•Evaluation of surface roughness effect on multiaxial fatigue behavior of AM specimens.•Effect of surface machining and HIPing on multiaxial fatigue performance of AM specimens.•Fracture-mechanics ...based modeling of surface roughness effect on uniaxial and multiaxial fatigue performance.
Additive manufacturing (AM) has become a very popular topic recently due to its many advantages including short build cycles, convenience of customization, and most importantly the ability to build components with complex geometry. However, the surface condition of additive manufactured components is not always satisfactory, particularly with respect to fatigue performance. This is because the as-built surface tends to be rough and post surface treatments or processes such as machining and polishing may not be applicable to all AM parts. On the other hand, since many components are under cyclic loading consisting of normal and shear stresses, multiaxial fatigue behavior is one of the most important aspects to evaluate. This paper evaluates the surface roughness effect on fatigue behaviors of Ti-6Al-4V alloy samples additively manufactured by laser-based powder bed fusion method (L-PBF). Fully reversed axial, torsional, and combined axial-torsion fatigue tests were conducted on specimens with different surface conditions and with different post heat treatments (annealed and HIP). Fatigue life predictions were made using linear elastic fracture mechanic with satisfactory results, as compared to experimental results.
Ultra-precision machining (UPM) is capable of manufacturing a high quality surface at a nanometric surface roughness. For such high quality surface in a UPM process, due to the machining complexity ...any variable would be possible to deteriorate surface quality, consequently receiving much attention and interest. The general factors are summarized as machine tool, cutting conditions, tool geometry, environmental conditions, material property, chip formation, tool wear, vibration etc. This paper aims to review the current state of the art in studying the surface roughness formation and the factors influencing surface roughness in UPM. Firstly, the surface roughness characteristics in UPM is introduced. Then in UPM, a wide variety of factors for surface roughness are then reviewed in detail and the mechanism of surface roughness formation is concluded thoroughly. Finally, the challenges and opportunities faced by industry and academia are discussed and several principle conclusions are drawn.
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•The surface roughness characteristics in UPM is elaborated.•The factors and mechanism of surface roughness formation are reviewed in detail.•The challenges and opportunities faced by industry and academia are discussed.•The key issues are drawn to surface roughness formation in UPM.
The effect of various gadolinium contents on the number density and morphology of sulfide in Al-killed high-sulfur steel was investigated. Meanwhile, the effect of characterization of sulfide ...inclusions, i.e., number density and morphology on the cutting performance of steel also were studied. The evolution process of sulfide inclusions with the increasing T.Gd content from 0 ppm to 198 ppm in steel samples could be described as follows: MnS → (Gd-O-S)-MnS→(Gd-S)-MnS →Gd-S. As the gadolinium content in the steel increased, sulfide inclusions with an aspect ratio of < 3 increased from 26.1 % to 99.7 % and the number density of sulfides decreased from 438 #/mm2 to 80.4 #/mm2. Spherical sulfides could form micro-holes during cutting, facilitating the chip-breaking process, whereas long-strip MnS tended to self-break during cutting. The higher the proportion of C-type chips in the cutting process, the better the cutting performance of the material. Therefore, spherical sulfides exhibited superior modification effects on surface finishes compared to long-strip sulfides. In low-speed cutting, sulfide morphology predominantly affected surface roughness, while in high-speed cutting, the number density of sulfides became the dominant factor. The addition of gadolinium can effectively decrease the surface roughness of the material at various cutting parameters. Moreover, the Gd-O film can be formed on the tool surface was observed after the addition of gadolinium in the steel, which can increase the lubrication during the cutting process and reduce the tool surface wear.
•Novel heavy rare earth gadolinium for modifying MnS inclusion and enhancing cutting performance of material was proposed.•The mechanism of spherical sulfides was more favorable for improving the cutting properties of the steel was elucidated.•The morphology and number density of sulfide had various effects on the surface roughness at different cutting parameters.•The Gd-O film was observed on the tool surface, which reduced the tool surface wear.
We introduce analytic approximations for accurate real-time rendering of surfaces lit by non-occluded area light sources. Our solution leverages the Irradiance Tensors developed by Arvo for the ...shading of Phong surfaces lit by a polygonal light source. Using a reformulation of the 1D boundary edge integral, we develop a general framework for approximating and evaluating the integral in constant time using simple peak shape functions. To overcome the Phong restriction, we propose a low cost edge splitting strategy that accounts for the spherical warp introduced by the half vector parametrization. Thanks to this novel extension, we accurately approximate common microfacet BRDFs, providing a practical method producing specular stretches that closely match the ground truth in real-time. Finally, using the same approximation framework, we introduce support for spherical and disc area light sources, based on an original polygon spinning method supporting non-uniform scaling operations and horizon clipping. Implemented on a GPU, our method achieves real-time performances without any assumption on area light shape nor surface roughness.
In this research, a one-way abrasive flow machining (AFM) was sketched and built, and the impact of temperature on surface roughness (Ra) values and material removal rate (MRR) before and after each ...test have been investigated considering the SiC. Al2O3, and B2O3 particles as abrasive particles. The abrasive particles were dispersed at 35 wt.% in the prepared media. The findings revealed that the media containing Al2O3 abrasive particles had higher surface roughness compared to the SiC and B2O3 particles. The maximum variation of surface roughness for SiC, Al2O3, and B2O3 particles was observed at −196 °C, which was 2.991, 2.588, and 1.684, respectively. In addition, the material removal rate values decreased for all the prepared samples as the temperature was reduced. At lower temperatures, lower material removal rate values were recorded since the viscosity of the abrasive paste increased.
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•Temperature efficacy on surface roughness and material removal rate were analyzed.•Comparison between SiC, Al2O3, and B2O3 particles as abrasive particle was investigated.•The SEM morphologies of the worn surfaces represented that abrasive particles caused finer surfaces.•Media containing Al2O3 abrasive particles had higher surface roughness.•Material removal rates decreased with the temperature decrement.
•Fatigue behavior of additively manufactured Ti-6Al-4V is studied.•Effects of surface roughness and surface area are investigated.•Supporting fractography, including crack growth analysis, is ...presented.•The effect of specimen diameter on the fatigue strength is discussed.
Additive manufacturing has become an increasingly popular advanced manufacturing technique, however, many questions concerning the reliability of parts fabricated by methods such as laser powder bed fusion must be addressed. In this research, the effect of surface roughness and size is investigated by designing various additively manufactured Ti-6Al-4V specimen geometries. These as-built specimens were designed to specifically determine the effect of surface area and part diameter on the fatigue behavior of specimens fabricated diagonally from the substrate. Results indicate that the fatigue behavior is more sensitive to part diameter than surface area. Parts with diameters of 4.90 mm or less showed higher surface roughness on the down-skin surface. This variation diminished, however, for specimens with diameters larger than 4.90 mm. Additionally, as part diameter decreased, the difference between the load-bearing and nominal stress amplitudes, caused by surface roughness, increased, resulting in significant scatter in the high cycle fatigue data.
In this letter, we demonstrate high-performance AlGaN/GaN Schottky barrier diodes (SBDs) on Si substrate with a recessed-anode structure for reduced turn-on voltage Formula Omitted. The impact of the ...surface roughness after the recessed-anode formation on device characteristics is investigated. An improved surface condition can reduce the leakage current and enhance the breakdown voltage simultaneously. A low turn-on voltage of only 0.73 V can be obtained with a 50-nm recess depth. In addition, the different lengths of Schottky extension acting like a field plate are investigated. A high reverse breakdown voltage of 2070 V and a low specific ON-resistance of 3.8 Formula Omitted yield an excellent Balig's figure of merit of 1127 MW/cm2, which can be attributed to the low surface roughness of only 0.6 nm and also a proper Schottky extension of 2 Formula Omitted to alleviate the peak electric field intensity in the SBDs.
Inconel 625, a high-strength superalloy with excellent corrosion resistance, discovers wide applications in critical sectors such as aerospace, nuclear, marine, and petrochemical. Single-Point ...Incremental Forming (SPIF) has appeared as an adequate fabricating process for shaping superalloy components. This work used a systematic approach, implementing Response Surface Methodology (RSM) to explore the influence of SPIF process variables, including tool nose diameter, step size, tool spindle speed, and wall angle, on microhardness (MH) and surface roughness (SR). The experimental results have been analyzed to determine the influencing process variables and their optimal settings, which simultaneously enhance MH and reduce SR of Inconel 625 superalloy truncated cones using analysis of variance and the desirability function analysis approach. The most significant parameters that influence MH and SR were TND and SS, respectively. The development of quadratic models for MH and SR has been completed successfully. The maximum MH of 486.8 HV and minimum SR of 0.432 µm have been obtained at the optimal parametric setting of TND = 15 mm, SS = 0.4 mm, TSS = 900 rpm, and WA = 57.5° with the desirability values for MH, SR and combined are 0.832, 0.933, 0.881 respectively. The F-value of the MH model = 109.18 and SR Model = 78.24 implies that both models are significant and both models have excellent prediction strength. The percentage error between predicted and actual values of MH and SR in confirmation run results is less than 5 %.
•This study introduces the SPIF of Inconel 625, extending its use to critical sectors like aerospace and nuclear demand for high-performance materials, marking a novel approach to fabricating conical shapes.•Utilizing RSM, the research systematically investigates the impact of SPIF process variables on the microhardness and surface roughness of Inconel 625, setting a standard for Inconel 625 superalloy forming.•The study optimizes SPIF parameters to simultaneously improve the microhardness and reduce the surface roughness in Inconel 625 components, showcasing a balanced approach for quality enhancement.•The computation and validation of quadratic models for predicting microhardness and surface roughness based on SPIF parameters represent a major advancement, which shows significant prediction capability with less than 5 % prediction error.•The research identifies critical SPIF parameters and their optimal settings to achieve targeted responses in Inconel 625 components, offering practical guidelines for industry application and enhancing surface quality.
Friction is generated where solids touch, thus quantitative understanding of the microscopic contact area is crucial to predict macroscopic friction. All surfaces are rough, and typically small-scale ...roughness rather than macroscopic geometry sets the contact area. Rough contact theories have been developed that predict the contact area, using the surface topography and the mechanical properties of the solids as input. However, the validity of these theories remains under debate. Systematic comparison between theory and experiment has been lacking, due to the experimental difficulty to access the contact area, especially at small length scales where idealised assumptions of contact models may not hold. Here, we use a state-of-the-art fluorescence microscopy technique to directly access the contact area of a glass-glass contact with nanometric out-of-plane resolution. We systematically vary the roughness of the contact and carefully measure the surface topography across length scales. Comparison of high-resolution contact experiments to different contact theories enables us to unambigously conclude that only elastic Persson theory quantitatively describes experimental observations.
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