Investigation on crystallographic behaviors of nickel‐base single crystal alloy cooling holes with different spanwise injection angles

Film cooling as an important thermal protection technology is widely used in aviation and ground gas turbine blades. But film cooling holes reduce the strength of blade seriously, which have become a key region of crack nucleation. In this paper, the plastic behaviors of nickel‐base single crystal alloy turbine cooling holes in spanwise injection angles range from 0° to 40° are investigated on basis of crystallographic constitutive theory. The results show that there are both higher stress regions and lower stress regions around multi‐column cooling holes, where suffer stress interference. The maximum Mises stress occurs at the hole in the center column. The places where the maximum resolved shear stresses occurs change with load and spanwise injection angle. The maximum Mises stress around holes with injection angle of 0° is lowest. With the injection angle increases, the maximum Mises stress increases until injection angles up to 30°. In all the slip systems, the resolved shear stress of hexahedral slip system is most sensitive to the changing of spanwise injection angle and load.     

The effects of slant angle on local stress distribution around cooling hole in nickel‐based single crystal

Based on crystal plasticity theory, plate specimens with a cooling hole were adopted to investigate the stress distribution and crystallographic slip characteristics, the effects of crystallographic orientations taken into consideration. The slant angles are 0°, 15°, 30° and 45°. The results show that severe stress concentrations and high stress gradients present at the cooling holes. Stress distribution changes significantly with different slant angles and crystallographic orientations. Slip bands advancing to specific directions initiate around the holes and the characteristics of the slip band vary with slant angles. Four apparent maximum values occur along the hole in the three orientations and the locations of the maximum values are much dependent on the slant angles. The influences of slant angle on the activating law of the slip systems are remarkable.     

Solution of periodic group circular hole problems by using the series expansion variational method

This paper investigates the periodic group circular holes composed of infinite groups with numbering from j = ? ∞, …, ?2, ?1, 0, 1, 2, … to j = ∞ placed periodically in an infinite plate. The same loading condition and the same geometry are assumed for holes in all groups. The series expansion variational method (SEVM) is used for the solution of the periodic group circular hole problems. After using the SEVM, the boundary value problem is then reduced to an algebraic equation for the undetermined coefficients in the series expansion form, which is formulated on the central group. The influences on the central group from central group itself and many neighbouring groups are evaluated exactly. The influences on the central group from remote groups from j = ? ∞, ?(M + 2), ?(M + 1), M + 1, M + 2 to j = ∞ are approximately summed up into one term. This suggested technique is called the remainder estimation technique (RET) hereafter. It is proved from the computed results that the RET is very effective for the solution of the periodic group hole problems. Finally, several numerical examples are given and the interaction between the groups is addressed. Comparison between various sources of computation is presented. In the uniaxial tension in y‐direction, the stacking effect of the stacked groups is studied. Copyright © 2006 John Wiley & Sons, Ltd.     

Energetics and Escape of Interchain‐Delocalized Ion Pairs in Nonpolar Media

The electron acceptor F4TCNQ p‐dopes aggregates “nanowires” of poly(3‐hexylthiophene) in nonpolar solvents but does not dope unaggregated chains. The standard free energy change for the charge transfer to form an ion pair is ΔG°_et = ‐0.21 eV. The dissociation constant to produce free ions in toluene by DC conductivity is K°_d = 1 × 10^‐8 ± 50% (ΔG°_d = 0.48 ± 0.05 eV). This remarkably large K°_d, for ions in such a low polarity medium, may reflect interchain delocalization of the hole. The particular characteristics of this material system enables determination of both ΔG°_et and ΔG°_d, to find the overall free energy change from the two neutral species to completely separated ions in nonpolar media. It is endergonic by +0.27 ± 0.05 eV in contrast to ‐0.6 eV estimated from reported HOMO LUMO differences, illustrating the challenges that persist in determining such energetics. Steady state microwave conductivity experiments on doped aggregates confirm that holes in the aggregates cannot easily escape their dopant counterion, but at higher dopant concentrations, holes become mobile. These results provide insight into the mechanisms of charge separation involving intermolecularly delocalized charges in nonpolar media, an integral process in organic photovoltaic devices and doped molecular films.     

Sound Produced When a Vortex Pair is Swallowed by a Jet

An analysis is made of the sound generated during the high-Reynolds-number convection of a vortex pair in a jet of water exhausting from a large vessel through a slit aperture. The equations of motion are linearized about the classical free-streamline solution describing steady flow through the aperture. It is assumed that the vortex pair is swept through the aperture into the jet by the steady mean flow, with no account taken of the nonlinear influence on the motion of ‘images’ in the boundaries. Additional vorticity is shed from the edges of the aperture in order that the flow should remain smooth and continuous (the Kutta condition). This vorticity is convected away within a sheet of ‘bound’ vorticity on the mean free streamlines of the jet. A strong peak in the bound vorticity is established when the vortex pair enters the aperture. Both the incident and the shed vorticity generate sound, but their respective contributions to the acoustic pressure are of opposite phase. The dominant radiation in the water above the aperture is produced as the vortex enters the jet, and has the form of a pressure pulse of width ~h/M and monopole strength , where h is the width of the aperture, ρ _o the density of the water, v a typical flow velocity, and M is the jet Mach number.     

Aerodynamic Heating of a Thin Sharp-Nose Circular Cone in Supersonic Flow

The assumption of flow symmetry is made to investigate a supersonic flow (M_∞ = 5) past a thin circular cone with a half-angle θ _c = 4° and an isothermal surface (T _w0 = 0.5) by way of numerical integration of unsteady-state three-dimensional Navier-Stokes and Reynolds equations. The calculations are performed in a discrete range of variation of the Reynolds number (10⁴ ≤ Re ≤ 10⁸) and angle of attack (0° ≤ α ≤ 15°). The effect of the determining parameters of the problem on the structure of flow field and on aerodynamic heating of the body surface subjected to flow is demonstrated.     

Directional solidification of Ni base superalloy IN738LC to improve creep properties

Abstract

The high Cr, Ni base superalloy IN738LC has been directionally solidified on both laboratory and industrial scales using Bridgman and liquid metal cooling (LMC) methods respectively. In the Bridgman experiments, cylindrical rods were grown using a graphite chill with temperature gradient G = 5·0 K mm^-1 and a water cooled copper chill with G = 8·5 K mm^-1, and a wide range of withdrawal rates of R = 60, 120, 240, 600, and 1200 mm h^-1. In the LMC rigs, several turbine blades were grown using a wide range of withdrawal rates of R = 120, 225, 330, 420, and 630 mm h^-1. Grain and dendritic structures in both cylindrical and turbine blade specimens were evaluated in longitudinal and transverse directions. Dendritic segregation of rods was determined with SEM as a function of processing parameters. Some specimens were given a two stage heat treatment followed by tension tests at 25 and 650°C and creep tests at 152 MPa and 982°C, 340 MPa and 850°C, and 586 MPa and 760°C. It was shown that at R = 600 mm h^-1 with water cooled copper chill, directionally solidified rods with a well orientated dendritic structure and better segregation pattern gives higher tensile properties at 25°C and creep properties at 340 MPa and 850°C. Tension and creep tests of turbine blades showed that although the yield and tensile strength of directionally solidified specimens are in the range of conventionally cast ones, the creep properties of the blades have been significantly improved using the LMC process.     

Application of B-spline approximation to symmetric buckling problems of truncated shallow spherical shells subjected to line loads

By using cubic B-spline approximations, reasonably accurate solutions are obtained for line-loaded shallow spherical shells with a centre hole within a wide range of values of the geometrical parameter K (0 ≤ K ≤ 400, $ K = \sqrt {12(1 - v^2)} 2f/h $, f = shell rise, h = shell thickness). It was found that the buckling loads P_c as well as the buckling threshold of the geometrical parameter K_c increase monotonically as the radius of the centre hole β increases if the hole edge is reinforced with a rigid ring and the outer edge of the shell is simply supported. However, the effect of the centre hole on P_c decreases rapidly as K increases and becomes negligible for K ≥ 45 and β ≤ 0.4.     

An experimental investigation of phase transformation superplastic diffusion bonding of titanium alloy to stainless steel

The solid-state direct diffusion bonding of a near α-phase titanium alloy to an austenitic stainless steel by means of the phase transformation superplasticity (PTSP) caused by the cycles of heating and cooling has been carried out. The test results showed that, under the conditions of T_max = 890°C, T_min = 800°C, cyclic number of heating and cooling N = 10 cycles, specific pressure P = 5 MPa, heating rate V_h = 30°C/s and cooling rate V_c = 10°C/s, the ultimate tensile strength of the joint reached its maximum value (307 MPa), and the bonding time was only 120 s. In the phase transformation superplastic state, the deformation of titanium alloy has a character of ratcheting effect and it accumulates with the cycles of heating and cooling. The observations of tensile fracture interface showed that both the brittle intermetallic compound (FeTi) and the solid solution based on β-Ti were formed on the interface, and the more in quantity and the smaller in size the solid solutions are, the higher the ultimate tensile strength is.     

Influence of non‐proportional bending with torsion on fatigue life of 10HNAP steel within the range of crack initiation and propagation

The paper presents a precise analysis of the influence of non‐proportional loading of specimens on fatigue life during initiation and propagation of fatigue cracks. Simulation of the fatigue life of specimens was based on relations describing propagation rate of the fatigue cracks. The Paris and Forman relations were applied; they were integrated after previous introduction of relationships for the equivalent range of the stress intensity factor ΔK_eq and including the phase shift angle ? between amplitudes of the bending moment and the torsional moment. Under bending with torsion, range of the equivalent stress intensity factor ΔK_eq includes ranges of stress intensity factors for loading modes I and III, i.e. ΔK_I and Δ K_III. The performed tests of 10HNAP constructional steel under cyclic bending with torsion allowed us to determine the influence of the phase shift angle ? on the fatigue life. It has been proved that increase of the phase shift angle from ?= 0° to ?= 60° and the ratio of amplitude of the bending moment M_ag to amplitude of the torsional moment M_as equal to 1.33, 2 and 4 cause increase of the fatigue life of the tested specimens. The maximum increase of the fatigue life of specimens made of 10HNAP steel was 73% (M_ag/M_as= 2, ?= 45°).     

Surface integrity studies on abrasive water jet cutting of AISI D2 steel

This article investigates the 3D surface topography and 2D roughness profiles, and micrographs were analyzed in the abrasive water jet (AWJ) cutting of AISI D2 steel kerf wall cut surfaces by varying water jet pressures and jet impact angles. In 3D surface topography, roughness parameters such as Sq, Ssk, Sp, Sv, Sku, Sz, and Sa were improved by various jet impact angles with different water jet pressures. However, the roughness parameters Ssk and Sku strongly depend on the water jet pressure and jet impact angle. This is confirmed by kerf wall cut profile structures. Fine irregularities of peaks and valleys are found on the AWJ cut surfaces, as evident from 2D roughness profiles. The scanning electron microscope micrographs confirm the production of an upper zone not very much damaged and a lower striation free bottom zone, by using the jet impact angle of 70° with a water jet pressure of 200?MPa. Finally, the results indicate a jet impact angle of 70° maintaining the surface integrity of D2 steel better than normal jet impact angle of 90°. The results are useful in mating applications subjected to wear and friction. This has resulted in enhancement of the functionality of the AWJ machined D2 steel components.     

Mit Wärme Kälte erzeugen

A steam jet cooling plant Steam jet cooling plants with water as a medium to be cooled are preferably used to chill down to 0°C and below. Since most industrial enterprises have steam and cooling water supply nets already, steam jet cooling plants can be installed there quite easily. They are characterised by ‐ low investment costs, ‐ robust and simple construction, ‐ immediate response to changes of the required cooling capacity, ‐ very low maintenance and spare parts costs. Under certain conditions even hot water or waste steam (low‐pressure, vacuum or wet steam) can be used as a motive medium. A surplus of steam, perhaps, which occurs during the summer may be used for cooling purposes, easily. Below a steam jet cooling plant for a district cooling system is described which has been installed with the company Energieversorgung Gera GmbH (Gera, Germany). Since then, it has been worked successfully. The maximum chilling capacity is 600 kW (12°C/6°C).     

强化研磨微纳加工参数对轴承套圈滚道表面硬度的影响

目的 探明不同加工参数对加工表面平均硬度的影响规律。方法 用强化研磨微纳加工技术对6012深沟球轴承内圈滚道表面进行强化处理,通过设置不同的喷射压力、加工时间、喷射角度及钢珠配比获得加工试样。采用洛氏硬度计分别检测加工前后套圈滚道表面硬度,并分析其随各参数变化的规律。结果 加工时间为5 min,喷射角度为45°,喷射压力为0.4～0.6 MPa时,表面硬度随喷射压力的增大而增大,0.6 MPa后维持在HRC61.60附近;喷射压力为0.6 MPa,喷射角度为45°,加工时间为1～5 min时,表面硬度及其增量随时间增加而增大,其后在HRC61.50附近徘徊;喷射压力为0.6MPa,加工时间为5min,喷射角度为35°～55°时,试样表面硬度及其增量先减小后增大,喷射角度达50°后,表面硬度达最大值HRC63.45;钢珠配比则对试样表面硬度影响不大,加工所得试样在HRC61.67～HRC61.80之间。结论 试样表面硬度及其增量随喷射压力、加工时间及喷射角度的增加而增加,且受加工时间影响最大。当加工时间为5 min,喷射压力为0.6 MPa,喷射角度为50°时,可获得较高的平均表面硬度。     

Modeling an increase in the lift and aerodynamic efficiency of a thick Göttingen airfoil with optimum arrangement

The Reynolds equations closed using the Menter shear-stress-transfer model modified with allowance for the curvature of flow line have been numerically solved jointly with the energy equation. The obtained solution has been used to calculate subsonic flow (at M = 0.05 and 5° angle of attack) past a thick (24% chord) Göttingen airfoil with variable arrangement of a small-sized (about 10% chord) circular vortex cell with fixed distributed suction Cq = 0.007 from the surface of a central body. It is established that the optimum arrangement of the vortex cell provides a twofold decrease in the bow drag coefficient Cx, a threefold increase in the lift coefficient Cy, and an about fivefold increase in the aerodynamic efficiency at Re = 10⁵ in comparison to the smooth airfoil.

     

Phase growth competition in solid/liquid reactions between copper or Cu3Sn compound and liquid tin-based solder

Interfacial reaction between solid ?-Cu₃Sn compound and liquid Sn at 250 °C is studied for the first time. The reaction product formed at the ?-Cu₃Sn/liquid Sn interface consists of the single η-Cu₆Sn₅ phase. The growth kinetics of the η phase formed at the incremental ?/liquid Sn couple (?/η/Sn configuration) is compared to that of η phase formed at the classical Cu/liquid Sn couple (Cu/?/η/Sn configuration). The experimental method consists first in processing of intimate interfaces by dipping peaces of solid ?-Cu₃Sn compound and Cu in liquid Sn for 1 s at 250 °C. Afterwards, isothermal holding of such pre-performed couples for 10, 30, 120 and 480 min at 250 °C are performed for both couples. A theoretical analysis of the growth kinetics of η phase and comparison of its growth in both configurations are performed.     

Strength variation of gas cooling turbine blade pin‐fin with different array

As an important measure of cooling, the pin fin array has been widely used in the cooling blade of turbine. However, most of the cracks in turbine blade are found near the pin fin due to stress concentration. In order to study the strength variations of pin fin in various shapes and with various longitudinal and transverse pitches, this paper establishes 10 rectangular, 3 elliptical and 1 diamond‐shaped slab models of pin fin array. The results indicate the existence of high stress area and low stress area around the pin fin. In the rectangular pin fin model, the maximum equivalent stress is detected on the side perpendicular to the load applied, the low stress area is on the side parallel to the load applied, and the high and low stress areas are semi‐elliptically distributed along their own track. For a rectangular pin fin array, the equivalent stress along each side of the bottom first increases and then decreases, with the maximum equivalent stress at the corners and the minimum at mid‐point of each side; along the height direction, the minimum equivalent stress of a rectangular pin fin array is near the ends while that of a square pin fin array is at the mid‐points. Under the same conditions, the stress of the rectangular pin fin array decreases with the decrease of the aspect ratio (h₁/b). The position of the maximum stress around the elliptical pin fin array varies from the two axis ratio (a/b). When a/b is 2, the maximum equivalent stress around the bottom is at the positions with a horizontal angle of 75°/120°/255°/300°; when a/b is 1, the maximum equivalent stress is at the positions with a horizontal angle of 60°/135°/240°/315°; and when a/b is 0.5, the maximum equivalent stress is at the positions with a horizontal angle of 45°/150°/220°/330°. Under the same conditions, the stress of a round pin fin array is smaller than that of a square one. In all the analytical models, the diamond‐shaped pin fin array presents the largest equivalent stress and the highest stress concentration.     

气体分配器结构对压力波制冷机性能影响的研究

在膨胀比ε=2～6、射流激励频率f=10～240Hz范围内,研究了气体分配器喷射孔相对深度b／d、振荡管与喷射孔的间距δ和振荡管轴线与喷管中心线错位角度ψ等结构参数对压力波制冷机性能的影响。实验结果表明：压力波制冷机的制冷效率η随b／d的增加先增大后减小,存在一个合适的相对充气时间比范围,在本文的实验范围内,喷射孔相对深度b／d推荐值为0．5,而增大δ与ψ值均会导致η急剧下降,所得结论对压力波制冷机的优化设计有一定指导意义。     

Granular discharge and clogging for tilted hoppers

We measure the flux of spherical glass beads through a hole as a systematic function of both tilt angle and hole diameter, for two different size beads. The discharge increases with hole diameter in accord with the Beverloo relation for both horizontal and vertical holes, but in the latter case with a larger small-hole cutoff. For large holes the flux decreases linearly in cosine of the tilt angle, vanishing smoothly somewhat below the angle of repose. For small holes it vanishes abruptly at a smaller angle. The conditions for zero flux are discussed in the context of a clogging phase diagram of flow state vs tilt angle and ratio of hole to grain size.     

A Correlation Study for the Positional Dependence of Friction Factor in Dilute Phase Flows

Results of a comprehensive study on the flow friction factor data collected on suspensions of solid granular particles of semolina, fly ash, and alumina having a size range of 75.5?µm ≤ d_p ≤ 275?µm in air are presented. The experimental study was composed of 250 separate test cases in which airflow Reynolds number Re = UD/ν and loading ratio M_p/M_a were varied systematically covering the ranges of 50,000 ≤ Re ≤ 100,000 and 5% ≤ M_p/M_a ≤ 25%. An upward flow field with variable inclinations α of 10°, 20°, and 30° with the horizontal plane and a horizontal flow field, i.e, 0° inclination, were used to determine the influence of gravitational forces. Local static pressure gradients measured along the flow field with distance x were used to determine local air-particle friction factor f_{p + a}, which was observed to be under the influence of particle type, M_p/M_a, Re, and flow line inclination, α. The proposed correlation for the variation of f_{p + a} with x/D was evaluated to reach a generalized form exhibiting interactive influence of Re, M_p/M_a?, α, and particle type.