Weibull probability distribution for reactor steel 20MnMoNi55 cleavage fracture in transition temperature

This paper presents the results and methods used for determining of fracture toughness of reactor steel, denoted as 20MnMoNi55, typically used for structures working at low temperatures, in transition temperature area. In addition, the effect of test specimen geometry and temperature on fracture toughness was investigated in order to predict the fracture behavior and probability of failure. Failure probabilities (i.e. cleavage fracture) in the function of J(c) for large test specimens, CT100 and CT200 were determined based on the results obtained by testing of small CT50 specimens, for the purpose of direct savings and decreased costs of specimen testing. Failure probability, represented using Weibull distribution of experimental data, will provide a clear insight into material behavior at different temperatures. Other factors affecting the obtained test results will also be discussed

Weibull probability distribution for reactor steel 20MnMoNi55 cleavage fracture in transition temperature

This paper presents the results and methods used for determining of fracture toughness of reactor steel, denoted as 20MnMoNi55, typically used for structures working at low temperatures, in transition temperature area. In addition, the effect of test specimen geometry and temperature on fracture toughness was investigated in order to predict the fracture behavior and probability of failure. Failure probabilities (i.e. cleavage fracture) in the function of J(c) for large test specimens, CT100 and CT200 were determined based on the results obtained by testing of small CT50 specimens, for the purpose of direct savings and decreased costs of specimen testing. Failure probability, represented using Weibull distribution of experimental data, will provide a clear insight into material behavior at different temperatures. Other factors affecting the obtained test results will also be discussed

Structural Integrity Assessment of Welded Pipeline Designed with Reduced Safety

The main goal of this paper was to assess the integrity of welded joints in the main pipeline of the reversible hydropower plant "Bajina Bašta". Japanese steel Sumiten 80P (SM 80P) was used as the parent material. European recommendation for pipeline safety factor is equal to 1.7 and this value was used for calculations of the RHPP "Bajina Bašta", whereas the value recommended by Japanese standards is 2.1. A relatively small safety factor, which is different from the Japanese recommendation (since the material itself is Japanese), represented one of the main reasons for a detailed investigation of the pipeline structural integrity and safety, using the prototype. In the case of pressure vessels, the welded joint is a location of stress concentration, which can act in the same way as residual stresses. Assessment of prototype test results is possible to perform based on stress and strain calculations of vessels with ideal geometry. For this reason, the solution for thin-walled vessels is given, both in elastic and elastic-plastic areas. Numerous tests were performed in order to obtain a reliability assessment necessary for the construction of the pipeline, since the consequences of potential failure would be disastrous in this case. A numerical simulation, based on the experimentally determined mechanical properties of the material used, was also performed in order to obtain the stress/strain distribution. These results were then compared to the experimentally obtained ones, and it was concluded that there is a good level of compliance between numerical and experimental results

Structural Integrity Assessment of Welded Pipeline Designed with Reduced Safety

The main goal of this paper was to assess the integrity of welded joints in the main pipeline of the reversible hydropower plant "Bajina Bata". Japanese steel Sumiten 80P (SM 80P) was used as the parent material. European recommendation for pipeline safety factor is equal to 1.7 and this value was used for calculations of the RHPP "Bajina Bata", whereas the value recommended by Japanese standards is 2.1. A relatively small safety factor, which is different from the Japanese recommendation (since the material itself is Japanese), represented one of the main reasons for a detailed investigation of the pipeline structural integrity and safety, using the prototype. In the case of pressure vessels, the welded joint is a location of stress concentration, which can act in the same way as residual stresses. Assessment of prototype test results is possible to perform based on stress and strain calculations of vessels with ideal geometry. For this reason, the solution for thin-walled vessels is given, both in elastic and elastic-plastic areas. Numerous tests were performed in order to obtain a reliability assessment necessary for the construction of the pipeline, since the consequences of potential failure would be disastrous in this case. A numerical simulation, based on the experimentally determined mechanical properties of the material used, was also performed in order to obtain the stress/strain distribution. These results were then compared to the experimentally obtained ones, and it was concluded that there is a good level of compliance between numerical and experimental results

Fracture behavior of reactor steel 20MnMoNi 55 in the transition temperature region

The fracture represents the final phase of crack propagation, and the causes of their occurrence or partial crack propagation in the real constructions made of ferritic steels can be different. Along with cracks, influences such as stress concentration and low temperature contribute to fracture being “faster” and have an impact on the fracture mechanics parameters, as well as on the fact that fracture is more likely to occur due to cleavage. The parameters discussed in this study are Jc and rc (parameter, i.e. distance between fatigue crack tip and cleavage initiation site) by testing of C(T)50 specimen in the transition temperature region. Grooved C(T) specimens were made of reactor steel 20MnMoNi 55 with two thickness values, since an additional goal of this study was to present the influence of thickness of tested specimens. Along with it, other parameters that have influence on the understanding of transition temperature region and fracture in this region of ferritic steel are presented

Fracture behavior of reactor steel 20MnMoNi 55 in the transition temperature region

The fracture represents the final phase of crack propagation, and the causes of their occurrence or partial crack propagation in the real constructions made of ferritic steels can be different. Along with cracks, influences such as stress concentration and low temperature contribute to fracture being “faster” and have an impact on the fracture mechanics parameters, as well as on the fact that fracture is more likely to occur due to cleavage. The parameters discussed in this study are Jc and rc (parameter, i.e. distance between fatigue crack tip and cleavage initiation site) by testing of C(T)50 specimen in the transition temperature region. Grooved C(T) specimens were made of reactor steel 20MnMoNi 55 with two thickness values, since an additional goal of this study was to present the influence of thickness of tested specimens. Along with it, other parameters that have influence on the understanding of transition temperature region and fracture in this region of ferritic steel are presented

Direct measurement of the J integral on a pressure vessel

Direktno merenje J integrala je analizirano u odnosu na uticaj heterogenosti i ojačavanja materijala, kao i različitih graničnih uslova, a u cilju primene na posude pod pritiskom sa prslinom u zavarenom spoju. Pokazano je da su neophodne modifikacije originalnog izraza. Takođe su razmatrane mogućnosti primene direktnog merenja J integrala kao metode procene integriteta posude pod pritiskom.Direct measurement of J integral has been analysed in respect to the effect of material (heterogeneity and strengthening) and different boundary conditions, enabling its application to pressure vessels with a crack in welded joint. It has been shown that modifications of the original expression are needed. The possibility of applying direct measurement of J integral for pressure vessel integrity assessment has been considered

Load and deformation effects on brittle fracture of ferritic steel 20mnmoni 55 in temperature transition region

It is known that the load level, the way deformation is applied and the level of plastic strain, all can 'aid' or 'hinder' the occurrence of brittle fracture, but the question is - to what extent? These influential factors are analysed by testing of C(T)50 specimens made of ferritic steel 20MnMoNi 55 at two temperatures within the transition temperature range. The effect of displacement rates is analysed by testing C(T) specimens at -60 degrees C, while the effect of plastic strain is analysed by introducing an initial fatigue crack with low and high stress intensity factor threshold values of Delta K, by testing the C(T) specimens at -90 degrees C, in accordance with ASTM 1820 standard. The analysis of these influences involves interpretation of test results for parameters J(c), CMOD, and r(c). Conclusions based on this analysis can be used in further studies which involve understanding of ductile to brittle transition region, as well as the general fracture behaviour of ferritic steels

Load and deformation effects on brittle fracture of ferritic steel 20mnmoni 55 in temperature transition region

It is known that the load level, the way deformation is applied and the level of plastic strain, all can 'aid' or 'hinder' the occurrence of brittle fracture, but the question is - to what extent? These influential factors are analysed by testing of C(T)50 specimens made of ferritic steel 20MnMoNi 55 at two temperatures within the transition temperature range. The effect of displacement rates is analysed by testing C(T) specimens at -60 degrees C, while the effect of plastic strain is analysed by introducing an initial fatigue crack with low and high stress intensity factor threshold values of Delta K, by testing the C(T) specimens at -90 degrees C, in accordance with ASTM 1820 standard. The analysis of these influences involves interpretation of test results for parameters J(c), CMOD, and r(c). Conclusions based on this analysis can be used in further studies which involve understanding of ductile to brittle transition region, as well as the general fracture behaviour of ferritic steels

Fatigue life analysis of the integral skin-stringer panel using xfem

Fatigue life of integral skin-stringer panels produced by laser beam welding (LBW) is analysed. This type of panel is used in airframe construction where fatigue and damage tolerance are of paramount importance, since aircrafts must be designed to tolerate relatively large fatigue cracks. The analysed integral skin-stringer panel is made of AL-AA 6156T6/2.8 mm, where stringers are laser beam welded to the airframe skin. By using the extended finite element method (XFEM), fatigue life of simple flat plate, as well of the skin-stringer panel, are numerically simulated in order to investigate the effect of stringers