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Influence of notch width and length on crack initiation in 3PB specimens
Seitl, Stanislav ; Klusák, Jan ; Keršner, Z.
The paper presents the influence of the various notch depths for the range of starting notch width on a crack initiation in three-point bending specimens. These specimens are the most frequently used for fracture laboratory testing, especially of quasi-brittle cement-based composites. It is shown that the values of fracture toughness obtained from the tests of specimens with larger widths with various length of the starting notch can be overestimated.
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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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Estimation of generalized stress intensity factors by means of mean value of strain energy density factor
Klusák, Jan
The contribution deals with bi-material wedges whose stress field is characterized by two stress singular terms. The exponents of stress singularity are generally in the interval (0; 1). For these cases each of the singularities covers both normal and shear mode of loading. Because of the inherently combined loading mode, it is advantageous to utilize the strain energy density concept. A mean value of the strain energy density factor taken from a numerical solution of particular materials junction is compared to its analytical representation to ascertain values H1 and H2. These values enter to stability criterion to indicate if crack is initiated in the wedge tip.
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Reliability assessment of bodies with general singular stress concentrator
Klusák, Jan
The paper presents a method leading to reliability assessment of bodies with general singular stress concentrator. The method uses combination of analytical and numerical procedures to determine fracture-mechanics parameters. The approach is based on comparison of fracture behaviour of body with a crack and a body with a general singular stress concentrator. The goal of the paper is to determine value of applied stress that leads to initiation of failure of construction.
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Kritérium stability bi-materiálového vrubu se dvěma singularitami
Klusák, Jan
Interfaces with a step change of material properties occur often in technical constructions. In combination with a sharp notch it usually leads to singular stress distribution in a vicinity of such a wedge. The existence of two singularities seems to be the main problem within study of this stress concentrator. The other problem is that each singularity does not correspond to particular mode of loading. The presented contribution studies stress distribution in a bi-material wedge vicinity and shows a method of solution of the problems in case of existence of multiple stress singularity
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Comparison of stability criteria of V-notched body under combined mode of loading
Klusák, Jan ; Knésl, Zdeněk
The stability criteria of V-notched bodies under combination of loading modes I and II are suggested and compared in the article. Methodology of stability criterion suggestion is based on analogy between behaviour of body with a crack and with a V-notch. Analytical approach to suggestion of stability criteria and methods of numerical estimation of magnitudes controlling stability of the concentrators are shown in the article. Corresponding evaluations are obtained from finite element method system ANSYS. Suggested criteria are mutually compared.
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