Abrasion Pattern Research Articles

Effect of Grinding Media Grading on Liner Wear and Load Behavior in a Ball Mill by Using Rocky DEM

The liner is a wear-prone component in ball mills, subject to continuous impacts, squeezing, and abrasion from the grinding media during operation. Its service performance directly affects the working efficiency of the ball mill. The service life of mining ball mill liners is about 8 months, and frequent downtimes occur due to liner wear and loss of effectiveness, with liner replacement accounting for about 6% of the total cost, resulting in huge economic losses. This paper focuses on a Φ305 mm × 150 mm experimental ball mill, using the discrete element software Rocky Discrete Element Method (DEM) (software version number Rocky 2022 R2) for simulation modeling analysis. With Φ10 mm and Φ20 mm mono-size particle simulations serving as reference groups, this study investigates the motion states and liner abrasion patterns under different liner heights for both sizes of grinding media in Equilibrium Quality Manufacturer (EQM) and Original Equipment Manufacturer (OEM) gradations. The results indicate that the impact of liner height on the wear of the ball mill liners is related to the size and gradation of the grinding media. The degree of liner wear from highest to lowest is as follows: EQM > Φ20 mm > OEM > Φ10 mm. Due to the effect of the cylinder end cap, the wear at the axial center of the ball mill liner is more severe than at both ends, and the wear on the facing side of the liner is more severe than on the backside. A thorough study of the influence of ball mill grinding media gradation on the wear pattern of liners is of great theoretical significance for optimizing liner structures, improving grinding efficiency, and promoting energy saving and cost reduction in ball mills. This study provides theoretical guidance for understanding the mechanisms behind liner wear in ball mills and predicting the liner lifespan.

A strategy of hob-grinding the cylindrical riblet surface for drag reduction by the grinding wheel with ordered abrasive pattern

A strategy of hob-grinding the cylindrical riblet surface for drag reduction by the grinding wheel with ordered abrasive pattern

Phase Transformation and Mechanical Behaviour of Different Heat-Treated Nickel-Titanium Rotary Instruments

ObjectivesThis study evaluated the phase composition, phase transformation behaviour, and mechanical properties of five heat-treated NiTi instruments. MethodsProTaper NEXT (M-wire, PTN), ProTaper Gold (Gold-wire, PTG), One Curve (C-wire, OC), EdgeTaper Platinum (Fire-wire, ETP), NeoNiTi (electrical discharge machining-wire, NNA), and ProTaper Universal (conventional wire, PTU, control) with #25-tip size were tested (n = 12/group) for cyclic fatigue resistance (number of cycles to failure; NCF) and torsional resistance (angle of rotation to fracture and maximum torque at fracture [ultimate torsional strength]). The geometry and fracture surfaces of the tested instruments were examined by scanning electron microscopy. The phase transformation temperature and phase composition of the instruments were evaluated using differential scanning calorimetry and X-ray diffraction. Data were statistically analysed using one-way ANOVA and Tukey's post hoc test, with the significance level set at 5%. ResultsPTG showed the highest NCF (P < .05) at 37°C, while ETP exhibited the highest angle of rotation to fracture, ultimate torsional strength, and stiffness (P < .05). Scanning electron microscopy demonstrated typical clusters of fatigue striations and numerous cracks after cyclic fatigue fracture, whereas there was a concentric abrasion pattern with a dimple and microvoids at the centre after torsional fracture. In differential scanning calorimetry curves, austenite-finishing temperatures of heat-treated instruments were higher than 37°C, whereas that of PTU was lower than 37°C. PTU showed strong peaks of austenite at 25 and 37°C, whereas ETP showed a strong peak of R-phase at 25°C, but mostly austenite phase at 37°C in X-ray diffraction. ConclusionsGeometry, alloy type, and phase transformation temperatures of NiTi instruments affected their mechanical behaviour. Clinical relevancePTG showed the highest NCF, suitable for markedly curved canals. ETP had the highest torsional resistance, appropriate for narrow and constricted canals.

Abrasion Behaviors of Silica-Reinforced Solution Styrene-Butadiene Rubber Compounds Using Different Abrasion Testers.

Solution styrene-butadiene rubber (SSBR) is widely used to improve the properties of tire tread compounds. Tire wear particles (TWPs), which are generated on real roads as vehicles traverse, represent one of significant sources of microplastics. In this study, four SSBR compounds were prepared using two SSBRs with high styrene (STY samples) and 1,2-unit (VIN samples) contents, along with dicyclopentadiene resin. The abrasion behaviors were investigated using four different abrasion testers: cut and chip (CC), Lambourn, DIN, and laboratory abrasion tester (LAT100). The abrasion rates observed in the Lambourn and LAT100 abrasion tests were consistent with each other, but the results of CC and DIN abrasion tests differed from them. The addition of the resin improved the abrasion rate and resulted in the generation of large wear particles. The abrasion rates of STY samples in the Lambourn and LAT100 abrasion tests were lower than those of VIN samples, whereas the values in the CC and DIN abrasion tests were higher than those of VIN samples. The wear particles were predominantly larger than 1000 μm, except for the VIN sample in the DIN abrasion test. However, TWPs > 1000 μm are rarely produced on real roads. The size distributions of wear particles > 1000 μm were 74.0-99.5%, 65.9-93.4%, 7.2-95.1%, and 37.5-83.0% in the CC, Lambourn, DIN, and LAT100 abrasion tests, respectively. The size distributions of wear particles in the Lambourn and LAT100 abrasion tests were broader than those in the other tests, whereas the distributions in the CC abrasion test were narrower. The abrasion patterns and the morphologies and size distributions of wear particles generated by the four abrasion tests varied significantly, attributable to differences in the bound rubber contents, crosslink densities, and tensile properties.

Study on Microstructure and Wear Resistance of WC-based Cermet Coatings Prepared by HVAF

Abstract To mitigate the risk of vapor corrosion damage to the overflow mechanical parts, WC-based metal-ceramic coatings were applied to the surface of a 45-gauge steel substrate by supersonic air-assisted flame spraying (HVAF). The mechanical and wear-resistant qualities of the coating were identified by Vickers micro-hardness, ball-disc friction, and wear test, as well as optics, scanning electron, X-ray diffractometer, and white light interferometer systems. The findings demonstrate the layered structure of the WC-based coating, which is made up of the bonded phase and its distribution of hard phase particles that are diffusely dispersed. The coating is free of cracks, inclusions, and other defects, and its structure and organization are dense with a porosity of 0.86 ± 0.05%. The phenomenon of oxidative decarburization did not occur in the process of preparing the WC hard phase for WC-based metal-ceramic coatings. As a result, the coating’s micro-hardness of 11.83 ± 0.55 GPa is eight times that of the substrate. The results of comparing the three-dimensional abrasion patterns of the coating and the substrate reveal that the coating has superior abrasion resistance because its width and depth of abrasion are smaller than that of the substrate and a lot of furrows have formed on the substrate material’s surface. In contrast, the sprayed layer only had faint traces of abrasion. After three years of actual service, the impeller surface coating is essentially unaltered, which effectively addresses the issue of vapor corrosion damage to the slurry pump’s impeller and extends the pump’s service life to guarantee the overflow mechanical components operate safely and steadily.

Field monitoring and modelling of sediment transport, hydraulics and hydroabrasion at Sediment Bypass Tunnels

Sediment Bypass Tunnels (SBTs) are proven to be an effective measure to reduce or even stop reservoir sedimentation by bypassing sediment laden flows around reservoir dams to the downstream river reach. They are mostly used in Switzerland, Japan, and Taiwan. However, hydraulic and sedimentological operating conditions and the resistance of the invert materials against hydroabrasive erosion affect their cost-effectiveness. Hydroabrasion is a pressing issue at SBTs, other hydraulic structures and steep bedrock rivers exposed to high sediment transport rates under supercritical flow conditions. The present study was therefore conducted to address this issue by aiming at improving knowledge on abrasion mechanics and calibrating a mechanistic saltation abrasion model enhanced by Demiral-Yüzügüllü (2021). To this end, the abrasion resistance of fourteen different invert materials installed at Solis, Pfaffensprung and Runcahez SBTs in Switzerland was quantified by annual 3D laser scanning and the hydraulic conditions and sediment transport rates were regularly monitored between 2017 and 2021. The analysis of invert scans and hydraulic conditions revealed that Prandtl’s first and second kinds of secondary currents occurring in the bends and straight sections of the SBTs, respectively, and the observed abrasion patterns were strongly interrelated. The tested potassium aluminate cement and steel fibre concretes, granite, cast basalt and steel plates had better abrasion resistance against impact of sediment-laden flows compared to other materials. Sediment mineralogical composition i.e., bulk hardness relative to the invert material properties significantly affected hydroabrasion. The enhanced abrasion prediction model was calibrated with the present data and a quasi-constant abrasion coefficient of kv = (4.8 ± 2.2) × 104 was obtained. The enhanced model is well-suited for both laboratory and field scales. The present findings will contribute to the sustainable utilization and operational safety of hydraulic structures, optimization of SBT and reservoir operations regarding bypassing efficiency and reservoir lifetime and modelling of bedrock river erosion.

Taphonomic significance of Aristotle's 'Wheel Paradox': an example with the cerithid gastropod Cerithium atratum (Born, 1778) from Conceição Lagoon, Santa Catarina State, Southern Brazil

In the book Mechanical Problems, attributed to Aristotle, the author relates the differential degrees of wearing and rounding of pebbles and shells moved by waves on the seashore to the variable radii and diameters of these particles. This phenomenon, which became known as Aristotle’s ‘Wheel Paradox,’ seems to explain the pattern of abrasion observed in shells of gastropods Cerithium atratum (Born) found in Conceição Lagoon, on the Island of Santa Catarina, Brazil. In situ observations show that the elongated turriform shells of C. atratum deposited at shallow (&lt; 30 cm) depths on a sandy bottom with pavements of disarticulated valves of Anomalocardia flexuosa Gmelin are subject to bidirectional wave-generated currents under fairweather conditions. The 47 specimens analyzed exhibit a pattern of abrasion characterized by the loss of the shell wall, apparently proceeding from the wider last whorl toward the narrow apex, culminating in the exposure of the columella. Experiments designed to test whether this pattern could be related to the ‘Wheel Paradox’ principle show that under bidirectional flow, the shells describe circles on the vertical plane around the longitudinal axis (rolling) and a pendulum movement (revolution) on the horizontal plane centered on the apex. The whorls located farther from the apex have larger diameters and describe broader arc segments. Thus, they have higher tangential velocities and travel longer paths, which could explain why they are abraded earlier than the narrower whorls. Recognizing similar abrasion features in fossil shells can provide information on the local paleo-currents, hydrodynamics, and relative time-averaging of death assemblages and allow distinguishing between natural or anthropogenic modification in archaeological specimens. Although the effects vary between shells with different shapes, Aristotle’s ‘Wheel Paradox’ principle explains the general abrasion pattern among gastropods under certain hydrodynamic conditions. Keywords: Actualistic Taphonomy, Aktuopaläontologie, shell abrasion, shell orientation, biostratinomy, hydrodynamics

The Coastline Change Pattern of Gresik Beach around the Madura Strait, Indonesia

The coastal region is characterized by dynamic changes in its coastline, which can be attributed to various factors. However, the main causes of change along the Gresik coast have yet to be thoroughly studied. Therefore, this research aims to examine the patterns of coastline change along the Gresik coast around the Madura Strait and the influence of wind-generated waves on them. Specifically, the study focuses on four coastal zones: Ujung Pangkah, Sidayu, Bungah, and Manyar districts. The research utilizes satellite imagery and geographic information systems (GIS) as well as methods for calculating ocean waves to analyze the coastline change patterns. The study also examines the impact of ocean wave energy on coastal abrasion and accretion. The findings revealed that the accretion rate in the study area was higher than the erosion rate. The accretion in the coastal area of Gresik is attributed to the flow of the Bengawan Solo River, which carries sediment from upstream. The accretion and abrasion areas for the entire period from 2002 to 2019 were 1063.16 ha and 425.23 ha, respectively. The study also found that the mangrove areas exhibit a higher rate of accretion than abrasion, indicating their potential as a reliable indicator of the effects of sea level rise resulting from global warming.This study revealed that the northern part of Ujung Pangkah District and Bungah District experienced the highest abrasion patterns, whereas no abrasion was observed in Sidayu District. Between 2002 and 2019, the abrasion areas in Ujung Pangkah and Bungah districts totaled 243.96 ha and 178.29 ha, respectively. Wind-generated waves were likely the primary cause of the abrasion in these areas, though other factors may also have contributed to coastline changes. It is essential to consider these factors for effective coastal management in the region.

An internal cooling grinding wheel: From design to application

The cooling and lubrication conditions during the grinding process significantly impact the nickel-based superalloy's final service performance. The existing jet cooling and heat pipe technology can solve the heat conduction problem in the grinding process of superalloy. Still, managing cooling, lubrication, and chip removal are difficult. This paper describes the design and fabrication of a novel central fluid-through internal cooling slotted grinding wheel with an ordered grain pattern to improve the grinding machinability of a nickel-based superalloy. The pressurized grinding fluid was ejected into the grinding zone via the pipe and tool holder from the lower-end face of the inner cooling wheel. The structure of the grinding wheel was optimized using computational fluid dynamics (CFD). The flow field in the grinding area achieved the highest overall flow rate, distribution homogeneity, and effective exit flow when the internal flow channel had four through-holes. The exit for the inner runner is located at the abrasive edge and diamond staggered pattern. Single-layer brazing was used to create cubic boron nitride (CBN) abrasive rings with various abrasive patterns. The internal cooling wheel matrix and various components were prepared according to the optimized grinding wheel geometry model. A grinding test bench was built to conduct an experimental study of grinding the nickel-based alloy GH4169. The results show that, under the same conditions, a diamond-shaped staggered pattern obtains lower grinding temperature, lower surface roughness, better surface morphology, and more significant residual compressive stress distribution than an abrasive cluster diagonal circular staggered pattern or disordered pattern. The average effective flow rate calculated by CFD is increased by 42.3% when compared to the disordered pattern. In the experiment, compared to the disordered arrangement, with the increase of grinding wheel’s rotating speed and coolant pressure, the average grinding temperature of abrasive grain with diamond-interleaved arrangement decreases by 58.2% and 51.7% respectively, and its surface hardening degree decreases by 11.1% and 11.7% respectively.

Nonlinear Vibration Feature Recognition Method for Reciprocating Compressor Cylinder Based on VMD-Multifractal Spectrum

The failure probability of piston ring abrasion occupies the forefront in reciprocating compressor cylinder assembly. Due to the reciprocating friction between the piston ring and cylinder liner, the local vibration signal contains typical nonstationary characteristics with a seriously overlapped frequency band of impact signals, while the different featured signals are coupled with each other. Therefore, the identification of cylinder friction and abrasion fault modes has always been a hot and difficult problem in fault diagnosis of reciprocating compressors. In order to monitor the friction and abrasion between low linear speed nonmetallic piston ring and cylinder liner of reciprocating compressor in refinery and provide a theoretical basis for preventive maintenance, an analysis method based on VMD-multifractal spectrum was presented in this paper. First, the feasibility of the proposed method was proven based on the cylinder vibration experiment of a reciprocating compressor in the laboratory. Then, an in-service reciprocating compressor in a refinery was taken as the research object, from which the cylinder friction vibration signals were processed by using variational mode decomposition to obtain a band-limited intrinsic mode function (BLIMF). Multifractal detrended fluctuation analysis is employed in the final abrasion pattern identification. The results show that the proposed method based on VMD-multifractal spectrum analysis can effectively obtain the abrasion state of a piston ring, which can avoid blind overhaul or provide the basis for preventive maintenance and a practicable engineering route for the study of the piston ring abrasion degree.

Influences of test conditions of sandblasting on replicability of abrasion pattern of concrete subjected to hydrodynamic action

To determine the most suitable test conditions for sandblasting to evaluate the abrasion resistance against hydrodynamic action, a series of abrasion tests using hardened cement pastes with different water-cement ratios were performed under multiple combinations of air pressure and distance of the blast gun from the surface of a specimen. It was confirmed that the sharpness at the bottom of an abraded part, which largely influences the stability of the determination of the abrasion level, did not depend on the air pressure or the distance. Also, it was revealed that the relative value of the abrasion depth of materials with different abrasion resistances varied depending on the combination of air pressure and distance. This result indicates that when concrete is worn by sandblasting, the concrete surface exhibits different abrasion patterns depending on the conditions of sandblasting because the abrasion resistance of mortar matrix is usually lower than that of coarse aggregate. From the aspect of replicability of the abrasion pattern of concrete surfaces confirmed in in-service structures where coarse aggregates protrude, the combination of an air pressure of 200 kPa and a distance of 50 mm was determined as the most suitable test condition for sandblasting, and the applicability of the determined test condition to the replication of the abrasion pattern was validated.

PREDIKSI POLA ABRASI DALAM RANGKA MITIGASI BENCANA DI KECAMATAN GEROKGAK, KABUPATEN BULELENG, BALI

Gerokgak Subdistrict has seen a significant change in coastline during the past 20 years, from 1997 to 2017, with the largest change being around 620.6 meters. Of the several factors that cause coastline changes, abrasion is one of the most detrimental factors. Change in coastline caused by abrasion can be categorized as disasters because it is destructive and detrimental, as it threatens ecosystems or buildings behind the coastline. Judging from the tendency of development in Gerokgak District that inclines towards the coast, abrasion could be a devastating disaster for most of the people of Gerokgak Subdistrict. Structures such as PLTU Celukan Bawang, hotels on the beach, temples on the beach, and fish ponds owned by the government and the community will become easy targets for abrasion. Previous research resulted in an analysis of shoreline change from shoreline extraction every five years over a 25-year period. There are 6 coastlines resulting from shoreline extraction in 1995-2020. In this study, the six samples of coastline data that have been obtained will be used to draw a general conclusion on abrasion pattern and then this abrasion pattern will be used to produce extrapolation of the abrasion pattern every five years for the next 10 years, namely 2025 and 2030. This study produced extrapolation calculations for 2025 and 2030 which were achieved using the linear regression method with the aim that a linear coastline pattern could be formed as a consideration for decision making for abrasion disaster mitigation policies that occurred in Gerokgak Subdistrict .

Study on abrasive wear pattern of ethylene propylene dyne monomer (EPDM) rubber compound

Ethylene Propylene Dyne Monomer (EPDM) rubber is an important and dominant elastomer. In the present experimental work an indigenous EPDM rubber of low, medium and high hardness values have been selected for abrasive wear study in a two-body abrasion tester ‘TR-605′ (Ducom) in dry condition. Needless to be mentioned that this indigenously developed material in the laboratory of NEL, Kolkata has no prior data related to tribological characteristics. Moreover, all rubber materials have its own complex characteristics and unlike metallic materials the overall property prediction of any viscoelastic material is quite difficult. This is the motivation and novelty consideration of conducting the present study. Four experimental factors like hardness of rubber, abrasive grade, load on the job and cycle time have been selected judiciously at three levels each for the laboratory experimentations. Optimum combinations have been obtained through Taguchi’s design of experiment (DOE) technique. The results have been validated through confirmatory trials with the optimum combination of factor levels. The predicted response being 27.92 the obtained response after additional confirmatory trial has been noticed as 28.61. Hence, the accuracy of the prediction is considerably satisfactory. The surface abrasion patterns have been characterized by SEM study (SEM: JEOL, JSM-6360, model 75 82). The abraded surfaces have been coated with a very thin film of palladium (Pd) using an ion sputtering machine (Auto Fine Coater: JEOL, JFC-1600) before SEM studies. Finally, the conclusions have been made highlighting the possible future researches in the related field.

Identification of Gait and Personal Factors Associated with Shoe Abrasion Patterns.

Shoe abrasion data can be used as major evidence to distinguish suspects, but their actual application in the field is limited due to a lack of associated empirical studies. This study analyzed the significant factors of shoe abrasion by identifying significant differences between gait, personal characteristics, and shoe abrasion patterns. Experiments were conducted on 291 Korean subjects, and data were analyzed using cluster analysis and cross-tabulation analysis with data collected to identify significant factors. As a result, overall, medial abrasion was very rare and would be useful for human identification. The greater the gait characteristics of the knee valgus, the greater the inner abrasion characteristics shown. In the case of knee varus, outer abrasion characteristics occurred more often. Additionally, in the double support phase while walking, the greater the tilt to the left or right, the more the outer parts of the shoes tend to wear out. Men have the characteristic of wearing out the outer side of their shoes more compared to women. Regarding human body dimensions, there were significant differences between the abrasion patterns of the shoes with some body dimensions. The results of this study could be used effectively in the identification of suspects using shoe abrasion patterns.

Test method for abrasion behavior of tire tread compounds using the wear particles

The abrasion behavior of model tire tread compounds was characterized by the shapes and size distributions of their wear particles. Carbon black-filled NR/BR vulcanizates with varying compositions (NR/BR = 100/0, 80/20, and 60/40) were used. These were thermally aged at 80 °C for 30 days. The wear particles produced from the aged specimen had rougher shapes than those produced from the unaged specimen. The size distributions of wear particles for the aged specimen were smaller than those for the unaged specimen. The wear particles produced from the NR = 100 sample had a larger size distribution than those produced from the NR/BR blend samples. The size distributions of wear particles smaller than 500 μm were found to be closely related to the crosslink density irrespective of the rubber composition and thermal aging. The aged samples exhibited narrower abrasion patterns than their unaged samples. Furthermore, the spacing and depth decreased as the BR content increased. The abrasion patterns were closely related to the size distributions of wear particles. The abrasion rates and the number of wear particles significantly increased after the thermal aging. The abrasion behavior was mainly affected by the crosslink density, rubber composition, presence of antidegradants, and tensile strength. By analyzing the shapes and size distributions of the wear particles and the crosslink densities, the abrasion behavior could be further elucidated.

A stable foraging polymorphism buffers Galápagos sea lions against environmental change

Understanding the ability of animals to cope with a changing environment is critical in a world affected by anthropogenic disturbance.1 Individual foraging strategies may influence the coping ability of entire populations, as these strategies can be adapted to contrasting conditions, allowing populations with foraging polymorphisms to be more resilient toward environmental change.2,3 However, environmentally dependent fitness consequences of individual foraging strategies and their effects on population dynamics have not been conclusively documented.4,5 Here, we use biologging data from endangered Galápagos sea lion females (Zalophus wollebaeki) to show that benthically foraging individuals dig after sand-dwelling prey species while pelagic foragers hunt in more open waters. These specialized foraging behaviors result in distinct and temporally stable patterns of vibrissae abrasion. Using vibrissae length as a visual marker for the benthic versus pelagic foraging strategies, we furthermore uncovered an environment-dependent fitness trade-off between benthic and pelagic foragers, suggesting that the foraging polymorphism could help to buffer the population against the negative effects of climate change. However, demographic projections suggest that this buffering effect is unlikely to be sufficient to reverse the ongoing population decline of the past four decades.6 Our study shows how crucial a deeper understanding of behavioral polymorphisms can be for predicting how populations cope within a rapidly changing world. VIDEO ABSTRACT.

Significance of abrasion patterns in Recent pectinoid bivalve shells

Significance of abrasion patterns in Recent pectinoid bivalve shells

Design and evaluation of an internal-cooling grooved grinding wheel

To improve the grinding performance of superalloys, a bowl-type internal-cooling grinding wheel with a phyllotactic abrasive pattern has been developed. The internal structure of the grinding wheel is optimized as a two-stage cavity with eight transitional holes by computational fluid dynamics (CFD). And the outlet of the internal channel is set at the center of the abrasive zone to enhance the heat transfer of the coolant. Innovatively, the internal channel is prepared as an independent module through 3D printing technology to explore the influence of different channel diameters (1, 2, 3 mm) on the grinding performance of the grinding wheel. The simulation results show that when the diameter of internal channel is 1 mm, the coolant will be unevenly distributed within the grinding zone. As the diameter of the internal channel increases, the fluidity of the coolant increases, and the phyllotactic abrasive pattern can promote the uniform flow of the coolant within the grinding zone. The experiments of grinding Inconel 718 (flood, internal cooling) demonstrate that the internal cooling method provided better cooling and lubrication performance. Compared to the flood cooling, the grinding temperature of the 1- and 3 mm-diameter internal channels decreased by 23.0%, 48.2%, and the surface roughness decreased by 24.6% and 58.7%, respectively. The residual compressive stress on the machined surface increased by 122.36 MPa and 279.51 MPa, respectively. Further, with the increase of internal-channel diameter, the workpiece surface morphology becomes smoother.

실험계획법을 이용한 Al 합금의 마모 특성에 관한 연구

The purpose of this study is to improve the wear characteristics of Al7075 alloy, which is widely used as a material for aircraft parts. Ti, a high-hardness metal, was coated thinly on the surface of the Al7075 alloy using DC magnetron sputtering. Thin film coating was performed by configuring an orthogonal array according to design of experiments. Then the wear loss and the friction coefficient of the test piece were measured through an abrasion test. A prediction model that can improve the wear characteristics was derived, and it was shown to be valid. In addition, the characteristic of wear loss was remarkable when the wear surface showed comparatively clear abrasion pattern and also the grain of Ti thin film was bigger. When the wear surface showed irregular abrasion pattern and also the grain of Ti thin film was finer, the characteristic of coefficient of friction was remarkable.

Long-distance trade and consumption of mollusks in the Byzantine and Early Islamic periods in the Negev Desert

Recent archaeological excavations in the Negev desert in the southern Levant have yielded a variety of mollusk shells originating from the Mediterranean Sea, the Nile River, and the Red Sea, uncovered in the trash mounds and settlements of Byzantine and Early Islamic sites. These remains indicate that aquatic products were among the merchandised comestibles transported across long distances. Three shellfish taxa manifest such transportation: (1) the small clam, Donax trunculus, commonly found in the exposed sandy wash zones of the Eastern Mediterranean coast; (2) the large freshwater mussel, Chambardia rubens, whose habitat stretches from the Nile River to western Africa; and (3) the large conch, Lambis truncata, commonly found in the shallow waters of the Red Sea. The breakage and abrasion patterns of the shell fragments of these three species suggest that they were collected as live specimens and not as empty shells washed ashore. The other taxa, however, were mostly collected as empty shells to be used, for example, as ornaments.