Modelling of three-point bending test of beams with steel inclusion situated in the middle of the span

The aim of this paper is to present the numerical model of the fracture response of the test specimens with a steel inclusion in the shape of the prisms which length is equal to the specimen’s width. Specially designed fine-grained cement-based matrix specimens of the nominal dimension 40 x 40 x 160mm with inclusion of 8 x 8 x 40mm and central edge notch serves to determine of the influence of the interfacial transition zone on the effective mechanical fracture parameters of composite. The numerical models of three-point bending test of these specimens are created in ATENA software

Effect of the Mechanical Fracture Parameters of Inclusion on Fracture Behaviour of Cement Composite

This paper concerns the results of research into the effect of the mechanical fracture parame- ters of inclusion material on the fracture response of specially designed cement-based composite speci- mens. These specimens of the nominal dimensions 40 × 40 × 160 mm with inclusion in the shape of prisms with nominal dimensions of 8 × 8 × 40 mm were pro- vided with an initial central edge notch and tested in the threee-point bending configuration. The aim of this paper is to analyse the effect of the mechanical fracture parameters of inclusions material on the ef- fective mechanical fracture parameters of cement-based composite. The results of this research indicate the de- pendence of the effective mechanical fracture parame- ters of cement-based composite on the Young’s modulus of inclusion material

3D Scanning as an Effective Tool for Controlling the Dimensions of Test Specimens

3D laser scanning is a powerfull tool that digitally captures the shape of physical objects using a laser light crosses. In this work, the 3D laser scanning technology is used for the 3D shape capture of specially designed specimens. These specimens pre- viously made of fine-grained cement-based composite of the nominal dimensions 40 × 40 × 160 mm with in- clusion in the shape of prisms with nominal dimen- sions of 8 × 8 × 40 mm were provided with an initial central edge notch and tested in the threee-point bend- ing configuration. The aim of this paper is to study the macrostructure of fracture surfaces via 3D scanning technology, measure the area of ligament, verify the de- signed notch depth and evaluate the fracture tough- ness and specific fracture energy based on the mea- sured dimensions. The results indicate that the mea- sured notch depth is lower than the designed one thus the differences between fracture toughness calculated for designed notch depth and for the measured one is ap- proximately 10 %. In addition, the fracture toughness is overestimated when considering the design values

Fracture of selected building composites in the vicinity of aggregate-matrix-interface

Rozhraní mezi zrnem kameniva a matricí představuje v cementových kompozitech nejslabší článek. Aktuálnost tématu je o to větší zejména u vysokohodnotných a vysokopevnostních betonů, kde je potřeba eliminace, příp. redukce, těchto slabých článků. Cílem této práce je stanovit vliv tohoto rozhraní na lomové chování cementových kompozitů. Za tímto účelem byly navrženy a provedeny lomové experimenty, které byly doplněny o výsledky nanoindentačních zkoušek a snímky mikrostruktury rozhraní pořízené pomocí rastrovací elektronové mikroskopie. Na základě těchto dat byl následně vytvořen numerický model v SW ANSYS, umožňující na základě poznatků zobecněné lomové mechaniky stanovit hodnoty lomové houževnatosti rozhraní. Závěrem práce je dokázáno, že vlastnosti rozhraní mají nezanedbatelný vliv na lomové chování cementových kompozitů a právem mu přísluší označení „nejslabší článek“.The interface between aggregate grains and matrix in cementitious composites is their weakest element. The topic is particularly significant in the case of high performance and high strength concrete technology for which the eliminination or reduction of these weak links are necessary. The aim of this thesis is to determine the influence of the interface on the fracture behaviour of the cementitious composites. The fracture experiments were performed for this purpose and were complemented by the nanoindentation’s results and scanning electron microscopy results. Numerical model was created in ANSYS software on the basis of these data and the fracture toughness values of the interface were evaluated by means of the generalized fracture mechanics principles. Conclusion of the thesis is proof that the interface properties have a significant influence on the fracture behaviour of cementitious composites.

A Crack Approaching the Edge of the Aggregate

In this work, the influence of a crack approaching the edge of the amphibolite inclusion on fracture behaviour of cement composite is investigated. Specimens of the nominal dimensions 40 × 40 × 160 mm with polygonal amphibolite inclusion of 8 × 8 × 40 mm were provided with an initial central edge notch with a depth 12 mm, which was made by diamond blade saw. To determine the influence of polygonal cavity on fracture behaviour, fracture tests were conducted via three-point bending. The aim of this work is to analyse the behaviour of such specimen by means of finite element method (FEM) principles in Ansys, Inc. software. For this reason, a simplified 2D model was created for plane strain conditions. The crack propagation assessment was based on generalized fracture mechanics approaches using a criterion of an average value of tangential stress determined in dependence on the polar angle coordinate θ. The results of numerical analysis indicate that the debonding in the close vicinity of the bottom edge of the inclusion occurred. In other words, imperfect compaction of the fresh mixture and a smooth surface of the aggregate leaded to the formation of poor interface with lower mechanical-fracture parameters. Further, cutting of the initial notch by a diamond saw blade results in a precrack length greater than expected.Ostrav

Numerical study of specimen with steel inclusion: Influence of interfacial transition zone

In this paper, the influence of the interfacial transition zone (ITZ) between steel inclusion and fine-grained cement-based composite on fracture behaviour is investigated. Specimens of the nominal dimensions 40 × 40 × 160 mm with the steel inclusion of the prismatic shape with nominal dimensions 8 × 8 × 40 mm were provided with an initial central edge notch with a depth 12 mm. The aim of this paper is to analyse the behaviour of such specimen by means of numerical modelling by finite element method (Ansys software). A simplified 2D model (plane strain) based on the fracture test configuration was created. The crack propagation assessment was based on the criterion of the average value of tangential stress calculated over certain distance d in dependence on the polar coordinate. It is assumed that the crack is initiated when the average stress reaches its critical value, which depends on the fracture toughness of the material and on the distance d. From the detailed numerical analysis of the described fracture test, we concluded that the crack propagation path depends strongly on the fracture properties of ITZ. The central inclusion works as an obstacle to crack propagation only in the initial stage of failure. The mechanical fracture parameters of the ITZ strongly influence the overall fracture behavior of test specimen

Effect of petrographic composition and chemistry of aggregate on the local and general fracture response of cementitious composites

This paper concerns the results of research into the influence of the composition of rock inclusions on the fracture response of cement-based composite specimens. Specially designed specimens of the nominal dimensions 40 × 40 × 160 mm with inclusions in the shape of prisms with nominal dimensions of 8 × 8 × 40 mm were provided with an initial central edge notch with a depth of 12 mm. These specimens, which were made of fine-grained cement-based composite with different types of rock inclusion – amphibolite, basalt, granite, and marble – were tested in the three-point bending configuration. Fracture surfaces were examined via scanning electron microscopy and local response in the vicinity of rock inclusions was characterized via the nanoindentation technique. The aim of this paper is to analyse the influence of the chemical/petrographic composition of rock inclusions on the effective mechanical fracture parameters of cement-based composites, as well as on the microstructural mechanical parameters of the interfacial transition zone. The results of this research indicate the significant dependence of the effective fracture parameters on the petrographic and related chemical composition of the rock inclusions

CHARACTERIZATION OF CEMENT-BASED COMPOSITE EXPOSED TO HIGH TEMPERATURES VIA ULTRASONIC PULSE METHOD

In this paper, the attention is paid to the investigation of the influence of high temperature acting on specimens made from specially designed cement-based composite. The experimental programme was carried out on six sets of beam specimens with the dimensions of 20 × 40 × 200 mm. The specimens were loaded to a pre-set temperature of 100, 200, 400, 600, 800 and 1000 °C and then the temperature was kept for 60 minutes. When the temperature loading had been done, the specimens were left to cool down to the ambient temperature. After that, the ultrasonic pulse method was used to determine the degree of damage of temperature loaded specimens. The measured data obtained by this non-destructive method are in high correlation with values of informative compressive strength of the composite obtained after the temperature loading of specimens

Influence of rock inclusion composition on the fracture response of cement-based composite specimens

This paper concerns the results of research into the influence of the composition of rock inclusions on the fracture response of cement-based composite specimens. Specially designed specimens of the nominal dimensions 40 × 40 × 160 mm with inclusions in the shape of prisms with nominal dimensions of 8 × 8 × 40 mm were provided with an initial central edge notch with a depth of 12 mm. These specimens, which were made of fine-grained cement-based composite with different types of rock inclusion – amphibolite, basalt, granite, and marble – were tested in the three-point bending configuration. Fracture surfaces were examined via scanning electron microscopy and local response in the vicinity of rock inclusions was characterized via the nanoindentation technique. The aim of this paper is to analyse the influence of the chemical/petrographic composition of rock inclusions on the effective mechanical fracture parameters of cement-based composites, as well as on the microstructural mechanical parameters of the interfacial transition zone. The results of this research indicate the significant dependence of the effective fracture parameters on the petrographic and related chemical composition of the rock inclusions