Synchrotron strain scanning for residual stress measurement in cold-drawn steel rods

Cold-drawn steel rods and wires retain significant residual stresses as a consequence of the manufacturing process. These residual stresses are known to be detrimental for the mechanical properties of the wires and their durability in aggressive environments. Steel makers are aware of the problem and have developed post-drawing processes to try and reduce the residual stresses on the wires. The present authors have studied this problem for a number of years and have performed a detailed characterization of the residual stress state inside cold-drawn rods, including both experimental and numerical techniques. High-energy synchrotron sources have been particularly useful for this research. The results have shown how residual stresses evolve as a consequence of cold-drawing and how they change with subsequent post-drawing treatments. The authors have been able to measure for the first time a complete residual strain profile along the diameter in both phases (ferrite and cementite) of a cold-drawn steel rod

Optimisation of post-drawing treatments by means of neutron diffraction

The mechanical properties and the durability of cold-drawn eutectoid wires (especially in aggressive environments) are influenced by the residual stresses generated during the drawing process. Steelmakers have devised procedures (thermomechanical treatments after drawing) attempting to relieve them in order to improve wire performance. In thiswork neutron diffraction measurements have been used to ascertain the role of temperature and applied force – during post-drawing treatments – on the residual stresses of five rod batches with different treatments. The results show that conventional thermomechanical treatments are successful in relieving the residual stresses created by cold-drawing, although these procedures can be improved by changing the temperature or the stretching force. Knowledge of the residual stress profiles after these changes is a useful tool to improve the thermomechanical treatments instead of the empirical procedures used currently

Evolution of residual stresses induced by machining in a Nickel based alloy under static loading at room temperature

Tensile residual stresses are very often generated on the surface when machining nickel alloys. In order to determine their influence on the final mechanical behaviour of the component residual stress stability should be considered. In the present work the evolution of residual stresses induced by machining in Inconel 718 under static loading at room temperature has been studied. An Inconel 718 disc has been face turned and specimens for tensile tests have been extracted from the disc. Then surface residual stresses have been measured by X-ray diffraction for initial state and different loading levels. Finally, a finite element model has been fitted to experimental results and the study has been extended for more loading conditions. For the studied case, it has been observed that tensile residual stresses remain stable when applying elastic loads but they increase at higher loads close to the yield stress of the material

New iterative method to obtain the softening curve in concrete.

Abstract An original procedure to determine the softening curve in concrete has been proposed by the authors. This inverse method combines experimental results, finite element simulations and an iterative algorithm to adjust the experimental data. The end product of the process is a softening curve that allows us to very accurately reproduce the experimental curves. The proposed method calculates the fracture energy from the cohesive softening curve model, which in turn is iteratively determined by adjusting experimental load-displacement data of three-point bending tests. The procedure has been successfully applied to two conventional concretes

Representative Stress-Strain Curve by Spherical Indentation on Elastic-Plastic Materials

Tensile stress-strain curve of metallic materials can be determined by the representative stress-strain curve from the spherical indentation. Tabor empirically determined the stress constraint factor (stress CF), ψ, and strain constraint factor (strain CF), β, but the choice of value for ψ and β is still under discussion. In this study, a new insight into the relationship between constraint factors of stress and strain is analytically described based on the formation of Tabor’s equation. Experiment tests were performed to evaluate these constraint factors. From the results, representative stress-strain curves using a proposed strain constraint factor can fit better with nominal stress-strain curve than those using Tabor’s constraint factors

¿Dónde está el tronco coronario izquierdo?

La incidencia de anomalías coronarias es baja en la población general, oscilando entre el 0.46-1.55%, y la agenesia de tronco coronario izquierdo (TCI) es una de las menos observadas1, 2. Se trata de una entidad extremadamente rara en la que no existe el ostium coronario izquierdo y el TCI termina ciegamente3. De los casos publicados, el 50% afectan a la edad pediátrica, y entre ellos, el 30% se asocia a otras anomalías coronarias4. Puede aparecer aisladamente, como en los pacientes que aquí mostramos, o asociada a otras enfermedades, como la homocistinuria, la ataxia de Friedreich, el síndrome de Hurler, la progeria y el síndrome rubeólico5. Se presentan 2 casos clínicos representativos de esta enfermedad de baja prevalencia en la población general. El primer caso se trata de un varón de 59 años con hipercolesterolemia y extabaquismo como factores de riesgo cardiovascular. Es derivado a nuestro centro para la realización de una coronariografía por angina de esfuerzo, con ergometría clínicamente negativa y eléctricamente positiva con descenso del segmento ST de 2mm en el tercer estadio del protocolo de Bruce. El cateterismo muestra una agenesia del TCI con visualización de un vaso hipoplásico submilimétrico. La arteria descendente anterior se visualiza a través de la arteria coronaria anómala, que nace de la rama marginal aguda precoz desde el segmento proximal de la coronaria derecha (CD). El trayecto anómalo presenta efecto kinking y compresión sistólica. La circunfleja se visualiza a través de la arteria conal, con salida independiente en cañón de escopeta ligeramente craneal al ostium de la CD, con trayecto anómalo y efecto kinking sin evidente efecto milking. La CD es dominante, de gran calibre y sin estenosis angiográficamente significativas..

Thermo-Mechanical Treatment Effects on Stress Relaxation and Hydrogen Embrittlement of Cold-Drawn Eutectoid Steels

The effects of the temperature and stretching levels used in the stress-relieving treatment of cold-drawn eutectoid steel wires are evaluated with the aim of improving the stress relaxation behavior and the resistance to hydrogen embrittlement. Five industrial treatments are studied, combining three temperatures (330, 400, and 460 °C) and three stretching levels (38, 50 and 64% of the rupture load). The change of the residual stress produced by the treatments is taken into consideration to account for the results. Surface residual stresses allow us to explain the time to failure in standard hydrogen embrittlement test