Toughness Requirements Research Articles

Comparison of ASME pressure–temperature limits on the fracture probability for a pressurized water reactor pressure vessel

The ASME Code Section XI-Appendix G defines the normal reactor startup (heat-up) and shut-down (cool-down) operation limits according to the fracture toughness requirement of reactor pressure vessel (RPV) materials. This paper investigates the effects of different pressure-temperature limit operations on structural integrity of a Taiwan domestic pressurized water reactor (PWR) pressure vessel. Three kinds of pressure-temperature limits based on different fracture toughness requirements – the KIa fracture toughness curve of ASME Section XI-Appendix G before 1998 editions, the KIC fracture toughness curve of ASME Section XI-Appendix G after 2001 editions, and the risk-informed revision method supplemented in ASME Section XI-Appendix G after 2013 editions, respectively, are established as the loading conditions. A series of probabilistic fracture mechanics analyses for the RPV are conducted employing ORNL’s FAVOR code considering various radiation embrittlement levels under these pressure-temperature limit conditions. It is found that the pressure-temperature operation limits which provide more operational flexibility may lead to higher fracture risks to the RPV. The cladding-induced shallow surface breaking flaws are the most critical and dominate the fracture probability of the RPV under pressure-temperature limit transients. Present study provides a risk-informed reference for the operation safety and regulation viewpoint of PWRs in Taiwan.

Real Time LP Decoding of LDPC Codes for High Correction Performance Applications

The alternate direction method of multipliers is a recent linear programming error correcting approach which improves the decoding performance of LDPC codes compared with the best BP decoding techniques. In this letter, an efficient implementation of the ADMM LP decoding algorithm on a multicore architecture is presented. Its throughput performance level is about one order of magnitude higher than related works on the same multicore target. The proposed decoder’s throughput reaches up to 100 Mb/s which makes it viable for real time applications with tough error correction requirements.

Improvement of strength and toughness: The effect on the weldability of high-strength steels used in offshore structures

The effect of strength and toughness on the weldability of high-strength steels is very vital consideration in the offshore oil and gas industries. Improved impact toughness of high-strength steels in offshore structures enables viable exploitation of hydrocarbons in technologically challenging conditions. This article reviews improvements in the weldability and impact toughness of high-strength steels. Steels with high strength are associated with high carbon content and addition of alloying elements as they induce hardness which leads to a higher risk of brittle fracture and hydrogen-induced cracking needs. The combination of high strength with high toughness was studied by examining the toughening mechanism of thermomechanical-controlled processing steels, which have higher strength than conventional steel plates but meet the conflicting requirements of strength, toughness and weldability. The thermomechanical-controlled processing production process entails controlled rolling process combined with accelerated cooling or direct quenching to ensure stable mechanical properties of thermomechanical-controlled processing products in welded constructions. It is concluded that due to their very fine grain size and refined heat-affected zone structure, thermomechanical-controlled processing steels can be an effective cost-saving means for fabrication of offshore structures, particularly in shipbuilding, offshore platforms and pipelines for high-operating pressures.

State-of-the-Art Fracture Characterization. II: Correlations between Charpy V-Notch and the Master Curve Reference Temperature

AbstractMany material toughness specifications, including a fracture control plan (FCP) for highway bridges introduced in 1978, in part rely on Charpy V-notch (CVN) requirements and associated correlations to set material toughness values at acceptable levels that will prevent brittle fracture in bridges. However, it has long been recognized that this is an indirect approach because CVN impact energy is not a direct measure of fracture toughness. Significant advances in the understanding of fracture mechanics and material behavior have taken place in the four decades since the FCP was established. These advancements are in part due to the large amount of fracture toughness data that has been generated, allowing for statistical evaluation. As a result, this provides an opportunity to evaluate CVN toughness correlations. Overall, these advances allow a more rational approach to establishing material toughness requirements for bridge steels including (1) the ability to characterize the scatter of fracture da...

Brittle Fracture Prevention Model for Pressure Based on Master Curve Approach

The brittle fracture prevention model is of great importance to the safety of pressure vessels. Compared to the semi-empirical approach adopted in various pressure vessel standards, a model based on Master Curve technique is developed in this paper. Referring to ASME nuclear code, the safety features including the lower bound fracture toughness and a margin factor equal to 2 for the stress intensity factor produced by primary stress are adopted in the new model. The technical background of the brittle fracture model in ASME VIII-2 has been analyzed and discussed, and then its inappropriate items have been modified in the new model. Minimum design temperature curves, impact toughness requirements, and temperature adjustment for low stress condition are established on the basis of new model. The comparison with the relevant curves in ASME VIII-2 is also made. The applicability of the new model is verified by the measured fracture toughness and impact toughness data of several kinds of pressure vessel steels. The results suggest that the minimum design temperature and the impact test requirements derived by the new model are compatible with each other. More testing data of different steels to check this model is necessary for further engineering application.

КОМПЛЕКСНЫЙ КОНТРОЛЬ КАК ФАКТОР ИНДИВИДУАЛИЗИРОВАННОГО УПРАВЛЕНИЯ ПОДГОТОВКОЙ СПОРТИВНОГО РЕЗЕРВА В ОРИЕНТИРОВАНИИ

Aim. Sport reserve training processes is are based on the set of characteristics of management, assessment of morphofunctional genetic features, age-related psychophysiological and informational components of physical fitness and their correlations, and the revealing of sport performance criteria. Organization. Basic evaluation of fitness involves gravitational and ballistic motor actions (MA), combination with survey training, special physical exercises, strength endurance development, stretching, and relaxation. Modern sports form extreme conditions of activity and impose tough requirements to the athlete’s body, scientific and technological support, organization and implementation of training process and competitions. In this respect, the scientific research concerning almost all kinds of sport focuses on the complex control of athletes’ functional status and fitness. Results. The paper specifies energy-supply components influencing sport performance in cyclic endurance-training sports. The main metabolic values were within the reference limits. Cardiac cycle values were wihtin the range of 0.89 ± 0.02 and 0.98 ± 0.03 s; PO2 interval was within the range of 0.17 ± 0.02 s and 20.15 ± 0.01 s (0.125–0.165s). O2RS complex was within the range of 0.10 and 0.8 s (0.06 – 0.10 s). The critical systole duration was 0.37 ± 0.004 and 0.36 ± 0.003 s (0.355–0.400 s). Myocardial mass was 195.60 ± 5.30 and 199.72 ± 6.12, and left ventricular contraction was – 63.40 ± 4.27% and 60.29 ± 3.89%. Most indicators of respiratory and gas exchange functions in orienteering athletes were within the reference limits. Conclusion. Criteria determining the possibility to include the given indicators in the control program and technology are their informational value, reliability, and correspondence to the sport training process direction. The most informative parameters in the control process are the indicators relevant to the specific of loads applied at the given stage of training. The preparedness of main functional systems in the athlete’s body changes not only from stage to stage in the course of the long-term training, but aso during different cycles of training.

Multicomponent High-Strength Low-Alloy Steel Precipitation-Strengthened by Sub-nanometric Cu Precipitates and M2C Carbides

HSLA-115 is a novel high-strength low-alloy structural steel derived from martensitic Cu-bearing HSLA-100. HSLA-100 is typically used in conditions with overaged Cu precipitates, to obtain acceptable impact toughness and ductility. Present work on HSLA-115 demonstrates that incorporating sub-nanometric-sized M2C carbides along with Cu precipitates produces higher strength steels that still meet impact toughness and ductility requirements. Isothermal aging at 823 K (550 °C) precipitates M2C carbides co-located with the Cu precipitates and distributed heterogeneously at lath boundaries and dislocations. 3D atom-probe tomography is used to characterize the evolution of these precipitates at 823 K (550 °C) in terms of mean radii, number densities, and volume fractions. These results are correlated with microhardness, impact toughness, and tensile strength. The optimum combination of mechanical properties, 972 MPa yield strength, 24.8 pct elongation to failure, and 188.0 J impact toughness at 255 K (−18 °C), is attained after 3-hour aging at 823 K (550 °C). Strengthening by M2C precipitates offsets the softening due to overaging of Cu precipitates and tempering of martensitic matrix. It is shown that this extended yield strength plateau can be used as a design principle to optimize strength and toughness at the same time.

RADIATION CONDITIONS IN KALUGA REGION 30 YEARS AFTER CHERNOBYL NPP ACCIDENT

The article describes radiation conditions in the Kaluga region 30 years after the Chernobyl NPP accident. The Chernobyl NPP accident caused radioactive contamination of nine Kaluga region territories: Duminichsky, Zhizdrinsky, Kuibyshevsky, Kirovsky, Kozelsky, Ludinovsky, Meshchovsky, Ulyanovsky and Hvastovichsky districts. Radioactive fallout was the strongest in three southern districts: Zhizdrinsky, Ulyanovsky and Hvastovichsky, over there cesium-137 contamination density is from 1 to 15Ci/km. According to the Russian Federation Government Order in 2015 there are 300 settlements (S) in the radioactive contamination zone, including 14 settlements with caesium-137 soil contamination density from 5 to 15 Ci/ km2 and 286 settlements with the contamination density ranging from 1 to 5 Ci/km2. In the first years after the Chernobyl NPP accident in Kaluga region territories, contaminated with caesium-137, there were introduced restrictive land usage, were carried out agrochemical activities (ploughing, mineral fertilizer dressing), there was toughened laboratory radiation control over the main doze-forming foodstuff. All these measures facilitated considerable decrease of caesium-137 content in local agricultural produce. Proceeding from the achieved result, in 2002 there took place the transition to more tough requirements SanPiN 2.3.2.1078-01. Analysis of investigated samples from Zhizdrinsky, Ulyanovsky and Hvastovichsky districts demonstrated that since 2005 meat samples didn’t exceed the standard values, same for milk samples since 2007. Till the present time, the use of wild-growing mushrooms, berries and wild animals meat involves radiation issues. It was demonstrated that average specific activity of caesium-137 in milk samples keeps decreasing year after year. Long after the Chernobyl NPP accident, the main products forming internal irradiation doses in population are the wild-growing mushrooms and berries. Population average annual effective doses, caused90by Chernobyl fallouts, do not exceed 1 mSv/year. In 2014 AAEDmaximum calculated value for adultpopulation of 0,91 mSv was established in the following settlements:, Martynki village(Ulyanovsky district) and Lovatyanka village (Hvastovichsky district). The doses, accumulated in the period after the accident, are generally not high. According to calculations numerical value of forecasted accumulated doses varies from 0,23 to 21 mSv. Maximum calculated values of 21 mSv are established in Hvastovichsky district (Lovatyanka village) and Ulyanovsky district (Martynki village). Between 1986 and 2005, the effective irradiation doses did not exceed 29 mSv. Hence, in 70 years after the Chernobyl NPP accident standard value of 70 mSv will not be exceeded in the Kaluga region settlements. After 30 years, the main cause of population internal exposure is consumption of products from private subsidiary farms and especially of wild-growing products. There was conducted radiation monitoring of local agricultural foodstuff produce and of products from the forest. It demonstrated that caesium-137 average specific activity in samples of milk from private subsidiary farms in settlements of Zhizdrinsky, Ulyanovsky and Hvastovichsky districts decreased several-fold. It is between 20,0 Bq/l in 2007 and 1,7 Bq/l in 2015. In 2015, maximum levels of caesium-137 contamination in milk was 3,1% of the standard value, in potatoes - 4,7%, in meat - 4,4%.Average specific activity of caesium-137 in forest mushrooms samples from Zhizdrinsky, Ulyanovsky and Hvastovichsky districts doesn’t decline. Peaks of average caesium-137 activity were observed in 2012, 2013 and 2014; they depend on mushrooms abundance, species, dry summer weather and locations of sampling in the forest. In 2015 in three southern districts, the maximum content of caesium-137 in mushrooms exceeded the permissible level (500 Bq/kg) 4,5-fold; about 2% of the samples do not correspond to it. The maximum contamination of berries with caesium-137 also exceeds the permissible level (160 Bq/kg) nearly 5-fold, and about 43% of samples don’t correspond to it. Obtained results have demonstrated that long after the Chernobyl NPP accident (30 years) the main part of population internal exposure is caused by consumption of wild- growing mushrooms and berries. In the recent years, milk consumption does not play a considerable role in forming of internal dose any more. Conclusion: in 30 years since Chernobyl NPP accident in the Kaluga region radiation and environment conditions have considerably improved on the territories with radionuclides contamination. However, problems remain. The major task for mitigation of the Chernobyl NPP accident consequences is comprehensive radiation, social and economic rehabilitation of the contaminated territories.

Computational technology for analysis of 3D meso-structure effects on damage and failure of concrete

Methodology for analysis of meso-structure effects on longer-scale mechanical response of concrete is developed. Efficient algorithms for particle generation and packing are proposed to represent 3D meso-structures as collections of discrete features distributed randomly in a continuous phase. Specialised to concrete, the continuous phase represents mortar, while the features are aggregates and voids. Intra- and inter-phase cohesive zones are used for failure initiation and crack propagation. A Monte Carlo approach is proposed to analyse the effects of meso-structure geometrical (volume density, size distribution and shape of features) and physical (strength and energy of cohesive zones) properties, whereas a number of model realisations with identical properties are used for statistical analysis. The results present the relative significance of each meso-structure parameter for the emergent load capacity (tensile strength), damage evolution via micro-crack coalescence and macro-crack patterns, and failure energy density (toughness) of concrete. The proposed methodology is an effective tool for meso-structure optimisation in the design of concrete structures with prescribed requirements for strength and toughness.

Testing Methods on Ceramic Rolling Elements for Hybrid Bearings

Abstract Different manufacturing routes for ceramic balls and rollers used in hybrid bearings can lead to different microstructures and mechanical properties of a silicon nitride grade, even being delivered by one supplier. This fact, experienced by the authors, makes it necessary to do testing on the different balls or rollers themselves. This will make sure that the minimum properties on strength, fracture toughness, and microstructure requirements according to ASTM F2094/F2094M-14 and ISO 26602 are fulfilled on the bearing component and not only on special bar samples prepared for bending tests. A first approach done in the bearing industry was a simple crush test of two or three balls on top of each other. This gave a very rough estimate of a “static load rating.” The material resistance to cracks and Hertzian contact damage was tested by indentations with tungsten carbide spheres or doing impact strength testing. A first approach for “real” strength measurement of ceramic spheres was introduced by using a diametrally compressed “C-Sphere” specimen. This was further developed to be more easily machinable and was simply called “Notched ball test.” A similar test was also developed in recent times for ceramic cylindrical roller rollers, called the “Notched roller test.” The goal of this paper was to discuss and summarize test methods for strength and combinations of strength with other properties or effects like toughness and/or residual stresses for ceramic rolling elements that have been established so far for hybrid bearings. This supported the understanding for the need to establish the notched ball test, which was already established as a National Standard ÖNORM M6341:2013 in Austria, and also in ISO and ASTM.

ADVANTAGES OF STEEL FIBRE REINFORCED CONCRETE IN INDUSTRIAL FLOORS

Ground floor slabs are integral to the efficient operation of an industrial facility. A well designed and constructed floor will increase productivity, reduce maintenance of the building and increase the life of the equipment using the floor. Industrial floor slab has common requirements of high strength, toughness, crack control and durability among others. Most of the industrial floors are constructed using the conventional grade slab where reliance is only on the strength of concrete, and reinforcement is used only for crack control and shrinkage. The use of steel fibres in concrete is advantageous over conventional grade slab wherein the residual load carrying capacity of fibres is used and thus, increases the strength and toughness and gives economy in floor thickness apart from saving in construction time. This paper gives an insight into the advantages of steel fibre reinforced concrete in industrial floors. This work is based on structural design experience of the authors in steel fibre reinforced concrete floor slab for industrial projects and in particular the project recently completed for a food and beverage industry.

Study on the fracture toughness of friction stir welded API X80

Mixed results regarding fracture toughness in friction stir welded HSLA steels have been reported. The range of welding parameters used in these recent studies has been very limited. With only a few welding parameters tested, the effect of spindle speed, travel speed, and heat input on the fracture toughness of friction stir welded HSLA steel remains unknown. To understand how the friction stir welding process parameters affect fracture toughness, double sided welds in API X80 were performed and analyzed. Results show that at room temperature friction stir welded API X80 exceeded industry minimum fracture toughness requirements in both the API Standard 1104 and DNV-OS-F101 by 143% and 62%, respectively. The process parameters of spindle speed and heat input have been shown to effectively control the fracture toughness of the stir zone. Relationships have been established that show that fracture toughness increased by 85% when spindle speed decreased by 59% and heat input decreased by 46%.

Propriedades Mecânicas e Microestruturais de Juntas Soldadas pelo Processo a Arco Submerso com Elevado Aporte Térmico

Resumo Este trabalho tem por objetivo apresentar um estudo das propriedades mecânicas e microestruturais de juntas soldadas de aço carbono obtidas pelo processo a arco submerso automatizado com elevada energia de soldagem, visando o aumento de produtividade na fabricação de tubulações para equipamentos de ancoragem. Foram soldadas juntas de aço ASTM A-572 Gr.50 com 25mm de espessura pelo processo a arco submerso em passe único, com energia de soldagem variando de 7,8 até 14,0 kJ/mm. As juntas foram avaliadas através de ensaios de impacto Charpy-V realizados à temperatura de 0°C, microdureza Vickers com carga de 1 kgf. e metalográficos em corpos-de-prova retirados do metal de solda e zona termicamente afetada. Os resultados mostraram que as juntas soldadas apresentaram tenacidade ao impacto superior aos mínimos requeridos para a utilização na soldagem de aços C-Mn baixa liga com requisitos de impacto de 34 Joules à 0°C. Foi observado um aumento significativo da produtividade, sem prejuízo das propriedades mecânicas, permitindo a fabricação de tubulações para equipamentos de petróleo com redução significativa do tempo envolvido na fabricação.

External Actors and Regime Change

This article explores how the study of post-communism has transformed comparative politics by adding a substantial role for external actors to existing theories of democratization. The big, overarching finding is dramatic: external actors can, under certain conditions, tip the balance in favor of democracy by offering strong rewards to elites, conditional on complying with tough requirements. External actors can also influence the performance of the state—and how the state treats its citizens. The main causal player is the European Union. This simple finding is consequential for all three major strands of democratization theory. The article goes on to explore how the leverage of the European Union has shaped the trajectories of political change in the new and credible future EU members in East Central and South Eastern Europe. The great variation among existing and candidate members can be largely explained by different domestic conditions, even though there are many areas where the EU’s use of its leverage could have been improved.

Evaluation of RPV according to alternative fracture toughness requirements

Recently, US NRC revised fracture toughness requirements as 10CFR50.61a to reduce the conservatism of 10CFR50.61. However, unlike previous studies relating to the initial regulation, structural integrity evaluations based on the alternative regulation are not sufficient. In the present study, PTS and P-T limit curve evaluations were carried out by using both regulations and resulting data were compared. With regard to the PTS evaluation, the results obtained from the alternative requirements were satisfied with the criterion whereas those obtained from the initial requirements did not meet the criterion. Also, with regard to the P-T limit curve evaluation, operating margin by 10CFR50.61a was greater than that by 10CFR50.61.

Discounts and Investment Performance of Chinese PIPEs

The Chinese private investment in public equity (PIPE) market offers a unique window into China’s capital markets and their regulatory environment and culture. Chinese PIPEs share many common features with their counterparts in other countries, such as price discounts relative to their publicly traded sister share prices, lock-ups creating illiquidity and incentive distortions, concentrated positions with a few buyers, and a preferred financing tool for companies without other options. But some characteristics of this market are specific to China. Since the regulatory guidelines were introduced in 2006, PIPEs have become the main and, most of the time, the only available equity financing option for listed companies. PIPE applications with the China Securities Regulatory Commission (CSRC) are often approved within a few months, whereas IPOs and seasoned equity offerings can take a couple of years to approve (if they’re ever approved at all) and are subject to much tougher requirements. In recent years, the IPO option was simply closed most of the time by the CSRC. As a result, PIPE offerings are, on average, more than 35% of the total shares outstanding and can be as high as 90% or more. PIPE deals are distributed across industries, much like the structure of the Chinese economy: PIPE financing is dominated by firms in industries that have experienced the worst capacity overexpansion, with relatively few deals done in industries that have minimal overcapacity issues. The authors analyze determinants of PIPE discounts, post-PIPE financial performance changes, and post-PIPE excess stock returns. They discuss and design optimal investment strategies to take advantage of PIPE offerings in China and backtest the strategies. The authors conclude that on a risk-adjusted basis, Chinese PIPEs present attractive opportunities.

Mechanical properties of low alloy high phosphorus weathering steel

Mechanical behaviour of two low alloy steels (G11 and G12) was studied with respect to different phosphorus contents. Tensile strength and yield strength increased while percentage elongation at fracture decreased on increasing phosphorus content. The SEM and light optical photomicrograph of low phosphorus steel (G11) revealed ferrite and pearlite microstructure. On increasing phosphorus content from 0.25 wt.% to 0.42 wt.%, the morphology of grain changed from equiaxed shape to pan-cake shape and grain size also increased. The Charpy V notch (CVN) impact energy of G11 and G12 steel at room temperature was 32 J and 4 J respectively and their fractographs revealed brittle rupture with cleavage facets for both the steels. However, the fractograph of G11 steel after tensile test exhibited ductile mode of fracture with conical equiaxed dimple while that of G12 steel containing 0.42 wt. % P exhibited transgranular cleavage fracture. Based on this study, G11 steel containing 0.25 wt. % P could be explored as a candidate material for weathering application purpose where the 20?C toughness requirement is 27 J as per CSN EN10025-2:2004 specification.

Myocardial Cell Pattern on Piezoelectric Nanofiber Mats for Energy Harvesting

The paper presents in vitro contractile myocardial cell pattern on piezoelectric nanofiber mats with applications in energy harvesting. The cell-based energy harvester consists of myocardial cell sheet and a PDMS substrate with a PVDF nanofiber mat on. Experimentally, cultured on specifically distributed nanofiber mats, neonatal rat ventricular cardiomyocytes are characterized with the related morphology and contraction. Previously, we have come up with the concept of energy harvesting from heart beating using piezoelectric material. A bio-hybrid energy harvester combined living cardiomyocytes, PDMS polymer substrate and piezoelectric PVDF film with the electrical output of peak current 87.5nA and peak voltage 92.3mV. However, the thickness of the cardiomyocyte cultured on a two-dimensional substrate is much less than that of the piezoelectric film. The Micro Contact Printing (μCP) method used in cell pattern on the PDMS thin film has tough requirement for the film surface. As such, in this paper we fabricated nanofiber-constructed PDMS thin film to realize cell pattern due to PVDF nanofibers with better piezoelectricity and microstructures of nanofiber mats guiding cell distribution. Living cardiomyocytes patterned on those distributed piezoelectric nanofibers with the result of the same distribution as the nanofiber pattern.

Evaluation of P-T Limit Curves According to Alternative Fracture Toughness Requirements

During the heat-up and cool-down processes of nuclear power plants, temperature and pressure histories are to be maintained below the P-T limit curve to prevent the non-ductile failure of the RPV(Reactor Pressure Vessel). The ASME Code Sec. XI, App. G describe the detailed procedure for generating the P-T limit curve. The evaluation procedure is containing the evaluation methods of RTNDT using 10CFR50.61. However, recently, Alternative fracture toughness requirements were released 10CFR50.61a. Therefore, in this study, RTNDT of RPV according to the 10CFR50.61a was calculated and used for evaluation of P-T limit curve of a typical RPV under cool-down condition. As a result, it was proven that the P-T curve obtained from 10CFR50.61 is conservative because RTNDT value obtained from the alternative fracture toughness requirements are significantly low.

Influence of Welding Wire Selection on the Strength and Toughness of Welded Armor Steel Joints*

Abstract Since MIL-A-46100D high hardness armor steel plates with excellent resistance to penetration exhibit high strength, selecting the proper electrode used in the gas metal arc welding process is particularly important to obtain a weld joint with high quality satisfying the adequate strength and toughness requirements at the same time. Selecting a consumable electrode with a lower strength than the armor material enhances the ductility and the toughness, reduces the risk of cracking in the weld zone, but it may lead to a considerable loss in strength of welded armor steel joints as well. Thus, an optimization of strength and toughness is required in welding high hardness armor steel plates. Within the scope of this study, two different austenitic stainless solid wires, one of which conforms to AWS 5.9 and the other one to AWS 5.28, and two different cored wires conforming to AWS 5.29 standards were analyzed and compared with respect to weld joint strength and toughness. Although weld joints fabricated with solid wires were superior in weld toughness, weld joints with austenitic cored wires exhibited considerably higher tensile strengths without a significant loss in toughness.