Koldiffusionens inverkan på utmattnings-hållfastheten hos varmvalsade sexkantsstänger;The influence of carbon diffusion on the fatigue strength of hot rolled hexagonal rods

Helstångsborr och konstång kallas bergborrverktyg, som tillverkas av sexkantiga stänger med inre hål för ledning av spolvatten. Dessa spolhål är klädda med ferritiskt rostfritt stål. Innan valsning borras ett centrerat hål i stålämnet som ska valsas. I det borrade hålet appliceras ett rör av ferritiskt rostfritt stål och i det röret skjuts en manganstålskärna in. Efter valsning dras kärnan ut och ett spolhål med invändigt foder av rostfritt stål bildas. Under uppvärmningen och valsningen av stålämnet sker normalt en koldiffusion från manganstålskärnan till det rostfria fodret. Fodrets syfte är att skydda spolhålets yta mot erosion och korrosion.Syftet med arbetet var att hitta en metod som garanterar uppkolning av det invändiga fodret, samt att utreda vad uppkolningen betyder för den mekaniska hållfastheten i stängerna. Ett laboratorieförsök visade att det var bra, med avseende på uppkolning, att blanda stearat i kärnbestrykningsmedlet. Kärnbestrykningsmedlet penslas på manganstålskärnan innan den förs in i stålämnet som ska valsas, dess syfte är att minska friktionen vid kärnutdragningen efter valsning.Ett försök utfördes i valsverket med stearat i kärnbestrykningsmedlet. En grundlig undersökning utfördes på två hetor som valsats med stearat-bestrykningsmedel, samt på en traditionellt tillverkad heta för att ha som referens. Hetorna kapades till provstänger om 1,5 m, totalt undersöktes 55 st.Utvärderingen av verksförsöket visade att stängernas kvalitet blir tillräckligt bra om ingenting oförutsett händer i produktionen, oavsett om koltillskott är tillsatt i bestrykningsmedlet eller inte. Arbetet gav inte en garanterande metod, men visade att stängerna normalt håller hög kvalitet.

Livskvalitet och fatigue vid Multipel Skleros : en systematisk litteraturstudie

Syftet med denna systematiska litteraturstudie var att beskriva hur livskvaliteten påverkas hos personer med Multipel Skleros (MS) och vad som kan göras för att öka livskvaliteten. I syftet ingick även att beskriva hur personer med MS upplever fatigue som är ett av huvudsymtomen av sjukdomen samt vad som kan göras för att lindra följderna av fatigue. Artiklarna har sökts i databaserna Elin@Dalarna och Cinahl, tillgängliga via Högskolan Dalarnas proxyserver och granskats med hjälp av en granskningsmall för att säkerställa att de var av en god kvalitet. Sökord som användes var: “multiple sclerosis”, “quality of life”, “nursing” och “fatigue”. Av de artiklar som användes i resultatet var 10 kvantitativa, fyra kvalitativa i en användes båda ansatserna. Resultatet visade att personer med MS generellt sett har en sämre livskvalitet än den övriga befolkningen. Mycket av patienternas livskraft går åt till att bara klara av det dagliga livet. Många personer med MS upplever en stor frustration relaterad till att vilja men inte kunna. Ofta har den försämrade livskvaliteten sin orsak i det sociala livet. Fatigue har ofta en stor påverkan på livet för personer med MS. Det finns en mängd varierande icke farmakologiska behandlingsmetoder som med fördel kan användas för att öka livskvaliteten och minska följderna av fatigue. Exempel på dessa är kylväst, träning och yoga.

Qualidade física e fisiológica de semente de soja colhida com sistema de trilha axial sob diferentes velocidades de operação e rotações do cilindro trilhador

A colheita mecanizada é ferramenta fundamental no processo produtivo das grandes culturas; se não for realizada adequadamente, poderá resultar em danos mecânicos severos às sementes, acarretando, prejuízos significativos na colheita, particularmente devido à redução da qualidade. Visando a avaliar os danos causados na colheita mecanizada de soja, o presente trabalho teve como objetivo estudar o efeito do sistema de trilha axial sobre a percentagem de bandinhas, impurezas e sementes quebradas de soja cv. M-Soy 8001, em função da velocidade de trabalho e rotação do cilindro trilhador. O delineamento experimental utilizado foi o inteiramente casualizado, em parcelas subdivididas, avaliando-se duas rotações do cilindro trilhador (400 e 500 rpm) e três velocidades de operação (3,5; 4,5 e 5,5 km h-1), com três repetições. Os resultados obtidos indicam que as combinações de velocidade de operação e rotações do cilindro de trilha avaliadas não afetam as variáveis vigor, impurezas, bandinha, emergência em areia e índice de velocidade de germinação e que o aumento da rotação de 400 para 500 rpm ocasiona o aumento de sementes quebradas.

Absence of gluonic components in axial and tensor mesons

A quarkonium-gluonium mixing scheme previously developed to describe the characteristic of the pseudoscalar mesons is applied to axial and tensor mesons. The parameters of the model are determined by fitting the eigenvalues of a mass matrix. The corresponding eigenvectors give the proportion of light quarks, strange quarks and glueball in each meson. However, the predictions of the model for the branching ratios and electromagnetic decays are incompatible with the experimental results. These results suggest the absence of gluonic components in the states of axial and tensor isosinglet mesons analyzed here.

Unusual Yang-Lee edge singularity in the one-dimensional axial-next-to-nearest-neighbor Ising model

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Influence of anodization on the fatigue strength of 7050-T7451 aluminium alloy

In recent years, with higher demand for improved quality and corrosion resistance, recovered substrates have been extensively used. Consequently residual stresses originated from these coatings reduce the fatigue strength of a component. Due to this negative influence occasioned by corrosion resistance protective coatings, an effective process like shot peening must be considered to improve the fatigue strength. The shot peening treatment pushes the crack sources beneath the surface in most of medium and high cycle cases due to the compressive residual stress field (CRSF) induced. The aim of this study was to evaluate the influence on the fatigue life of anodic films grown on 7050-T7451 aluminium alloy by sulphuric acid anodizing, chromic acid anodizing and hard anodizing. The influence on the rotating and reverse bending fatigue strength of anodic films grown on the aluminium alloy is to degrade the stress life fatigue performance of the base material.A consistent gain in fatigue life in relation to the base material was obtained through the shot peening process in coated specimens, associated to a residual stress field compressive near the surface, useful to avoid fatigue crack nucleation and delay or even stop crack propagation.

Effect of electroless nickel interlayer on the fatigue strength of chromium electroplated AISI 4340 steel

Deposition of wear-resistant hard chromium plating leads to a decrease in the fatigue strength of the base material. Despite the effective protection against wear and corrosion, fatigue life and environmental requirements result in pressure to identify alternatives or to improve conventional chromium electroplating mechanical characteristics. An interesting, environmentally safer and cleaner alternative for the replacement of hard chronic plating is tungsten carbide thermal spray coating, applied by high velocity oxyfuel (HVOF) process.To improve the fatigue strength of aeronautical steel chromium electroplated, shot peening is a successfully used method. Multiple lacer systems of coatings are considered to have larger resistance to crack propagation in comparison with simple layer.The aim of this study was to analyze the effect of nickel underplate on the fatigue strength of hard chromium plated AISI 4340 steel in two mechanical conditions: HRc 39 and HRc 52.Rotating bending fatigue tests results indicate that the clectroless nickel plating underlayer is responsible for the increase in fatigue strength of AISI 4340 steel chromium electroplated. This behavior may be attributed to the largest toughness/ductility and compressive residual stresses which, probably, arrested or delayed the inicrocrack propagation from the hard chromium external layer. The compressive residual stress field (CRSF) induced by the electroplating process was determined by X-ray diffraction method. The evolution of fatigue strength compressive residual stress field CRSF and crack sources are discussed and analyzed by SEM. (c) 2006 Elsevier Ltd. All rights reserved.

The effect of WC-17Co thermal spray coating by HVOF and hard chromium electroplating on the fatigue life and abrasive wear resistance of AISI 4340 high strength steel

One of the most interesting alternatives for replacement of hard chrome plating is tungsten carbide thermal spray coating applied by the high velocity oxy-fuel (HVOF) process which presents a safer, cleaner and less expensive alternative to chromium plating. The objective of this research is to compare the influence of the tungsten carbide-17cobalt (WC- 17Co) coating applied by high velocity oxy fuel (HVOF) process with that of hard-chromium electroplating on the fatigue strength and abrasive wear of AISI 4340 steel.

Effects of surface treatments on the fatigue strength of AISI 4340 aeronautical steel

Internal residual stresses significantly influence the fatigue strength of coated materials. It is well known that chromium plating is the most used electrodeposited coating for important industrial applications. However, pressure to identify alternatives or to improve the chromium electroplating process have increased in recent years, related to the reduction in fatigue strength of the base material and to environmental requirements. The high efficiency and fluoride free hard chromium electroplating there called accelerated) is an improvement to the conventional process. One environmentally safer and cleaner alternative to hard chromium plating is tungsten carbide thermal spray coating applied by the High Velocity Oxy-Fuel (HVOF) process. To increase the fatigue strength of chromium plated materials, coating thickness and microcracks density are important parameters to be controlled. Techniques as compressive residual stresses induced by shot peening and multilayers, are also used. The aim of this study was to analyse the effects on AISI 4340 steel, in the rotating bending fatigue behaviour, of the: tungsten carbide thermal spray coating applied by HP/HVOF process; chemical nickel underplate, and shot peening process applied before coating deposition, in comparison to hard chromium electroplatings. Rotating bending fatigue test results indicate better performance for the conventional hard chromium plating in relation to the accelerated hard chromium electroplating. Tungsten carbide thermal spray coating and accelerated hard chromium plate over nickel resulted in higher fatigue strength when compared to samples conventional or accelerated hard chromium plated. Shot peening showed to be an excellent alternative to increase fatigue strength of AISI 4340 steel hard chromium electroplated. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

Residual stress influence on fatigue lifetimes of electroplated AISI 4340 high strength steel

Residual stresses play an important role in the fatigue lives of structural engineering components. In the case of near surface tensile residual stresses, the initiation and propagation phases of fatigue process are accelerated; on the other hand, compressive residual stresses close to the surface may increase fatigue life. In both decorative and functional applications, chromium electroplating results in excellent wear and corrosion resistance. However, it is well known that it reduces the fatigue strength of a component. This is due to high tensile internal stresses and microcrack density. Efforts to improve hard chromium properties have increased in recent years. In this study, the effect of a nickel layer sulphamate process, as simple layer and interlayer, on fatigue strength of hard chromium electroplated AISI 4340 steel hardness - HRc 53, was analysed. The analysis was performed by rotating bending fatigue tests on AISI 4340 steel specimens with the following experimental groups: base material, hard chromium electroplated, sulphamate nickel electroplated, sulphamate nickel interlayer on hard chromium electroplated and electroless nickel interlayer on hard chromium electroplated. Results showed a decrease in fatigue strength in coated specimens and that both nickel plating interlayers were responsible for the increase in fatigue life of AISI 4340 chromium electroplated steel. The shot peening pre-treatment was efficient in reducing fatigue loss in the alternatives studied.

Effects of electroplated zinc-nickel alloy coatings on the fatigue strength of AISI 4340 high-strength steel

Recovered substrates have been extensively used in the aerospace field. Cadmium electroplating has been widely applied to promote protective coatings in aeronautical components, resulting in excellent corrosion protection combined with a good performance in cyclic loading. Ecological considerations allied to the increasing demands for corrosion resistance have resulted in the search for possible alternatives. Zinc-nickel (Zn-Ni) alloys have received considerable interest recently, because these coatings show advantages such as a good resistance to white and red rust, high plating rates, and acceptance in the market. In this study, the effect of electroplated Zn-Ni coatings on AISI 4340 high-strength steel was analyzed for rotating bending fatigue strength, corrosion, and adhesion resistance. The compressive residual stress field was measured by x-ray diffraction prior to fatigue tests. Optical microscopy documented coating thickness, adhesion characteristics, and coverage extent for nearly all substrates. Fractured fatigue specimens were investigated using scanning electron microscopy (SEM). Three different Zn-Ni coating thicknesses were tested, and comparisons with the rotating bending fatigue data from electroplated Cd specimens were performed. Experimental results differentiated the effects of the various coatings on the AISI 4340 steel behaviour when submitted to fatigue testing and the influence of coating thickness on the fatigue strength.

Evaluation on fatigue strength of AISI 4340 steel aluminum coated by electroplating and IVD processes

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Evaluation of fatigue behavior on repaired carbon fiber/epoxy composites

The continuous use of structural polymer composites in aeronautical industry has required the development of repairing techniques of damages found in different types of laminates. The most usually adopted procedure to investigate the repair of composite laminates has been by repairing damages simulated in laminated composite specimens. This work shows the influence of structural repair technique on mechanical properties of a typical carbon fiber/epoxy laminate used in aerospace industry. When analyzed by tensile test, the laminates with and without repair present tensile strength values of 670 and 892 MPa, respectively, and tensile modulus of 53.0 and 67.2 GPa, respectively. By this result, it is possible to observe a decrease of the measured mechanical properties of the repaired composites. When submitted to fatigue test, it is observed that in loads higher than 250 MPa, this laminate presents a low life cycle (lower than 400,000 cycles). The fatigue performance of both laminates is comparable, but the non-repaired laminate presented higher tensile and fatigue resistance when compared with the repaired laminate.

Improvement in the fatigue strength of chromium electroplated AISI 4340 steel by shot peening

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)