Non-uniform Surface Roughness Research Articles

Mass finishing of additively manufactured Ti6Al4V parts: An investigation of surface finish dependency on build orientation and processing conditions

Poor surface finish of as-built metal Additive Manufacturing (AM) remains a key challenge in fabricated parts. Metal AM parts typically require postprocessing to improve surface finish before application. Furthermore, different surface orientations and scanning strategies in Powder-Bed-Fusion (PBF) metal AM are prone to result in non-uniform surface roughness across different surfaces of a part. In recent years, Mass Finishing (MF) technologies, such as Centrifugal Disc Finishing (CDF), are gaining popularity in improving AM surfaces due to its fixture-free, batch-processing, and relatively low costs. There is a critical need to study the surface finish dependency on AM build orientation and MF processing conditions. In this study, Ti6Al4V ASTM-E8b tensile bars were fabricated in 45⁰ and 90⁰ orientation via Laser Powder Bed Fusion (L-PBF) to investigate the effects of CDF processing conditions on upward facing surface (up-skin), downward facing surface (down-skin), and side facing surface (side-skin). The surface roughness evolution on each type of surface were collected via laser scanning profilometry. It was found that both processing speed and processing time of CDF were statistically significant factors in improving AM surface roughness, however, processing time had higher impact. Furthermore, different build orientation demonstrated different surface roughness reduction rate and material removal rate. It was found that side-skin had the highest average roughness reduction, and the down-skin exhibited the least roughness reduction. In addition, this study found that the surface with the highest initial surface roughness (down-skin) had the least material removal rate, and that the highest material removal rate was observed in surface with higher periodicity (side-skin). Findings from this study will help the AM community in decision-making of CDF conditions to prevent over-finishing and under-finishing. In addition, the investigation of surface evolution dependency on AM build orientation can further improve the understanding of key mechanisms of AM + MF hybrid manufacturing system.

Effect of a new pattern of surface roughness on flow field and erosion rate of a cyclone

Abstract This paper evaluates the impact of a special design of non-uniform surface roughness on the operating parameters of a gas–solid cyclone numerically. The cyclone surface is divided into 32 separate rings with different roughness heights when the roughness height varies from 0.2 to 3 mm. The results show that the tangential velocity is reduced and the axial velocity is enhanced by increasing the height of non-uniform roughness. It is observed that the cyclone with smooth walls can collect 7 μm solid particles while 3.7 and 2.77 μm particles can be separated by one-inlet and two-inlet cyclones, respectively. For the cut-off size diameter of d 50, the one-inlet cyclone with smooth walls can collect the particles with a diameter of 1.24 µm, while the cyclone with R Nu = 0.2, 0.5, 1, 2, and 3 mm can collect 1.3, 1.6, 1.8, 0.83, and 1.88 µm particles, respectively. The results demonstrate that the erosion rate decreases with the roughness and this reduction is larger for the one-inlet cyclone.

Scaling effects in the alternating-current poling of thin PIN-PMN-PT single crystals

AC-poling of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystals with a thickness of 0.06–0.16 mm was studied in this paper. Compared with DC-poled samples, enhancements in piezoelectric and dielectric properties can be obtained when the thickness is above 0.1 mm. However, inconsistency in poling effects was found in the crystals with thickness below 0.1 mm. To elucidate why such scaling effect arises, surface roughness was measured by an atomic force microscopy to correlate surface morphology and poling effects. It was found that non-uniform surface roughness led to inconsistent and decreased properties. Furthermore, temperature-dependent dielectric permittivity spectra were measured to explore how crystal thickness affects the thermal stability of ferroelectric phases. It is noted that complex changes in crystallographic symmetries emanate by decreasing thickness. Such phenomena can be attributed to more influential effects of surface morphology when thickness is reduced. We hope this work suggests a clue for solving the scaling effects of AC-poling on relaxor-PbTiO3 single crystals.

Performance deterioration of axial compressor rotor due to uniform and non-uniform surface roughness

Surface roughness is a significant source of performance loss in gas turbine engines. The fan and compressor, being the initial components of the gas turbine engine, are more prone to surface roughness effects due to the ingestion of debris at low atmospheric conditions. This paper attempts to numerically study the impact of uniform and non-uniform surface roughness on axial compressor rotor performance. NASA rotor 37 is used as the validation test case for the numerical methodology, and the results show a good match between the experimental and computational fluid dynamics data. Detailed flow field analysis indicates that there is a reduction in rough blade performance and the overall flow turning that reduces the work done by the rotor. The location sensitivity studies shock location is the major contributor to the overall loss in the performance. Also, the study of non-uniform roughness on blade performance shows that roughness on the leading edge is the major contributor to the loss as compared to the trailing edge and so does roughness on the shroud as compared to the roughness on the hub. An interesting observation is that for the given configuration and roughness height, near the shroud, the role of the tip vortex is more pronounced than the role of surface roughness on the performance.

Impact of non-uniform surface roughness on the erosion rate and performance of a cyclone separator

The present study investigates the influence of non-uniform surface roughness on the performance and erosion rate of a Staimand cyclone separator. Non–uniform roughness is considered for the cylindrical part, cone, and vortex finder of the cyclone. Three-dimensional simulations are performed using the Reynolds stress turbulence model (RSM). The Eulerian-Lagrangian approach is used for tracking solid particles. The results reveal that non-uniform surface roughness affects the flow pattern, collection efficiency, erosion rate, and pressure drop significantly. The maximum tangential velocity in the cyclones with the roughened surfaces is 1.3 times the inlet velocity. The maximum tangential velocity is reduced when the range of roughness height decreases. As the range of roughness height is enhanced, the axial velocity increases considerably. For instance, at the axial position of y = 0.75D, the value of axial velocity is about 0.34 and 0.08 times the inlet velocity for states 1 and 6 of the descending non-uniform roughness (DNUR) case, respectively. It is observed that the pressure drop in the cyclones with non-uniformly roughened surfaces is less than that in the cyclone with smooth walls. For the cut-off size diameter d100, four states of the ascending non-uniform roughness (ANUR) cyclone can completely collect the particles with diameters of 4.8, 4.9, 5, and 6 µm, while the smooth-walled cyclone can collect 7-µm particles with the collection efficiency of 100%. Besides, it is demonstrated that the erosion rate of cyclones with non-uniformly roughened walls is less than that of smooth-walled one for all mass loads.

Interpreting the radiative properties of advanced high strength steel strip using a hybrid thin film/geometric optics model

Advanced high strength steel (AHSS) alloys derive their mechanical performance through a carefully controlled intercritical annealing process. Unfortunately, variations in spectral emissivity caused by selective oxidation and non-uniform surface roughness imparted by cold-rolling impact the accuracy of the pyrometrically-inferred temperatures used for process control. This study evaluates the spectral reflectance of cold-rolled and annealed AHSS in the visible and near-infrared spectra, with the objective of improving the reliability of pyrometry. Reflectance measurements reveal that both thin film interference and roughness significantly impact the radiative properties of AHSS over the wavelengths important to pyrometry; these results are interpreted empirically using electron microscopy and optical profilometry. Predictions using a thin film interference model and a hybrid model, which accounts for both wave interference and roughness effects, generally underestimate the reflectances of oxidized AHSS having rough states. For most of these samples, the weaker interference effect observed in the measured reflectances are attributed to the rugged and non-uniform oxide morphology.

3D 프린팅 기술 적용 용이성을 위한 Ku-밴드 헬리컬 안테나 정합부 전기적 등가 변환 설계

In this study, we design and build a helical antenna operating at the Ku-band using a hybrid 3D printing technology. A non-uniform surface roughness can reduce the conductivity of printed metals. Therefore, through simulation and equations, we demonstrate that a triangular metallic matching section of a helical antenna can be equivalently replaced with a strip-line matching section. As the proposed antenna has fewer physically printed parts, the reduction in the conductivity of the printed metallic parts at high frequencies is avoided. The simulated results are verified experimentally. The impedance characteristics are well matched, whereas the absolute value of the gain is degraded. This might be owing to the non-exact expectation of the material characteristic of the immersed epoxy used for adhesion of the printed antenna part and connector in the simulation.

The machined surface of magnesium AZ31 after rotary turning at air cooling condition

Magnesium is a lightweight metal that is widely used as an alternative to iron and steel. Magnesium has been applied in the automotive industry to reduce the weight of a component, but the machining process has the disadvantage that magnesium is highly flammable because it has a low flash point. High temperature can cause the cutting tool wear and contributes to the quality of the surface roughness. The purpose of this study is to obtain the value of surface roughness and implement methods of rotary cutting tool and air cooling output vortex tube cooler to minimize the surface roughness values. Machining parameters that is turning using rotary cutting tool at speed the workpiece of (Vw) 50, 120, 160 m/min, cutting speed of rotary tool of (Vt) 25, 50, 75 m/min, feed rate of (f) 0.1, 0.15, 0.2 mm/rev, and depth of cut of 0.3 mm. Type of tool used is a carbide tool diameter of 16 mm and air cooling pressure of 6 bar. The results show the average value of the lowest surface roughness on the speed the workpiece of 80 m/min, cutting speed of rotary tool of 50 m/min, feed rate of 0.2 mm/rev, and depth of cut of 0.3 mm. While the average value of the highest surface roughness on the speed the workpiece of 160 m/min, cutting speed of rotary tool of 50 m/min, feed rate of 0.2 mm/rev, and depth of cut of 0.3 mm. The influence of machining parameters concluded the higher the speed of the workpiece the surface roughness value higher. Otherwise the higher cutting speed of rotary tool then the lower the surface roughness value. The observation on the surface of the rotary tool, it was found that no uniform tool wear which causes non-uniform surface roughness. The use of rotary cutting tool contributing to lower surface roughness values generated.

Spot nanofinishing using ball nose magnetorheological solid rotating core tool

The spot nanofinishing of surface plays an important role for improving the surface quality of miniature mechanical, electronics, and optics components. The nano-level finishing of these miniature components is highly demanded in today’s industry to fulfill the operational and functional requirement. The principal innovation of the present work is generating uniform magnetic field at the end of a magnetizable rotating core tool for providing a uniform surface roughness on a spot finishing of precision components. To fulfill this requirement, a ball nose magnetorheological nanofinishing process based on solid rotating core tool is developed. The existing ball end magnetorheological finishing (BEMRF) process uses a rotating core with central hole for flow of polishing fluid at the tool end surface. Due to central hole inside the rotating core, a non-uniform magnetic flux density has been experienced at the tool end surface which may result in non-uniform surface roughness in spot finishing, i.e., on a fixed location without any X-Y-axis linear feed rates. The magnetostatic finite element analysis clearly revealed the uniform magnetic flux density at the end surface of the solid rotating core tool than existing BEMRF tool core having central hole. The experimentation has been carried out for spot finishing on ferromagnetic workpiece surface in order to study the variation in surface roughness values. The present ball nose magnetorheological finishing process with solid rotating core tool produced uniform average surface roughness values as 20 nm from 290 nm after 90 min of spot finishing on the ferromagnetic workpiece surface. The experimental results confirmed the effectiveness of generating uniform magnetic field at the end of a magnetizable rotating core tool for a spot uniform nanofinishing of precision components.

Numerical Analysis of the Effects of Nonuniform Surface Roughness on Compressor Stage Performance

Gas turbine performance degradation over time is mainly due to the deterioration of compressor and turbine blades, which, in turn, causes a modification of the compressor and turbine performance maps. Since the detailed information about the actual modification of the compressor and turbine performance maps is usually unavailable, the component performance can be modeled and investigated by the following: scaling the overall performance map, using stage-by-stage models of the compressor and turbine, and scaling each single stage performance map to account for each stage deterioration, or performing 3D numerical simulations, which allow to both highlight the fluid-dynamic phenomena occurring in the faulty component and grasp the effect on the overall performance of each affected component. In this paper, the authors address the most common and experienced source of loss for a gas turbine, i.e., compressor fouling. With respect to the traditional approach, which mainly aims at the identification of the overall effects of fouling, authors investigate a microscale representation of compressor fouling (i.e., blade surface deterioration and flow deviation). This allows (i) a more detailed investigation of the fouling effects (e.g., mechanism, location along blade height, etc.), (ii) a more extensive analysis of the causes of performance deterioration, and (iii) the assessment of the effect of fouling on stage performance coefficients and on stage performance maps. In this paper, the effect of nonuniform surface roughness on both rotor and stator blades of an axial compressor stage is investigated by using a commercial CFD code. The NASA Stage 37 test case is considered as the baseline geometry and a numerical model already validated against experimental data available in literature is used for the simulations. Different nonuniform combinations of surface roughness levels are imposed on rotor and stator blades. This makes it possible to highlight how the localization of fouling on compressor blades affects compressor performance both at an overall and at a fluid-dynamic level.

G206 不規則粗面の粗さパラメータと摩擦抵抗との関係に関する実験的研究(GS2 乱流の諸問題,一般セッション)

Experimental investigation on the Relationship between roughness parameter of non-uniform surface roughness and flow resistance has been carried out. In this experiment, we evaluated non-uniform surface roughness of various surface by the optical method and measured friction coefficient over each surface roughness. As an evaluation of non-uniform surface roughness, we measured surface roughness profiles of each surface by a laser displacement sensor and calculated some roughness parameters such as the root mean square roughness. One important result indicates that the friction coefficient increases logarithmically with increasing root mean square roughness. Moreover, to discuss the effect of non-uniform roughness in detail, the Probability Density Function (PDF) of the roughness height were analyzed. As a result, the frictional drag over the rough surface can be mostly evaluated by the root mean square roughness when the probability density distribution of the surface roughness profile has Gaussian distribution.

Interferometric study of pyrite surface reactivity in acidic conditions

Production of acid mine drainage (AMD) is in large part due to pyrite oxidation. The tie-in between environmental remediation and pyrite oxidation requires understanding pyrite oxidation in aqueous systems. In this study, ex-situ measurements using vertical scanning interferometry (VSI) were utilized to investigate pyrite surface reactivity under AMD conditions, such as pH 1 (HCl), an O2-saturated atmosphere, and room temperature, including (1) ex-situ measurements using vertical scanning interferometry (VSI) and (2) solution chemistry measurements using a flow reactor. In the former, two fragments were immersed in the acidic solution for 27 days at undersaturation with respect to pyrite. Weathered surfaces of pyrite that showed surface history (e.g., existence of terraces, steps, etch pits, and non-uniform surface roughness) were selected to examine surface topography changes with time.

Influence of Corrosion on the Fatigue Properties of Al 7075-T6

Abstract Chloride ion attack on Al 7075-T6 in aqueous hydrochloric acid leads to localized corrosion and subsequent initiation of fatigue cracks on the surface. Pitting is observed when the specimen is exposed to a corrosive environment. Microcracks, voids, extrusions, and intrusions are then formed during the fatigue process. From a global viewpoint, all of the corrosion and fatigue damage appears to be randomly oriented, resulting in a change in the surface roughness. The Laser Speckle Sensor technique is used to detect the minute surface texture change, associated with the damage caused by corrosion and fatigue. Nonuniform surface roughness is observed due to corrosion. The corrosion pits tend to coalesce along the rolling direction. The change in surface roughness is significant around the crack tip during the fatigue process. As a result there are synergistic activities; the surface roughness caused by corrosion and fatigue leads to crack initiation, and the crack growth further increases surface roughness.

Surface-layer flow in complex terrain: Comparison of models and full-scale observations

Four models of surface boundary-layer flow in complex terrain are compared with observations made at Blashaval Hill, North Uist, Scotland. The field experiment is described by Mason and King (1985). Three of the models are derived from the two-dimensional theory of Jackson and Hunt (1975) and are described in Mason and King (1985), Walmsley et al. (1986) and Troen and Petersen (1989). The fourth is a mass-consistent code based on Traci et al. (1979). The model results are in good agreement with each other and are generally within the observed range of variation ( ~ ± 16%) in normalized wind speed. For most wind direcions (7 of 11), model results of normalized wind speed at the summit were within 7% of the observed mean values. For some wind directions, calculations using the “Guidelines” of Walmsley et al. (1989) suggested that variations in surface roughness were important. This led us to apply one of our models incorporating nonuniform surface roughness. The lack of significant improvement for cases when water lay upstream of Blashaval Hill is attributed to compensating changes at summit and reference sites and to very local effects on the wind data. Sensitivity to topography lying to the west and northwest of Blashaval was also investigated. Results suggested an influence from those distant topographic features for some wind directions. When those features were incorporated, maximum errors in normalized wind speed at the summit were reduced from 18 to 13%.

Measurement and Prediction of the Effects of Nonuniform Surface Roughness on Turbulent Flow Friction Coefficients

The status of prediction methods for friction coefficients in turbulent flows over nonuniform or random rough surfaces is reviewed. Experimental data for friction factors in fully developed pipe flows with Reynolds numbers between 10,000 and 600,000 are presented for two nonuniform rough surfaces. One surface was roughened with a mixture of cones and hemispheres which had the same height and base diameter and were arranged in a uniform array. The other surface was roughened with a mixture of two sizes of cones and two sizes of hemispheres. These data are compared with predictions made using the previously published discrete element prediction approach of Taylor, Coleman, and Hodge. The agreement between the data and the predictions is excellent.

An improved method for integrating the Mixed Spectral Finite Difference (MSFD) model equations

In their Mixed Spectral Finite Difference (MSFD) model for flow over complex terrain, Beljaars et al. (1987) solve a set of coupled, second-order ordinary differential equations (ODEs) for the first-order perturbations to the logarithmic velocity profile caused by nonuniform surface roughness and topography. To solve this set of ODEs, they employ a Forward Euler Shooting Method. It is demonstrated here that the shooting method is computationally unstable for this problem. An absolutely stable finite-difference method based on a block tridiagonal LU factorization of the finite-difference matrix is presented. The advantages of the present algorithm over the method used by Beljaars et al. are demonstrated both by theoretical argument and numerical experiment.