Search

Fatigue life evaluation of welded joints under multiaxial loading usually refers to stresses normal to the weld and shear stresses. Stresses parallel to the weld are not considered in most experiments or the well-known Gough-Pollard criterion. Hence, the Gough-Pollard criterion has recently been extended to include all stress components at the weld surface. In this paper, both the original and, for the first time, the extended Gough-Pollard criterion are applied to different welded specimens under multiaxial loading that includes stresses parallel to the weld. As shown, the original criterion is insufficient to evaluate such stress states. This is because the calculated fatigue life becomes less conservative as the stresses parallel to the weld become more significant. The extended criterion, on the other hand, shows greatly improved accuracy while significantly reducing the likelihood of non-conservative results. In conclusion, the extended Gough-Pollard criterion can describe fatigue life under multiaxial loading better than the original version and provides reliable and conservative results for welded joints. The main findings are valid for the nominal, the hot spot, and the notch stress concept.

In the case of cyclically loaded brazed joints, especially in safety-relevant components like common rail systems for common rail direct fuel injection, it is necessary to reliably estimate the fatigue strength, considering the influence of different manufacturing processes, manufacturing parameters, and failure behavior. In this paper, induction-brazed, vacuum-brazed, and continuous furnace-brazed joints are used to develop a reliable approach to assess the fatigue life. Therefore, the specimens were characterized and tested under load control using constant amplitudes. It is found that the local brazing geometry in conjunction with the surface condition, which differs by different topography values and by the position and number of initial defects, have the most influence on the failure behavior and consequently on the fatigue strength. Irrespective of this, however, it is shown that the fatigue strength can be estimated sufficiently well even with a simplified finite element modeling that uses idealized fillet radii and by taking support effects into account.

Brazing is a joining technique used in many industries for components that consist of many individual parts. Many of these components are cyclically loaded during service. For this reason, reliable approaches to assess the service life must be developed. For this purpose, it is necessary to gain knowledge about factors influencing the fatigue strength and the damage behavior. In this paper induction, vacuum- and continuous furnace brazed shear and peel specimen with different brazing gap widths are analyzed. Therefore, the specimens were characterized, measuring the geometry of the specimens and surface condition of the brazing radii, and tested under load control using constant amplitudes. It is found that the manufacturing process and the parameters used have a significant influence on the mechanical properties of the brazing material, the surface condition and the profile of the fillet radii. These properties have again an influence on the damage behavior and the fatigue strength. In particular crack-like defects of varying severity, which can extend deep into the brazing material, that are located in highly stressed areas of the fillet radii have a significant influence on the fatigue strength. It is also found that, regardless of the brazing process used, there is a tendency in the area of the brazing gap width for the number and size of defects to increase with increasing gap size, which can negatively affect fatigue strength depending on the damage behavior.

For laser welding, gaps should normally be avoided to ensure stable weld processes and high weld quality. Nonetheless, sometimes, gaps are resulting from non-optimal weld preparation in industrial applications. Within this investigation, the effects of a defocussed beam and laser beam oscillation on gap bridging abilities at reduced ambient pressure were investigated. For reference purpose, conventional laser welding with zero gap at ambient pressure was performed, too. The resulting weld geometry was investigated and correlated to gap bridging strategies and weld quality groups according to ISO 13919–1. The welds were characterized regarding their hardness and weld microstructure. Residual stress was determined by means of X-ray diffraction, and tensile tests as well as fatigue tests were conducted. The fatigue tests were evaluated by the nominal stress approach, the critical distance approach, and the stress averaging approach and correlated to weld quality measures. Resulting from this, fatigue resistance of laser welded butt welds with gap can be estimated by the FAT160 design S–N curve. The stress evaluation parameters for the determination of keff-values (ρ*= 0.4 mm, a= 0.1 mm) were confirmed.

Brazing in a continuous belt furnace is a quite cost-effective way of joining components consisting of many individual parts. It is extensively used in many industrial sectors like the automotive or in the energy industry. Even though many components are cyclically loaded during service up to now, no approaches to assess the lifetime under in-service loads are available. In order to assess the fatigue strength of brazed joints, three different specimen types have been investigated: peel and shear as well as a component-like specimens. The specimens were characterized and tested under load control using constant and variable amplitudes. Subsequently, the fatigue life of these joints was assessed by linear-elastic notch stresses. A reference S-N curve and characteristic damage sums were derived that enable to perform a reliable fatigue assessment. Further parameters which seem to have a strong influence on the fatigue life, the surface topology, and the overall quality of the braze were identified. Their influence is discussed.

Residential sector emissions of aerosols, primarily from solid fuels burned for cooking and heating purposes, are high in black carbon, a component that absorbs radiation efficiently across a wideband of wavelengths. Mitigation of residential sector emissions has been suggested as a method to rapidly reduce anthropogenic global warming. This study presents model results from a regional model with coupled chemistry, aerosols, and dynamics over an East Asian domain for January 2014 to investigate the radiative effects of residential sector emissions. Model results are evaluated against surface measurements of particulate matter and remote sensing products, comparing well but with a high aerosol optical depth bias over Sichuan and low single scattering albedo over many locations. We calculate effective radiative forcing of residential sector aerosols at the top of the atmosphere of +1.22 W/m2over Eastern China, +1.04 W/m2due to shortwave and +0.18 W/m2due to longwave forcing. We decompose the shortwave forcing into component parts and find the direct radiative effect is the dominant component (+0.79 W/m2), with a smaller contribution from semidirect effects (+0.54 W/m2) partly countered by negative indirect effects (−0.29 W/m2). The effective radiative forcing varies from 0.20 to 1.97 W/m2across a reasonable range of black carbon to total carbon emission ratios for the residential sector. Overall, this study shows that mitigation of the residential sector is likely a viable method to locally reduce short‐term atmospheric warming in China, but efforts are needed to reduce uncertainty in composition of residential sector emissions to be confident in this conclusion. Residential sector emissions found to have a positive effective radiative forcing over ChinaThis radiative forcing is mainly due to the direct effect, with some contribution from the semidirect effectHigh sensitivity to uncertainty in fraction of black carbon emitted from the residential sector

Wenn man annimmt, dass poröse Sinterstähle unter schwingender Beanspruchung durch Anrissbildung an großen Poren in hochbeanspruchten Werkstoffpartien versagen, lässt sich die Weibullsche Fehlstellenstatistik für Volumenfehler anwenden. Unter dieser Prämisse wurden in zwei abgeschlossenen Forschungsvorhaben (AVIF A253 und AVIF A270) Proben und Bauteile aus zwei höherfesten Sinterstählen untersucht. Variiert wurden Probengröße und -geometrie, Art der Beanspruchung (Torsions-, Flachbiege- und Axialbelastung), Dichte und Spannungsverhältnis R. Die Vielzahl an Versuchsergebnissen erlaubte eine umfassende mathematische Beschrei-bung der Schwingfestigkeit von Proben bei konstanter Amplitude und Spannungsverhältnissen zwischen R = −5 und R = 0,5. Die Auswertung der Probenergebnisse wurde anschließend ohne jede Änderung auf Bauteile angewandt. Die Genauigkeit, mit der die Schwingfestigkeit von Bauteilen vorhergesagt wurde, war sehr zufriedenstellend. Eine Schlüsselstellung nimmt bei dieser Methode das so genannte hochbelastete Volumen in der Umgebung lokaler Spannungsspitzen ein. Mit dem hochbelasteten Volumen werden die Effekte von äußeren, geometrischen Kerben, Belastungsart und Proben- oder Bauteilgröße zu einem einzigen Zahlenwert zusammengefasst. Assuming that porous sintered steels fail under cyclic loading by crack initiation from larger pores in highly loaded material zones, Weibull’s weakest link statistics for volume defects can be applied. With this premise, specimens and structural parts from two higher strength sintered steels were studied in two recently finished research projects (AVIF A253 and AVIF A270). The parameters investigated were specimen size and geometry loading mode (torsion, plane bending and axial loading), density and stress ratio R. The wealth of experimental results permitted a comprehensive mathematical description of the fatigue performance under constant ampli-tude loading of specimens at stress ratios between R = −5 and R = 0.5. The evaluation of the specimen results was subsequently applied to the fatigue strength of structural parts without any amendments. The precision, with which the fatigue performance of parts could be predicted, was very satisfactory. Applying this method, a key position is assigned to the socalled highly loaded volume surrounding local stress peaks. With the highly loaded volume the effects of external geometrical notches, loading mode and specimen or part size are contracted in a single numerial figure.

This paper comprises a brief methodical analysis and practical application of both the stress averaging approach according to Neuber and the critical distance approach according to Taylor for a fatigue assessment on welded steel structures under axial loading. The stress averaging approach, as established theoretically by Neuber, is discussed and compared to the effective notch stress approach with a reference radius rref= 1 mm and also to the rref= 0.05 mm concept which is usually applied for thin-walled structures. Furthermore, both approaches are applied for an assessment of 38 individual test series. As a result of the evaluations, a microstructural length ρ* = 0.40 mm is recommended. For the critical distance approach, a distance a= 0.10 mm was derived. Fatigue design (FAT) values are recommended for the practical application. Compared to the notch stress approach with a radius rref= 0.05 mm, it was possible to improve the assessment quality significantly. The non-local approaches should be preferred to the rref= 0.05 mm concept, especially for welded components using thin sheets for which the radius of 1 mm cannot be applied.

Typically, for a fatigue strength assessment of a welded structure, the influence of welding residual stresses has to be considered. An easy applicable approach is given within the framework of the IIW recommendations; the design S-N curves can be upgraded in case of medium or low residual stresses. A relaxation or redistribution of tensile residual stresses, which is often accompanied by an increase in fatigue life, cannot be considered. To obtain a better understanding of the residual stresses and their influence on the fatigue strength, fatigue tests have been performed on longitudinal stiffeners in as-welded and stress relieved state with both stress ratios R= −1 and R= 0. Local strains and stresses were measured using strain gauges and X-ray diffraction technique to get insight into the local material’s response due to global loading close to the weld toe. The crack initiation and propagation phase was detected by a camera. FE models were set up to reproduce the observed material behavior in the notch for the crack initiation phase. By numerical analysis it could be shown that, due to sharp notches at the weld toe with an average toe radius of r= 0.05 mm, a stress redistribution occurs during the first load cycle. This leads to a fatigue strength, which is, particularly at higher load amplitudes, independent from mean as well as from initial residual stresses. A comparison of fatigue data derived on longitudinal stiffeners from literature confirms this effect. For lower load amplitudes instead, mean and residual stresses gain more influence. In this investigation a reliable assessment of the crack initiation period could be performed with strain-based concepts using damage parameter PSWTfor a mean stress assessment. All fatigue tests could be transformed into a single damage parameter PSWT-N curve with a low scatter if residual stresses as well as the distortion of the specimens are regarded.

Purpose.Global mental health movements increasingly highlight social integration as a key outcome for mental health services. This creates a pressing need to better articulate and measure this outcome. Much of the work in social integration thus far has been in high-income countries (HIC), and is not directly applicable across diverse socio-cultural environments. We discuss promising concepts and measures of social integration with potential for global cross-cultural application. Then, we present some of the challenges of developing measures for global and cross-cultural use, and suggest ways to confront these challenges. Although we focus primarily on adults with severe mental disorders in low- and middle-income countries (LMIC), the questions we raise are also relevant to children, other mental disorders and HIC.Findings.We identify and describe four distinct conceptual frameworks for social integration that have emerged over the past decade. Then, we discuss the challenge of developing corresponding measures, and the further challenge of developing global cross-cultural measures. We suggest that a key concept shared across much previous and emerging work is active participation in community and civic life. As a platform for future development of global cross-cultural measures of this and other concepts, we propose guidelines and present examples of feasible, previously used strategies.Summary.Emerging concepts of social integration hold great promise, but as yet, there are no corresponding measures suitable for global cross-cultural use. We propose that it is feasible to develop such measures, and that their development will facilitate the advance of community mental health services and the science of global mental health.

For the application of the notch stress approach, local stresses at the notch root have to be calculated. This demands a fine discretization of the finite element model in the notch leading for complex structures to large finite element models which are difficult to handle and take a high amount of calculation time. This paper contains the detailed investigation of the required finite element mesh in the notch area for application of the notch stress approach. Based on small-scale specimens, various meshing rules are applied and compared to each other. As the most important factor for the efficiency of a finite element mesh, the element shape in the notch root was identified. It should be chosen according to the stress gradients: The higher the stress gradients are, the smaller the element edge length should be modeled. The shape of the subsequent elements inside the volume has no major influence on the accuracy of the calculation. Recommendations for practical use are given for various element types, including commonly used tetrahedron and hexahedron element with linear and quadratic shape function. Expected numerical errors for the chosen mesh configuration are indicated.

The use of PM materials is rapidly expanding with an increasing concentration on highly loaded structural parts such as synchroniser hubs, gears, sprockets or shifting forks. The successful implementation of PM materials for such parts depends on a reliable fatigue design concept. Such a design concept has to consider the local durability, especially in fatigue critical sharply notched areas, depending on the local density of the material and stress gradients. This paper summarises different design methods in order to transfer the fatigue behaviour of specimens to components by considering sharply notched areas. Four different local approaches have been investigated: the highly stressed volume approach, the stress gradient approach, the critical distance method and the stress averaging method according to Neuber. The design methods have been analysed on the basis of fatigue testing results of unnotched and notched fatigue specimens and of synchroniser hubs made from a 4% Ni diffusion‐alloyed steel material (Distaloy AE+0.6%C). The transferability of characteristic fatigue properties from specimens to a sharply notched component, a synchroniser hub, is presented and the practicability of the design methods demonstrated and discussed. These investigations showed that the most reliable concept was the highly stressed volume approach. The accuracy of the approach can be comprehended separating statistical and so called material support effect.

The local fatigue strength of a laserbeam weld of a complex engine component, which joins a PM with a formed sheet component, was assessed by the notch stress concept with the fictitious reference radius of rref = 0.05 mm. First, simplified specimens, following the main geometric dimensions of the parts, were manufactured. On these specimens the fatigue strength was identified by tests and the notch stresses calculated by finite element analysis. Based on these results a design SN‐curve was derived to assess the fatigue strength of the engine component. The numerical assessment of the welded joint was verified by proof tests with the component. The assessment could be improved by considering statistical and stress gradient dependent size effects according to the concept of the highly stressed volume.

In the present paper a method is described for the fatigue assessment of multiaxial loaded welded joints in structures made from thin steel sheets. The focus is on seam welds under nonproportional loading, assuming a constant angular phase shift between cycles leading to stress components acting at the seam welds. Fatigue analyses are using a local stress approach based on stresses derived by Theory of Elasticity. Furthermore, potentials of considering statistical size effects in order to analyse weld start and end points are outlined.

The authors evaluated the efficacy of an erbium,chromium: yttrium,scandium,gallium,garnet (Er,Cr:YSGG) laser-powered hydrokinetic system (HKS) versus that of rotary instrumentation for root canal débridement.

Some newly synthesized compounds of the type [(Me3Si)3X¹X²(SiMe3)3] (X¹, X² = Si, Ge, or Sn) together with some related compounds bearing triisopropylsilyl or -stannyl groups are characterized by single-crystal X-ray crystallography. The structural data are compared to similar compounds already known. The interaction of silyl groups connected to different central atoms such as Si, Ge, and Sn is analyzed.

The reaction of chloropermethylcyclohexasilanes Si6Me12-nCln (n = 1−3) with lithium silanolates affords the siloxy derivatives Si6Me12-n(OR)n (n = 1−3; R = SiMe3, SiMe2-t-Bu). All compounds exhibit bathochromically shifted first UV absorption maxima and room-temperature photoluminescence in solution with emission maxima near 340 nm and remarkably enhanced luminescence intensity as compared to the data for Si6Me12. The solution photoemission spectra of the corresponding aminocyclohexasilanes Si6Me12-n(NR2)n (n = 1, 2; R = −SiMe3), which are accessible from Si6Me12-nCln and LiN(SiMe3)2, do not show any luminescence above 300 nm. Crystal structure analyses of the 1,3- and 1,4-disubstituted derivatives exhibit the cyclohexasilane ring in the chair conformation with the −OR or −NR2 groups in either axial or equatorial positions, depending on the steric bulk of the hetero substituents.

Reactions of silylated silyl-, germyl-, and stannyl anions with group 6 halogenpentacarbonyl metalates gave the respective pentacarbonyl metalate derivatives. With the exception of a stannylated chromate all compounds were obtained in good yields and selectivity. An alternative approach employing group 6 metal hexacarbonyls in the reaction with the group 14 anions worked equally well. All compounds were fully characterized spectroscopically, and four compounds were subjected to single-crystal structure analysis.

By the reactions of potassium tert-butoxide with a number of oligosilylgermanes, oligosilylgermylpotassium compounds were generated. Their chemistry very much resembles that of the analogous oligosilylsilylpotassium compounds. However, the ease of formation is even more pronounced in the case of the germyl anions. Again potassium tert-butoxide proved to be a highly selective metalation reagent, leading to no unwanted cleavage of Si−Ge or Ge−Ge bonds. A number of new and potentially useful oligosilylgermyl mono- and dianions have been prepared in this manner.

Some newly synthesized di-, tri-, penta-, and hexasilanes bearing trimethylsilyl groups together with some previously reported related compounds were analyzed using single-crystal X-ray crystallography. The structure analyses were compared to similar compounds already known. The influence of bulky tris(silyl)silyl groups on the Si−Si skeleton was studied.

ABSTRACTOur understanding of endodontic infections and treatment of endodontic disease has increased significantly over the last decade. This article is an update of those findings. Aspects that are reviewed include: portal of entry for microorganisms, virulence and pathogenicity of organisms, descriptions of primary and recurrent endodontic infections, and treatment of endodontic infections.

The reaction of hexakis(trimethylsilyl)disilane with 2 equiv of potassium tert-butyl alcoholate and 18-crown-6 gives 1,2-dipotassiotetrakis(trimethylsilyl)disilane (1) in almost quantitative yield. Transmetalation with magnesium bromide allows for the derivatization of the dianion. After exchange of one or two trimethylsilyl groups for phenyl substituents in the starting material, the 1,2-dipotassio compounds (13, 16) could still be obtained. Treatment of 1 with 1,2-dibromoethane gives octakis(trimethylsilyl)cyclotetrasilane (8), which also can be converted into a 1,3-dipotassiocyclotetrasilane (11).

The reactions of bridged tris(trimethylsilyl)silyl fragments with 2 molar equiv of potassium tert-butoxide allow the generation of α,ω-oligosilyl dianions (1a, 2a, 3a, 4a). Depending on the nature of the spacer between the oligosilyl units, these compounds can be used to generate either linear or cyclic derivatives. They are especially attractive for the formation of homo- and heterocyclosilanes, as exemplified by the synthesis of sila-, stanna-, and zirconocenacyclosilanes. A linear bis(potassiumsilyl)acetylene (4a) was used to bridge two zirconocene units, (Cp2Zr(Cl)Si(SiMe3)2CCSi(SiMe3)2Zr(Cl)Cp2) (11).

A number of differently substituted oligosilyl potassium compounds have been prepared by reaction of the respective trimethylsilylated precursors with potassium tert-butoxide. It has been demonstrated that in the presence of larger trialkylsilyl groups always trimethylsilyl groups are removed selectively. This selectivity enables the syntheses of oligosilylanions with different sterical demand. By transmetalation of the oligosilyl potassium compounds with halides of less electropositive metals also the reactivity of the silyl anions can be controlled.

Abstract: Acute CT/MRI findings were examined in a prospective, longitudinal study of 60 children 0–6 years of age hospitalized for moderate to severe traumatic brain injury (TBI). TBI was categorized as either inflicted (n=31) or noninflicted (n=29). Glasgow Coma Scale scores and perinatal history were comparable in both groups. Acute CT/MRI studies were visually inspected by a radiologist blind to group membership. Compared with the noninflicted TBI group, the inflicted TBI group had significantly elevated rates of subdural interhemispheric and convexity hemorrhages as well as signs of pre-existing brain abnormality, including cerebral atrophy, subdural hygroma, and ex vacuo ventriculomegaly. Intraparenchymal hemorrhage, shear injury, and skull fractures were more frequent after noninflicted TBI. Subarachnoid hemorrhage and infarct/edema occurred with comparable frequency in both groups. Characteristic acute neuroimaging findings of inflicted TBI included multiple extraaxial hemorrhages in addition to the mild atrophy, subdural hygromas, and ventriculomegaly that suggest prior brain abnormality.

Male and female Japanese quail 21 weeks old, that were given total body doses of 60Co γ-rays ranging from 0 to 30 Gy, showed a peak in mortality at 6-8 days post-irradiation. The LD 50/30 was 22·5 Gy, and the LD 90/30 was 26·7 Gy. No differences were evident in mortality between males and females. The reduction in egg production by 30 days post-irradiation was related linearly to the dose, for doses above 6 Gy. The reduction in egg weight (30 days post-irradiation laying period) was also related linearly to the dose.

The in vitro activity of ceftriaxone, a new parenteral cephalosporin, was tested against 450 strains isolated from blood cultures and compared with that of various other antibiotics. The compound was comparable to cefotaxime for all species tested. Its was more potent than cefoperazone, cefamandole and ticarcillin in inhibitingEnterobacteriaceae (Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, indole-positiveProteus spp. andSerratia marcescens). The MIC95 of ceftriaxone for these strains was 0.5Μg/ml. The drug was less active againstStaphylococcus aureus than cefamandole, cloxacillin and vancomycin, but most isolates were inhibited by 4Μg/ml. AgainstPseudomonas aeruginosa, ceftriaxone was comparable in activity to ticarcillin (MIC95=64Μg/ml), and inferior to cefoperazone, ceftazidime and cefsulodine. Levels of ceftriaxone in serum and various body fluids were determined by bio-assays. Due to its very long half-life (8 h), ceftriaxone serum levels 24 h after i.v. or i.m. injection of 1 and 2 g were still above the MIC95 of all strains tested exceptPseudomonas aeruginosa. Levels in bile, synovial and cerebro-spinal fluids were high.

Two-core LPS antibodies, the rabbit J5 polyclonal antiserum and the human anti-lipid A IgM mAb HA-1A, did not improve the survival of mice challenged with E. coli O111 or P. aeruginosa 3, or with the LPS extracted from them, and did not decrease the incidence of Shwartzman reactions in rabbits challenged with O111 LPS. In contrast, O side chain-specific rabbit antisera were protective in these models. The protection afforded by O side chain-specific antisera against endotoxin lethality was associated with decreased LPS-induced serum TNF and IL-6 levels, whereas core LPS antibodies had no effect on TNF or IL-6 levels. The absence of reduction of LPS-induced cytokines levels by core LPS antibodies suggests that these antibodies are not able to prevent the interactions between LPS and target cells.