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

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

El aumento de la fragilidad con el tamaño en estructuras de hormigón

The cohesive crack model and the equivalent crack are summarized. These models allow quantitative predictions in concrete structures of the increase in brittleness as size increases; the well known size effect. In the second part, two applications of the cohesive crack model are briefly described; one for plain concrete and the other related to beams with minimum reinforcement.En este artículo se comentan dos métodos utilizados para modelizar el proceso de fractura del hormigón; el modelo de la fisura cohesiva y el de la fisura equivalente. A partir de estos modelos se puede predecir cuantitativamente el aumento de la fragilidad de un elemento estructural al aumentar su tamaño, fenómeno conocido como efecto del tamaño. En la segunda parte se muestran dos aplicaciones de la Mecánica de la Fractura al hormigón; una para el hormigón en masa y otra para vigas débilmente armadas

Brittle or Quasi-Brittle Fracture of Engineering Materials: Recent Developments and New Challenges

1 Department of Management and Engineering, University of Padova, Stradella San Nicola 3, 36100 Vicenza, Italy 2 Departamento de Ciencia de Materiales, Universidad Politecnica de Madrid, E. T. S. de Ingenieros de Caminos Canales y Puertos C/ Profesor Aranguren s/n, 28040 Madrid, Spain 3 Fatigue and Fracture Research Laboratory, Center of Excellence in Experimental Solid Mechanics and Dynamics, School of Mechanical Engineering, Iran University of Science and Technology, Narmak, Tehran 16846, Iran 4Department of Mechanical Engineering & Aeronautics, Institute of Strength Physics and Material Science, Siberian Branch of Russian Academy of Sciences, Tomsk 634021, Russia 5 Laboratory of Technology & Strength of Materials (LTSM), Department of Mechanical Engineering & Aeronautics, University of Patras, 26500 Patras, Greec

Failure analysis of prestressed anchor bars

Three broken steel bars from a sewed crack in a dam are reported. The inspection of the fracture surfaces of the prestressed bars suggests that fractures were triggered by small cracks and by the inherent brittleness of the bars, as fracture toughness was about 40 MPa m1/2. The analysis of the failures shows that the usual design requirements for prestressing bars fail to warn against brittle failures if some damage exists. Some recommendations, based on the concept of damage tolerance, are suggested to avoid similar unfortunate incidents

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

Emergence of supercontraction in regenerated silkworm (Bombyx mori) silk fibers

The conditions required for the emergence of supercontraction in regenerated silkworm (Bombyx mori) silk fibers are assessed through an experimental approach that combines the spinning of regenerated fibers with controlled properties and their characterization by 13C solid-state nuclear magnetic resonance (NMR). Both supercontracting and non-supercontracting regenerated fibers are produced using the straining flow spinning (SFS) technique from 13C labeled cocoons. The short-range microstructure of the fibers is assessed through 13C CP/MAS in air and 13C DD/MAS in water, and the main microstructural features are identified and quantified. The mechanical properties of the regenerated fibers and their microstructures are compared with those of natural silkworm silk. The combined analysis highlights two possible key elements as responsible for the emergence of supercontraction: (1) the existence of an upper and a lower limit of the amorphous phase compatible with supercontraction, and (2) the existence of two ordered phases, β-sheet A and B, which correspond to different packing arrangements of the protein chains.Ministerio de Economía y Competitividad MAT2016-75544- C2-1-RMinisterio de Economía y Competitividad MAT2016-79832-RMinisterio de Economía y Competitividad DPI2016-78887-C3-1-RConsejería de Educación Comunidad de Madrid NEUROCENTRO-B2017/BMD-3760Ministerio de Educación, Ciencia y Cultura JP26248050Ministerio de Economía y Competitividad DPI2016-78887-C3-1-

Emergence of supercontraction in regenerated silkworm (Bombyx mori) silk fibers

The conditions required for the emergence of supercontraction in regenerated silkworm (Bombyx mori) silk fibers are assessed through an experimental approach that combines the spinning of regenerated fibers with controlled properties and their characterization by 13 C solid-state nuclear magnetic resonance (NMR). Both supercontracting and non-supercontracting regenerated fibers are produced using the straining flow spinning (SFS) technique from 13 C labeled cocoons. The short-range microstructure of the fibers is assessed through 13 C CP/MAS in air and 13 C DD/MAS in water, and the main microstructural features are identified and quantified. The mechanical properties of the regenerated fibers and their microstructures are compared with those of natural silkworm silk. The combined analysis highlights two possible key elements as responsible for the emergence of supercontraction: (1) the existence of an upper and a lower limit of the amorphous phase compatible with supercontraction, and (2) the existence of two ordered phases, ß-sheet A and B, which correspond to different packing arrangements of the protein chains

Straining Flow Spinning of Artificial Silk Fibers: A Review

This work summarizes the main principles and some of the most significant results of straining flow spinning (SFS), a technology developed originally by the authors of this work. The principles on which the technology is based, inspired by the natural spinning system of silkworms and spiders, are presented, as well as some of the main achievements of the technique. Among these achievements, spinning under environmentally friendly conditions, obtaining high-performance fibers, and imparting the fibers with emerging properties such as supercontraction are discussed. Consequently, SFS appears as an efficient process that may represent one of the first realizations of a biomimetic technology with a significant impact at the production level.Ministerio de Economía y Competitividad MAT2016-75544-C2-1-RMinisterio de Economía y Competitividad MAT2016-79832-RMinisterio de Economía y Competitividad CPI2016-78887-C3-1-RComunidad de Madrid NEUROCENTRO-B2017Comunidad de Madrid BMD-376