Helical Angle Research Articles

A grinding process method of solid end mills groove with segmented unequal helical angles by cutting edges offset and interference

Solid end mills with variable helical angles within a certain range can effectively mitigate cutting vibration and enhance the machining quality. However, the grinding process for these helical grooves is complex, and the existing disclosed process method cannot grind those helical grooves accurately. This study proposes a two-pass grinding method for the helical groove with variable helical angles. First, a cutting edge model with variable helical angles is established by edge offset to guide the grinding process. Second, to ensure the required cross-section parameters while avoiding overcutting and edge discontinuity, a novel optimization algorithm for determining the grinding wheel posture, and calculation rules of related process parameters for the two-pass grinding process are proposed. Finally, the verification is conducted and the results show that the maximum relative error of cross-section parameters is 1.254 % in simulation machining, which indicates the theoretical modeling of posture optimization and cutting edge are correct, and the two-pass grinding process is effective. Furthermore, this approach can be extended to grinding other complex structures with helical grooves.

Flow Characteristics and Heat Transfer Performances of Quadrant Helical Baffle Heat Exchanger with Grooved Joint

Helical baffle heat exchanger has a wide application in many industrial fields because of its high efficiency and low resistance. A new structure of the grooved helical baffle is proposed to strengthen the stability between the overlapped baffles during the spiral flow of fluid. Based on this structure, the liquid water was selected as the working medium in the tube side and shell side, the flow field characteristics and heat transfer performances of the quadrant helical baffle heat exchanger are numerically analyzed using software FLUENT 2017. The results show that when the helical angle is large (50°) and the overlapped amount is small (0.5), the comprehensive performance of the heat exchanger is the best. Therefore, the heat exchanger performance can be improved by choosing the appropriate combination of helical angle and overlapped amount. The correlation formula of the shell side heat transfer coefficient with helical angle, overlapped amount and mass flow rate is obtained by means of regression analysis, which can provide a reference for engineering application and optimal design of grooved helical baffle heat exchanger.

To flat or not to flat? Exploring the impact of flat-side design on rotary instruments using a comprehensive multimethod investigation.

To assess the influence of a flat-side design on the geometry, metallurgy, mechanical performance and shaping ability of a novel nickel-titanium rotary instrument. Sixty-five new 25-mm flat-side rotary instruments (size 25, taper 0.04) and their nonflat-side prototypes (n = 65) were assessed for major deformations and examined regarding macroscopic and microscopic design, determination of nickel and titanium elements ratio, measurement of phase transformation temperature and evaluation of mechanical performance parameters including time/cycles to fracture, maximum torque, angle of rotation, maximum bending and buckling strengths and cutting ability. Additionally, unprepared canal areas, volume of hard tissue debris and percentage reduction of dentine thickness were calculated for each tested instrument after preparing mesial canals of mandibular molars (n = 12), using micro-CT imaging. Statistical analyses were performed using the U-Mann-Whitney test and independent Student t-test (α = 5%). The number of spirals (n = 8) and blade direction (clockwise) were similar between both flat and nonflat instruments, whilst the helical angles were equivalent (⁓25°). Flat-instruments showed inconsistencies in the homogeneity of the gold colour on the flat-side surface, blade discontinuity, and incomplete and variable S-shaped cross-sections. The titanium-to-nickel ratios were equivalent, but significant differences in the R-phase finish and austenitic start phase transformation temperatures were observed between the flat and nonflat-side instruments. The flat-side instruments demonstrated superior cutting ability compared to the nonflat instruments, as well as, significantly lower values for time to fracture, rotation to fracture and maximum torque to fracture (p < .001). No statistical difference was observed between tested instruments regarding angle of rotation (p = .437), maximum bending (p = .152) and buckling load (p = .411). Preparation protocols using flat and nonflat instruments did not show any statistically significant differences (p > .05). All flat-side instruments exhibited deformation after shaping procedures. The flat-side instrument showcased enhanced cutting ability compared to its nonflat counterpart. However, it exhibited inferior performance in terms of time, rotation and maximum torque to fracture, along with distinct phase transformation temperatures. No differences were observed in the titanium-to-nickel ratios, angle of rotation, maximum bending, buckling load, preparation time, percentage of untouched canal walls, volume of hard tissue debris and percentage reduction of dentine thickness.

Damage diagnosis and fretting wear performance analysis of short suspenders in cable-supported bridges

Bridge suspenders with short length suffer from significant damage, usually following short service life, heavy casualties and property losses. In this paper, damage in the short suspenders was investigated macroscopically by inspection and field measurement. Inter-wire fretting wear due to different axial deformation and lateral shrinkage deformation of the wires with helical angle was confirmed as one of the damage cause. To investigate the fretting wear effect in the short suspender, refined FE models of the wire rope were generated by using parametric modeling method. Furthermore, inter-wire deformations and contact stresses were simulated and analyzed. Investigation of damage mechanism and fretting wear performance analysis of the short suspender contributes to the understanding of damage mechanism and the service safety of bridge cables.

Controlling the Fiber Stress Distribution with Variable-Frequency Step Roll for Tunable Spun Yarn Structures.

The dynamic regulation of fiber stress distribution in the yarn-forming triangle area is critical for controlling variable composite yarn structures, including siro and sirofil composite yarns. In this study, comparison analyses of the variable geometric structure and stress distribution during the yarn-forming process, which involves step rolls with asymmetrical fiber control, have been carried out using ring-spinning technology. The geometric analyses show that partly staple fibers are continuously controlled while other fibers intermittently lack stress restraint, resulting in cyclically changed helical angles and wrapping density in the yarn-forming triangle area. The yarn structure model displayed that periodically distributed staple fibers occur in siro composite yarn, while sirofil composite yarn shows gradual periodic changes with uniform thickness variations, caused by cyclical changes in the stress distribution between filaments, and the strand altered the yarn-forming zone shapes from symmetrical to offset. Then, a systematic comparison of variable composite yarns with different frequencies (high, medium and low frequency) revealed that low-frequency step roll with wider grooves resulted in an intermittent output of staple fibers with less stress restraint, resulting in more pronounced structural variation in the siro and sirofil composite yarns with a slight yarn quality deterioration.

A contribution to structural reliability analysis of composite high-pressure hydrogen storage tanks

Although composite high-pressure tanks are a subject of growing interest, especially for hydrogen storage applications, a detailed structural reliability analysis still needs to be improved. This work aims to provide a probabilistic investigation of the mechanical response of composite high-pressure hydrogen storage tanks using the Monte Carlo Simulation method. A performance function based on the circumferential model of composite pressure cylinders is employed with five random design variables. According to the results, the internal pressure and the helical layer thickness are the foremost parameters significantly impacting the structural reliability of the tank, whereas, the helical layer thickness and winding angles have a minor influence. In addition, high coefficients of variation values cause the contraction of the safety margin potentially leading to the failure of the composite hydrogen high-pressure tank. The obtained results were validated with experimental tests available in the literature

Cardiac Pulsatile Helical Deformation of the Thoracic Aorta Before and After Thoracic Endovascular Aortic Repair of Type B Dissections.

Type B aortic dissections propagate with either achiral (nonspiraling) or right-handed chiral (spiraling) morphology, have mobile dissection flaps, and are often treated with thoracic endovascular aortic repair (TEVAR). We aim to quantify cardiac-induced helical deformation of the true lumen of type B aortic dissections before and after TEVAR. Retrospective cardiac-gated computed tomography (CT) images before and after TEVAR of type B aortic dissections were used to construct systolic and diastolic 3-dimensional (3D) surface models, including true lumen, whole lumen (true+false lumens), and branch vessels. This was followed by extraction of true lumen helicity (helical angle, twist, and radius) and cross-sectional (area, circumference, and minor/major diameter ratio) metrics. Deformations between systole and diastole were quantified, and deformations between pre- and post-TEVAR were compared. Eleven TEVAR patients (59.9±4.6 years) were included in this study. Pre-TEVAR, there were no significant cardiac-induced deformations of helical metrics; however, post-TEVAR, significant deformation was observed for the true lumen proximal angular position. Pre-TEVAR, cardiac-induced deformations of all cross-sectional metrics were significant; however, only area and circumference deformations remained significant post-TEVAR. There were no significant differences of pulsatile deformation from pre- to post-TEVAR. Variance of proximal angular position and cross-sectional circumference deformation decreased after TEVAR. Pre-TEVAR, type B aortic dissections did not exhibit significant helical cardiac-induced deformation, indicating that the true and false lumens move in unison (do not move with respect to each other). Post-TEVAR, true lumens exhibited significant cardiac-induced deformation of proximal angular position, suggesting that exclusion of the false lumen leads to greater rotational deformations of the true lumen and lack of true lumen major/minor deformation post-TEVAR means that the endograft promotes static circularity. Population variance of deformations is muted after TEVAR, and dissection acuity influences pulsatile deformation while pre-TEVAR chirality does not. Description of thoracic aortic dissection helical morphology and dynamics, and understanding the impact of thoracic endovascular aortic repair (TEVAR) on dissection helicity, are important for improving endovascular treatment. These findings provide nuance to the complex shape and motion of the true and false lumens, enabling clinicians to better stratify dissection disease. The impact of TEVAR on dissection helicity provides a description of how treatment alters morphology and motion, and may provide clues for treatment durability. Finally, the helical component to endograft deformation is important to form comprehensive boundary conditions for testing and developing new endovascular devices.

A Theoretical and Experimental Study on the Power Loss of Gearbox Based on Dimensionless Analysis

Abstract A prediction model of gearbox power loss based on dimensionless analysis is proposed. First, the dimensional model of gearbox power loss is established based on similarity criterion, dimensional harmony principle, and fluid mechanics π theorem. Then, the experimental study is carried out on a power loss test bench. Based on the measured data and multiple linear regression method, the coefficients of the influencing factors are calculated, including gear design parameters, lubrication oil parameters, and operating conditions. To validate the prediction model, the gear pairs were tested under various operating conditions, and two new gear sets with different helical angles were also included. The comparison results show good consistency between the measured data and predicted values. The proposed model can be employed to effectively predict the power loss of gearbox and improve the gearbox efficiency.

Comparative analysis of reciprocating and flat-side heat-treated rotary single-file systems: Design, metallurgical characteristics, and mechanical performance.

To compare two flat-side single-file rotary instruments with three single-file reciprocating systems through a multimethod assessment. A total of 290 new NiTi single-file rotary (AF F One Blue 25/0.06 and Platinum V.EU 25/0.06) and reciprocating (One Files Blue R25, Reciproc Blue R25, Reciproc R25) instruments were selected, carefully examined for any major deformations, and evaluated regarding their macroscopic and microscopic design, nickel and titanium elements ratio, phase transformation temperatures, and mechanical performance (time/rotation to fracture, maximum torque, angle of rotation, microhardness, maximum bending, and buckling strengths). One-way anova post hoc Tukey, T-test, and nonparametric Mood's median tests were used for statistical comparisons (α = 5%). Tested instruments had identical blade counts and near-identical helical angles of approximately 24° (rotary instruments) and 151° (reciprocating instruments). The flat-side analysis revealed a few inconsistencies, such as discontinuity segments, different orientations, and gaps in the homogeneity of the bluish colour. Microscopically, flat-side instruments exhibited blade discontinuity and an incomplete S-shaped cross-section. The surface finish was smoother for One Files Blue and more irregular for both rotary instruments. There were distinct phase transformation temperatures amongst all instruments. All heat-treated instruments were in R-phase arrangement, and Reciproc was in R-phase plus austenite at test temperature (20°C). Compared with the reciprocating instruments, both flat-side instruments exhibited lower results in the cyclic fatigue tests using two different clockwise kinematics, maximum torque, angle of rotation, and maximum buckling strength (p < .05). The rotary systems also exhibited low flexibility (p < .05). AF F One Blue had the lowest microhardness, whilst Reciproc had the highest value. This multimethod investigation revealed that the flat-side rotary instruments underperformed the reciprocating instruments regarding cyclic fatigue (with two different clockwise kinematics), maximum torque, angle of rotation, maximum buckling strength, and flexibility. Manufacturing inconsistencies were also observed in some of the flat-side instruments, including discontinuity segments, different orientations, and in the homogeneity of their bluish colour given by the heat treatment.

Determining the helical tilt angle and dynamic properties of the transmembrane domains of pinholin S2168 using mechanical alignment EPR spectroscopy

The lytic cycle of bacteriophage φ21 for the infected E. coli is initiated by pinholin S21, which determines the timing of host cell lysis through the function of pinholin (S2168) and antipinholin (S2171). The activity of pinholin or antipinholin directly depends on the function of two transmembrane domains (TMDs) within the membrane. For active pinholin, TMD1 externalizes and lies on the surface while TMD2 remains incorporated inside the membrane forming the lining of the small pinhole. In this study, spin labeled pinholin TMDs were incorporated separately into mechanically aligned POPC (1-palmitoyl-2-oleoyl-glycero-3-phosphocholine) lipid bilayers and investigated with electron paramagnetic resonance (EPR) spectroscopy to determine the topology of both TMD1 and TMD2 with respect to the lipid bilayer; the TOAC (2,2,6,6-tetramethyl-N-oxyl-4-amino-4-carboxylic acid) spin label was used here because it attaches to the backbone of a peptide and is very rigid. TMD2 was found to be nearly colinear with the bilayer normal (n) with a helical tilt angle of 16 ± 4° while TMD1 lies on or near the surface with a helical tilt angle of 84 ± 4°. The order parameters (~0.6 for both TMDs) obtained from our alignment study were reasonable, which indicates the samples incorporated inside the membrane were well aligned with respect to the magnetic field (B0). The data obtained from this study supports previous findings on pinholin: TMD1 partially externalizes from the lipid bilayer and interacts with the membrane surface, whereas TMD2 remains buried in the lipid bilayer in the active conformation of pinholin S2168. In this study, the helical tilt angle of TMD1 was measured for the first time. For TMD2 our experimental data corroborates the findings of the previously reported helical tilt angle by the Ulrich group.

Determine the Complete Configuration of Single-Walled Carbon Nanotubes by One Photograph of Transmission Electron Microscopy.

Developing a convenient method to determine the complete structure of single-walled carbon nanotubes (SWNTs) is important to achieve the fully controlled growth of this nanomaterial. However, approaches that can identify handedness at the atomic level with simple equipment, operation, and data analysis are still lacking. Here, the SWNTs/graphene (Gr) vertical heterostructures are artificially constructed with aligned interfaces to realize the lattice interpretation of SWNT upper and lower walls separately by only one transmission electron microscopy image, thus transforming the 3D handedness information to projected 2D space. Gr displays prominent out-of-plane deformation at the interface, promoting the energetic advantage for the aligned interface construction. The interfacial alignment between the SWNT and Gr shows no obvious dependence on either the helical angle or diameter of SWNTs. The half-wrapping of SWNTs by deformed Gr also triggers diversified alterations in electronic structures based on theoretical calculations. 27 specimens with SWNTs prepared by two disparate methods are examined, implying equal handedness distribution in the randomly aligned SWNTs grown on quartz and potential handedness enrichment in horizontal SWNT arrays grown on a-sapphire. This work provides a simple strategy for chiral discrimination and lays a characterization foundation for handedness-selective growth of nanomaterials.

Output Prediction of Helical Microfiber Temperature Sensors in Cycling Measurement by Deep Learning

The inconsistent response curve of delicate micro/nanofiber (MNF) sensors during cycling measurement is one of the main factors which greatly limit their practical application. In this paper, we proposed a temperature sensor based on the copper rod-supported helical microfiber (HMF). The HMF sensors exhibited different light intensity-temperature response relationships in single-cycle measurements. Two neural networks, the deep belief network (DBN) and the backpropagation neural network (BPNN), were employed respectively to predict the temperature of the HMF sensor in different sensing processes. The input variables of the network were the sensor geometric parameters (the microfiber diameter, wrapped length, coiled turns, and helical angle) and the output optical intensity under different working processes. The root mean square error (RMSE) and Pearson correlation coefficient (R) were used to evaluate the predictive ability of the networks. The DBN with two restricted Boltzmann machines (RBMs) provided the best temperature prediction results (RMSE and R of the heating process are 0.9705 °C and 0.9969, while the values of RMSE and R of the cooling process are 0.786 6 °C and 0.997 7, respectively). The prediction results obtained by the optimal BPNN (five hidden layers, 10 neurons in each layer, RMSE=1.126 6 °C, R=0.995 7) were slightly inferior to those obtained by the DBN. The neural network could accurately and reliably predict the response of the HMF sensor in cycling operation, which provided the possibility for the flexible application of the complex MNF sensor in a wide sensing range.

An analytical method for the meshing characteristics of asymmetric helical gears with tooth modifications

This paper establishes a time-varying meshing stiffness (TVMS) analytical method for asymmetric helical gear pairs based on the potential energy principle and slice method. The method considers the adjacent teeth' influence on the deformation of the gear body part. The proposed method is verified the reasonableness by finite element (FE) analysis. The basic parameters of asymmetric helical gear such as helical angle, pressure angle and tooth width are estimated for the meshing characteristics. The results show that the increase of helix angle, pressure angle of the driving side, normal modulus and tooth width will affect the contact ratio and maximum meshing stiffness of helical gears. The variation of these parameters can minimize the fluctuation of the TVMS curve when the overlap contact ratio reaches an integer. The variation trend of the loaded-static transmission error (LSTE) is opposite to that of the TVMS curve. The load share ratio (LSR) on a pair of gear pairs will decrease with the increase of the degree of reattachment. Furthermore, the influence of tooth modifications on TVMS is estimated by using the proposed method. The mean value of stiffness is reduced after the tooth modifications. The TVMS curve changes more gently after the tooth tip modification.

Comparison Between 180° and 360° Double Helix Capacitance Sensors for Measuring Water Holdup of Horizontal Oil–Water Stratified Flows

Flows of two immiscible liquids in horizontal pipes are often encountered in the petroleum industry. The complicated flow structures, which appear in horizontal oil–water two-phase flow, bring a great challenge to flow measurement. In this article, to investigate the feasibility of the double helix capacitance sensors for measuring the water holdup of the horizontal oil–water two-phase flow, the finite-element method (FEM) is applied to analyze the sensitivity distributions of the sensors with the helical angles of 180° and 360°. Then, a horizontal oil–water two-phase flow test system is built. An experimental study is performed to compare the water holdup measurement characteristics of the two different double helix capacitance sensors. Overall, the 180° double helix capacitance sensor is found to have better characteristics in the measurement of water holdup. The conclusion is supported by the sensor sensitivity compensation characteristics analysis with the FEM. Based on the measurement of water holdup, an experimental correlation is established between the water holdup and the water cut, and better results are obtained in the water cut prediction.

Artificial Helical Screws of 2D Materials with Archimedean Spiral Arrangement

AbstractHelix structures, which are frequently observed in nature, act as versatile structural templates for complex functionalities with asymmetry and anisotropy. However, atomically thin 2D materials, including graphene, transition metal dichalcogenides (TMDs), and MXenes, do not have inherent chirality in their planar geometry and cannot easily form such a structure. This study presents the macroscopic self‐assembly of 2D materials for helical screws with an Archimedean spiral arrangement. The naturally triggered spontaneous rotation upon the 1D fiber assembly of 2D materials forms helical screws consisting of multiple helices and perversions. For a clear understanding of the morphological evolution of helical screws, variations in the helical pitch and angle are systematically analyzed considering thermodynamic and kinetic conditions. Subsequently, the influence of spontaneous helix formation on the properties of the 2D assembled fibers is investigated in terms of the solvent‐driven actuator performance and electrical and electrothermal properties. The suggested approach provides a new perspective on the directed self‐assembly of inherently achiral 2D materials toward chiral helix formation.

Experimental investigation on flow condensation pressure drop of R134a in microfin tube at high mass flux

Abstract To clarify the influencing mechanisms of the experimental condition and the tube structure on the pressure drop of heat transfer fluid, the two-phase flow condensation pressure drop of R134a inside the microfin tube was experimentally studied at high mass flux, which is different from other conventional researches. The experimental result shows the pressure drop is proportional to mass flux and fin helical angle, and is inversely proportional to condensation temperature and coolant Reynolds number. Moreover, the experimental data of pressure drop was compared with the predicted value of some existing correlations for the microfin tube. It can be found that the correlations of Cavallini et al., Han et al. and Haraguchi et al. show a good prediction effect with mean relative deviation (MRD) of 13.89, 16.08 and −2.19%, respectively. The correlations of Pierre/0.053, Kedzierski et al. and Choi et al. all underestimate most of the experimental data of the pressure drop inside the tube, and their prediction deviations are &amp;gt;10%. That is, the application effect of the separated flow model is better than that of the homogeneous flow model. Finally, the Kedzierski et al. correlation was improved to realize a high-precision prediction of the fluid flow mechanism inside the tube. Because the prediction deviation of the improved correlation between the experimental value and the predicted value was greatly reduced, its prediction deviation is &amp;lt;10% for R134a and R410A; therefore, it can be said the improved correlation has a good predictive result for the pressure drop.

Optimization of cutting power and power efficiency during particleboard helical milling

AbstractWith the aim of providing scientific guidance for the application of spiral cutters in particleboard machining, this work studied the influence of milling parameters on milling power and power efficiency during helical milling of particleboard. And the response surface methodology was applied to optimize the milling parameters to reduce machining energy consumption and improve energy efficiency. The factors of milling depth, spindle speed and helical angle were selected as input parameters, and the mathematical models between the input parameters and the response parameters were established. Then, the significant influence of each factor and the interaction of two factors were determined by variance analysis, and the change trend of milling power and power efficiency was studied by response surface methodology. Results showed that the milling depth had the greatest impact on milling power and power efficiency, followed by the spindle speed and helical angle. An increase in the milling depth and spindle speed resulted in an increase in milling power and power efficiency, while the increased helical angle resulted in a decrease in milling power and power efficiency. The optimized values of helical angle, spindle speed and milling depth were 54°, 5650 min−1 and 1.3 mm, respectively.

Alfvén continuum in the presence of a magnetic island in a cylinder configuration

In this work, the effect of a magnetic island on Alfvén waves is studied. A physical model is established wherein Alfvén waves propagate in the presence of a magnetic island in a cylindrical geometry. The structure of the Alfvén wave continuum is calculated by considering only the coupling caused by the periodicity in the helical angle of the magnetic island. The results show that the magnetic island can induce an upshift in the Alfvén continuum. Moreover, the coupling between different branches of the continuous spectrum becomes more significant with increasing continuum mode numbers near the boundary of the magnetic island.

Unique structures and material properties of the skin in different body regions of three species of fish.

Benefitting from its unique helically arranged fiber structures, fish skin is a superior biological protective tissue. Reported here is a study of the microscopic morphological characteristics and mechanical properties of the skin of three species of fish, that is, Taihu white fish (Erythroculter ilishaeformis), grouper (Cichlasoma managuense), and yellowfin seabream (Ditrema temminckii Bleeker), revealing the special protective mechanisms of fish skin. Experiments involving scanning electron microscopy show that the stratum compactum is the main part of fish skin and comprises helically stacked fibers, with the helical ply angles of the fibrous layers differing significantly for the different fish species and in different regions of their bodies. Tension and penetration experiments show that fish skin provides a fish's body with considerable mechanical protection from lacerations and bites inflicted by its natural enemies. Moreover, the mechanical tests show that fish skin has two different defensive mechanisms against tension and penetration loads, thereby offering a novel idea for designing body armor that is both flexible and tough.

Mathematical model and deviation analysis of machining cutters for internal gears with double contact points

An internal meshing gear pair that includes double contact points is proposed by the authors. For further performance evaluation and engineering application, special machining cutters for generating tooth surfaces are studied in this paper. General formulas and mathematical models of tooth surfaces of the hobbing cutter for the pinion are derived based on the actual tooth profile. Solid models of the three-dimensional hobbing cutter are established and calculation formulas of deviation conditions between the ideal tooth surface and the generated tooth surface are deduced. Deviation analysis considering the parameters of helical angle and pitch circle radius is discussed. Numerical simulations of the hobbing process are also carried out. While for the internal gear, tooth profile of skiving cutter is designed and forming formulas of tooth surfaces of the skiving cutter are derived. Solid models of the three-dimensional cutter are established, and the deviation calculation method of tooth surfaces is also provided. The research results lay the essential theoretical foundations and engineering analysis for practical applications of the new internal gears.