Differences in stress tolerance and brood size between a non-indigenous and an indigenous gammarid in the northern Baltic Sea

Differences in stress tolerance and reproductive traits may drive the competitive hierarchy between nonindigenous and indigenous species and turn the former ones into successful invaders. In the northern Baltic Sea, the non-indigenous Gammarus tigrinus is a recent invader of littoral ecosystems and now occupies comparable ecological niches as the indigenous G. zaddachi. In laboratory experiments on specimens collected between June and August 2009 around Tva¨rminne in southern Finland (59°500N/23°150E), the tolerances towards heat stress and hypoxia were determined for the two species using lethal time, LT50, as response variable. The brood size of the two species was also studied and some observations were made on maturation of juveniles. Gammarus tigrinus was more resistant to hypoxia and survived at higher temperatures than G. zaddachi. Brood size was also greater in G. tigrinus than in G. zaddachi and G. tigrinus matured at a smaller size and earlier than G. zaddachi. Hence, there are clear competitive advantages for the non-indigenous G. tigrinus compared to the indigenous G. zaddachi, and these may be further strengthened through ongoing environmental changes related to increased eutrophication and a warming climate in the Baltic Sea region

Estuarine macrofauna affects benthic biogeochemistry in a hypertrophic lagoon

Coastal lagoons display a wide range of physico-chemical conditions that shape benthic macrofauna communities. In turn, benthic macrofauna affects a wide array of biogeochemical processes as a consequence of feeding, bioirrigation, ventilation, and excretion activities. In this work, we have measured benthic respiration and solute fluxes in intact sediment cores with natural macrofauna communities collected from four distinct areas within the Sacca di Goro Lagoon (NE Adriatic Sea). The macrofauna community was characterized at the end of the incubations. Redundancy analysis (RDA) was used to quantify and test the interactions between the dominant macrofauna species and solute fluxes. Moreover, the relevance of macrofauna as driver of benthic nitrogen (N) redundancy analysis revealed that up to 66% of the benthic fluxes and metabolism variance was explained by macrofauna microbial-mediated N processes. Nitrification was stimulated by the presence of shallow (corophiids) in combination with deep burrowers (spionids, oligochaetes) or ammonium-excreting clams. Deep burrowers and clams increase ammonium availability in burrows actively ventilated by corophiids, which creates optimal conditions to nitrifiers. However, the stimulatory effect of burrowing macrofauna on nitrification does not necessarily result in higher denitrification as processes are spatially separated

Investigation of low cycle fatigue crack opening size and closure stress

417-425In the recent years, a number of studies on the fatigue crack opening and crack closure load have been carried out. Present investigation serves as an intermediate point to complete a failure prediction model with a more practical value for determination of leak before the break (LBB) problem in pressure vessels and pipes. An attempt has been made to solve this problem by using analytical, numerical and experimental methods. Method of linear fracture mechanics at analytical investigation by using the analogy between the stress strain state at stress concentrator and the crack tip and strain intensity factor is adapted to the nominal elastic-plastic loading. Investigation has showed that numerical results are in good agreement with the experimental results. However, the proposed analytical model satisfactorily matches with the experiment in the middle of the crack, which is acceptable for LBB conception, and incorrect at the crack tip, which is non-acceptable for the fracture mechanics conception

Damage accumulation in stress concentration zones of parts with hardened surface under low cycle tension-compression and bending

This paper provides experimental and analytical evaluation of durability of nonhardened and hardened by EMT specimens of grade 45 steel with stress concentrators, under low cycle tension-compression and pure bending. For both type of loading modes was carried out durability analysis, taking into account fatigue and quasi-static damage depending on loading level and number of s. Stress and strain concentration coefficients were calculated by analytical and finite element methods (FEM) under elastic plastic cyclic loading. Performed analytical investigation showed, that suggested method for quasi-static and fatigue damage summation, when accumulated plastic strain and the width of the hysteresis loop are taken into account, provides a very good agreement with the experimental results at stress concentration zones of surface-hardened pans under tension-compression and bending

Temperature and hydrogen concentration influence on Zi -2.5Nb alloy mechanical and fracture toughness characteristics

This paper deals with an investigation of temperature and hydrogen concentration influence on Ignalina NPP RBMK-1500 unit 2 reactor fuel channel tube material - Zr-2.5Nb zirconium alloy (TMT-2) mechanical and fracture toughness characteristics. Two types of specimens were used in this study - tensile and compact semi-natural specimens. Testing temperatures were selected from 20 to 300°C that correspond various operating regimes of the reactor. Made-up hydrogen saturated specimens were tested at hydrogen concentration levels from 52 up to 140 ppm m order to examine hydrogen influence on mechanical and fracture toughness characteristics of the alloy. Dependence of fracture toughness to various mechanical characteristics of the alloy was analysed. Investigation has shown correlation of stress intensity factor Kc to modified plasticity criterion of the alloy

Fracture toughness of 19Mn5 steel pipe welded joints materials

This paper presents an investigation of Ignalina NPP reactor’s main circulated circuit (MCC) pipeline welded joints materials fracture toughness properties. Standard compact C(T)-1T specimens containing “V” and “K” – type welds were cut off from the various MCC pipe’s zones, produced from the 19Mn5 steel pipe and welded by electrodes UTP-068HH, YONI-13/55 and CT-36. Critical J – integraf JIc values were defined Rusing J–R curve test method, which results on determination of J – integral values as a function of crack extension ?a. The investigation enables to calculate critical crack length ?amax and ?ac sizes and J – integral JIc, Jmax and JPmax values, which are used to predict safe service lifetime of the cracked pipelines

Principles for modelling technological processes investigation into the strength and durability of automatic coupler SA-3 in railway carriages

The paper presents the durability analysis of the automatic coupler in railway carriages. The loading of the automatic coupler predetermined by the weight of a train, train speed and railway relief is a time-dependent variable. The finite element method was used for stress-strain state calculation taking into account acting forces. In order to reduce stress concentration, the geometry of the automatic coupler’s body was modified. Modelling results for different rounded radii demonstrated it was possible to reduce stress concentration up to 34%. Under maximum forces, plastic strain occurs in the automatic coupler’s body. The calculation of strain and stress state in the body of the automatic coupler shows it is under a static, low and high cycle loading. Therefore, to calculate the durability of the automatic coupler, the dependencies for low cycle nonstationary stress limited loading has been proposed evaluating low cycle quasi-static and fatigue damages. In order to evaluate high cycle fatigue damage, a linear law for the summation of loading cycles has been suggested. For low cycle damage evaluation, the calculation method for the summation of fatigue and quasi-static damages created at one loading cycle taking into account loading level and neglecting the sequence of cycles has been put forward. Thus, to calculate the automatic coupler for each specific case, it is necessary to determine the number of loading cycles at each loading level and to evaluate durability considering dependencies presented in this paper