|
Curves of equal fatigue lives under combined random stress
Svoboda, Jaroslav ; Fröhlich, Vladislav
The contribution deals with determining an influence of normal and tangential components of a stress on the total damage under combined random loading in tension-pressure and torsion. An experimental program ran with plain and notched tube specimens made out of low carbon steel ČSN 411523.1. Regression curves were obtained for several rations of standard deviations of the stress components. Basing on the regression curves, curves of equal fatigue lives were constructed. It is possible to use them for calculating asafe life of structures.
|
|
Analysis of crack propagation in vicinity of bi-material interface in framework two parameter fracture mechanics
Seitl, Stanislav ; Knésl, Zdeněk
Existence of the interface between regions with different elastic properties have a pronounced influence on the behaviour of cracks The aim of the present contribution is an analysis of a crack growing in a vicinity of the interface between two different elastic materials.. The basic assumption of the contribution corresponds to two-parameter linear elastic fracture mechanics. The values of stress intensity factor KI and KII corresponding to normal and shear mode of loading and the value of T-stress are calculated for a generally oriented crack approaching to the interface. The calculations are performed by finite element method for short and long cracks. The dependence of KI, KII and T values on the distance and the orientation of a crack with respect to the interface is studied. It is shown that short cracks are influenced by the presence of the interface more significantly in comparison with long cracks. The results contribute to better understanding of short cracks behaviour in relation to microstructure of material.
|
|
Important Markov-Chain Properties of (1,lambda)-ES Linear Optimization Models
Chotard, A. ; Holeňa, Martin
Several recent publications investigated Markov-chain modelling of linear optimization by a (1,lambda)-ES, considering both unconstrained and linearly constrained optimization, and both constant and varying step size. All of them assume normality of the involved random steps. This is a very strong and specific assumption. The objective of our contribution is to show that in the constant step size case, valuable properties of the Markov chain can be obtained even for steps with substantially more general distributions. Several results that have been previously proved using the normality assumption are proved here in a more general way without that assumption. Finally, the decomposition of a multidimensional distribution into its marginals and the copula combining them is applied to the new distributional assumptions, particular attention being paid to distributions with Archimedean copulas.
|
|
High-Quality Vector Field and Direct Vorticity Estimation Uusing the Affine Correlation Method
Gronát, Petr
We present a correlation method for direct vorticity computation of the fluid velocity field. The correlation method allows the affine transformation of a correlation window. It is shown that Lagrangian field of displacements is locally affine considering linear terms only. Using the Normalized-Cross-Correlation (NCC) combined with affine transformation and Newton-Raphson iterative method, six parameters defining this transformation are estimated. Subsequently, using these parameters, both displacement and vorticity can be computed, hence, these properties are being obtained for every single pixel directly during the correlation procedure.
|
|
Regression and correlation analysis of time development of the traffic accidents number at transportation of dangerous substances in a selected region.
VÁVRA, Martin
The aim of this thesis was to conduct a statistical survey and the measurement of statistical dependences of time development of the traffic accident rate at transportation of dangerous solid, liquid and gaseous substances, including their total number and also in case of leakage of these substances in a selected region "the Czech Republic". The purpose of the thesis was to verify statistical data, or more precisely, verification of two basic hypotheses H1 and H2, and five sub-hypotheses H11, H12, H13, H14, H15. For these verifications methods of descriptive and mathematical statistics were used, especially regression and correlation analysis in hypothesis H1. To verify hypothesis H2, nonparametric normality test as a technique of mathematical statistics was applied. Verification of hypotheses H1 and their sub-hypotheses H11, H12, H13, H14, H15 enabled to prove linear regression associated with negative correlation within the development of traffic accidents at transportation of dangerous substances in annual units of time (2002 to 2011). Verification of hypothesis H2 enabled to demonstrate normality in distribution of the number of accidents at transportation of dangerous substances within individual months of the monitored period from 2007 to 2011. As benefits of this thesis both the proposal of the sequence of statistical methods for examining the research topic and the application of the mentioned statistical methods to the number of traffic accidents at transportation of dangerous substances can be considered Based on the results of this study, possible follow-up research work may be suggested. A research is proposed which would survey the ways of prevention or other factors leading to negative correlation dependence. Another possibility of follow-up research work could be, for example, statistical surveys and the measurement of statistical dependences in regions of the CR or investigation of the theoretical distribution of the number of traffic accidents at transportation of dangerous substances within a different time unit.
|
|
The Influence of T-stress on Mixed Mode Fracture Criterion
Seitl, Stanislav
In this paper, two-parameter constraint based linear elastic fracture mechanics is used to modify brittle fracture criterions under combination of normal and shear loading (Mode I and II). The value of constraint is characterized by T-stress. The results contribute to better description of influence of the geometry of a body on its fracture behaviour.
|
|
Possibilites of improving the quality of beef by ageing
BENEŠ, Karel
Internal and external factors affect the quality of meat, however ageing affects final product. Main objective of this work was to determine the effects of ageing on selected physical factors (pH, colour, water holding capacity and texture shear force) which affect meat quality from consumer and further meat processing perspective. Measuring of those factors was performed in periodical time sequences (one day post-mortem and 14 days of ageing) and factors of raw and heat-modified meat were measured. There were two hundred and fifty-eight samples from Czech pied cattle used in research. Musculus longissimus lumborum et thoracis (sirloin) was analyzed. Statistically high shear force difference (P=0.001) was identified at heat-modified and aged samples (decrease from 22.574 kg to 14.885 kg). Decrease of shear force during ageing of raw meat samples was observed at normal pH (pH < 5.8) beef ? from 6.403 kg to 5.982 kg. Correlations between pH and water holding capacity was found at samples which undergone ageing (r = 0.879 ***) and also at one day post-mortem samples (r = 0.872 ***). Middle correlation was observed between colour and pH at all colour parameters ? L* (r = -0.479 ***), a* (r = -0.478 ***) and b* (r = -0.581 ***). Water holding capacity and pH have influence on shear force of raw beef and also heat-modified beef; this was confirmed by correlation analysis. Lightness (L*) and water holding capacity affect heat-modified samples texture which was confirmed with multi-regression linear analysis (R2 = 0.565). As shown above the influence of meat ageing on quality parameters is high and properly aged meat from young bulls has better texture values. If the aged beef will be sold regularly it could be expected that consumer demand will increase especially due to remove the inconsistency of the quality of beef.
|
|
A study of bi-material notches under a combined loading mode
Kopp, Dalibor ; Klusák, Jan
In the range of linear elastic fracture mechanics, the conditions for critical loading assessment of structures made of two dissimilar materials are usually based on the assumptions of a prevailing normal mode of loading. The same assumption is usually applied to the stability criterion of bi-material notches. However, in engineering practice there are cases of loading and failure close to the shear mode. The aim of the work is the study of the stress distribution in the vicinity of a bi-material notch subjected to a combination of normal and shear modes of loading. Further, the assessment of crack initiation from the stress concentrator is shown.
|
| |
|
Properties of friction connections for blade dampers
Půst, Ladislav ; Pešek, Luděk ; Radolfová, Alena
Experimental laboratory equipment for direct measurement of friction forces was designed and realized. It is based on stiff prescribed relative motion. After connecting with measuring apparatus, a series of friction characteristic measurements with various combination of friction surfaces (blade material 7N, 671, wolfram carbide, chromium carbide) were carried out. Three levels of normal forces at several frequencies of relative motion were applied at each combination. The evaluation was focused particularly on ascertaining the dry friction coefficients. The analytic expressions for various relation strips “friction force - velocity” of relative motions were derived. These expressions can be applied at evaluation of experimental data or/and at numerical solution of machine dynamic problems. Nonlinear models of friction processes were linearized by the equivalent linearizing method.
|
guest ::
