Polished Edge Research Articles

Kostenki 4 ground stone tools in the collection of Kunstkamera museum (MAE RAS)

Tools made of soft rock materials at the Upper Paleolithic sites are usually represented by pebbles that were used for various domestic purposes without intentional modification of their shape. In the Neolithic period, the anisotropic stone raw materials were processed for manufacturing tools (such as axes, adzes, chisels, etc.) by abrasion — grinding, cutting edge sharpening, surface polishing. During the Upper Paleolithic, the occurrences of this technology use are rare due to the lesser role of woodworking in the life of glacial hunters. An exception is a series of ground tools from the Pavlovian sites in Central Europe, as well as from a few Gravettian sites similar to them by culture in the Kostenki-Borshchevo locality on the river Don. The largest assemblage of the ground tools originating from the site Kostenki 4 (excavations by A.N. Rogachev in 1937–1938) is housed in MAE RAS. Among these items there are rounded biconvex and plano-convex items (discs), rod-shaped and bullet-shaped items, as well as objects and fragments with polished surfaces and edges. The site comprises materials of a full cycle of manufacturing polished products, including a set of raw materials — quartzite abrasive tiles, pebbles and pieces of slate, dolomite, marl. The major part of collection consist of a series of bifacially treated blanks and amorphous items with the localized grindings. Polished discs and rods stand out for their peculiarity even against the background of the Holocene Stone Age ground tools, remaining beyond typological analogies. The traces of utilization such as short scratches and dints have surface localization instead of cutting edges or tips. The function of these objects as retouchers was determined through a traceological examination by S.A. Semenov. However, the presence of commonly used pebble and flint retouchers in the collection, combined with labor costs during grinding and mass production of such items, leaves the question of their usage open. The article presents a description of polished items from the collection of Kostenki 4, stored in the MAE (Kunstkamera) of the Russian Academy of Sciences, as well as the results of studying the issues of their manufacture and functioning.

Study of Modified Offset Trajectory for Bonnet Polishing Based on Lifting Bonnet Method.

The inability to converge at the edge of a workpiece during polishing affects the edge profile accuracy and surface quality of the workpiece. In this study, a bias trajectory generation method based on the lifting bonnet method that can maintain the morphology of polished edges is presented. Firstly, by establishing the polishing parameters and the decreasing rule in line with the principles of the lifting bonnet method, we obtained the residual height spacing, the radius of the polishing area, the centre offset position, and the pressing depth for each offset trajectory. Subsequently, the modified bias trajectory algorithm correction coefficients were obtained by fitting the edge trajectories using cubic Bessel curves, which were multiplied with the bias amount to obtain the final modified bias trajectory. Finally, an experiment was designed to compare the edge effect of the modified bias trajectory with the traditional grating trajectory. The experimental findings indicate that the reduction in edge collapse following the implementation of the modified offset trajectory was 1.30 μm. In contrast, the edge collapse after polishing with the traditional grating trajectory amounted to 98.67 μm. Moreover, the edge collapse ensuing traditional polishing trajectory was 75.9 times more pronounced than that observed after using the modified offset trajectory. It is shown that the modified bias trajectory method can not only maintain the original edge morphology of the workpiece but can also promote the convergence of the edge effect to a certain extent.

Impact of Cutting Process Parameters on the Mechanical Quality of Processed Glass Edges

The inspection of glass edges is gaining in importance in research, as the strength of a glass edge has been found to be highly dependent on its processing. Glass edges are produced by cutting. Depending on their type, they may be additionally seamed, ground or polished in the grinding process. Cutting and grinding processes create mechanical interference in the brittle material, leaving flaws and cracks in the edge surfaces. The current state of the art presents cutting process parameters which correlate with minor flaws and a high glass edge strength. Research at the Technische Universität Dresden aims to understand the impact of grinding processes and to develop parameters for processing glass edges with a defined and reproducible optical and mechanical quality. To isolate observations of the grinding process from the cutting process, this paper examines the impact of cutting process parameters on further processed glass edges. Several different cutting parameter-sets formed the basis of various test series that were performed on specimens whose glass edges were processed by the same manufacturer. This paper presents an optical and mechanical examination of the specimens. The results show that higher optical and mechanical qualities of the cut edge and arrised edge can be obtained by adjusting the cutting process parameters. It had no major impacts on smooth ground and polished edges.

Fatigue behavior of hybrid continuous-discontinuous fiber-reinforced sheet molding compound composites under application-related loading conditions

Hybrid continuous-discontinuous sheet molding compound (SMC) composites are considered suitable candidates for structural automotive applications, due to their high mass-specific mechanical properties combined with high geometrical flexibility and low costs. Since structural automotive parts are subject to repeated loading, profound knowledge of their fatigue behavior is required. This paper presents an experimental study on the bending fatigue behavior of hybrid SMC with discontinuous glass fibers in the core and unidirectional continuous carbon fibers in the face layers. Effects of hybridization on the S-N behavior and stiffness degradation have been analyzed in constant amplitude fatigue tests under 3-point bending load at different temperatures and frequencies. Microscopic investigations on polished specimen edges were used to study the damage behavior. The ultimate flexural strength at quasi-static (UFSS) and fatigue strain rate (UFSF) of the hybrid composite was 54 % and 59 % higher than that of discontinuous SMC, respectively. In contrast, the flexural fatigue strength at 2.6⋅106 cycles increased by 258 %. The relative stiffness degradation of the hybrid composites was smaller during most of their fatigue lives due to the continuous carbon fiber reinforcement. The carbon fiber ply on the compression loaded side was the first ply to fail. Fatigue stress significantly decreased at 80 °C due to early kinking of the continuous carbon fiber-reinforced ply on the compression loaded side. Variation of frequency had no significant effect on the fatigue behavior of both discontinuous and continuous-discontinuous SMC.

High coupling efficiency, passive alignment setup for visible-range fiber-to-waveguide edge coupling

We present a method to passively edge couple multiple optical fibers with silicon nitride waveguides in the visible wavelengths. We efficiently convert the fiber mode to the waveguide mode using an inverse taper mode size converter and support passive alignment using a U-groove that centers the optical fiber to the inverse taper. In our prototypes, we measure a coupling efficiency of −4.2 dB per facet. To reduce light leakage to the silicon substrate, we use a 6-μm oxide layer, which also eliminates the additional processes of undercutting the silicon substrate underneath the waveguide. Furthermore, the U-groove structure has a polished edge surface for coupling, reducing the steps of edge polishing the die. Fabrication of this visible-range edge coupler is complementary metal–oxide–semiconductor-compatible, making it a highly scalable method for passively packaging multiple visible-range integrated photonics devices.

The mineralogy and structure of use-wear polish on chert

Polished edges of archaeological stone tools are commonly investigated to obtain information on the tools’ uses in prehistory. Yet to this day, it remains unclear what exactly such polishes are and how they form. Answering these questions should allow the elaboration of new interpretative methods based on objective measurements. Two major competing hypotheses of polish formation have been proposed: abrasion and the formation of a thin amorphous film on the chert or flint surface. We employ reflectance infrared spectroscopy, a technique particularly sensitive to thin amorphous films, to investigate these two hypotheses. We found no added amorphous layer that would have formed upon friction against bone, antler, ivory or wood. Our observations suggest polish formation by abrasion, notwithstanding previous claims of added amorphous surface structures. This has implications for our understanding of the physical processes taking place during friction of chert and flint against different materials. Our results also open the possibility to propose new pathways for identifying different use-wear processes, based on the degree of abrasion.

Measuring fibre orientation and predicting elastic properties of discontinuous long fibre thermoplastic composites

Elastic properties in critical areas of 3 D shells made from discontinuous long fibre (DLF) composites are difficult to determine via traditional methods, due to the heterogeneity of the material and the geometry of the part. In this paper, a method is proposed to predict the local modulus of DLF composites based on a micrograph of the polished edge of a specimen. The position and orientation of each fibre are extracted from the micrograph and used in conjunction with classical lamination theory to predict the elastic modulus. Fibre discontinuity is accounted for by including a correction factor based on the Cox formula for averaged elastic constants. Model predictions successfully matched the experimental tests results. In a previous study, material flow during compression moulding of recycled DLF panels led to anisotropic behaviour, which was hypothesized to be caused by chip alignment in the flow direction. By using the proposed method, chip alignment due to flow was confirmed and the anisotropy in the elastic modulus was accurately predicted.

Observation of edge effect in flexural fatigue test of composites using large field of view microscopy

Free-edge effects in fibre reinforced composites can produce premature damage at the composite edges due to mechanical, geometrical and hygro–thermal effects. Observation of damage on the free-edge of a composite plate is therefore different than what can be observed inside the material. The amount of individually broken fibres in a composite is counted by observing a test specimen with a polished edge and by cutting test specimens to observe damage inside the material. The amount of damage observed on a polished edge is found to greatly exceed that which is observed inside test specimens subjected to the same testing conditions. It is shown that the progression of important damage mechanisms can be observed on polished edges, but also that invalid damage mechanism may be observed using free-edge microscopy.

Using a Hierarchical Weibull model to Predict Failure Strength of Different Glass Edge Profiles

The edge strength of glass is analyzed using a Weibull statistical framework based on 78 data samples from a range of experiments recorded in literature. Based on the analysis, a 45 MPa strength value (computed as the lower bound in a one-sided confidence interval at the 75% level for the 5-percentile in the distribution) could be conservatively used with arrised, ground and polished edges when related to a reference length of 100 mm at an applied stress rate of 2 MPa/s. The size effect can be represented by the usual weakest-link scaling formula with the Weibull modulus taken to be 8.0, 12.0, 8.0 and 6.5, respectively, for as-cut, arrised, ground and polished edges. It is estimated that static fatigue is best accounted for with a value of stress corrosion parameter about n = 16. The results are obtained with random sampling MC in a hierarchical modelling approach with the Weibull parameters treated as nested random variables. By accounting for the influence of glass supplier as a mixed-effect in a linear statistical model, it is found that supplier effects are significant and important to consider along with others due to, e.g., stress rate and edge length exposed to maximum stress. The data samples which are limited to glass tested in an ambient environment using four-point bending fixture, show that Weibull statistics generally scatter considerably. Numerical investigations with random sampling show that shape parameter estimates scatter substantially when sample size is limited, which can explain some of the observed variability in shape more so for ground and polished edges than for as-cut and arrised. For the as-cut edge, it is suggested that the shape parameter is scale-dependent. The Weibull parameters are also estimated using a clustered likelihood estimator under the condition that the shape factor has constant value for each edge type.

Compact hard x-ray split-delay system based on variable-gap channel-cut crystals.

We present the concept and a prototypical implementation of a compact x-ray split-delay system that is capable of performing continuous on-the-fly delay scans over a range of ∼10 ps with sub-100 nanoradian pointing stability. The system consists of four channel-cut silicon crystals, two of which have gradually varying gap sizes from intentional 5deg asymmetric cuts. The delay adjustment is realized by linear motions of these two monolithic varying-gap channel cuts, where the x-ray beam experiences pairs of anti-parallel reflections, and thus becomes less sensitive in output beam pointing to motion imperfections of the translation stages. The beam splitting is accomplished by polished crystal edges. A high degree of mutual coherence between the two branches at the focus is observed by analyzing small-angle coherent x-ray scattering patterns. We envision a wide range of applications including single-shot x-ray pulse temporal diagnostics, studies of high-intensity x-ray-matter interactions, as well as measurement of dynamics in disordered material systems using split-pulse x-ray photon correlation spectroscopy.

Effect of Hydrogen-Ion-Implantation on Self-Separation of Free-Standing Gallium Nitride Wafers Grown By Hvpe

In recent years, free-standing Gallium Nitride (FS-GaN) wafers were utilized as substrates for high-brightness light-emitting-diodes (HB-LED), LASER diodes (LD) and power devices due to their characteristics, such as 3 times higher thermal conductivity than sapphire substrates and higher breakdown voltage than conventional Si substrates. The FS-GaN wafers grown by hydride vapor phase epitaxy (HVPE) demonstrated lower dislocation density (DD) than that of GaN wafers grown by metal-organic chemical vapor deposition (MOCVD) on sapphire substrates (template GaN wafer). However, one of big challenges for their commercializing is the crack free FS-GaN wafers during the HVPE GaN growth, which resulted in lowering the productivity and increasing the fabrication cost. The main cause of the cracking is the stress induced by the differences in thermal expansion coefficients (TEC) and lattice constants of sapphire and GaN. To overcome this issue, the design of GaN growth process with self-separation is the key technology. The self-separation technique consists of two key points, one is separation enhancement and the other is blocking edge-poly-GaN growth. In this study, we investigated the effect of hydrogen-ion-implantation on self-separation of FS-GaN wafers. In addition, the blocking effect of edge grinding of template GaN wafers was also investigated. Two-inch-diameter template GaN wafers with the GaN layer thickness of 5 μm were prepared and the hydrogen-ions were implanted with various dose conditions to enhance self-separation of FS-GaN wafers from the sapphires. The edges of the implanted template GaN wafers were then ground to eliminate the polished edge surfaces to deter the poly-GaN growth. 800-μm-thick GaN layers were grown by HVPE on the template GaN wafers, and the FS-GaN wafers were successfully self-separated during the cool-down process. Fig. 1 shows the edge images of the GaN on sapphire substrates after 300-μm-thick GaN layer was grown on the template GaN substrates. When the edge-grinding was utilized to template GaN substrate, the poly-GaN was grown less than that of the substrate without edge-grinding. Also, the poly-GaN was easily removed at the edge of the substrate by edge-grinding without additional process. Fig. 2 shows the hydrogen-ion-band inside the MOCVD-GaN layer with three different hydrogen-ion dose conditions. The sample with hydrogen-ion dose of 2.25 E17 H+/cm2 showed larger size of the hydrogen cavity than the samples with hydrogen-ion dose of 1.75 E17 and 2.0 E17 H+/cm2. Fig. 3 shows the wafer images after 800-μm-thick GaN grown on the edge-ground template GaN with three different hydrogen-ion-implantation conditions. The FS-GaN wafers with hydrogen-ion dose of 1.75 E17 and 2.0 E17 H+/cm2 were successfully self-separated from the sapphire substrates, while the sample with hydrogen-ion-dose of 2.25 E17 H+/cm2 was self-separated around 63% of the area. In our presentation, we will report how we achieved the self-separation of FS-GaN wafers without cracking by hydrogen-ion-implantation into the template GaN substrates, and discuss about the crystal quality of the grown FS-GaN samples. * This work was financially supported by the Brain Korea 21 Plus Program in 2018. Figure 1

The Study of lithic assemblages on deflation surfaces. The case study of Arroyo Verde, Northern Patagonia coast, Argentina

This paper focuses on surface lithic artefacts from Holocene coastal hunter gatherer occupations of Arroyo Verde archaeological locality (Rio Negro province, Northern Patagonia, Argentina). The study of lithic assemblages collected at a deflation surface surrounded by stabilised sand dunes near the coastline, shows that wind produce significant corrasion (wind abrasion) of artefacts and affects preservation of small and medium size artefacts. The sample is mainly composed of chert knapping debitage with abraded and polished edges and surfaces. The artefact size distribution suggests that a subset of the assemblage exhibits good preservation, possibly due to the recent subaerial exposure. Furthermore, carbonate and mould coatings were recorded over the artefacts surface in contact with the ground, which indicates the presence of humid conditions in the sand dunes deflation area. In order to explore the factors that affected assemblage stability conditions in the locus, a machine learning based decision tree was applied. The model predicts and defines a threshold at which the occurrence of instability conditions may appear. Also, it suggests that relative altitude of artefacts within the deflation hollow is the primary variable explaining the exposure conditions recorded in the artefacts and it points out processes of differential deflation over time. The data presented here illustrates how wind alters local surface materials and emphasizes that a taphonomic perspective is needed to assess the formation processes within northern Patagonia coastal archaeological assemblages.

Thermally deformable mirror to compensate for phase aberrations in high-power laser systems

We report on a thermally deformable mirror to compensate for aberrations in high-power laser systems, suitable for intracavity and extracavity implementation in laser oscillators and laser amplifiers. The adaptive mirror consists of a thin polished edge filter which is mounted on a heat sink. Local deformations of the adaptive mirror are yielded by absorbing the emission of a so-called “heating laser” in the rear-side cooled mirror substrate. Thus, imaging suitable intensity profiles on the mirror enable us to perform laterally highly resolved profiles of optical path differences (OPD) to compensate systematically for phase aberrations. For this, a digital light processing (DLP) micromirror array of a commercial projector, irradiated by a top-hat shaped “heating beam,” is mapped on the adaptive mirror. Achievable deformations of the adaptive mirror have been measured using a Shack–Hartmann wavefront sensor. A high lateral resolution of 0.1 μm/mm radius and a maximal OPD of 0.569 μm could be demonstrated successfully.

Characterisation of Carestream 3543C/4343C digital detectors; experience with quantitative image quality techniques in digital radiography

Our department has recently commissioned four new Carestream DR imaging systems and the associated flat panel detectors (at least two per unit). The primary aim of this study was to characterise the performance of the detectors, primarily Carestream DRX Plus 3543C/4343C detectors, using quantitative measures. These were then compared with the results obtained from detectors of other vendors within our hospital group. Metrics used include the pre-sampled modulation transfer function (MTF), normalised noise power spectrum (NNPS) and detective quantum efficiency (DQE). These were calculated as per IEC 62220-1:2003, with any deviations from this documented. RQA5 beam quality was achieved using a 21 mm Al insert. A 1 mm thick 10 cm x 10 cm polished tungsten edge was used for the calculation of MTF. Initial analysis was performed using the analysis software IQworks. Results are displayed both graphically and in tabular format, allowing easy comparison of MTF, NNPS and DQE with other vendors. Commentary includes practical advice in achieving these results and discussion on the observed differences in detector performance. A brief discussion on the significance of varying some measurement techniques is included. In addition, a comparison of relevant analysis software is provided; namely IQWorks, ImageJ plugin:COQ and programs developed by the NCCPM, Royal Surrey County Hospital, UK.

High cycle fatigue strength assessment methodology considering punching effects

Since a decrease of the fatigue strength may result from punching operations, this study proposes a methodology for designing punched parts against high cycle fatigue crack initiation. To reach this goal, high cycle fatigue tests are performed on different specimens configurations with either punched or polished edges. Due to punching effects, the fatigue strength of punched specimens is significantly decreased. Fracture surfaces observations reveal that crack initiation occurs always on a punch defect. Additional investigations are combined to characterize how the edges are altered by the punching operations. High tensile residual stress levels along the loading direction are quantified using X-Ray diffraction techniques. Furthermore, micro-hardness measurements and X-Ray diffraction results reveals a strong hardness gradient due to punching operation. For a better understanding of crack initiation mechanisms, the edge geometries have been scanned with 3D optical microscopy, allowing us to identify the most critical defect (and its real geometry) by comparing the edges before and after fatigue failure. Finally, FEA are performed on identified defects. A non-local high cycle multiaxial fatigue strength criterion has been used as post-processing of FEA to take into account the effect on the HCF strength of defects and the strong stress-strain gradients around them.

Waveguide magnetoplasmonic structure based on ferrite garnet film

The magnetoplasmonic structure, which is a planar multimode magnetooptical waveguide, 10 μm thick with plasmon resonance SiO2 / Cu coating on the surface is experimentally realized. With the total length of the magnetooptical waveguide 4.6 mm and the length of the SiO2 / Cu coating equal to 3.9 mm, the insertion loss of the structure for TM- and TE-polarized light was 22 and 4 dB, respectively, at a wavelength of 1550 nm. Linearly polarized light was launched into the magneto-optical waveguide using a SMF-28 single-mode optical fiber coupled to the polished input edge of the waveguide. The structure is of interest for use as miniature magnetically controlled modulators of light intensity.

Failure behavior of quasi-isotropic carbon fiber-reinforced polyamide composites under tension

In this paper, the microscopic failure behavior of quasi-isotropic carbon fiber-reinforced polyamide-6 (CF/PA6) laminates under tension was investigated experimentally. Laminates of two layups, namely [45°/0°/−45°/ 90°]s and [45°/0°/−45°/ 90°]2s, were made from CF/PA6 tapes of two different manufacturers and then subjected to tensile testing. Crack initiation and progression on the polished free edge of specimens were examined using optical microscopy, under several load levels. Crack growth behavior through the specimen width was also traced by observing the crack configurations in different sections in the specimen width direction. The effects of the spatial distribution of fiber on the microscopic damage events were elucidated. The difference in failure behavior between the present CF/PA6 laminates and conventional thermosetting CF/Epoxy laminate is discussed.

Do high frequency acoustic emission events always represent fibre failure in CFRP laminates?

When damage in carbon fibre reinforced composites (CFRP) is monitored by acoustic emission (AE), it is a common belief that high frequency AE events originate from fibre failure. This shows that this statement may not correspond to the reality, and matrix cracks can emit high frequency AE signals. Quasi-static tension of [−452/02/+452/902]s laminates was monitored by AE, Digital Image Correlation (DIC) on the surface of the sample and in-situ optical microscopy on the sample’s polished edge. Unsupervised k-means clustering algorithm was applied to the AE results. By comparison with the direct DIC and microscopic observations, the AE cluster with high frequency and low amplitude was found to correspond to directly observed matrix cracks.

Prevention of crack in stretch flanging process using hot stamping technique

Demand for enhancing of passenger safety as well as weight reduction of automobiles has increased the use of high strength steel sheets. As a sheet metal is a lightweight having high strength is suitable for producing automotive parts such as white body panel. The stretch flanging of the high strength steel sheet is a problem due to high springback and easy to crack. This study uses three methods to stretch flange the sheets; using lubricants, shear-edge polishing and hot stamping. The effectiveness of these methods will be measured by comparing the flange length of each methods can achieved. For stretch flange with lubricant and polished sheared edge, the flange length failed to achieve the target 15 mm while hot stamping improved the formability of the sheet and preventing the occurrence of the springback and crack. Hot stamping not only improved formability of the sheet but also transformed the microstructure into martensite thus improve the hardness and the strength of the sheet after been quenched with the dies.

Influence of shear cutting parameters on the fatigue behavior of a dual-phase steel

The influence of the edge condition of car body and chassis components made of steel sheet on fatigue behavior under dynamic loading presents a major challenge for automotive manufacturers and suppliers. The calculated lifetime is based on material data determined by the fatigue testing of specimens with polished edges. Prototype components are often manufactured by milling or laser cutting, whereby in practice, the series components are produced by shear cutting due to its cost-efficiency. Since the fatigue crack in such components usually starts from a shear cut edge, the calculated and experimental determined lifetime will vary due to the different conditions at the shear cut edges. Therefore, the material data determined with polished edges can result in a non-conservative component design. The aim of this study is to understand the relationship between the shear cutting process and the fatigue behavior of a dual-phase steel sheet. The geometry of the shear cut edge as well as the depth and degree of work hardening in the shear affected zone can be adjusted by using specific shear cutting parameters, such as die clearance and cutting edge radius. Stress-controlled fatigue tests of unnotched specimens were carried out to compare the fatigue behavior of different edge conditions. By evaluating the results of the fatigue experiments, influential shear cutting parameters on fatigue behavior were identified. It was possible to assess investigated shear cutting strategies regarding the fatigue behavior of a high-strength steel DP800.