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Aspects of fatigue and fracture of advanced building materials
Keršner, Z. ; Veselý, V. ; Seitl, Stanislav ; Pukl, R.
The paper is focused on ideas about subject-matter of the project Basic fatigue characteristic and fracture of advanced building materials. The effort of this grant is to gain new pieces of knowledge about behaviour of advanced building materials through the effective application of till this time not used methods of complex determining of physical-mechanical and performance qualities. These are predetermined to describe fatigue, fracture and microstructural characteristics. Mentioned qualities will be modelled on the level of continuum/multiphase composite. There is presumption that will be gained results describing fatigue behaviour of studied materials, especially for application in construction with demands for high durability, it is necessary to follow initiation and propagation of microcracks complexly.
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NONDESTRUCTIVE EVALUATION OF CONCRETE STRUCTURES BY NONLINEAR ULTRASONIC SPECTROSCOPY METHODS
Převorovský, Zdeněk ; Krofta, Josef ; Chlada, Milan
Facilities of nonlinear ultrasonic spectroscopy for defects detection in steel-reinforced concrete structures are discussed in the paper. Results are shown from non-destructive evaluation of concrete block samples reinforced with intact and corroded armature. Seven piezoelectric transducers were glued on the sample surface. One of them was used to harmonic excitation of the structure with frequency f1=45 kHz and stepwise growing amplitude. Among other 6 transducers one was multiplexed as a second transmitter of harmonic signal with f2=217 kHz and remaining sensors were receiving structural response on 2-frequency excitation. Most pronounced spectral differences between samples with corroded and intact reinforcement were observed on amplitude dependence of 3f1/2f1 ratio and f2-3f1 sidebands, which can be considered as nonlinear parameters characterizing concrete damage.
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Evaluation of notch geometry effect on behaviour of fracture toughness testing specimen
Seitl, Stanislav ; Klusák, Jan ; Keršner, Z. ; Knésl, Zdeněk
The basic fracture properties of cement-based composite are ascertained on the basis of test evaluations of the specimens in suitable test configurations. Three-point bending specimens with a central starting notch are the most frequently used specimen for laboratory testing. Through models of equivalent elastic cracks the critical crack length and effective fracture toughness (or toughness) can be calculated. The influence of the geometry of the starting notch in a three-point bend specimen on the resulting values of critical applied force and fracture toughness is studied in this paper. To this end, a crack initiation at the notch tip is numerically simulated. It is shown that the values of fracture toughness obtained for specimens with larger widths of starting notch can be overestimated.
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Concrete as a two-phase material: statistical/sensitivity modelling of failure
Keršner, Z. ; Náhlík, Luboš ; Knésl, Zdeněk
Concrete is represented as a two-phase material. Behaviour of a crack with its tip on the interface between two different materials ů hardened cement paste (matrix) and aggregate(particle) ů is modelled. Input variables of the model are considered as random variables using LHS method/FREET software. Then results of statistical/sensitivity analyses of output variable ů the critical stress for the intersection of coarse aggregate particle ů are presented.
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