantom and 2D skin dose distributions for 70 μm entrance and exit layers using DOSXYZnrc. For comparison, skin doses are also calculated in the absence of magnetic field, and using a 1D magnetic field with an unrealistically large fringe field. The effects of photon field size, air gap (longitudinal configuration), and angle of obliquity (transverse configuration) are also investigated. Realistic modeling of the 3D magnetic fields shows that fringe fields decay rapidly and have a very small magnitude at the linac head. As a result, longitudinal linac-MR systems mostly confine contaminant electrons that are generated in the air gap and have an insignificant effect on electrons produced further upstream. The increase in the skin dose for the longitudinal configuration compared to the zero B-field case varies from ∼1% to ∼14% for air gaps of 5-31 cm, respectively. (All dose changes are reported as a % of D(max).) The increase is also field-size dependent, ranging from ∼3% at 20 × 20 cm(2) to ∼11% at 5 × 5 cm(2). The small changes in skin dose are in contrast to significant increases that are calculated for the unrealistic 1D magnetic field. For the transverse configuration, the entrance skin dose is equal or smaller than that of the zero B-field case for perpendicular beams. For a 10 × 10 cm(2) oblique beam the transverse magnetic field decreases the entry skin dose for oblique angles less than ±20° and increases it by no more than 10% for larger angles up to ±45°. The exit skin dose is increased by 42% for a 10 × 10 cm(2) perpendicular beam, but appreciably drops and approaches the zero B-field case for large oblique angles of incidence. For longitudinal linac-MR systems only a small increase in the entrance skin dose is predicted, due to the rapid decay of the realistic magnetic fringe fields. For transverse linac-MR systems, changes to the entrance skin dose are small for most scenarios. For the same geometry, on the exit side a fairly large increase is observed for perpendicular beams, but significantly drops for large oblique angles of incidence. The observed effects on skin dose are not expected to limit the application of linac-MR systems in either the longitudinal or transverse configuration.

Vehicle queue effect on the characteristics of air flow, and exhaust scalar dispersion and distribution fields in the vehicle wake

The characteristics of air flow, and vehicular exhaust scalar (i.e., pollutant) dispersion and distribution fields in the near-wake region of a scale-model vehicle which was placed alone or behind the preceding one(s) in a closed-circuit wind tunnel facility were experimentally investigated for typical urban driving conditions. The wake structure behind a queue of studied vehicles is mainly dominated by the last one, while the preceding vehicle(s) will lead to a stronger downwash flow in the wake. For the vehicle with rear slant angle (α<30°) which has a pair of trailing vortices in the wake flow, the vehicular exhaust jet plume will be mainly trapped inside these two trailing vortices and fills an “m-shaped” scalar distribution region behind the vehicle. Half of the m-shaped region which is on the vehicular tailpipe exit side shares a larger portion of scalar distribution than the other half. This unbalanced scalar distribution is enhanced by the preceding vehicle(s). For the vehicle with rear slant angle (α>30°) which has a two-dimensional wake flow, the vehicular exhaust jet plume will be carried by such a wake flow to form an “n-shaped” scalar distribution region behind the vehicle with a peak scalar region at its center. The preceding vehicle(s) will further enlarge the n-shaped scalar distribution region and push the peak scalar region closer to the ground. It is clearly shown that the two- or three-dimensional flow behind the studied vehicle can provide different shapes of exhaust scalar dispersion and distribution fields in the vehicle wake.

Experimental investigation of material removal mechanism in single grit grinding

This paper presents an important investigation of material removal behaviour during single grit grinding, which provides critical insight of grinding mechanics for improving grinding efficiency and quality. During the investigation, CBN grits were used to perform scratch tests on En24T steel. Piles up ratio, chip removal strength, effective grit engage radius are introduced to measure material removal performance. It has been discovered that grit cutting edge shape has significant influence on ploughing and cutting actions. By comparing scratch tests using grits with single edge or multiple edges, it has demonstrated that cutting is more efficient with single edge grit. More ploughing actions appear in multiple edges scratches. Furthermore, material removal mechanism along a single scratch is investigated and found that material removal is more prominent at the grit entrance side of the scratch compared to the grit exit side of the scratch. The research findings provide critical information for grinding optimization.

Computational analysis of geometrical factors affecting experimental data extracted from hydrogen permeation tests: II – Consequences of trapping and an oxide layer

Although electrochemical permeation tests are used to determine the diffusion coefficients of hydrogen through metals, these measures are affected by various phenomena such as trapping or surface states. In this work, we analyzed the combined effects on diffusion of hydrogen trapping and the presence of an oxide layer at the exit side of the material. We numerically simulated the diffusion of hydrogen through a 1 mm thick martensitic steel membrane, using Finite Elements Method. Trapping densities are taken between 10−4 and 100 mol/m3, for an oxide layer 5 nm thick. We studied oxide layers with hydrogen diffusion coefficients between 10−21 and 10−10 m2/s. It appears that the diffusion is withheld by trapping and the oxide layer. However both parameters exhibit opposite effects on hydrogen subsurface concentrations; analytical equations have been proposed to correct the experimental results obtained by electrochemical permeation tests, using the material properties. It appears that the ratios between the membrane and the oxide diffusion coefficients and thicknesses guide the influence of trapping and the oxide layer.

Natural Convection in a Vertical Channel with Arrays of Flush-Mounted Heaters on Opposite Conductive Walls

Three-dimensional numerical study of natural convection in a vertical channel with flush-mounted discrete heaters on opposite conductive substrate walls is carried out in the present work. Detailed flow and heat transfer characteristics are presented for various Grashof numbers. The heat transfer effects on one wall by the presence of heaters on its opposite wall is examined. It is found that heat transfer rates on one wall are increased by the presence of heaters on its opposite wall. The thermal boundary layers on the opposite walls complement each other for enhanced heat transfer. The effects of spacing between the heated walls, spacings between heaters and substrate conductivity on flow and heat transfer are examined. Existence of optimum spacings between the heated walls for maximum heat transfer and mass flow are observed. It is found that the heat transfer and fluid flow do not follow the same optimum spacings. Mass flow rate reaches maximum value at a wall spacing greater than the spacing for maximum heat transfer. This is because the interaction of thermal boundary layers on individual walls ceases at a lower spacing before the velocity boundary layers separate each other. It is found that increased spacings between heaters reduce individual heater temperatures provided the heaters close to exit on both substrates avail sufficient substrate potions on the exit side. Insufficient substrate portions between the exit heaters and the exit cause abnormal local temperature rise in the exit heaters which are the hottest ones among all the heaters. Optimal heater spacings exist for minimum hottest heater temperature rise. Correlations are presented for dimensionless mass flow rate, temperature maximum, and average Nusselt number.

TU‐A‐BRA‐06: EPID Operation in a Bi‐Directional MRI‐Linac System: A Monte Carlo Study

Purpose: To examine via Monte Carlo simulation the dosimetric operation of an EPID inside a bi‐directional MRI‐Linac system. The proposed system is a 1 T MRI which supports both perpendicular (transverse) and inline (longitudinal) 6 MV MRIgRT. Methods: BEAMnrc Monte Carlo simulations were used to model a Varian 6 MV linac. Phase space files were produced below the MLCs and were inputs to Geant4 Monte Carlo simulations. These consist of transporting the radiation beam through a phantom and then on to a detailed model of a Varian EPID. The Geant4 simulations take place inside magnetic field maps matched to Finite Element Modeling of the MRI‐Linac system (COMSOL). Hence the EPID operation is simulated in the same conditions as a real MRI‐linac system. Various EPID SSD's were simulated in both inline and perpendicular field MRI‐linac systems. Dose to the EPID layers were taken for each field and compared with zero magnetic field. Results: The inclusion of the magnetic fringe field had little impact in the inline direction, however in the perpendicular direction the electron‐return effect (ERE) caused secondary electrons to return to the phosphor scoring level. This induced a lateral blur and overdosing of the images that was related directly to the SSD or strength of the fringe field in the transverse direction (5% at 0.25 T, 10% at 1 T). Including 1 cm of water material below the phosphor layer significantly reduced the ERE and improved the dose image quality. Conclusion: Novel Monte Carlo simulations of the operation of an EPID working inside a bidirectional field MRI‐linac have been performed. The main effect which induced an image or dose artifact was the ERE in the perpendicular field arrangement. This can however be almost eliminated by the use of an exit side bolus on the EPID.

A single-solenoid pulsed-magnet system for single-crystal scattering studies

We present a pulsed-magnet system that enables x-ray single-crystal diffraction in addition to powder and spectroscopic studies with the magnetic field applied on or close to the scattering plane. The apparatus consists of a single large-bore solenoid, cooled by liquid nitrogen. A second independent closed-cycle cryostat is used for cooling samples near liquid helium temperatures. Pulsed magnetic fields close to ~30 T with a zero-to-peak-field rise time of ~2.9 ms are generated by discharging a 40 kJ capacitor bank into the magnet coil. The unique characteristic of this instrument is the preservation of maximum scattering angle (~23.6°) on the entrance and exit sides of the magnet bore by virtue of a novel double-funnel insert. This instrument will facilitate x-ray diffraction and spectroscopic studies that are impractical, if not impossible, to perform using split-pair and narrow-opening solenoid magnets. Furthermore, it offers a practical solution for preserving optical access in future higher-field pulsed magnets.

Hole quality and burr reduction in drilling aluminium sheets

Optimization of the metal drilling process requires creation of minimum amount of burrs and uniform appearance of the drilled holes. In this paper, an experimental investigation was performed on 2mm sheets of wrought aluminium alloy Al99.7Mg0.5Cu-H24, using 1.6 and 2mm diameter drills. Cutting data, clamping conditions, and drill geometry were varied in order to optimize the process and reach the desired quality. The results revealed possible reduction of burr occurrence on both the entry and exit side of the sheet, requiring no additional deburring. The demand on the uniform appearance of drilled holes was fulfilled as well as high productivity achieved. Such optimized process results in a noticeable production cost reduction.

S134021 CFRP/Ti積層板のドリル加工面温度測定

Carbon reinforced plastics (CFRP) is increasingly being used in the aerospace industry because of the high strength-to-weight ratios. Material stacks comprising CFRP and titanium alloy are used for structures for aerospace applications, where high mechanical loads exist. Drilling is used to make holes for fastening the composites by bolting. The drilling temperature effects on the hole quality. In this study, the hole bottom surface temperature during drilling of CFRP/Ti composite is measured by using an infrared radiation pyrometer with an optical fiber. The optical fiber is inserted in the oil hole of carbide drill to measure the temperature. In the drilling of CFRP/Ti, the temperature is about 80 °C during drilling of CFRP, and the temperature rapidly increases to 270 C at the beginning of the drilling of titanium and it increases to 750 °C at the exit side of titanium. In the drilling of Ti/CFRP, the temperature is about 170 C at the beginning of the drilling of titanium and it increases to 700 °C at the exit side of the titanium, and the temperature is about 180 °C during drilling of CFRP.

Rotation of focal plane of magnetic analyzer in an isotope ratio mass spectrometer using curved shims

The inclination of focal plane from beam axis of the magnetic sector analyzer in an isotopic ratio mass spectrometer is an important design feature. For a stigmatic geometry mass spectrometer, the focal plane is normally inclined by an angle of ∼25° with respect to the principal trajectory which presents various complications in case the number of collectors is more than five. An attempt has been made by us to rotate this plane along a line normal to the principal trajectory (by using shims on exit side of magnetic analyzer) resulting in ease of design for the collector system. This paper presents theoretical explanation, computer simulation and experimental results on this development. Simulated results on optimum shim curvature are in good agreement with experimental data.

Microcavity enhanced optical absorption in subwavelength slits

We introduce a compact submicron structure consisting of multiple optical microcavities at both the entrance and exit sides of a subwavelength plasmonic slit filled with an absorbing material. We show that such microcavity structures at the entrance side of the slit can greatly enhance the coupling of the incident light into the slit, by improving the impedance matching between the incident plane wave and the slit mode. In addition, the microcavity structures can also increase the reflectivities at both sides of the slit, and therefore the resonant field enhancement. Thus, such structures can greatly enhance the absorption cross section of the slit. An optimized submicron structure consisting of two microcavities at each of the entrance and exit sides of the slit leads to ~9.3 times absorption enhancement at the optical communication wavelength compared to an optimized slit without microcavities.

Rubber friction: Comparison of theory with experiment

We have measured the friction force acting on a rubber block slid on a concrete surface. We used both unfilled and filled (with carbon black) styrene butadiene (SB) rubber and have varied the temperature from -10 °C to 100 °C and the sliding velocity from 1 μm/s to 1000 μm/s. We find that the experimental data at different temperatures can be shifted into a smooth master-curve, using the temperature-frequency shifting factors obtained from measurements of the bulk viscoelastic modulus. The experimental data has been analyzed using a theory which takes into account the contributions to the friction from both the substrate asperity-induced viscoelastic deformations of the rubber, and from shearing the area of real contact. For filled SB rubber the frictional shear stress σ(f) in the area of real contact results mainly from the energy dissipation at the opening crack on the exit side of the rubber-asperity contact regions. For unfilled rubber we instead attribute σ(f) to shearing of a thin rubber smear film, which is deposited on the concrete surface during run in. We observe very different rubber wear processes for filled and unfilled SB rubber, which is consistent with the different frictional processes. Thus, the wear of filled SB rubber results in micrometer-sized rubber particles which accumulate as dry dust, which is easily removed by blowing air on the concrete surface. This wear process seams to occur at a steady rate. For unfilled rubber a smear film forms on the concrete surface, which cannot be removed even using a high-pressure air stream. In this case the wear rate appears to slow down after some run in time period.

전기자동차용 배터리 팩 주위의 유동장 해석

The battery pack, a main component of NEV(Neighborhood Electric Vehicle), needs cooling system when it is charging or discharging to prevent the degradation of the battery charging efficiency. The purpose of this study is to analyse the effects of cooling methods, changing positions of inlet and outlet and changing area ratios of inlet and outlet. It has been observed that in the point of uniform cooling, suction from the exit side is more efficient than blowing from the inlet. And there is a suitable inlet/outlet area ratio in maximizing the mass flow rate. A commercial code, STAR-CCM+(ver. 4.02), was used for the numerical study.

Drilling CFRP Thermosets Using Mounted Points

Highly abrasive nature of carbon fibres and material-related problems like fibre or fibre bundle pullouts, matrix micro cracks and especially delamination of single or multiple laminate layers can be regarded as major problems when machining CFRP. This paper presents an approach using mounted points for drilling of fibre reinforced thermosets. The axial and thermal loads were recorded and quality criterions like the surface roughness, diameter deviation and the delamination at the tool exit side were quantified. Furthermore, an approach to improve the grinding process is presented. Results indicate that using mounted points are suitable for drilling operations in case of thermoset laminates.