Creep Resistance of S304H Austenitic Steel Processed by High-Pressure Sliding

Sheets of coarse-grained S304H austenitic steel were processed by high-pressure sliding (HPS) at room temperature and a ultrafine-grained microstructure with a mean grain size of about 0.14 µm was prepared. The microstructure changes and creep behavior of coarse-grained and HPS-processed steel were investigated at 500–700 °C under the application of different loads. It was found that the processing of S304H steel led to a significant improvement in creep strength at 500 °C. However, a further increase in creep temperature to 600 °C and 700 °C led to the deterioration of creep behavior of HPS-processed steel. The microstructure results suggest that the creep behavior of HPS-processed steel is associated with the thermal stability of the SPD-processed microstructure. The recrystallization, grain growth, the coarsening of precipitates led to a reduction in creep strength of the HPS-processed state. It was also observed that in the HPS-processed microstructure the fast formation of σ-phase occurs. The σ-phase was already formed during slight grain coarsening at 600 °C and its formation was enhanced after recrystallization at 700 °C.

Extremely Southward Migration of the Antarctic Circumpolar Current During the Last Interglacial

The Antarctic Circumpolar Current (ACC) acts as a critical component to regulate the global thermohaline circulation and climate. However, active debate remains about the relative strength of ACC during current/past warm periods and underlying driving mechanisms. Here, we present sortable silt mean grain size records from the Scotia Sea to infer the ACC strength over the past 160 ka. The 22-ka cycles of sortable silt mean grain size suggest that the precession-driven contraction/expansion of Subtropical Jet dominates the migration of ACC fronts, and thus ACC speed and potential Atlantic Meridional Overturning Circulation stability. We find that the bottom flow speed during MIS 5e was over three times faster than the Holocene, with no apparent difference in ACC speed between the Holocene and the Last Glacial Maximum. We suggest that a southward shift of oceanic fronts of ~5° could cause the additional speed-up of ACC during MIS 5e. This could induce warmer water flowing in the ACC to approach and melt the Antarctica continental ice shelves, with corresponding effects on global sea level and the global climate.

Applied Geology of Wellington Rocks for Aggregate and Concrete

<p>This study was initiated to examine geological aspects of Wellington greywacke-suite rocks in relation to their end use as an engineering material - aggregate, particularly for concrete. An attempt has been made to map (at least in part), identify and categorise rocks for quarrying in the Wellington region, to evaluate and quantify their properties as aggregates and to appraise their qualities in concrete - in short to equate rock geology to aggregate and concrete performance as a tool for resource management. Study of bedding 1ed to a classification into three lithofacies and some 70 representative samples were examined petrographically. For engineering purposes, Wellington rocks may be divided into two categories, greywacke and argillite, each having separate and distinct mineralogies and chemistries which do not alter significantly between lithofacies. Greywacke is coarser and may be distinguished from argillite texturally at a mean grain size of 5 phi (0.031 mm). Rock properties, in particular strength, modulus, density, hardness and degradation tendencies, are linked directly or indirectly with mean grain size. Argillites, though more dense, are generally weaker, softer, less elastic and degrade more readily than greywackes, the latter property being readily assessed from a newly devised test based on the destruction of chlorite by hydrochloric acid. As aggregates, greywackes produce similar particle shapes irrespective of grading. Argillites, which are generally more angular, produce concretes which are more difficult to work. Physical properties of aggregate, inherently those of its parent rock, are reflected in concrete made from it. The possibility of laumontite promoting cement alkali-silicate reaction is obviated by the mode of occurrence of minerals within the rock. Although argillite aggregates are unsuitable in certain environments and return lower strength in concrete than do greywacke aggregates, they still have a place in low strength concrete applications.</p>

Applied Geology of Wellington Rocks for Aggregate and Concrete

<p>This study was initiated to examine geological aspects of Wellington greywacke-suite rocks in relation to their end use as an engineering material - aggregate, particularly for concrete. An attempt has been made to map (at least in part), identify and categorise rocks for quarrying in the Wellington region, to evaluate and quantify their properties as aggregates and to appraise their qualities in concrete - in short to equate rock geology to aggregate and concrete performance as a tool for resource management. Study of bedding 1ed to a classification into three lithofacies and some 70 representative samples were examined petrographically. For engineering purposes, Wellington rocks may be divided into two categories, greywacke and argillite, each having separate and distinct mineralogies and chemistries which do not alter significantly between lithofacies. Greywacke is coarser and may be distinguished from argillite texturally at a mean grain size of 5 phi (0.031 mm). Rock properties, in particular strength, modulus, density, hardness and degradation tendencies, are linked directly or indirectly with mean grain size. Argillites, though more dense, are generally weaker, softer, less elastic and degrade more readily than greywackes, the latter property being readily assessed from a newly devised test based on the destruction of chlorite by hydrochloric acid. As aggregates, greywackes produce similar particle shapes irrespective of grading. Argillites, which are generally more angular, produce concretes which are more difficult to work. Physical properties of aggregate, inherently those of its parent rock, are reflected in concrete made from it. The possibility of laumontite promoting cement alkali-silicate reaction is obviated by the mode of occurrence of minerals within the rock. Although argillite aggregates are unsuitable in certain environments and return lower strength in concrete than do greywacke aggregates, they still have a place in low strength concrete applications.</p>

The Experimental Investigation of the Repeated-Loading Behaviour of the Sand-Rubber-Mixture (SRM)

Nowadays the waste rubber problems are concerned due to the environmental issues, storage, and recycling difficulty. However, the rubber base equipment has been widely used to protect structures for vibrations - that has been generated by the structure or induced from the vicinity area or the bedrock into the structure - due to the notable capability of absorbing energy. In this study, the repeated-loading behaviour of the Sand Rubber Mixture (SRM) has been investigated and the remarkable energy absorption properties of the mixture have been illustrated. The test soil material that has been used in this study was a well-graded sand (SW) with a mean grain size of 2 mm. The test martial rubber that has been used was grain particles with a uniform size of 4.76 mm. The sand rubber mixture (SRM) was prepared by using 7.5% rubber inclusion because it was found as the optimum rubber content. A series of force control repeated-loading CBR tests have been arranged. The effect of mixing rubber particles with the well-graded sand (SW test material) has been investigated. This shows the remarkable energy absorption capability of Sand Rubber Mixture (SRM) to protect the bed of a machine’s footing that is generating repeated loads. The SRM usage could be extended to be employed as a part of an energy absorption unit and dampers facilities beneath a machine footing or structures that are sensitive to the vibration to prevent destructive deformation and resonance phenomenon.

THE EFFECT OF THE WEAR DEGREE OF WORKING ELEMENTS IN A JAW CRUSHER ON THE OPERATING EFFECTIVENESS OF A TWO-STAGE GRANITE GRINDING SYSTEM

The article presents an analysis of the influence of the wear degree of working elements in a jaw crusher on the crushing process and on the quality of the crushed material. The evaluation of the operating effectiveness of a technological system comprising two crushers was based on the quality indicator of the crushed product, i.e. on the share of irregular grains for a fraction with a mean grain size of 31.5/63 mm at each of the two stages of crushing. The wear degree was monitored by performing microscopic observations of the plates in the fixed jaw and by measuring the critical geometric characteristics of the crusher, e.g., tooth height, jaw size, and discharge opening size, during the entire service life of the crusher.

Significantly Improved Colossal Dielectric Properties and Maxwell—Wagner Relaxation of TiO2—Rich Na1/2Y1/2Cu3Ti4+xO12 Ceramics

In this work, the colossal dielectric properties and Maxwell—Wagner relaxation of TiO2–rich Na1/2Y1/2Cu3Ti4+xO12 (x = 0–0.2) ceramics prepared by a solid-state reaction method are investigated. A single phase of Na1/2Y1/2Cu3Ti4O12 is achieved without the detection of any impurity phase. The highly dense microstructure is obtained, and the mean grain size is significantly reduced by a factor of 10 by increasing Ti molar ratio, resulting in an increased grain boundary density and hence grain boundary resistance (Rgb). The colossal permittivities of ε′ ~ 0.7–1.4 × 104 with slightly dependent on frequency in the frequency range of 102–106 Hz are obtained in the TiO2–rich Na1/2Y1/2Cu3Ti4+xO12 ceramics, while the dielectric loss tangent is reduced to tanδ ~ 0.016–0.020 at 1 kHz due to the increased Rgb. The semiconducting grain resistance (Rg) of the Na1/2Y1/2Cu3Ti4+xO12 ceramics increases with increasing x, corresponding to the decrease in Cu+/Cu2+ ratio. The nonlinear electrical properties of the TiO2–rich Na1/2Y1/2Cu3Ti4+xO12 ceramics can also be improved. The colossal dielectric and nonlinear electrical properties of the TiO2–rich Na1/2Y1/2Cu3Ti4+xO12 ceramics are explained by the Maxwell–Wagner relaxation model based on the formation of the Schottky barrier at the grain boundary.

Post-LGM glacial retreat drives aggradation in the interiors of the Kashmir Himalaya

Understanding the response of glaciated catchments to climate change is fundamental for assessing sediment transport from the high-elevation, semi-arid to arid sectors in the Himalaya to the foreland basin. The fluvioglacial sediments stored in the semi-arid Padder valley in the Kashmir Himalaya record valley aggradation during ~19-11 ka. We relate the valley aggradation to increased sediment supply from the deglaciated catchment during the glacial-to-interglacial phase transition. Previously-published bedrock-exposure ages in the upper Chenab valley suggest ~180 km retreat of the valley glacier during ~20-15 ka. Increasing roundness of sand-grains and reducing mean grain-size from the bottom to the top of the valley-fill sequence hint about increasing fluvial transport with time and corroborate with the glacial retreat history. Our result also correlates well with late Pleistocene-early Holocene sediment aggradation observed across most Western Himalayan valleys. It highlights the spatiotemporal synchronicity of sediment transfer from the Himalayas triggered by climate change.

Effect of Internal Electromagnetic Stirrings DC Casting on Grain Refinement and Segregation of Large-Sized Billet of 2219 Alloy

An advanced method called internal electromagnetic stirring (I-EMS) was investigated to resolve the engineering problems like coarse-grain, inhomogeneous structure and macrosegregation. The electromagnetic stirrer functioned with internal-cooling was inserted in the melt during DC casting. In this study, a round billet of 2219 alloy DC cast with a diameter of 880mm under I-EMS process condition was produced, and its structure and composition distribution were comparatively characterized. The results show that the mean grain size decreased from the range of 872, 1023, 332 μm to the range of 317, 438, 271 μm at different billet positions with I-EMS. I-EMS consequently produce superior grain refinement and homogeneity. The effect of I-EMS on the grain-refinement and macrosegregation was also discussed.

Small-Scale Morpho-Sedimentary Dynamics in the Swash Zone of a Megatidal Mixed Sand–Gravel Beach

On mixed sand–gravel beaches, impacts from gravel- and cobble-sized grains—mobilized by the energetic shorebreak—limit the utility of in situ instrumentation for measuring the small-scale response of the beach face on wave period time scales. We present field observations of swash zone morpho-sedimentary dynamics at a steep, megatidal mixed sand–gravel beach using aeroacoustic and optical remote sensing. Coincident observations of bed level and mean surficial sediment grain size in the swash zone were obtained using an array of optical cameras paired with acoustic range sensors. Lagrangian tracking of swash-transported cobbles was carried out using an additional downward-oriented camera. The principal objective of the study was to investigate linkages between sediment grain size dynamics and swash zone morphological change. In general, data from the range sensor and camera array show that increases in bed level corresponded to increases in mean grain size. Finer-scale structures in the bed level and mean grain size signals were observable over timescales of minutes, including signatures of bands of coarse-grained material that migrated shoreward with the leading edge of the swash prior to high tide berm formation. The direction and magnitude of cobble transport in the swash varied with cross-shore position, and with the composition of the underlying bed. These results demonstrate that close-range remote sensing techniques can provide valuable insights into the roles of cobble-sized versus sand-sized particle dynamics in the swash zone on mixed sand–gravel beaches.