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Determination of mechanical properties from microcompression test
Truhlář, Michal ; Kruml, Tomáš ; Kuběna, Ivo ; Petráčková, Klára ; Náhlík, Luboš
This paper describes a microcompression test of Al - 1.5 wt. % Cu thin film deposited on Si substrate. Microcompression combines the sample preparation with the use of ion focused beam (FIB) with a compression test carried out using nanoindenter. Cylindrical specimens (pillars) were prepared using FIB. The diameter of pillars was about 1.3 μm and their height was about 2 μm (equal to the film thickness). Stress-strain curves of the thin film were obtained. The results depend on crystallographic orientation of pillar. The paper is focused to an attempt to determine as precisely as possible Young modulus of the film using experimental data and finite element modelling.
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Numerical prediction of parasitic energy dissipation in wedge splitting tests on concrete specimens
Veselý, V. ; Holušová, Táňa ; Seitl, Stanislav
Undesirable energy dissipation taking place during wedge-splitting tests on cementitious composites and resulting in overestimation of the values of the determined fracture-mechanical characteristics of the tested materials is investigated in this paper via numerical simulations performed using a commercial finite element method tool with an implemented cohesive crack model. The rather broad range of cohesive behaviour of the studied materials was simulated through adjustments made to the corresponding characteristic length of the composite. The parasitic amount of energy is dissipated in fracture processes around the corners of the groove for the insertion of the loading platens, as these corners introduce rather strong stress concentrators to the specimen. This amount was extracted from simulated load-displacement curves and it was discovered that the amount considerably depends on the specimen proportions but its dependence on the level of material brittleness is not so significant.
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Low Cycle Fatigue and Analysis of the Cyclic Stress-strain Response in Superalloy Inconel 738LC
Tobiáš, Jiří ; Chlupová, Alice ; Petrenec, Martin ; Polák, Jaroslav
The paper describes the results of fatigue behavior study on cast polycrystalline nickel based superalloy tested at 23 and 800 °C. Cylindrical specimens of Inconel 738LC were cyclically strained under total strain control to fracture and multiple step tests were performed to study the effect of temperature on the internal and effective cyclic stress components. Fatigue life curves were approximated by the Manson- Coffin and Basquin laws. The resulting curves were shifted to lower fatigue lives with increasing temperature. The evolution of the effective and internal stress components and effective elastic modules were derived from the hysteresis loops which were analyzed according to the statistical theory of hysteresis loop. Cyclic stress-strain response at both temperatures and the changes of internal and effective stress components were discussed in relation to microstructural parameters of the superalloy.
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Modelling of ductile fracture for sub-sized three-point-bend geometry
Stratil, Luděk ; Hadraba, Hynek ; Kozák, Vladislav ; Dlouhý, Ivo
The contribution deals with the simulation of R-curve using complete Gurson model of ductile fracture. The R-curve was experimentally determined for a Eurofer97 steel on sub-sized three-point-bend geometry in previous study. To apply complete Gurson model the parameters describing the voids´ behaviour and characteristic length parameter need to be determined. The nucleation parameters were identified by single specimen method of smooth tensile test specimen and from metallographic examination of fracture micro-mechanism. The characteristic length parameter was derived by fitting load versus deflection curves of sub-sized specimens. The simulations of the tests were carried out by software ABAQUS in Standard and Explicit modules. The identification was supported by parametric studies. Comparing experimental and simulated R-curve the ductile tearing was not successfully achieved. Insufficient calibrated parameters as a result non-uniqueness problem of single specimen method were found.
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Long-term monitoring of mechanical damage on historical structures
Zíma, Pavel
Important information for the risk assessment of some damages on the historical structures represents data of failure development. Cracks in the load-bearing walls are one of the observed failures. This article focuses on remarkable method of damage measurement, their long-term monitoring and devices used for measurement
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Fatigue crack growth and delamination in fiber metal laminate (GLARE) during loading with positive mean stress
Chlupová, Alice ; Kozák, Vladislav
The aim of the paper is to present the results of a study on the damage of fiber metal laminate (GLARE) subjected to the low cycle fatigue loading with positive mean stress. The fatigue crack initiation and growth was observed on the surface of notched specimens and then the individual layers of fatigued specimens were removed by chemical etching and polishing to obtain data about cracks length and delamination shape and area. Mechanism of initiation and crack growth in this type of materials differs from homogeneous monolithic materials. The fatigue life in term of number of cycles to crack initiation depending on amplitude of local plastic deformation and local stress in the notch root was evaluated.
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Cyclic loading of masonry walls and its anti seismic reinforcing
Wünsche, Martin ; Hračov, Stanislav ; Pospíšil, Stanislav ; Urushadze, Shota
The damage of structural masonry walls is one of the most widespread harming injuries and cause of loss of serviceability and seismic capacity for a building. Therefore a research into possibilities which would improve these characteristics have been carried out within the 7th EC Framework programme project NIKER. The retrofitting approach is constrained by conservation requirements of minimum interventions which should not severely change the structural behavior and the structural appearance, and should prefer solutions without a necessity of total structural disassembling. This artikle provides an overview about the research that led to applications of the steel wire ropes and geo-nets ontoadobe brick walls.
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Trapped Vortex Ring
Tesař, Václav
Paper discusses an almost unknown and yet interesting operating principle of fluidic nomoving-part devices for flow control. The principle is based on the properties of vortex rings. A standing vortex ring is kept in a semi-toroidal recession positioned opposite to an annular nozzle from whichissues an annular fluid jet. The ring can exist in the recession with two alternative senses of rotation so that the annular jet is led to either the central exit through the centre of the vortex, or to the outer spacepast the outer vortex circumference.
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Application of chaotic dynamics in natural and technical sciences
Kratochvíl, C. ; Švéda, P. ; Hortel, Milan ; Škuderová, Alena ; Houfek, M.
During the entire 20th century there was a gradual transformation of scientific research, which has produced in science and technology especially in the extraordinary interest in complex dynamic systems. They are non-linear systems, operating environments and the irreversible complexity in their name means they have complex structures, relations and interactions (often of different physical nature). It turned out that an inherent attribute of these complex systems and chaos (deterministic and stochastic). The article will focus on some aspects of the manifestations of chaos, its spread, as well as identification, suppression and control. We will mention also other important phenomena - the possible emergence of a new order out of chaos.
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