Papers by Keyword: Fracture Mechanic

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Authors: Olaf van der Sluis, P.H.M. Timmermans, E.J.L. van der Zanden, J.P.M. Hoefnagels
Abstract: Stretchable electronics offer potential application areas in biological implants interacting with human tissue, while also facilitating increased design freedom in electronics. A key requirement on these products is the ability to withstand large deformations during usage without losing their integrity. Experimental observations show that delamination between the metal conductor lines and the stretchable substrate may eventually lead to short circuits while also the delaminated area could result in cohesive failure of the metal lines. Interestingly, peel tests show that the rubber is severely lifted at the delamination front caused by its high compliance. To quantify the interface in terms of cohesive zone properties, these parameters are varied such that the experimental and numerical peel-force curve and rubber-lift geometry at the delamination front match. The thus obtained interface properties are used to simulate the delamination behavior of actual three-dimensional stretchable electronics samples loaded in tension.
Authors: Pei Juan Lu, Jie Yang, Cong Bin Huang
Abstract: The relationship between surface crack tip stress intensity factor and calculated parameters of pavement structure is discussed and finite element models based on the fracture mechanics theory is created. From the study in this paper, the following conclusions can be drawn: As the load increases, stress intensity factor will decrease, and it may promote spread of the crack. Surface layer modulus has a great influence on stress intensity factor. In the condition of the same crack depth, stress intensity factor increases while surface layer modulus increases, stress intensity factor decreases gradually while the thickness of the surface layer increases. As base layer modulus increasing, stress intensity factor of surface layer decreases. With the increase of the modulus of subbase layer, stress intensity factor of surface layer decreases gradually. The earthen foundation module has a little big influence. With the increase of the earthen foundation module, stress intensity factor will decrease, so it can delay the appearance of the crack.
Authors: Hong Chang Qu, Sheng Li Zhang, Ling Ling Chen
Abstract: The bonding of fiber reinforced polymer (FRP) strips and plates to the concrete structures has been found to be an effective technique for flexural strengthening. The FRP is then under both pulling and peeling forces, resulting in a combination of shear sliding and opening displacement along the FRP/concrete interface. A novel experimental set-up is studied that a peeling load is applied on the FRP sheet by a circular rod placed into the central notch of the beam. Based on the linear-elastic fracture mechanics approach, a theoretical analysis is conducted on specimens representing the peeling behavior. From the numerical analysis, the load–displacement curves, load–stiffness of FRP sheet curves, and load–fracture energy curves affected by different variables are discussed. The peel load is related to the FRP sheet stiffness and to the interfacial fracture energy. Therefore, only two material parameters, the interfacial fracture energy of FRP–concrete interface and stiffness of FRP sheets, are necessary to represent the interfacial fracture behavior. The theoretical load–deflection curves of specimens agree well with the corresponding experimental results in the literatures.
Authors: Satoshi Hanawa, Masahiro Ishihara, Yoshinobu Motohashi
Abstract: In the structural design of ceramics components especially for graphite materials, it is important to apply the realistic fracture model in the design method so as to reduce the large safety margin. In this study, we proposed the multiaxial strength model by expanding the microstructure based brittle fracture model applicable to both uniaxial tensile and compressive stress conditions. The advantage of the model is a treatment of the microstructural information such as grain size, pore size and pore size distribution. The proposed model was applied to biaxial strength prediction of near isotropic nuclear graphite using grain/pore related microstructure parameters. Predicted results were compared with biaxial strength data, and it was found that the proposed fracture model showed fairly good strength prediction.
Authors: Lu Xiang, Wei Shen Zhu, Qing Song Ma, Kui Zhou
Abstract: A damage constitutive model was established to evaluate the stability of jointed rock masses around the underground caverns of Shuangjiangkou Hydropower Station. In this model, a second-order damage tensor was formulated to describe the initial geometric imperfection of jointed rock masses. A failure criterion for crack coalescence and a damage evolution equation were proposed by considering the secondary cracks induced by excavations according to the fracture mechanics principles. A subprogram under the framework of FLAC-3D was developed for the damage constitutive model and the damage evolution equation. The model and program were then applied in the stability assessment for the Shuangjiangkou underground cavern group.
Authors: J.J. Mecholsky Jr.
Abstract: The fracture surface records past events that occur during the fracture process by leaving characteristic markings. The application of fractal geometry aids in the interpretation and understanding of these events. Quantitative fractographic analysis of brittle fracture surfaces shows that these characteristic markings are self-similar and scale invariant, thus implying that fractal analysis is a reasonable approach to analyzing these surfaces. The fractal dimensional increment, D*, is directly proportional to the fracture energy, γ, during fracture for many brittle materials, i.e., γ = ½ E a0 D* where E is the elastic modulus and a0 is a structural parameter. Also, D* is equal to the crack-size-to-mirror-radius ratio. Using this information can aid in identifying toughening mechanisms in new materials, distinguishing poorly fabricated from well prepared material and identifying stress at fracture for field failures. Examples of the application of fractal analysis in research, fracture forensics and solving production problems are discussed.
Authors: M.X. Zhang, X.L. Lee, A.A. Javadi
Abstract: There is a macro-crack and micro-crack system in rock, which affects almost all the mechanical properties of rock, especially for the fracture mechanism. The propagation of pre-existing cracks in rock samples under load is fundamental to understanding of rock fracture mechanisms. It is evident that assumption of Griffith theory was not in accord with the fact that numerous cracks exist in rock. So, it is difficult to explain how the propagation of a micro-crack developed into macro-failure by conventional theories. In order to investigate the cause and results of fracture within the rock, the stress concentration around the micro-cracks was analyzed, which resulted in propagation of wing cracks and connecting adjacent original cracks, eventually leading to macro-failure. The experiments on gypseous samples with pre-existing parallel cracks (flat rectangular in shape) under compression were carried out. The fracture mechanism and the stress equilibrium condition at brittle rock were discussed. Based on the fracture mechanism of brittle rock, a strength criterion of rock was proposed.
Authors: Arno Plankensteiner, Bernhard Tabernig
Abstract: The optimization of CFC/Cu-interfaces for plasma facing divertor components in thermo-nuclear fusion reactors is proposed and demonstrated via an integrative numerical-experimental approach mainly comprising a macro-scale to micro-scale finite element modeling technique together with fracture mechanics tests. Results obtained by finite element analyses of real-scale CFC flat tile divertor components under high heat flux loading conditions are verified by the findings of tests in an ion beam high heat flux facility. From the macro-scale FE models of the full component the loading conditions are derived for micro-scale FE models that incorporate principal details of the micro-structured CFC/Cu-interface thus allowing to capture explicitly locally acting dissipative mechanisms which in turn at the macro-scale in fracture mechanics experiments increase the fracture toughness of the CFC/Cu-interface.
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.
Authors: Lukáš Řehořek, Zdeněk Chlup, Ivo Dlouhý, Aldo Roberto Boccaccini
Abstract: Fracture behaviour and mechanical properties are the key features when a material for given application is supposed to be selected. Advanced glass ceramics composites are perspective structural materials for many applications due to their low production expenses and satisfactory properties even at elevated temperatures. Borosilicate glass matrix composite reinforced by alumina platelets was investigated to describe toughening mechanisms and their changes in a wide range of temperatures (from room temperature up to glassy transition temperature Tg). The dissipation of energy by bridging and/or deflection of propagating crack by alumina platelets uniformly dispersed in the glass matrix were the main toughening mechanisms observed. The alumina platelets have a higher ability to deflect propagating crack in comparison with spherical or rectangular particles having the same volume. Three and four point bend test for Young’s modulus and flexural strength determination was used. Fracture toughness determination was conducted using chevron notch technique. More than 100% increase of fracture toughness was observed when 30% of alumina platelets were added in to borosilicate matrix.
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