Papers by Keyword: Work of Fracture

Abstract: The paper discusses creation of numerical models of the modified Compact Tension (CT) test configuration on specimens made of fine-grained cement composite. Numerical models of this test configuration are used for predictions of crack initiation and damage propagation and are important for the further evaluation of fracture parameters. To assemble the numerical models, ATENA FEM software was used. In this software, fracture of the structure/specimen caused by cracks, their initiation and progressive propagation throughout the loading process, can be modelled. In case of this study the material model for concrete based on cohesive law approach was used. The analysis is focused on evaluation of 2D and 3D numerical models created with real material properties obtained from experimental data.

Abstract: The paper presents an analysis aiming at capturing the phenomenon of quasi-brittle fracture based on the record of the fracture tests on notched specimens. A method of separation of the energy amounts released for the crack advance and that dissipated within the volume of the sizeable nonlinear zone at the crack tip – the fracture process zone– is introduced. The approach is tested on selected data of published experimental campaigns accompanied with own conducted numerical simulations.

Abstract: The paper presents an analysis with an attempt to capture the phenomenon of quasi-brittle fracture based on the record of the fracture test on a notched specimen via separation the energy amounts released for the crack advance and dissipated within the volume of the sizeable nonlinear zone at the crack tip – the fracture process zone (FPZ). The described approach is tested on selected data of published experimental campaigns accompanied with own conducted numerical simulations.

Abstract: The paper presents an analysis of the influence of the compressive (vertical) component of the loading force in the wedge splitting test on the values of fracture characteristics determined using standard procedures where this component is ignored. Particularly, a portion of work of fracture due to this compressive component of loading working on vertical displacements is investigated and given into relation with the common part of work of fracture calculated in the horizontal direction only. The results show that, based on the angle and width of the wedge used in the particular WST configuration, the portion of the work of fracture due to compressive loading can be considerable and should not be neglected.

Abstract: Factors determining the durability of a material include among others its thermal shock resistance, as a non-homogenous temperature field may trigger the formation and propagation of cracks. To evaluate thermal shock resistance by means of one of the resistance criteria: the R_st or R₄ parameter, it is necessary to know the work of fracture (γ_WOF), which is determined in a cracking test. Technical testing conditions influence the recording of crack propagation in a material sample. Ordinary and refractory castables are a group of materials in which the effect of temperature on the course of their cracking is among others related to the presence of deformations, internal stresses and cracks. Tests were performed for mullite, andalusite and boxite doped chromia castables, having known phase compositions, for which the temperature of liquid phase appearance in the matrix was calculated. A considerable increase in the value of castables γ_WOF at 900°C was noted compared to the values at 300°C and 600°C. In the group of the examined castables the highest γ_WOF value was obtained for andalusite castable. The applied methods of testing enabled simultaneous presentation of crack propagation in terms of energy (load vs. deformation) and kinetics (load vs. time).

Abstract: A kind of laminated composite named Al₂O₃/Nylon/Al with high work of fracture was prepared by a simple process using epoxy resin adhesives as binder in a leaky mold at a pressure of 5 MPa. Light microscopy and scanning electron microscopy were employed to observe the microstructures and crack propagation of the laminated composites. The flexural strength and fracture toughness were measured through three-point bending test, and the work of fracture of the laminated composite was calculated from load-displacement curves of three-point bending test. The experimental results show the composite have low Young's modulus and flexural strength, however, the work of fracture of the laminated composite appears to be high of 2850 J/m², and the fracture toughness reaches about 11 MPa•m^1/2. Analysis of microstructure and crack propagation reveals that the failure of the laminated composite exhibit distinctive characteristic.

Abstract: The mechanical behaviour of ceramic refractories formulated in the MgO-CaO-SiO2- ZrO2 system is analysed in terms of the room temperature Young´s modulus, the modulus of rupture and the work of fracture at 25 and 1100°C. The materials have been designed taking into account the phase equilibrium relationships to obtain MgO-CaZrO3-Ca2SiO4-Ca3Mg(SiO4)2 or MgO-CaZrO3-Ca3Mg(SiO4)2-c-ZrO2 as final crystalline phases. Different relationships between the proportion and sizes of the fines and the aggregates have been explored. The microstructure of the materials has been characterised in terms of density, crystalline phases and phase distribution and morphology. A combination of X-Ray diffraction (XRD) analyses and Reflected Light Optical Microscopy (RLOM) has been used. The relationships between the obtained phases and microstructures and the grain size distributions of the used raw materials have been established. The relationships between the mineralogical composition and the obtained microstructure and the mechanical behaviour are discussed.

Abstract: New laminate design for improved toughness in hexacelsian-alumina composite is introduced. The composite is based on crack deflection in a weak interphase in the alumina matrix and hexacelsian interphase. The strength and toughness of the laminated composite were studied both qualitatively by electronic microscopy and measuring flexure strength. The metastable hexacelsian interphases had partially microcracks to provide crack deflection in the composite, and the crack deflection noticeably proceeded along the meta-stable hexacelsian interphase. Load-deflection curve for the laminate showed improved work of fracture of 2.23 kJ/m2.

Abstract: A fracture toughness model of fibrous monolithic ceramics revealed that the major factor that contributed to the fracture toughness in ceramics was the actual energy absorbed by crack propagation rather than the total work of fracture. The load-displacement curve and the crack propagation path were predicted using the derived model mirror image with that of experimental data.

Abstract: In the present work, TZ-3Y20A/Mo multilayer composites were prepared by sedimentation method. Appropriate settling parameters were chosen and green bodies of multilayer composites were obtained by settling TZ-3Y20A powder and Mo powder in turn according to the designed individual layer thickness. Then green laminates were hot pressed at 1773K for an hour under the pressure of 20MPa. Three-point Bending and Single Edge Notched Beam (SENB) tests were adopted to evaluate the flexure strength and fracture toughness of the samples. The results showed that, compared to TZ-3Y20A ceramics, the fracture toughness and the work of fracture increased due to the layered structure. The microstructure and crack deflection of the fracture surface of the laminated composites was also observed by optical microscopy.