Advanced Materials Research Vols. 243-249

Abstract: Crack propagation behaviors at a mortar-aggregate interface in concrete under dynamic tensile loading conditions are investigated numerically. It is found, for a certain interfacial strength and aggregate size, that the crack can penetrate through the interface under an external load with its loading-rate higher than a threshold value. Moreover, for the crack penetration, the smaller the radius of an aggregate, the higher the loading-rate is needed. Therefore, concrete failure energy increase considerably with the loading-rate (or the strain-rate). Such a strain-rate effect on the strength of concrete is in agreement with previous experimental results.

Abstract: According to the deformation characteristics of global side torsion buckling for rectangle thin-walled aqueduct, the critical load of side torsion buckling for rectangle thin-walled aqueduct is deduced by Galerkin method. Influences of prestress and vertical deformation before buckling are considered. The variation rules of critical load are analyzed with four factors: span, flange width, ratio of height to width, thickness. The analysis results show that the aqueduct span is the biggest influence on the critical load of side torsion buckling for aqueduct; for rectangular thin-walled aqueduct, in conventional aqueduct section size and span, its critical stress of side torsion buckling is greater than concrete compressive strength design value , therefore side torsion buckling won't happen in usual aqueduct; if steel with high yield limit is used, stability check calculation must be carried out. Results and conclusions obtained can be referenced for the global stability design of thin-walled aqueduct.

Abstract: In this work, the spatial theoretical solutions of concentrated normal forces acting in the substrate and at the interface of semi-infinite coating materials have been deduced based on the image point method. The explicit solution is given in the series of the displacement functions corresponding to each image point. It is found that all displacement functions can be deduced by the order of the image point. Numerical analysis has been carried out to verify the theoretical deductions. It is found that the accurate enough theoretical solution can be obtained by only taking the displacement functions corresponding to the first several image points into account. The fundamental solutions for a concentrated force acting at interface of two bonded semi-infinite bodies is also deduced, which is necessary in the analysis of coating materials by using these theoretical solution as the fundamental solution.

Abstract: With numerical modeling in meso level, impaction of incorporating polypropylene fibers with two different geometry dimensions on flexural strength and toughness of hybrid fiber concrete has been studied in this paper. Mechanism of such hybrid fiber reinforcement has also been analyzed. The results show that hybrid of fibers with different geometric dimensions would bring about synergy, thus fiber enhancement effect could be demonstrated. Furthermore, the closer the incorporation ratio of these two kinds fibers are to each other, the more evident the enhancement will be produced. The most optimized hybrid ratio is in between 2:1 and 1:1.

Abstract: Response surface method has won numerous concerns in the reliability analysis of structure due to its simplicity and practicability, especially quadratic response surface taking no account of cross terms is most widely used. However, for the complex ultimate state curved surface corresponding to strongly nonlinear, the approximate accuracy of quadratic response surface is apparently not enough, causing a biggish error in estimation of reliability. Although, theoretically, higher order response surface method can resolve this problem, the sharp increase of undetermined coefficient reduces calculation efficiency, and even, cannot achieve. Therefore, on the basis of univariate analysis of multivariable function, an algorithm which can reasonably determine higher order response surface form is presented in this article, able to effectively reduce the number of undetermined coefficients in response surface, so as to reduce computational difficulties and put forward improving measures for possible problems; In addition, based on the tactics of number-theoretic setpoint, a type of scheme of number-theoretic selecting point applicable to response surface method has been developed. Finally, through the analysis of examples, the suggested algorithm was validated, with the result showing that the algorithm has good accuracy and efficiency.

Abstract: In this paper, the bodywork of lightg-duty cross-country bus, which is made of glass fibre reinforced plastic is comprehensively analysised by finite element analysis software, and its structure, load and movement status are discussed exhuastively. Meanwhile through more comprehensive calculation of the stress, displacement, natural frequency and vibration modes and other aspects under various conditions, providing a necessary theoretic basis for analysis of strength and stiffness and structural optimization.

Abstract: Detonation of low powder detonating fuse is studied in numerical simulation and experiments in bending conditions using LS_DYNA3D. The results show that pressure of the explosion and detonation velocity are decreased in the same section areas after bending. In bending conditions, detonation wave is similar to small angle corner diffraction. So the detonation velocity is lower than normal velocity.

Abstract: The distribution and spatiotemporal evolution law of the mining-induced fracture field was studied by means of damage mechanics. The damage variable correlated with the excavation process was introduced, which was used to describe the distribution characteristics of fractures in rock mass. In accordance with the damaged theory, the elastic finite element program was developed, by which the analysis of mining process of one coal seam was made of. The material damage accumulation taken into consideration, the distribution and evolution law of the volumetric strain, stress and damage field was obtained, which provided a theoretic reference for the design of gas drainage and improving the efficiency of gas extraction.

Abstract: A finite element program for elasto-plastic analysis of 3D beams and frame structures under large displacement/rotations is developed. The element is Timoshenko beam element based on mechanics of continuum. Constitutive equations for large displacements/rotations in elastic stage are expressed in an explicit way which is suitable for programming. The modification of constitutive equation is presented for the analysis of elasto-plastic problems. A fiber model is adopted for the calculation of stiffness matrix and internal forces. For solution of nonlinear finite element equations, general displacement control method and semi-modified stiffness matrix method is adopted. The results of numerical experimentation show that the program work well for 3D beams and frame structures under elasto-plastic large displacement/rotations.

Abstract: In this study, an interfacial spring element model with random defects was constructed based on the four-phase material model of concrete, which consists of aggregate, matrix, interfacial transition zone (ITZ), and initial defects distributing randomly within the ITZ. The ITZ is modeled by linear spring element of zero length. Simulation of concrete strength under uniaxial tension yielded numerical results that are consistent with reliable experimental data, thus proving that the model is reasonable and applicable. Then, the model was employed to analyze the influence of random initial defects on concrete strength. Results showed that increased initial defects in ITZ leads to a linear decrease in tensile strength of the concrete. Compared with the strength of concrete without initial defects, that of concrete with initial defects equal to 60 % of ITZ elements decreased by about 40%. Based on these results, this study recommends that the fraction of initial defects should be 30 % when using the proposed model to predict uniaxial tensile strength of normal-strength concrete.