STRETCHED EXPONENTIAL STRUCTURAL RELAXATION OF COMPOSITE MATERIALS INDUCED BY IMPURITIES DESORPTION IN VACUUM

1991 ◽  
Vol 05 (29) ◽  
pp. 1911-1918 ◽  
Author(s):  
G. KANIADAKIS ◽  
E. MIRALDI ◽  
G. FRULLA
Keyword(s):  
Experimental Data ◽  
Composite Materials ◽  
Power Law ◽  
Structural Relaxation ◽  
High Accuracy ◽  
Time Dependent ◽  
Carbon Fibres ◽  
Debye Relaxation ◽  
Exponential Time ◽  
Stretched Exponential

The isothermal desorption of impurities, mainly of water, in epoxy reinforced with carbon fibres, kept in vacuum, induces time dependent dimensional variations that do not follow a simple power law. Assuming that dispersive transfer phenomena support the release of the adsorbed vapour, and consequently a “non-Debye” relaxation process, a new method for analysing the experimental data is presented. High accuracy measurements confirm the stretched exponential time dependence of the shrinkage of the examinated samples.

scholarly journals Stretched Exponential Dynamics in Online Article Views

2021 ◽  
Vol 8 ◽  
Author(s):  
Yeseul Kim ◽  
Byung Mook Weon
Keyword(s):  
Power Law ◽  
Online Community ◽  
Exponential Model ◽  
Time Dependent ◽  
Stretched Exponential ◽  
Popularity Dynamics ◽  
Biexponential Model ◽  
Community Changes ◽  
Insight Into ◽  
Stretched Exponential Model

Article view statistics offers a measure to quantify scientific and public impact of online published articles. Popularity of a paper in online community changes with time. To understand popularity dynamics of article views, we propose a decay dynamics based on a stretched exponential model. We find that a stretched exponent gradually decreases with time after online publication following a power-law scaling. Compared with a simple exponential or biexponential model, a stretched exponential model with a time-dependent exponent well describes long-tailed popularity dynamics of online articles. This result gives a useful insight into how popularity diminishes with time in online community.

Theoretical and experimental studies of composite materials reinforced by carbon fabrics. Part 3: modeling and experimental studies of the carbon fabric structure

2019 ◽  
pp. 170-176
Author(s):  
B. M. Primachenko ◽  
K. O. Strokin
Keyword(s):  
Experimental Data ◽  
Composite Materials ◽  
Experimental Studies ◽  
High Accuracy ◽  
Carbon Fabric ◽  
Standard Methods ◽  
Uniformity Of Measurements ◽  
Fabric Structure ◽  
Experimental Values ◽  
Carbon Fabrics

As a result of modeling and experimental studies of composite materials reinforced with carbon fabrics, the main parameters of the structure of carbon fiber have been determined. The experimental data were processed according to the standard methods of the state system for ensuring the uniformity of measurements. Comparison of the predicted and experimental values of the parameters showed a sufficiently high accuracy of the developed mechanical-analytical model of the structure of carbon fabric.

POWER LAW AND STRETCHED EXPONENTIAL EFFECTS OF EXTREME EVENTS IN CHINESE STOCK MARKETS

2010 ◽  
Vol 09 (02) ◽  
pp. 203-217 ◽  
Author(s):  
XIAOJUN ZHAO ◽  
PENGJIAN SHANG ◽  
YULEI PANG
Keyword(s):  
Correlation Analysis ◽  
Power Law ◽  
Extreme Events ◽  
Stock Markets ◽  
Cross Correlation ◽  
Extreme Values ◽  
Cumulative Distribution ◽  
Stretched Exponential ◽  
Cross Correlation Analysis ◽  
Chinese Stock Markets

This paper reports the statistics of extreme values and positions of extreme events in Chinese stock markets. An extreme event is defined as the event exceeding a certain threshold of normalized logarithmic return. Extreme values follow a piecewise function or a power law distribution determined by the threshold due to a crossover. Extreme positions are studied by return intervals of extreme events, and it is found that return intervals yield a stretched exponential function. According to correlation analysis, extreme values and return intervals are weakly correlated and the correlation decreases with increasing threshold. No long-term cross-correlation exists by using the detrended cross-correlation analysis (DCCA) method. We successfully introduce a modification specific to the correlation and derive the joint cumulative distribution of extreme values and return intervals at 95% confidence level.

scholarly journals Polyconvex hyperelastic modeling of rubberlike materials

2021 ◽  
Vol 43 (7) ◽  
Author(s):  
Cyprian Suchocki ◽  
Stanisław Jemioło
Keyword(s):  
Experimental Data ◽  
Power Law ◽  
Curve Fitting ◽  
Constitutive Relations ◽  
Data Sets ◽  
Power Law Model ◽  
Stored Energy ◽  
Data Approximation ◽  
Exponential Power ◽  
Hyperelastic Models

AbstractIn this work a number of selected, isotropic, invariant-based hyperelastic models are analyzed. The considered constitutive relations of hyperelasticity include the model by Gent (G) and its extension, the so-called generalized Gent model (GG), the exponential-power law model (Exp-PL) and the power law model (PL). The material parameters of the models under study have been identified for eight different experimental data sets. As it has been demonstrated, the much celebrated Gent’s model does not always allow to obtain an acceptable quality of the experimental data approximation. Furthermore, it is observed that the best curve fitting quality is usually achieved when the experimentally derived conditions that were proposed by Rivlin and Saunders are fulfilled. However, it is shown that the conditions by Rivlin and Saunders are in a contradiction with the mathematical requirements of stored energy polyconvexity. A polyconvex stored energy function is assumed in order to ensure the existence of solutions to a properly defined boundary value problem and to avoid non-physical material response. It is found that in the case of the analyzed hyperelastic models the application of polyconvexity conditions leads to only a slight decrease in the curve fitting quality. When the energy polyconvexity is assumed, the best experimental data approximation is usually obtained for the PL model. Among the non-polyconvex hyperelastic models, the best curve fitting results are most frequently achieved for the GG model. However, it is shown that both the G and the GG models are problematic due to the presence of the locking effect.

Modal Analysis of the Axial Compressor Blade: Advanced Time-Dependent Electronic Interferometry and Finite Element Method

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Mykhaylo Tkach ◽  
Serhii Morhun ◽  
Yuri Zolotoy ◽  
Irina Zhuk
Keyword(s):  
Experimental Data ◽  
Mathematical Model ◽  
Finite Element ◽  
High Reliability ◽  
Axial Compressor ◽  
Time Dependent ◽  
Experimental Setup ◽  
Vibration Modes ◽  
Compressor Blades ◽  
Isoparametric Finite Element

AbstractNatural frequencies and vibration modes of axial compressor blades are investigated. A refined mathematical model based on the usage of an eight-nodal curvilinear isoparametric finite element was applied. The verification of the model is carried out by finding the frequencies and vibration modes of a smooth cylindrical shell and comparing them with experimental data. A high-precision experimental setup based on an advanced method of time-dependent electronic interferometry was developed for this aim. Thus, the objective of the study is to verify the adequacy of the refined mathematical model by means of the advanced time-dependent electronic interferometry experimental method. The divergence of the results of frequency measurements between numerical calculations and experimental data does not exceed 5 % that indicates the adequacy and high reliability of the developed mathematical model. The developed mathematical model and experimental setup can be used later in the study of blades with more complex geometric and strength characteristics or in cases when the real boundary conditions or mechanical characteristics of material are uncertain.

Light-Induced Metastable Defects or Light-Induced Metastable H Atoms in a-Si:H Films?

1997 ◽  
Vol 467 ◽  
Author(s):  
C. Godet
Keyword(s):  
Experimental Data ◽  
Characteristic Time ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Exponential Time ◽  
Mobile Species ◽  
Hydrogenated Amorphous ◽  
Two Parameter ◽  
Metastable Defect ◽  
Trapping Sites

ABSTRACTIn hydrogenated amorphous silicon (a-Si:H) films, the increase of the metastable defect density under high-intensity illumination is usually described by an empirical two-parameter stretched-exponential time dependence (characteristic time τSE and dispersion parameter β). In this study, a clearly different (one-parameter) analytic function is obtained from a microscopic model based on the formation of metastable H (MSH) atoms in a-Si:H films. Assuming that MSH atoms are the only mobile species, only three chemical reactions are significant : MSH are produced from doubly hydrogenated (SiH HSi) configurations and trapped either at broken bonds or Si-H bonds, corresponding respectively to light-induced annealing (LIA) and light-induced creation (LIC) of defects. Competition between trapping sites results in a saturation of N(t) at a steady-state value Nss. A one-parameter fit of this analytical function to experimental data is generally good, indicating that the use of a statistical distribution of trap energies is not necessary.

Model of vibration in drilling into fibre-reinforced composite materials

2009 ◽  
Vol 223 (9) ◽  
pp. 1107-1114
Author(s):  
B W Huang
Keyword(s):  
Composite Materials ◽  
Vibration Amplitude ◽  
Time Dependent ◽  
Process Time ◽  
Drilling Process ◽  
Improve Product Quality ◽  
Analysis Model ◽  
Inhomogeneous Materials ◽  
Reinforced Composite ◽  
Twisted Beam

A model of the dynamic drill characteristics while drilling through fibre-reinforced composite materials (FRCMs) is investigated in this study. Anisotropic and inhomogeneous materials such as FRCMs, which are used to improve product quality, make it possible to improve production rate and avoid drill breakage. Such materials were used to study the dynamic characteristics of the drilling process. A theoretical analysis model for drilling composite materials is proposed. A pre-twisted beam is used to simulate the drill. A moving Winkler-type elastic foundation is used to approximate the drilling process time-dependent boundary. Numerical analysis indicates that the vibration amplitude changes significantly as the drill moves through composite material.

scholarly journals Verification of Brittle Fracture Criteria for Bimaterial Structures

2014 ◽  
Vol 8 (1) ◽  
pp. 44-48
Author(s):  
Grzegorz Mieczkowski ◽  
Krzysztof Molski
Keyword(s):  
Experimental Data ◽  
Composite Materials ◽  
Cyclic Loading ◽  
Brittle Fracture ◽  
Axial Loading ◽  
Loading Conditions ◽  
Fracture Criteria ◽  
Interfacial Cracks ◽  
Theoretical Results ◽  
Brittle Fracture Criteria

Abstract The increasing application of composite materials in the construction of machines causes strong need for modelling and evaluating their strength. There are many well known hypotheses used for homogeneous materials subjected to monotone and cyclic loading conditions, which have been verified experimentally by various authors. These hypotheses should be verified also for composite materials. This paper provides experimental and theoretical results of such verifications for bimaterial structures with interfacial cracks. Three well known fracture hypotheses of: Griffith, McClintock and Novozhilov were chosen. The theoretical critical load values arising from each hypotheses were compared with the experimental data including uni and multi-axial loading conditions. All tests were carried out with using specially prepared specimens of steel and PMMA.

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