Lower Shelf Research Articles

Creep crack growth rate predictions in 316H steel using stress dependent creep ductility

Short and long term trends in creep crack growth (CCG) rate data over test times of 500–30 000 h are available for Austenitic Type 316H stainless steel at 550°C using compact tension, C(T), specimens. The relationship between CCG rate and its dependence on creep ductility, strain rate and plastic strain levels has been examined. Uniaxial creep data from a number of batches of 316H stainless steel, over the temperature range 550–750°C, have been collected and analysed. Power-law correlations have been determined between the creep ductility, creep rupture times and average creep strain rate data with stress σ normalised by flow stress σ0·2 over the range 0·2<σ/σ0·2<3 for uniaxial creep tests times between 100 and 100 000 h. Creep ductility exhibits upper shelf and lower shelf values which are joined by a stress dependent transition region. The creep strain rate and creep rupture exponents have been correlated with stress using a two-stage power-law fit over the stress range 0·2<σ/σ0·2<3 for temperatures between 550 and 750°C, where it is known that power-law creep dominates. For temperature and stress ranges where no data are currently available, the data trend lines have been extrapolated to provide predictions over the full stress range. A stress dependent creep ductility and strain rate model has been implemented in a ductility exhaustion constraint based damage model using finite element (FE) analysis to predict CCG rates in 316H stainless steel at 550°C. The predicted CCG results are compared to analytical constant creep ductility CCG models (termed NSW models), assuming both plane stress and plane strain conditions, and validated against long and short term CCG test data at 550°C. Good agreement has been found between the FE predicted CCG trends and the available experimental data over a wide stress range although it has been shown that upper-bound NSW plane strain predictions for long term tests are overly conservative.

Analysis of notch effect in the apparent fracture toughness and the fracture micromechanisms of ferritic–pearlitic steels operating within their lower shelf

The fracture resistance of materials is generally higher in notched conditions that in cracked conditions. In other words, when the notch radius increases there is also an increase in the apparent fracture toughness, which is that exhibited in notched conditions. This paper presents an analysis of the notch effect on two ferritic–pearlitic steels operating within their corresponding lower shelf, and develops an experimental programme, composed of 28 CT characterisation specimens and 72 CT validation specimens, together with finite elements analysis with the aim of validating the apparent fracture toughness predictions provided by the Theory of Critical Distances. The results have shown how this theory provides reasonable predictions of the apparent fracture toughness of the materialThe research is completed with the analysis of the evolution of fracture micromechanisms when the notch radius increases, revealing a direct relation between this evolution and the apparent fracture toughness observations.

Dusk but not dawn burrow emergence rhythms of &lt;i&gt;Nephrops norvegicus&lt;/i&gt; (Crustacea: Decapoda)

The Norway lobster, Nephrops norvegicus , can be captured by haul nets only during the emergence from its burrow. In the last few decades, an extensive field research revealed distinct diel (24-h–based) catchability patterns at different depths. Laboratory experiments suggested that burrow emergence (used as a proxy of catchability) is endogenously controlled via a circadian system. Results were usually presented in terms of mean effects without a quantification of inter-individual variability and arrhythmia. Here, we studied the burrow emergence of 52 adult Nephrops by an infrared actograph endowed with an artificial burrow. Animals were exposed to 12-12 h light-darkness cycle, simulating photic condition of the lower shelf. Forty-five animals showed rhythmic emergence (87%), while seven were arrhythmic (13%). Rhythmic animals were clustered according to their timing of emergence: 54% at dusk and 4% at dawn. Moreover, other animals showed fully diurnal or nocturnal emergence (10% and 19%, respectively). The comparison of our results with those derived from temporally scheduled trawling indicates that bimodal catch patterns observed in shelf populations are poorly observed during individual experiments in the laboratory, where the same light conditions are simulated. Nephrops burrow emergence seems to be the result of a mixed endogenous-exogenous control, while arrhythmia could also be present in the wild.

Assessment of notched structural steel components using failure assessment diagrams and the theory of critical distances

When the structural integrity of notched components is analysed, it is generally assumed that notches behave as cracks, something which generally provides overconservative results. The proposal of this paper consists, on the one hand, in the application of the theory of critical distances for the estimation of the notch fracture toughness and, therefore, for the conversion of the notched situation into an equivalent cracked situation in which the material develops a higher fracture resistance. On the other hand, once the notch fracture toughness has been defined, the assessment is performed using the failure assessment diagram methodology, and assuming that the notch effect on the limit load is negligible. The methodology has been applied to 336 CT notched fracture specimens made of two different structural steels, covering temperatures from the corresponding lower shelf up to the upper shelf, providing satisfactory results and a noticeable reduction in the overconservatism derived from the analyses in which the notch effect is not considered.

Evaluation of the ductile–brittle transition temperature in the NESC-I material using small punch testing

Small punch (SP) fracture testing with subsequent SEM fractographic analysis was applied to an A 508 Class 3 reactor pressure vessel (RPV) steel, used originally in the NESC-I spinning cylinder experiment, in order to determine the SP ductile–brittle transition temperature of both the base material and the sub-clad heat affected zone. In addition to the evaluation of the SP transition temperature, TSP, corresponding to the mean value of upper and lower shelf SP fracture energies, three alternative procedures were assessed. The SP transition temperatures were then compared to original NESC-I data obtained using conventional testing methods, which yielded values of the empirical correlation factor α consistent with those reported in literature for RPV steels of similar composition. The evaluation of the fracture mode transition temperature TFM from the SP test was identified as a viable procedure, in particular for the case when lower shelf energy data cannot be obtained due to technical limitations associated with very low testing temperatures.

Sponge assemblages of the deep Weddell Sea: ecological and zoogeographic results of ANDEEP I–III and SYSTCO I expeditions

The aim of this study is to analyze the community structure, ecology and distribution of deep Weddell Sea sponge faunas. Analysis was performed on the basis of sponges sampled during ANDEEP I–III and SYSTCO I expeditions (2002–2008) by RV Polarstern. The material obtained comprises about 800 sponge specimens, representing 129 species, within these are 95 species of demosponges (including 15 new to science), 25 hexactinellid species (7 new) and 9 calcarean species (5 new). Sponges were sampled at 51 stations in depths between 500 and 5,500 m. At most stations, sponge densities were very low, and many species are represented by one or two specimens only. Community structure by Bray–Curtis similarity was analyzed as well as depth range and spatial distribution of the most common species. Zoogeographic affinities of sampled faunas are analyzed. Three associations of sponges are found in the deep Weddell Sea: (1) The Polymastia/Tentorium community, (including Rossella associations) distributed on the lower shelf and continental slope. (2) The Bathydorus community, distributed on the continental slope and upper abyssal. (3) The Caulophacus community, associated with Cladorhizidae, is characteristic for the abyssal plains. The associations follow each other successively both bathymetrically and geographically, from shallow to deep, from shelf and ridge structures into the open abyssal. A distinct faunistic boundary between shelf and deep sea is not present. In general, the sponge fauna of the deep Weddell Sea is regionally restricted and shows stronger affinities only to the sponge fauna of the subantarctic islands.

Evaluation of fracture toughness by notched small punch tests with Weibull stress method

The fracture toughness obtained by pre-notched (pre-cracked) small punch specimens is much higher than that obtained by conventional single edge notch bending (SENB) or by compact tension specimens. In this paper, an equivalent Weibull stress method has been introduced. The tests with 0.4T SENB specimens and linear notched small punch specimens were carried out at 77K. At this temperature (on lower shelf), the results of both test methods show scatter but not significant. The loads at fracture of both types of specimen were used to determine the Weibull stress parameter, m, and the Weibull stress, σw, with finite element method. Base on the assumption that Weibull stress parameters are material constants, the m which could meet a condition that σw0.4TSENB=σwLNSP was regarded as Weibull stress parameter, m. The critical J integral of 1T SENB JcITSENB at 77K has been estimated with m and σw deduced by 0.4T SENB and LNSP specimens.

Changes in distribution and range structure of Arctic cephalopods due to climatic changes of the last decades

The warming of Arctic waters over the last decades has been confirmed by the results of numerous studies. New data on distribution of cephalopods in the Arctic were obtained from the research cruises of PINRO (Russia) and IMR (Norway) during 2006–2011. Teuthowenia megalops and Todaropsis eblanae were found in the Arctic for the first time, at distances of more than 1000 km and 2500 km outside of their ranges, respectively. The demersal species T. eblanae inhabiting the lower shelf and upper continental slope has presumably spread into the Barents Sea by the eastern branch of the Norwegian Current, and further by the southern branch of the North Cape coastal current, as far as the Murman shelf. The bathypelagic species T. megalops is carried to the Arctic evidently by the deep-water warm Atlantic Currents. The new spreading areas of both species are obviously the non-reproductive zones of their ranges. Foraging shoals of Todarodes sagitatus were recorded in the Arctic in 2010 for the first time in the last 25 years, which can be related to not only the warming of Arctic waters, but also the fluctuation of Todarodes levels in the main part of the range in the Northern Atlantic. The native Arctic species Gonatus fabricii has expanded its range to the eastern part of the Barents Sea and to the adjacent part of the Kara Sea. In these areas of Arctic waters, warming is particularly noticeable and the ongoing climatic changes are leading to boreal cephalopods spreading into the Polar Basin. This may impact species relations in vulnerable Arctic ecosystems.

Microstructural and fracture toughness characterisation of a high-strength FeCrMoVC alloy manufactured by rapid solidification

A newly-developed high-speed steel manufactured using a rapid solidification technique was investigated. Microstructural observations were conducted with the aim of comprehensively characterising the material. Furthermore, fracture toughness tests were carried out to determine the linear-elastic plane-strain fracture toughness KIc at both room temperature (20°C) and −40°C. A fatigue precracking method was developed to provide stable crack propagation from a manufactured chevron-notch at a ratio of minimum to maximum stress of R=−1. The results of the fracture toughness tests demonstrated that, in comparison to other tool steels, the material exhibits relatively high fracture toughness values. Furthermore, the lower shelf of KIc is already reached at room temperature. Fracture toughness is considered to be a matrix property due to the high matrix hardness. An analysis of the influence of notch tip radius ρ on notch fracture toughness KA revealed a linear correlation between the square root of the notch tip radius and KA. Upon examination of the influence of notch tip radius on fracture toughness measurements, the assumption was made that the critical notch tip radius is approximately 90μm.

Fitting small data sets in the lower ductile-to-brittle transition region and lower shelf of ferritic steels

The use of a 3-parameter Master Curve approach where the Weibull modulus is 4 and a minimum toughness value of 20MPam1/2 is now well accepted and standardised. The standard allows the use of a minimum of six specimens, tested at a single temperature, to produce the Master Curve. However, the examination of a small data set can lead to difficulties when trying to fit to this standard formula especially if the toughness is larger than 20MPam1/2. A small data set obtained from lower shelf testing of a ferritic pressure vessel steel is used to explore some of the issues related to the Weibull modulus and minimum toughness and how a user might try to fit such data. Finite element models are used to show that enhanced minimum toughness values larger than 20MPam1/2 are unlikely to have arisen from warm pre-stressing. The implications for the Master Curve of the different fitting options are also briefly explored.

Effect of vanadium addition on the microstructure and mechanical properties of the ODS ferritic steels

In this work, the effects of vanadium addition in the range of 0.3–3% (in weight percent) for an oxide dispersion strengthened reduced activation ferritic (ODS RAF) steel were investigated. Samples of the V-modified steel have been prepared using elemental (Fe, Cr, W, Ti) and Y2O3 powders with the nominal composition of Fe–14Cr–2W–0.3Ti–0.3Y2O3. Consolidated and heat treated samples were investigated using Scanning Electron Microscopy and Scanning Transmission Electron Microscopy equipped with Electron Energy Loss Spectroscopy detector. Hardness and Charpy impact tests (KLST specimens) were also performed. The microstructure investigations revealed numerous particles of the size up to 0.5μm. They are primarily Ti–Cr–V oxides located at the grain boundaries and inside the grains. These particles increase hardness and significantly reduce fracture resistance of the ODS RAF alloys developed here. However, it should be noted that the 0.3% V-ODS steel has unexpectedly the lowest transition temperature of about 282K and that the 1–3% V-ODS steels, in spite of the transition temperature about 373K, exhibit almost two times higher the lower shelf energy values in comparison with the 0.3% V-ODS and 0% V-ODS steels.

High strain rate behavior, transformation-induced plasticity and fracture toughness characterization of cast and additionally tempered Fe85Cr4Mo8V2C1 alloy manufactured using a rapid solidification technique

This study focuses on the characterization of the microstructures of an FeCrMoVC alloy in two states (an as-cast and a heat-treated state) as well as the compressive strain rate-dependent material and fracture toughness behavior. Both microstructures consist of martensite, retained austenite and complex carbides. Tempering results in a transformation of retained austenite into martensite, the precipitation of fine alloy carbides, and diffusion processes. High yield stresses, flow and ultimate compressive strength values at a relatively good deformability were measured. The yield and flow stresses at the onset of deformation are higher for the heat-treated state due to higher martensitic phase fractions and fine precipitations of alloy carbides respectively. Compressive deformation causes a strain-induced transformation of retained austenite to α′-martensite. Hence, both high-strength alloys are TRIP-assisted steels (TRansformation-Induced Plasticity). However, the martensitic transformation is more pronounced in the as-cast state due to higher phase fractions of retained austenite already in the initial state. Examinations of strained microstructures showed decreased crystallite sizes with increasing deformation. It is assumed that, during plastic deformation, the amount of low angle grain boundaries increases while the incremental formation of α′-martensite leads to decreased crystallite size. In general, lower microstrains were determined in the heat-treated state as a consequence of stress relaxation during tempering. In comparison to commercially available tool steels, the determined fracture toughness K Ic of both variants revealed relatively high fracture toughness values. It was found that the lower shelf of K Ic is already reached at room temperature. Higher loading rates \( \dot{K} \) resulted in lower dynamic fracture toughness K Id values. Notch fracture toughness K A measurements indicate that the critical notch tip radii of the examined materials are slightly smaller than 0.09 mm.

Impact Toughness of Ultrafine-Grained Interstitial-Free Steel

Impact toughness of an ultrafine-grained (UFG) interstitial-free (IF) steel produced by equal-channel angular extrusion/pressing (ECAE/P) at room temperature was investigated using Charpy impact tests. The UFG IF steel shows an improved combination of strength and impact toughness compared with the corresponding coarse-grained (CG) one. The CG IF steel samples underwent a transition in fracture toughness values with decreasing temperature because of a sudden change in fracture mode from microvoid coalescence (ductile) to cleavage (brittle) fracture. Grain refinement down to the submicron (≈320 nm) levels increased the impact energies in the upper shelf and lower shelf regions, and it considerably decreased the ductile-to-brittle transition temperature (DBTT) from 233 K (−40 °C) for the CG steel to approximately 183 K (−90 °C) for the UFG steel. Also, the sudden drop in DBTT with a small transition range for the CG sample changed to a more gradual decrease in energy for the UFG sample. The improvement in toughness after UFG formation was attributed to the combined effects of grain refinement and delamination and/or separation in the heavily deformed microstructure. Although an obvious change from the ductile fracture by dimples to the brittle fracture by cleavage was recognized at 233 K (−40 °C) for the CG steel, no fully brittle fracture occurred even at 103 K (−170 °C) in the UFG steel.

The Construction and Testing of a Combined Solar and Mechanical

The combined solar and mechanical dryer was constructed to use solar energy and electrical energy either separately or in combination to conduct air drying. There was various arrangement of drying condition for mechanical drying system such as using either 1KH-1F or 1KH-2F or 2KH-1F or 2KH-2F. While for solar drying either no fan or one fan or two fans were used. Different drying conditions were applied by changing the heating source and flow of air. The highest temperature was obtained in 2KH-1F condition for mechanical drying and convection gives highest temperature among different solar drying alternatives. The temperature in upper shelf for different solar operational condition ranged from 1.53 to 1.67 times of ambient temperature (25°C- 31°C) at peak time and 1.28 to 1.36 for lower shelf. The air velocity was 0.35 m/sec and 0.70 m/sec for 1-fan and 2-fan respectively.The performance of dryer was evaluated by drying potato slices having thickness 3, 5 and 7 mm. In both methods, drying rate increases with the increasing temperature and decreases with the increasing slice thickness following the power law equation. The values for the index ‘n’ of the power law equation are less than 2 (range from 0.53 to 1.42) for all the conditions, this indicating that external resistance to mass transfer was significant and internal resistance to mass transfer did not control the drying process under the given conditions. The effect of temperature on Diffusion co-efficient (De) follows Arrhenius type relationship. While analyzing the effect of temperature, the maximum activation energy for diffusion of water from Potato (7 mm thick slices, at upper shelf) was found to be 7.656 Kcal/g-mole and 8.252Kcal/g-mole for mechanical and solar conditions respectively.DOI: http://dx.doi.org/10.3329/jesnr.v4i2.10132J. Environ. Sci. &amp; Natural Resources, 4(2): 35-40, 2011

Comparison of ductile-to-brittle transition curve fitting approaches

Ductile-to-brittle transition (DBT) curve fitting approaches are compared over the transition temperature range for reactor pressure vessel steels with different kinds of data, including Charpy-V notch impact energy data and fracture toughness data. Three DBT curve fitting methods have been frequently used in the past, including the Burr S-Weibull and tanh distributions. In general there is greater scatter associated with test data obtained within the transition region. Therefore these methods give results with different accuracies, especially when fitting to small quantities of data. The comparison shows that the Burr distribution and tanh distribution can almost equally fit well distributed and large data sets extending across the test temperature range to include the upper and lower shelves. The S-Weibull distribution fit is poor for the lower shelf of the DBT curve. Overall for both large and small quantities of measured data the Burr distribution provides the best description.

Component Crystallization and Physical Collapse during Freeze-Drying of &lt;small&gt;L&lt;/small&gt;-Arginine–Citric Acid Mixtures

Component crystallization and physical collapse during freeze-drying of aqueous solutions containing protein-stabilizing L-arginine and citric acid mixtures were studied. Freeze-drying microscopy (FDM) and thermal analysis of the solute-mixture frozen solutions showed collapse onset at temperatures (T(c)) approximately 10°C higher than their T(g)'s (glass transition temperatures of the maximally freeze-concentrated solute phase). Experimental freeze-drying of these solutions at a low chamber pressure showed the occurrence of physical collapse at shelf temperatures close to or slightly higher than the T(c). Slower ice sublimation at higher chamber pressures induced the physical collapse from lower shelf temperatures. The large effect of chamber pressures on the collapse-inducing shelf temperatures confirmed significance of the sublimation-related heat loss on the sublimation interface temperature during the primary drying. Drying of the single-solute L-arginine solution resulted in cake-structure solids composed of its anhydrous crystal. Thermal and powder X-ray diffraction (PXRD) analysis suggested slow crystal nucleation of L-arginine dihydrate in the frozen solutions. Characterization of the frozen solutions and freeze-dried solids should enable rational formulation design and process control of amino acid-containing lyophilized pharmaceuticals.

Consideration on lower shelf of fracture toughness for brittle crack arrest

Consideration on lower shelf of fracture toughness for brittle crack arrest

The development of rhythm regularity, neuromuscular strategies, and movement smoothness during repetitive reaching in typically developing children

IntroductionThis study examined the development of paced coordinated reaching characterized by the successful entrainment of the movement to an external pacer, synchronous muscle activations and movement smoothness. MethodsThirty children, 5–10years of age, and ten adults were instructed to repeatedly reach for and move an object from a lower shelf to an upper shelf in time to a metronome. Surface electromyography data were recorded. Amplitude and cross-correlations were calculated on three muscle pairs crossing the shoulder and elbow. A motion capture system captured the space curve accelerations of hand, forearm and upper arm segments to quantify movement smoothness. ResultsThe 5–6year old children showed the greatest amount of temporal variability, followed by 7–10year olds and then the adults. Correlations between muscle pairs stabilizing the shoulder girdle were higher in each group as compared to the other two muscle pairs but the correlations for all pairs were consistently higher for adults. Movement smoothness for children 9–10years of age was closer to an adult-like pattern with respect to control of the upper arm, but the hand segment had the greatest variability across groups. ConclusionsThe increased temporal variability and decreased movement smoothness of the hand and forearm segments suggest that control of more distal musculature may be more difficult in children. The neuromuscular strategies adopted by adults were more optimal than those adopted by children as reflected by smoother and more consistent reaching.

The ductile to brittle transition for C–Mn steel with an ultrafine grain ferrite/cementite microstructure

The Charpy impact energy was measured as a function of temperature for plain C–Mn steel with an ultrafine grain ferrite/cementite (UGF/C) microstructure and with a coarse-grain ferrite/pearlite (CGF/P) microstructure. Instrumented Charpy impact tests were carried out at 273 K and 77 K for the UGF/C microstructure. The steel with the UGF/C microstructure exhibited an upper shelf energy lower than the steel with the CGF/P microstructure, a higher lower shelf energy and the transition in impact energy occurred more gradually at a lower temperature. The ductile to brittle transition in the steel with the UGF/C microstructure was caused by a decrease in energy absorbed by ductile fracture rather than a change of fracture mode from ductile fracture to cleavage as occurred for the CGF/P microstructure. The fracture surface of the UGF/C steel in the upper shelf region contained large dimples and numerous small dimples whereas the fracture surface in the lower shelf region contained small dimples and cleavage facets. A lower amount of energy was absorbed in the transition region and the lower shelf region due to the decrease of dimple diameter and depth. Nevertheless, some energy was absorbed in the lower shelf because there were some small dimples even at the liquid helium temperature. In contrast, essentially no energy was absorbed in the lower shelf for the CGF/P steel because of typical cleavage fracture. The UGF/C microstructure has a high cleavage fracture stress.

Characterization of the seafloor at the SYSTCO stations based on video observations and ground truthing sedimentology

An underwater camcorder mounted on a lander frame was used to image the sedimentary conditions and the epibenthic fauna at the seafloor along the SYSTCO transect. Four stations were monitored; on the lower shelf (600 m), continental slope (2000 m), abyssal plain (5300 m), and on top of a seamount (2100 m). The sediment surface was filmed for different time lengths between 3 and 19 min, while the camera was towed over distances ranging from 11 to 187 m, resulting in areas filmed between 4 and 71 m 2 per station. From the gathered images, epifauna was counted and identified to the lowest possible taxonomic level. For ground truthing, two to three replicate multicorer samples per station were vertically sectioned per centimeter down to 5 cm depth and analyzed for sediment granulometry. Differences in the sedimentary characteristics could be related to both water depth and topography according to the multicorer samples. The video footage from each station showed a range of different sediment surface types and widely varying epifaunal abundance, the lowest number of readily identifiable organisms being present on the abyssal plain and the highest on the lower shelf.