A methodology is presented to directly measure the damage properties and strain softening response of laminated composites by conducting over-height compact tension (OCT) and compact compression (CC) ...tests. Through the use of digital image correlation (DIC) technique, and analysis of the measured surface displacement/strain data, the strain-softening response of composites is constructed. This method leads to a direct determination of the Mode I translaminar fracture properties with the assumption that the shear stress is negligible around the damage zone and the crack growth occurs in the symmetric opening mode. Using this methodology, and by correlating the observed failure mechanisms with the strain-softening curves, the interaction of failure mechanisms leading to the final failure and also the distinction between the tensile and compressive failure mechanisms can be studied. The effectiveness of the method in accurate identification of the damage parameters is demonstrated through sectioning and deplying techniques. As a consistency check and further verification of the method, the obtained strain-softening curves are fed into a numerical damage mechanics model and successfully used to simulate the detailed response of the very same OCT and CC specimens from which the strain-softening curves were extracted.
Two-dimensional thermoelastic analysis of functionally graded thick-walled cylinder is investigated under thermal and mechanical loadings and based on the Pasternak foundation. The first-order shear ...deformation theory is used to describe the displacement field. Fundamental governing differential equations of system are obtained by energy method and Euler equations. Effect of gradation of material properties and Pasternak foundation parameters are considered as important results of this study. The obtained results indicate that the end supports have considerable effect on the longitudinal distribution of components. Furthermore, it can be concluded that with increasing the non-homogeneous index, both radial and axial displacements decreases.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Delamination is the major defect for drilling of composite laminates. There exist different nondestructive tests (NDTs) to reveal delaminated zone, including digital photography, X-ray CT scanning, ...and ultrasonic C-Scan. Different delamination factors were presented to quantify delamination extension. In this paper, some difficulties regarding revealing damaged zone in drilling of woven carbon fiber-reinforced plastics laminates are discussed. In addition, different NDTs as well as available delamination factors are examined. For NDTs, clarity of pictures, applicability, and reliability are compared to help researchers select proper option. The result of this study demonstrates that compare to other available factors, the adjusted delamination factor Fda varies in wider ranges in normal engineering applications. It is less sensitive to the implemented NDT and it presents different values for different delamination extension patterns. Therefore, pattern-sensitive factor Fda is more suitable to quantify damaged zone. However, for cases with low circularity parameter f, like drilling of unidirectional composite laminates with extended damaged zone, Fda may be replaced by easily measured diameter delamination factor Fd.
A new computational approach is developed to predict the impact behaviour of fabric panels based on the detailed response of the smallest repeating unit (unit cell) in the fabric. The unit cell is ...constructed and calibrated using measured geometrical (weave architecture, crimp, voids, etc.) and mechanical properties of the fabric. A pre-processor is developed to create a 3D finite element mesh of the unit cell using the measured fabric cross-sectional micro-images. To render an efficient method for simulation of multi-layer packs, these unit cells are replaced with orthotropic shell elements that have similar macroscopic (smeared) mechanical properties as the unit cell. The aim is to capture the essence of the response of a unit cell in a single representative shell element, which would replace the more complicated and numerically costly 3D solid model of the yarns in a crossover. The 3D finite element analysis of the unit cell is used to provide a baseline mechanical response for calibrating the constitutive model in the equivalent shell representation. This shell element takes advantage of a simple physics-based analytical relationship to predict the behaviour of the fabric's warp and weft yarns under general applied displacements in these directions. The analytical model is implemented in the commercial explicit finite element code, LS-DYNA, as a user material routine (UMAT) for shell elements. Layers of fabric constructed from these specialized elements are stacked together to create fabric targets that are then analysed under projectile impact. This approach provides an efficient numerical model for the dynamic analysis of multi-layer fabric structures while taking into account several geometrical and material attributes of the yarns and the fabric.
In close-aperture Z-scan experiments, a small aperture is conventionally located in the far-field thereby enabling the detection of slight changes in the laser beam profile due to the Kerr-lensing ...effect. In this work, by numerically solving the Fresnel-Kirchhoff diffraction integrals, the amount of transmitted power through apertures has been evaluated and a parametric study on the role of the various parameters that can influence this transmitted power has been done. In order to perform a comprehensive analysis, we have used a nonlinear phase shift optimized for nonlocal nonlinear media in our calculations. Our results show that apertures will result in the formation of symmetrical fluctuations on the wings of Z-scan transmittance curves. It is further shown that the appearance of these fluctuations can be ascribed to the natural diffraction of the Gaussian beam as it propagates up to the aperture plane. Our calculations reveal that the nonlocal parameter variations can shift the position of fluctuations along the optical axis, whereas their magnitude depends on the largeness of the induced nonlinear phase shift. It is concluded that since the mentioned fluctuations are produced by the natural diffraction of the Gaussian beam itself, one must take care not to mistakenly interpret them as noise and should not expect to eliminate them from experimental Z-scan transmittance curves by using apertures with different sizes.
Fuzzy C-mean (FCM) is the most well-known and widely-used fuzzy clustering algorithm. However, one of the weaknesses of the FCM is the way it assigns membership degrees to data which is based on the ...distance to the cluster centers. Unfortunately, the membership degrees are determined without considering the shape and density of the clusters. In this paper, we propose an algorithm which takes the FCM clustering results and re-fuzzifies them by taking into account the shape and density of the clusters. The algorithm first defuzzifies the FCM clustering results. Then the crisp result is fuzzified again. Re-fuzzification in our algorithm has some advantages. The main advantage is that the fuzzy membership degrees of data points are obtained based on the shape and density of clusters. Adding the ability to eliminate noise and outlier data is the other advantage of our algorithm. Finally, our proposed re-fuzzification algorithm can slightly improve the FCM clustering quality, because the data points change their clusters according to similarity to the shape and density of their respective clusters. These advantages are supported by simulations on real and synthetic datasets.
•The pure parsimony haplotyping problem has been considered in this manuscript.•A corresponding number is assigned to each haplotype and genotype.•Using numbers, instead of sequences, would lead to ...less complexity of the new model.•A polynomial IP model is presented which does not have any variable nor constraint corresponding to heterozygous sites.•The new model is smaller than the previous models, specially for instances which have many heterozygous sites.
Pure parsimony haplotyping (PPH) problem is important in bioinformatics because rational haplotyping inference plays important roles in analysis of genetic data, mapping complex genetic diseases such as Alzheimer's disease, heart disorders and etc. Haplotypes and genotypes are m-length sequences. Although several integer programing models have already been presented for PPH problem, its NP-hardness characteristic resulted in ineffectiveness of those models facing the real instances especially instances with many heterozygous sites. In this paper, we assign a corresponding number to each haplotype and genotype and based on those numbers, we set a mixed integer programing model. Using numbers, instead of sequences, would lead to less complexity of the new model in comparison with previous models in a way that there are neither constraints nor variables corresponding to heterozygous nucleotide sites in it. Experimental results approve the efficiency of the new model in producing better solution in comparison to two state-of-the art haplotyping approaches.
In this paper, the ducting model has been generalized by considering the temporal pulse shape function used to formulate it. This generalized form of the ducting model can be used to describe the ...propagation of laser pulses with various temporal shapes. In particular, propagation of Gaussian shaped laser pulses has been simulated. The model results have been compared with the results of the multi-focus structure and the moving nonlinear foci models, and it is shown that good correspondence exists between the results of our ducting model and those of the other two models. Our simulation results indicate that the Gaussian laser pulse creates a multi-focus structure inside the nonlinear Kerr medium which moves inside it at a very fast velocity. It is shown that this fast movement of focal points can create filaments in the form of conical frustums during pulse propagation.
Knowing the Gaussian beam parameters, such as its radius of curvature and spot size during propagation in nonlinear Kerr media, is of paramount importance in describing the observable far-field ...diffraction ring patterns as well as in design and stability analysis of Kerr-lens mode-locked resonators. Specifically, the sign of the beam radius of curvature after exiting these media has been proposed to be of assistance in recognizing their optical nonlinearity sign through determining the type of diffraction ring pattern in the far field. In order to be able to trace the evolution of the beam parameters in the Gaussian beam formalism, we have used the common aberration-free theory. We have shown that the nonlinear propagation problem of a fundamental Gaussian beam in a Kerr medium with an intensity-dependent index of refraction can be handled by assuming a ducting index profile along the propagation direction. Knowing the familiar ABCD matrix of a duct, the evolution of the mentioned beam parameters can be traced during propagation using the ABCD law in Gaussian beam theory. We have validated our ducting model by comparing its results with the outcomes of one widely used and accepted model which has been known to yield consistent results when electronic optical nonlinearity prevails. We have shown that when thermal optical nonlinearity is dominant, as in diffraction ring observation experiments, our ducting model yields sensible results and should be used. Our model predicts that when the sign of the thermal nonlinearity and the beam radius of curvature on the entrance plane of the medium are positive, the sign of the beam radius of curvature on the exit plane may have either sign, depending on the medium thickness used in the experiment. Hence, two types of diffraction ring pattern may be obtained using the same medium with two different thicknesses and this may cast doubt on the validity of the methods proposing the detection of the optical nonlinearity signs by observing these patterns. We have proposed a simple procedure for experimentally obtaining the two different types of diffraction pattern from the same medium.
In this paper, classification of subspecies of Alosa caspia (Eichwald, 1838) was examined using morphometric and molecular methods. Preliminarily, four groups of Alosa caspia were identified based on ...morphometric analyses of specimens taken from the south Caspian Sea. Based on molecular analyses, two of three clades created in a phylogenetic tree with different sequences encoding a certain type of protein were found; therefore, it was assumed that Alosa caspia had no subspecies in the south Caspian Sea. Specimens obtained from different sites were placed in similar clades, which is in contradiction with the idea that the members of each subspecies belong to a separate geographic region. Our morphological results confirm the existence of three subspecies of Alosa caspia, while the phylogenetic analysis based on the cytochrome b oxidase gene does not support the traditionally morphological subdivision of Alosa caspia into three subspecies. The phenotypic differences in the specimens can be generalized to the effect of their different environmental conditions, and from the molecular results it can be concluded that this species does not have any subspecies. Indeed, the selected fragment of cytochrome b was not able to separate the studied groups from one another. It seems, according to these results, that the specimens studied were populations of Alosa caspia species in the south Caspian Sea.
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