Stress Triaxial Constraint and Fracture Toughness Properties of X90 Pipeline Steel

The X90 pipeline steel with high-strength and high-toughness become the most popular pipeline steel. Due to the stress triaxial constraint and fracture toughness properties are the key factors for the stable work of pipeline steel, the research on the fracture toughness of X90 is a great significance to promote the engineering application of high-strength pipeline steel. In order to investigate the stress triaxial constraint and fracture toughness properties of X90 pipeline steel, the experimental rules with different grooves size are proposed using the common toughness experiment and the corresponding numerical models are established in this paper. The resistance curves and fracture toughness of each type of specimens are obtained and compared with that of finite element analysis. Furthermore, the stress distribution, J-integral distribution and stress triaxial constraint of the specimen are analyzed, as well as the influence of side grooves size on the determination of fracture toughness is also discussed. The results obtained from the study will provide a reference to the fracture toughness evaluation research and application of X90 pipeline steel.

ON THE MACRO HYDRODYNAMIC DESIGN OF HIGHLY EFFICIENT MEDIUM- SPEED CATAMARANS WITH MINIMUM RESISTANCE

A new class of fuel-efficient and environmentally friendly twin-hull vessels is currently under development. Compared to high-speed catamarans, a significant reduction in speed combined with an increase in deadweight tonnes will lead to a highly efficient medium-speed catamaran design. Recently-built conventional and high-speed ferries are compared to each other in terms of length, speed, deadweight and transport efficiency to classify the new design. The goal of this study is to find a preliminary macro design point for minimum total resistance by considering the main particulars of the catamaran vessel: block coefficient, prismatic coefficient and slenderness and separation ratios of the demihulls. Publications containing recommendations towards the optimum hull form parameters for moderate Froude numbers are reviewed and existing experimental data analysed to identify parameters for this new class of vessel. Designs with varied L/BOA-ratios and constant deck area are compared to find configurations of low total resistance for carrying a nominated deadweight at a particular speed, the associated change of the light ship weight has been taken into account. Two different model test series of catamaran models have been considered and their resistance curves agreed to each other. Recommendations are made; with the most important being the vessel should not exceed a speed of Fr = 0.35, with optimal prismatic coefficients around CP ≈ 0.5 and low transom immersion. This study presents the preliminary design of medium-speed single and twin-hull vessels for operations close to hump speed.

Preparation of PSFO and LPSFO Nanofibers by Electrospinning and Their Electronic Transport and Magnetic Properties

In this paper, Pr0.5Sr0.5FeO3 (PSFO) and La0.25Pr0.25Sr0.5FeO3 (LPSFO) nanofibers were prepared by electrospinning and subsequent calcination, and their morphology, microstructure, electronic transport and magnetic properties were studied systematically. The temperature-dependent resistance curves of PSFO and LPSFO nanofibers were measured in the temperature range from 300 K down to 10 K. With the temperature lowering, the resistance increased gradually and the then decreased sharply due to the occurrence of ferromagnetic metal phase. The metal-insulator transition temperature was about 110 K and 180 K for PSFO and LPSFO nanofibers separately. The electronic conduction behavior above the transition temperature can be described by one-dimensional Mott’s variable-range hopping (VRH) model. The hysteresis loops and the field-cooled (FC) and zero-field-cooled (ZFC) curves showed that both PSFO and LPSFO nanofibers exhibit ferromagnetism. Although the doping of La reduces the overall magnetization intensity of the material, it increases the ferromagnetic ratio of the system, which may improve the performance of LPSFO in solid oxide fuel cell.

Effect of Zinc Coating on Delay Nugget Formation in Dissimilar DP600 - AISI304 Welded Joints Obtained by the Resistance Spot Welding Process

This paper researches the effect of zinc coating of galvanized DP600 steel on the dynamic resistance and the delayed nugget formation of dissimilar DP600 - AISI304 welded joints, obtained with resistance spot welding process (RSW). The RSW evaluations consisted of determining, from the dynamic resistance curves, the time involved in the different stages of the process, particularly the beginning of nugget formation. The experimental results showed that, from the dynamic resistance curves, it is possible to identify 8 distinct stages during the welding of galvanized DP600 steel and AISI304 stainless steel. In the case of the welding of uncoated DP600 steel with AISI304, only 6 stages are identified (except for stages 2 and 3), which are directly related to the heating, softening and melting of the galvanic coating. The energy used in stages 2 and 3, causes a delay in the beginning of nugget formation for welded joints obtained with galvanized DP600 steel compared to uncoated DP600 - AISI304 welded joints, reaching values between 37.28 ms and 52.29 ms for the welding conditions analyzed. Monitoring the time duration of stages 2 and 3, as defined from the analysis of the dynamic resistance curves, could be used as a tool to predict the beginning of nugget formation in the welding of galvanized steels, to avoid undesirable phenomena such as expulsion and to guarantee the quality of the welded joints.

Metal Oxide Nanostructure-Based Gas Sensor for Carbon Dioxide Detection

To increase the sensitivity and efficiency of a gas sensor, nanostructured ZnO and Co3O4 layers were obtained by hydrothermal synthesis directly on the electrode surface, eliminating the use of binders. Scanning electron microscope images showed that the resulting nanostructured coatings were characterised by good adhesion to the surface and high porosity, which opened up the possibility of their further use in the process of developing a gas sensor. The efficiency of the obtained nanostructured coatings and their sensitivity at room temperature to various concentrations of CO2 were determined. The resistance curves of the samples were obtained as a function of gas concentration in the chamber, for Co3O4 and ZnO nanostructures.

An Investigation of Different Factors On Durability of Metakaolin Geopolymer Cement Mortar

In the preliminary part of this research, orthogonal experiments were conducted to identify metakaolin admixture and activator content as the two main influencing factors through four factors that mainly affected the basic properties of metakaolin geopolymer specimens. It is crucial to study the durability of construction materials under harsh environments. Therefore, this experiment mainly tested the anti-permeability, sulfate corrosion resistance, and freezing-thawing resistance of metakaolin geopolymer pastes with different ratio of metakaolin admixture and alkali activators content.The results indicated that with the changes of metakaolin and activator content,both of two anti-permeability curves increased firstly and then decreased.The sulfate corrosion resistance showed that both weight loss curves firstly decreased and then increased trend.Corrosion resistance curves increased first and then decreased in different curing time.Freezing-thawing resistance tests indicated that weight loss rate and strength loss rate declined and then ascended.Moreover,the microscopic SEM and FT-IR experiments were used to more directly reflect the patterns of durability changes.

R-Curve Characterization of Crumb Rubber Modified Asphalt Mixtures Incorporating Warm Mix Additive at Low Temperatures

In a previous research by authors, a methodology was developed to derive J-R curves for Hot Mix Asphalt (HMA) mixtures using an elastic-plastic approach where a comprehensive understanding of crack propagation regime could be achieved. In this research, the effect of crumb rubber modification of HMA binder is studied in terms of R-curves and crack propagation at low temperatures. Mode I Single edge notched beam (SE(B)) fracture tests were conducted in temperature levels of 0 °C, -10 °C, and -20 °C. PG58-22 and PG64-22 binders were used in the fabrication of HMA samples. Modified specimens consist of 20% crumb rubber along with the incorporation of 3% warm mix admixture. Crack growth resistance curves were obtained in SE(B) tests by means of image processing and recording of the progressive crack length. Elastic-plastic J-R curves revealed that crumb rubber modified mixtures exhibit higher crack growth resistance for each bitumen performance grade. As well, increased ductility and cohesive energy can be observed according to the R-curves as the mixtures are modified by crumb rubber.