Failure Analysis of High Density Polyethylene Butt Weld Joint

This article discusses a detailed failure analysis conducted on high density polyethylene which acts as the liner of composite compresses natural gas cylinder. Leakage from the cylinder was observed after about 2000 cycles of hydrostatic pressure testing at 250 bars. Visual inspection revealed that the leakage occurred from the circumferential fusion joint between the cylinder and dome section. The cylinder and dome sections were produced from different techniques and joined together by using a heated tool butt welding process conducted by a local manufacturer. The joined components work as an integral part. The investigation was carried out using various techniques including mechanical, thermal and metallurgical examination. Fractography of the failed joint surface showed stepwise marks typical of a fatigue failure. Mechanical testing results showed that the strength of dome section was significantly lower than that of the cylinder section. Moreover, both the tensile and fatigue strength of joint was also almost half that of the cylinder. The fracture surface of the broken welded joint showed brittle failure. The melting points of both the cylinder and the dome sections were found almost same by differential scanning calorimeter but large difference was found between the melt point indexes of both sections. The results suggested that the failure was actually a stress cracking via a process of slow crack growth, which occurred due to use of a dome material having inferior properties and very high melt flow index. These properties inhibited proper fusion and resulted in a poor weld joint. Consequently, the weld joint of lower strength eventually failed in macroscopically brittle manner upon cyclic loading.     

Modelling heat transfer and dissolved species concentrations within PWR crud

The crud formed on PWR fuel tends to contain “chimneys” penetrating down to the metal surface. This provides an opportunity for wick-boiling to occur. This is associated with the generation of very high concentrations (many tens of times the bulk values) of dissolved species within the crud, and associated significant increase in the local saturation temperature. These both have consequences for cladding corrosion, and the accumulation of boron in the crud contributes to the phenomenon termed “axial offset anomaly”. We present here detailed, coupled two-dimensional models of these processes, which allow the three linked phenomena, heat conduction, advection and diffusion of species in the water, and diffusion of the water itself, to be modeled and their aggregate effect to be seen.     

Humic Acid from Livestock Dung: Ecofriendly Corrosion Inhibitor for 3SR Aluminum Alloy in Alkaline Medium

Humic acids (HAs) extracted from cow, goat, and poultry dung were studied. Extraction was performed by treating the source materials with acid hydrolysis using hydrochloric acid (HCl) before alkaline extraction with sodium hydroxide (NaOH). Yields of 3.33, 2.67, and 1.28% dry weight were obtained from cow, goat, and poultry dung respectively. The extracted humic acids were characterized using Fourier transform-infrared (FT-IR) and ultraviolet-visible (UV-vis) spectroscopy techniques. The results obtained were in good agreement with commercial HA (Sigma-Aldrich). The humic acid extracted from cow dung was used to evaluate its corrosion inhibition potential for alkaline-induced corrosion of 3SR aluminum alloy using weight loss and electrochemical (potentiodynamic polarization) techniques at 30°–60°C. Results obtained show that the humic acid functions as an excellent corrosion inhibitor for aluminum alloy in 0.1 M NaOH solution. Corrosion inhibition efficiency increased with increase in humic acid concentration but decreased with rise in temperature. Results from potentiodynamic polarization measurements show that the HA behaved mostly as a mixed-type inhibitor. Adsorption of the humic acid was found to obey the Langmuir adsorption isotherm at all concentrations and temperatures studied. The mechanism of physical adsorption has been proposed based on the trend of inhibition efficiency with temperature. The proposed mechanism was also corroborated by kinetic and thermodynamic parameters obtained.     

Electrostatic bonding of high-T c superconducting films to any substrate

Complete integration of high-T _c thin-film superconducting technology with other electronic technologies requires hybrid structures with both technologies on the same substrate. This is difficult to do with direct growth of the superconductor on certain substrates (GaAs, InP) because of the high temperatures required for formation of the superconductor. A method is proposed to circumvent this problem by using electrostatic forces and appropriate thin-film materials to bond superconducting films to any substrate at 300°C. The same principle can be applied to the bonding of other devices on other substrates.     

Hydration of tetracalcium aluminoferrite in presence of lime and sulfates

The first part of the paper describes conduction calorimetric and SEM studies of the initial first hour hydration of C₄AF and C₃A with water and saturated solutions of lime, gypsum and gypsum with lime. Lime accelerates while gypsum and gypsum with lime strongly retard the hydration of C₄AF. In case of C₃A, the effect is less pronounced. The second part deals with the hydration of C₄AF at later stages in presence of various additives and the same results as above are obtained. Anhydrite has very little influence while the presence of C₃A reduces the effect of gypsum and hemihydrate on hydration of C₄AF. A detailed investigation of the hydration process by means of X-RD, DTA, SEM and calorimetry has also been made.     

Evolution of microstructure and mechanical properties during quenching and tempering of ultrahigh strength 0.3C Si–Mn–Cr–Mo low alloy steel

Effects of quenching and tempering treatments on the development of microstructure and mechanical properties of ultrahigh strength 0.3C Si–Mn–Cr–Mo low alloy steel were investigated. Samples were austenitized at 1123–1323 K for 2400 s and oil quenched (OQ) to produce mixed microstructures. Tempering was carried out at 473–773 K for 2–3 h. Phase transformation temperatures were measured using dilatometer. The microstructures were characterized using optical and scanning electron microscope. SEM–EDS analysis was carried out to determine the type and size of non-metallic inclusions. Volume percent of retained austenite was measured by X-ray diffraction technique. Hardness, tensile properties, and impact energies were also determined for all heat treated conditions. Fractography of impact specimens were done using stereomicroscope and SEM. The results showed that newly developed steel exhibited peak hardness, yield strength, and tensile strength of about 600 HV, 1760 MPa, and 1900 MPa, respectively, when OQ from 1203 K and tempered in between 473 and 573 K, combined with adequate ductility and impact toughness. Decrease in hardness and strength was observed with increasing tempering temperature whereas the impact energy was stable up to 623 K, however, impact energy was found to decrease above 632 K due to temper martensite embrittlement.     

Institutions, routines, and crises: Post-earthquake housing recovery in Mexico City and Los Angeles

This is a study of how planning institutions deal with crisis recovery; that is, recovery from situations marked by complexity, uncertainty, and sudden change that increasingly characterize contemporary cities. Based on an analytical framework derived from institutional literature and planning theory, the study examines two successful housing recovery programs during crisis situations: the Renovación Habitacional Popular program in Mexico City following the 1985 earthquake, and the Ghost Town program in Los Angeles following the 1994 earthquake. The study addresses the following research questions: In what manner were the planning institutions successful, if at all? Which familiar and established institutional arrangements, policies, programs, and practices (ie routines) did they adopt when faced with large, unexpected shocks (ie crises)? How do institutional actors in different political-economic contexts respond to similar crisis situations? What are the lessons of these institutional actions for future crises, and for normal operations in planning? The study argues that planning institutions perform successfully during crises due primarily to routines, which are usually overlooked or decried as being bureaucratic. Planning institutions responded effectively to the crises by adapting institutional routines quickly and efficiently to new circumstances. While these routines can be constraints under normal conditions, they also act as powerful tools during exceptional times, serving as catalysts to release the disciplined energy of institutions to perform effectively, resolve problems, and re-establish order.     

Measurement of microwave surface resistance of patterned superconducting thin films

A simple and versatile measurement technique has been demonstrated for characterization of thin film superconductors and the substrates on which they are deposited. Unlike other state of the art measurements that characterize only the top layer of unpatterned thin films in end-plate replacement or perturbation-type cavity arrangements, we test the sample under conditions very close to those of actual microwave circuit applications. Measurements on a laser deposited, thin-film YBCO superconductor, patterned in the form of a meander line on a LaAlO₃ substrate, show a microwave surface resistance one order of magnitude lower than that of copper at 79 K and 11 GHz. At 1.4 GHz and 79 K, an improvement by over two orders of magnitude is observed. This is the first demonstration of superior microwave performance of a comb filter structure using a HTS thin film. The research portion performed at Sarnoff was supported by the Strategic Defense Initiative Organization under Contract SDIO84-88-C-0044.     

Dynamic Hand Gesture Recognition Using 3D-CNN and LSTM Networks

Recognition of dynamic hand gestures in real-time is a difficult task because the system can never know when or from where the gesture starts and ends in a video stream. Many researchers have been working on vision-based gesture recognition due to its various applications. This paper proposes a deep learning architecture based on the combination of a 3D Convolutional Neural Network (3D-CNN) and a Long Short-Term Memory (LSTM) network. The proposed architecture extracts spatial-temporal information from video sequences input while avoiding extensive computation. The 3D-CNN is used for the extraction of spectral and spatial features which are then given to the LSTM network through which classification is carried out. The proposed model is a light-weight architecture with only 3.7 million training parameters. The model has been evaluated on 15 classes from the 20BN-jester dataset available publicly. The model was trained on 2000 video-clips per class which were separated into 80% training and 20% validation sets. An accuracy of 99% and 97% was achieved on training and testing data, respectively. We further show that the combination of 3D-CNN with LSTM gives superior results as compared to MobileNetv2 + LSTM.