Análisis de daño y estudio de tensiones residuales en componentes mecánicos

Conferencia invitadaUnderstanding the effect of residual stresses in critical for the structural integrity of railway and other mechanical components [1–3]. The most important methods for residual stress measurements are introduced, together with their main advantages and disadvantages [4]. Neutron and synchrotron strain measurements performed in European Synchrotron Radiation Facility (France) [5], Institut Laue Langevin (France) [1], Diamond Light Source (UK) [6,7] and ISIS Neutron and Muon Source (UK) are described. They allow the in-plane components of the stress tensor acting in cross-sectional rail slices to be mapped [8–10]. Alternative techniques such as laboratory X-rays and magnetic measurement systems MAPS are also depicted, showing coarser detail but similar trends than previous methods. Stress balancing appears to be worst in zones where significant plastic deformation takes place [11,12]. In addition, the measurements are complemented with contour method analysis to map the longitudinal stress components. REFERENCES [1] J.F. Kelleher, Residual Stress in Railway Rails, PhD thesis, University of Manchester, School of Materials, 2006. [2] B. Moreno, A. Martin, P. Lopez-Crespo, J. Zapatero, J. Dominguez, Estimations of fatigue life and variability under random loading in aluminum Al-2024T351 using strip yield models from NASGRO, International Journal of Fatigue. 91 (2016) 414–422. [3] C.A. Simpson, S. Kozuki, P. Lopez-Crespo, M. Mostafavi, T. Connolley, P.J. Withers, Quantifying fatigue overload retardation mechanisms by energy dispersive X-ray diffraction, Journal of the Mechanics and Physics of Solids. 124 (2019) 392–410. [4] P.J. Withers, H.K.D.H. Bhadeshia, Residual stress. Part 1 - Measurement techniques, Materials Science and Technology. 17 (2001) 355–365.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Departamento de Ingeniería Civil, de Materiales y Fabricació

Difracción de rayos X y difracción de neutrones en estudios de fatiga y fractura de materiales

Conferencia invitada de Joseph F KelleherThe fatigue behaviour of polycrystalline metals is often studied through crack propagation analysis [1,2]. Nevertheless, understanding the mechanical processes that take place right at the crack tip [3,4] would also involve considering the deformation developing at the plastic zone and the contact between the crack faces over a portion of the loading cycle [5–7]. Paris law or newer models such as Forman equation are commonly used to interpret growth data [8], but cannot be used to generalise for complex loading scenarios, such as multiaxial loads [9–11] or variable amplitude loads [2]. Diffraction methods are a powerful tool to characterise crack tip strains and stresses [12]. The basics principles of neutron and synchrotron diffraction for measuring bulk properties are discussed [13,14], with special emphasis on grain size effects [15,16], transition between plane stress and plain strain conditions [17], measurement of the plastic zone and development of shielding effects at the crack tip [18]. REFERENCES [1] P. Lopez-Crespo, P.J. Withers, F. Yusof, H. Dai, A. Steuwer, J.F. Kelleher, T. Buslaps, Overload effects on fatigue crack-tip fields under plane stress conditions: surface and bulk analysis, Fatigue and Fracture of Engineering Materials and Structures. 36 (2013) 75–84. [2] B. Moreno, A. Martin, P. Lopez-Crespo, J. Zapatero, J. Dominguez, Estimations of fatigue life and variability under random loading in aluminum Al-2024T351 using strip yield models from NASGRO, International Journal of Fatigue. 91 (2016) 414–422. [3] C. Bathias, Retrospective view on the role of the plastic zone at a fatigue crack tip, Fatigue and Fracture of Engineering Materials and Structures. 19 (1996) 1301–1306. [4] P. Lopez-Crespo, D. Camas, F. V Antunes, J.R. Yates, A study of the evolution of crack tip plasticity along a crack front, Theoretical and Applied Fracture Mechanics. 98 (2018) 59–66.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Departamento de Ingeniería Civil, de Materiales y Fabricació

Programmable Control of Nucleation for Algorithmic Self-Assembly

Algorithmic self-assembly, a generalization of crystal growth processes, has been proposed as a mechanism for autonomous DNA computation and for bottom-up fabrication of complex nanostructures. A `program' for growing a desired structure consists of a set of molecular `tiles' designed to have specific binding interactions. A key challenge to making algorithmic self-assembly practical is designing tile set programs that make assembly robust to errors that occur during initiation and growth. One method for the controlled initiation of assembly, often seen in biology, is the use of a seed or catalyst molecule that reduces an otherwise large kinetic barrier to nucleation. Here we show how to program algorithmic self-assembly similarly, such that seeded assembly proceeds quickly but there is an arbitrarily large kinetic barrier to unseeded growth. We demonstrate this technique by introducing a family of tile sets for which we rigorously prove that, under the right physical conditions, linearly increasing the size of the tile set exponentially reduces the rate of spurious nucleation. Simulations of these `zig-zag' tile sets suggest that under plausible experimental conditions, it is possible to grow large seeded crystals in just a few hours such that less than 1 percent of crystals are spuriously nucleated. Simulation results also suggest that zig-zag tile sets could be used for detection of single DNA strands. Together with prior work showing that tile sets can be made robust to errors during properly initiated growth, this work demonstrates that growth of objects via algorithmic self-assembly can proceed both efficiently and with an arbitrarily low error rate, even in a model where local growth rules are probabilistic.Comment: 37 pages, 14 figure

Scale-invariance in gravity and implications for the cosmological constant

Recently a scale invariant theory of gravity was constructed by imposing a conformal symmetry on general relativity. The imposition of this symmetry changed the configuration space from superspace - the space of all Riemannian 3-metrics modulo diffeomorphisms - to conformal superspace - the space of all Riemannian 3-metrics modulo diffeomorphisms and conformal transformations. However, despite numerous attractive features, the theory suffers from at least one major problem: the volume of the universe is no longer a dynamical variable. In attempting to resolve this problem a new theory is found which has several surprising and atractive features from both quantisation and cosmological perspectives. Furthermore, it is an extremely restrictive theory and thus may provide testable predictions quickly and easily. One particularly interesting feature of the theory is the resolution of the cosmological constant problem.Comment: Replaced with final version: minor changes to text; references adde

Energy-resolved neutron imaging for reconstruction of strain introduced by cold working

Energy-resolved neutron transmission imaging is used to reconstruct maps of residual strains in drilled and cold-expanded holes in 5-mm and 6.4-mm-thick aluminum plates. The possibility of measuring the positions of Bragg edges in the transmission spectrum in each 55 × 55 µm2 pixel is utilized in the reconstruction of the strain distribution within the entire imaged area of the sample, all from a single measurement. Although the reconstructed strain is averaged through the sample thickness, this technique reveals strain asymmetries within the sample and thus provides information complementary to other well-established non-destructive testing methods

Is there a link between overactive bladder and the metabolic syndrome in women? : A systematic review of observational studies

This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.To conduct a systematic review to determine whether there is an association between metabolic syndrome (MetS) and lower urinary tract symptoms (LUTS) or overactive bladder (OAB) in women. We systematically reviewed English language observational studies on the effect of MetS (or component factors) on the presence of OAB or LUTS in women. We searched PubMed, Web of Science and The Cochrane Library with no date restrictions, checked reference lists and undertook citation searches in PubMed and Google Scholar. Studies were assessed for risk of bias. Because of heterogeneity, results were not pooled, but are reported narrativelyPeer reviewe

Experimental and numerical investigation of residual stress effects on fatigue crack growth behaviour of S355 steel weldments

Fatigue crack growth tests have been conducted on S355 G10+M structural steel which is widely used in the fabrication of offshore structures. Fracture mechanics tests have been performed on compact tension specimens with the crack tip located in the heat affected zone. All tests were performed at room temperature in air and the obtained results are compared with the literature data available on a range of offshore structural steels and also the recommended BS7910 trends using the 2-stage law and simplified law. The specimen orientation, with respect to the location of the extraction within the welded plate, has also been examined and discussed in this work. Residual stress measurements have been performed prior to testing by using the neutron diffraction technique. Finally, a numerical model has been developed in order to calculate the effective stress intensity factor range in the presence of residual stresses. The results have shown that the residual stresses play a key role in the fatigue life of the welded structures, especially in the near threshold regio