scholarly journals Principal Features of Fatigue and Residual Strength of Composite Materials Subjected to Constant Amplitude (CA) Loading

Materials ◽  
2019 ◽  
Vol 12 (16) ◽  
pp. 2586 ◽  
Author(s):  
Alberto D’Amore ◽  
Luigi Grassia
Keyword(s):  
Experimental Data ◽  
Residual Strength ◽  
Stress Ratio ◽  
Cyclic Stress ◽  
Constant Amplitude ◽  
General Validity ◽  
Robust Test ◽  
Sudden Drop ◽  
Stochastic Nature ◽  
Two Parameter

This paper summarizes the principal features of composites’ responses when subjected to constant amplitude (CA) cyclic loadings. The stochastic nature of the responses; the absence of a detectable fatigue limit; the sudden drop of strength; the general validity of the strength-life equal-rank assumption (SLERA); and, ultimately, the residual strength-life equal-rank assumption (RSLERA) are discussed on the basis of the selected experimental data available in literature. The objective is defining a robust test in order to ascertain the reliability of the phenomenological models. A two-parameter phenomenological model accounting for the maximum cyclic stress, σmax, and the stress ratio, R = σmin/σmax, was used for guidance through the phenomenology of fatigue. It is concluded that the robustness of the models dealing with fatigue can be checked only when the characteristics of the composites’ responses are described simultaneously with fixed parameters.

Application of the R-Curve Concept to Fatigue Crack Growth

1978 ◽  
Vol 100 (4) ◽  
pp. 416-420 ◽  
Author(s):  
D. P. Wilhem ◽  
M. M. Ratwani
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Extension ◽  
Stress Ratio ◽  
Cyclic Stress ◽  
Crack Growth Resistance ◽  
Resistance Curve ◽  
Cyclic Stress Ratio ◽  
Wide Range

Crack growth resistance for both static (rising load) and for cyclic fatigue crack growth has been shown to be a continuous function over a range of 0.1 μm to 10 cm in crack extension for 2024-T3 aluminum. Crack growth resistance to each fatigue cycle of crack extension is shown to approach the materials ordinary undirectional static crack resistance value when the cyclic stress ratio is zero. The fatigue crack extension is averaged over many cycles and is correlated with the maximum value of the crack tip stress intensity, Kmax. A linear plot of crack growth resistance for fatigue and static loading data shows similar effects of thickness, stress ratio, and other parameters. The effect of cyclic stress ratio on crack growth resistance for 2219 aluminum indicates the magnitude of differences in resistance when plotted to a linear scale. Prediction of many of these trends is possible using one of several available crack growth data correlating techniques. It appears that a unique resistance curve, dependent on material, crack orientation, thickness, and stress/physical environment, can be developed for crack extensions as small as 0.076 μm (3 μ inches). This wide range, crack growth resistance curve is seen of immense potential for use in both fatigue and fracture studies.

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.

Experimental Study on the Combined Effect of Cyclic and Static Loads on the Mechanical Properties of the Saturated Soft Clay Material

2016 ◽  
Vol 723 ◽  
pp. 843-848
Author(s):  
Yi Wei ◽  
Ying Zhu ◽  
Jing Ni
Keyword(s):  
Mechanical Properties ◽  
Cyclic Load ◽  
Stress Ratio ◽  
Axial Strain ◽  
Soft Clay ◽  
Cyclic Stress ◽  
Excess Pore Pressure ◽  
Static Loads ◽  
Cyclic Stress Ratio ◽  
Excess Pore

The combined effect of cyclic and static loads on the mechanical properties of the soft clay was experimentally investigated by conducting undrained cyclic triaxial tests on Shanghai clay. The results show that an increment in either static or cyclic load increases excess pore pressures and axial strains. For a given value of combined cyclic and static loads, the mechanical properties of the soft clay are more sensitive to the cyclic load. Furthermore, the accumulated excess pore pressure and axial strain for a larger cyclic stress ratio and a lower combined stress ratio might overcome that for a lower cyclic stress ratio and a higher combined stress ratio. The mechanical properties of the soft clay after the cyclic load was unloaded were also discussed. It was observed that the excess pore pressure and axial strain under the static load alone decrease gradually with time. The trend of them largely depends on the ratio of cyclic load to static load.

scholarly journals MODELLING CHLORIDE DIFFUSION IN CONCRETE WITH INFLUENCE OF CONCRETE STRESS STATE

2017 ◽  
Vol 23 (7) ◽  
pp. 955-965 ◽  
Author(s):  
Jian WANG ◽  
Pui-Lam NG ◽  
Weishan WANG ◽  
Jinsheng DU ◽  
Jianyong SONG
Keyword(s):  
Experimental Data ◽  
Diffusion Coefficient ◽  
Stress State ◽  
Diffusion Model ◽  
Stress Ratio ◽  
Chloride Diffusion ◽  
Influence Coefficient ◽  
Chloride Diffusion Coefficient ◽  
Stress Influence ◽  
Concrete Stress

Under coastal or marine conditions, chloride erosion is the major accelerating factor of reinforcement corrosion. Therefore, it is of vital importance to investigate the chloride diffusion model. Research reveals that the concrete stress state has great influence on chloride diffusion; therefore a stress influence coefficient was incorporated in chloride diffusion coefficient model by many researchers. By referring to the experimental data from eight different researchers, the law between stress influence coefficient and concrete stress ratio is studied in detail, and equations relating the stress influence coefficient with the concrete stress ratio are established. Compared with three typical existing groups of equations, it is found that the proposed equations give the most accurate estim.ation of the stress influence coefficient. Hence, the proposed equations can be adopted to improve the valuation of chloride diffusion coefficient, and a modified chloride diffusion model is put forward. Three groups of experimental data are used to validate the modified chloride diffusion model, which is shown to be reasonable and having high prediction accuracy.

scholarly journals Speed-detachment tradeoff and its effect on track bound transport of single motor protein

2018 ◽  
Author(s):  
Mohd Suhail Rizvi
Keyword(s):  
Experimental Data ◽  
Random Walk ◽  
Power Law ◽  
Average Distance ◽  
Motor Protein ◽  
Fixed Duration ◽  
Biological Cells ◽  
Single Motor ◽  
Stochastic Nature ◽  
Time Required

AbstractThe transportation of the cargoes in biological cells is primarily driven by the motor proteins on filamentous protein tracks. The stochastic nature of the motion of motor protein often leads to its spontaneous detachment from the track. Using the available experimental data, we demonstrate a tradeoff between the speed of the motor and its rate of spontaneous detachment from the track. Further, it is also shown that this speed-detachment relation follows a power law where its exponent dictates the nature of the motor protein processivity. We utilize this information to study the motion of motor protein on track using a random-walk model. We obtain the average distance travelled in fixed duration and average time required for covering a given distance by the motor protein. These analyses reveal non-monotonic dependence of the motor protein speed on its transport and, therefore, optimal motor speeds can be identified for the time and distance controlled conditions.

scholarly journals Some New Fractional-Calculus Connections between Mittag–Leffler Functions

Mathematics ◽  
2019 ◽  
Vol 7 (6) ◽  
pp. 485 ◽  
Author(s):  
Hari M. Srivastava ◽  
Arran Fernandez ◽  
Dumitru Baleanu
Keyword(s):  
Experimental Data ◽  
Fractional Calculus ◽  
Fractional Derivative ◽  
Fractional Integral ◽  
Integral Expression ◽  
Potential Applications ◽  
The One ◽  
Two Parameter

We consider the well-known Mittag–Leffler functions of one, two and three parameters, and establish some new connections between them using fractional calculus. In particular, we express the three-parameter Mittag–Leffler function as a fractional derivative of the two-parameter Mittag–Leffler function, which is in turn a fractional integral of the one-parameter Mittag–Leffler function. Hence, we derive an integral expression for the three-parameter one in terms of the one-parameter one. We discuss the importance and applications of all three Mittag–Leffler functions, with a view to potential applications of our results in making certain types of experimental data much easier to analyse.

Diffraction properties of a strongly bent diamond crystal used as a dispersive spectrometer for XFEL pulses

2019 ◽  
Vol 26 (4) ◽  
pp. 1069-1072 ◽  
Author(s):  
Liubov Samoylova ◽  
Ulrike Boesenberg ◽  
Aleksandr Chumakov ◽  
Vladimir Kaganer ◽  
Ilia Petrov ◽  
...  
Keyword(s):  
Experimental Data ◽  
Energy Spectrum ◽  
Strain Gradient ◽  
Free Electron ◽  
Diamond Crystal ◽  
Energy Spectra ◽  
Theoretical Modelling ◽  
Free Electron Lasers ◽  
X Ray ◽  
Stochastic Nature

Self-amplified spontaneous emission (SASE) enables X-ray free-electron lasers (XFELs) to generate hard X-ray pulses of sub-100 fs duration. However, due to the stochastic nature of SASE, the energy spectrum fluctuates from pulse to pulse. Many experiments that employ XFEL radiation require the resolution of the spectrum of each pulse. The work presented here investigates the capacity of a thin strongly bent diamond crystal to resolve the energy spectra of hard X-ray SASE pulses by studying its diffraction properties. Rocking curves of the symmetric C*(440) reflection have been measured for different bending radii. The experimental data match the theoretical modelling based on the Takagi–Taupin equations of dynamical diffraction. A uniform strain gradient has proven to be a valid model of strain deformations in the crystal.

Bounding Solutions for Performance of Vibratory Plows

1974 ◽  
Vol 96 (3) ◽  
pp. 954-959
Author(s):  
L. J. Scerbo ◽  
D. L. Pope
Keyword(s):  
Velocity Vector ◽  
Constant Amplitude ◽  
System Parameters ◽  
Soil Model ◽  
Simple Equations ◽  
Two Parameter

This paper discusses the reduction in the applied drawbar force required to penetrate soil with vibrating plows. Harmonically forced linear and orbital motions of a plow blade are investigated. A rigid blade, vibrating with constant amplitude and a two-parameter soil model is used to represent the system. The assumption that the soil force opposes the instantaneous blade velocity vector is sufficient to describe the soil-blade interaction. Bounding solutions, which relate applied drawbar force to average plowing speed and other system parameters, are obtained as simple equations. These equations put into perspective the relative merits of each of these vibratory motions.

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