Papers by Keyword: Boundary Effect

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Authors: Kai Duan, Xiao Zhi Hu
Abstract: This paper explores the ligament-dependent behaviour of specific work of fracture of polymeric materials using a recently-developed modified EWF model. It is demonstrated that the non-linear relationship between specific work of fracture (wf) and ligament length (l) is a result of specimen boundary influence on the evolution of plastic zone. A transition ligament (l*) is defined, below which, the height of under-developed plastic zone is equal to the ligament length, and as a result, a linear wf-l relation will be observed. The plastic zone will saturate at the transition ligament, and its height will no longer increase when l > l*. This will result in a non-linear wf-l relation. Experimental wf-l data available in the literature are analysed using the modified EWF model and very good agreements are achieved.
Authors: Kai Duan, Xiao Zhi Hu
Abstract: The recently-developed boundary effect concept and associated asymptotic model are used to explain the size effect phenomena in fracture of quasi-brittle materials. It is demonstrated that the size dependence of the fracture toughness and strength of quasi-brittle materials is indeed due to the influences of specimen boundaries on the failure mode and therefore, on the strength of the specimen. To verify the boundary effect concept, fracture tests on a high strength concrete reported by Karihaloo et al are analysed and predicted using the asymptotic model. The results show that the predictions of the asymptotic boundary effect model agree very well with those experimental results.
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: 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: Bin Xia, Xin Liang Liu, Fanyu Kong
Abstract: Human's daily action is generally contacted by space boundary naturally or unconsciously. Moreover, the existence of boundary influents human's behavior and experience at any moment. Good space boundary will create places full of vitality and have an positive effect on activities in space. Otherwise, space boundary could also exert a negative influence on human’s activity. This thesis, on the modern cognitive theory, expounds problems of boundary effect of exterior space of architecture in the perspective of architectural psychology.
Authors: Hai Feng Sun, Li Ping Jing, Qing Hai Wei, Xian Chun Meng
Abstract: Shaking table test is an important method to study on the problem of the soil-structure dynamic interaction. The property of the soil container directly affects the accuracy of the result. A laminar shear container was designed for shaking table test. And a shaking table test on soil-underground structure dynamic interaction which structure lay in clay was conducted. The results of the test show that the container eliminated the boundary effect when the dynamic load was applied in only one horizontal direction. Meanwhile, the stiffness of the soil container could be changed according to the change of the model soil, which is applicable to decrease the boundary effect.
Authors: Ping Wang, Long Hou, S.M. Asce
Abstract: This paper presents a self-made apparatus which has been used for estimating the adverse influence induced by some factors. There are two main factors that can make significant impact on the result of slope model tests: boundary effect and porosity effect. The relationship between the sliding angle and boundary effect can be achieved when the soil is at a loose condition of packing. The angle will decrease as the slope thickness increases and it will keep at a rough constant value when the thickness is relatively big, namely, the influence induced by the boundary effect which can be ignored at that time. In this paper, a theoretical method is employed to quantify and confirm this relationship. Corresponding predicted results agree well with the experimental results. But this conclusion is not suitable to dense soil. Special attention is also given to dense soil within a given porosity range, and a comparison between boundary effect and porosity is described. It could be seen clearly that the porosity is a stronger factor to the variation of the sliding angle than the boundary condition. These conclusions are valuable to a practitioner in taking modification work for such type of apparatus to get an optimal resolution for the latter experiment.
Authors: Shah Neyamat Ullah, Yu Xia Hu, David White, Samuel Stanier
Abstract: The effect of the centrifuge strongbox boundary on the penetration resistance of a spudcan foundation in uniform clay has been studied using Large Deformation FE analysis. Both smooth and rough strongbox boundaries were considered with various strongbox sizes. The spudcan penetration resistance and soil flow mechanisms were analysed. It was observed that, when the strongbox size was reduced, the spudcan penetration resistance was decreased for a smooth boundary and increased for a rough boundary. The depth of cavity formed above the spudcan during its penetration, in most cases, was determined by the soil flow around mechanism without cavity wall failure. However, cavity wall failure could be initiated when a smooth strongbox boundary was very close to the spudcan. The strongbox boundary effect on the spudcan penetration resistance can be avoided when the distance of the strongbox boundary to the spudcan centre is larger than 1.5 times of spudcan diameter for a rough boundary; or 2 times of spudcan diameter for a smooth boundary.
Authors: Shu You Wang, Jian Bing Men, Jian Wei Jiang
Abstract: The influence of radial and axial boundary effect on penetration effect are calculated, numerical simulation are executed to compute the kinetic projectile against deep hard target by finite element code, the boundary effects were achieved for different velocity range. Result shows that the minimal Dt/Dp (diameter ratio of target to projectile) for impact velocity 600m/s is 17.5, while the minimal Dt/Dp for impact velocity 900m/s is 20. Furthermore, the depth of equivalent target to substitute semi-infinite target is twice of penetration depth limit for impact velocity 300m/s, and 1.6 times respectively, for impact velocity 600m/s, 900m/s.
Authors: Jia Bo Qiu, Zhi Yuan Mei
Abstract: Composite sandwich structures have been used more and more widely in the underwater structures, therefore deformation problems under deep-water hydrostatic pressure can not be ignored. For the deformation properties of composite sandwich structures under deep-water hydrostatic pressure, the paper carried out theoretical and test research. First, the paper analyzed the surface deformation features as well as the law of the element’s cross-sectional dimension, the core thickness and elastic modulus to the surface deformation by establishing theoretical analysis model; The results show that the deformation area can be divided into central area and boundary area, and the boundary effect is an important factor affecting the deformation, the core parameters can affect the reach of boundary effect. Second, the paper carried out hydrostatic test of composite sandwich structural element model, and then verified the theoretical analysis model’s rationality and accuracy by comparing the test results and theoretical results.
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