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Buildings consume a large amount of energy during all stages of their life cycle. One of the most efficient ways to reduce their consumption is to use thermal insulation materials; however, these generally have negative effects on the environment and human health. Bio-insulations are presented as a good alternative solution to this problem, thus motivating the study of the properties of natural or recycled materials that could reduce energy consumption in buildings. Fique is a very important crop in Colombia. In order to contribute to our knowledge of the properties of its fibers as a thermal insulator, the measurement of its thermal conductivity is reported herein, employing equipment designed according to the ASTM C 177 standard and a kinetic study of its thermal decomposition from thermogravimetric data through the Coats–Redfern model-fitting method.
Gabriel García Sánchez; Rolando Guzmán López; Roberto Gonzalez-Lezcano. Fique as a Sustainable Material and Thermal Insulation for Buildings: Study of Its Decomposition and Thermal Conductivity. Sustainability 2021, 13, 7484 .
AMA StyleGabriel García Sánchez, Rolando Guzmán López, Roberto Gonzalez-Lezcano. Fique as a Sustainable Material and Thermal Insulation for Buildings: Study of Its Decomposition and Thermal Conductivity. Sustainability. 2021; 13 (13):7484.
Chicago/Turabian StyleGabriel García Sánchez; Rolando Guzmán López; Roberto Gonzalez-Lezcano. 2021. "Fique as a Sustainable Material and Thermal Insulation for Buildings: Study of Its Decomposition and Thermal Conductivity." Sustainability 13, no. 13: 7484.
Gabriel Fernando García Sánchez; Rolando Guzmán Lopez; Adriana Restrepo-Osorio; Emil Hernandez Arroyo. Fique as thermal insulation morphologic and thermal characterization of fique fibers. Cogent Engineering 2019, 6, 1 .
AMA StyleGabriel Fernando García Sánchez, Rolando Guzmán Lopez, Adriana Restrepo-Osorio, Emil Hernandez Arroyo. Fique as thermal insulation morphologic and thermal characterization of fique fibers. Cogent Engineering. 2019; 6 (1):1.
Chicago/Turabian StyleGabriel Fernando García Sánchez; Rolando Guzmán Lopez; Adriana Restrepo-Osorio; Emil Hernandez Arroyo. 2019. "Fique as thermal insulation morphologic and thermal characterization of fique fibers." Cogent Engineering 6, no. 1: 1.
The present study will focus on superficial modification by alkalization of cellulose fibres obtained from Fique leaf as reinforcement in polymer matrices to produce a natural fiber composite that can be suitable for industrial purposes. Fique fiber is a hard vegetable fiber derived from a Colombian plant (Agave furcarea). An appropriate treatment, namely alkalization, of the fiber was chosen and carried out, but will be customized for this specific study to be more environmental-friendly and economical. A higher fiber-to-solution ratio as well as a low concentration would decrease the price of the treated fibers. The changes introduced to the surface morphology by the abovementioned treatment is then examined using a scanning electron microscope (SEM), Thermogravimetric analysis (TGA), Differential scanning calorimetry (DSC) and FTIR analysis, and untreated and treated samples were.
R E Guzmán; S Gómez; O Amelines; G M Aparicio. Superficial modification by alkalization of cellulose Fibres obtained from Fique leaf. IOP Conference Series: Materials Science and Engineering 2018, 437, 012015 .
AMA StyleR E Guzmán, S Gómez, O Amelines, G M Aparicio. Superficial modification by alkalization of cellulose Fibres obtained from Fique leaf. IOP Conference Series: Materials Science and Engineering. 2018; 437 (1):012015.
Chicago/Turabian StyleR E Guzmán; S Gómez; O Amelines; G M Aparicio. 2018. "Superficial modification by alkalization of cellulose Fibres obtained from Fique leaf." IOP Conference Series: Materials Science and Engineering 437, no. 1: 012015.
The procedures used to estimate structural modal parameters as natural frequency, damping ratios, and mode shapes are generally based on frequency methods. However, methods of time-frequency analysis are highly sensible to the parameters used to calculate the discrete Fourier transform: windowing, resolution, and preprocessing. Thus, the uncertainty of the modal parameters is increased if a proper parameter selection is not considered. In this work, the influence of three different time domain windows functions (Hanning, flat-top, and rectangular) used to estimate modal parameters are discussed in the framework of ISO 18431 standard. Experimental results are conducted over an AISI 1020 steel plate, which is excited by means of a hammer element. Vibration response is acquired by using acceleration records according to the ISO 7626-5 reference guides. The results are compared with a theoretical method and it is obtained that the flat-top window is the best function for experimental modal analysis.1. IntroductionPhysical behavior of complex engineering systems can be studied through prediction and simulation analysis by means of specialized software [1, 2]. Thus, it is possible to check abnormal performance with the help of monitoring methods based on simulation tools. In particular, the analysis of structural dynamics can be addressed by determining modal parameters defined by mode shapes, natural frequencies, and damping ratios. In this sense, by means of Operational Modal Analysis it is possible to conduct nondestructive testing, fatigue analysis, and issues concerned with field in structural analysis [3]. These tasks also involve updated finite element models used to predict the dynamic behavior of the structure reliability [4]. For instance, an application of modal analysis is the assessment of highway-bridge by dynamic testing and finite-element model updating [5]. Also, damage detection has been carried out in reinforced concrete beams by using modal flexibility residuals [6].Because of the importance of modal analysis in the field of structural analysis, well established procedures to obtain proper estimations of modal parameters are required. Although there exists a huge documentation about methods used for modal analysis [7, 8], their practical implementation is still difficult because there are many parameters involved in the procedure, which must be decided by engineers of different areas and knowledge. In this sense, the 7626 standard ISO specifies a guideline of methodological steps to conduct experiments in order to obtain the frequency response measurement and the 18431 ISO describes the procedures for time-frequency analysis of vibrational records. Thus, by considering the recommendations of the ISO standards, the further estimation of modal model parameters by means of well-known modal analysis methods (as, e.g., peak-picking or least squares among others) is facilitated.In this paper, a practical implementation of the abovementioned ISO standards with a special emphasis on computing the natural frequency values is demonstrated. Thus, the influence of using three domain window functions (Hanning, flat-top, and rectangular) to estimate natural frequencies is discussed. Experimental results are conducted over an AISI 1020 steel plate, which is excited by means of a hammer element.2. Theoretical FrameworkThe procedure used in this paper to estimate the natural frequencies of a modal model is based on the analysis of measurements from Frequency response functions (FRFs). In this sense, the extraction of relevant frequency information is performed by applying spectrum estimation techniques to structural vibrational records. Thus, FRFs are approximated by the cross-power spectral density (PSD) between the vibrational responses.In this section, the conceptual issues involved in the estimation of structural natural frequencies by means of FRFs are detailed. Also, fundamentals of methods used to estimate the frequency decomposition are presented, focusing on given details about the parameters with great influence for its implementation.2.1. Frequency Response Functions (FRFs)Dynamical model of structures is constructed on physical knowledge and fundamental laws of motion according to [9]where , , and are the stiffness, damping, and mass matrices, respectively. Likewise, and denote the forcing vector and displacement. Assuming that is a delta-correlated exciting force and using properties demonstrated in the Natural Excitation Technique (NExT), it is possible to write the law motion of (1) in the form of [9] where is a vector of correlation functions for all positive lags , between the displacement vector and a reference signal, which must be uncorrelated with respect to excitation signal. Thus, (2) establishes that correlation function between acceleration records and a reference signal can be treated as free vibration data, which allows determining modal characteristics of the structures.Moreover to law motion and NExT equations used in methodologies for modal parameter identification, the FRF relationship in structures must be specified. The FRF for one n-degree of freedom system represented by (1) or (2) can be written in the form of partial fractions as is expressed in (3) (classical pole/residue) [10, 11].where is the output PSD matrix, is the total number of modes of interest, is the pole of the mode, is the modal damping (constant decay), is the damped natural frequency, and the superscript denotes complex conjugate. The typical PSD curve for the FRF determined by (3) is depicted in Figure 1.Figure 1: Typical FRF of an -degree of freedom system.According to Figure 1, the modes located at the peak can be identified from spectral density through common signal processing as discrete Fourier transform.2.2. Frequency Domain Decomposition (FDD)Classical approach used to estimate modal parameters is often referred to as Peak-Peaking (PP), which is a nonparametric method essentially developed in frequency domain. The main advantages of this method are its user-friendliness, simple use, and fast results obtaining. In this method, average normalized power spectral densities and frequency response functions between all the measurement points of the structure are evaluated [12]. As a result, first the natural frequencies are simply taken from the observation of the peaks on the graphs of the magnitude of the response (Figure 1). Next, damping ratios () are calculated from the sharpness of the peaks obtained by half power band method. Then, the mode shapes are calculated from the ratios of the peak amplitudes at various points in the structure [13]. Finally, modal participation factors are computed to scaled mode shapes by using measures of force exciting. In order to apply the PP method, its procedure can be summarized as follows:(i)Determine the natural frequencies by means of the PSD computed from acceleration records by identifying all frequencies present at peaks .(ii)Estimate damping ratios by means of the loss factor which depends of the half power band frequencies as is illustrated in Figure 2.Figure 2: Half power band frequencies.According to Figure 2, the half power band comprises the frequencies where the PSD amplitude decays by 3 dB with respect to its maximum value. At once the half power band is determined; the loss and damping factors are computed by using In this paper an enhanced method known as frequency domain decomposition (FDD) is used instead, which is an extension of PP method. It consists of three main steps [14]:(i)Estimate the power spectral density matrix at discrete frequencies.(ii)Do a singular value decomposition of the power spectral density.(iii)For an n-degree of freedom system, then pick the dominating peaks in the power spectral density. These peaks correspond to the mode shapes.FDD technique removes disadvantages associated with classical PP method as, for example, the difficulty to detect close modes and bias estimation. Furthermore FDD reduces the uncertainty or hardness (even impossible) of damping estimation. Also, it keeps the user-friendliness giving a feeling of the data it is dealing with.2.3. Spectrum EstimationFrequency response functions between input and output are approximated as cross-power spectral densities between responses while the impulse response functions are approximated by cross-correlations between responses. Cross-PSDs are obtained using Welch method (FFT based method) [15]. Welch’s periodogram averaging with overlapping is a method which introduces improved properties based on basic periodogram methods:(i)Simple Periodogram. Quotient of the squared magnitude of the Fourier transform of the signal and length of the signal.(ii)Modified Periodogram. Certain window other than rectangular window that is applied to the signal before taking the Fourier transform. Windows solve the leakage problem.(iii)Bartlett Periodogram Averaging. Averaging of the different blocks of the signal, which decrease variance of the signal at the expense of resolution.Thus, the cross-power spectra between and some discrete signal, computed through Welch’s method, are expressed by (5). Therefore, the cross-PSD can be defined as the Fourier Transform of the cross-correlation function .According to (5), the Welch method divides the signal into blocks and then increases the averaging by taking overlaps of the blocks. Thus, the samples of are divided into overlapping sections with samples in each block, each of which is then windowed by the WINDOW . Finally, it averages the periodograms of the overlapping sections to form , the power spectral density estimation of .2.4. Windowing EffectIn estimating power spectral density (PSD) of a signal, there are two tradeoffs. One is frequency resolution and the other is noise in the signal. To obtain a good estimation of PSD, we should have large length of the signal but during measurements we have finite length of signal. If we take small b
Jhonatan Camacho-Navarro; R. Guzmán-López; Sergio Gómez; Marco Flórez. Comparison of the Time Domain Windows Specified in the ISO 18431 Standards Used to Estimate Modal Parameters in Steel Plates. Advances in Acoustics and Vibration 2016, 2016, 1 -7.
AMA StyleJhonatan Camacho-Navarro, R. Guzmán-López, Sergio Gómez, Marco Flórez. Comparison of the Time Domain Windows Specified in the ISO 18431 Standards Used to Estimate Modal Parameters in Steel Plates. Advances in Acoustics and Vibration. 2016; 2016 ():1-7.
Chicago/Turabian StyleJhonatan Camacho-Navarro; R. Guzmán-López; Sergio Gómez; Marco Flórez. 2016. "Comparison of the Time Domain Windows Specified in the ISO 18431 Standards Used to Estimate Modal Parameters in Steel Plates." Advances in Acoustics and Vibration 2016, no. : 1-7.
J.L. Pérez-Castellanos; R. Guzmán-López; Alexis Rusinek; Juan Meléndez. Temperature increment during quasi-static compression tests using Mg metallic alloys. Materials & Design 2010, 31, 3259 -3269.
AMA StyleJ.L. Pérez-Castellanos, R. Guzmán-López, Alexis Rusinek, Juan Meléndez. Temperature increment during quasi-static compression tests using Mg metallic alloys. Materials & Design. 2010; 31 (7):3259-3269.
Chicago/Turabian StyleJ.L. Pérez-Castellanos; R. Guzmán-López; Alexis Rusinek; Juan Meléndez. 2010. "Temperature increment during quasi-static compression tests using Mg metallic alloys." Materials & Design 31, no. 7: 3259-3269.
R. Guzman; Juan Meléndez; J. M. Aranda; Y. E. Essa; Rolando Guzmán Lopez; J. L. Pérez-Castellanos. Measurement of Temperature Increment in Compressive Quasi-Static and Dynamic Tests Using Infrared Thermography. Strain 2009, 45, 179 -189.
AMA StyleR. Guzman, Juan Meléndez, J. M. Aranda, Y. E. Essa, Rolando Guzmán Lopez, J. L. Pérez-Castellanos. Measurement of Temperature Increment in Compressive Quasi-Static and Dynamic Tests Using Infrared Thermography. Strain. 2009; 45 (2):179-189.
Chicago/Turabian StyleR. Guzman; Juan Meléndez; J. M. Aranda; Y. E. Essa; Rolando Guzmán Lopez; J. L. Pérez-Castellanos. 2009. "Measurement of Temperature Increment in Compressive Quasi-Static and Dynamic Tests Using Infrared Thermography." Strain 45, no. 2: 179-189.