Creep crack growth analysis using <Emphasis Type="Italic">C</Emphasis><Subscript><Emphasis Type="Italic">t</Emphasis></Subscript>-parameter for internal circumferential and external axial surface cracks in a pressurized cylinder

Creep crack growth at elevated temperatures is a critical consideration in estimating the remaining life of high temperature structural components and in deciding their inspection interval. In this study, creep crack growth analyses for external radial-axial and internal radial-circumferential surface cracks in a pressurized cylinder were conducted by an analytical method. The effect of crack depth and crack length on the variations in C _t and remaining life predictions were investigated for surface cracks with various initial aspect ratios. It was observed that the remaining life of an internal radial-circumferential surface crack was approximately 53 times longer than that of an external radial-axial surface crack for the same crack size and loading conditions with 316 stainless steel material. It was also observed that the variations in remaining life, crack propagations, and the C _t values were considerably sensitive to the crack location and crack depth. Convergence of crack aspect ratio was not observed when the crack depth ratio was increased. Since the method is independent of material properties and location of the crack geometries, it can be extended to various material properties and various locations of the surface crack geometries.     

MoS<Subscript>2</Subscript> Films Formed by <Emphasis Type="Italic">In-contact</Emphasis> Decomposition of Water-soluble Tetraalkylammonium Thiomolybdates

Synthesis and tribological evaluation of three tetraalkylammonium thiomolybdate (R₄N)₂MoS₄ (R = methyl, propyl, or ammonia) aqueous-based lubricant additives on a ball-on-disk tribometer was carried out for a steel–aluminum contact. Tests were performed at the same conditions of load, entrainment speed, sliding distance, temperature, and concentration of MoS₂ to compare the activity (lubrication effect) of the thiomolybdates prepared. A friction reduction is observed for the three salts compared to pure water; however, significant differences in friction coefficient are observed depending on the alkyl group. SEM/EDAX and Raman analysis of the wear tracks reveal the in-contact formation of a MoS₂-lubricating film, rich in molybdenum and sulfur.     

Two-Body Abrasive Wear of the Outside Shell Surfaces of Mollusc <Emphasis Type="Italic">Lamprotula fibrosa</Emphasis> Heude, <Emphasis Type="Italic">Rapana venosa</Emphasis> Valenciennes and <Emphasis Type="Italic">Dosinia anus</Emphasis> Philippi

Natural biological surfaces and biomaterials have some distinguishing properties for adapting themselves to natural surroundings. The outside shell surfaces of mollusc species often undergo the abrasive wear action from the sand particles in water sand slurry in natural conditions. The two-body abrasive wear behavior of the outside shell surfaces of three mollusc species Lamprotula fibrosa Heude, Rapana venosa Valenciennes and Dosinia anus Philippi was examined. Abrasive material used for tests were quartz sand (96.5 wt.%) with three different size ranges and powdered bentonite (3.5 wt.%). The two-body abrasive wear tests were run on a rotary disc type abrasive wear testing machine. The results showed that the abrasion resistance of the outside shell surfaces of the three mollusc species was higher when the corrugations on the shell surfaces were perpendicular to the sliding direction of the abrasive material than that when the corrugations on the shell surfaces were parallel to the sliding direction of the abrasive material. Basically, the shell of Lamprotula fibrosa Heude possessed the highest abrasion resistance among the three species of shell; the abrasion resistance of the shell of Rapana venosa Valenciennes was the lowest; and the abraded depth of the three species of shell increased with an increased abrasive particle size and relative sliding velocity. The abraded surfaces were observed with scanning electron microscope.     

Nonparametric estimation of a density and its derivatives: The <Emphasis Type="Italic">L</Emphasis><Subscript>2</Subscript>-approach

The nonparametric estimates of a density and its derivatives are considered within the scope of the L ₂-approach. New sets of weight functions with a bounded support are proposed for constructing admissible (unimprovable in the space metric L ₂(?∞, ∞)) estimates of the density itself and its derivatives to the third order, inclusive.     

Modeling the formation of silicon nanoclusters during annealing SiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> layers

The mechanism of formation of silicon nanoclusters in layers of nonstoichiometric composition is studied by Monte Carlo simulation. Interest in silicon nanoclusters (Si-nc) coated with an oxide layer is due to their applications in modern optoelectronics and nanoelectronics. A lattice Monte Carlo model is proposed to study atomic processes in the Si-SiO₂ system. The formation of silicon nanoclusters during annealing of single SiO layers and SiO₂-SiO-SiO₂ layered structures is studied. Along with the diffusive motion of particles, the model takes into account the formation and collapse of mobile molecules of silicon monoxide. It is shown that accounting for transport of silicon under high-temperature annealing due to the motion of SiO accelerates the formation of Si-nc. Dependences of the size of nanoclusters on temperature, annealing time, and the composition of the SiO _x layer are obtained. It is found that annealing of silica films containing layers of nonstoichiometric composition can lead to the formation of silicon nanoclusters or cavities.     

Substrate dependence of the scratch resistance of CrN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> coatings on steel

Hard CrN_x coatings were sputter deposited on hot work tool steel (HWTS) and high speed steel (HSS) in an industrial PVD reactor. Coatings were deposited under various nitrogen flows. The thickness, density, hardness, elastic modulus, composition, and stress were determined for the coatings. The specimens were subjected to scratch testing. Two different failure mechanisms were investigated: chipping and complete coating removal. For all specimens, the coating-to-substrate adhesion was that good that adhesion did not limit the scratch resistance. Therefore, the minimum loads at which a given type of failure was initiated were not a measure for the coating-to-substrate adhesion. The scratch resistance was better for coatings on HSS than for coatings on HWTS. This is due to the higher hardness of the HSS. Substrate independent measures for the scratch resistance of the coating were obtained by considering critical track widths instead of critical loads. The hardening of the coating--substrate systems due to the coating was investigated. The uncoated substrates exhibited track width independent scratch hardness. For the coated specimens the scratch hardness increased with increasing track width until chipping of the coating occurred. Complete coating removal coincided with a decrease in hardness. Although the elastic properties, hardness, and thickness of all coatings were more or less equal, CrN_1.0 coatings outperformed CrN_0.6 coatings in scratch tests both on HSS and on HWTS.     

Friction and wear properties of CN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/SiC in water lubrication

Amorphous carbon nitride coatings (a-CN_x) were deposited on SiC disk by ion beam assisted deposition (IBAD). The tribological behavior of a-CN_x coating sliding against SiC ball in water was investigated and compared with that of SiC/SiC system at room temperature. The influences of testing conditions on friction coefficient and specific wear rate of both kinds of tribopairs were studied. The worn surfaces on disks were observed by scanning electron microscope (SEM). The results indicate that the running-in period of a-CN_x/SiC was shorter than that of SiC/SiC system in water. At a sliding velocity of 120 mm/s, the mean steady-state friction coefficients of SiC/SiC (0.096) was higher than that of a-CN_x/SiC (0.05), while at 160 mm/s, lower friction coefficient (0.01) was obtained for SiC/SiC in water. With an increment of normal load, the mean steady-state friction coefficients after running-in first decreased, reaching a minimum value, and then increased. For self-mated SiC, the specific wear rate of SiC ball was a little higher than that of SiC disk, while for a-CN_x/SiC, the specific wear rate of SiC ball were 10 times smaller than that of a-CN_x coating. Furthermore, the specific wear rate of SiC ball sliding against a-CN_x coating was reduced by a factor up to 100~1000 in comparison to that against SiC in water. The wear mechanism of SiC/SiC system in water is related to micro-fracture of ceramic and instability of tribochemical reaction layer. Conversely, wear mechanism for a-CN_x/SiC is related to formation and transfer of easy-shear friction layer.     

Silicon radiation detectors (<Emphasis Type="Italic">Review</Emphasis>)

The modern status of the field of development of silicon detectors of charged particles and x/γ rays is considered. The types and characteristics of spectrometric detectors are briefly described; the predominant attention is given to track devices. The results of studies of the radiation resistance of silicon detectors are presented.     

Aqueous Lubrication of SiC and Si<Subscript>3</Subscript>N<Subscript>4</Subscript> Ceramics Aided by a Brush-like Copolymer Additive,Poly(<Emphasis Type="SmallCaps">l</Emphasis>-lysine)-<Emphasis Type="Italic">graft</Emphasis>-poly(ethylene glycol)

We have examined the adsorption properties of poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG)—a brush-like polymer—on Si₃N₄ and SiC surfaces and determined its impact on the aqueous lubrication of Si₃N₄ and SiC at various speeds and applied loads. The addition of PLL-g-PEG in aqueous solution reduces the interfacial friction forces significantly for self-mated sliding contacts of these two ceramics, as compared to lubrication with water or buffer solution alone. For SiC, the improved lubricating performance by addition of PLL-g-PEG was apparent for all tested speeds (from 1.4 to 185 mm/s under 2 N load). For Si₃N₄, the effect was more apparent in the slow-speed regime (≤20 mm/s under 2 N load) than in the high-speed regime (>100 mm/s), where extremely low coefficients of friction (μ ≤ 0.006) are readily achieved by aqueous buffer solution alone. It was further observed that the optimal lubricating effect with Si₃N₄ is achieved when the tribopairs are first run-in in polymer-free aqueous buffer to render the sliding surfaces smooth, after which the PLL-g-PEG copolymer is added to the buffer solution.     

<Emphasis Type="Italic">A Fuzzy TOPSIS Method for Robot Selection</Emphasis>

A fuzzy TOPSIS method for robot selection is proposed, where the ratings of various alternatives versus various subjective criteria and the weights of all criteria are assessed in linguistic terms represented by fuzzy numbers. The values of objective criteria are converted into dimensionless indices to ensure compatibility between the values of objective criteria and the linguistic ratings of subjective criteria. The membership function of each weighted rating is developed by interval arithmetic of fuzzy numbers. To avoid complicated aggregation of fuzzy numbers, these weighted ratings are defuzzified into crisp values by the ranking method of mean of removals. A closeness coefficient is defined to determine the ranking order of alternatives by calculating the distances to both the ideal and negative- ideal solutions. A numerical example demonstrates the computational process of the proposed method. ID="A1"Correspondance and offprint requests to: Dr T.-C. Chu, Department of Management and Information Technology, Southern Taiwan University of Technology, 1 Nan-Tai Street, Yung-Kang City, Tainan County 710, Taiwan. E-mail: mrchu@mail.stut.edu.tw     

Investigating the 1/<Emphasis Type="Italic">z</Emphasis><Superscript>2</Superscript>-filtering in tomography algorithms

The filtering of projections in tomography algorithms, which is based on the regularization of distribution 1/z ², is investigated. Numerical simulations validate that changing the filter support will substantially improve the tomograms. Comparison of the results of reconstruction by the 1/z ²-filtering algorithm and the Shepp-Logan algorithm shows that the reconstruction accuracy of the latter is worse when the number of angles of observation is small or a high noise is present in the projection data.     

<Emphasis Type="Italic">A Binary Morphology-Based Filtering Algorithm for Reverse Engineering</Emphasis>

A laser scanner is a common surface measurement tool in reverse engineering (RE). The point cloud obtained from a laser scanner usually has some noisy points. An algorithm based on a binary morphology technique is presented to identify the noisy points. After removing the noisy points, the filtered point cloud can be used to reconstruct the surface of a 3D object. The filtering algorithm described can remove both the points at a "far" distance from the scanned object and the "prods" on the surface of the object. ID="A1"Correspondance and offprint requests to: Dr C. L. Wang, Department of Mechanical Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong. E-mail: wangcl@ust.hk     

Macrotribological Studies of Poly(<Emphasis Type="Italic">L</Emphasis>-lysine)-<Emphasis Type="Italic">graft</Emphasis>-Poly(ethylene glycol) in Aqueous Glycerol Mixtures

We have investigated the tribological properties of surfaces with adsorbed poly(L-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) sliding in aqueous glycerol solutions under different lubrication regimes. Glycerol is a polar, biocompatible liquid with a significantly higher viscosity than that of water. Macrotribological performance was investigated by means of pin-on-disk and mini-traction-machine measurements in glycerol-PLL-g-PEG-aqueous buffer mixtures of varying compositions. Adsorption studies of PLL-g-PEG from these mixtures were conducted with the quartz-crystal-microbalance technique. The enhanced viscosity of the glycerol-containing lubricant reduces the coefficient of friction due to increased hydrodynamic forces, leading to a more effective separation of the sliding partners, while the presence of hydrated polymer brushes at the interface leads to an entropically driven repulsion, which also helps mitigate direct asperity–asperity contact between the solid surfaces under boundary-lubrication conditions. The combination of polymer layers on surfaces with aqueous phases of enhanced viscosity thus enables the friction to be reduced by several orders of magnitude, compared to the behavior of pure water, over a large range of sliding speeds. The individual contributions of the polymer and the aqueous glycerol solutions in reducing the friction have been studied across different lubrication regimes.     

End-grafted Sugar Chains as Aqueous Lubricant Additives: Synthesis and Macrotribological Tests of Poly(<Emphasis Type="SmallCaps">l</Emphasis>-lysine)-<Emphasis Type="Italic">graft</Emphasis>-Dextran (PLL-<Emphasis Type="Italic">g</Emphasis>-dex) Copolymers

Comb-like graft copolymers with carbohydrate side chains have been developed as aqueous lubricant additives for oxide-based tribosystems, in an attempt to mimic biological lubrication systems, whose surfaces are known to be covered with sugar-rich layers. As adopted in the previous studies of the graft copolymer poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG), which showed both excellent lubricating and antifouling properties, a similar approach was chosen to graft dextran chains onto the same backbone, thus generating PLL-g-dex. PLL-g-dex copolymers readily adsorb from aqueous solution onto negatively charged oxide surfaces. Tribological characterization at the macroscopic scale, either under pure sliding conditions or a mixed sliding/rolling contact regime, shows that PLL-g-dex is very effective for the lubrication of oxide-based tribosystems. The relative lubricating capabilities of PLL-g-dex copolymers compared with PLL-g-PEG copolymers were observed to be highly dependent on the molecular structure of the copolymers (in particular, side-chain density along the backbone) and the measurement conditions (in particular, time between tribocontacts); the PLL-g-dex copolymers with a low degree of grafted side chains (≤20% grafting of available protonated primary amine groups along the backbone) showed better lubricating performance than their PLL-g-PEG counterparts at high tribocontact frequency (≥ca. 0.32 Hz).     

<Emphasis Type="Italic">Joint Design of Continuous Sampling Plans and Specification Limits</Emphasis>

This paper explores the problem of integrating a Type I continuous sampling plan (CSP-1 plan) and the design of specification limits based on Taguchi’s quality loss function. By adopting the minimax-regret principle, we can obtain the economic specification limits and the optimal inspection policy. This study is an extension of Kapur and Wang’s work. ID="A1"Correspondance and offprint requests to: C.-H. Chen, Department of Industrial Management, Southern Taiwan University of Technology, 1 Nan-Tai Street, Yung-Kang City, Tainan 710, Taiwan, Republic of China. E-mail: chench@mail.stut.edu.tw     

<Emphasis Type="Bold">Monitoring of Ultraprecision Machining Processes</Emphasis>

New demands are being placed on monitoring systems in the manufacturing environment because of recent developments in machining technology and machine tool design. In-process sensors are used to generate control signals to improve both the control and productivity of manufacturing systems. Numerous different sensors are available for monitoring and controlling the machining environment including force, power, and acoustic emission (AE) sensors. This paper first discusses the requirements for sensor technology for precision manufacturing process monitoring in general. Details are also given about AE and its application for process characterisation and monitoring in ultraprecision machining.     

A Memetic Algorithm for the <Emphasis Type="SmallCaps">n</Emphasis>/2/Flowshop/α<Emphasis Type="SmallCaps">F </Emphasis>+ β<Emphasis Type="SmallCaps">C</Emphasis><Subscript>max</Subscript> Scheduling Problem

Machine scheduling has been a popular area of research during the past four decades. Its object is to determine the sequence for processing jobs on a given set of machines. The need for scheduling arises from the limited resources available to the decision-maker. In this study, a special situation involving a computationally difficult n/2/Flowshop/ αF + βCmax flowshop scheduling problem is discussed. We develop a memetic algorithm (MA, a hybrid genetic algorithm) by combining a genetic algorithm and the greedy heuristic using the pairwise exchange method and the insert method, to solve the n/2/Flowshop/ αF + βCmax flowshop scheduling problem. Preliminary computational experiments demonstrate the efficiency and performance of the proposed memetic algorithm. Our results compare favourably with the best-known branch-and-bound algorithm, the traditional genetic algorithm and the best-known heuristic algorithm.     

<Emphasis Type="Bold">Reconfigurable Computing for Tool-Path Computation</Emphasis>

Tool-path generation is one of the most complex problems in computer-aided manufacturing. Although some efficient strategies have been developed to solve it, most of them are only useful for 3- and 5-axis standard machining. The algorithm called virtual digitising computes the tool path by means of a virtually digitised model of the surface and a geometry specification of the tool and its motion, so it can be used even in non-standard machining (retrofitting). This algorithm is simple, robust, and avoids the problem of tool-surface collision. However, its computing cost is high. Presented in the paper there is a virtual digitising optimisation that takes advantage of reconfigurable computing (using field programmable gates arrays) in order to improve the algorithm speed. A comparative study will show the gain and precision achieved.     

<Emphasis Type="Italic">Continuous Secondary Ultrasonic Electropolishing of an SKD61 Cylindrical Part</Emphasis>

An effective ultrasonic-aided electropolishing system using low-cost electrodes for polishing cylindrical parts is developed. The process can be integrated with the primary processes of traditional turning, drawing, form rolling, or extrusion to achieve a good surface finish for moulds. Ultrasonic energy is applied to the electrolyte for residue discharge during electropolishing. Both continuous and pulsed direct current are tested in the study. The controlled factors include the chemical composition and concentration of the electrolyte, the electrolyte temperature, the flowrate of electrolyte, the initial gap width, and the rotational speed of the workpiece. The experimental parameters are the frequency and power of the ultrasonic vibration, electrical current density, pulse period, rotational speed of the electrode, the electrode feedrate, and the electrode geometry. The incorporation of ultrasonics is found to be more effective than the use of pulsed current, without sacrificing the polishing time. An average surface roughness of 0.3 μm can be obtained by this method. ID="A1"Correspondance and offprint requests to: Professor H. Hocheng, Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu, Taiwan. E-mail: hocheng@pme.nthu.edu.tw     

<Emphasis Type="Italic">Bootstrap Confidence Interval of the Difference Between Two Process Capability Indices</Emphasis>

The process capability index, C_pk, is extensively used to assess process performance in manufacturing industry. Statistical hypothesis testing or an interval estimation of a single C_pk had been derived under a normally distributed process. However, the difference between two process capability indices, C_{pk 1} - C _{pk 2} , cannot be inferred statistically because of the complexity of the sampling probability theory. This study proposes a bootstrap resampling simulation method to construct the biased corrected percentile bootstrap (BCPB) confidence interval of (C _{pk 1} - C _{pk 2} ), which can be used to select the better of two suppliers. The various simulation results indicate that the bootstrap confidence interval of (C _{pk 1} - C _{pk 2} ) can be employed to evaluate effectively the difference between the performance of two suppliers. ID="A1"Correspondance and offprint requests to: Dr. J.-P. Chen, Department of Industrial Engineering and Management, National Chin-Yi Institute of Technology, 35 Lane 215 Section 1, Chung Shan Road, Taiping, Taichung 411, Taiwan. E-mail: chen504@chinyi.ncit.edu.tw