The Influence of Pearlite Volume Fraction on Rayleigh Wave Propagation in A572 Grade 50 Steel

The acoustoelastic effect is the interaction between ultrasonic wave velocity and stress. To estimate the stress a perturbation signal is introduced and the shift in time of flight is measured at the receiving location. In addition to the stress, the wave velocity can be affected by the amount of phases in the material’s microstructure. This study investigates the changes in Rayleigh wave velocity for A572 grade 50 steel as a function of stress and pearlite phase volume fraction. In order to obtain different amounts of pearlite the samples are heat treated at 970 °C for time durations of 30 min, 1 hour, 2 hours and 4 hours and then furnace cooled. The acoustoelastic coefficient for 0.5 and 1 MHz perturbation frequency is calculated by uniaxial loading of each heat treated plate while measuring ultrasonic wave velocity. The results are compared for pearlite phase volume fraction obtained from optical microscopy and hardness measurements

Reestructuración cognitiva y técnicas psicoeducativas para la regulación emocional en deportistas

Introducción: Dentro del deporte planificado hacia la competición y el alto rendimiento, los desarrollos de las capacidades mentales del deportista tienen una importancia definitoria a la hora marcar resultados. Diversas son las técnicas empleadas, entre ellas destaca la reestructuración cognitiva. Objetivo: La presente investigación se enfocó en demostrar los beneficios de la reestructuración cognitiva y el aprendizaje de técnicas psicoeducativas para la regulación emocional en deportistas. Metodología: La presente investigación se constituyó en un estudio experimental de caso, al tratarse de una menor de edad. Se cumplieron todos los parámetros éticos para este tipo investigación. La participante fue una adolescente de 13 años, perteneciente a la disciplina de escalada deportiva. Se utilizaron como reactivos psicológicos las pruebas: POMS, Motivación de Pelletier y CSAI-2R. Las intervenciones psicoeducacionales se realizaron dos veces por semana, con una duración de 50 minutos; esto durante un microciclo de planificación de dos meses. Resultados: Como resultados de los reactivos aplicados, resalta: la prueba Profile of Mood States (POMS), que demostró una baja puntuación en el ítem de vigor, que conllevó a la exploración personal, y simultáneamente, se complementó la evaluación psicológica y deportiva con la prueba de ansiedad precompetitiva CSAI-2R, que identificó el 65 %, de ansiedad cognitiva, y el 88 % de ansiedad somática. Conclusiones: Se destacaron los resultados diferenciales en las pruebas de POMS y CSAI-2R, que indicaron puntuaciones bajas en la esfera psicológica; este proceso de intervención fue un instrumento de “contención emocional”, en el caso puntual de la deportista

The Detection of Burn-Through Weld Defects Using Noncontact Ultrasonics

Nearly all manufactured products in the metal industry involve welding. The detection and correction of defects during welding improve the product reliability and quality, and prevent unexpected failures. Nonintrusive process control is critical for avoiding these defects. This paper investigates the detection of burn-through damage using noncontact, air-coupled ultrasonics, which can be adapted to the immediate and in-situ inspection of welded samples. The burn-through leads to a larger volume of degraded weld zone, providing a resistance path for the wave to travel which results in lower velocity, energy ratio, and amplitude. Wave energy dispersion occurs due to the increase of weld burn-through resulting in higher wave attenuation. Weld sample micrographs are used to validate the ultrasonic results

Characterization of GMAW (Gas Metal Arc Welding) Penetration Using Ultrasonics

Welding defects such as lack of penetration, undercutting, crater crack, burn-through and porosity can occur during manufacturing. Assessing weld quality using nondestructive evaluation methods is important for the quality assurance of welded parts. In this paper, the measurement of weld penetration, which is directly related to weld integrity, is investigated by means of ultrasonics. Both linear and nonlinear ultrasonic methods are studied to assess their sensitivities to weld penetration. Welded plates with different penetration depths controlled by changing weld heat input are manufactured using gas metal arc welding (GMAW). Microscopic properties are assessed after the ultrasonic measurements are completed. Numerical models are built using the weld profile obtained from macrographs to explain the relationship between linear ultrasonic and weld penetration. A quantitative correlation between weld morphology (shape, width and depth) and the energy of linear ultrasonic signal is determined, where the increase of weld bead penetration exceeding the plate thickness results in decrease of the energy of the ultrasonic signal. Minimum detectable weld morphology using linear ultrasonics is defined depending on the selected frequency. Microhardness measurement is conducted to explain the sensitivity of nonlinear ultrasonics to both weld penetration and heterogeneity in weld. The numerical and experimental results show that the weld geometry influences the ultrasonic measurement other than the materials’ properties

Interfacial Effects on Lithium Superoxide Disproportionation in Li-O₂ Batteries

During the cycling of Li-O₂ batteries the discharge process gives rise to dynamically evolving agglomerates composed of lithium–oxygen nanostructures; however, little is known about their composition. In this paper, we present results for a Li-O₂ battery based on an activated carbon cathode that indicate interfacial effects can suppress disproportionation of a LiO₂ component in the discharge product. High-intensity X-ray diffraction and transmission electron microscopy measurements are first used to show that there is a LiO₂ component along with Li₂O₂ in the discharge product. The stability of the discharge product was then probed by investigating the dependence of the charge potential and Raman intensity of the superoxide peak with time. The results indicate that the LiO₂ component can be stable for possibly up to days when an electrolyte is left on the surface of the discharged cathode. Density functional calculations on amorphous LiO₂ reveal that the disproportionation process will be slower at an electrolyte/LiO₂ interface compared to a vacuum/LiO₂ interface. The combined experimental and theoretical results provide new insight into how interfacial effects can stabilize LiO₂ and suggest that these interfacial effects may play an important role in the charge and discharge chemistries of a Li–O₂ battery

Raman Evidence for Late Stage Disproportionation in a Li–O₂ Battery

Raman spectroscopy is used to characterize the composition of toroids formed in an aprotic Li–O₂ cell based on an activated carbon cathode. The trends in the Raman data as a function of discharge current density and charging cutoff voltage provide evidence that the toroids are made up of outer LiO₂-like and inner Li₂O₂ regions, consistent with a disproportionation reaction occurring in the solid phase. The LiO₂-like component is found to be associated with a new Raman peak identified in the carbon stretching region at ∼1505 cm^–1, which appears only when the LiO₂ peak at 1123 cm^–1 is present. The new peak is assigned to distortion of the graphitic ring stretching due to coupling with the LiO₂-like component based on density functional calculations. These new results on the LiO₂-like component from Raman spectroscopy provide evidence that a late stage disproportionation mechanism can occur during discharge and add new understanding to the complexities of possible processes occurring in Li–O₂ batteries

Lithium Superoxide Hydrolysis and Relevance to Li–O₂ Batteries

Fundamental understanding of reactions of lithium peroxides and superoxides is essential for the development of Li–O₂ batteries. In this context, an investigation is reported of the hydrolysis of lithium superoxide, which has recently been synthesized in a Li–O₂ battery. Surprisingly, the hydrolysis of solid LiO₂ is significantly different from that of NaO₂ and KO₂. Unlike KO₂ and NaO₂, the hydrolysis of LiO₂ does not produce H₂O₂. Similarly, the reactivity of Li₂O₂ toward water differs from LiO₂, in that Li₂O₂ results in H₂O₂ as a product. The difference in the LiO₂ reactivity with water is due to the more exothermic nature of the formation of LiOH and O₂ compared with the corresponding reactions of NaO₂ and KO₂. We also show that a titration method used in this study, based on reaction of the discharge product with a Ti­(IV)­OSO₄ solution, provides a useful diagnostic technique to provide information on the composition of a discharge product in a Li–O₂ battery