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Stress-intensity factor solutions for embedded elliptical cracks in round bars subjected to tensile load
Get PDFIn this paper, stress-intensity factor solutions are presented for an embedded elliptical crack in a round bar subjected to tensile load. The stress-intensity factors (SIF) are presented in a tabulated form and were obtained from three-dimensional finite-element analyses of this crack configuration. The solutions provide the stress-intensity factor as a function of three dimensionless parameters representative of the crack size, the crack aspect ratio of the elliptical flaw and its relative position in the cross section. The dimensionless parameters cover ranges that allow most internal flaw shapes in practice to be considered. In order to validate the numerical model developed, some particular cases are compared with solutions of embedded elliptical flaws in different geometries available in the literature. Afterwards, a sequential methodology for fatigue crack growth is presented, including the conditions for the recategorization from the internal elliptical crack to a semi-elliptical surface crack. A comparison of the predicted crack paths with experimental results of fatigue crack propagation initiated from internal defects in round bars is also presented. This experimental validation shows the capability of the proposed SIF solutions for the study of the fatigue crack propagation initiated from internal defects in this geometry.JCyL project reference BU-002-P20, co-financed with FEDER funds
Rotation Forest for multi-target regression
Get PDFThe prediction of multiple numeric outputs at the same time is called multi-target regression (MTR), and it has gained
attention during the last decades. This task is a challenging research topic in supervised learning because it poses additional
difficulties to traditional single-target regression (STR), and many real-world problems involve the prediction of multiple
targets at once. One of the most successful approaches to deal with MTR, although not the only one, consists in transforming
the problem in several STR problems, whose outputs will be combined building up the MTR output. In this paper, the
Rotation Forest ensemble method, previously proposed for single-label classification and single-target regression, is adapted
to MTR tasks and tested with several regressors and data sets. Our proposal rotates the input space in an efficient and novel
fashion, avoiding extra rotations forced by MTR problem decomposition. Four approaches for MTR are used: single-target
(ST), stacked-single target (SST), Ensembles of Regressor Chains (ERC), and Multi-target Regression via Quantization
(MRQ). For assessing the benefits of the proposal, a thorough experimentation with 28 MTR data sets and statistical tests
are used, concluding that Rotation Forest, adapted by means of these approaches, outperforms other popular ensembles,
such as Bagging and Random Forest.Ministerio de Economía y Competitividad of the Spanish Government under project TIN2015-67534-P (MINECO-FEDER, UE), by the Junta de Castilla y León under project BU085P17 (JCyL/FEDER, UE) (both projects co-financed through European Union FEDER funds), and by the Consejería de Educación of the Junta de Castilla y León and the European Social Fund with the EDU/1100/2017 pre-doctoral grant
La Universidad de Burgos a la Catedral de Burgos en su VIII Centenario
No full textLa Universidad de Burgos se ha sumado a la celebración del VIII Centenario de la Catedral de Burgos con esta monografía sobre la investigación, la gestión y la difusión que, desde nuestra institución y hasta la fecha, se ha hecho en torno a dicha basílica.
Así, se aúnan los testimonios científicos y/o personales de personal docente e investigador, de administración y servicios y de estudiantes y compendia la producción bibliográfica de quienes, a lo largo de la historia de la UBU, han contribuido al conocimiento de la seo. Todo ello es fruto de la participación voluntaria de quienes han querido contribuir a esta edición
A critical accounting project for Latin America? Objects of knowledge or ways of knowing
Get PDFThis article explores the basis of a critical accounting project in Latin America and suggests a
critique inspired by the decolonial project to reinvigorate critical accounting. The paper draws on
Santos’ (2009) sociology of absences to explore the epistemic assumptions present in interpretive
and critical accounting studies focusing on Latin America to achieve these aims. The analysis
reveals that the critical accounting studies analyzed often mobilize Anglo-Euro-Centric logics that
limit the ability of Latin America to think itself and impede the dialogue on equal terms between
contemporaries, as suggested by the decolonial project. The paper presents avenues for critical
accounting research in Latin America, assessing the effects of the Anglo-European institutionalization of modes of doing research for Latin America and calling for authenticity, more attention
to the existence of alternative ways of knowing in the global South and for the creation of protected spaces that care for those alternatives and grant an equal exchange of ideas.The Spanish Ministry of Science & Innovation provided financial support for this research (Grant RTI2018-099920-B-I00). A previous draft of this paper was presented at the Qualitative Research and Critical Accounting (QRCA) 2019 Conference, at an special issue webminar in September 2020 and at research seminars in Durham University Business School and ESSEC Business School. We are very grateful for the comments made by Yves Gendron, Giovanna Michelon, Daniel Martínez and Hector J. Sarmiento to previous drafts, two anonymous reviewers and the editors of this special issue. Of course, the views and remaining mistakes are obviously the authors’ exclusive responsibility. We are immensely indebted to Conny Beck for her encouragement to submit our manuscript to this special issue
Ring Hoop Tension Test for yield strength estimation: Numerical analysis for a novel correlation method and applicability for mechanical testing of tubes and pipes
Get PDFThe tubes and pipes manufacturing industry characterizes the mechanical properties of their products with a
wide selection of standards, but most of them are qualitative testing methodologies. To estimate the mechanical
properties from a quantitative point of view there are limited options in standards. In that sense, the standard
tensile test is the preferred alternative by the manufacturers, but this option limits the mechanical estimation
for the longitudinal direction of the tube–pipe product. Particular efforts have been made to design an
alternative mechanical testing procedure to characterize the mechanical properties in the hoop direction of
pipes and tubes. The Ring Hoop Tension Test (RHTT) was designed to fill this gap, but it shows limitations
related to the required tooling and the influence of the frictional contact between the tooling and the ring
specimen. In the nuclear industry, the Small Ring Test (SRT), a miniature test derivated from the RHTT, has
been investigated in recent years. In this investigation, a novel RHTT was designed to overcome the limitations
of SRT and RHTT, and a new procedure was implemented to estimate the yield strength of tubes and pipes.
Numerical FEM simulations were performed to reach an optimum estimation method for the yield strength with
the specific geometry of the SRT and a wide selection of pipe geometries with the RHTT. A set of hypothetical
materials were designed to perform these analyses, taking into account the influence of Young’s modulus,
proportional limit, hardening coefficient (based on the Ramberg–Osgood law), and presence of Lüders bands
straining. To verify the results obtained from this numerical FEM analysis, experimental tests (standard tensile
tests and RHTTs) and metallographic analysis were performed on aluminum Al 6063 T6 and copper C12200
R360 tubes, showing the capability of this optimized RHTT to estimate the yield strength in the hoop direction
for anisotropic tubes and pipes
Multiamperometric-SERS detection of melamine on gold screen-printed electrodes
Get PDFA new, simple and fast protocol to generate gold-based SERS substrates is presented in this work. Melamine is a
compound widely used in the industry that can be toxic for humans if consumed even in low concentrations.
EC-SERS is an excellent alternative to classical methods to detect and quantify this compound because Raman
spectroscopy provides a fingerprint of the molecules, providing very good sensitivity. In this work, timeresolved Raman spectroelectrochemistry is employed to generate a SERS substrate and to detect melamine,
all in a single experiment. The dynamic character of this technique provides valuable information about the
interaction of the molecule with the generated substrate. An optimization of the spectroelectrochemical
method based on a multi-pulse amperometric detection has been performed. The new protocol presented in
this work shows significant figures of merit in a very short experiment time, just 25 s.Authors acknowledge the financial support from Agencia Estatal de Investigación/Ministerio de Ciencia e Innovacion /10.13039/ 501100011033 (Grant PID2020-113154RB-C21) and Ministerio de Ciencia, Innovación y Universidades (Grant RED2018-102412-T). W. Ch. thanks JCyL for his postdoctoral fellowship (Grant BU297P18). S.H. and M.P-E. thank JCyL and European Social Fund for their predoctoral fellowships
Hammer rebound index as an overall-mechanical-quality indicator of self-compacting concrete containing recycled concrete aggregate
Get PDFThe hammer rebound index has traditionally been solely and exclusively used to estimate the compressive
strength of vibrated concrete. Its use has recently been extended to the prediction of the compressive strength of
Self-Compacting Concrete (SCC) and concrete produced with Recycled Concrete Aggregate (RCA). The conventional use of the hammer-rebound test is further developed in this paper, by demonstrating how it can be used
to estimate the overall mechanical behavior of SCC containing RCA. To do so, nine SCC mixes with different
contents and fractions (coarse, fine, and powder) of RCA are analyzed. Following a simple-linear-regression
validation and property standardization procedure, the hammer rebound index is then expressed as a linear
combination of four mechanical properties, adjusted through a multiple regression. The hammer rebound index
is therefore expressed as a weighting of both the mean value of compressive behavior (arithmetic mean of
compressive strength and modulus of elasticity) amounting to a weight of 72.8%, and the mean value of bendingtensile behavior (arithmetic mean of splitting tensile strength and flexural strength) amounting to a weight of
27.2%. The hammer rebound index can therefore be construed as an overall-mechanical-quality performance
indicator of the SCC containing RCA, which can also yield predictions of every mechanical property. In this way,
the application of the hammer rebound index could likewise be of use in rehabilitation, pathology, and healthmonitoring works where a full characterization of the mechanical performance of SCC with RCA is required,
facilitating the use of SCC with RCA in real structures.The authors wish to express their gratitude to the following government ministries, agencies, and universities for funding this research: the Spanish Ministry of Universities, MICIN, AEI, EU, ERDF and NextGenerationEU/ PRTR [PID2020-113837RB-I00; 10.13039/501100011033; TED2021- 129715B-I00; FPU17/03374; PRX21/00007]; the Junta de Castilla y León (Regional Government) and ERDF [UIC-231, BU119P17]; the University of Burgos [SUCONS, Y135.GI]; and, finally, the University of Padova