Small Taper Angle Research Articles

Microgrooves with Small Taper Angle Processed by Nanosecond Laser in Closed Flowing Water.

To improve the capability of nanosecond lasers to process structures with a high aspect ratio, a new method of nanosecond laser processing in closed flowing water was proposed in this paper. The microgrooves on a stainless steel 304 surface were processed by the new method, and the influence of processing parameters on the microgrooves was studied. The comparative experiments of laser processing in still water and overflowing water were also carried out, and the unusual phenomenon of laser processing in different flowing water was discovered by a high-speed camera. The results showed that the flowing velocity played a crucial role in underwater laser processing, and that high flowing velocity could timely remove bubbles in closed flowing water, thus obtaining higher processing efficiency. As the depth of the groove increased, the bubbles firstly affected the processing of the sidewall, causing a circular transition between the sidewall and bottom surface. The reflection of the laser beam by the bubble could cause secondary processing on the sidewall, resulting in a decrease in the taper angle. Based on the above research, the microgroove with a width of 0.5 mm, aspect ratio of 3, and taper angle of 87.57° was successfully processed by a nanosecond laser in closed flowing water. Compared to conventional nanosecond laser processing, laser processing in closed flowing water was more advantageous in processing microgrooves with a small taper angle and high aspect ratio.

Simulation and Experiment Study on Cone End Billet Method in Upsetting Billet with a Large Height-to-Diameter Ratio

A novel upsetting method, called Cone End Billet Upsetting (CEBU), is proposed in this paper to control bulging during the upsetting of large height-to-diameter ratio (LHDR) billets. This new upsetting method is mainly characterized by prefabricating a conical shape at the billet end, which aims to reduce the friction effect between the billet end and the anvil. In order to validate CEBU, the metal flow characteristics during upsetting of LHDR billets with traditional upsetting (TU) and CEBU were analyzed and compared by the finite element method. Experiments were also carried out to examine the deformation characteristics and microstructure of pure copper samples. The results show that, compared with TU, CEBU has a great advantage in restraining bulging and enhancing the compaction effect of upsetting. Meanwhile, bulging can be eliminated in CEBU with a 50% reduction ratio. In addition, aided by the cone end, the metal flow is no longer sensitive to the friction effect at the billet end. From the point of view of restraining bulging, a small taper angle is necessary prior to use. Furthermore, to avoid instability deformation, the height-to-diameter ratio of the billet should be below 3.0. CEBU is effective in suppressing the generation of bulging, but it also increases the pre-forming process for the end of the billet. The study on CEBU in this article is under laboratory conditions, and exploring the industrial application of CEBU will be the focus of our future research.

Hysteretic performance of self-centering buckling-restrained braces with embedded friction spring

This paper proposes an alternative configuration of an all-steel assembly self-centering buckling-restrained brace (FSBRB) fabricated by combining a buckling-restrained brace and friction spring. The hysteretic performance of the FSBRB is investigated using low-cycle fatigue tests, and the accuracy and applicability of the theoretical hysteretic model are verified by comparing the theoretical, test, and simulation results. The test results show that the hysteresis curve of the FSBRB exhibits a symmetric flag shape with stable hysteresis performance under cyclic loading. The recommended minimum pre-pressure of the friction spring is not less than four times the yield force of the buckling-restrained brace to achieve a full self-reset. The friction spring also has non-negligible energy dissipation capacity, which accounts for 60% of the total energy dissipation of the FSBRB under the zero residual displacement condition. The equivalent viscous damping ratio of the brace is approximately 20%. The parameter analysis results obtained by simulation show that the change in taper angle has the greatest influence on peak force and residual displacement. Moreover, the friction coefficient mainly affects energy consumption, and pre-pressure ratio has a strong relationship with the yield force of the brace. Accordingly, to achieve the self-centering capacity, the FSBRB design scheme with small taper angle, friction coefficient, and pre-pressure ratio is selected priority to attain the performance objective and reduce the force requirement of connecting parts.

Influence of taper angle on the inner field and separation performance of a hydrocyclone

ABSTRACT Taper angle is an important factor for characterizing a hyrocyclone’s separation performance. Appropriate setting of the taper angle can contribute to particle grading and separation performance of the hydrocyclone. Through numerical analysis, this study investigated the flow fields and separation performances of the hydrocyclones with different taper angles in depth. Moreover, the numerical simulation results were compared with experimental data of the conventional hydrocyclone for accuracy validation. The results showed that the tangential velocity, axial velocity, and the diameter of air core increased with the increasing taper angle. At a too large or a too small taper angle, the inner flow field would become unstable, thereby leading to the increasing number of dislocated particles and reducing the particle separation precision. For the hydrocyclone with a diameter of 75 mm, the separation precision of fine particles can be remarkably enhanced by setting the taper angle of 15°, accompanied with the improvement of product quality. The present data can provide the related enterprises with favorable guidance and a theoretical foundation for further designing the taper angle of novel hydrocyclones.

Effect of abutment neck taper and cement types on the amount of remnant cement in cement-retained implant restorations: an in vitro study.

PURPOSEThe present study aims to analyze the effect of abutment neck taper and types of cement on the amount of undetected remnant cement of cement-retained implant prostheses.MATERIALS AND METHODSThree neck taper angles (53°, 65°, 77°) and three types of cement (RMGI: resin-modified glass ionomer, ZPC: zinc phosphate cement, ZOE: zinc oxide eugenol cement) were used. For each group, the surface percentage was measured using digital image and graphic editing software. The weight of before and after removing remnant cement from the abutment-crown assembly was measured using an electronic scale. Two-way ANOVA and Duncan & Scheffe’s test were used to compare the calculated surface percentage and weight of remnant cement (α = .05).RESULTSThere were significant differences in remnant cement surface percentage and weight according to neck taper angles (P < .05). However, there were no significant differences in remnant cement surface percentage and weight on types of cement. No interaction was found between neck taper angles and types of luting cement (P > .05). The wide abutment with a small neck taper angle showed the most significant amount of remnant cement. And the types of luting cement did not influence the amount of residual cement.CONCLUSIONTo remove excess cement better, the emergence profile of the crown should be straight to the neck taper of the abutment in cement-retained implant restoration.

FE analysis of single-lap adhesive joints with tapered adherends

Adhesive joints are becoming increasingly popular in various industrial sectors. However, in spite of numerous recent studies in literature, the design phase of the adhesive joint is still challenging. The main issue in the design phase is the determination of the stress distribution in the adhesive layer under external mechanical loads. In the present study, a classical adhesive joint is analysed in comparison to its modified geometric configuration (i.e. tapered) aimed at reducing the magnitude of stress peaks. In particular, a single-lap joint with steel adherends bonded with a commercial epoxy adhesive is analysed. A 3D FE analysis is conducted to determine the distribution of normal and shear stresses in the mid-plane of the adhesive layer. The results obtained from the present study show that the inclusion of a small taper angle (i.e. 5°) leads to a remarkable reduction of normal stresses (up to 30%) compared to the classical configuration. It is observed that the further increase of the taper angle (up to 15°) does not lead to significant reductions of the stress peaks. The trend in shear stresses, on the other hand, is in contrast: an increase in the taper angle leads to an increase in the shear peaks. The method of tapering the adherends is effective in reducing the normal stresses, which are responsible for triggering the failure in the adhesive joint.

Solid rocket motor internal ballistics using an enhanced surface-vorticity panel technique

This work explores the use of surface-mesh flow solvers to model solid rocket internal ballistics with arbitrary grain geometry. Specifically, a surface-vorticity approach, originally intended for external flow applications, is adapted for internal flow analysis using boundary conditions that are suitable for solid rocket motors. In this study, an enhanced panel code is shown to be capable of resolving internal rocket flowfields with a striking level of fidelity and with such a degree of computational efficiency to make it valuable in the conceptual and preliminary design of rocket motors. In this process, the vortex paneling approach embodied within FlightStream® is refined using boundary conditions appropriate for solid rocket rotational flows. The simulation results are then compared to existing analytical solutions for cylindrical and planar chamber configurations exhibiting small taper angles and uniform headwall injection. For a more realistic validation case, the space shuttle's reusable solid rocket motor (RSRM) is examined. Guided by the analytical models, simple rotational and compressibility corrections are incorporated into the solver, and the results are subsequently compared to two other computational models and experimental measurements gathered from qualification motors. For the basic configurations, our results are shown to agree well with theoretical predictions. For the RSRM case, the corrected solution agrees well with the validation data in the first half of the motor; however, it becomes less robust in the aft region unless a recirculation zone boundary patch is applied; the latter approximates the added vorticity introduced by intersegmental gaps and the submerged nozzle effects.

Spindle assembly with adjustable output characteristics

A method for controlling the output characteristics of spindle assemblies based on the use of tapered gas bearings with a small taper angle is proposed. An experimental bench for studying the performance characteristics of these bearings is described. The results of researches of gas-static bearings with a small taper angle are presented. Keywords: spindle assembly, gas-static support, small taper angle, experiment. avkosm@knastu.ru

Green Picosecond Laser Machining of Thermoset and Thermoplastic Carbon Fiber Reinforced Polymers.

There has been an increase in demand for the development of lightweight and high-strength materials for applications in the transportation industry. Carbon fiber reinforced polymer (CFRP) is known as one of the most promising materials owing to its high strength-to-weight ratio. To apply CFRP in the automotive industry, various machining technologies have been reported because it is difficult to machine. Among these technologies, picosecond laser beam-induced machining has attracted great interest because it provides negligible heat transfer and can avoid tool wear. In this work, we conducted and compared machining of 2.15 mm-thick thermoset and 1.85 mm-thick thermoplastic CFRPs by using a green picosecond laser. The optimized experimental conditions for drilling with a diameter of 7 mm led to a small taper angle (average ~ 3.5°). The tensile strength of the laser-drilled specimens was evaluated, and the average value was 570 MPa. Our study indicates that green picosecond laser processing should be considered as a promising option for the machining of CFRP with a small taper angle.

Taper angle dependence of the dynamical transmission of several-hundred-keV protons through PC conical capillary

The dynamical transmission of intermediate-energy protons through a polycarbonate (PC) conical capillary with taper angle from 0.48° to 2° are simulated. The results show that for small taper angle of 0.48°, the transmission of 100 keV protons is dominated by the deposited-charge-assisted specular reflection. This reflection effect decreases with the increase of the taper angle. When the taper angle is increased to 2°, the transmission of the protons is mainly influenced by small angle scattering, which is consistent with the experimental data. The asymptotic transmission rate decreases with the increase of the capillary taper angle. These results suggest that the deposited-charge-assisted specular reflection is significant in focusing several-hundred-keV protons.

Highly Efficient High-Brightness 970-nm Ridge Waveguide Lasers

In this letter we present new results on high power 970 nm ridge waveguide lasers based on an extreme double asymmetric epitaxial design. Due to an improved lateral-longitudinal design an M2-value below 1.1 and efficiency over 60% could be maintained at power levels slightly above 2 W. The lasers consist of a narrow mode-filter section at the back facet, a relatively broad section at the front facet for high power capability, and a tapered section in between with a very small taper-angle. We achieved the highest reported conversion efficiency for 1 W single lateral mode power to date of 67%, as well as the highest lateral (linear) brightness of 7.5 W/mm $\bullet$ mrad with 55% efficiency at 2.5 W. Results of first life time tests are presented which show the potential for commercial use.

How far does a subduction wedge follow lubrication dynamics?

Applications of the lubrication dynamics in subduction zones generally assume very small wedge taper angles (α < 1°), satisfying the condition of flow within the subduction wedge sub-parallel to the bounding plates. However, many subduction systems have their plate interfaces with α far exceeding 1°. This article aims to address a fundamental question - is the lubrication theory valid for subduction wedges with α ≫ 1°? We test the validity by comparing its analytical solutions with the results obtained from the numerical solutions of full-form Stokes equations, and constrain α limit (<20°) in applying the lubrication theory with errors <5%. We also use this theory to evaluate the magnitude of dynamic pressure in subduction wedges as a function of subduction velocity, wedge geometry and its viscosity, and then demonstrate how such dynamic pressure eventually controls the overriding plate deformation and extrusion channel formation in convergent tectonics. Drops in dynamic pressure facilitate gravitational collapse of the overriding plate, which in turn initiates the extrusion channel in a wedge.

Расчет напряженно-деформированного состояния заготовки при вытяжке с утонением стенки через матрицу с малым углом конусности

The paper considers computing the stress-strain state of a workpiece during drawing with wall thinning through a die with a small taper angle. A manufacturing process for a sleeve usually includes several drawing operations, whereas recommendations for the final drawing operation are a low extent of deformation and using dies with a small taper angle of (2°--4°). We present a diagram for drawing with wall thinning, delineating all deformation stages recorded on the chart showing force as a function of tool path. We computed the stress-strain state and deformation in the workpiece wall during the final operation of drawing through a die with a small taper angle α ≤ 4°. We provide equilibrium equations in toroidal coordinates and compute stress-strain state parameters and extents of deformation for the axisymmetric problem statement. No longer assuming a plane strain state, we compute the stress-strain state and extent of deformation in the workpiece wall during drawing with wall thinning through a die with a small taper angle α = 2°--4°. We show that at the stage when intermediate product walls are formed, for a small taper angle it is reasonable to consider the process of drawing with wall thinning to be monotone.

Impact of Process Parameters on the Quality of Deep Holes Drilled in Inconel 718 Using EDD

Advanced engineering materials (e.g., nickel or titanium alloy) are being increasingly applied to produce parts of gas turbines in the aerospace industry. To improve the durability of these parts, many holes, with a length-to-diameter aspect ratio greater than 20:1, are created in their structure. The quality of the holes significantly affects the cooling process of the elements. However, it is challenging to machine materials by conventional methods. When machining a hole with a high aspect ratio, the major problem is effective flushing of the machining area, which can improve the hole’s surface integrity and dimensional accuracy. Consequently, the electro-discharge drilling (EDD) process is good alternative for this application. This paper presents the results of an analysis of the EDD of Inconel 718 alloy. An experiment was conducted to evaluate the impact of process parameters (pulse time, current amplitude, and discharge voltage) on the process’s performance (linear tool wear, taper angle, drilling speed, the hole’s aspect ratio, and surface roughness (Ra and Rz)). The results show that EDD provides us with the possibility to drill holes with an aspect ratio greater than 10:1. The results also demonstrate that holes with an aspect ratio greater than 10:1 and a small taper angle value have a significantly decreased quality of internal surface, especially at the bottom of the hole. This indicates that an insufficient amount of debris is removed from the bottom of the hole.

Counter-Rotating Electrochemical Machining of a Convex Array Using a Cylindrical Cathode Tool with Multifold Angular Velocity

A modified counter-rotating electrochemical machining (CRECM) method is proposed for machining a convex array on rotary part, in which a small cylindrical cathode tool rotates in the opposite direction to and at n times the angular velocity of the anode workpiece. The trajectories of the cathode tool and the profiles of the convex structure were analyzed numerically. The electrolyte flow distributions in immersed and enclosed flow mode were simulated. The results indicated that tapered, straight, and inverted tapered sidewalls can be obtained for cathode tools with different radii, and the enclosed flow mode can give a better flow of electrolyte. Experiments were conducted using small cathode tools with different radii in a specially designed electrolyte cell. Five convex structures were fabricated on the surface of the anode workpiece using a small cathode tool with a single concave cavity. The sidewalls were near straight with small taper angles of 0.71° and −0.61°. Moreover, a cylindrical anode workpiece with an extensive convex array on the surface was fabricated successfully using a small cathode tool with multiple convex cavities. This indicated that the proposed method can offer a superior machining ability for the rotary part with array structures.

Laser micromachining of silicon in air and ice layer

Thermal damage is an important drawback of laser micromachining process, and several techniques have been developed to control and limit heat induced by laser during the ablation. A novel method presented in this study is to perform the laser micromachining in ice, where the ablation take places while a workpiece is cooled in a thin ice layer. This technique is expected to limit the excessive heat conducting toward the workpiece material and also to prevent the cut debris depositing in the work surface as usually found in the dry laser ablation. Silicon wafer was used as a work sample to be cut in this study. The effects of ice temperature, ice layer thickness and average laser power on cut dimensions were experimentally investigated, and the predictive models for cut width and depth based on energy balance theorem were also formulated in this paper. Although some optical disturbances due to ice-water-vapor transitions limited the cut depth obtained, a clean and narrow cut with small taper angle was achievable when silicon was cut in ice layer. According to the findings of this study, the ice-assisted laser micromachining process could be a promising method for minimizing thermal damage in the laser ablation of silicon. In addition, this technique could also be of high potential for processing other heat-sensitive materials for micro-manufacturing applications.

Slope stability and exact solutions for cohesive critical Coulomb wedges from Mohr diagrams

This paper deals with questions of the stability and structural characteristics of submarine sedimentary slopes and accreting wedges and with a theoretical treatment, based on the assumption of a Rankine limit equilibrium state of (effective) stress in a rigid-plastic Coulomb material. For plane states of stress in uniformly sloping layers, this allows one to extract stability criteria in terms of generalized earth pressure coefficients, as well as exact cohesive critical taper solutions directly from a Mohr diagram. While an approximate solution of Dahlen et al. (1984), for small taper angles, demands an upward convex surface, cohesive Rankine state solutions require curved detachments, in agreement with curved slip lines, in the shallower part of a cohesive Coulomb-plastic slope. It is further reiterated that in such materials water loading will not affect the stability of normally pressured slopes and that solutions for subaerial (dry) and submarine (normally pressured) non-cohesive critical tapers are identical, with obvious implications for scaled physical (sand box) model experiments.

Tapering-induced enhancement of light extraction efficiency of nanowire deep ultraviolet LED by theoretical simulations

A nanowire (NW) structure provides an alternative scheme for deep ultraviolet light emitting diodes (DUV-LEDs) that promises high material quality and better light extraction efficiency (LEE). In this report, we investigate the influence of the tapering angle of closely packed AlGaN NWs, which is found to exist naturally in molecular beam epitaxy (MBE) grown NW structures, on the LEE of NW DUV-LEDs. It is observed that, by having a small tapering angle, the vertical extraction is greatly enhanced for both transverse magnetic (TM) and transverse electric (TE) polarizations. Most notably, the vertical extraction of TM emission increased from 4.8% to 24.3%, which makes the LEE reasonably large to achieve high-performance DUV-LEDs. This is because the breaking of symmetry in the vertical direction changes the propagation of the light significantly to allow more coupling into radiation modes. Finally, we introduce errors to the NW positions to show the advantages of the tapered NW structures can be projected to random closely packed NW arrays. The results obtained in this paper can provide guidelines for designing efficient NW DUV-LEDs.

Determining the machining parameters for femtosecond laser helical drilling of aluminosilicate glass substrate

In this work, a new laser helical drilling method with high geometrical accuracy is proposed for aluminosilicate glass (ASG) substrates. Laser drilling was performed from the bottom of the substrate to reduce the taper angle. The 400 μm-thick ASG substrates were drilled via a femtosecond laser beam with a wavelength of 1552 nm and a pulse duration of 800 fs. By applying this newly suggested method, thru-holes can be produced with a high roundness accuracy that is less than 20 μm, a small taper angle, low surface roughness of the sidewall, and high quality laser-drilled edges without cracks or chippings for hole diameters of 0.5, 1, 2, and 3 mm. Correlations are proposed between laser drilling parameters, such as ablation depth, scanning speed, vertical motion speed, and helical layer pitch, each of which are critical variables in drilling thru-holes in ASG substrates. Good surface quality of thru-holes can be experimentally obtained using the machining parameter values estimated by the proposed theory.

Effect of taper angle on the performance of jet pumps for a loop-structured thermoacoustic engine

Gedeon streaming, which circulates throughout the loop configuration with a time-averaged manner in the oscillating flow, can considerably deteriorate the efficiency of traveling-wave thermoacoustic engine. A jet pump is characterized by a tapered channel with different opening areas, which can produce a time-averaged pressure drop to suppress Gedeon streaming. Three jet pumps with different taper angles, i.e., 5°, 9°, 15°, are studied. Following Iguchi's hypothesis, the turbulent oscillating flow can be considered as a steady flow. The flow structures though the jet pumps are numerically simulated. Meanwhile, an experimental apparatus has been built to measure the performance of jet pump operating in the turbulent oscillating flow. The results show that the simulation is in a good agreement with the experiment data for the jet pumps with small taper angles. For the jet pump with 15° taper angle, the simulation results match well with the experiment data when the velocity at small opening of jet pump is higher than 50 m/s. However, when the velocity is lower, the simulation results deviate from the experiment data considerably, which can be attributed to the flow separation in the diverging direction operated differently in the steady flow and oscillating flow at lower velocity.