Ildiko Merta - Academia.edu (original) (raw)
Papers by Ildiko Merta
Analytisches Model der Querkrafttragfähigkeit kreisförmiger Stahlbetonbauteile
In this work, a shear capacity model of reinforced concrete members with circular cross section t... more In this work, a shear capacity model of reinforced concrete members with circular cross section transversely reinforced with circular hoops has been developed. The proposed model is based on the truss analogy by adding a concrete contribution term to the capacity of the shear reinforcement.An additional deviatoric shear resisting mechanism of hoops - present solely in members with curved transverse reinforcement - was identified and expressed analytically. It is explained by the fact that a curved reinforcing bar under tension induces compression in radial direction as well. The component of this compressive force in the direction of external shear could thus be considered as an additional shear enhancing mechanism of the hoops. Its magnitude is expressed through the friction force that is present between the concrete and steel after the section is cracked and the bond partially destroyed. The concrete shear capacity has been derived by a parameter study and by applying a curve fit ...
Polymers, Mar 31, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Frattura ed Integrità Strutturale, 2014
In the present paper, the well-known wedge splitting test (WST) is applied on specimens with diff... more In the present paper, the well-known wedge splitting test (WST) is applied on specimens with different geometries (S= 150, 200, 300 mm) and variants of the specimens’ configurations. K-calibration (B1) and T-stress (B2) calibration curves for such specimens are introduced. The objective was to compare and discuss the values of the calibration curves dependent on the specimen’s geometries and on three different specimens' configurations: homogenous specimen; specimen with marble plates forming the groove for load application and specimen with glued marble plates.
Sustainability
The cement industry could potentially consume large amounts of solid industrial waste in order to... more The cement industry could potentially consume large amounts of solid industrial waste in order to improve its sustainability. The suitability of selected quarry and mine waste as secondary raw materials (SRM) was examined for the sustainable production of cement following the concept of a circular economy. The chemical, mineralogical, and radiological characterization of SRM was conducted in this study. Its potential use in low-carbon and low-energy belite-sulfoaluminate cement was investigated by incorporating the examined SRM into cement clinker. Various characterization methods were used to characterize the cement, including X-ray powder diffraction (XRD), thermal analysis (DTA/TG), and isothermal calorimetry. Depending on the chemical composition of the waste, lower or higher amounts were allowed to be incorporated into the raw clinker mixture for a targeted clinker phase composition. Among the samples, differences were observed in the phase composition of synthesized clinkers, ...
Materials Proceedings
This article presents a methodology applied to the design of a tailor-made program for teaching s... more This article presents a methodology applied to the design of a tailor-made program for teaching staff that addresses the needs of high-level educational institutions in the Eastern and South-Eastern European (ESEE) region. The tailor-made program was implemented as a one-week online course for 22 “Trainees” from six ESEE universities earlier in 2021. “Trainees” from six participating universities are currently developing acceleration programs, planned to occur continuously until 2024, increasing the percentage of the trained academic staff to >50% at each of the six universities. During that period, 240 students will benefit from 140 improved RawMaterials-related courses, improving their learning and understanding.
Comparison of physical and mechanical properties of cementitious mortars reinforced with natural and synthetic fibres prior and after wet/dry cycles
In this research, the physical and mechanical properties of cement-based mortars reinforced with ... more In this research, the physical and mechanical properties of cement-based mortars reinforced with hemp, flax and polypropylene fibres, exposed to accelerated aging of wet/dry cycles, were studied and compared with their initial properties, prior aging. The mortar mixture was made with Portland cement as a binder, cement/sand/water ratio of 1:1:0.4 by weight and with sand of particle size between 0.4-0.8mm. As fibre reinforcement short hemp, flax and polypropylene fibres with dosage of 1,0 vol% (volume ratio) within the matrix was used. The results show that both the density and compressive strength of all composites increased after accelerated aging. The highest density increase was observed by hemp fibre mortars (up to 11.6%) whereas the highest increase in compression strength exhibited flax fibre reinforced mortars (up to 57.97%). When exposed to accelerated aging of wet/dry cycles, all mortars loss their initial flexural strength, however the lowest loss was observed by natural f...
The aim of this research was to investigate how the curing temperature influences the mechanical ... more The aim of this research was to investigate how the curing temperature influences the mechanical properties of fibre reinforced alkali activated matrices. The mortar matrix contained fly ash as a binder, sodium water glass as an activator and sand with a particle size between 0.4 and 0.8 mm. As reinforcement hemp fibres of 10 mm in length and of volume ratio 1% of the composite were used. The prism mortars had dimension of 40 × 40 × 160 mm3 and were cured under three different temperatures: 20 °C, 60 °C and 80 °C.
Concrete is one of the most widely used building material in civil engineering. However, as a ver... more Concrete is one of the most widely used building material in civil engineering. However, as a very brittle material it has low tension strength and fracture energy. As a result, cracks develop whenever loads give rise to tensile stresses exceeding the tensile strength of concrete. The addition of different fibres to concrete matrix substantially enhances the energy absorption capacity of the plane concrete [1, 2, 3]. Consideration of the fracture energy is important since it determines the ductility and crack resistance of the structure assuring the safety and integrity of the structural element prior to its complete failure. [4]. Concrete is typically reinforced with steel or synthetic fibres like carbon, glass, or aramid. Despite of their advantages the high material costs, the high energy-consuming process by the production, and their adverse environmental impact has initiated the search of new environmental friendly and sustainable alternatives. A considerable research effort is...
The application of natural fibres as fibre reinforcement in cementitious matrices such as concret... more The application of natural fibres as fibre reinforcement in cementitious matrices such as concrete has launched extensive research interest in recent decades. The main concern, however, is the durability of fibres in the alkaline environment of cement. In this research project the durability of hemp fibres in the alkaline environment of cement matrix in terms of tension strength loss has been experimentally investigated. The objective was to find the most effective protective agent which will reduce water absorption of fibres and, in a long-term preserves the tension strength loss of fibres. The protective substances used to saturate the fibres providing the water resistance protection were: linseed oil, linseed oil with catalyst, paraffin, and beam wax. The protected and unprotected hemp fibres were than immersed in saturated lime solution and Lawrence solution simulating the alkaline environment. Accelerated aging tests have been carried out in order to simulate a time elapse of 2...
Influence of the NaOH-treated hemp fibres on the properties of fly-ash based alkali-activated mortars prior and after wet/dry cycles
Construction and Building Materials
Physical and mechanical properties of hemp fibre reinforced alkali-activated fly ash and fly ash/slag mortars
Construction and Building Materials
Transactions of the VŠB – Technical University of Ostrava, Civil Engineering Series
Multi-parameter fracture mechanics is nowadays quite extensively applied when cracked structures/... more Multi-parameter fracture mechanics is nowadays quite extensively applied when cracked structures/specimens are investigated. The reason was that it has been shown that it can be helpful and bring results that are more accurate when for describing of fracture processes a larger region around the crack tip is used. This can be typical for material like concrete or other materials with quasi-brittle behaviour. Various relative crack length configurations were chosen in order to investigate the importance of the higher-order terms of the Williams expansion (WE) on the crack-tip stress field distribution in Wedge splitting test specimen. The higher-order terms were calculated by means of the over-deterministic method from displacements of nodes around the crack tip obtained by a finite element analysis in different radial distances from the crack tip. The effect of the constraint level (second member of WE) was investigated. Although the third and higher terms of the Williams series are very often neglected, their influence on the opening stress values was investigated and discussed.
Life Cycle Assessment of Natural Fibre Reinforced Cementitious Composites
Key Engineering Materials
Three cementitious composites containing different natural fibres (flax, hemp and sea-grass) were... more Three cementitious composites containing different natural fibres (flax, hemp and sea-grass) were evaluated from an environmental perspective by means of Life Cycle Assessment (LCA) method applying the cradle-to-gate approach. The environmental impact of these composites was compared to that of cementitious composites reinforced with conventional synthetic polyacrilonitrile (PAN) fibres. The functional unit was the production of one cubic meter of cementitious composites ready-for-use. The results show that generally the environmental footprint of composite with synthetic fibres is bigger than the footprint of the composites with added natural fibres. Exceptions may only be the impacts on eutrophication and freshwater aquatic ecotoxicity, which are significantly affected by cultivation of crops. Flax and hemp cultivation is associated with emissions to soil and water. For this reason, the composite mixture with flax fibres has a significantly greater impact on eutrophication and fre...
Procedia Structural Integrity
During their operation, modern aircraft engine components are subjected to increasingly demanding... more During their operation, modern aircraft engine components are subjected to increasingly demanding operating conditions, especially the high pressure turbine (HPT) blades. Such conditions cause these parts to undergo different types of time-dependent degradation, one of which is creep. A model using the finite element method (FEM) was developed, in order to be able to predict the creep behaviour of HPT blades. Flight data records (FDR) for a specific aircraft, provided by a commercial aviation company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model needed for the FEM analysis, a HPT blade scrap was scanned, and its chemical composition and material properties were obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D rectangular block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade. Therefore such a model can be useful in the goal of predicting turbine blade life, given a set of FDR data.
Numerical Stress Analysis of the Biaxial Tension-Compression Wedge-Splitting Test in Vicinity of the Crack Tip
Key Engineering Materials
Wedge-splitting test is widely used fracture mechanical test for its stability in measurement dur... more 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.
In the present paper, the well-known wedge splitting test (WST) is applied on specimens with diff... more In the present paper, the well-known wedge splitting test (WST) is applied on specimens with different geometries (S= 150, 200, 300 mm) and variants of the specimens' configurations. K-calibration (B 1) and T-stress (B 2) calibration curves for such specimens are introduced. The objective was to compare and discuss the values of the calibration curves dependent on the specimen's geometries and on three different specimens' configurations: homogenous specimen; specimen with marble plates forming the groove for load application and specimen with glued marble plates.
Quasi-brittle Behaviour of Composites as a Key to Generalized Understanding of Material Structure
Procedia Engineering
Abstract Quasi-brittle type of fracture behaviour is viewed from a unique perspective in the pape... more Abstract Quasi-brittle type of fracture behaviour is viewed from a unique perspective in the paper. This view explains and extends the classification of fracture of materials, as it is commonly understood, and might provide a way to a more general understanding of this phenomenon. The proposed approach separates the ‘effective’ (brittle) fracture phenomenon from the evolution of the nonlinear zone at the crack tip. This separation is performed on the energetic level, the evaluated work of fracture, as well as on the level of geometrical description of the two separated entities which are the products of the fracture phenomenon: The crack surface and the nonlinear zone around the crack front. The approach is introduced here mainly from the philosophical and theoretical standpoint, its verification and validation is included only partially.
Size and boundary effects on notch tensile strength and fracture properties of PMMA bone cement
Polymer Testing
Abstract Poly (methyl methacrylate) bone cement is widely used for anchoring total joint replacem... more Abstract Poly (methyl methacrylate) bone cement is widely used for anchoring total joint replacements. In such an application, tensile and fracture properties of the cement are particularly important as they have strong implications for the stability of the implant in the bone bed and, hence, its life. Being a quasi-brittle material, it is to be expected that any mechanical property of bone cement would be size-dependent. This issue has not been addressed in the literature. In the present work, tests using modified wedge-splitting specimens were carried out to determine the size and boundary effects on the notch tensile strength ( σ N T ) and on two fracture parameters, namely, specific fracture energy ( G f ), and characteristic length based on the notch tensile strength ( l c h s p l ) of a widely used approved brand, Palacos® R. Size and boundary effects, of varying magnitudes, on each of these properties were found. For example, 1) for geometrically-similar specimens (specimen height (W) was varied from 15 mm to 36 mm but ratio of length of the starter crack (a) to W was fixed), the general trend was marked decrease in σNT with increase in W for a given a/W; and 2) for identical-sized specimens (W was fixed but a/W was varied from 0.06 to 0.81), the general trend was moderate decrease in Gf with increase in a/W for a given W. A validated boundary effect model presented in the literature and results from some of the specimens used in the present experimental work were used to compute the size-independent specific fracture energy and transition ligament length of the cement brand to be 2096 N m−1 and 4 mm, respectively.
Proceedings of the 9th International Conference on Fracture Mechanics of Concrete and Concrete Structures, 2016
The paper presents a fracture-mechanics study conducted on a novel test configuration based on a ... more The paper presents a fracture-mechanics study conducted on a novel test configuration based on a combination of the wedge splitting and the bending test geometry. Four variants of this configuration differing in parameters of the specimen shape and boundary conditions were considered in the study. These selected variants exhibit significantly different stress state conditions at the crack tip, or, more generally, in the whole specimen ligament. The variation of the crack-tip stress constraint is of a crucial importance for the study because the expected differences in the fracture process zone extent and the amount of energy dissipation related to this zone is of particular interest here. An extensive experimental campaign was conducted on concrete specimens made of the same mixture. Processing and evaluation of the test data using the standard work of fracture technique was accompanied with numerical simulations by means of finite elements with implemented cohesive crack model to correlate the amount of energy dissipation with the simulated damaged zone extent. Variations of the fracture energy and also the stress/inelastic strain distribution with the change of the crack-tip constraint parameter and the notch length are observed. 1 INTRODUCTION, MOTIVATION A novel method for evaluation of fracturemechanical parameters of quasi-brittle cementitious composites was introduced recently [1] by the Brno University of Technology (BUT) partner of the joint research presented in this paper. The method should eliminate drawbacks of most of the established models for determination of those characteristics, which is the dependence of values the fracture properties determined from fracture tests on laboratory specimens on the specimen size, geometry and its boundaries. Capturing these effects shall be achieved via a detailed incorporation of the fracture process zone (FPZ) existence into the evaluation
Evaluation of Wedge Splitting Fracture Tests Using the Double-K Model: Analysis of the Effect of Hemp Fibre Dosage and Length in Concrete Specimens
Solid State Phenomena, 2016
This paper deals with the results obtained from the employment of a selected fracture model to ev... more This paper deals with the results obtained from the employment of a selected fracture model to evaluate wedge splitting fracture tests carried out on hemp fibre concrete specimens. The research work was focused mainly on the effect of the dosage and length of hemp fibres on the initiation part of crack propagation in concrete specimens, and on critical crack opening displacement. Concrete mixtures with different volumetric dosages (0.5, 1.0 and 2.0 %) and fibre lengths (10, 20 and 40 mm) were prepared, and six identical specimens were cast from each mixture. Specimens were also cast from a reference mixture, which was without fibres. The specimens were provided with an initial notch and tested using the wedge splitting test method. Load versus crack mouth opening displacement diagrams were recorded during testing and (after data filtering and appropriate modifications) subsequently evaluated using the Double-K fracture model. This model allows the evaluation of two material paramete...
Analytisches Model der Querkrafttragfähigkeit kreisförmiger Stahlbetonbauteile
In this work, a shear capacity model of reinforced concrete members with circular cross section t... more In this work, a shear capacity model of reinforced concrete members with circular cross section transversely reinforced with circular hoops has been developed. The proposed model is based on the truss analogy by adding a concrete contribution term to the capacity of the shear reinforcement.An additional deviatoric shear resisting mechanism of hoops - present solely in members with curved transverse reinforcement - was identified and expressed analytically. It is explained by the fact that a curved reinforcing bar under tension induces compression in radial direction as well. The component of this compressive force in the direction of external shear could thus be considered as an additional shear enhancing mechanism of the hoops. Its magnitude is expressed through the friction force that is present between the concrete and steel after the section is cracked and the bond partially destroyed. The concrete shear capacity has been derived by a parameter study and by applying a curve fit ...
Polymers, Mar 31, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Frattura ed Integrità Strutturale, 2014
In the present paper, the well-known wedge splitting test (WST) is applied on specimens with diff... more In the present paper, the well-known wedge splitting test (WST) is applied on specimens with different geometries (S= 150, 200, 300 mm) and variants of the specimens’ configurations. K-calibration (B1) and T-stress (B2) calibration curves for such specimens are introduced. The objective was to compare and discuss the values of the calibration curves dependent on the specimen’s geometries and on three different specimens' configurations: homogenous specimen; specimen with marble plates forming the groove for load application and specimen with glued marble plates.
Sustainability
The cement industry could potentially consume large amounts of solid industrial waste in order to... more The cement industry could potentially consume large amounts of solid industrial waste in order to improve its sustainability. The suitability of selected quarry and mine waste as secondary raw materials (SRM) was examined for the sustainable production of cement following the concept of a circular economy. The chemical, mineralogical, and radiological characterization of SRM was conducted in this study. Its potential use in low-carbon and low-energy belite-sulfoaluminate cement was investigated by incorporating the examined SRM into cement clinker. Various characterization methods were used to characterize the cement, including X-ray powder diffraction (XRD), thermal analysis (DTA/TG), and isothermal calorimetry. Depending on the chemical composition of the waste, lower or higher amounts were allowed to be incorporated into the raw clinker mixture for a targeted clinker phase composition. Among the samples, differences were observed in the phase composition of synthesized clinkers, ...
Materials Proceedings
This article presents a methodology applied to the design of a tailor-made program for teaching s... more This article presents a methodology applied to the design of a tailor-made program for teaching staff that addresses the needs of high-level educational institutions in the Eastern and South-Eastern European (ESEE) region. The tailor-made program was implemented as a one-week online course for 22 “Trainees” from six ESEE universities earlier in 2021. “Trainees” from six participating universities are currently developing acceleration programs, planned to occur continuously until 2024, increasing the percentage of the trained academic staff to >50% at each of the six universities. During that period, 240 students will benefit from 140 improved RawMaterials-related courses, improving their learning and understanding.
Comparison of physical and mechanical properties of cementitious mortars reinforced with natural and synthetic fibres prior and after wet/dry cycles
In this research, the physical and mechanical properties of cement-based mortars reinforced with ... more In this research, the physical and mechanical properties of cement-based mortars reinforced with hemp, flax and polypropylene fibres, exposed to accelerated aging of wet/dry cycles, were studied and compared with their initial properties, prior aging. The mortar mixture was made with Portland cement as a binder, cement/sand/water ratio of 1:1:0.4 by weight and with sand of particle size between 0.4-0.8mm. As fibre reinforcement short hemp, flax and polypropylene fibres with dosage of 1,0 vol% (volume ratio) within the matrix was used. The results show that both the density and compressive strength of all composites increased after accelerated aging. The highest density increase was observed by hemp fibre mortars (up to 11.6%) whereas the highest increase in compression strength exhibited flax fibre reinforced mortars (up to 57.97%). When exposed to accelerated aging of wet/dry cycles, all mortars loss their initial flexural strength, however the lowest loss was observed by natural f...
The aim of this research was to investigate how the curing temperature influences the mechanical ... more The aim of this research was to investigate how the curing temperature influences the mechanical properties of fibre reinforced alkali activated matrices. The mortar matrix contained fly ash as a binder, sodium water glass as an activator and sand with a particle size between 0.4 and 0.8 mm. As reinforcement hemp fibres of 10 mm in length and of volume ratio 1% of the composite were used. The prism mortars had dimension of 40 × 40 × 160 mm3 and were cured under three different temperatures: 20 °C, 60 °C and 80 °C.
Concrete is one of the most widely used building material in civil engineering. However, as a ver... more Concrete is one of the most widely used building material in civil engineering. However, as a very brittle material it has low tension strength and fracture energy. As a result, cracks develop whenever loads give rise to tensile stresses exceeding the tensile strength of concrete. The addition of different fibres to concrete matrix substantially enhances the energy absorption capacity of the plane concrete [1, 2, 3]. Consideration of the fracture energy is important since it determines the ductility and crack resistance of the structure assuring the safety and integrity of the structural element prior to its complete failure. [4]. Concrete is typically reinforced with steel or synthetic fibres like carbon, glass, or aramid. Despite of their advantages the high material costs, the high energy-consuming process by the production, and their adverse environmental impact has initiated the search of new environmental friendly and sustainable alternatives. A considerable research effort is...
The application of natural fibres as fibre reinforcement in cementitious matrices such as concret... more The application of natural fibres as fibre reinforcement in cementitious matrices such as concrete has launched extensive research interest in recent decades. The main concern, however, is the durability of fibres in the alkaline environment of cement. In this research project the durability of hemp fibres in the alkaline environment of cement matrix in terms of tension strength loss has been experimentally investigated. The objective was to find the most effective protective agent which will reduce water absorption of fibres and, in a long-term preserves the tension strength loss of fibres. The protective substances used to saturate the fibres providing the water resistance protection were: linseed oil, linseed oil with catalyst, paraffin, and beam wax. The protected and unprotected hemp fibres were than immersed in saturated lime solution and Lawrence solution simulating the alkaline environment. Accelerated aging tests have been carried out in order to simulate a time elapse of 2...
Influence of the NaOH-treated hemp fibres on the properties of fly-ash based alkali-activated mortars prior and after wet/dry cycles
Construction and Building Materials
Physical and mechanical properties of hemp fibre reinforced alkali-activated fly ash and fly ash/slag mortars
Construction and Building Materials
Transactions of the VŠB – Technical University of Ostrava, Civil Engineering Series
Multi-parameter fracture mechanics is nowadays quite extensively applied when cracked structures/... more Multi-parameter fracture mechanics is nowadays quite extensively applied when cracked structures/specimens are investigated. The reason was that it has been shown that it can be helpful and bring results that are more accurate when for describing of fracture processes a larger region around the crack tip is used. This can be typical for material like concrete or other materials with quasi-brittle behaviour. Various relative crack length configurations were chosen in order to investigate the importance of the higher-order terms of the Williams expansion (WE) on the crack-tip stress field distribution in Wedge splitting test specimen. The higher-order terms were calculated by means of the over-deterministic method from displacements of nodes around the crack tip obtained by a finite element analysis in different radial distances from the crack tip. The effect of the constraint level (second member of WE) was investigated. Although the third and higher terms of the Williams series are very often neglected, their influence on the opening stress values was investigated and discussed.
Life Cycle Assessment of Natural Fibre Reinforced Cementitious Composites
Key Engineering Materials
Three cementitious composites containing different natural fibres (flax, hemp and sea-grass) were... more Three cementitious composites containing different natural fibres (flax, hemp and sea-grass) were evaluated from an environmental perspective by means of Life Cycle Assessment (LCA) method applying the cradle-to-gate approach. The environmental impact of these composites was compared to that of cementitious composites reinforced with conventional synthetic polyacrilonitrile (PAN) fibres. The functional unit was the production of one cubic meter of cementitious composites ready-for-use. The results show that generally the environmental footprint of composite with synthetic fibres is bigger than the footprint of the composites with added natural fibres. Exceptions may only be the impacts on eutrophication and freshwater aquatic ecotoxicity, which are significantly affected by cultivation of crops. Flax and hemp cultivation is associated with emissions to soil and water. For this reason, the composite mixture with flax fibres has a significantly greater impact on eutrophication and fre...
Procedia Structural Integrity
During their operation, modern aircraft engine components are subjected to increasingly demanding... more During their operation, modern aircraft engine components are subjected to increasingly demanding operating conditions, especially the high pressure turbine (HPT) blades. Such conditions cause these parts to undergo different types of time-dependent degradation, one of which is creep. A model using the finite element method (FEM) was developed, in order to be able to predict the creep behaviour of HPT blades. Flight data records (FDR) for a specific aircraft, provided by a commercial aviation company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model needed for the FEM analysis, a HPT blade scrap was scanned, and its chemical composition and material properties were obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D rectangular block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade. Therefore such a model can be useful in the goal of predicting turbine blade life, given a set of FDR data.
Numerical Stress Analysis of the Biaxial Tension-Compression Wedge-Splitting Test in Vicinity of the Crack Tip
Key Engineering Materials
Wedge-splitting test is widely used fracture mechanical test for its stability in measurement dur... more 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.
In the present paper, the well-known wedge splitting test (WST) is applied on specimens with diff... more In the present paper, the well-known wedge splitting test (WST) is applied on specimens with different geometries (S= 150, 200, 300 mm) and variants of the specimens' configurations. K-calibration (B 1) and T-stress (B 2) calibration curves for such specimens are introduced. The objective was to compare and discuss the values of the calibration curves dependent on the specimen's geometries and on three different specimens' configurations: homogenous specimen; specimen with marble plates forming the groove for load application and specimen with glued marble plates.
Quasi-brittle Behaviour of Composites as a Key to Generalized Understanding of Material Structure
Procedia Engineering
Abstract Quasi-brittle type of fracture behaviour is viewed from a unique perspective in the pape... more Abstract Quasi-brittle type of fracture behaviour is viewed from a unique perspective in the paper. This view explains and extends the classification of fracture of materials, as it is commonly understood, and might provide a way to a more general understanding of this phenomenon. The proposed approach separates the ‘effective’ (brittle) fracture phenomenon from the evolution of the nonlinear zone at the crack tip. This separation is performed on the energetic level, the evaluated work of fracture, as well as on the level of geometrical description of the two separated entities which are the products of the fracture phenomenon: The crack surface and the nonlinear zone around the crack front. The approach is introduced here mainly from the philosophical and theoretical standpoint, its verification and validation is included only partially.
Size and boundary effects on notch tensile strength and fracture properties of PMMA bone cement
Polymer Testing
Abstract Poly (methyl methacrylate) bone cement is widely used for anchoring total joint replacem... more Abstract Poly (methyl methacrylate) bone cement is widely used for anchoring total joint replacements. In such an application, tensile and fracture properties of the cement are particularly important as they have strong implications for the stability of the implant in the bone bed and, hence, its life. Being a quasi-brittle material, it is to be expected that any mechanical property of bone cement would be size-dependent. This issue has not been addressed in the literature. In the present work, tests using modified wedge-splitting specimens were carried out to determine the size and boundary effects on the notch tensile strength ( σ N T ) and on two fracture parameters, namely, specific fracture energy ( G f ), and characteristic length based on the notch tensile strength ( l c h s p l ) of a widely used approved brand, Palacos® R. Size and boundary effects, of varying magnitudes, on each of these properties were found. For example, 1) for geometrically-similar specimens (specimen height (W) was varied from 15 mm to 36 mm but ratio of length of the starter crack (a) to W was fixed), the general trend was marked decrease in σNT with increase in W for a given a/W; and 2) for identical-sized specimens (W was fixed but a/W was varied from 0.06 to 0.81), the general trend was moderate decrease in Gf with increase in a/W for a given W. A validated boundary effect model presented in the literature and results from some of the specimens used in the present experimental work were used to compute the size-independent specific fracture energy and transition ligament length of the cement brand to be 2096 N m−1 and 4 mm, respectively.
Proceedings of the 9th International Conference on Fracture Mechanics of Concrete and Concrete Structures, 2016
The paper presents a fracture-mechanics study conducted on a novel test configuration based on a ... more The paper presents a fracture-mechanics study conducted on a novel test configuration based on a combination of the wedge splitting and the bending test geometry. Four variants of this configuration differing in parameters of the specimen shape and boundary conditions were considered in the study. These selected variants exhibit significantly different stress state conditions at the crack tip, or, more generally, in the whole specimen ligament. The variation of the crack-tip stress constraint is of a crucial importance for the study because the expected differences in the fracture process zone extent and the amount of energy dissipation related to this zone is of particular interest here. An extensive experimental campaign was conducted on concrete specimens made of the same mixture. Processing and evaluation of the test data using the standard work of fracture technique was accompanied with numerical simulations by means of finite elements with implemented cohesive crack model to correlate the amount of energy dissipation with the simulated damaged zone extent. Variations of the fracture energy and also the stress/inelastic strain distribution with the change of the crack-tip constraint parameter and the notch length are observed. 1 INTRODUCTION, MOTIVATION A novel method for evaluation of fracturemechanical parameters of quasi-brittle cementitious composites was introduced recently [1] by the Brno University of Technology (BUT) partner of the joint research presented in this paper. The method should eliminate drawbacks of most of the established models for determination of those characteristics, which is the dependence of values the fracture properties determined from fracture tests on laboratory specimens on the specimen size, geometry and its boundaries. Capturing these effects shall be achieved via a detailed incorporation of the fracture process zone (FPZ) existence into the evaluation
Evaluation of Wedge Splitting Fracture Tests Using the Double-K Model: Analysis of the Effect of Hemp Fibre Dosage and Length in Concrete Specimens
Solid State Phenomena, 2016
This paper deals with the results obtained from the employment of a selected fracture model to ev... more This paper deals with the results obtained from the employment of a selected fracture model to evaluate wedge splitting fracture tests carried out on hemp fibre concrete specimens. The research work was focused mainly on the effect of the dosage and length of hemp fibres on the initiation part of crack propagation in concrete specimens, and on critical crack opening displacement. Concrete mixtures with different volumetric dosages (0.5, 1.0 and 2.0 %) and fibre lengths (10, 20 and 40 mm) were prepared, and six identical specimens were cast from each mixture. Specimens were also cast from a reference mixture, which was without fibres. The specimens were provided with an initial notch and tested using the wedge splitting test method. Load versus crack mouth opening displacement diagrams were recorded during testing and (after data filtering and appropriate modifications) subsequently evaluated using the Double-K fracture model. This model allows the evaluation of two material paramete...