Papers by Keyword: Fractal Analysis

Abstract: The effect of interfacial adhesion reduction at intensification of the nanofiller initial particles aggregation was found. It can be described with a simple empirical equation. The indicated equation precision is enough for prediction of the particulate-filled polymer nanocomposites reinforcement degree. The physical grounds of this effect can be described within the framework of fractal analysis.

Abstract: In this paper, the structures of spatial self-organization of steels after thermos-cyclic exposure were studied, using the fractal formalism method. It is shown that the structures, observed after cyclic heat exposure, can be characterized by the presence of the invariance property of their structure at different scale levels.

Abstract: The paper proposes an approach to study the mechanism of deformation of epoxy polymers based on the methods of fractal calculations. The advantages of the method for determining the fractality index of the deformation curves of polymer samples using the minimum coverage method are shown. An algorithm for the quantitative determination of the location of the "critical" points of the deformation curves of polymer samples under tension is proposed. It is shown that the use of the developed methodology for the fractal analysis of time series on the basis of a set of points of deformation curves of epoxy polymer samples under tension, provides valuable information about the processes occurring in the structure of composite materials affected by mechanical loads and various aggressive factors.

Abstract: The introduction of carbon greatly improves the high temperature performance of magnesia bricks. In order to explore the influence of carbon content on the fracture toughness and the fracture mechanism of magnesia-carbon bricks, two different carbon content (10wt% and 14wt%) magnesia-carbon bricks were investigated in this work. The fracture toughness and microstructure were characterized by fractal analysis of fracture surface and scanning electron microscope respectively. The results indicated that the strength of magnesia-carbon bricks was strengthened with the carbon content increasing. It was demonstrated that magnesia-carbon bricks with the higher carbon content presented higher fracture toughness as a consequence of lower apparent porosity and compact bonding between matrix and magnesia aggregates.

Abstract: The developments of the high power proton accelerators become a worldwide interest to provide various applications, where the targets are demanded to efficiently produce secondary beams and to survive intensive MW class proton beam power supplied by the accelerators. Solid metal targets might be melted by very high heat flux that is caused by the intensive proton beam bombardment. In fact, the incident occurred at J-PARC (Japan Proton Accelerator Research Complex), in which the gold solid target was locally melted to explosively jet molten gold. The molten gold jet collided with a structural beryllium flange plate that has a function of vacuum boundary. Some parts of molten gold were splashed and the other stuck on the flange plate. The relationship between the impact velocity and the morphology of the sticking pattern on the plate was quantitatively evaluated by introducing fractal analysis. It was found that the fractal dimension is correlated with the impact velocity and might be a useful factor to indicate the localized impact force and behavior.

Abstract: The shape of particles building the solid phase of soils is an important factor influencing soil behaviour. Three parameters defining the characteristics of particle shape: roundness, angularity and texture are the most commonly analyzed. The most difficult issue is texture determination due to its complex nature. Quantitative evaluation of this parameter creates serious problems, however, is not impossible. A new mathematical tool, such as fractal geometry, may be helpful. Through the use of power law, fractal analysis allows to designate fractal dimension that specifies the complexity of the tested object.

Abstract: Commercial activated carbon has been activated with KOH in order to investigate the effect of textural characteristics on CO₂ storage behaviors. The KOH activation has significantly enhanced the textural properties of the adsorbents, as compared to the pristine sample. CO₂ adsorption tests on the activated carbons were measured at 298 K and pressures up to 5.0 MPa, and the Langmuir-Freundlich isotherm was used to fit the adsorption data. The CO₂ uptake for the resulting adsorbents was significantly higher than that of the starting adsorbent in the studied pressure range. To better understand the structures and their influences on the CO₂ uptake, fractal analysis was conducted for the adsorbents on the basis of Frenkel-Halsey-Hill (FHH) equation. Fractal dimensions (D₁ and D₂) that calculated from N₂ adsorption data were discussed. The results showed that the two fractal dimensions have different influences on CO₂ adsorption capacity. There was a negative linear correlation between CO₂ maximum uptake and D₁, while CO₂ adsorption capacity increased with fractal dimension D₂ increasing. Therefore, it was concluded that appropriate pore structure fractal dimension with narrower PSDs within the microporous range had higher CO₂ adsorption capacity for the adsorbents.

Abstract: A hydraulic servo system is a typical feedback control system. Health assessment of a hydraulic servo system is usually difficult to realize when traditional methods based on sensor signals are utilized. An approach for health assessment of hydraulic servo systems based on multi-fractal analysis and Gaussian mixture model (GMM) is proposed in this study. A GRNN neural network is employed to establish a fault observer for the hydraulic servo system. The observer is utilized to simulate the system output under normal state. The residue is then generated by subtracting the estimated output from the actual output. The residue’s feature is extracted by fractal analysis. After the feature extraction, the overlap between the current feature vectors and the normal feature vectors is obtained by applying GMM. The confidence value (CV) can be obtained in advance; this value is employed to characterize the health degree of the current state and consequently implement the health assessment of the hydraulic servo system. Lastly, two common types of fault, namely, burst and gradual, are applied to validate the effectiveness of the proposed method.

Abstract: This study discusses changes in the value of fractal parameters determined based on functions of structure S(t), generated in different directions of anisotropy of the examined surfaces. The analyzed material consisted of AFM calibration standards TGT1, PG and TGZ1 which were used as models of strongly isotropic and anisotropic surfaces. The topography of the examined surfaces was imaged by atomic force microscopy. The obtained results indicate that all surfaces can be described mathematically to identify fractal parameters in any anisotropic direction.

Abstract: This study presents the results of an analysis of the domain structure of supersaturated X2CoCrMoAl20-15-3 maraging steel. The analyses was carried out using the magnetic force microscopy method in a two pass mode. Obtained magnetic results were subjected to numerical analysis. The dimensions of spontaneously magnetized regions and their orientation were determined by analyzing the autocorrelation function of changes in the resonant frequency of the MFM probe. The use of fractal analysis was proposed to describe the domain structure.