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This study analyzes the effects of post-weld heat treatment (PWHT) on the mechanical properties and microstructures of SA-508 Gr.1a welds and proposes a new PWHT exemption criterion based on nonductile fracture evaluation considering welding residual stress. The welding coupons were prepared with submerged-arc welding, gas-tungsten arc welding, and shielded-metal arc welding, using ferritic steel, SA-508 Gr.1a. The microstructure of the heat-affected zone (HAZ) was analyzed using optical microscopy, electron-back-scatter diffraction and Vickers hardness testing. The mechanical properties of the welds were evaluated by uniaxial tensile test, transverse side bend test, Charpy V-notch impact test and side bend test. Bainite and ferrite structures formed mainly in the HAZ, and the grain size became coarser with proximity to the surface and fusion line. The mechanical properties did not depend strongly on PWHT, weldment thickness or welding techniques, and they satisfied the welding procedure qualification test specified in the ASME Boiler & Pressure Vessel code. Welding residual stresses were considered in assessing structural integrity using nonductile fracture evaluation. A margin of safety against nonductile fracture with residual stress was calculated for Korean Standard Nuclear Power Plant steam-generator welds, using its design parameters and operating conditions, and this safety margin is suggested as an acceptance criterion for residual stress for exemption from PWHT. Graphic abstract

A method for evaluating residual stress using an instrumented indentation test was developed some decades ago. More recently, another method was developed, using a Knoop indenter. The conversion factor ratio, which is one of the key factors in the evaluation algorithm, has been taken to be 0.34, although this value comes from an experimental result and its physical meaning has not been examined. Here we examine the physical meaning of this conversion factor from the previous residual stress model, and calculate its ratio using analytical model of the stress field beneath the indenter. In this process, we assumed that the conversion factor ratio was the ratio of the projected area of the plastic zone generated during the Knoop indentation test. An analysis of the stress field beneath the indenter was performed by FE simulation. Actual nanoindentation was conducted after Knoop indentation testing, using the interface-bonding technique, to identify the plastic zone. In addition, the conversion factor ratio was also calculated for the case where residual stress was present, and the geometric ratio of the Knoop indenter was different. A comparison of our results with those from previous studies showed that the conversion factor ratio obtained using our assumption was in good agreement with previous studies. (Received May 20, 2020; Accepted June 15, 2020)

A bearing is an essential mechanical element that is used to fix the axis of a rotating machine and helps rotate the shaft while supporting its weight and load. Numerous types of bearings have been developed depending on the functions and sizes of the machines in which they are utilized. In particular, power generating units such as gas turbines use medium or large hydraulic bearings for smooth operation. White metal is a tin alloy and a soft material that is often bonded to the inner surfaces of medium and large bearings to lubricate and protect the bearing shafts. Currently, gravity or centrifugal casting is used to bond the white metal to the surface of the bearing material. The casting process requires pretreatments such as chemical treatment and preheating and has many disadvantages with respect to the work environment, worker safety, productivity, and potential for automation. In this study, the process of binding white metal to bearings is simplified and improved by applying a laser cladding using powdered white metal. Depositing a metal that has a very low melting point compared to the base metal is different from the conventional cladding process; therefore, the focus of this work is to analyze the new cladding procedure for various process conditions. White metal specimens fabricated with this laser cladding were evaluated using cross-section images, hardness tests, and energy-dispersive X-ray spectroscopy analysis.

We investigated the analytic relation between hardness and compressive yield stress using an expanding cavity model (ECM) for nanoporous gold (np-Au). We prepared three np-Au samples with ligament sizes 30.61, 59.36 and 116.33 nm by free-corrosion dealloying and post heat treatment. The indentation contact morphology was examined to estimate the hardness accurately from the nanoindentation load-depth curve. Unlike conventional dense metals, the deformation was confined to the projected contact area, and the center of the residual impression was dominated by densification. The projected contact area estimated by the Oliver–Pharr method was overestimated, so that a new contact area function was proposed that considered the indentation contact morphology of np-Au. It was confirmed that a hardness value taking into account the indentation contact morphology of np-Au matches well with the hardness derived by direct measurement of the residual impression. We modeled the ratio of hardness to compressive yield stress for np-Au using an ECM. The scaling factors, which represent the extra strain-hardening in the core in the ECM, were analyzed for np-Au and dense metals. An ECM that better matches np-Au is suggested based on the scaling factor resulting from densification beneath the indenter.

We introduce a class of ultra-light and ultra-stiff sandwich panels designed for use in photophoretic levitation applications and investigate their mechanical behavior using both computational analyses and micro-mechanical testing. The sandwich panels consist of two face sheets connected with a core that consists of hollow cylindrical ligaments arranged in a honeycomb-based hexagonal pattern. Computational modeling shows that the panels have superior bending stiffness and buckling resistance compared to similar panels with a basketweave core, and that their behavior is well described by Uflyand-Mindlin plate theory. By optimizing the ratio of the face sheet thickness to the ligament wall thickness, panels maybe obtained that have a bending stiffness that is more than five orders of magnitude larger than that of a solid plate with the same area density. Using a scalable microfabrication process, we demonstrate that panels as large as 3x3 cm^2 with a density of 20 kg/m^3 can be made in a few hours. Micro-mechanical testing of the panels is performed by deflecting microfabricated cantilevered panels using a nanoindenter. The experimentally measured bending stiffness of the cantilevered panels is in very good agreement with the computational results, demonstrating exquisite control over the dimensions, form, and properties of the microfabricated panels., Comment: Main: 26 pages, 10 figures. Supporting information: 5 pages, 4 figures

We suggest a method for accurately estimating the uncertainty of indentation yield strength determined from the modified Meyer relation as a mathematical function of the measurement, taking into account Type A and Type B uncertainty. Using this method, we quantitatively compared the expanded uncertainty level of the yield strength as measured by instrumented indentation testing (IIT) and uniaxial tensile testing, and propose a dominant measurand that affects the final expanded uncertainty of the indentation yield strength. To interpret the difference in uncertainty between IIT and uniaxial tensile testing, we investigated the effect of the major sources of uncertainty in the IIT system: sample surface roughness and angular misalignment between the surface normal of the sample and the symmetric axis of the indenter. The surface roughness was controlled using 400-, 1000- and 2000-grit paper and the misalignment angle ranged over 0°, 1° and 2°. Acceptable surface roughness and standard uncertainty of misalignment angle are proposed that give the IIT similar uncertainty to uniaxial tensile testing.

International audience; We demonstrate the electrical properties of nano energy harvesters (NEHs) with various textiles for smart textiles that can be applied to the next generation wearable electronics. Output voltages and currents of NEHs with various fabrics, such as a cotton, rayon and wool that have different triboelectricity were measured. Cotton, rayon and wool shows the maximum output voltages of 1.250, 3.313 and 4.063 V, respectively. In addition, output currents of those textiles were 0.75, 4.4, 1.063 lA, respectively. Wool, in particular, which has the highest triboelectricity of 350 V exhibits the highest output voltage.

In this study, we characterize the viscoelastic behavior of polymers using nanoindentation. We applied the indentation representative stress approach and elastic solution to the Maxwell model and determined that there was a linear relationship between the inverses of the initial unloading stiffness and indentation unloading rate. From nanoindentation tests with various unloading rates on poly(dimethylsiloxane), the linear relationship between the indentation unloading rate and the initial unloading stiffness was confirmed. We have suggested two parameters such as, elastic coefficient and viscous coefficient, represent the viscosity and elasticity of the polymer material based on their relation. In order to check the dependency of the elastic and viscous coefficients on mechanical properties, we performed nanoindentation on poly(dimethylsiloxane) with different crosslinking densities by mixing different proportions of curing agent. The viscosity and elasticity depend on the crosslinking density of polymer, and it was confirmed that the elastic coefficient and viscous coefficient obtained from nanoindentation varied with the same trend depending on crosslinking density. (Received November 14, 2018; Accepted March 27, 2019)

Ceramics materials have some useful tribological properties. Therefore, they are used in a variety of industrial fields, which strongly require the severity of operating condition and higher reliability of tribosystem. In this paper, silicon nitride, silicon carbide, cermet, titania and alumina were tested under rolling friction to evaluate wear rate and clarify wear mechanism of ceramic materials based on fracture mechanics. From the experimental result, a wear model of ceramic materials was proposed and analyzed using linear elastic fracture mechanics. Finally, the new non-dimensional parameter, Sc, for the estimation of the ceramic wear rate was introduced and a wear equation was obtained.

Residual stress is generally evaluated using indentation by comparing the indentation curves of stressed and stress-free states. Here, we suggest a new method that can evaluate surface residual stress without indentation testing on stress-free specimen using stress-independent indentation parameters and an analysis of indentation contact morphology for the stress-free state. We found that several indentation parameters are independent of the stress by Vickers indentation testing on various stress states. The indentation contact morphology can be represented by indentation parameters including stress-independent ones, and by applying the stress-independent parameters obtained from the stressed state to the indentation contact depth function, we can estimate an indentation curve for stress-free state. The estimated curve matches well with the experimental stress-free indentation curve, and it was also confirmed that the applied stress values evaluated by comparing the estimated curve with the stressed indentation curve agree well with the reference values obtained from strain gauge.

We suggest a new method to evaluate stress directionality, the ratio of principal stresses, using nanoindentation by introducing a modified Berkovich indenter that is extended in one direction from the Berkovich indenter. In a nonequibiaxial stress state, the indentation load-depth curves are shifted differently as the extended axis of the indenter is placed in accordance with each principal direction. The indentation load-difference is proportional to each principal stress and the slopes are defined by the normal and parallel conversion factors whose ratio is constant at 0.58. The suggested method was verified by indentation tests using five nonequibiaxial stressed specimens. The evaluated stress directionality results show agreement with the applied reference values within ±20%. Furthermore, we calculated the conversion factor ratios for other modified Berkovich indenters extended to different degrees through finite element analysis and confirmed that the conversion factor ratio was inversely proportional to the extension of the modified Berkovich indenter.

The problem of environmental pollution from CO2 emissions is drawing worldwide attention. With this trend, within the automotive industry, development of lightweight parts and application examples are increasing to react to environmental regulations and to obtain better mileage. Furthermore, with the demands of the time to cut energy consumption and to protect the environment, recycling aluminum, which is being widely used for daily necessities as well as for industrial purposes, is important. Recycling aluminum can be critical in environmental protection, resource saving, and both pollution and waste prevention. The demand in aluminum alloy is increasing since it provides better intensity, lower density and superior corrosion resistance when compared with steels. In particular, the Al-Si-Cu Aluminum alloy, which possesses outstanding castability and mechanical properties, is extensively utilized for automotive parts as a cylinder head, among others. Thus, this study will use test pieces melting and casting commercial A319 ingot and other pieces remelting cutting chips which are discharged and processed from automotive parts manufactured with A319 alloy to investigate changes in microstructure, hardness and tensile tests. Through these processes, this study aims to research the possibilities of remelted A319 alloy to be utilized as a casting material based on characteristic comparison of the material.

A lab-scale linear cutting machine was manufactured to investigate the rock-cutting mechanism and a range of design factors of point attack pick cutters. Tests were performed on three samples with different strengths, and measured cutting forces were used to calculate the specific energy, an indicator of cutting efficiency. We proposed design conditions such as cut spacing, depth, skew angle , and attack angle for the cutting head to achieve efficient rock cutting while minimizing specific energy. In addition, the structural stability of the pick cutter and holder with respect to skew angle was analyzed. The relation between structural stability and durability is discussed in terms of the resultant force and skew angle. A series of finite element analyses explored the structural stability of the pick assembly. The results indicated two sites of concentrated stress that depend on the skew angle and can accelerate undesired abrasion of the pick, and a positive skew angle appears advantageous in terms of both cutting efficiency and structural stability.

Research on additive manufacturing (AM) is being actively conducted in various fields in order to efficiently manufacture complex three-dimensional structures. In particular, metal powder feedstock and lasers are being used by the manufacturing industry to fabricate mechanical components and parts, such as propellers, fuel nozzles, and vehicle equipment. We developed an approach, scanning- directed energy deposition (S-DED), in which a high-throughput DED method with a scanning nozzle was established that could create metal beads of exceptional quality with high productivity using metal powder. The S-DED nozzle was designed based on a numerical simulation of the particle fluid flow, which was verified through a deposition experiment. Before the simulation, the deposition efficiency and shape of the bead were assumed according to the shape of the nozzle and the distance between the nozzle and the surface of the base material. The optimal inlet supply angle was determined by changing the powder flow inside the nozzle; the optimal number of outlet channels was determined by analyzing the amount of powder deposited by the laser beam irradiated on the base material. It was found that the laser beam improved the productivity by shaping the existing Gaussian beam into an 8 × 3 square flat-top beam. As a result of the simulation, it was proved that the angle of the inlet (that supplied powder to the nozzle) influenced the flow of powder finally captured in the laser beam. Based on the simulation, the angle of inlet was selected as 75°, and the number of outlet and cooling channels was five and three, respectively. A cross section of the specimen was analyzed using a single bead and multiple layers.

In instrumented indentation testing (IIT), residual stress can be evaluated by shift in indentation load-depth curves for stress-free and stressed states. Although the average surface residual stress is able to be evaluated with Vickers indenter, in order to know stress directionality, another indentation tests with two-fold symmetric indenter, for example, Knoop indenter, are needed. As some necessities for evaluating nonequibiaxial residual stress within small indent area, we suggest a novel way to evaluate directionality of residual stress, p, using wedge indenter characterized by two parameters, edge length and inclined angle. We develop wedge-indentation-mechanics model based on predetermined conversion factors which are determined by IITs for various uniaxial stressed states combining with finite element analysis simulations. By utilizing the developed model, directionality of residual stress is evaluated through two serial wedge IITs with respect to principal directions. We find good agreements between applied residual stress and residual stress evaluated by the developed model for biaxial tensile stress states.

We examine the performance optimization of a drifter used for top-hammer drilling. The performance of the drifter is determined mainly by its percussion power, which is the product of the impact rate and impact energy. We selected design parameters influencing percussion performance with the goal of optimizing the percussion power output, and verified the validity of the drifter analysis model through a comparison with laboratory test results. The design parameters that influence the drifter’s percussion performance have been selected efficiently through screening design method, and these parameters were analyzed using the Taguchi method. As a result, the robust design values against noise factor have been proposed applying the Taguchi method to selected design parameters.

International audience; A comparative study of the electrical performance of triboelectric nanogenerators (TENGs) with plain-and 2/1 twill-woven cotton textiles was conducted. Furthermore, the microstructures of the cotton fiber surfaces were examined to understand the fundamental mechanical interaction among the cotton fibers in the TENGs. The TENG with 2/1 twill-woven cotton textiles exhibited higher output voltages compared to that with plain-woven cotton textiles. The difference in the output voltage between the two types of TENGs resulted from the difference in triboelectric charge generation between the constituent cotton textiles. The higher output voltage of the TENG with 2/1 twill-woven cotton textiles was attributed to the higher density in triboelectric interactions among the cotton fiber molecules.

Because frit bonding material is brittle, sudden impacts such as dropping may damage the bonding significantly. Strain-rate-controlled in-situ nano-indentation testing, which can determine localized material properties, was carried out on the frit-bonded specimen, especially on the frit bonding matrix and the filler. The results were compared with the drop-impact fracture behavior to understand the fracture characteristics. Mechanical properties at static condition or low strain rate did not show proper relationship with the fracture tendency of the drop tested result of the frit bonding. From the relationship between fracture toughness and the ratio of modulus/hardness, fracture characteristics at the drop impact situation could be estimated by the values at the high strain rate nano-indentation. The ratio between modulus and hardness on frit matrix showed close relationship with drop impact fracture. Though crack propagation path deflected at filler interface, filler property gave less influence on fracture tendency of drop impact fracture due to its small volume fraction. The properties of frit matrix were crucial to the fracture characteristics of the frit bonding.

The instrumented indentation technique (IIT) is a novel method for evaluating mechanical properties such as tensile properties, toughness and residual stress by analyzing the indentation load-depth curve measured during indentation. It can be applied directly on small-scale and localized sections in industrial structures and structural components since specimen preparation is very easy and the experimental procedure is nondestructive. We introduce the principles for measuring mechanical properties with IIT: tensile properties by using a representative stress and strain approach, residual stress by analyzing the stress-free and stressed-state indentation curves, and fracture toughness of metals based on a ductile or brittle model according to the fracture behavior of the material. The experimental results from IIT were verified by comparing results from conventional methods such as uniaxial tensile testing for tensile properties, mechanical saw-cutting and hole-drilling methods for residual stress, and CTOD test for fracture toughness.

Residual stress is a major factor in failure and fracture in structures or electronic components. Various testing methods are used to measure residual stress: there are saw-cutting, holedrilling, X-ray diffraction and layer-removing methods. In particular, instrumented indentation testing (IIT) has many advantages: it is a simple and non-destructive procedure that can be used for in-field testing. In previous research, we proposed an algorithm for evaluating the magnitude and directionality of residual stress using an asymmetric Knoop indenter with long and short axes in the ratio 7.11:1. Indenting in different directions with a Knoop indenter creates different indentation load-depth curves depending on the residual stress state. In addition, the directionality of the residual stress can be expressed as a function of the load difference ratio calculated from these load-depth curves. However, When the Knoop indentation test is performed at small indentation depths, experimental issues such as surface preparation or indentation normality can become significant as the load difference decreases. In order to solve these issues, we introduce a wedge indenter, that makes it possible to select the edge length independent of indentation depth. We can thus decrease indent size when working in a small testing area. The load difference between the stress-free and stressed state is related to the sensitivity of residual stresses, and a wedge indenter can maximize the sensitivity to residual stress. In this study, we suggest a way to use the wedge indenter and verify the model using cruciform bending specimens and finite element analysis.

Generally, post-weld heat treatment is applied to decrease welding residual stress and improve the mechanical properties and microstructure of weldment, and its performance has been recommended for many years [1, 2]. However, current steel-making technology has improved significantly and, steel toughness levels have generally improved substantially [1]. Additionally for several quenched and tempered steels, it is reported that in some cases, mechanical properties such as tensile strength and impact toughness are degraded after post-weld heat treatment [3]. In addition, for large steel assemblies, post-weld heat treatment can be expensive, so that there is an economic incentive to avoid post-weld heat treatment [2]. The research presented here suggests a way to exempt post-weld heat treatment for SA-508 Grade 1A material, which is used for pressure vessels in nuclear power plants, by considering both mechanical properties and residual stress to simplify the welding procedure. Weldments made of 120 mm thick SA-508 Grade 1A should be post-weld heat treated, according to current ASME BPV Code. In order to increase the PWHT exemption thickness to 120 mm, we performed mechanical tests using welding coupons without PWHT; the test results satisfied current mechanical property criteria. We present a residual stress acceptance criterion based on brittle fracture criteria in this research.

Atomic force microscopy (AFM) is one of the frequently used microscopy techniques to capture high-resolution images in science and engineering. Since the spatial resolution limit of AFM has been mostly reached and no further improvement is likely, much of the recent attention in the development of new AFM has been on improvement of speed. We present a photo-thermal, high-speed atomic force microscope scan head capable of exciting cantilevers photo-thermally and detecting cantilever motions with an optical beam bounce technique. The design features a unique Z-collar that permits direct mounting of a Z-scanner onto a microscope objective lens to achieve a high mechanical bandwidth. We demonstrate the performance of the developed scan head by imaging data tracks of a Blu-ray disk in tapping and contact modes.

Laser Surface Texturing(LST) is a surface engineering process used to improve tribological characteristicsof materials by creating patterned microstructures on the mechanical contact surface. In LST technology, a pulsatedlaser beam is used to create arranged dimples on a surface by a material ablation process, which can improve such asload capacity, wear resistances, lubrication lifetime, and reduce friction coefficients. In the present study, the effect ofmulti-scale LST on lubricant regime was investigated. A pulsed Nd:YAG laser was applied on the bearing steel(AISI52100) to create arranged dimples. To optimize the surface texturing effect on friction, multi-scale texture dimples withsome specific formula arrays were fabricated by combining circles, ellipses and the laser ablation process. The tri-bological testing of multi-scale textured surface was performed by a flat-on-flat unidirectional tribometer under lubri-cation and the results compared with that of the non-textured surface. Through an increase in sliding speed, thebeneficial effect of multi-scale LST performance was achieved. The multi-scale textured surface had lower frictioncoefficient performances than the non-textured surface due to the hydrodynamic lubrication effect.Keywords: laser surface texture (레이저 표면 텍스처), lubrication regime (윤활영역), friction (마찰), surfacemodification (표면개질)

Laser surface texturing (LST) has been recognized as a viable, fast and accurate technology for surface engineering that is used to produce significant improvements in tribological performance of sliding surfaces, including their load carrying capacity, wear resistance, lubrication lifetime and reduced friction coefficients. In this study, we present the results of the combination effect of solid lubricant and LST steel surfaces on the tribobological properties. To improve the surface texturing effect on friction and wear, different multi-dimple patterns with some specific formula arrays were fabricated by laser ablation process by combining circles and triangles, and circles and squares on the surface of steel. The friction and wear test were performed using a pin-on-disc unidirectional tribometer under dry and coated MoS2, and the results compared with that of untextured surface. The influence of normal load, sliding speed and texture area density on the friction performance of multi-dimple patterns was also investigated by the Taguchi method. The results showed that the texture surface with the high dimple density had low friction at low and high applied load under dry friction. When combining the solid lubricant with dimples, the textured specimens improved the tribological performance for most applied loads. A variance analysis of the experimental data indicates that the texture area density had the highest contribution on friction coefficient and wear life followed by load and sliding speed. In general, multi-dimple textured surface had excellent tribological properties than the untextured surface under dry friction and coated MoS2 film demonstrated the potential of multi-dimple textured surface as a viable engineering surface for friction reduction and extend wear life.

Sensitive skin is a relatively common dermatologic condition and no optimal treatments have been established so far. Low-level laser/light therapy (LLLT) has been used for its biostimulative effect in various clinical settings. The purpose of this study was to investigate whether low-level laser/light therapy can improve sensitive skin clinically and to evaluate the effects of LLLT on skin in vitro. Twenty-eight patients complaining of sensitive skin were treated with low-level polarized light, and clinical results were evaluated using subjective and objective method. To investigate possible working mechanism of LLLT on skin, cultured human keratinocytes pretreated with nontoxic concentration of sodium lauryl sulfate (SLS) were used. Cytokines released from irritated keratinocytes after LLLT were analyzed. All patients showed subjective and objective improvement after treatment. No adverse effects were reported. The average number of LLLT sessions required to achieve clinical improvement was 9.9, and cumulative dose of LLLT was 71.3 J/cm(2) on the average. Erythema index decreased significantly after LLLT treatment (p = 0.017). In vitro assay showed that LLLT significantly reduced the release of VEGF from SLS-pretreated keratinocytes (p = 0.021). Our results suggest that LLLT could be a useful and safe treatment modality for sensitive skin, and modification of inflammatory cytokines released from irritated keratinocytes may be considered as one of plausible mechanisms in sensitive skin treated with LLLT.

Different treatment time and bias voltage with RF Ar plasma were used to improve tribological properties of NBR (Nitrile Butadiene Rubber). Chemical structure analyses of NBR by Attenuated Total Reflectance (ATR) were performed to clarify the functionality modification after the plasma treatment. In addition, wetting experiments were carried out by measuring the contact angle of distilled water drops on the NBR surface. ATR analysis revealed that the number of - C = O , - C - O , O - H functional groups increased after the argon plasma treatment. The functional groups led to changes in the contact angle from 100 to 50 degrees. The results showed that form-like nanostructures on the NBR was observed at the bias voltage of -400 V. The friction test showed that coefficient of friction after modified NBR in lubricated condition decreased from 0.25 to 0.15 with the increasing bias voltage due to the surface structure formations and better bonding with grease lubricant.

The adhesion force between a chloride-isobutene-isoprene rubber (CIIR) and stainless steel ball was studied. To decrease the adhesion force, the CIIR rubber was treated with high-density microwave plasma employing oxygen and argon gases. The experimental results showed that the adhesion force decreases with increasing the time of oxygen and argon plasma treatments. In addition, the contact microscope measurements revealed different surface structure with two gases. The real contact area also decreased with treatment time and dramatic changes were observed after 5 min treatment of CIIR rubber. The field emission scanning electron microscope image also showed that the subsurface of CIIR rubber pattern has changed with various plasma treatments. These results imply change in the morphology of CIIR rubber surface by plasma treatment is one reason for the decrease in adhesion forces.

This paper has reported the effect of oxygen and argon plasma treatments of CIIR rubber using Attenuated Total Reflectance (ATR) and surface energy measurements. Plasma treatment led to changes in the surface energy from 31 to 45.7 mN/m. Plasma treatment conditions influenced both the changes in surface energy and stability, and they also became more difficult to obtain good contact angle measurements. However, plasma treatments made the interfacial properties to be stabilized. ATR measurements revealed that changes in surface energy with treatment time are due mostly to increased oxygen functionality.

The fractional quantitative computed tomography (fQCT) to determine both quantity and distribution of bone mineral was evaluated based on the mechanical properties of trabecular bone. Using quantitative computed tomography (QCT), bone mineral density was measured at 46 areas from 5 bovine tibias. Subsequently, fQCT was measured by the proportion of pixels showing a bone mineral density greater than 290 mg/ml. Based on the mechanical properties of the bone specimens, the QCT and the fQCT were compared. The fQCT showed a significant correlation with the compressive strength with superiority to the QCT.

Adhesion between rubbers and metals is often the main cause of machine trouble. Therefore, efficient utilization of rubber in dynamic and static applications requires the modification of the adhesion property of the rubber surface without affecting the bulk characteristics. In this work, we have studied the mechanism of the reduction in adhesion force between medical rubber, chloride-isobutene-isoprene rubber (CIIR), and stainless steel by using surface wave-excited plasma treatment of the rubber surface with oxygen and argon gases. Experimental results showed that surface roughness derivations increased by about 10 times across the treatment, at maximum, corresponding to the increase in time. In addition, the micro-scale Young’s modulus of treated CIIR sheet increased by about 6.3 times at maximum from that of the untreated CIIR sheet. These changes in Young’s modulus and roughness at the surface of CIIR sheet are considered to be the main reasons for the plasma-assisted reduction of adhesion force between stainless steel ball (SUS 440C, JIS) and CIIR sheet.

Very high cycle fatigue (VHCF) tests were carried out to find the fatigue characteristics of a super-long life range by using a cantilever type rotational bending fatigue test machine on three kinds of specimens in bearing steel which were quenched and tempered in air (A: non-shot peened and B: shot peened after heat treatment) and under vacuum environment(C: non-shot peened) in this study. S-N curves obtained from the VHCF tests of the B and C specimens tend to come down again in the super-long life (109 cycles) range due to fish-eye type cracking, while most of the A and B specimens were fractured by surface defects such as scratches and slip lines. This duplex S-N behavior of bearing steel has to be reviewed by the change of the fracture modes.

Adhesion, or the binding of different materials at an interface, is of general interest to many branches of technology, e.g., micro-electronics, tribology, manufacturing, construction, etc. In addition, varieties of plasma treatments for the adhesion control of polymers are still extensively studied by a lot of researchers. However, there is a lack of research that decreases the adhesion force by using plasma treatment devices. Thus, this paper study to decrease the adhesion force between a medical rubber, chloride-isobutene-isoprene rubber (CIIR), and stainless-steel SUS440C by using oxygen plasma treatment. The different adhesion forces were measure after plasma treatment with various methods. The elastic modulus was increased by oxygen plasma treated to the CIIR specimen. The results show that the elastic modulus was increased 15% to 28% as the plasma treated to the CIIR specimen. Experiment results showed that the adhesion force decreased by about 95-99.8% by using oxygen plasma treatments between CIIR and SUS440C. The different adhesion forces were explained based on the morphology and Attenuated Total Reflectance (ATR) FTIR.

As welding residual stress is a primary factor in serious failure or fracture of plants, many testing methods such as X-ray diffraction, hole-drilling, and saw-cutting are used to evaluate this welding residual stress. Instrumented Indentation Testing (IIT) is an attractive testing method for evaluating welding residual stress because it is nondestructive and can be used in-field. The material properties can be obtained by Instrumented Indentation Testing in field using attachments like magnetic device or chain device. In general, the principle of evaluation of residual stress with IIT is based on comparing the load-depth curves obtained from stress-free state and stressed state which are same material. However, as the mechanical properties of welds are altered during welding process, it is difficult to obtain the load-depth curve for stress-free state of welds. In this research, in order to estimate the load-depth curve for the stress-free state, we consider the relation between k value of Kick’s law which is related to the slope of the load-depth curve and the hardness value which is independent of residual stress state. The relation between maximum load and maximum indentation depth which is k value of Kick’s law is similar to the concept of hardness and as a result, the ratio of k value between two materials is almost equal to the ratio of their hardness values. To validate this research, we compare the load-depth curve of stress-free material with the load-depth curve which is estimated from hardness ratio.Copyright © 2015 by ASME

The influence of nano-sizeWS2powders on the tribological behavior of ta-C coatings by the filtered cathodic vacuum arc (FCVA) method under boundary lubrication conditions has been investigated. In order to characterize and understand tribological behaviors of nano-sizeWS2powders added to the synthetic oil (poly-alpha-olefin 6), lubricants with different mixture ratios, ranging from 2 to 8 wt%, have been prepared. ta-C coatings fabricated by FCVA method showed that the G-peak in the obtained Raman spectrum was shifted from 1520 to 1586 cm−1, indicating the sp3content increased for samples with the thickness of 156 nm. The average friction coefficient decreased proportionally as the nano-sizeWS2compositions increased up to 4 wt% in PAO6. After the friction test, structures and particle sizes ofWS2phases were also precisely characterized by using XRD and SEM.