Publications by authors named "Ana María Camacho"

11 Publications

  • Page 1 of 1

Reliability Prediction of Acrylonitrile O-Ring for Nuclear Power Applications Based on Shore Hardness Measurements.

Polymers (Basel) 2021 Mar 19;13(6). Epub 2021 Mar 19.

Department of Manufacturing Engineering, Universidad Nacional de Educación a Distancia (UNED), 28040 Madrid, Spain.

The degradation of polymeric components is of considerable interest to the nuclear industry and its regulatory bodies. The objective of this work was the development of a methodology to determine the useful life-based on the storage temperature-of acrylonitrile O-rings used as mechanical sealing elements to prevent leakages in nuclear equipment. To this aim, a reliability-based approach that allows prediction of the use-suitability of different storage scenarios (that involve different storage times and temperatures) considering the further required in-service performance, is presented. Thus, experimental measurements of Shore A hardness have been correlated with storage variables (temperature and storage time). The storage (and its associated hardening) was proved to have a direct effect on in-service durability, reducing this by up to 60.40%. Based on this model, the in-service performance was predicted; after the first three years of operation the increase in probability of failure (POF) was practically insignificant. Nevertheless, from this point on, and especially, from 5 years of operation, the POF increased from 10% to 20% at approximately 6 years (for new and stored). From the study, it was verified that for any of the analysis scenarios, the limit established criterion was above that of the storage time premise considered in usual nuclear industry practices. The novelty of this work is that from a non-destructive test, like a Shore A hardness measurement, the useful life and reliability of O-rings can be estimated and be, accordingly, a decision tool that allows for improvement in the management of maintenance of safety-related equipment. Finally, it was proved that the storage strategies of our nuclear power plants are successful, perfectly meeting the expectations of suitability and functionality of the components when they are installed after storage.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/polym13060943DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8003519PMC
March 2021

Prediction of Mechanical Properties by Artificial Neural Networks to Characterize the Plastic Behavior of Aluminum Alloys.

Materials (Basel) 2020 Nov 19;13(22). Epub 2020 Nov 19.

Department of Manufacturing Engineering, Universidad Nacional de Educación a Distancia (UNED), Juan del Rosal 12, 28040 Madrid, Spain.

In metal forming, the plastic behavior of metallic alloys is directly related to their formability, and it has been traditionally characterized by simplified models of the flow curves, especially in the analysis by finite element simulation and analytical methods. Tools based on artificial neural networks have shown high potential for predicting the behavior and properties of industrial components. Aluminum alloys are among the most broadly used materials in challenging industries such as aerospace, automotive, or food packaging. In this study, a computer-aided tool is developed to predict two of the most useful mechanical properties of metallic materials to characterize the plastic behavior, yield strength and ultimate tensile strength. These prognostics are based on the alloy chemical composition, tempers, and Brinell hardness. In this study, a material database is employed to train an artificial neural network that is able to make predictions with a confidence greater than 95%. It is also shown that this methodology achieves a performance similar to that of empirical equations developed expressly for a specific material, but it provides greater generality since it can approximate the properties of any aluminum alloy. The methodology is based on the usage of artificial neural networks supported by a big data collection about the properties of thousands of commercial materials. Thus, the input data go above 2000 entries. When the relevant information has been collected and organized, an artificial neural network is defined, and after the training, the artificial intelligence is able to make predictions about the material properties with an average confidence greater than 95%.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/ma13225227DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7699297PMC
November 2020

Special Issue of the Manufacturing Engineering Society 2019 (SIMES-2019).

Materials (Basel) 2020 May 5;13(9). Epub 2020 May 5.

Department of Manufacturing Engineering, Industrial Engineering School, Universidad Nacional de Educación a Distancia (UNED), St/Juan del Rosal 12, E28040 Madrid, Spain.

The Special Issue of the Manufacturing Engineering Society 2019 (SIMES-2019) has been launched as a joint issue of the journals "Materials" and "Applied Sciences". The 29 contributions published in this Special Issue of Materials present cutting-edge advances in the field of manufacturing engineering focusing on additive manufacturing and 3D printing, advances and innovations in manufacturing processes, sustainable and green manufacturing, manufacturing of new materials, metrology and quality in manufacturing, industry 4.0, design, modeling, and simulation in manufacturing engineering and manufacturing engineering and society. Among them, these contributions highlight that the topic "additive manufacturing and 3D printing" has collected a large number of contributions in this journal because its huge potential has attracted the attention of numerous researchers over the last years.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/ma13092133DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7254364PMC
May 2020

Considerations on the Applicability of Test Methods for Mechanical Characterization of Materials Manufactured by FDM.

Materials (Basel) 2019 Dec 19;13(1). Epub 2019 Dec 19.

Department of Manufacturing Engineering, Universidad Nacional de Educación a Distancia (UNED), 28040 Madrid, Spain.

The lack of specific standards for characterization of materials manufactured by Fused Deposition Modelling (FDM) makes the assessment of the applicability of the test methods available and the analysis of their limitations necessary; depending on the definition of the most appropriate specimens on the kind of part we want to produce or the purpose of the data we want to obtain from the tests. In this work, the Spanish standard UNE 116005:2012 and international standard ASTM D638-14:2014 have been used to characterize mechanically FDM samples with solid infill considering two build orientations. Tests performed according to the specific standard for additive manufacturing UNE 116005:2012 present a much better repeatability than the ones according to the general test standard ASTM D638-14, which makes the standard UNE more appropriate for comparison of different materials. Orientation on-edge provides higher strength to the parts obtained by FDM, which is coherent with the arrangement of the filaments in each layer for each orientation. Comparison with non-solid specimens shows that the increase of strength due to the infill is not in the same proportion to the percentage of infill. The values of strain to break for the samples with solid infill presents a much higher deformation before fracture.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/ma13010028DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6981797PMC
December 2019

An Experimental and Numerical Analysis of the Compression of Bimetallic Cylinders.

Materials (Basel) 2019 Dec 7;12(24). Epub 2019 Dec 7.

Instituto de Engenharia Mecânica, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal.

This paper investigates the upsetting of bimetallic cylinders with an aluminum alloy center and a brass ring. The influence of the center-ring shape factor and type of assembly fit (interference and clearance), and the effect of friction on the compression force and ductile damage are comprehensively analyzed by means of a combined numerical-experimental approach. Results showed that the higher the shape factor, the lower the forces required, whereas the effect of friction is especially important for cylinders with the lowest shape factors. The type of assembly fit does not influence the compression force. The accumulated ductile damage in the compression of bimetallic cylinders is higher than in single-material cylinders, and the higher the shape factor, the lower the damage for the same amount of stroke. The highest values of damaged were found to occur at the middle plane, and typically in the ring. Results also showed that an interference fit was more favorable for preventing fracture of the ring than a clearance fit. Microstructural analysis by scanning electron microscopy revealed a good agreement with the finite element predicted distribution of ductile damage.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/ma12244094DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6947522PMC
December 2019

One-year rehospitalisations for congestive heart failure in Portuguese NHS hospitals: a multilevel approach on patterns of use and contributing factors.

BMJ Open 2019 09 3;9(9):e031346. Epub 2019 Sep 3.

Departamento de Políticas e Gestão dos Sistemas de Saúde, Escola Nacional de Saúde Pública, Universidade Nova de Lisboa, Lisboa, Portugal.

Objectives: Identification of rehospitalisations for heart failure and contributing factors flags health policy intervention opportunities designed to deliver care at a most effective and efficient level. Recognising that heart failure is a condition for which timely and appropriate outpatient care can potentially prevent the use of inpatient services, we aimed to determine to what extent comorbidities and material deprivation were predictive of 1 year heart failure specific rehospitalisation.

Setting: All Portuguese mainland National Health Service (NHS) hospitals.

Participants: A total of 68 565 hospitalisations for heart failure principal cause of admission, from 2011 to 2015, associated to 45 882 distinct patients aged 18 years old or over.

Outcome Measures: We defined 1 year specific heart failure rehospitalisation and time to rehospitalisation as outcome measures.

Results: Heart failure principal diagnosis admissions accounted for 1.6% of total hospital NHS budget, and over 40% of this burden is associated to patients rehospitalised at least once in the 365-day follow-up period. 22.1% of the patients hospitalised for a principal diagnosis of heart failure were rehospitalised for the same cause at least once within 365 days after previous discharge. Nearly 55% of rehospitalised patients were readmitted within 3 months. Results suggest a mediation effect between material deprivation and the chance of 1 year rehospitalisation through the effect that material deprivation has on the prevalence of comorbidities. Heart failure combined with chronic kidney disease or chronic obstructive pulmonary disease increases by 2.8 and 2.2 times, respectively, the chance of the patient becoming a frequent user of inpatient services for heart failure principal cause of admission.

Conclusions: One-fifth of patients admitted for heart failure are rehospitalised due to heart failure exacerbation. While the role of material deprivation remained unclear, comorbidities considered increased the chance of 1 year heart failure specific rehospitalisation, in particular, chronic kidney disease and chronic obstructive pulmonary disease.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1136/bmjopen-2019-031346DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6731885PMC
September 2019

Special Issue of the Manufacturing Engineering Society (MES).

Materials (Basel) 2018 Oct 31;11(11). Epub 2018 Oct 31.

Department of Manufacturing Engineering, Industrial Engineering School, Universidad Nacional de Educación a Distancia (UNED), St/Juan del Rosal 12, E28040 Madrid, Spain.

Research in the field of materials is very broad, ranging from studies on the structure and properties at the atomic or molecular level to the most complex or sophisticated applications that can be done with them, as well as studies about other aspects related to their processing, use or management. The Special Issue of the Manufacturing Engineering Society (MES), published in the Section "Manufacturing Processes and Systems" of the journal , focuses, mainly, on the applications and key processing aspects of materials, collecting a set of 48 original papers focused on the field of manufacturing engineering and materials processing.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/ma11112149DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6266078PMC
October 2018

Analysis of Favorable Process Conditions for the Manufacturing of Thin-Wall Pieces of Mild Steel Obtained by Wire and Arc Additive Manufacturing (WAAM).

Materials (Basel) 2018 Aug 16;11(8). Epub 2018 Aug 16.

Applied Materials Division, Argonne National Laboratory, 9700 Cass Ave, Lemont, IL 60439, USA.

One of the challenges in additive manufacturing (AM) of metallic materials is to obtain workpieces free of defects with excellent physical, mechanical, and metallurgical properties. In wire and arc additive manufacturing (WAAM) the influences of process conditions on thermal history, microstructure and resultant mechanical and surface properties of parts must be analyzed. In this work, 3D metallic parts of mild steel wire (American Welding Society-AWS ER70S-6) are built with a WAAM process by depositing layers of material on a substrate of a S235 JR steel sheet of 3 mm thickness under different process conditions, using as welding process the gas metal arc welding (GMAW) with cold metal transfer (CMT) technology, combined with a positioning system such as a computer numerical controlled (CNC) milling machine. Considering the hardness profiles, the estimated ultimate tensile strengths (UTS) derived from the hardness measurements and the microstructure findings, it can be concluded that the most favorable process conditions are the ones provided by CMT, with homogeneous hardness profiles, good mechanical strengths in accordance to conditions defined by standard, and without formation of a decohesionated external layer; CMT Continuous is the optimal option as the mechanical properties are better than single CMT.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/ma11081449DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6119905PMC
August 2018

The Influence of Manufacturing Parameters on the Mechanical Behaviour of PLA and ABS Pieces Manufactured by FDM: A Comparative Analysis.

Materials (Basel) 2018 Aug 1;11(8). Epub 2018 Aug 1.

Department of Manufacturing Engineering, Universidad Nacional de Educación a Distancia (UNED), Madrid 28040, Spain.

This paper presents a comparative study of the tensile mechanical behaviour of pieces produced using the Fused Deposition Modelling (FDM) additive manufacturing technique with respect to the two types of thermoplastic material most widely used in this technique: polylactide (PLA) and acrylonitrile butadiene styrene (ABS). The aim of this study is to compare the effect of layer height, infill density, and layer orientation on the mechanical performance of PLA and ABS test specimens. The variables under study here are tensile yield stress, tensile strength, nominal strain at break, and modulus of elasticity. The results obtained with ABS show a lower variability than those obtained with PLA. In general, the infill percentage is the manufacturing parameter of greatest influence on the results, although the effect is more noticeable in PLA than in ABS. The test specimens manufactured using PLA perform more rigidly and they are found to have greater tensile strength than ABS. The bond between layers in PLA turns out to be extremely strong and is, therefore, highly suitable for use in additive technologies. The methodology proposed is a reference of interest in studies involving the determination of mechanical properties of polymer materials manufactured using these technologies.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/ma11081333DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6119930PMC
August 2018

Determination of Actual Friction Factors in Metal Forming under Heavy Loaded Regimes Combining Experimental and Numerical Analysis.

Materials (Basel) 2016 Sep 1;9(9). Epub 2016 Sep 1.

Department of Manufacturing Engineering, Universidad Nacional de Educación a Distancia (UNED), Madrid 28040, Spain.

Tribological conditions can change drastically during heavy loaded regimes as experienced in metal forming; this is especially critical when lubrication can only be applied at the early stage of the process because the homogeneous lubricant layer can break along the die-workpiece interface. In these cases, adopting a constant friction factor for the lubricant-surface pair may not be a valid assumption. This paper presents a procedure based on the use of dual friction factor maps to determine friction factors employed in heavy loaded regimes. A finite element (FE) simulation is used to obtain the friction factor map for the alloy UNS A96082. Experiments were conducted using four lubricants (aluminum anti-size, MoS₂ grease, silicone oil, and copper paste) to determine the actual friction curves. The experimental procedure is based on the application of lubricant only at the beginning of the first stage of ring compression, and not at intermediate stages as is usual in typical ring compression tests (RCTs). The results show that for small reductions ( < 20%), the conventional RCT can be applied because the tribological conditions remain similar. For large reductions ( > 20%), it is recommended to obtain an average value of the friction factor for every lubricant-surface pair in the range of deformation considered.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/ma9090751DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5457090PMC
September 2016

Application of an instrumental and computational approach for improving the vibration behavior of structural panels using a lightweight multilayer composite.

Sensors (Basel) 2014 Mar 11;14(3):4960-80. Epub 2014 Mar 11.

Department of Construction and Manufacturing Engineering, Universidad Nacional de Educación a Distancia (UNED), C/Juan del Rosal 12, Madrid 28040, Spain.

This work presents a hybrid (experimental-computational) application for improving the vibration behavior of structural components using a lightweight multilayer composite. The vibration behavior of a flat steel plate has been improved by the gluing of a lightweight composite formed by a core of polyurethane foam and two paper mats placed on its faces. This composite enables the natural frequencies to be increased and the modal density of the plate to be reduced, moving about the natural frequencies of the plate out of excitation range, thereby improving the vibration behavior of the plate. A specific experimental model for measuring the Operating Deflection Shape (ODS) has been developed, which enables an evaluation of the goodness of the natural frequencies obtained with the computational model simulated by the finite element method (FEM). The model of composite + flat steel plate determined by FEM was used to conduct parametric study, and the most influential factors for 1st, 2nd and 3rd mode were identified using a multifactor analysis of variance (Multifactor-ANOVA). The presented results can be easily particularized for other cases, as it may be used in cycles of continuous improvement as well as in the product development at the material, piece, and complete-system levels.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/s140304960DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4003977PMC
March 2014