Circular Pits Research Articles

Offerings from the land and sea: A rare prehistoric ritual pit from west Moloka‘i, Hawaiian Islands

The archaeological record and ethnohistoric sources are combined to infer a ritual function of an isolated 40 cm diameter circular pit located above the high tide line at Kawa‘aloa bay, west Moloka‘i, Hawaiian Islands that was densely filled with bones of fish (Kuhlia sandvicensis), Green sea turtle (Chelonia mydas) and the extirpated Hawaiian goose (Branta sandvicensis). Beyond their obvious food value, ethnohistoric sources describe the ritual importance of these animals in late prehistoric Hawai‘i. There were no oven stones, charcoal, blackened sediment, or fire-reddened sand at the base of the pit suggesting a combustion feature. This pit currently is the only example of ritual evidence situated outside the confines of temple or shrine sites. AMS radiocarbon dating places deposition as early as the 14th century CE—perhaps two centuries after colonisation of the archipelago. It is only with consideration of the ethnohistoric literature, coupled with archaeology, that the significance of this pit is revealed.

Corrosion degradation of aluminium alloys using a computational framework

The paper describes the corrosion based degradation of aluminium alloys using an analytical and numerical framework. The corrosion rate was calculated using analytical equations for aluminium sheets subjected to a corrodent. Parametric analysis for the pit morphology, diameter, depth and distribution on the plate was conducted using finite element analysis. A comparison between elliptical and circular pits of the same area was also made for stress magnification using numerical analysis. It was observed that the stress generated at constant load when a specimen corrodes due to pitting is directly proportional to the pit diameter and pit depth. Zigzag pit morphologies due to the combined effect of mechanical degradation and corrosion have the highest stress at the corners of the pattern, while circular pits have the highest stress at the centre of the pit. The zigzag pit morphology has more detrimental effects than circular pits. For multiple distributed pits, the pits closer to the specimen edges exhibit higher stress values than those near the centre of the specimen. The effect of multiple or quantitatively increased number of pits having smaller geometric properties has a more detrimental effect than a single pit with larger geometric attributes.

Brachyoxylon fossil woods with traumatic resin canals from the Upper Cretaceous Cerro Fortaleza Formation, southern Patagonia (Santa Cruz Province, Argentina)

Two silicified fossil woods from outcrops of the Cerro Fortaleza Formation (Campanian, Upper Cretaceous) in Los Hornos Hill, Santa Cruz Province, Argentina are described. Based on their anatomical characteristics, both specimens were assigned to a new species of the fossil genus Brachyoxylon Hollick and Jeffrey, B. patagonicum sp. nov. They are characterized by having distinct growth ring boundaries, absence of axial parenchyma, uniseriate rays, mixed and uniseriate intertracheary radial pitting, and araucarioid cross-fields with 1–8 circular half-bordered pits per cross-field. In turn, one specimen has three rows of axial traumatic resin canals parallel to the growth rings were identified close to the middle of the growth rings or close to the latewood. Approximately 45% of Brachyoxylon species present traumatic resin canals, which suggests that they are a common feature of this fossil genus. Alternatively, the specimen with the canals shows biological remains (hyphae) and wood fungal degradation patterns, which may be thought as some of those of possible organisms contributing to the formation of the resin canals. This record provides fresh evidence attesting to the abundance and widespread distribution of Cheirolepidiaceae in the Cretaceous of Patagonia.

Surface integrity evolution of a Ni-based single crystal superalloy by laser shock peening

The single crystal superalloy SRR99 experimental samples were single point treated by laser shock peening (LSP) with laser pulse energy of 5–7 J. The surface morphology, micro-hardness, surface residual stress and surface microstructure of samples prior and after LSP were determined by corresponding characterization instrument. From the surface morphology, a circular pit was formed in surface, which due to the severe plastic deformation induced by LSP, and the diameter & maximum relative height of circular pit were increase with laser pulse energy. From the micro-hardness and residual stress test results of samples, these were increased after LSP treatment. In detail, the initial microhardness and residual stress were 398 HV and -498 MPa, with laser pulse energy of 5 J, the microhardness and residual stress were increased to 455 HV and -843 MPa, when the laser pulse energy was increased to 7 J, the microhardness and residual stress were increased to 512 HV and -942 MPa. In addition, the surface roughness of samples was increased too, which reflect the severe plastic deformation. By observing the microscopic morphology of the bottom of the pit, it is found that there are convex structure and crater shape defect structures on the bottom surface, and the formation of these structures may affect the surface roughness of the shock area. Although LSP caused certain degree of twist deformation of the shape of the γ' phase, the original strengthening method characteristics of the matrix phase and strengthening phase was not destroyed, which still maintained the creep strength and thermal fatigue properties of superalloy. The experiment show that LSP can cause significant work hardening effect on the surface of superalloy, and the generated high residual compressive stress can effectively delay the initiation and propagation of cracks. Therefore, LSP technology can effectively improve the fatigue life of single crystal blade components.

Performance improvement of turning operation during processing of AISI 304 with novel textured tools under minimum quantity lubrication using hybrid optimization technique

ABSTRACT Manufacturing cost and productivity in machining systems can be significantly affected by the optimized input sources. Further, metal cutting industries have shown curiosity toward surface textured tools due to gain in productivity. In this context, new textured tools were developed and machinability studies were carried out on AISI 304 material under eco-friendly technique namely Minimum Quantity Lubrication (MQL) with so developed tools. The novel textured tools were fabricated by making circular micro pit holes on the rake face of the tungsten carbide tool using laser technology. In this work, a new weighted gray relation analysis (WGRA) integrated Jaya algorithm is proposed to determine the best cutting parameters. From the result, it is found that 54%, 7% respective reduction in surface roughness (Ra) and tool wear (Vb) and 27% increment in material removal rate (MRR) at the optimum conditions determined by the proposed optimization technique. It is concluded that the proposed work meets the environmental sustainability requirements and improved the turning process performance.

A fossil carbonate rocky shore in the Kalcit Quarry: a new insight into echinoid shallow marine bioerosion (Miocene; Czech Republic)

ABSTRACT A Miocene fossil rocky coastline is well preserved in Kalcit Quarry near Brno. It differs from the few preserved coeval coastlines of the Central Paratethys in the dominance of borings attributable to echinoids. These borings are represented by roughly smooth shallow circular pits interpreted as dwelling traces of echinoids. Ichnotaxonomically, they can be placed in the ichnospecies Circolites kotoucensis Mikuláš, 1992. Besides usual individual pits, two discernible varieties of composite Circolites were found: (1) linear chains of pits interconnected by a smoothed joint bottom; and (2) spirally folded pits resembling a rosacean flower. The linear chains are morphologically very similar to narrow forms of Planavolites homolensis Mikuláš, 1992 and to Ericichnus bromleyi Santos and Mayoral, 2015. This similarity demonstrates the necessity of a review of the diagnoses of all the hitherto described ichnogenera attributed to boring echinoids, i.e., Circolites, Ericichnus, and Planavolites. We suggest that linear or planar traces with smoothed bottoms should be considered a composite of neighbouring Circolites, provided that the remains of individual pits are still discernible in the ground plan. Ericichnus is now considered as junior synonym of Planavolites Mikuláš, 1992.

Modeling the Filling Rate of Faeces in Ordinary Pit Latrines

Faecal sludge deposited into the pit latrine is subject to biodegradation. The aim of this research was to develop model for the filling rate of faeces in ordinary pit latrine together with the effect of shape factor on such fillings to prepare the minds of users on the filling characteristics of the pit based on contents, usage and environmental factors. Consequently, faecal sludges sampled from 100 pits already filled were subjected to laboratory analyses for their physico-chemical and biological characteristics. Models for the actual filling rate of faeces in ordinary pit latrines were derived using BOD, COD, VS, and TS data, calibrated and verified. For a more critical situation, models were also derived for the filling rates considering pit shapes that gave the actual pit filling in comparison with the general condition. From the results, the actual filling rate was lower than those obtained using BOD, VS and TS. However, the COD gave filling rate closer to the actual filling rate than other parameters since TS could not be used to assess the filling rate of faeces in pit latrines. The pits exhibited low filling rate in terms of BOD in 2 pits. In terms of COD, the filling rate was higher compared with that of BOD. Low filling rate was observed with volatile solids and only 3 pits exhibited moderately high filling rates whereas total solids had the highest number of pits with high filling rates. The filling rates for both the square and rectangular pits increased by 26.5% from 40 – 90 ℓ/capita/year to 50 – 112 ℓ/capita/year due to the shape factor and this was above the values obtained in existing models while that of the circular pit remained the same. Reduction in pit volume and increase in filling rate by faeces was due to dead corners as a result of clogging, thereby reducing the area available for faecal infiltration into the surrounding soil. Circular pits are more stable because of the natural arching effect of the ground around the hole and there are no corners to concentrate the stresses. Pits with flat sides are much more likely to develop clogging resulting to dead corners than the circular pit. From this study, it is therefore evident that the shape of pit latrine determines the actual volume and the filling rate of faeces in pit latrine taking into consideration geological and environmental factors. Thus for optimal design, our engineers should take note of the pit shape factor. Thus, the model can be used to determine the filling rate of ordinary pit latrines considering soil characteristics, ground conditions and other favourable conditions.

Modeling the Filling Rate of Faeces in Ordinary Pit Latrines

Faecal sludge deposited into the pit latrine is subject to biodegradation. The aim of this research was to develop model for the filling rate of faeces in ordinary pit latrine together with the effect of shape factor on such fillings to prepare the minds of users on the filling characteristics of the pit based on contents, usage and environmental factors. Consequently, faecal sludges sampled from 100 pits already filled were subjected to laboratory analyses for their physico-chemical and biological characteristics. Models for the actual filling rate of faeces in ordinary pit latrines were derived using BOD, COD, VS, and TS data, calibrated and verified. For a more critical situation, models were also derived for the filling rates considering pit shapes that gave the actual pit filling in comparison with the general condition. From the results, the actual filling rate was lower than those obtained using BOD, VS and TS. However, the COD gave filling rate closer to the actual filling rate than other parameters since TS could not be used to assess the filling rate of faeces in pit latrines. The pits exhibited low filling rate in terms of BOD in 2 pits. In terms of COD, the filling rate was higher compared with that of BOD. Low filling rate was observed with volatile solids and only 3 pits exhibited moderately high filling rates whereas total solids had the highest number of pits with high filling rates. The filling rates for both the square and rectangular pits increased by 26.5% from 40 – 90 ℓ/capita/year to 50 – 112 ℓ/capita/year due to the shape factor and this was above the values obtained in existing models while that of the circular pit remained the same. Reduction in pit volume and increase in filling rate by faeces was due to dead corners as a result of clogging, thereby reducing the area available for faecal infiltration into the surrounding soil. Circular pits are more stable because of the natural arching effect of the ground around the hole and there are no corners to concentrate the stresses. Pits with flat sides are much more likely to develop clogging resulting to dead corners than the circular pit. From this study, it is therefore evident that the shape of pit latrine determines the actual volume and the filling rate of faeces in pit latrine taking into consideration geological and environmental factors. Thus for optimal design, our engineers should take note of the pit shape factor. Thus, the model can be used to determine the filling rate of ordinary pit latrines considering soil characteristics, ground conditions and other favourable conditions.

Development of Models for the Rational Design of Different Shapes of Pit Latrine

Specific models for the rational design of pit latrines of different shapes and sizes are presently non-existent. What exist are general design models irrespective of the shape and size of latrine which may not give the actual design parameters needed. This research was limited to the derivation of models that will aid the design of the capacity of pit latrines of different shapes and dimensions for different population of users and under different soil formations and ground conditions. The objective of this research was to derive models for the rational design of pit latrines of different shapes using data collected from 500 different household pit latrines already filled up. Thus, models were derived for different latrine pit shapes and sizes using data collected through the administration of designed questionnaire on 500 households having pit latrines already filled up. Models were developed specifically for different latrine shapes whereas those of other researchers were generalized. These models were calibrated and verified for the rational design of pit latrines of different shapes and sizes. The regression coefficients for calibration were 0.75, 0.65, and 0.50 and for verification are 0.97, 0.98 and 0.99 for square, circular and rectangular pits respectively. The implication of this research is availability of design models for the construction of different pit latrine shapes.

Development of Models for the Rational Design of Different Shapes of Pit Latrine

Specific models for the rational design of pit latrines of different shapes and sizes are presently non-existent. What exist are general design models irrespective of the shape and size of latrine which may not give the actual design parameters needed. This research was limited to the derivation of models that will aid the design of the capacity of pit latrines of different shapes and dimensions for different population of users and under different soil formations and ground conditions. The objective of this research was to derive models for the rational design of pit latrines of different shapes using data collected from 500 different household pit latrines already filled up. Thus, models were derived for different latrine pit shapes and sizes using data collected through the administration of designed questionnaire on 500 households having pit latrines already filled up. Models were developed specifically for different latrine shapes whereas those of other researchers were generalized. These models were calibrated and verified for the rational design of pit latrines of different shapes and sizes. The regression coefficients for calibration were 0.75, 0.65, and 0.50 and for verification are 0.97, 0.98 and 0.99 for square, circular and rectangular pits respectively. The implication of this research is availability of design models for the construction of different pit latrine shapes.

Cutting performance of micro-textured PCBN tool

To study the effect of micro-texture on the cutting performance of polycrystalline cubic boron nitride (PCBN) tools, five types of micro-textures (circular pits, elliptical grooves, transverse grooves, composite grooves, and wavy grooves) were applied to the rake surface of PCBN tools by an optical fiber laser marking machine. Through a combination of three-dimensional cutting simulations and experiments, the influences of micro-texture on chip–tool contact area, cutting force, chip morphology, shear angle, and surface roughness during the cutting process were analyzed. The results indicated that the chip–tool contact area and cutting force of both non-textured and micro-textured tools increased with increasing cutting speed, while the shear angle decreased with increasing cutting speed. The chip–tool contact area and cutting force of the five types of micro-textured tools were smaller than those of the non-textured tool. The chip–tool contact area and cutting force obtained by the wavy-groove micro-textured tool were the smallest. The chip radius produced by the five types of micro-textured tools was smaller than that produced by the non-textured tool, and the chip morphology was more stable. The transverse-groove micro-textured tool had a better chip breaking effect. The chip radius generated by the elliptical-groove micro-textured tool was 0.96 cm, while that generated by the wavy-groove tool varied from 0.55 cm to 1.26 cm. The presence of a micro-texture reduced the surface roughness of the workpiece by 11.73%–56.7%. Under the same cutting conditions, the five types of micro-textured tools gave a smaller chip–tool contact area, cutting force, chip radius, and surface roughness and a larger shear angle than the non-textured tool. In addition, the elliptical-groove and wavy-groove micro-textured tools had better cutting performance.

The effect of laser shock processing on mechanical properties of an advanced powder material depending on different ablative coatings and confinement medias

Based on the effect of confinement media and ablative coating, laser shock processing (LSP) is a surface modification processing with properties of high efficiency, cleaning, and non-pollution. At room temperature, water is used as the common confinement media and black tape is used as ablative coating in LSP. However, due to the instability of water and black tape at high temperature, warm laser shock processing (WLSP) favors silicone oil as confinement media and aluminum foil as ablative coating, where aluminum foil is pasted on specimen surface by thin vacuum grease. Due to the differences in confinement media and ablative coating, this work focuses on the effect of confinement media and ablative coating on surface quality and mechanical property of FGH98 powder material treated by LSP. FGH98 specimens were strengthened by LSP at room temperature with different confinement medias and ablative coatings. Three groups were divided based on confinement media and ablative coating: water+black tape, water+aluminum foil, and silicone oil+aluminum foil. The group of black tape and silicone oil was removed for the absence of practical significance in engineering. 2D and 3D surface topography was observed by white-light interference surface profilometer (WLI). In addition, surface microhardness and compressive residual stress were determined. The results show that a circular pit is induced by LSP, and its shape is similar to the shape of the Gaussian curve. Compared with the other groups, the 2D surface topography of the circular pit section in the silicone oil+aluminum foil group is smoother, which would delay crack initiation. After LSP treatment, surface microhardness is improved by 7.8-10.6%, and compressive residual stress raises from 355MPa to 896MPa in the first group. According to the comparison of residual stress and surface quality, the effect of confinement media and ablative coating groups on laser shock pressure is ranked in order: water+black tape > water+aluminum foil > silicone oil+aluminum foil. The main reasons for that group order are that shock pressure may be consumed by grease cream and the reduced acoustic impedance of silicone oil is lower than that of water.

Experimental rain prints and gas escape structures as a framework for interpreting circular imprints in shales of the Pottsville Formation (Pennsylvanian, Alabama)

AbstractCoal‐bearing, fine‐grained clastic rocks of the Pennsylvanian Pottsville Formation contain well‐preserved vertebrate and invertebrate trace fossils and disarticulated plant fossils. These fossil‐bearing rocks also contain small, circular imprints that resemble raindrop impressions but have also been interpreted as structures formed by gas bubble escape from wet sediment. Because rain prints are associated with arid, subaerially exposed depositional conditions and gas escape structures with water‐saturated, organic rich sediments, the interpretation of the circular structures profoundly impacts the palaeoenvironmental reconstruction and interpretation of the life habits of the trace‐makers. In this project, rain prints and gas escape structures were produced to compare these two hypotheses regarding mode of formation and to gain insight into interpretations of similar circular pits in the geological record. The results indicate that gas escape structures form most readily in fine‐grained sediment under water‐saturated conditions, in contrast to rain prints, which form most readily in unsaturated sand. A comparison with experimental structures suggests that the Pottsville shales preserve gas escape structures, not raindrop impressions, suggesting that the environment was rarely desiccated. Because rain prints and gas escape structures are superficially similar, genetic interpretations should not be based on these similarities, but rather on the differences observed between them. Reexamination of circular pits in the sedimentary rock record might require adjustment of environmental interpretations.

Study on the Loess Immersion Test of Metro Line 2 in Xi’an, Shaanxi Province, China

With the implementation of China’s western development and “One Belt, One Road” initiative, there are more and more projects in the collapsibility loess area, and the collapsibility loess problem encountered in the construction is becoming more and more prominent. In this paper, the collapsibility loess of the south extension section of Xi’an Metro Line 2 is investigated, and its collapsibility characteristics are studied through a large-scale site immersion test. The test site was a 15 m diameter circular test pit, which took 35 days for water injection and 60 days for observation after water stopped. The test results showed that the maximum self-weight collapsibility of the soil layer in the test pit is 32 mm, and the deformation amount is 10.05 mm in Q3 and 9.55 mm in Q2. The maximum deformation amount of 32 mm is less than 70 mm in the shallow marker; it may be caused by the paleosol layer as a bridge to provide a support to the overlying soil layer. The shape of the sphere of influence after immersion resembles a trumpet, slightly protruding outwards from the paleosol. The scope of influence between the infiltrated and saturated zones gradually increases with depth, and the saturated zone is generally smaller than the infiltrated zone. The research results of this paper can provide technical support and reference for the construction of Xi’an Metro Line 2 and other related projects in the region.

Study on Friction and Wear Behaviors of Micro Texture Shape and Its Modified Surface

The 304 stainless steel has good mechanical properties and is widely used in industrial manufacturing. In this paper, take 304 stainless steel as the substrate material, the five micro texture shapes, such as groove array, square column array, circular pit array, regular hexagon column array and trapezoid column array, on the surface of 304 stainless steel were carved by nanosecond laser engraving machine under the same parameters, and then were immersed in 0.5mol/l perfluorodecyl trimethoxysilane ethanol solution at 45 °C for 5 hours. Five type super-hydrophobic surfaces were obtained. A series of friction and wear experiments were conducted out and the influence of different micro texture on the friction and wear to the 304 stainless steel surface was analyzed. The results show that the square column array has the best friction and wear resistance, and its friction coefficient is 0.16, which is the lowest in all other micro texture shapes. It can be used as a reference for improving the friction and wear resistance of metal surface.

Effect of Sand Fines Concentration on the Erosion-Corrosion Mechanism of Carbon Steel 90° Elbow Pipe in Slug Flow.

Erosion-corrosion of elbow configurations has recently been a momentous concern in hydrocarbon processing and transportation industries. The carbon steel 90° elbows are susceptible to the erosion-corrosion during the multiphase flow, peculiarly for erosive slug flows. This paper studies the erosion-corrosion performance of 90° elbows at slug flow conditions for impact with 2, 5, and 10 wt.% sand fines concentrations on AISI 1018 carbon steel exploiting quantitative and qualitative analyses. The worn surface analyses were effectuated by using laser confocal and scanning electron microscopy. The experiment was conducted under air and water slug flow containing sand fines of 50 µm average size circulated in the closed flow loop. The results manifest that with the increase of concentration level, the erosion-corrosion magnitude increases remarkably. Sand fines instigate the development of perforation sites in the form of circular, elongated, and coalescence pits at the elbow downstream and the corrosion attack is much more obvious with the increase of sand fines concentration. Another congruent finding is that cutting and pitting corrosion as the primitive causes of material degradation, the 10 wt.% sand fines concentration in carrier phase increases the erosion-corrosion rate of carbon steel up to 93% relative to the 2 wt.% sand fines concentration in slug flow.

2500 years of charcoal production in the Low Countries: The chronology and typology of charcoal kilns and their relation with early iron production

The study of archaeological remains of charcoal kilns is a fast growing field of research. The history and evolution of different types of (pre)historical charcoal production features is still poorly understood however. Based on a large number of radiocarbon dated charcoal kilns from Belgium and the Netherlands, covering c. 2500 years, a typology and chronology of charcoal kilns is presented. The oldest charcoal production features date to the late Iron Age, though many of these dates seem to suffer from an old-wood effect and might actually date to the Early Roman period. Both Iron Age and Roman period charcoal production is done in rectangular pit kilns. During the Early Middle Ages, there is a shift to circular pit kilns which become the dominant kiln type during the High Middle Ages. From c.1300 CE onwards, charcoal is no longer produced in pit kilns, but a new kiln type, i.e. the mound kiln is used. The size of the charcoal (pit) kilns decreases from the Roman period till c. 1300 CE when, with the use of mound kilns the volume of produced charcoal dramatically increases. These changes in kiln size most likely reflect changes in both the organisation, scale and technology of iron production in the Low Countries.

Investigation on turning process performance using hybrid-textured tools under dry and conventional cooling environment

ABSTRACT In the context of the surface texture of the tool, turning process performance is sensitively affected by the surface texture geometry, design, and working environment. Therefore, present work focused on the fabrication of new texture design tools (an amalgamation of linear microgrooves and circular pit holes) and machinability evaluation of so developed tools in turning of AISI 304 material under dry and conventional cutting environment, respectively. Machinability measures considered in the work are cutting zone temperature (T), average surface roughness (Ra), and tool wear (Vb). Results indicated that the machinability of AISI 304 was significantly improved with the hybrid tools under conventional cooling compared to dry cutting conditions, respectively. Further, Scanning Electron Microscope (SEM) analysis revealed that adhesion wear is identified as the major tool wear mechanism in hybrid tools under both cutting environments. Furthermore, observed few surface defects in machined samples under conventional cooling conditions, respectively.

Study on tribological properties of 35CrMo steel after laser textured

35CrMo is a commonly used alloy structural steel, which is often used to process mechanical parts, but the friction of mechanical parts usually causes failure. In order to reduce the friction coefficient between parts and extend the service life, laser processing technology is used to improve the friction performance of 35CrMo. The circular pit texture was constructed on the 35CrMo using a nanosecond pulsed laser. The two-dimensional and three-dimensional morphology of the surface before and after texturing were observed using a scanning electron microscope (SEM) and a white light interferometer (WLI). The of the sample surface was measured using a vertical universal friction and wear tester, which was reduced from 0.55 of the unprocessed texture to 0.31 of the 60 % of the textured surface density. Through research, it is found that the decrease in friction coefficient is caused by the increase in surface roughness. This treatment method is beneficial to extend the service life of 35CrMo parts.

Effect of different micro-texture shape on corrosion resistance of metal surface

The 304 stainless steel is widely used in daily life. In this paper, the 304 stainless steel was taken as the substrate material and then the five different micro texture shapes were carved on them by nanosecond laser engraving machine under the same parameters. These shapes are the groove array, the square column array, the circular pit array, the regular hexagon column array and the trapezoid column array. Then these samples were immersed in 0.5mol/l perfluorodecyl trimethoxysilane ethanol solution at 45 °C for 5 hours. Five type super-hydrophobic surfaces were obtained. A series of corrosion experiments were conducted out and the influence of different micro texture on the corrosion resistance to the 304 stainless steel surface was analyzed. The results show that the square column array has the best corrosion resistance, and its corrosion rate is4.20mm.a−1, which is the lowest in all other micro texture shapes. It can be used as a reference for improving the corrosion resistance of metal surface.