Hydrogen effects on mechanical performance of nodular cast iron

The ferritic nodular cast iron grade EN-GJS-400-15 intended for use as the load-bearing part of canisters for long-term disposal of spent nuclear fuel was studied in order to evaluate its sensitivity to the hydrogen-induced effects on mechanical performance. Hydrogen was introduced in the cast iron electrochemically from 1N H2SO4 solution under controlled cathodic potential. Hydrogen uptake in the course of tensile testing was measured using hydrogen thermal desorption method. It was found that plastic deformation of the specimens in the continuous hydrogen charging results in a remarkable increase of hydrogen uptake in the studied cast iron. Constant extension rate tests (CERT) and constant load tests (CLT) performed under continuous electrochemical hydrogen charging showed a remarkable reduction of elongation to fracture in CERT and time to fracture in CLT as compared to the corresponding values obtained by testing in air and water environments. The most important finding is that hydrogen increases dramatically the creep rate of the cast iron in CLT already at applied load of about 0.5 x yield stress. The tensile tests were followed with SEM observations of the hydrogen-induced cracking appearance on the tensile specimen outer and fracture surfaces. The obtained results are discussed in terms of the specific role of the graphite nodules as abundant sources of hydrogen and the nodule distribution in the cast iron matrix in the mechanisms of hydrogen-induced cracking

Monitoring of ticks and tick-borne pathogens through a nationwide research station network in Finland

In 2015 a long-term, nationwide tick and tick-borne pathogen (TBP) monitoring project was started by the Finnish Tick Project and the Finnish Research Station network (RESTAT), with the goal of producing temporally and geographically extensive data regarding exophilic ticks in Finland. In the current study, we present results from the first four years of this collaboration. Ticks were collected by cloth dragging from 11 research stations across Finland in May September 2015-2018 (2012-2018 in Seili). Collected ticks were screened for twelve different pathogens by qPCR: Borrelia afzelii, Borrelia garinii, Borrelia valaisiana, Borrelia burgdorferi sensu stricto, Borrelia miyamotoi, Babesia spp., Anaplasma phagocytophilum, Rickettsia spp., Candidatus Neoehrlichia mikurensis, Francisella tularensis, Bartonella spp. and tick-borne encephalitis virus (TBEV). Altogether 15 067 Ixodes ricinus and 46 Ixodes persulcatus were collected during 68 km of dragging. Field collections revealed different seasonal activity patterns for the two species. The activity of I. persulcatus adults (only one nymph detected) was unimodal, with activity only in May July, whereas Ixodes ricinus was active from May to September, with activity peaks in September (nymphs) or July August (adults). Overall, tick densities were higher during the latter years of the study. Borrelia burgdorferi sensu lato were the most common pathogens detected, with 48.9 +/- 8.4% (95% Cl) of adults and 25.3 +/- 4.4% of nymphs carrying the bacteria. No samples positive for F. tularensis, Bartonella or TBEV were detected. This collaboration project involving the extensive Finnish Research Station network has ensured enduring and spatially extensive, long-term tick data collection to the foreseeable future.Peer reviewe

Dwell Effects on High Temperature Fatigue Damage Mechanisms: Part II

The mechanisms controlling deformation and failure under high temperature creep-fatigue conditions of materials are examined in this paper. The materials studied were pure alloys, solder alloys, copper alloys, low alloy steels, stainless steels, titanium alloys, tantalum alloys, and Ni-based alloys. The deformation and failure mechanisms were different (fatigue, creep, oxidation and their interactions) depending on test and material parameters employed. Deformation mechanisms, such as cavity formation, grain boundary sliding, intergranular (IG) and transgranular (TG) damage, oxidation, internal damage, dislocation cell formation, and other damage mechanisms are very important in order to gain knowledge of fatigue behavior of materials. The observed mechanisms can be categorized as follows: (a) depending on the test parameters employed, a high NCR resulted in high strain levels. The damage was due to creep-fatigue interaction by mixed TG and IG cracking, creep damage by cavity formation and surface damage by oxidation. Oxidation damage was found to depend on a critical temperature and compression and tension dwell periods in a cycle. (b) Dwell sensitivity was effective only below a certain strain range, and once this threshold was exceeded NCR value was not affected with a further increase in dwell time. (c) Microstructures changed depending on test temperature, dwell time, and strain range. Triple point cracking and cavities were formed as a result. New precipitation occurred depending on temperature, strain range and dwell time. Some precipitates were beneficial in blocking the grain boundary damage by creep, whereas other precipitates changed the dislocation substructure promoting more damage. (d) Depleted regions on the grain boundaries developed due to exposure at high temperatures resulting in the formation or propagation of IG cracks. (e) Dwell cycles evolved mean stresses in tension and compression directions. Mean stress in tension was more deleterious and caused dwell sensitivity. (f) Dwell sensitivity was also dependent on material condition and discontinuities present in a material. These mechanisms are summarized in this paper

Dwell Effects on High Temperature Fatigue Damage Mechanisms: Part II

The mechanisms controlling deformation and failure under high temperature creep-fatigue conditions of materials are examined in this paper. The materials studied were pure alloys, solder alloys, copper alloys, low alloy steels, stainless steels, titanium alloys, tantalum alloys, and Ni-based alloys. The deformation and failure mechanisms were different (fatigue, creep, oxidation and their interactions) depending on test and material parameters employed. Deformation mechanisms, such as cavity formation, grain boundary sliding, intergranular (IG) and transgranular (TG) damage, oxidation, internal damage, dislocation cell formation, and other damage mechanisms are very important in order to gain knowledge of fatigue behavior of materials. The observed mechanisms can be categorized as follows: (a) depending on the test parameters employed, a high NCR resulted in high strain levels. The damage was due to creep-fatigue interaction by mixed TG and IG cracking, creep damage by cavity formation and surface damage by oxidation. Oxidation damage was found to depend on a critical temperature and compression and tension dwell periods in a cycle. (b) Dwell sensitivity was effective only below a certain strain range, and once this threshold was exceeded NCR value was not affected with a further increase in dwell time. (c) Microstructures changed depending on test temperature, dwell time, and strain range. Triple point cracking and cavities were formed as a result. New precipitation occurred depending on temperature, strain range and dwell time. Some precipitates were beneficial in blocking the grain boundary damage by creep, whereas other precipitates changed the dislocation substructure promoting more damage. (d) Depleted regions on the grain boundaries developed due to exposure at high temperatures resulting in the formation or propagation of IG cracks. (e) Dwell cycles evolved mean stresses in tension and compression directions. Mean stress in tension was more deleterious and caused dwell sensitivity. (f) Dwell sensitivity was also dependent on material condition and discontinuities present in a material. These mechanisms are summarized in this paper

Weldability of superalloys alloy 718 and ATI (R) 718Plus (TM) - A study performed by Varestraint testing

In this study, the old and well-known alloy 718 is compared with the newly developed ATI (R) 718Plus (TM) from the weldability point of view. This is done in order to gain new information that have not been documented and established yet among the high-temperature materials with high strength, oxidation resistance, thermal stability and sufficient weldability, yet. ATI (R) 718Plus (TM) shows a lower sensitivity to hot cracking than alloy 718 with approximately 10 mm total crack length (TCL) difference in Varestraint testing. In the solution-annealed condition at 982 degrees C for 4.5 h followed by air cooling, the crack sensitivity is decreased as compared to the mill-annealed condition. Along the crack path and also ahead of the crack tip, gamma-Laves eutectic is present in both alloys. The microhardness measurements showed similar hardness level of 250 HV in the weld metal of both alloys and even in the parent material of alloy 718. ATI (R) 718Plus (TM) parent metal had hardness of 380 HV and a small increase of less than 50 HV was observed for both studied alloys in the heat affected zone (HAZ). For the same grain size of ATI (R) 718Plus (TM) (8.3 mu m) and alloy 718 (15.6 mu m), the susceptibility to liquation cracking may increase with increasing grain size. With a small grain size, there is a possibility to accommodate more trace elements (B, S, P) due to the larger grain boundary area. The impurity elements were found in relatively small precipitates, typically borides (0.2 mu m), phosphides (0.1 to 0.5 mu m) and carbo-sulphides. The solidification sequence of alloy 718 and ATI (R) 718Plus (TM) is relatively similar, where the liquid starts to solidify as gamma-phase followed by gamma/MC reaction at about 1260 degrees C and then final gamma/Laves eutectic reaction at around 1150 degrees C. Detailed knowledge about weldability of alloy 718 and ATI (R) 718Plus (TM) can be used for material selection

Varestraint Weldability Testing of ATI 718Plus (R)-Influence of Eta Phase

This study investigates the effect of eta phase on hot cracking susceptibility of ATI 718Plus (R). Two heat treatment conditions of 950 degrees C/1 h and 950 degrees C/15 h having different amounts of eta phase were tested by longitudinal Varestraint testing method. The heat treatment at 950 degrees C/15 h exhibited the highest amount of cracking. This was related to the higher amount of eta phase precipitation during the long dwell heat treatment which aided to extensive liquation during welding

Improved modelling of electric loads for enabling demand response by applying physical and data-driven models:project RESPONSE

Accurate load and response forecasts are a critical enabler for high demand response penetrations and optimization of responses and market actions. Project RESPONSE studies and develops methods to improve the forecasts. Its objectives are to improve 1) load and response forecast and optimization models based on both data-driven and physical modelling, and their hybrid models, 2) utilization of various data sources such as smart metering data, weather data, measurements from substations etc., and 3) performance criteria of load forecasting. The project applies, develops, compares, and integrates various modelling approaches including partly physical models, machine learning, modern load profiling, autoregressive models, and Kalman-filtering. It also applies non-linear constrained optimization to load responses. This paper gives an overview of the project and the results achieved so far.acceptedVersionPeer reviewe