Camacho-Navarro, J.; Ruiz, M.; Villamizar, R.; Mujica, L.E.; Pérez, O. Key engineering materials Vol. 713, p. 107-110 DOI: 10.4028/www.scientific.net/KEM.713.107 Data de publicació: 2016-09-30 Article en revista
Pipe leaks detection has a great economic, environmental and safety impact. Although several methods have been developed to solve the leak detection problem, some drawbacks such as continuous monitoring and robustness should be addressed yet. Thus, this paper presents the main results of using a leaks detection and classification methodology, which takes advantage of piezodiagnostics principle. It consists of: i) transmitting/sensing guided waves along the pipe surface by means of piezoelectric device ii) representing statistically the cross-correlated piezoelectric measurements by using Principal Component Analysis iii) identifying leaks by using error indexes computed from a statistical baseline model and iv) verifying the performance of the methodology by using a Self Organizing Map as visualization tool and considering different leak scenario. In this sense, the methodology was experimentally evaluated in a carbon-steel pipe loop under different leaks scenarios, with several sizes and locations. In addition, the sensitivity of the methodology to temperature, humidity and pressure variations was experimentally validated. Therefore, the effectiveness of the methodology to detect and classify pipe leaks, under varying environmental and operational conditions, was demonstrated. As a result, the combination of piezodiagnostics approach, cross-correlation analysis, principal component analysis, and Self Organizing Maps, become as promising solution in the field of structural health monitoring and specifically to achieve robust solution for pipe leak detection.
Quiroga , J.; Quiroga, J.; Mujica, L.E.; Villamizar, R.; Ruiz, M. Key engineering materials Vol. 713, p. 288-292 DOI: 10.4028/www.scientific.net/KEM.713.288 Data de publicació: 2016-09-30 Article en revista
In this paper, a guided wave temperature robust PCA-based stress monitoring
methodology is proposed. It is based on the analysis of the longitudinal guided wave propagating
along the path under stress. Slight changes in the wave are detected by means of PCA via statistical
T2 and Q indices. Experimental and numerical simulations of the guided wave propagating in
material under different temperatures have shown significant variations in the amplitude and the
velocity of the wave. This condition can jeopardize the discrimination of the different stress
scenarios detected by the PCA indices. Thus, it is proposed a methodology based on an extended
knowledge base, composed by a PCA statistical model for different discrete temperatures to
produce a robust classification of stress states under variable environmental conditions.
Experimental results have shown a good agreement between the predicted scenarios and the real
Quiroga, J.; Quiroga , J.; Mujica, L.E.; Villamizar, R.; Ruiz, M. Key engineering materials Vol. 713, p. 329-333 DOI: 10.4028/www.scientific.net/KEM.713.329 Data de publicació: 2016-09-30 Article en revista
In this investigation, a flow rate estimation guided wave based scheme in pipes is
proposed. The effect of the fluid over the propagation of longitudinal waves has been
experimentally studied by using several laminar flows of water transported by a steel pipe. Results
have shown a decrease of the guided wave pattern repeatability and the signal energy as the flow
rate increase as a result of the energy leakage from the pipe to the fluid. A Matlab® script is used to
excite the PZT actuator via picoscope 2208 of Picotech®, the captured signal is acquired also by the
picoscope and the data is processed in Matlab. The test bench utilized is composed by a 1” sch 40
A-106 pipe, a needle valve and a centrifugal pump provides the flow energy. A couple of PZTs are
used in a picth-catch configuration to produce and capture the longitudinal waves along the cross
section of the pipe.
Nowadays, the model order reduction techniques have become an intensive research eld because of the increasing interest in the computational modeling of complex phenomena in multi-physic problems, and its conse- quent increment in high-computing demanding processes; it is well known that the availability of high-performance computing capacity is, in most of cases limited, therefore, the model order reduction becomes a novelty tool to overcome this paradigm, that represents an immediately challenge in our research community. In computational multiscale modeling for instance, in order to study the interaction between components, a di erent numerical model has to be solved in each scale, this feature increases radically the computational cost. We present a reduced model based on a multi-scale framework for numerical modeling of the structural failure of heterogeneous quasi-brittle materials using the Strong Discontinuity Approach (CSD). The model is assessed by application to cementitious materials. The Proper Orthogonal Decomposition (POD) and the Reduced Order Integration Cubature are the pro- posed techniques to develop the reduced model, these two techniques work together to reduce both, the complexity and computational time of the high-delity model, in our case the FE2 standard model
This paper presents a FE2 multi-scale framework for numerical modeling of the structural failure of heterogeneous quasi-brittle materials. The model is assessed by application to cementitious materials. Using the Continuum Strong Discontinuity Approach (CSD), innovative numerical tools, such as strain injection and crack path field techniques, provide a robust, and mesh-size, mesh-bias and RVE-size objective, procedure to model crack onset and propagation at the macro-scale.
The strengthening mechanisms which are operative in bainite are very
bainite packet, small width of the laths, dislocation density and size and number of carbide particles
C), among others. Bainite packet size has been traditionally c
onsidered as the value measured
by optical microscopy (OM), as electron back scattered diffraction (EBSD) technique is relatively
recent. In a V
microalloyed steel with bainitic microstructure of C=0.38%
V=0.12% and N=
0.0214% the average length and width
of ferrite laths and of cementite carbides were measured. On
the other hand, the bainite packet size was measured by OM and EBSD with a
These values of the microstructural units have been taken in account to calculate the effective
given by Griffith’s model for cleavage fracture. It was concluded that bainite
packet size determined by EBSD with a misorientation angle crit
of 15º was the
microstructural parameter that controls cleavage crack propagation. Given
the relationship between
the average unit crack path (UCP) and the bainite packet size, it was concluded that the
surface energy of cleavage fracture (
would be between 71.6 and 82.6 J m
Minguella-Canela, J.; Villegas, M.; Poll, B.; Tena, G.; Calero, J.; Ginebra, M.P.; Korkusuz, F. Key engineering materials Vol. 631, p. 269-274 DOI: 10.4028/www.scientific.net/KEM.631.269 Data de publicació: 2014-08-07 Article en revista
The development of open source 3D printers and the continuously growing utilization of ceramic compounds in the field of medicine among others, meet in the possibility to adapt these machines in a way to permit better controlling, high resolution, automatic, printing of scaffolds, spacers and other 3D parts not possible without this kind of machines and technology. Due to the large number of applications inside the field of medicine it is required a high capacity to create structures that can reach the needs in each case. Furthermore, the possibility to modify easily and quickly these structures as the tests are being done is also very interesting for investigation. These machines allow, thanks to its open source nature, these features and more as they are not closed to changes in order to meet the needs of its users. Therefore, the focus of the present work has been to materialize and improve a head extruder for Advanced Technical Ceramics Compounds. The tests undertaken and the results outcome demonstrate the feasibility of the technology for being applied in such mentioned cases as well as the improvement on the solutions (initial and improvements) for producing automatic casting.
Baino, F.; Tallia, F.; Novajra, G.; Minguella-Canela, J.; Montealegre, M.; Korkusuz, F.; Vitale-Brovarone, C. Key engineering materials Vol. 631, p. 236-240 DOI: 10.4028/www.scientific.net/KEM.631.236 Data de publicació: 2014-07-28 Article en revista
Over the last two decades, the philosophy behind an optimal fixation of orthopaedic implants progressively evolved towards “bone-conservative” solutions and, accordingly, the researchers’ attention moved from simple mechanical fixation of the prosthesis to host bone by using screws or acrylic cement to new strategies based on a physico-chemical bond (surface modification) in order to minimize bone resection/loss and maximize tissue-implant integration. This research work explores the feasibility of a novel bioceramic single-piece acetabular cup for hip joint prosthesis that can be anchored to the patient’s pelvic bone by means of a bone-like trabecular coating (scaffold) able to promote implant osteointegration.
Dumitru, F.D; Ghiban, B.; Cabrera, J.; Higuera, O.; Gurau, G.; Ghiban, N. Key engineering materials Vol. 583, p. 32-35 DOI: 10.4028/www.scientific.net/KEM.583.32 Data de publicació: 2014 Article en revista
Being the lightest structural element, magnesium a
nd its alloys has attracted significant
interest in the last years, but because of its hexa
gonal close packed structure, magnesium presents
relatively low strength and ductility. One of the m
ethods to improve the mechanical properties of
the processed materials is through Severe Plastic D
eformation (SPD). ZK60 magnesium alloy
samples were subjected to 4 passes of equal-channel
angular pressing (ECAP) at a processing
temperature of 250°C, following route A. The micros
tructure was determined with an Olympus
BX51 optical microscope. Differential Scanning Calo
rimetry (DSC) was used to estimate the stored
energy and the recrystallization temperature after
each ECAP pass
The paper presents an experimental research on the use of Textile Reinforced Mortar (TRM) for the strengthening of brick load bearing masonry walls subjected to eccentric loading. Particular attention is given to the case of slender walls and to the ability of TRM reinforcement to enhance the response of such walls against buckling failure. The research has allowed the study of the influence of different mortar and fibre grid types and the possible benefit of using anchors to improve the connection between the walls and the external reinforcement. The experimental campaign has consisted of twelve tests on full scale wall specimens using a specific testing device designed to create a hinged boundary condition at the top and bottom wall ends. It has been observed that TRM reinforcement provides a significant increase of over 100% of the initial load bearing capacity under eccentric axial load. Moreover, a stiffer and more homogeneous behavior is noticed when TRM is applied. A simplified analytical method to calculate the ultimate axial-bending combination for TRM strengthened brick masonry walls, in agreement with the experiments, is also presented.
This work presents a method of strengthening concrete structures based on textiles of high strength and mortars. The combination of textiles and mortars produces a new composite material with cementitious matrix. This material can be used for the reinforcement of concrete beams under bending loads. We tested several combinations of fibers: glass, Poliparafenil Benzobisoxazol (PBO), steel and carbon fibers with mortar and we used them to reinforce precast concrete beams. All the specimens were tested with a four-point load test. We discuss the performance of the specimens and we compare the ultimate results with the formulae from FRP codes.
The structure of many historical buildings relies on unreinforced masonry load-bearing walls. In the case of large slenderness or significant eccentricity of the vertical compressive loads the mechanism formation failure mode is likely. Considering the second order bending effects and the tensile strength of the masonry is essential to accurately calculate the load-bearing capacity of these structures, which is required for maintenance tasks. An analytical methodology has proposed with this aim. This original method, the Southwell plot method and the formulations from two standard codes (ACI-530 and Eurocode-6) are applied to calculate the resistance of 18 experimentally tested walls to conclude that the proposed methodology brings correct results, the standards are conservative and the Southwell plot method is the most suitable for the analysis of the considered cases but it is not always applicable.
Gharibnezhad, F.; Mujica, L.E.; Rodellar, J.; Fritzen, C.P Key engineering materials Vol. 569-570, p. 916-923 DOI: 10.4028/www.scientific.net/KEM.569-570.916 Data de publicació: 2013-07-08 Article en revista
Principal Component Analysis (PCA) and Wavelet Transform (WT) are two well-known signal processing tools that are widely used indifferent fields. PCA plays a vital role in statistical analysis as a dimensional reduction tool. Besides, WT has proven its ability to overcome many of the limitation of the others among various time-frequency analyzers. The present work attempts to use the properties and advantages of both methodologies together in damage detection. To achieve this aim, PCA is applied on ridges of wavelet transform of measured signals from the structure. The results show that the proposed combination improves the accuracy of detection comparing with PCA damage detection based on original data captured from sensors. According to the result, when PCA uses the ridges of transformed data, the identifications of damages are more clear and accurate. This work involves experiments with an aluminum beam using piezoelectric transducers as sensors and actuators. Damages are introduced into the structure as a cut in several steps enlarging the depth of cut.
Zugasti, E.; Mujica, L.E.; Anduaga, J.; Martinez, F. Key engineering materials Vol. 569-570, p. 620-627 DOI: 10.4028/www.scientific.net/KEM.569-570.620 Data de publicació: 2013-07-08 Article en revista
Damage Detection problem in Structural Health Monitoring (SHM) is widely studied by many researchers, therefore lots of damage detection algorithms can be found in the literature. Feature Selection / Extraction methods are essential in the accuracy of these algorithms, they provide the suitable data to be used. The main goal of this work is to improve the input data to be the most representative for the damage detection problem. This is done using different Feature Selection / Extraction methods (PCA, UmRMR, and a combination of both). After taking the representative features, the results are tested using a damage detection method; the NullSpace in this case. The data has been collected from a Laboratory Offshore tower model. The different results are compared (different preprocessing vs Raw data) and these show how the correct preselection of the data can improve damage detection.
Avila-Haro, J.; Gonzalez-Drigo, J.R.; Vargas, Y.; Pujades, L.G.; Barbat, A. H. Key engineering materials Vol. 525-526, p. 537-540 DOI: 10.4028/www.scientific.net/KEM.525-526.537 Data de publicació: 2013-05-02 Article en revista
Barcelona, as well as a large number of cities in the Mediterranean basin, has a housing stock composed of a large number of unreinforced brick masonry buildings. Motivated by different factors, the enlargement of the city (Eixample in Catalan) was held from the second half of the 19th century and the beginning of the 20th, a period in which a large number of buildings of this type
were built, many of which are still used as dwellings. Although the buildings were built individually, some of them are linked to adjacent buildings by
the side walls. This feature leads to the analysis of the buildings as isolated structures and also as an aggregate. Barcelona is located in a seismic region of low to moderate hazard, with macroseismic intensity between the grades VI and VII of the European macroseismic scale EMS'98. Based on the
deterministic and probabilistic response spectra for the different types of soils present in Barcelona obtained in the work of Irizarry (2004), the seismic risk of four individual buildings and an aggregate is evaluated. The buildings are modeled and analyzed using the TREMURI program and MATLAB routines under the guidance of RISK-UE project.
FBGs are excellent strain sensors, because of its low size and multiplexing capability. Tens to hundred of sensors may be embedded into a structure, as it has already been demonstrated. Nevertheless, they only afford strain measurements at local points, so unless the damage affects the strain readings in a distinguishable manner, damage will go undetected. This paper show the experimental results obtained on the wing of a UAV, instrumented with 32 FBGs, before and after small damages were introduced. The PCA algorithm was able to distinguish the damage cases, even for small cracks. Principal Component Analysis (PCA) is a technique of multivariable analysis to reduce a complex data set to a lower dimension and reveal some hidden patterns that underlie.
FBGs are excellent strain sensors, because of its
low size and multiplexing capability.
Tens to hundred of sensors may be embedded into a s
tructure, as it has already been demonstrated.
Nevertheless, they only afford strain measurements
at local points, so unless the damage affects the
strain readings in a distinguishable manner, damage
will go undetected. This paper show the
experimental results obtained on the wing of a UAV,
instrumented with 32 FBGs, before and after
small damages were introduced. The PCA algorithm wa
s able to distinguish the damage cases, even
for small cracks. Principal Component Analysis (PCA
) is a technique of multivariable analysis to
reduce a complex data set to a lower dimension and
reveal some hidden patterns that underlie.
This paper is an exploratory study that aims to evaluate the prospects for the use of wood in residential construction in Brazil. For this purpose, a survey about the evolution of the stock of wooden houses was conducted. Social, environmental and economic indicators, which could interfere with the flow of Brazilian residential construction, were analyzed. The first results indicate that the stock of wooden houses has had a discrete growth (1.42%, from 1970 to 2009), but the percentage in the total number of houses has decreased (13.6%). Supply for housing demand has been provided by masonry. The population increase and the GDP demonstrated correlation with the building of houses and the changes in percentage between materials applied to it. Masonry is the construction technique preferred by the Brazilian. Most potential consumers (60.8%) declared that they could live in a wooden house. The aspects that would negatively influence the decision of living in a wooden house concerned market value, durability, fire and insect attack; and positively, was the material, construction process and patrimonial value. The image of a wooden house may be a greater problem than the material.
Nowadays, β type Ti-based alloys have been developed for load transfer clinical
applications due to their superelasticity, shape memory effect, low elastic modulus and high
damping capacity . These properties promote bone regeneration and make them promising
candidates for being used in load transfer implantology. The objective of the present work is to
achieve a material with shape memory properties and/or low elastic modulus. The influence of cold
work on the thermoelastic martensitic transformation and elastic modulus of the Ti-16.2Hf-24.8Nb-
1Zr alloy has been investigated to determine optimal conditions. The homogenized vacuum arc
melted button was heat treated at 1100ºC during 2 hours and quenched. Samples of each alloy were
microstructurally and mechanically characterized after being cold rolled from 5 up to 95%. The
elastic response for each condition was evaluated by instrumented nanoindentation by using a
Berkovich tip and a spherical tip. A decrease in elastic modulus was observed when increasing the
cold work percentage. The lowest value, 44 GPa, similar to that of cortical bone, was found in the
95% cold worked condition.
Del Valle, S.; Engel, E.; Braak, S.; Planell, J. A.; Ginebra, M.P. Key engineering materials Vol. 361-363, p. 1051-1054 DOI: 10.4028/www.scientific.net/KEM.361-363.1051 Data de publicació: 2008-01 Article en revista
In this work we examine the effect of the ionic exchange in cell behaviour of two apatite substrates with the same chemical composition but different microstructures (Coarse and Fine) by culturing cells with their extracts. A higher decrease in Ca and a higher increase in P concentrations were detected in the culture medium extracts from the finer apatite substrate in accordance with its higher specific surface area. A decrease in cell proliferation was observed when cells were cultured with the Fine extract in comparison with cells in contact with the Coarse extract or the control group. Although the higher ionic exchange, this could not explain the drastic decrease in cell proliferation observed on Fine apatite substrates, so a strong interaction with the underlying microstructure that modulates cell behaviour is also present.
Gaillard, Y.; Jimenez-Pique, E.; Bartsch, M.; Anglada, M. Key engineering materials Vol. 333, num. -, p. 277-280 DOI: 10.4028/www.scientific.net/KEM.333.277 Data de publicació: 2007-03 Article en revista
Engel, E.; Asin, L.; Delgado, J.; Aparicio, C.; Planell, J. A.; Ginebra, M.P. Key engineering materials Vol. 284-286, p. 117-120 DOI: 10.4028/www.scientific.net/KEM.284-286.117 Data de publicació: 2005-04 Article en revista