Demodulation-derived damage metrics for nonlinear wave modulation-based health monitoring of structures

Nonlinear wave modulation (NWM) is a promising technique for structural health monitoring and contact-type damage detection. In NWM, the severity of the damage is proportional to the intensity of the modulation. Spectral analysis is often employed to calculate the Modulation Index (MI), and the damage intensity. According to some recent studies, damage metrics obtained by demodulation of the sensory signal can provide more information about the damage than spectral MIs. The Hilbert Transform (HT), Synchronous Demodulation (SD), Short-Time Fourier Transform (STFT), and more recently, In-Phase/Quadrature Homodyne Separation (IQHS) have been used to demodulate the sensory signal and extract effective damage metrics in the NWM technique. The objective of this work is to investigate demodulation methods to obtain reliable amplitude and frequency modulation damage indicators. The drawbacks of the HT and original IQHS methods are discussed, and a Modified-IQHS (M-IQHS) method is proposed to address them. The M-IQHS is validated analytically and experimentally, with the latter taking place in a sandwich panel setup with a loose bolt as the damage, and the results are compared to their HT and original IQHS-derived counterparts. The results show that the M-IQHS can improve NWM damage detection by providing precise modulation metrics for any range of pump frequency, including ultrasonics. It can also provide information about the MI distribution for signals with multiple sidebands. Furthermore, of the demodulation algorithms developed for NWM so far, M-IQHS is the most noise-resistant.</p

Assessing Criteria of Rural Women Empowerment

ABSTRACT Empowering means, evolution and developing activities through nongovernmental organizations (NGOS) that lead empowerment to improve economic dimensions. Enabling is process that, during it, people of society do activities to overcome barriers of advancement that finally cause their domination to determine their own density. The term &quot;enabling&quot; means overcoming fundamental inequalities. So it is different from self-reliance. Rural women&apos;s financial self-reliance has many social &amp; economic influence as it made them self-sufficiency, it changes economic behavior and it makes women independent, it will be effective in economic development in family &amp; society , it also improve the women&apos;s roles in society and it causes self-confidence in women , it builds family strength and it causes to respect the women rights more than before and women will become equal with men in all their rights, of course we won&apos;t have patriarchy in the family . The women&apos;s empowerment in the rural society will increase because of all the aspects of rural women&apos;s selfreliance and will be confirmed their position

A MICROMECHANICAL APPROACH TO NUMERICAL MODELING OF YIELDING OF OPEN-CELL POROUS STRUCTURES UNDER COMPRESSIVE LOADS

Today, interconnected open-cell porous structures made of titanium and its alloys are replacing the prevalent solid metals used in bone substitute implants. The advent of additive manufacturing techniques has enabled manufacturing of open-cell structures with arbitrary micro-structural geometry. In this paper, rhombic dodecahedron structures manufactured using SLM technique and tested by Amin Yavari et al. (2014) are investigated numerically using ANSYS and LS-DYNA finite element codes for the modeling of the elastic and postyielding behavior of the lattice structure, respectively. Implementing a micro-mechanical approach to the numerical modeling of the yielding behavior of open-cell porous materials is the main contribution of this work.One of the advantages of micro-mechanical modeling of an open-cell structure is that, in contrast to the macro-mechanical finite element modeling, it is not necessary to obtain several material constants for different foam material models through heavy experimental tests. The results of the study showed that considering the irregularity in defining the cross-sections of the struts decreases both the yielding stress and densification strain of the numerical structure to the values obtained from the experimental tests. Moreover, the stress-strain curve of the irregular structure was much smoother in two points of yielding and densification, which is also observable in experimental plots. Considering the irregularity in the structure also decreased the elastic modulus of the lattice structure by about 20-30%. The post-densification modulus was more influenced by irregularity as it was decreased by more than 50%. In summary, it was demonstrated that using beam elements with variable cross-sections for constructing open-cell biomaterials could result in numerical results sufficiently close to the experimental data

Analytical/Empirical Study on Indentation Behavior of Sandwich Plate with Foam Core and Composite Face Sheets

Sandwich structures are widely used in aerospace, automobile, high speed train and civil applications. Sandwich structures consist of two thin and stiff skins and a thick and light weight core. In this study, the obligatory mandate of a sandwich plate contact constitutes a flexible foam core and composite skins with a hemispherical rigid punch has been studied by an analytical/empirical method. In sandwich structures, calculation of force distribution under the punch nose is complicated, because the core is flexible and the difference between the modulus of elasticity of skin and core is large. In the present study, an exponential correlation between the contact force and indentation is proposed. The coefficient and numerical exponent were calculated using the experimental indentation results. A model based on a high-order sandwich panel theory was used to study the bending behavior of sandwich plate under hemispherical punch load. In the first method, the force distribution under the punch nose was calculated by the proposed method and multiplied to deformation of related point in the loading area to calculate the potential energy of the external loads. In the second method, the punch load was modeled as a point force and multiplied to deformation of maximum indented point. The results obtained from the two methods were compared with the experimental results. Indentation and bending tests were carried out on sandwich plates with glass/epoxy skins and a styrene/acrylonitrile foam core. In the bending test, a simply support condition was set and in the indentation test the sandwich specimens were put on a rigid support. Indeed, in this position the punch movement was equal the indentation. The comparison between the analytical and experimental results showed that the proposed method significantly improved the accuracy of analysis

The Effect of Dynamic Assessment on L2 Grammar Acquisition by Iranian EFL Learners

This study investigated the effect of dynamic Assessment (DA) on the acquisition of L2 grammar by EFL learners. The focus was on teaching Conditional Type II, or Unreal Conditional, which is a difficult structure for language learners to acquire. To this end, two intact classes of intermediate EFL learners, each consisting of 23 male students were assigned to control and experimental groups. They were pre-tested and post-tested (immediately and delayed post-test) using a written grammaticality judgment task. Multivariate Analysis of Covariance (ANCOVA) was run to analyze the data. The results revealed that the experimental group significantly outperformed the control group (p<0.05) on both immediate and delayed post-tests. The findings point to the advantage of implementation of DA in L2 grammar instruction in classroom contexts

Ballistic analysis of fiber metal laminates impacted by flat and conical impactors

In the present study, the ballistic limit of GLARE is investigated experimentally and numerically. Ballistic tests were conducted using one stage gas gun. In the experimental part, the ballistic limit of GLARE was determined. The effect of aluminum lamina thickness and the nose shape of projectile on the ballistic limit were also investigated. The experimental results show that the ballistic limit of GLARE impacted by a flat projectile is higher than in the case of a conical nose projectile, and that by decreasing the aluminum laminate thickness from 0.5 mm to 0.3 mm, the Specific Perforation Energy (SPE) is increased. In the numerical section, the penetration process was simulated using LS\u2013DYNA software. The validation of the finite element model was done by experimental results. The effects of various involved parameters such as laminate thickness, mass and radii of impactor were also investigated. The numerical results prove the efficiency of GLARE over bare aluminum laminate with equal thickness, due to the lower deflection and higher SPE. Furthermore, the less the mass of the impactor or the greater the diameter of the flat projectile, the greater the ballistic limit of GLARE. Reasonable agreement is concluded between the numerical and experimental results