Results 1 - 10 of 2038
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[en] As an effort to enhance the reliability and accuracy of the instrumented impact testing, a new pendulum type of test apparatus has been designed and constructed at the Technical Research Centre of Finland (VTT). The new tester contains several novel features which help to avoid the drawbacks of the normal designs and which make the impact testing more reliable and appropriate from the fracture mechanics point of view. For that purpose the tester is equipped with a fully computerized data acquisition system and an optical COD measuring device. The latter has been developed and constructed through the co-operation between Materialpruefungsanstalt (MPA) and VTT. In the new testing facility the determination of fracture toughness is based on the application of the optical COD measuring device. In this paper testing equipment and procedures are described and discussed. (orig./HP)
[en] Crack initiation and growth in the Charpy V-notch test are investigated for controlled deflections of the specimen applied both by slow bending and by impact. Charpy test specimens were deformed to various deflections, heat-tinted to mark the crack extensions, and broken apart at low temperature to allow measurement of the crack extensions. These measurements provide estimates of crack initiation as defined by various criteria. The loading point at which crack initiation occurs depends on the particular definition being used for ''initiation,'' but in all cases it is well before the maximum load is reached. When initiation is defined as the first observable micro-initiation away from the ductile blunting of the notch root, the experimental results are in good agreement with computer modeling predictions
[en] Calibration specimens have been manufactured for checking the performance of a pendulum impact testing machine that has been configured for testing subsize specimens, both half-size (5.0 x 5.0 x 25.4 mm) and third-size (3.33 x 3.33 x 25.4 mm). Specimens were fabricated from quenched-and-tempered 4340 steel heat treated to produce different microstructures that would result in either high or low absorbed energy levels on testing. A large group of both half- and third-size specimens were tested at -40 degrees C. The results of the tests were analyzed for average value and standard deviation, and these values were used to establish calibration limits for the Charpy impact machine when testing subsize specimens. These average values plus or minus two standard deviations were set as the acceptable limits for the average of five tests for calibration of the impact testing machine
[en] The objective of the present work is to teach the criteria proposed by the ASME VIII code division 1 to determine when an impact test should be carried out on a base metal and on a welded joint using the general requirements specified in general requirements, which is defined in part UG,of the ASME VIII code div. 1. Charpy impact the can be used to evaluate the toughness of metallic materials that are listed in ASME II and Article QW-422 ASME IX. This paper presents a methodology through flow diagrams that allows the student to determine in a simple way when and how to carry out the Charpy test on a welded joint or a base metal. This methodology was applied to students of the Technical University of Madrid in the last years of university. Future work will explain how to determine the Charpy impact for the [UCS, UHT and UHA] parts of ASME VIII div. 1.
[es]El objetivo del presente trabajo es enseñar los criterios propuestos por el código ASME VIII división 1 para determinar cuándo se debe realizar una prueba de impacto en un metal base y en una unión soldada utilizando los requisitos generales especificados en los requisitos generales, que se definen en parte UG, del código div ASME VIII. 1. El impacto Charpy se puede utilizar para evaluar la tenacidad de los materiales metálicos que se enumeran en ASME II y en el Artículo QW-422 de ASME IX. Este documento presenta una metodología a través de diagramas de flujo que le permite al estudiante determinar de manera simple cuándo y cómo realizar la prueba de Charpy en una unión soldada o un metal base. Esta metodología se aplicó a estudiantes de la Universidad Politécnica de Madrid en los últimos años de universidad. El trabajo futuro explicará cómo determinar el impacto de Charpy para las partes [UCS, UHT y UHA] de ASME VIII div. 1.
[en] The method described in this paper deals with the choice of the temperature at which a Charpy energy of 28 J (3.5 daJ/cm2) must be obtained, so that a structure displaying a crack of given dimensions, made of steel with yield stress Rsub(e) and thickness e, operating at temperature Tsub(s), will provide some safety against brittle fracture. This method is based on linear elastic fracture mechanics which, in some cases (thick plates, static loading), allows the quantitative prediction of fracture conditions. Owing to the correlation between Ksub(ic) and Charpy results established at IRSID, the no-fracture conditions based upon Ksub(ic) are converted into Charpy conditions. These no-fracture conditions are then extended to the case of thicknesses lower than the one necessary for plane strain and to the case of dynamic loading. From the obtained relations, it is possible to draw charts indicating at which temperature Charpy specimens must be tested, so that brittle fracture will not occur from a given crack in a structure of given thickness and yield stress, operating at a given temperature
[fr]La methode presentee dans cette etude a pour but de definir la temperature a laquelle doit etre obtenue une energie de rupture de 28 J (resilience KCV = 3,5 kgm/cm2) pour qu'en presence d'un defaut de dimensions connues, une structure en acier de limite d'elasticite Rsub(e) et d'epaisseur donnees, travaillant a une temperature de service Tsub(s), presente une certaine securite vis-a-vis du risque de rupture fragile en service. Cette methode est basee au depart sur les connaissances acquises en mecanique lineaire elastique de la rupture qui permettent dans certains cas precis (fortes epaisseurs, sollicitation statique), de prevoir quantitativement le risque de rupture. Grace a la correlation mise au point a l'IRSID entre Ksub(ic) et la resilience Charpy V, les conditions de non-rupture basees sur Ksub(ic) sont traduites en termes de conditions sur la resilience. Les conditions de non-rupture sont alors elargies au cas des epaisseurs plus faibles que celle necessaire a l'existence d'un etat de deformations planes dans la piece fissuree, ainsi qu'au cas des sollicitations dynamiques. A partir des relations ainsi etablies, il est possible de tracer des abaques indiquant a quelle temperature doit etre realise l'essai de resilience pour que la rupture ne se propage pas a partir d'un defaut de dimensions donnees dans une structure en acier ayant une limite d'elasticite et une epaisseur connues, travaillant a une temperature de service donnee
[en] Measurement of fracture energy using drop weight tear test (DWTT) specimen with large dimensions (as an alternative to small Charpy test sample) gives more realistic results. Although large amounts of test data are available from DWTT experiments on different pipeline steels (base metal), apparently no information has been reported for fracture energy of welded seam of these pipe steels. In the current study, the fracture energy of spirally welded steel pipe was measured using DWTT specimens with two different notches (i.e. pressed and with chevron notch) and compared with base metal (BM) fracture energy. The test samples were machined from an actual gas pipe with a spiral seam having 1219 mm outside diameter and 14.3 mm wall thickness. The DWT tests were conducted on an impact machine with 30 kJ capacity equipped with Wheatstone load-cell. The measured total fracture energy in pressed-notch (PN) specimen (6211 J) was around 5% higher than that of chevron-notch (CN) specimen (5890 J). Based on the measurements, in both specimens a correction factor of 1.8 was suggested for welded seam (the fracture initiation energy was around 43% of the total fracture energy). Since the test samples were taken from a real pipe with original thickness, this result was more realistic than those previously reported for conventional Charpy fracture test specimens for similar steel material. The fracture energies for weld metal (WM) specifications were less than that of the base metal (7085 J). Therefore, immediate attention must be paid to DWTTs of WM in pipelines, which had not been investigated before, and the results indicate the importance of urgent improvement of the toughness of welded zone in manufacturing processes, which requires further research. Since, there is no standard for WM in the DWTT, the results of this research can lead to the development of new standards based on WM DWTT. (paper)
[en] The specimen strength ratio (R sub(sb)) determined for precraked Charpy specimens fractured in dynamic bending was correlated with plane strain fracture toughness (K sub(Id)) obtained through valid measurements of the J-integral at the moment of fracture initiation in various microstructures of the AISI 4140 steel. The results indicate a linear relationship between K sub(Id) and R sub(sb) for the microstructures considered in this work. The range of validity of this linear correlation is presented and discussed in terms of the ASTM E399 specimen size criterion. (Author)
[pt]A razao de resistencia em flexao, R sub(sb), de amostras Charpy pre-trincadas do aco AISI 4140 em varios estados microestruturais, foi determinada atraves de ensaios de impacto instrumentado e em seguida correlacionada com os valores da tenacidade sob condicoes de deformacao planar, K sub(Id), obtidos a partir de medidas validas da Integral-J no momento de iniciacao da fratura J sub(Id). Os resultados indicam uma relacao entre K sub(Id) e R sub(sb), englobando todas as microestruturas consideradas. A faixa de validade desta correlacao linear e apresentada e discutida em termos do criterio de tamanho dos corpos de prova adotado pela ASTM. (Autor)
[en] Microhardness measurements have been employed for studying zones of plasticity at the surface and in the bulk of a material. Stress intensities are estimated and their distribution in the plastic zone near the crack tip is established. The size of plastic zone at the crack front has been found from microhardness measurements. By solving the corresponding boundary-value problems of the theory of plastic flow in heterogeneous solids, stresses in the vicinity of the crack tip at plane deformation have been estimated
[en] Fracture behaviour of different welded joints of 15 MnNi 6 3 and 20 MnMoNi 5 5 steel is studied by testing Charpy-V impact, fracture mechanics specimens as well as wide plate specimens of different sizes. The influence of welding conditions and stress relief heat treatment on the failure behaviour of the heat affected zones is examined. Fracture mechanics test data are used in order to predict failure loads of the wide plates by the R6-procedure and by FE-calculations. (orig.)