Rounded Edges Research Articles

A hair-splitting way to get dull

Metallurgy Razors eventually become dull after shaving even though the blade is about 50 times harder than the hair. Whereas edge rounding and brittle cracking of a blade's hard coating were thought to be responsible, a detailed microstructural investigation by Roscioli et al. shows a different mechanism. A combination of out-of-plane bending, microstructural heterogeneity, and asperities—microscopic chips along the smooth edge—sometimes caused fracture to occur if the conditions lined up. This fracture originated at the hair-edge asperity interface and created chipping that dulled a blade faster than other processes. Science , this issue p. [689][1] [1]: /lookup/doi/10.1126/science.aba9490

Optimization of the geometry of facades based on the results of studies of wind effects

This article considers the possibility of reducing the wind load on building structures by optimizing their shape. The general algorithm for creating an architectural project using simulation engineering calculations is presented. The ANSYS Student software package analyzed the simplest methods of architectural shaping: bevels of ribs, rounding of edges, rounding of faces, vertical and horizontal articulations.

Flow around a 5:1 rectangular cylinder: Effects of upstream-edge rounding

A sensitivity analysis of highly-resolved large-eddy simulations of the flow around a 5:1 rectangular cylinder to the introduction of a small rounding of the upstream edges is presented. Different values of the edge radius of curvature are considered, in a range such that they might reasonably be ascribed to manufacturing tolerances. A stochastic approach is adopted in order to build response curves of the quantities of interest as a function of the radius of curvature. The considered computational set-up, characterized by a fine numerical resolution and a low subgrid-scale (SGS) dissipation, predicts for the body having perfectly sharp edges a short mean recirculation length on the cylinder side, in disagreement with experimental data. On the other hand, even for the smallest considered radius of curvature, the length of the mean recirculation region increases significantly and, hence, the agreement with the experimental data is much improved. It is observed that the sharp edge introduces a higher level of turbulent fluctuations in the shear-layer at separation, which, if not artificially damped by numerical or SGS dissipation, grows faster and leads to a further upstream roll-up of the shear-layers and, hence, to a shorter mean recirculation region than in simulations with rounded edges.

A 1.4-million-year-old bone handaxe from Konso, Ethiopia, shows advanced tool technology in the early Acheulean

In the past decade, the early Acheulean before 1 Mya has been a focus of active research. Acheulean lithic assemblages have been shown to extend back to ∼1.75 Mya, and considerable advances in core reduction technologies are seen by 1.5 to 1.4 Mya. Here we report a bifacially flaked bone fragment (maximum dimension ∼13 cm) of a hippopotamus femur from the ∼1.4 Mya sediments of the Konso Formation in southern Ethiopia. The large number of flake scars and their distribution pattern, together with the high frequency of cone fractures, indicate anthropogenic flaking into handaxe-like form. Use-wear analyses show quasi-continuous alternate microflake scars, wear polish, edge rounding, and striae patches along an ∼5-cm-long edge toward the handaxe tip. The striae run predominantly oblique to the edge, with some perpendicular, on both the cortical and inner faces. The combined evidence is consistent with the use of this bone artifact in longitudinal motions, such as in cutting and/or sawing. This bone handaxe is the oldest known extensively flaked example from the Early Pleistocene. Despite scarcity of well-shaped bone tools, its presence at Konso shows that sophisticated flaking was practiced by ∼1.4 Mya, not only on a range of lithic materials, but also occasionally on bone, thus expanding the documented technological repertoire of African Early Pleistocene Homo.

Performance analysis of hotspot using geometrical and operational parameters of a microchannel pin-fin hybrid heat sink

In the present study, numerical investigation of hotspot heat transfer in a microchannel pin-fin hybrid heat sink is accomplished. The proposed heat sink consists of 20 microchannels at background zone and 143 pin-fins at hotspot zone. Therefore, the effect of parameters including geometrical properties (pin-fin shape, pin-fin angle and microchannel wall wave amplitude), Reynolds number and hotspot heat flux on different decisive parameters of heat sinks are investigated. Parameters such as average pressure drop, pumping power, mean absolute temperature difference (MATD) at background zone, MATD at hotspot zone and thermal resistance are considered as performance parameters. The results show that rectangular pin-fin with rounded edges have better thermal performance than NACA airfoil. Besides, increasing the NACA airfoil angle increases the heat transfer and consequently leads to decrease in hotspot temperature. Also, numerical results show that increasing the wall wave amplitude increases the heat transfer rate.

Influence of tool material properties on the wear behavior of cemented carbide tools with rounded cutting edges

Tool wear and life of cutting tools are significant evaluation criteria of machining processes. However, the occurring wear mechanisms are influenced by a number of factors such as the process parameters, tool geometry and the material properties of the tool and workpiece. Previous research has shown a high potential for the use of adapted cutting edge microgeometries on cemented carbide cutting tools. The optimal cutting edge rounding is strongly dependent on the tool material properties. However, the influence and relation between the properties of the cemented carbide tool, the microgeometry and the resulting tool wear are not yet completely understood. In this study the tool wear is investigated by systematically varying the mechanical and thermophysical properties of the tool material, the tool microgeometry and cutting process parameters. Significant influencing variables of tool wear are identified and existing relationships quantified. Results show that the occurring wear mechanisms depend on the cutting edge microgeometry as well as the mechanical properties of the cemented carbide. During continuous machining the minimum required cutting edge rounding is a function of the cemented carbide’s fracture toughness. This knowledge allows an adaption of the cutting edge microgeometry depending on the substrate properties to reduce the tool wear and achieve a longer tool life.

Cranial trepanation and healing process in modern patients-Bioarchaeological and anthropological implications.

The diagnosis of cranial trepanation in the archaeological record has always been a big challenge for archaeologists. The identification is first and foremost based on the shape and edges of the opening, and in cases where the individual survived, the shape and edges resulted from both the surgical procedure and the healing process. Because of the lack of reliable data on the osseous remodelling process of the skull, it is difficult to distinguish true trepanations from some pathological or physiological defects called pseudotrepanations. Furthermore, it is challenging to investigate the post-operative survival time. The purpose of this paper was to summarize observations made on a total of 90 archaeological samples of cranial lesions interpreted as 'partially' or 'completely' healed trepanations, and compare them with 14 modern case studies. Observations made on monitoring post-operative scans of modern patients, at varying times after craniotomy, provided a preliminary timetable for the successive post-surgery bony changes in the skull, and confirmed that the process of osseous remodelling does lead to smooth and rounded edges of the profile of the opening. However, contrary to what has been observed in several archaeological case studies, none of the cases shows a complete closure of the cranial vault. The sharp vertical edges of the opening become bevelled at late stages of healing, which has to be taken into consideration when interpreting the procedures and methods in past population. By bridging bioarchaeology and medical sciences, this study adds to previous discussions on the diagnosis of healed trepanation in the archaeological record, by providing detailed descriptions of morphological changes at various healing stages, that may help archaeologists to identify ancient trepanations more accurately.

On the machining behavior of carbon fiber reinforced polyimide and PEEK thermoplastic composites

AbstractPolyimide (PI) and polyetheretherketone (PEEK) are superior high‐performance thermoplastics being extensively used in the fields of fiber‐reinforced polymer composites. However, there is very limited literature addressing the machining behavior of the PI and PEEK composites. The present paper aims to conduct a comparative study into the machining characteristics of these two representative high‐performance thermoplastic matrix composites under varying cutting conditions. Machinability aspects of the carbon/PI and carbon/PEEK thermoplastic composites were evaluated in terms of drilling forces, machining temperatures, delamination damage, surface morphologies, hole dimensional accuracy and tool wear. The results indicate that the carbon/PEEK composites generally show a much poorer machinability than the carbon/PI composites in terms of higher drilling forces, higher cutting temperatures, larger delamination extents and excessive tool wear. Since the carbon/PEEK composites exhibit certain ductility leading to the continuous chip formation, the cut hole surface morphologies and dimensional accuracy are much better than those gained in the carbon/PI composites. Both the cutting speed and the feed rate affect significantly the drilling forces and the resulting delamination damage. The fundamental wear mechanisms of drilling carbon/PI composites are abrasion wear in the form of edge rounding and slight chip adhesion, while for the carbon/PEEK composites, they are abrasion, serious chip adhesion because of the high drilling temperatures promoted at the drill‐work interface and catastrophic failures of coating peeling and edge fracture.

Clinical presentation and prognostic factors affecting surgical outcomes of secondary macular holes after retinal vein occlusions.

To describe clinical presentation, morphological features and surgical outcomes of macular hole (MH) secondary to retinal vein occlusion (RVO). This prospective interventional study evaluated eight eyes with atypical MH (secondary to RVO) and data regarding medical management, pars plana vitrectomy, postoperative anatomical hole closure, visual acuity improvement, morphological features of hole were noted till the last follow-up. Eight eyes with full-thickness MH in an RVO eye were followed-up for a minimum period of 3months postoperatively. Five subjects had a RVO episode which occurred more than 6months before the onset of the recent symptoms (Group 1; 4 branch RVO and 1 central RVO), and 3 subjects had a recent onset branch RVO within 6months (Group 2). All FTMH cases except one showed closure at the last follow-up. Visual acuity of all eyes improved from 0.91 ± 0.57 logMAR to 0.5 ± 0.3 logMAR (p = 0.093). At baseline, visual acuities of the two groups had no significant difference. Postoperatively,group 1 holes had better visual prognosis, than Group 2 holes, further substantiated by persistence of subretinal fluid in Group 2 eyes till last follow-up. Minimum hole diameter was higher in the recent RVO group, although anatomical closure was obtained in all of these eyes. Most holes had favorable morphological hole features like raised configuration with rounded edges. In the presence of favorable morphological features, secondary macular holes associated with retinal vein occlusion may show optimal outcomes after surgery. It is not clear whether acutely created holes in recent onset RVO should be operated early. Older holes may have better prognosis.

Cross-Sectional Performance of Hollow Square Prisms with Rounded Edges

Hollow-section columns are one of the mechanically superior structures with high buckling resistance and high bending stiffness. The mechanical properties of the column are strongly influenced by the cross-sectional shape. Therefore, when evaluating the stability of a column against external forces, it is necessary to reproduce the cross-sectional shape accurately. In this study, we propose a mathematical method to describe a polygonal section with rounded edges and vertices. This mathematical model would be quite useful for analyzing the mechanical properties of plants and designing plant-mimicking functional structures, since the cross-sections of the actual plant culms and stems often show rounded polygons.

General Mode-Matching Analysis of a 2-D Truncated PEC Wedge Covered With a Magnetodielectric Semicircular Boss

A general mode-matching technique is proposed to analyze a 2-D truncated perfect electric conductor (PEC) wedge covered with a magnetodielectric semicircular boss, where a radial length of the wedge is semi-infinite. A system of simultaneous equations of the TM- and TE-modes is obtained using a mode-matching technique, partial overlapping regions, and Graf’s addition theorem. Our solutions are computed to yield the echowidth characteristics of concave, convex, and truncated PEC wedges, including thick PEC half-planes with sharp and rounded edges. Their scattering results are compared with a commercial electromagnetic software package and show favorable agreement. Appropriate change of the permittivity and permeability of a semicircular boss results in radar cross-section (RCS) reduction of the truncated wedge, where optimization is automatically conducted by a binary genetic algorithm (GA). Our approach is fundamentally useful and applicable to the structural design of an integrated mast or superstructure on modern warships.

EFFECT OF THE PLASTIC STRAIN AND DRAWING QUALITY ON THE FRICTIONAL RESISTANCE OF STEEL SHEETS

The aim of the research presented in this article is to investigate the frictional resistance of steel sheets with different drawing quality. Friction tests have been carried out using the bending under tension (BUT) test which simulates the contact conditions at the rounded edges of the punch and die in sheet metal forming operations. The effect of sheet deformation and temper state on the value of the coefficient of friction has been studied. It was found that increasing the value of elongation of the sheet is associated with an increase in the value of the COF for both friction conditions analysed. The intensity of work hardening, by changing the mechanical properties of the sheet, is a factor that changes contact conditions. The lubricant which is typically used in plastic working provided a reduction of frictional resistance by approximately 3.6-14%, depending on the degree of sheet deformation.

Isolation and Characterization of Lipid-Producing Bacillus sp. TC14

In order to obtain microbes producing microbial oil from environment, a strain, marked as TC14 was isolated by replica plating and Sudan Black staining on the selected media. Its colony is smooth; milk white, slightly transparent, round edge, sticky. Its cell is long-rod, G-, intracellular lipid granule. The results of physiological and biochemical research: catalase, denitrification and fluorescent pigment tests are negative; metachromatic granule staining, amylolysis, lecithinase tests are positive. According to its sequencing result of 16S rDNA, strain TC14 is classified and belonged to Bacillus, namely sp. TC14. The optimum inoculation temperature is 35°C and the most suitable initial pH value is 10. The intracellular lipid of strain TC14 is extracted by the way of hydrochloric acid hydrolysis and the calculated ratio of oil-production is 5.08%.

A novel finite element investigation of cutting force in orthogonal cutting considering plough mechanism with rounded edge tool

The plough phenomenon generated by the micro-scale cutting edge plays an important role in tool wear, chip formation and surface integrity. In this study, the plough mechanism in orthogonal cutting with rounded edge tool is investigated by finite element method (FEM). The separation line is developed to determine the contact behavior between rounded edge tool and workpiece. Especially, the workpiece material flow is explored in detail with the definition of separation line. Three contact regions are identified and three frictional force components along the cutting edge are proposed. Then, the Johnson-Cook constitutive model and Johnson-Cook ductile damage criteria are used to describe the plastic deformation and damage mechanics in the cutting simulation with ABAQUS. A developed method based on finite element analysis is proposed to identify three force components individually, including separation line determination based on nodal displacement and three contact region determination with partition function. The accuracy and correctness of the novel FEM model are validated by a series of orthogonal cutting processes. Moreover, the nonlinearly increase relationship between specific cutting energy and edge radius is discussed considering size effect.

The influence of protruding silicon particle shape on the friction performance of Al–Si alloy

The surface of Al–Si alloy samples was produced by chemical etching and laser finishing. After both chemical etching and laser finishing, the silicon particles could be exposed on the surface, resulting in improving the friction performance of Al–Si alloy. The edge shapes of the protruding silicon particles were different in the two surface treatments. Besides, the edges of protruding silicon particles were sharp after chemical etching. As a result, the edges were damaged in friction, and even some of silicon particle could shed. Then, it was easy for the abrasive wear to occur on the surface. There were obvious vortices on both sides of protruding silicon particle with sharp edge in the fluid region, resulting in a comparatively weak lubrication. In contrast, the edges of protruding silicon particles were round after laser finishing. Moreover, silicon particles could be closely combined with aluminum matrix due to the rapid cooling after being heated by laser, meanwhile, it was difficult for them to be separated from the matrix during friction. There were no vortices occurring on both sides of protruding silicon particle with round edge in fluid region, presenting excellent lubrication. Besides, the samples by laser finishing owned a low friction coefficient. Thus, the Al–Si alloy samples by laser finishing, with round edges of silicon particle, exhibiting a better friction performance. Consequently, the micro-mechanisms of friction performance associated with the edge shape of protruding silicon particle such as better lubrication and uniform stress distribution of rounded edge were determined.

Experimental research of picosecond laser based edge preparation of cutting tools

In this study, using ultrafast lasers of 10 ps pulse duration as a precise and efficient method for cutting edge preparation is researched. Cutting edge preparation is an important step within cutting tool manufacturing, while unprepared sharp cutting edges show low stability, which leads to tool failure by high mechanical and thermal loads during the turning processes [C. F. Wyen, W. Knapp, and K. Wegener, Int. J. Adv. Manuf. Technol. 59, 899–914 (2012)]. The rounding of the edges requires laser manufacturing with high precision and minimal heat accumulation; thus, ultrafast lasers have been used in other investigations [M. Stolze, T. Herrmann, and J. L'huillier, Proceedings of ICALEO, Orlando, USA, ICALEO, Orlando, FL, October 23–27 (J. Laser Applications, Orlando, 2011)]. In the authors’ study, the effects of edge roundness on the cutting tool material WC-Co alloy were experimentally investigated. Samples with three different grain sizes and percentages of cobalt were used in the authors’ study. The experiments were carried out on the free surfaces of cutting tools under varying laser parameters including laser wavelength, fluence, and spatial pulse overlap (PO) in air or by using process gases (helium and oxygen). The impact of all these different laser parameters on the various material sorts was investigated. As a result, no reduction of the hardness of the original material was observed that could have a negative effect on the cutting ability of laser rounded cutting tools. By analyzing the surface quality of the ablated areas processed with different laser parameters mentioned above, a surface roughness below Ra = 0,15 μm was generated by using optimal fluence at both wavelengths of 1064 nm (IR) and 532 nm (VIS) and using a 70% spatial PO. Thus, a well-defined cutting edge with radii of 20–40 μm could be prepared.

Influence of Size Effect on Cutting Edge Rounding and Surface Roughness in Micro-Milling of Ti-6Al-4V

The quality of cutting depends most on the cutting tool condition. Towards having a good quality finish, cutting tolerance becomes a major concern, especially when machining at micro-scale where highly precise cutting is desired. This research investigates the size-effect during the micro-milling of Ti-6Al-4V under dry condition where the observations were made on cutting edge rounding (CER) and workpiece surface roughness. The result showed that the lower the feed rate, the greater rounding on the cutting edges were observed. Similar trend in result was obtained when measuring the surface roughness. The best feed rate for both observations was at 60 mm/min, where this setting has brought the mechanism to shearing, as the ratio between undeformed chip thickness and cutting edge radius started at 1.

Effect of Lubrication on Friction in Bending under Tension Test-Experimental and Numerical Approach

This paper is aimed to determine the value of coefficient of friction (COF) at the rounded edge of the die in the sheet metal forming operations using the bending under tension (BUT) test. The experimental part of the investigations is devoted to the study of the frictional resistances of low alloy steel sheet under different strains of the specimen, surface roughnesses of the tool and for different lubrication conditions. Three oils are destined for different conditions of duties in the stamping process. Numerical modeling of the material flow in the BUT test has been conducted in the MSC.Marc program. One of the objectives of the numerical computations is to know the type of the contact pressure acting on the cylindrical surface countersample in the BUT test by assuming the anisotropic properties of the metallic sheet. It has been found that the COF in the rounded edge of the die does not vary with increasing sheet elongation. Taking into account that normal pressure increases with increasing specimen elongation and workpiece material is subjected to strain hardening phenomenon, the COF value is very stable during the friction test. The effectiveness of the lubrication depends on the balance between two mechanisms accompanied by friction process: roughening of workpiece asperities and adhesion of the contacting surfaces. In the case of high surface roughness of tool due to a dominant share of ploughing, all of the lubricants used were not able to decrease the COF in a sufficient extent. The used lubricants were able to reduce the value of friction coefficient approximately by 3–52% in relation to the surface roughness of rolls.

Fabrication of Edge Rounded Polylactic Acid Biomedical Stents by the Multi-Axis Micro-Milling Process

This paper presents the first try to fabricate degradable polylactic acid (PLA) biomedical stents with round edges by the multi-axis micro-milling process. Conventionally biomedical stents are produced by laser processing. Post-processing operations are usually required to handle sharp edges and thermal defects of the stent due to laser processing. A computer graphics software package was used to design the strut structures with round corners of the PLA stent. A PLA tube was first created using injection molding, and a degradable biomedical stent was then fabricated through micro-milling by using a five-axis computer numerical control (CNC) machine tool. This study investigated the error in the rotation center that can occur during five-axis micro-milling. Data obtained from experiments on center-of-rotation errors were substituted into homogeneous coordinate conversion formulas. Center-of-rotation errors in the five-axis machine tool were compensated for improving the milling precision (A and C axes) to be within 5 μ m. Furthermore, milling parameter optimization experiments were conducted, which determined the optimal conditions for milling PLA to be a spindle speed of 60,000 rpm, feed per tooth of 0.005 mm, and feed rate of 600 mm/min, and achieved the minimum burr 0.01 mm and the average surface roughness (Ra) 0.4 μ m. These optimal cutting parameters will be used in the following actual stent processing experiments. Finally, the error compensation and optimal parameters were combined in a CAM software package and layered spiral micromilling to machine the actual stent. The experimental results revealed that the combination of five-axis micro-milling led to the successful fabrication of a degradable biomedical stent (stent diameter = 6 mm, strut width = 0.3 mm, and radius at round corners = 0.1 mm). The machined actual stent had cross-section height and width errors within 0.01 mm, and arc depth of cut variation within 6 μ m. In addition, the PLA stent machining results indicated a rebound of approximately 33% at the strut round edge machining. This work may also open up future possibilities for complex three-dimensionally structured biomedical stents for better performance and special functionality.

Numerical Prediction of the Flow Structure Inside Components of Industrial Glass Furnace Systems

An important aspect in the glass production industry is related to the heat recovery of the combustion gases. It is usually obtained throughout the use of well-tested technologies, such as regenerative towers with refractory material. For an effective heat recovery, a good distribution of the flow rate at the entrance of the chambers is crucial. The use of Computational Fluid Dynamics (CFD) allows the detailed analysis of the gas evolution during the process; the same would be impractical with experimental measurements, due to prohibitive ambient local conditions. The CFD approach during the design phase typically considers CAD geometries without the level of details related to technological features of the actual installed configuration (i.e. sharp edges vs rounded edges). A brand new built furnace has blunt edges in every connection between 3D walls of refractory blocks. The above edges will be rounded by the erosion-corrosion process due to the harsh chemical/mechanical/thermal environmental conditions inside the plant components (i.e. regenerative chambers, connecting ducts, furnace). The purpose of this work is to evaluate the influence of the geometrical details of the CAD (with focus on the edges connecting adjacent walls), due to technological or erosion aspects, on the flow structure in the furnace components.