Three-parameter approach for elastic–plastic fracture of the semi-elliptical surface crack under tension

Systematic three-dimensional elastic–plastic finite element analyses are carried out for a semi-elliptical surface crack in plates under tension. Various aspect ratios (a/c) of three-dimensional fields are analyzed near the semi-elliptical surface crack front. It is shown that the developed J–Q annulus can effectively describe the influence of the in-plane stress parameters as the radial distances (r/(J/σ₀)) are relatively small, while the approach can hardly characterize it very well with the increase of r/(J/σ₀) and strain hardening exponent n. In order to characterize the important stress parameters well, such as the equivalent stress σ_e, the hydrostatic stress σ_m and the stress triaxiality R_σ, the three-parameter J–Q_T–T_z approach is proposed based on the numerical analysis as well as a critical discussion on the previous studies. By introducing the out-of-plane stress constraint factor T_z and the Q_T term, which is determined by matching the finite element analysis results, the J–Q_T–T_z solution can predict the corresponding three-dimensional stress state parameters and the equivalent strain effectively in the whole plastic zone. Furthermore, it is exciting to find that the values of J-integral are independent of n under small-scale yielding condition when the stress-free boundary conditions at the side and back surfaces of the plate have negligible effect on the stress state along the crack front, and the normalized J tends to a same value when φ equals about 31.5° for different a/c and n. Finally, the empirical formula of T_z and the stress components are provided to predict the stress state parameters effectively.     

TiF4 gel effects on tubular occlusion of eroded/abraded human dentin

This in situ study evaluated the tubular occlusion caused by 4% TiF₄ gel on the surface of eroded/abraded dentin. Sixty human dentin samples were eroded in vitro and assigned into six groups (n = 10) according to the in situ surface treatment and number of cycling days: 4% TiF₄ gel applied once (TiF₄1), twice (TiF₄2), or three times (TiF₄3) followed by 2, 4, and 6 days of erosive/abrasive in situ cycling, respectively. Control groups (no treatment) were subjected to 2 (C1), 4 (C2), and 6 (C3) days of erosive/abrasive in situ cycling only. A seventh group (n = 10) was comprised by in vitro uneroded samples (UN), subjected to 6 days of in situ erosive/abrasive cycling. Each cycling day consisted on six erosive (0.5% citric acid, pH 2.6) and one abrasive events. Environmental scanning electron microscopy micrographs were taken. For all groups, blinded examiners assessed dentin tubules occlusion using visual scores (0—unoccluded, 1—partially occluded by granular deposits, 2—partially occluded by reduction in tubular lumen into diamond shape, 3—completely occluded) on images captured prior and after the in situ phase. Scheirer‐Ray‐Hare test demonstrated that treatments significantly affected tubule occlusion (p < .001). Dunn's test showed that tubule occlusion in TiF₄3 was significantly higher than in C1. Tubule occlusion in remaining groups did not differ from that observed in groups TiF₄3 and C1. Tubule occlusion was significantly higher after in situ phase. It may be suggested that TiF₄, when applied three times, was able to positively change tubule occlusion of dentin samples.     

Ionic liquids as lubricants of polystyrene and polyamide 6-steel contacts. Preparation and properties of new polymer-ionic liquid dispersions

Room-temperature ionic liquids (ILs) have been used as external lubricants in polystyrene (PS) and polyamide 6 (PA6)-steel contacts and as internal lubricants in new polymer-IL dispersions. 1−C _n H_2n+1−3−CH₃-imidazolium X⁻ [X=BF₄; n=2 (IL1), 6 (IL2), 8 (IL3). X=PF₆; n=6 (IL4). X=CF₃SO₃; n=2 (IL5). X=(4−CH₃C₆H₄SO₃); n=2 (IL6)] ionic liquids give low friction and extremely mild wear in PS/AISI 316L stainless steel contacts, independently of IL composition. For AISI 52100 steel pins a tribocorrosion reaction produces FeF₂ and increases friction. PS+IL1 (1; 1.35; 3 wt.% IL1) dispersions show lower dry friction and wear against AISI 52100 as IL1 proportion increases, but the lowest friction, with a one order of magnitude reduction with respect to PS, is reached for PS+1%IL1 once the skin layer has been worn out. Increasing IL1 content to 10 wt.% produces an heterogeneous material with non-uniform IL distribution. IL4 reduces friction and wear in PA6+3%IL4 dispersions against AISI 316L, although the lowest values are obtained with IL4 as external lubricant. The cryofracture surfaces of the polymers have been examined and the thermal stability of the polymers in the presence of ILs has been determined.     

High-resolution large-strain measurement of plastically deformed specimen by Fourier phase correlation

The Fourier phase correlation method is applied to position circular marks one by one printed on the specimen before and after deformation in order to measure the large plastic strain. This method is extremely sensitive to the differences between the profile of a mark and noise. Therefore, it detects marks easily even under non-uniform illumination without any processing such as flattening illumination, noise exclusion and boundary enhancement in image transformation into binary codes. In addition, a new method of moving reference images (MRI) to position the observed marks in the sub-pixel range is proposed. The MRI technique introduces the theoretical resolution 1/n (n: number of divisions of one pixel). The MRI method enables the positions of the deformed marks to be determined with a resolution of ±0.1 pixel (standard deviation σ_p is 0.042 pixel). Strain of the tensile specimen can be measured within an error of ±0.0015 (standard deviation σ_ε=0.00055).     

Structure and morphology of Mg–Al–Fe‐mixed oxides derivedfrom layered double hydroxides

The influences of the nature and the extent of M(III) ion substitution on the structure, morphology and surface properties of layered double hydroxides, LDHs [Mg_1?x M(III)_x(OH)₂](CO₃)_x/n·mH₂O, M(III) being Al or/and Fe and x= M(III)/[(Mg+M(III)], and derived mixed oxides were investigated. Three series: Mg?Al, Mg?Al?Fe and Mg?Fe were synthesized using low supersaturation co‐precipitation method at constant pH, with different Mg : Al : Fe ratio and x in the wide range from 0.15 to 0.7 in order to obtain complex, multi‐phase systems with disordered structure, developed surface area, acid–base and redox properties favourable for catalytic application. The morphology of LDHs and their derived mixed oxides did not change considerably although pronounced changes in structural and surface properties occur by thermal decomposition. The increase in Al amount, as well as the deviation of M(III) content from the optimal range for the single LDH phase synthesis, causes the formation of smaller particles and decrease of mixed oxide crystallite size. The nature and amount of M(III) influence the development of surface area, after thermal treatment, depending mainly on the presence of smaller mesopores, not visible by scanning electron microscope. Although the particle size has no considerable influence on the value of the surface area, it was observed that the samples with smaller particles (Mg–Al and Mg–Al–Fe series) have also higher surface area compared with the samples with larger particles (Mg–Fe series).     

The sectorial co-ordinate of non-linearly elastic beams of three thin-walled open cross-sections

A beam lamina of thin-walled open cross-section is considered. The sectional forces are a bimoment B and a Vlasov torsional moment M_w. The material is assumed to be non-linearly elastic with the constitutive equation = K|σ|ⁿ sgn σ in uniaxial tension. A slight redefinition of the generalized sectorial moment of inertia I⁽ⁿ⁾_ω is given. The sectorial co-ordinate as a function of n is determined for three commonly used cross-sections.     

New synthetic esters with a complex structure considered as tribological fluids

The paper presents results concerning synthesis and characterisation as lubricant fluids of some esters of different monocarboxylic acids with variable chain length, along with aliphatic‐aromatic complex alcohols and/or with superior alcohols (exclusive of aliphatic). The monocarboxylic acids taken into account were n‐butyric, n‐octanoic and oleic, respectively, while the alcohols considered were isodecyl and isotridecyl as purely aliphatic, and 2‐phenoxy‐ethanol, 2‐[(o‐sec‐butyl)phenoxy]ethanol and 2‐[(p‐nonyl)phenoxy]ethanol, as part of the complex aliphatic‐aromatic alcohols group. Under these circumstances, it became possible to study the influence of the structure on the main physico‐chemical properties of these synthetic oils as well as on their tribological representative features. The results recorded certified the validity of the proposed research programme. Copyright © 2009 John Wiley & Sons, Ltd.     

Vlasov torsion of non-linearly elastic beams of thin-walled open cross-section

A beam lamina of thin-walled open cross-section is considered. The sectional forces are a bimoment (warping moment) B and a Vlasov torsional moment M_w. A formula for the sectorial co-ordinate containing three unknowns and being suitable for numerical calculations is given. The material is assumed to be non-linearly elastic with the constitutive equation = K|σ|ⁿ sgn σ in uniaxial tension. The relation M_w = B′ is shown to hold also for n ≠ 1. The location of the centre of twist as a function of n is determined for a monosymmetric I cross-section. The torsion-bending analogue for beams is found to be valid also for n ≠ 1.     

Development of the delamination evaluation parameters (I) — the delamination aspect ratio and the delamination shape factors —

Although the previous researches evaluated the fatigue behavior of A1/GFRP laminates using the traditional fracture mechanism, their researches were not sufficient to do it : the damage zone of A1/GFRP laminates was occurred at the delamination zone instead of the crack-metallic damages. Thus, previous researches were not applicable to the fatigue behavior of Al/GFRP laminates. The major purpose of this study was to evaluate delamination behavior using the relationship between crack length(a) and delamination width(b) in A1/GFRP laminate. The details of investigation were as follows : 1) Relationship between the crack length(a) and the delamination width(b), 2) Relationship between the delamination aspect ratio(b/a) and the delamination area rate ( (A_d)_n/ (A _d ) a_ll) , 3) The effect of delamination aspect ratio(b/a) on the delamination shape factor (f _s ) and the delamination growth rate (dA _d /da). As results, it was known that the delamination aspect ratio(b/a) was decreased and the delamination area rate ( (A _d ) _n / (A _d ) _All ) was increased as the normalized crack size(a/W) was increased. And, the delamination shape factors (f _s ) of the ellipse-II (f _s3 ) was greater than of the ellipse-1 (f _s2 ) but that of the triangle (f_s1) was less than of the ellipse-I (f _s2 ).     

Compositional analysis of mixed–cation-anion III–V semiconductor interfaces using phase retrieval high-resolution transmission electron microscopy

Employing exit‐plane wave function (EPWF) reconstruction in high‐resolution transmission electron microscopy (HRTEM), we have developed an approach to atomic scale compositional analysis of III‐V semiconductor interfaces, especially suitable for analyzing quaternary heterostructures with intermixing in both cation and anion sub‐lattices. Specifically, we use the focal‐series reconstruction technique, which retrieves the complex‐valued EPWF from a thru‐focus series of HRTEM images. A study of interfaces in Al_0.4Ga_0.6As–GaAs and In_0.25Ga_0.75Sb–InAs heterostructures using focal‐series reconstruction shows that change in chemical composition along individual atomic columns across an interface is discernible in the phase image of the reconstructed EPWF. To extract the interface composition profiles along the cation and anion sub‐lattices, quantitative analysis of the phase image is performed using factorial analysis of correspondence. This enabled independent quantification of changes in the In–Ga and As–Sb contents across ultra‐thin interfacial regions (approximately 0.6 nm wide) with true atomic resolution, in the In_0.25Ga_0.75Sb–InAs heterostructure. The validity of the method is demonstrated by analyzing simulated HRTEM images of an InAs–GaSb–InAs model structure with abrupt and graded interfaces. Our approach is general, permitting atomic‐level compositional analysis of heterostructures with two species per sub‐lattice, hitherto unfeasible with existing HRTEM methods.     

Turbulent mixing flow characteristics of solid-cone type diesel spray

The intermittent spray characteristics of the single-hole diesel nozzle (d_n=0.32 mm) used in the fuel injection system of heavy-duty diesel engines were experimentally investigated. The mean velocity and turbulent characteristics of the diesel spray injected intermittently into the still ambient were measured by using a 2-D PDPA (phase Doppler particle analyzer). The gradient of spray half-width linearly increased with time from the start of injection, and it approximated to 0.04 at the end of the injection. The axial mean velocity of the fuel spray measured along the radial direction was similar to that of the free air jet within R/b=1.0-1.5 regardless of elapsing time, and its non-dimensional distribution corresponds to the theoretical velocity distributions suggested by Hinze in the downstream of the spray flow fields. The turbulent intensity of the axial velocity components measured along the radial direction represented the 20-30% of the Ū_cl and tended to decrease in the outer region. The turbulent intensity in the trailing edge was higher than that in the leading edge.     

Burgers vector determination in deformed perovskite and post-perovskite of CaIrO3 using thickness fringes in weak-beam dark-field images

The thickness-fringe method [Ishida et al., Philosophical Magazine 42 (1980) 453] for complete determination of the character of a dislocation Burgers vector has been performed in CaIrO₃ perovskite and post-perovskite deformed at high pressures and high temperatures. By selecting several main zone axes and determining the number of terminating thickness fringes at the extremity of a dislocation from a wedge-shaped thin-foil specimen in weak-beam dark-field transmission electron microscope (TEM) images, the Burgers vectors were unambiguously determined. The results demonstrate that [1 0 0] screw and edge dislocations on the (0 1 0) slip plane are dominant in the post-perovskite phase. Curved [1 0 0] and [0 1 0] dislocations and straight 〈1 1 0〉 screw dislocations on a potential (0 0 1) slip plane were identified in the perovskite phase as well as a high density of {1 1 0} twins. Low-angle tilt boundaries consisting of different groups of parallel edge dislocations on the {1 1 0} and (0 0 1) planes indicate diffusion-assisted climb in perovskite at high temperatures. The differences in dislocation microstructures could be due to activations of limited numbers of slip systems for post-perovskite and of a large number of multiple slip systems for perovskite, which may result in the strong crystallographic preferred orientation (CPO) in post-perovskite and the lack of CPO in deformed perovskite.     

High‐contrast optical microscopy of graphene sheets

In the way of making graphene an industry‐friendly material, it must be mass‐produced with high‐quality and reduced cost over large areas. Assisted by machine‐learning techniques, rapid, nondestructive and accurate determination of large graphene sheets on SiO₂/Si substrates has been made possible in recent years by the optical microscopy method. Optimization of the substrate to achieve the maximum contrast can further extend the application of the optical microscopy method for quality control of the mass‐produced graphene. Graphene/n₂/n₃three‐layer structures, where n₂ and n₃ are refractive indices, are routinely used for identifying the number of graphene layers by optical reflection microscopy. In this paper, two analytical equations are derived that can be easily used for high‐contrast optical imaging of graphene sheets without any need to resort to the cumbersome numerical methods. One of the equations is derived for choosing the best material with refractive index n₂ that when coated on a substrate with refractive index n₃, maximizes the optical contrast. The other equation is derived for finding the best thickness of the SiO₂ layer in graphene/SiO₂/Si structures, which are in common use for fabrication of graphene‐based devices. The results are implemented in a MATLAB GUI, see Supporting Information, to assist the users in using the equations.     

Nanoparticle detachment: a possible link between macro- and nanotribology?

Although particle detachment is a common phenomenon associated with most tribological processes, it seldom occurs that each piece of elemental debris can be considered as the result of a single event. Such an association has been revealed by the systematic study of a specific system, where a pin of graphite is made to rub against thoroughly polished steel. While the discontinuous nature of the transfer film allows a quantitative assessment of the volume of transfer h _e to be made by 3D optical-profilometry, the linear dependence of the rate of particle detachment dh _e/dn (n=number of rubbing cycles) with the logarithm of sliding speed v strongly suggests the existence of a particular type of stick–slip, where each stick may lead to the detachment of a debris particle. The variations in size of these debris with environment as revealed by AFM, further suggest that the global rate of particle detachment is of the form: dh _e/dn=Nx _i , where N is the number of stick–slip events per rubbing cycle, x the proportion of stick events leading to a cohesive rupture, and _i the mean volume of an elemental particle. While this relation is apparently supported by most experimental results, its actual validation can only be made by experiments at the level of single (nanoscale) asperities, carried out under well-controlled experimental conditions.     

Automated Microscope-Absorption-Spectrophotometry Of Rock-Forming Minerals In The Range 40,000–5000 Cm−1 (250–2000 Nm)

To measure polarized absorption spectra of microcrystals of 3dⁿ-ion bearing silicate minerals, computer processed, microscope-spectrophotometric methods have been developed. Absorbance, log (I₀/I), can be measured with high relative accuracy (near u.v. and vis: ±0·002 to 0·001; n.i.r.: ±0·004 to 0·002), and relatively small spectral band widths are available. Hence, weak spin-forbidden dd-bands of 3dⁿ-ions can be recognized alongside spin-allowed dd-transitions without artificial broadening of absorption bands due to finite resolution. The smallest area from which absorption spectra can be taken is 8 μm in diameter. As one example of the many applications in mineralogy and material sciences, absorption spectra of a natural spessartine garnet, Spess_69·7Alm_30·0Gross_0·05, containing Mn²⁺, Fe²⁺, and traces of Fe³⁺ as 3dⁿ-ions, and of a pure Mn²⁺-garnet, Spess₆₇Gross₃₃, are presented. From these it is evident that bands in natural spessartines at ～ 26,900, 23,200 cm^?1 which were assigned to dd-transitions in Fe³⁺⁽⁶⁾, have to be reassigned to Mn²⁺⁽⁸⁾. Comparison of spectra obtained with the microscopic equipment described with those obtained by means of conventional macroscopic equipment prove that the methods described produce true spectra.     

Structural and mechanical properties of (Cr,Ni) N single and gradient layer coatings deposited on mild steel by magnetron sputtering

Ternary single and gradient layer (Cr, Ni) N thin films were deposited on the mild steel substrate by unbalanced magnetron sputtering technique in order to evaluate mechanical properties for machine tools and automotive applications. Microstructure, chemical composition, surface morphology and phase analysis were carried out using field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy and X-ray diffraction, respectively. Both single and gradient layer of (Cr, Ni) N coatings show a significant increment in mechanical properties such as hardness, adhesion strength and surface roughness along with the reduction of friction coefficient. Mechanical tests revealed that the hardness of the gradient layer increased up to 3.1 times due to the formation of Cr₂N and Ni phase whereas single layer showed the least friction. Single layer CrNiN layer exhibited 27.2% less surface roughness (R_a) in comparison with gradient layer. High values of surface roughness, hardness, thickness and friction could be correlated with high film-to-substrate adhesion (L_c2) for the gradient layer.     

Bonding of Hard Disk Lubricants with OH-Bearing End Groups

Typical lubricants for magnetic hard disks comprise the central perfluoropolyether section and the short hydrocarbon end groups bearing hydroxyl unit(s). It had been shown earlier that chemical bonding of these lubricants to the carbon overcoat of disks involves (1) dangling bonds shielded inside the carbon, (2) transfer of the hydrogen atom of the hydroxyl unit to a dangling bond site, and (3) attachment of the remaining alkoxy system, R–CF₂–CH₂–O^·, to the carbon surface as a pendant ether unit. Dangling bonds at or near the surface react immediately with H₂O or O₂ in the atmosphere. It follows that, in order to bond, the hydrocarbon end group must move into crevices of the carbon film. It was postulated that the bonding rate would depend on the length of the hydrocarbon end-group, –(CH₂) _n –OH. The longer the hydrocarbon sector is, the faster and the more extensively the bonding would proceed. Bonding rates were examined for a set of samples differing only in the dimension of the hydrocarbon end-group. Results clearly in accordance with the postulate were obtained. The sample set included two novel lubricants, D-2TX2 and D-2TX4, with the following end-groups, –O–CF₂–CH₂–O–(CH₂) _n=2,4–OH. Excellent bonding rate, coverage, and potential anticorrosion property were revealed for these lubricants.     

Scanning tunnelling microscopy of 1-D and 2-D charge-density wave systems

We have used a new variable temperature scanning tunnelling microscope (STM) to study quasi-1D and 2-D charge-density wave (CDW) systems. The 1-D systems, typified by NbSe₃ and TaS₃, are of special interest since they exhibit unusual transport phenomena associated with moving CDW above a threshold electric field. In the case of NbSe₃, room temperature STM images show both major and subtle details of the lattice structure. At present, however, images taken below the Peierls transition temperature of T_P=144 K resolve major lattice details but are not sufficiently clear to resolve the CDW. On the other hand, for the fully gapped CDW system orthorhombic-TaS₃, the CDW modulation superimposed on the lattice structure and having the correct period of four times the S-S spacing of 3·3 Å, is observed below T_P=215 K. Above T_P, the main observable feature is the S-S spacing along the chains. STM measurements have also been performed on the 2-D CDW system 1T-TaS₂ in its incommensurate, nearly commensurate, fully commensurate and trigonal phases. For the nearly commensurate phase, STM images show uniform commensurability with a relatively low concentration of small, time-varying discommensurations in contrast to models pradicting a regular domain structure. In the trigonal phase, however, evidence is seen for the striped phase composed of long, nearly parallel discommensurations.     

In situ formation of tribologically effective oxide interfaces in SiC‐based ceramics during dry oscillating sliding

The tribological behaviour of single‐phase SiC as well as both SiC–TiC and SiC–TiC–TiB₂ composite materials sliding against aluminium oxide has been investigated at room temperature with regard to the formation of wear‐reducing interfaces. The experiments were carried out in dry air for reasons of excluding the strong influence of water vapour. The introduction of the titanium phases into the SiC microstructure reduces the system wear by more than a factor of ten. The coefficient of friction is only slightly reduced but stabilised with time. The relatively abrasive oxide interface in the Al₂O₃/SiC pairing is altered to a soft and malleable oxide interface in the Al₂O₃/SiC–TiC–TiB₂ pairing. The wear reduction is mainly caused by a change of the wear mechanism so that the formed soft oxide wear debris is transferred to the counterbody, thus shifting the sliding plane further into the layer. This revised version was published online in July 2006 with corrections to the Cover Date.     

Using target costing concept in loss function and process capability indices to set up goal control limits

This paper depicts the relationship among the loss function, process capability indices and control charts to establish goal control limits by extending the target costing concept. The specification limits derived from the reflected normal loss function is linked through the C _pm value, computed either directly from the raw data or given by management or engineers, to conventional control charts to obtain goal control limits. The target value can be taken into consideration directly. The advantages of applying the target costing philosophy are also discussed. This paper explains, from a quantitative approach, that reducing process variation is not enough to solve quality problems. In fact, reducing process variation should be used along with bringing the process mean to the target value.A list of symbols K: The maximum-loss parameter in the reflected normal loss function - : The shape parameter in the reflected normal loss function, /4 - T: The target value - : The distance from the target value to the point where K first occurs (tolerance or specification limit) - E(L(y)): The expected loss associated with the reflected normal loss function - : The average value (mean) of a population - : The standard deviation of a population - _T : The standard deviation from the target value of a population - : The estimated standard deviation of - : The new process standard deviation when 2 are applied - n: The sample size of the subgroup - d ₂: The parameter used to estimate , determined by n - D ₄, D ₃, and A ₂: The parameters in and R control charts, determined by n - c ₄: the parameter used to estimate , determined by n - B ₄, B ₃, and A ₃: The parameters in and S control charts, determined by n - L(y): The general loss function - L ₁(y): The general loss function when the quality improvement is implemented - h: The parameter used to determine L ₁(y), where L ₁(y)=hK - f(y): The probability density function