Papers by Keyword: Fracture Energy

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Authors: Xiao Qin Li, Bao Qi Chen, Ying Xian Li
Abstract: This paper concerns the simulation of Mode I fracture with a local concrete damage model in explicit finite element code LSDYNA. A reliable modeling of fracture is essential in the analysis of tension-dominated problems, as well as the prediction of concrete damage due to cracking. A special focus of this paper is placed on an effective representation of the tensile localization in finite element modeling while generalized macro material properties are employed to modeling meso-scale problems. An investigation into the use of a typical damage plasticity concrete model within LSDYNA Explicit, based on the crack band theory, is described in detail. The main focus of the current paper is on the tensile softening branch.
Authors: Zhong Hu Zhao
Abstract: Fracture energy, which reflects the split property of brittle materials, is a significant parameter. For present tests of measuring it, the indirect test itself has insuperable disadvantage, while the direct tension test, in spite of an ideal way, is too limited to be widely applied in ordinary labs for its over high requirement for the test machine. The paper analyzed the disadvantage of the direct tension machine and improved it: a new elastic foundation of lower clamper replaced the original rigid one. Using the improved machine, the complete stress-strain tensile curve of the brittle materials was obtained easily. Further, the fracture energy could be calculated. Basing on studies, the paper recommended it may as well to get the fracture energy by improved direct tension machine.
Authors: J.R. Moon
Abstract: It is now fairly well established that to achieve low values of the Paris exponent for the growth of fatigue cracks in PM steels, high values of fracture toughness are required. Fracture toughness is related to other measures of toughness, such as impact tests and the mechanical work that the material can absorb before fracturing. All of these are functions of the basic ductility of the material. A coherent picture of all these inter-relationships is presented.
Authors: Michele Buonsanti, Antonella Pontari
Abstract: A new stress function modelling the fails in biological tissue is here proposed. Under the assumption that the cell membrane may be modelled as neo-Hookean materials, we develop the problem in the framework of non-linear elasticity. We attempt to model the ice nucleation phenomenon when freezing and thawing occurs in cellular cryo-preservation. The ice seed generated surface can be either soft or wrinkled and, when the latter emerges a punch contact against the cell membrane takes place. Restricting our attention on opportune mono-dimensional sub-set, we extend the multiple critical points theorem at our model. We find a particular solution in agreement to the classical fracture models besides a response function in accordance to the stress and strain field distribution in biological materials.
Authors: Dariusz Alterman, Juan Vilches, Thomas Rainer Neitzert
Abstract: The relationship between various steel strip geometries and the bonding energy through pull-out tests of aerated concrete specimens is investigated. Prismatic concrete samples containing embedded steel strips with and without holes of differing sizes and quantities were analysed. Improvements of the bonding energy through pull-out tests by 70% are possible by increasing the number of holes on a steel strip from one to four while maintaining a constant surface area. The energy increased even up to 130% for strips containing holes compared to strips without. In addition, the tests have been carried out with a novel easy to assemble set-up containing a freely adjustable ball-joint and a plate with embedded bolts to avoid eccentricity during pull-out tests.
Authors: Kai Duan, Xiao Zhi Hu
Abstract: In this paper, the extensively-reported “size effect” phenomena in fracture mechanics tests are explained using the boundary effect concept. It is pointed out that the widely-observed size effect in fracture, including the dependence of the fracture energy on ligament, strength and fracture toughness on crack and/or ligament and the strength of geometrically similar specimens on characteristic size, is in fact, due to the boundary influence on the crack tip damage zone. Furthermore, the recently-developed asymptotic model is used to demonstrate that the dependence of strength on crack and ligament lengths as well as on the characteristic size of geometrically similar specimens is a result of the dominance of the distance of the crack tip to specimen boundaries on the specimen failure mode. To verify further the boundary effect concept, the asymptotic model is also applied to two sets of selected experimental data available in the literature, and the implications are discussed.
Authors: Long Quan Liu, Zheng Qiang Yao, Xue Ping Zhang, G.J. Yuan
Authors: Ondřej Holčapek, Pavel Reiterman, Petr Konvalinka
Abstract: This contribution brings summary of refractory hydraulic binder issue. The refractory cement composites (or refractory concrete) represent very specific area of modern material engineering. We can find its use in special monolithic structures in industry, for fire-resistance brick, protection cladding, etc. The composition brings opportunity for using aluminous cement with different amount of Al2O3, according to temperature level. Hydration process and products together with the decomposition due high temperatures is described in this paper. Also the risk of conversion metastable hydration to stable one is described. The issue of possible bonds between filler and binder is shown (hydraulic, ceramic and chemical). Paper also describes values of fracture energy of aluminous cement pastes with various water to cement ratio after temperature loading.
Authors: Yan Hua Zhao, Shi Lang Xu, Zhi Min Wu, Hong Bo Gao
Abstract: The apparent size effect of the specific fracture energy of concrete according to the RILEM procedure has been confirmed by numerous published works. The paper offers an explanation for this size effect by considering the specimen boundary influence on local fracture energy over the ligament length, which is closely associated with the measured fracture energy of concrete. To address this boundary influence, boundary affected length is introduced, over which local fracture energy is different from that in the bulk far away from the surface of the specimen. Based on previous work, a continuous smooth function is hypothesized to simulate the distribution of local fracture energy. At the same time, the model established was compared to the existing models, i.e. Perturbed Ligament Model (PLM) and Bilinear Model (BLM). Some test results from wedge splitting specimen in the literature were used to verify these three models. The results show that the true fracture energy of concrete, irrespective of the specimen size, could be obtained from the measured values directly from RILEM, and is less sensitive to determination approach. The predicted boundary affected length when the crack reaches the specimen surface is more close to the value of the perturbation length in PLM.
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