Papers by Author: Stanislav Seitl

Abstract: The subject of the study presented in this paper is to quantify the effect of fiber content on the mechanical and mainly fatigue response of fine-grained cement-based composites. The reference cement-based composite was without fibers. Three types of fibers were used as dispersed reinforcement: tire cords (waste material), steel, and polypropylene. For each type of fiber, mixtures with varying reinforcement levels per volume were prepared: 0.0 % (reference composite), 0.5 %, 1.0 %, and 1.5 %. Prismatic specimens 40 mm × 40 mm × 160 mm were prepared and tested. A total of 10 composite variants were investigated. The ages of the specimens for the static three-point bending tests were 28 days, for the compression tests were 28, 120, and 275 days. While for the fatigue tests, it was approximately between 110 and 180 days. The obtained compressive strength values for the above-mentioned composite ages were approximated by a selected exponential function and the results of the fatigue tests were standardized to a nominal age of 28 days using them. All used types of reinforcement increase the strength values of the composites even from the lowest fiber doses. A positive effect of fiber dosage above 0.5 % on the fatigue behavior of composites was shown only in the case of reinforcement with commercial steel fibers.

Abstract: The use of S355 high strength steel in civil engineering to design bridges, its elements or simple engineering parts allows material and economical savings meeting the strict construction requirements. The knowledge of the fatigue resistance of material plays the key role during design and maintenance of the bridge structures. This contribution brings a comparison of the fatigue crack growth resistance of two standard S355 J0 and S355 J2 steel grades. Differences in chemical composition and the texture of material structure could generally play a role in the fatigue crack growth. This study shows that in the case of studied steels the chemical composition has an influence on material fatigue behaviour, whereas the texture of material structure is irrelevant.

Abstract: Wedge-splitting test is widely used fracture mechanical test for its stability in measurement during the testing and many papers were published. However, the biaxial wedge-splitting test is relatively a new method and the numerical stress analysis of such test is necessary. Especially the investigation of the stress fields in the vicinity of the crack tip. In this contribution, influence of various biaxial stress level is discussed on values of first and second terms of William’s expansion.

Abstract: Concrete used in civil structures is usually made on cement-based matrix and natural aggregates (such as sand, gravel, crushed stone, etc.). Ceramic waste aggregate is considered as a perspective replacement of a part of natural aggregate in modern environmentally oriented building material. Concrete with natural aggregate partially replaced by ceramic waste aggregate usually show different mechanical characteristics than ordinary concrete. This paper introduces the pilot study of fatigue parameters of six concrete mixtures with various amount of ceramic waste. The experimentally obtain results are compared and discussed.

Abstract: A simplified model of a crack approaching a bi-material interface is modelled by means of the finite element method in order to investigate the significance of the higher-order terms of the Williams expansion for the proper approximation of the opening crack-tip stress near the bi-material interface. The discussion on results is presented and the importance of the higher-order terms proved.

Abstract: Attention to the fatigue cracks in steel structures and bridges has been paid for long time. In spite to efforts to eliminate the creation and propagation of fatigue cracks throughout the designed service life, cracks are still revealed during inspections. Note, that depending on location of initial crack, the crack may propagate from the edge or from the surface. The theoretical model of fatigue crack progression is based on linear fracture mechanics. Steel specimens are subjected to various load (tension, three-and four-point bending, pure bending etc.). The calibration functions for short edge cracks are compared for various load and the discrepancies are discussed.

Abstract: The paper focuses on a numerical modelling of the initial chevron notch in test specimens subjected to the three-point bending test geometry configuration. The plane model is used with variable thicknesses of the layers with plane stress condition. The number of layers is being investigated and the influence of some input parameters like relative crack length, breadth of initial notch, etc. is evaluated by value of the stress intensity factor for tension loading mode.

Abstract: Fracture properties of quasi-brittle cementitious composites are typically determined from the load–displacement response recorded during a fracture test by using the work-of-fracture method or possibly other relevant fracture models. Our contribution is focused on a set of experimental tests which are used to study the fracture behaviour on notched dog-bone-shaped specimens made of cementitious materials. These specimens are subjected to modified compact tension (ModCT) test under a specific range of eccentricity of the tensile load. This type of test generates a stress state in the specimen ligament which combines a direct tension with a defined level of bending due to eccentricity of the tensile load. Several values of relative notch length are also considered. While the crack propagates, a variety of stress states, resulting in variations in the crack-tip stress and deformation constraint, appears in the ligament zone because of the changes in the eccentricity of the applied load, which influences the fracture behaviour of the investigated specimens. The K-calibration, T-stress, CMOD and COD curves for ModCT specimens are introduced and variations of these curves with varying load eccentricity are discussed.

Abstract: Cement-based composites are traditionally used building materials. Concrete is the basic representative of this type of materials which exhibit the so called quasi-brittle response. Quantification of mechanical fracture parameters is performed using fracture tests on specimens with a stress concentrator. Load versus crack mouth opening displacement (P–CMOD) diagrams are recorded during these tests. In order to correctly evaluate these diagrams, an advanced own developed software tool was used for the data filtering and appropriate modifications. In this paper, the programmed Java utility is generally introduced and its utilization demonstrated on the set of recorded P–CMOD diagrams, which are further evaluated using Double-K fracture model.

Abstract: The alkali-activated concrete is prepared as a new potential material for the production of concrete elements developed by ZPSV, a. s. company. Note that civil engineering structures are usually made of ordinary Portland cement (OPC) based concrete but today, the cement industry is responsible for emitting between 6% and 7% of all the CO₂ emission into the atmosphere. Therefore, it is essential to seek different binders to provide environmental friendly materials. One possible alternative is the application of alkali-activated concrete. The optimal design of concrete mixture was studied in this investigation. Two types of concrete have a similar application and therefore the fatigue parameters can be compared. To this aim, specimens were prepared and tested under static (compressive cube strength) and cyclic loading (fatigue parameters − Wöhler curve). The experimentally obtained results (both mechanical and fatigue) of both types of concrete are compared and the suitability of these types of composites for its application is discussed.