Large Half Angle Research Articles

Investigation of the stress-strain state of a wire during high-speed monolithic drawing

This article presents the results of analytical studies conducted using computer modeling in the QForm package. The influence of technological parameters of high-speed monolithic drawing on the stress-strain state and strain rate of the wire made of steel grade 10 was assessed. A billet with a diameter of 3.5 mm was drawn into a wire with a diameter of 3.0 mm through monolithic dies with a half-angle of 3; 4; 5; 6; 7 and 8° at a friction coefficient of 0; 0.05 and 0.10. The drawing speed was taken to be 10, 20, and 40 m/s. The analysis has established that increasing the value of the half-angle of the drawing leads to the occurrence of tensile stresses and strains in the surface layers of the wire. The value of the friction coefficient has a significant effect on the stress-strain state of the wire during drawing, increasing its value leads to increased unevenness of deformation along the section and increases the values and depth of penetration of tensile stresses and strains along the wire section. It has been established that the half-angle of the drawing die has a significant effect on the uniformity of the distribution of strain rates over the wire cross section. The maximum strain rate during drawing in monolithic dies can exceed twice the average strain rate. An increase in the die half-angle from 3 to 8° leads to an increase in the strain rate up to 2.5 times. The localization of high strain rates at large half-angles of wires with is concentrated in the central part of the wire. An increase in the drawing speed from 10 to 40 m/s leads to an increase in the strain rate up to 5 times. As a result of the research, it was shown that the QForm package is applicable for computer simulation of the drawing process in a monolithic die. The adequacy of the obtained results of the numerical experiment allows us to recommend it for conducting studies of the effect of technological parameters on the stress-strain state of wire of various assortment

Study on nucleation and propagation of median cracks generated by scratching single crystal silicon

As a widely used semiconductor material, single crystal silicon inevitably suffers from sub-surface damage in mechanical processing, and the study of stress field generated by scratching single crystal silicon is of great significance for the prediction and control of subsurface damage. However, few studies have extended the calculation model of scratching-induced stress field to single crystal silicon and linked the scratching-induced stress field to the nucleation and propagation of median cracks. So in this paper, the calculation model of the stress field generated by scratching Si (100) plane along different crystal directions is established by the superposition of the elastic stress field and the residual stress field. According to the calculation model, the stress field distribution beneath conical scratch indenter is obtained, and then the nucleation and propagation laws of median cracks generated by scratches in different directions are analyzed. It is found that the nucleation position of median cracks generated by scratching is on the elasto-plastic interface at the front end of conical scratch indenter, and the function relationship between the propagation direction of median cracks and the half-angle of conical scratch indenter is obtained. The prediction results of median crack propagation direction are in good agreement with experimental results. Further, by analyzing the maximum value of the tensile stress generated by scratching and the fracture toughness of the median crack crystal plane, it is found that the length of the median crack generated by the scratch in [01¯1] direction is longer than that generated by the scratch in [001¯] direction under the same condition, and the large half-angle of conical scratch indenter will inhibit the propagation of median cracks.

Active mixing in diverging microchannels

In this study, active mixing in diverging microchannels is investigated experimentally. Using a custom-built dynamic pressure generator as the actuation source, the influences of the half-angle of the diverging section and the phase difference of the two actuating pressures in mixing performance are explored. Two flow characteristics, hydrodynamic instability and fluid lamellae, are identified as the main mechanisms leading to mixing enhancement. Even at very low Reynolds numbers, flow instability occurs in large half-angle diverging micromixers. The resulting tendril structures provide extra stretching and folding of the interface, and the degree of mixing increases accordingly. Nevertheless, flow instability alone is insufficient. To achieve excellent mixing in the diverging microchannels, the presence of both mechanisms is necessary. While pulsatile pressures vary in-phase, incoming streams flow collaterally and there is no fluid lamella effect. The concentration field is highly inhomogeneous even though tendril structures appear near the throat. In contrast, flow remains quite stable under anti-phase actuation. Fluid flows reciprocally between the two upstream branches during more than three quarters of a cycle, and patterns a series of fluorescence bands. Mixing is limited to molecular diffusion and performs poorly. When the phase difference shifts away from 0 and π, mixing performance improves significantly. To obtain the best results, a phase difference between 0.25π and 0.5π (or 1.5π and 1.75π) and a diverging micromixer with a large half-angle are preferred.

Fifth-order aberration analysis of a combined electrostatic-magnetic focusing-deflection system

This paper shows how we derived a basic fifth-order geometrical aberration formula for combined electrostatic-magnetic focusing-deflection systems with superimposed fields for electron beam lithography equipment. The formula takes into account relativistic effects and includes four-fold aberration. It enables us to evaluate the system tolerance. The aberration coefficients are classified according to the half angle of the aperture, α, the size of the image, β, the magnetic deflection distance, γ m, and the electrostatic deflection distance, γ e, defined in the image plane. The number of fifth-order geometrical aberration coefficient formulas derived by this classification process is 380. We used an algebraic language to formulate equations for the coefficients and incorporated them into a program capable of analyzing fifth-order geometrical aberrations. This approach permits the analysis of two-stage deflectors (e.g., a major one using magnetic deflection and a minor one using electrostatic deflection). We then used this tool to analyze specific focusing-deflection systems. The results show good agreement with the experimental results. So, this tool promises to be highly effective in the analysis of fifth-order aberrations for systems which have a large deflection or an apertune with a large half angle.

Effects of water and ice layers on the scattering properties of diffuse reflectors

Measurements were made of the angular distribution of power scattered from a diffuse reflector illuminated by a laser beam directed normal to the surface of the reflector. Experiments were performed on dry, wet, and ice-covered planar targets. They revealed that the diffuse component of scattered power from a wet or icecovered target is reduced by an amount proportional to the inverse of the square of the index of refraction of the layer, which is consistent with simple theory. Backscattered radiation from a water-or ice-covered target was found to be enhanced compared with that from a dry target in the region about a cone centered on the line normal to the target. The half-angles of the cones for dry, water-covered, and ice-covered targets were 2.5, 12.5, and 30 degrees , respectively. The large half-angles of the covered targets may be due to multiple reflections within the layer. Small air bubbles in the ice and the roughness of the ice surface may be responsible for the particularly large increase in half-angle of the ice-covered target.

Viscous Hypersonic Flow Past Blunted Cones at Small Angles of Attack

Theme V ISCOUS hypersonic flow over spherically blunted cones of large half angles is calculated at small angles of attack in the plane of symmetry of the flowfield. Time-dependent viscous shock-layer equations in body-oriented coordinates are used to describe the flowfield. The shock wave is treated as a discontinuity, across which the shock relations are used to compute the flow conditions behind the shock. A timedependent second-order finite-difference method is used to solve the equations for a perfect gas. The local CourantFriedrich-Lewy time increment is used to advance the solution in time at each grid point. A fourth-order damping is used to damp the oscillations in the flow quantities. The numerical results of the present analysis for quantities such as shock standoff distance, surface pressure distribution, and heating rates compare well with the existing theoretical and experimental results.