Maximum Surface Height Research Articles

Improving the formability and quality of CMT additively manufactured aluminum thin-wall parts via laser stabilization effect

In the recent past, the deposition efficiency has been one of the most concerned problems in aluminum additive manufacturing. In this research, a comparative study on the formation quality, microstructures and mechanical properties of aluminum alloy thin-wall structures between the oscillating laser-arc hybrid additive manufacturing (O-LHAM) and wire-arc additive manufacturing (WAAM) at high deposition speed was performed. The formation quality of the additively manufactured thin-wall parts under O-LHAM was significantly improved compared with WAAM. The molten pool overflow was significantly eliminated due to the higher support force on the molten pool, thus the surface roughness Sa and the maximum surface height difference Sz of O-LHAM thin walls were reduced by 13% and 22%, respectively. Compared with thin wall manufactured via WAAM, the microstructure of O-LHAM mainly consisted of coarse columnar grains and showed anisotropic characteristics due to the increased heat accumulation. Moreover, owing to the higher porosity in the interlayer combination regions of WAAM sample, the elongation of thin walls manufactured via O-LHAM was higher than WAAM in both horizontal and vertical directions, reaching 36.8% and 32.5%, respectively. This work will provide more guidance on thin-wall additive manufacturing with high deposition efficiency.

Numerical simulation of surface roughness effects on low-cycle fatigue properties of additively manufactured titanium alloys

Additive manufacturing (AM) is a complex process involving a multiscal physical phenomena (solid–liquid-gas), often resulting in poor surface quality. Although surface treatments such as polishing or chemical treatment can improve surface quality, localized sub-grain stress concentrations induced by surface roughness anomalies are still easily formed, which can lead to the reduction and dispersion of fatigue properties in AM alloys. In this study, a numerical simulation model is proposed to study the association between surface roughness and fatigue properties of AM alloys. Based on the continuum damage mechanics modeling framework, an idealised grain/grain boundary model is generated by employing the Voronoi tessellation meshing technology. The numerical simulations are performed for the model with different surface geometric states. The correlation between surface roughness geometric features and fatigue properties is analyzed and discussed. A parameter “G” which comprehensively considers the influence of the maximum surface height (Rz) and correlation length (Lcor) is proposed to quantify the influence of surface roughness geometric features on the fatigue properties of AM alloys. This finding can be of great significance in improving the surface integrity of components to increase service life.

Characterization of the Maximum Height of a Surface Texture.

Average surface height and maximum amplitude can affect surface functions. In the industry, these parameters can be obtained based on profile measurements. However, variability in maximum profile height is high. A more stable parameter can be obtained from the results of the areal surface topography measurements as the average value of the parallel profiles. The aim of this study is to establish this parameter directly from the result of the areal surface texture by correcting the maximum surface height to material ratios in the range of 0.13-99.87%. This method was tested by measuring 100 surface topographies with a stylus profilometer and a white light interferometer. It can be utilized correctly for deterministic textures and random one- and two-process surfaces for which the correlation between neighboring profile ordinates is not very high. In other cases, the method should be modified. Employing this method, the maximum profile amplitude Pt and parameters characterizing the average profile height Pq, Pa, and the ratios Pq/Pa and Pp/Pt describing the shape of the profile ordinate distribution can be correctly estimated. Pq/Pa and Pp/Pt were more stable than the kurtosis Pku and skewness Psk. The corrected maximum height S±3σ can be adopted as a parameter that characterizes the areal surface texture as more stable than the maximum surface height St. Pq/Pa and Pp/Pt were more steady than kurtosis Pku and skewness Psk.

Elimination of defects in laser metal deposited TiCp/Ti6Al4V composite by synchronous ultrasonic impact treatment

TiCp/Ti6Al4V composites produced by laser metal deposition (LMD) are usually characterized by internal defects and resultant deteriorated mechanical properties. In the present work, a synchronous ultrasonic impact treatment (UIT) was introduced during LMD of TiCp/Ti6Al4V composites. The effect of synchronous UIT on the defects was investigated. The defects in the LMDed composites are sub-spherical pores distributed in the interlayer region. With the assistance of UIT, the maximum surface height difference reduces from 200.2 ± 0.5 μm to 25 ± 0.5 μm and the internal porosity decreases from 1.95% to 0.09%, which is attributed to inhibiting the nucleation of defects and increasing molten pool flow. This work may provide a solution to effectively reduce the defects in additively manufactured parts.

Effect of Different Forms of Fluoride Application on Surface Roughness of Rhodium-Coated NiTi Orthodontic Wires: A Clinical Trial.

Objectives: This study aimed to assess the effect of different forms of fluoride application on surface roughness of rhodium-coated nickel-titanium (NiTi) orthodontic wires. Materials and Methods: This randomized clinical trial was conducted on 15 patients randomly divided into three groups: toothbrush with Oral-B toothpaste only, Oral-B toothpaste, and daily mouthwash, Oral-B toothpaste, and sodium fluoride gel. The surface roughness indices of orthodontic wires including arithmetic mean height (Sa), root mean square height, root mean square gradient, developed interfacial area ratio (Sdr) and maximum surface height were measured by atomic force microscopy at baseline and after 6 weeks of application in the patients' mouths. Data were analyzed by paired t-test, ANOVA, Games-Howell, and Tukey-HSD tests (P<0.05). Results: All surface roughness parameters in all three groups showed a significant increase after intervention, except for Sa in the toothpaste-only group (P=0.057) and Sdr in the sodium fluoride gel group (P=0.064). Conclusion: The surface roughness of rhodium-coated NiTi orthodontic wires increases following the use of different forms of fluoride.

Enamel Evaluation after Debonding of Fixed Retention and Polishing Treatment with Three Different Methods.

Lack of standardization of the retention phase has led to many studies of stability of movements and characteristic of retainers, disregarding the enamel repercussions of fixed retention on this phase. This study aimed to analyze different methods of enamel polishing after detachment of orthodontic retainers. Forty-five healthy premolars were divided into three groups according to the polishing bur after debonding, and four specimens without intervention were used as control. A 0.038 × 0.015 inches gold chain was bonded between the premolars and then removed. The adhesive remnant was removed with three types of burs according to the study groups (Group 1: white stone at high speed; Group 2: high-speed handpiece with a 30-blade tungsten carbide bur; Group 3: low-speed handpiece and a 30-blade tungsten bur). After debonding and polishing, all samples were analyzed with a confocal microscopy on surface roughness parameters: Sa: Arithmetic mean of the height of the surface. Rq: Square mean of the height of the surface and Sz: Maximum surface height. Mechanical tests were carried out to determine the bonding stress of the retention adhered to the teeth using an electromechanical testing machine. The adhesion stress was 8.23 MPa (±0.87). The quality of the refinement of the enamel after debonding is essential in order to preserve its integrity. The use of the 30-blade tungsten carbide bur provides a smooth enamel surface after polishing.

Influence mechanism of laser defocusing amount on surface texture in direct metal deposition

Direct metal deposition is a promising additive manufacturing, but the surface quality of as-built parts has been a prominent issue limiting its immediate application. The laser beam exerts different influence mechanisms on the surface texture of the top surface and sidewalls, which are the main contour surfaces of as-built parts during multi-axis deposition. In this paper, the deposition height deviation and the deposition height instability were proposed to characterize the surface texture on the top surface, and the surface maximum height was used for the sidewalls. The correlation between the laser defocusing amount and the surface texture parameters was quantitatively studied. Results show that the deposition height deviation under the positive laser defocusing state is smaller than that under the negative laser defocusing state, although the laser defocusing distance is the same. The deposition height presents a self-stable phenomenon under the positive laser defocusing state. The surface quality on sidewalls is better under the negative laser defocusing state than that under the positive laser defocusing state. In addition, the influence mechanism of the laser defocusing amount was analyzed on the formation of multiple overlapped tracks on the top surface. Three formation mechanisms of adhered protrusions on sidewalls were revealed through a high-speed camera, namely particle adhesion, powder adhesion, and agglomeration adhesion. The research can be utilized to guide the dynamic adjustment of the laser defocusing amount to improve the forming quality. • The deposition height presents a self-stable phenomenon under the positive laser defocusing state. • The surface maximum height is suitable to characterize the surface texture on sidewalls. • A large laser defocusing distance under the NLDS is preferred to obtain a better surface quality on sidewalls. • Adhered protrusions are categorized into particle adhesion, powder adhesion, and agglomeration adhesion.

On the Use of Surface Roughness Parameters

In most practical applications, surface roughness is characterized by just one or two parameters (numbers). I show that the standard maximum surface height parameters fluctuate strongly between different surface realizations (or measurements), and should not be used in the design of engineering components. I show how some roughness parameters depend on the size of the roll-off region in the surface roughness power spectra, and introduce a new height parameter which is very reproducible. The numerical results presented agree well with experimental observations.Graphical

The mechanism of process parameters influencing the AlSi10Mg side surface quality fabricated via laser powder bed fusion

PurposeFor the laser powder bed fusion (L-PBF) technology, the side surface quality is essentially important for industrial applicated parts, such as the inner flow parts. Contour is generally adopted at the parts’ outline to enhance the side surface quality. However, the side surface roughness (Ra) is still larger than 10 microns even with contour in previous studies. The purpose of this paper is to study the influence of contour process parameters, laser power and scanning velocity on the side surface quality of the AlSi10Mg sample.Design/methodology/approachUsing L-PBF technology to manufacture AlSi10Mg samples under different contour process parameters, use a laser confocal microscope to capture the surface information of the samples, and obtain the surface roughness Ra and the maximum surface height Rz of each sample after analysis and processing.FindingsThe results show that the side surface roughness decreases with the increase of the laser power at the fixed scanning velocity of 1,000 mm/s, the side surface roughness Ra stays within the error range as the contour velocity increases. It is found that the Ra increases with the scanning velocity increasing and the greater the laser power with the greater Ra increases when the laser power of contour process parameters is 300 W, 350 W and 400 W. The Rz maintain growth with the contour scanning velocity increasing at constant laser power. The continuous uniform contour covers the pores in the molten pool of the sample edge and thus increase the density of the sample. Two mechanisms named “Active adhesion” and “Passive adhesion” cause sticky powder.Originality/valueFormation of a uniform and even contour track is key to obtain the good side surface quality. The side surface quality is determined by the uniformity and stability of the contour track when the layer thickness is fixed. These research results can provide helpful guidance to improve the surface quality of L-PBF manufactured parts.

Effect of surface roughness on tensile ductility of artificially corroded steel plates

Physically, corrosion damage results in a reduction in thickness and a change in surface geometry due to differential corrosion rates on the surface of a steel member. The effects of thickness reduction on the mechanical characteristics of structural steel have been investigated intensively, but the same cannot be said for the surface configuration. This study investigated the variation of corrosion thickness and surface roughness characteristics with increasing corrosion degradation and their contribution to a reduction in the tensile ductility of corroded steel. Twenty-two SS400 type steel plates were corroded by an underwater accelerated exposure (bubbling) test. Specimens were exposed for a varying number of days after which measurement and evaluation of thickness reduction and surface roughness characteristics were conducted. Then, the remaining load and elongation capacity were determined experimentally from the standard uniaxial tensile test. The distribution of the surface strains was studied employing digital image correlation techniques. Findings from this work revealed that surface unevenness due to corrosion causes stress concentration and uneven yielding, and strain localization after yielding during the tensile test. This translated to an early attainment of maximum load, resulting in reduced ductility in corroded specimens. A general trend is such that ductility decreases with increasing surface roughness. A plastic ductility loss of up to 80% is experienced when maximum surface height ratio, ζsz ≥ 0.9 and average surface height ratio, ζsa ≥ 0.15. Finally, empirical equations for estimating the remaining tensile ductility of corroded steel based on surface roughness characteristics were proposed.

Early Healing Evaluation of Commercially Pure Titanium and Ti-6Al-4V Presenting Similar Surface Texture: An In Vivo Study.

This study evaluated the osseointegration of commercially pure titanium (Ti) grade-2 (G2) and Ti-6Al-4V alloy (G5) implants with the same geometry and surface treatment. Thirty-six dental implants with a grit-blasted acid-etched surface were used (n = 18, each). Two implants, one per group, were installed in each subject, in the radius diaphysis (n = 18 beagle dogs), with interchanged fixture position (proximal-distal) between animals for a balanced number of devices per group and time in vivo (1, 3, and 6 weeks). Similar topographical parameters between G2 and G5 were observed for average surface roughness, root mean square, developed surface ratio, maximum height of surface, and density of summits. Removal torque was significantly higher for G5 than for G2. No differences were observed for bone-to-implant contact and bone-area-fraction occupancy. Removal torque significantly increased with time for both groups. At 1 week, new bone formation in direct contact with the implant surface and osteogenic tissue migration was observed with an increase in woven bone formation at 3 weeks followed by the onset of lamellar bone formation at 6 weeks. Although both surfaces were biocompatible and osteoconductive, increased removal torque was observed for Ti-6Al-4V compared with commercially pure Ti implants.

Surface roughness evolution during early stages of mechanical cyclic loading

The effect of crystal size and initial dislocation density on surface roughness evolution in FCC single crystals during the early number of cycles of mechanical cyclic loading is investigated using three dimensional discrete dislocation dynamics simulations. Crystals having size less than 2μm show early development of surface slip localization, while larger ones show a more uniform distribution of surface steps. The surface roughness is found to increase with increasing number of loading cycles with larger crystals showing a high roughening rate compared to smaller crystals. Double cross-slip is observed to be the main mechanism that derives the development, growth and thickening of surface slip bands. The maximum surface height, which is an indicator of the surface stress concentration is observed to increase linearly with the number of loading cycles and quadratically with the crystal size for the simulated number of cycles. Finally, the results are shown to be in agreement with experimental results and provide further physics based understanding on the mechanisms controlling the evolution of the surface roughness.

Variability of areal surface topography parameters due to the change in surface orientation to measurement direction

Several random surface topographies were analyzed. They were measured by optical (Talysurf CCI Lite) method. They represent one- and two-process anisotropic and isotropic surfaces. These surfaces were rotated of ± 1° and ± 2° by two methods: on the plane table (before measurement) and virtually (after measurement) using the software TalyMap Gold. After each measurement or surface rotation, each surface was levelled. Then, the forms were removed using polynomial of the 3rd degree. Areal surface topography parameters from standard ISO 25178 were calculated. The relative deviations of parameters were determined. The tendency of surface topography changes characteristic to various surface types were analyzed. It was found that change in orientation to the measurement direction of both isotropic and anisotropic surfaces could be substantial source of the measurement uncertainty. Functional parameter Smr and also feature parameters Sda, Sha, Sdv, Shv, and Spd are the mostly sensitive on measurement orientation. Statistical amplitude parameters Sa and Sq are more stable than parameters describing maximum surface height, like Sz, Sp, and Sv. The effect of surface orientation to measurement direction on values of functional parameters from V group was small. It was shown that changes of Sdq, Sdr, and Spc parameters describing hybrid properties due to surface rotation before measurement were smaller than those caused by change in surface orientation after measurement.

Rayleigh‐Taylor instability, lithospheric dynamics, surface topography at convergent mountain belts, and gravity anomalies

AbstractSurface topography and associated gravity anomalies above a layer resembling continental lithosphere, whose mantle part is gravitationally unstable, depend strongly on the ratio of viscosities of the lower‐density crustal part to that of the mantle part. For linear stability analysis, growth rates of Rayleigh‐Taylor instabilities depend largely on the wave number, or wavelength, of the perturbation to the base of the lithosphere and weakly on this viscosity ratio, on plausible density differences among crust, mantle lithosphere, and asthenosphere, and on ratios of crustal to total lithospheric thicknesses. For all likely densities, viscosities, and thicknesses, the Moho is drawn down (pushed up) where the base of the lithosphere subsides (rises). For large viscosities of crust compared to mantle lithosphere (ratios &gt; ~30), a sinking and thickening mantle lithosphere also pulls the surface down. For smaller viscosity ratios, crustal thickening overwhelms the descent of the Moho, and the surface rises (subsides) above regions where mantle lithosphere thickens and descends (thins and rises). Ignoring vertical variations of viscosity within the crust and mantle lithosphere, we find that the maximum surface height occurs for approximately equal viscosities of crust and mantle lithosphere. For large crust/mantle lithosphere viscosity ratios, gravity anomalies follow those of surface topography, with negative (positive) free‐air anomalies over regions of descent (ascent). In this case, topography anomalies are smaller than those that would occur if the lithosphere were in isostatic equilibrium. Hence, flow‐induced stresses—dynamic pressure and deviatoric stress—create smaller topography than that expected for an isostatic state. For small crust/mantle viscosity ratios (&lt; ~10), however, calculated surface topography at long wavelengths is greater than it would be if the lithospheric column were in isostatic equilibrium, and at short wavelengths local isostasy predicts surface deflections of the wrong sign. For the range of wavelengths appropriate for convergent mountain belts (~150–600 km), calculated gravity anomalies are negative over regions of lithospheric thickening, especially when allowance for flexural rigidity of a surface layer is included. Correspondingly, calculated values of admittance, the ratio of Fourier transforms of surface topography and free‐air gravity anomalies, are also negative for wave numbers relevant to mountain belts. For essentially all mountain belts, however, measured free‐air anomalies and admittance are positive. Whether gravitational instability of the lithosphere affects the structure of convergent belts or not, its contribution to the topography of mountain belts seems to be small compared to that predicted for isostatic balance of crustal thickness variations.

Effects of Surface Roughness and Abnormal Surface Layer on Fatigue Strength

The purpose of this research is to evaluate the effects of surface roughness in normalized steel and the effects of abnormal surface layer in carburized steel on the fatigue strength that is considered as the limit of no crack initiation. Normalized and Carburized test pieces with crowned round notches were used in the fatigue tests, the normalized test pieces have different surface roughnesses and the carburized test pieces have different surface microstructures on the notch surface. The changes in fatigue strength due to the differences in the notch surface roughness and surface microstructure were investigated. As the conclusions, fatigue strength will be certainly increased by decreasing the surface maximum height, and removing the abnormal surface layer formed during carburized treatment leads to a marked increase in fatigue strength.

Hydrodynamics of rotating liquid mirrors I Synchronous disturbances

The effects of axis alignment errors, planetary rotation, and tidal forces on rotating liquid mirrors are analyzed. These produce a surface distortion that decreases exponentially with distance inward from the rim with a characteristic length l= square root of 3hf/2, where h is the thickness of the fluid and f is the focal length. Even a small tilt of the rotation axis can produce a significant deformation of the optical surface. The maximum surface height error is 3epsilonl, where epsilon is the tilt angle and is typically of the order of 1.5 microm for a 1 arc sec tilt. The main optical effect of the wave is to produce a ring, with angular diameter 6epsilon, offset by half of the diameter in the direction opposite the tilt. This diamond ring aberration can be avoided by accurate alignment of the rotation axis or by masking the outer few centimeters of the mirror. Planetary rotation produces a small deformation of the order of 100 nm for a 10 m telescope at low latitude on Earth. This deformation can be canceled by a small tilt of the rotation axis. Tidal forces produced by the Moon, or by the Earth in the case of a lunar telescope, produce an inconsequential, subnanometer, surface deformation.

Polarization anisotropy in the electroluminescence of m-plane InGaN–GaN multiple-quantum-well light-emitting diodes

InGaN – GaN multiple-quantum-well light-emitting diodes were fabricated on (101¯0) m plane GaN films grown on (101¯0) m plane 4H–SiC substrates. The [0001] axis of the epitaxial film is parallel to the [0001] axis of the substrate. The surface is striated, with features running perpendicular to the c axis and a maximum surface height difference of 45nm. Electroluminescence shows strong polarization anisotropy, with 7× more light emitted with polarization perpendicular to the c axis compared to parallel to the c axis. An Ahrrenius fit of the polarization ratio indicates that there is a 49meV difference in the energy gap between the two polarization states. This suggests that a high polarization ratio can be maintained at the high temperatures (&amp;gt;150°C) and drive current densities required for high-power light-emitting diode applications.