Pin Length Research Articles

Assessment of unintended shifts during frame-based stereotactic radiosurgery using cone beam computed tomography image guidance.

To investigate the frequency, magnitude and possible causes of frame-shifts that may occur between treatment planning and treatment delivery when performing Gamma Knife radiosurgery with rigid frame-based immobilization. Differences between computed tomography (CT) framed fiducial stereotactic coordinate reference and cone beam computed tomography stereotactic coordinates after image registration were recorded for 49 frame-based GK radiosurgery cases performed using the Gamma Knife Icon. Parameters recorded include rotational shifts, translational shifts, and the GK-computed Maximum Shot Displacement (MSD) between the two stereotactic coordinate spaces. Other patient-specific parameters were collected and linear regression analysis was performed to evaluate predictors of increased displacement. The median values of rotational shifts were: pitch 0.14°, yaw 0.17°, and roll 0.13°. The median absolute values of translational shifts were: left-right 0.39mm, anteroposterior 0.14mm, and superior-inferior 0. 22mm. The median value of MSD was 0.71mm. Twelve cases (24.5%) had a MSD of greater than 1.0mm. Male gender was associated with increased MSD (p = 0.013) and translational shifts (root-mean-squared value, p = 0.017). Cases with large differences between right and left sided pin lengths were also associated with increased MSD (p = 0.011). The use of CBCT image guidance in frame-based GK radiosurgery allows unintended frame shifts to be identified and corrected. A significant fraction (24.5%) of patients had large enough shifts to result in a MSD of greater than 1.0mm. Male gender and eccentrically placed frames were associated with increased MSD, and particular care should be taken in these cases.

Dissimilar friction stir lap welding of aluminum to brass: Modeling of material mixing using coupled Eulerian–Lagrangian method with experimental verifications

The intermetallic compounds formation and inter-material mixing have a critical impact on achieving a sound joint with fine mechanical properties in the case of dissimilar metal friction stir welding. In this investigation formation of intermetallic compounds as well as material flow that results in inter-material mixing during friction stir lap welding of aluminum and brass are studied. First, the 2.5-mm-thick aluminum sheet was laid on the same-thickness brass sheet and then, friction stir lap welding was applied using a tool with 4-mm pin length and 6-mm pin diameter. Next, experimental investigations were performed using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, microhardness, and tensile shear test to probe the chemical compositions and intermetallic formation in the stir zone. Moreover, the coupled Eulerian–Lagrangian method is employed to simulate the stir zone formation during the process to further study inter-material mixing. In this method, the workpiece is modeled using Eulerian formulation, while Lagrangian formulation is utilized to model the tool. The model successfully predicts the stir zone formation and inter-material mixing in the aluminum–brass interface. Results shows that by increasing tool rotational speed from 500 to 2000 r/min the amount of inter material mixing significantly increases. Therefore, to achieve a joint with the highest strength in friction stir lap welding of aluminum–brass, the rotational speed should be lowered as much as it can produce defect-free joint.

Increasing the conversion efficiency of KTP crystal using the pump-power technique

In this study, the effect of pumping power on the conversion efficiency of nonlinear crystal (KTP) was investigated using laser pump-power technique. The results showed that the higher the pumping power values, the greater the conversion efficiency (η) and, as the crystal thickness increases within limitations, the energy conversion efficiency increases at delay time of (0.333 ns) and at room temperature. Efficiency of 80% at length of KTP crystal (L = 1.75 X 10-3 m) and Pin = 28MW, and also, compare the experimental results with numerical results by using MATLAB program.

Effect of adding SiC nanoparticles to nugget zone of thick AA5083 aluminium alloy joined by using double-sided friction stir welding

In the present paper, the SiC nanoparticles were added in interface joints of thick AA5083 aluminium plates. Double-sided friction stir welded (DS-FSWed) was used to study the influences of added nanoparticles on joint characteristics. Also, the effects of different parameters such as rotational and traverse speeds, pin lengths, and the number of passes were studied. The macro and microstructural features as well as fracture surfaces of tensile specimens were studied using optical and scanning electron microscopies (SEM), respectively. The mechanical properties (tensile and hardness tests) of the nanocomposite weldments and base metal were investigated. Furthermore, fracture toughness test was employed to study the resistance of the base metal and the optimum weldments to crack growth. The results show that by changing the rotational and traverse speeds as well as pin length, the defect-free nanocomposite joint can be achieved. The SiC nanoparticles were added to joint area caused to considerable decrease in the grain size as well as an increase in the hardness of stir zone (SZ) which were compared to the base metal and without powder sample. According to the results, under the optimum conditions for the nanocomposite welds (i.e., rotational speed of 80 rpm, traverse speed of 1000 mm/min, and the pin length of 6 mm), the distribution of the powders was uniform and a defect-free welded joint was obtained. In this case, the tensile strength and fracture toughness reached 84 % and 89 % relative to those of the base metal, respectively.

Influence of high voltage polarity in multi-pin upward electrospinning system on the Fiber morphology of poly (vinyl alcohol)

This study was carried out to evaluate the influence of high voltage polarity on a newly designed multi-pin upward electrospinning spinneret to produce poly (vinyl alcohol) nanofibers. Two different high voltage polarity configurations were applied to the spinneret and collector, namely collector charging configuration (configuration-1) and spinneret charging configuration (configuration-2). The outcomes demonstrated that the collector charging configuration is better in case of upward multi-pin electrospinning setup, to their conservative framework in terms of stable Taylor cone formation, smaller fiber diameter and less bead formation. Electrical field profile in the electrospinning zone was investigated using finite element modelling for both the configurations. No difference in electric field intensity norm (|E|) was observed near the tip of the pins for both the polarities (configurations). Although having the same magnitude, the dominant electrical field component, Ez for configuration -1 is found to be of opposite sign to that of configuration -2. The electrostatic simulations also suggested that all the pins were not at the same potential and that there was a minor difference in pin potentials. Also, optimizations of pin length to reduce the potential differences between the pins were theoretically estimated through COMSOL3D simulation software.

Friction stir lap welding of AA2024-T4 with drastically different thickness

Friction stir lap welding is a promising technology to obtain high-strength joints of Al alloys in aviation and aerospace industries. Despite extensive studies performed on thin-wall structures, few works were conducted to join the plates with drastically different thickness, such as the joining of aircraft skins and panels. In this paper, 2.5-mm and 25-mm-thick AA2024-T4 plates were joined with a circumferential notches shape pin. The influence of pin length on joint features and mechanical properties was investigated. The pin improved the material flow behavior and stirred the materials violently, which were beneficial to reducing the interface migration and facilitating the joining of interfaces. The hook defects were eliminated. The failure load firstly increased with the pin length from 2.6 mm to 2.7 mm and then decreased when the pin length increased from 2.7 mm to 3.1 mm. The failure load reached 7.97 kN due to sufficient material intermixing with strong mechanical joining and large bearing area with metallurgical bonding. The selection of pin length should consider the deformation of thick plates, which acted as backing plates with lower elasticity modulus than typical backing plates made of steel.

Mechanical behavior of friction stir welded high-density polyethylene sheets

In the present work, sheets of high-density polyethylene, reinforced with strips of polypropylene using a friction stir welding technique were executed. Welding was carried out using a friction stir welding tool of 20 mm shoulder diameter and 5 mm for both pin diameter and pin length with zero tilt angle, the percentages of polypropylene added to the welding zone were 15, 20, 25, 30% (as a percentage of the added polypropylene to the welding zone), the recommended high tool rotation speed and low tool travel speed (520 rpm, 20 mm/min, respectively) were applied in all tests, the plunge depth was 0.5 mm (the penetration depth of tool shoulder from workpiece surface), dwell time at the event of submerging the pin into the faying surfaces and before initiating the tool travel speed was 45 seconds. Mechanical tests, represented by flexural and impact tests, exhibited an improvement in the mechanical properties of the welded specimens for the case of 25% added polypropylene. Friction stir welding has extraordinary potential to create imperfection-free joints and to initiate a high-quality weldment of high-density polyethylene sheets reinforced by polypropylene strips.

Four-electrodes DBD plasma jet device with additional floating electrode

A Dielectric Barrier Discharge (DBD) plasma jet in a four electrodes configuration was investigated in order to improve the discharge parameters, such as, plasma power and rotational and vibrational temperatures of molecular species in the plasma plume. The improvement attempts were made by introducing an auxiliary floating electrode in a form of a metallic pin inside the DBD device. That piece was placed near the bottom of the main device, centered in relation to the four powered electrodes, which were covered with a dielectric material. By using metallic pins with different lengths, it was observed that there were considerable variations of the plasma parameters as a function of the pin length. Two carrier gases were tested: argon and helium. With helium as the working gas, it was found that there is an optimal pin length that maximizes the plasma power and its vibrational temperature. In addition, it was verified that for the pin of optimum length the relative intensity of light emissions from OH and NO species achieved higher values than in other conditions studied.

Poboljšanje osobina metala šava i ZUT kod zavarivanja MAG postupkom primenom zavarivanja trenjem sa alatom

Steel is one of the most widely used engineering materials and it is popularly welded in fabrication industries using Gas metal arc welding (GMAW) process. The microstructure obtained in the heat affected zone is often characterized with large grain size. Depending on the GMAW process parameters, the weld metal may consist of Allotrimorphic ferrite if the heat input is high. Therefore, the weld metal and the heat affected zone may have poor weld metal toughness. Efforts have been made to modify the microstructure of the weld metal by performing friction stir processing. Initially bead on plate welding was performed on mild steel plate using GMAW process using standard 1.2 mm consumable wire and CO2 as the shielding gas. The top surface of the weld was processed using a tungsten carbide tool. The weld reinforcement was removed using milling process and the area to be processed was made smooth before performing FSP. The plate was secured in an FSW machine and friction stir processing was carried out with a FSW tool having pin length of 2 mm. The GMAW weld and the weld that has been subsequently modified using FSP were characterized using standard techniques. The microstructure of the top face showed an improvement from Widmanstätten to fine equiaxed structure after being friction stir processed. The microstructure in the HAZ also got refined. It is expected that this structure would improve the mechanical properties of the weld particularly on the surface.

Forming of pin on thick plate by open extrusion

A special-shaped part that is a small pin formed on a plate has been required to fit a plastic pulley into the pin for a lightweight construction. This formed part is stronger and more reliable than a small pin bonded with a plate. In this study, a process of open extrusion to form the pin on the plate and the forming conditions are proposed. Conventional extrusion indicates a critical overload to form a small pin by FEM analysis when the billet is constrained with a container. Open extrusion using no container enables to form a longer pin with 1.6 = l / d under a low forming load, where d of the pin diameter is 3.0 mm and l of the pin length is 4.7 mm on a copper plate with a thickness of 2.3 mm.

Experimental determination of buoyancy induced convection heat transfer characteristics in a rectangular cavity with cylindrical porous medium fixed between pin fins

The present work aims to investigate the heat transfer characteristics of heated cylindrical pins within an air-filled rectangular enclosure experimentally in a natural convection dominated regime. The experiments are performed to analyze the effects of fin spacing (25 mm ≤ S ≤ 100 mm) and Rayleigh number (248,659 ≤ Ra ≤ 578,395) as key factors at constant pin height (l = 25 mm) and pin diameter (d = 10 mm) values. The results confirm the existence of optimum fin spacing providing maximum heat transfer enhancement. The investigation is extended further to quantify the effects of the presence of cylindrical porous pins with the uniform diameter (dp = 15 mm), pin length (lp = 20 mm) and calculated porosity of 19.3% by volume on the thermal performance of the system. The results reveal the improved system performance due to the presence of a porous medium for all tested system configurations. Some new empirical correlations predicting system performance are also proposed those demonstrate the satisfactory qualitative behavior of system performance.

Influence of tool rotational speed on the mechanical and microstructural properties of AISI 316 Austenitic stainless steel friction stir welded joints

Fabrication of steel joints using fusion welding technique will result in defects like hot cracking, and heavy residual stresses along with coarse microstructural features in the weldments. To overcome these problems, friction stir welding (FSW) technique was employed to fabricate steel joints. Tungsten based alloy tool is used in this investigation to withstand high dynamic frictional forces at elevated temperature generated during welding. Tool shoulder diameter of 25 mm, pin diameter of 3 mm and pin length 2.9 mm was employed to carry out the friction stir welding on SS316 steel plate of 3 mm. Sound joints produced at a constant welding speed of 40 mm min−1, axial load of 15 kN at different tool rotational speed of 600 rpm and 700 rpm. In accordance with ASTM standards, Tensile, Compression, Micro hardness and impact tests were carried out to assess the mechanical properties of weld joints and the base metal. Mechanical testing results showed that tensile and hardness of the welded material was improved in compared with base metal. However, the impact strength of the welded metal is reduced. Furthermore, the base metal and welded metal were subjected to study microstructural analysis using optical and scanning electron microscopy. EDS and XRD analysis were also carried out on welded zone to understand about the formation of new phases in weld zone and it is surroundings.

Enhanced heat transfer in pin fin heat sink working with nitrogen gas–water two-phase flow: variable pin length and longitudinal pitch

In the current study, thermal–hydraulic characteristics of nitrogen gas–water two-phase flow through a plate–pin fin heat sink are investigated experimentally. Water flow through the smooth case, i.e., heat sink without pin fin, is considered as baseline. Four new models of the pin fin with variable longitudinal pitch and pin length having low-to-high and high-to-low arrangements are proposed. They are named for short as LP–LH, LP–HL, PL–LH, and PL–HL. The results indicate that in all heat sinks, the Nusselt number values of the two-phase flow in comparison with those of the single-phase flow are higher, but the friction factor values of the two-phase flow in comparison with those of the single-phase flow are lower. Also, the friction factor and the Nusselt number of both the single-phase flow and the two-phase flow in the heat sinks with pin fin are greater than those in the heat sink without pin fin. The highest values of the Nusselt number are recorded for PL–HL at water mass flow rate of 0.0093 kg s−1 and gas volume flow rate of 0.8 L min−1. At these flow rates in PL–HL, the Nusselt number of the two-phase flow is increased about 45.6% relative to the single-phase flow.

Microstructure and mechanical properties of Al/steel dissimilar welds fabricated by friction surfacing assisted friction stir lap welding

Al/steel dissimilar welds were obtained by friction stir lap welding (FSLW) with an Al interlayer, which was fabricated by friction surfacing (FS). In present study, the tool pin was totally plunged into the Al plate and interlayer without stirring steel, which avoided the tool wear. The Al plate and interlayer were remarkably intermixed as pin length increased. A diffusion layer, instead of the intermetallic layer, was found at the Al/steel interface, indicating the enhanced atomic migration and related interfacial bonding. The maximum failure load of the joints of 2.8kN was reached when the 2.5mm pin tool was used. The heterogeneous microstructure, which was caused by the intermixing, was responsible for the fracture, according to the fracture profiles. Necking and dimples were depicted from the fractographies, indicating that the joints were failed by plastic fracture.

Accuracy of Linear Measurements Made on Cone Beam Computed Tomography Scans at Different Magnifications

Objective: This study aimed to evaluate the accuracy of linear measurements made on CBCT (New Tom VGi) scans with different image magnifications.
 Methods: Forty-two titanium pins were inserted into seven dry sheep mandibles. Lengths of the pins were measured using a digital caliper with 0.01 mm readability, and the mandibles were radiographed using a CBCT unit. After reconstruction of CBCT images, three experienced radiologists measured the length and diameter of titanium pins at100%, 200% and 400% magnifications. Accuracy of measurements was analyzed using descriptive statistics and one-way analysis of variance (ANOVA) P<0.05 was considered statistically significant. Inter observer reliability was calculated using the intra class correlation coefficient (ICC) test.
 Results: The mean differences of linear measurements from the actual lengths of pins were 0.1960 mm, 0.2143 mm and 0.2047 mm at 100%, 200% and 400% magnifications, respectively (P>0.05). The mean differences of linear measurements from the actual diameters of pins were 0.2206 mm, 0.2063 mm and 0.1984 mm at 100%, 200% and 400% magnifications, respectively (P>0.05). Inter observer reliability of pin length measurements was estimated to be0.285, 0.707 and 0.479 at 100%, 200% and 400%magnifications, respectively. Inter observer reliability of pin diameter measurements was 0 .078, 0.469 and 0.587 at 100%, 200% and 400%magnifications, respectively.
 Conclusion: Based on the results, image magnification does not affect the accuracy of linear measurements made on CBCT scans. Inter observer reliability of pin length measurements was good at 200% magnification, while it was below the acceptable range at other magnifications. For measurement of pin diameters, this index was below the acceptable range at all magnifications.

Accuracy of Linear Measurements Made on Cone Beam Computed Tomography Scans at Different Magnifications

Objective: This study aimed to evaluate the accuracy of linear measurements made on CBCT (New Tom VGi) scans with different image magnifications.
 Methods: Forty-two titanium pins were inserted into seven dry sheep mandibles. Lengths of the pins were measured using a digital caliper with 0.01 mm readability, and the mandibles were radiographed using a CBCT unit. After reconstruction of CBCT images, three experienced radiologists measured the length and diameter of titanium pins at100%, 200% and 400% magnifications. Accuracy of measurements was analyzed using descriptive statistics and one-way analysis of variance (ANOVA) P<0.05 was considered statistically significant. Inter observer reliability was calculated using the intra class correlation coefficient (ICC) test.
 Results: The mean differences of linear measurements from the actual lengths of pins were 0.1960 mm, 0.2143 mm and 0.2047 mm at 100%, 200% and 400% magnifications, respectively (P>0.05). The mean differences of linear measurements from the actual diameters of pins were 0.2206 mm, 0.2063 mm and 0.1984 mm at 100%, 200% and 400% magnifications, respectively (P>0.05). Inter observer reliability of pin length measurements was estimated to be0.285, 0.707 and 0.479 at 100%, 200% and 400%magnifications, respectively. Inter observer reliability of pin diameter measurements was 0 .078, 0.469 and 0.587 at 100%, 200% and 400%magnifications, respectively.
 Conclusion: Based on the results, image magnification does not affect the accuracy of linear measurements made on CBCT scans. Inter observer reliability of pin length measurements was good at 200% magnification, while it was below the acceptable range at other magnifications. For measurement of pin diameters, this index was below the acceptable range at all magnifications.

Microstructural Evolution and Mechanical Behavior of Friction-Stir-Welded DP1180 Advanced Ultrahigh Strength Steel

Friction stir lap welding of a DP1180 advanced ultrahigh strength steel was successfully carried out by using three welding tools with different pin lengths. The effects of the welding heat input and material flow on the microstructure evolution of the joints were analyzed in detail. The relationship between pin length and mechanical properties of lap joints was studied. The results showed that the peak temperatures of all joints exceeded Ac3, and martensite phases with similar morphologies were formed in the stir zones. These martensite retained good toughness due to the self-tempering effect. The formation of ferrite and tempered martensite was the main reason for the hardness reduction in heat-affected zone. The mechanical properties of the lap joints were determined by loading mode, features of lap interface and the joint defects. When the stir pin was inserted into the lower sheet with a depth of 0.4 mm, the lap joint exhibited the maximum tensile strength of 12.4 kN.

Probing vortex-shedding at high frequencies in flows past confined microfluidic cylinders using high-speed microscale particle image velocimetry

Vortex-shedding from micropins has the potential to significantly enhance and intensify scalar transport in microchannels, for example by improving species mixing. However, the onset of vortex-shedding and the mixing efficiency are highly sensitive to the confinement imposed by the microchannel walls. In this work, the time dependent flow past a cylindrical pin in microchannels with different levels of confinement was studied experimentally. The onset of vortex-shedding in such flows is associated with high, kilohertz range frequencies that are difficult to resolve using conventional laser-based microscale particle image velocimetry (μPIV) techniques. Hence, in this study, a high-speed μPIV technique was implemented in order to obtain time-resolved measurements of the velocity fields downstream of the micropin to estimate the corresponding vortex-shedding frequencies and quantify the mixing in the pin wake. The vertical confinement (pin length to diameter ratio) was found to delay the onset of vortex-shedding. When vortex-shedding was present, the shedding frequency and the corresponding Strouhal numbers were found to be greater in channels with higher lateral confinement for the same Reynolds number. Finite-time Lyapunov exponent analysis was performed on the acquired velocity fields to estimate the mixing performance. The results clearly illustrated the significant enhancement in both the mixing in the wake and the mass flux across the centerline of the wake induced by vortex-shedding.

Freeze-Thaw Induced Gully Erosion: A Long-Term High-Resolution Analysis

Gullies are significant contributors of sediment to streams in the southeastern USA. This study investigated gully erosion in the clay-rich soils of east Tennessee under a humid subtropical climate. The aims of this study were to (1) estimate long-term erosion rates for different gully geomorphic settings, (2) compare patterns of erosion for the different settings, and (3) model the response of gully erosion to freeze-thaw events. Erosion was measured weekly from June 2012 to August 2018 using 105 erosion pins distributed in gully channels, interfluves, and sidewalls. Erosion rates were estimated from average slopes of lines of best fit of pin lengths versus time. Maximum and minimum temperature was calculated daily using an on-site weather station and freeze-thaw events were identified. Gully erosion was modeled using antecedent freeze-thaw activity for the three geomorphic settings. Long-term erosion rates in channels, interfluves, and sidewalls were 2.5 mm/year, 20 mm/year, and 21 mm/year, respectively; however, week-by-week erosion was statistically different between the three settings, indicating different erosive drivers. Models of erosion with lagged freeze-thaw variables explained up to 34.8% of the variability in erosion variables; sidewall erosion was most highly related to freeze-thaw activity. Freeze-thaw in prior weeks was an important variable in all erosion models.

Assessment of AA7075/SiO2 surface composites fabricated by friction stir processing (FSP)

Friction stir processing (FSP) was developed based on the same principles of friction stir welding (FSW) mainly to enhance the surface properties of various materials and to produce surface composites. In this work surface composites of AA7075 as the metal matrix that reinforced with ultra-fine sized SiO2 particles were developed using FSP. A groove of 3 mm depth and 1.2 mm width was made on the surface of AA7075 to provide the highest reinforcement volume fraction on the produced surface composites. FSP tool with a square profiled tool pin of 3.5 mm pin length and of 5mm pin side was used. The FSP parameters used were 600 rpm and 50 mm/min. The developed surface composites were evaluated using different metallographic techniques to investigate the macro and micro features. Also the hardness profile was measured across the processed zone. The surface composites achieved by three consecutive passes of processing showed uniform particle distribution across the stirring zone of the surface composite. Moreover, the surface composite hardness was improved by 10-30% compared to the unreinforced alloy. The tool with a square profiled tool pin enables obtaining sound surface without any visible defects.