Advanced Materials Research Vols. 446-449

Abstract: Natural frequencies and mode shapes of axisymmetric and non-axisymmetric vibration of stepped thin circular plates were calculated with self-programmed program. Three-node annular elements were used in the program.Results of axisymmetric vibration obtained by the self-programmed program and those by ANSYS program were compared.It shows that self-programmed program can calculate axisymmetric vibration as well as non-axisymmetric vibration.The accuracy of self-programmed program is higher than ANSYS method.

Abstract: In the paper, not only the internal force and displacement of structure during subway tunnel construction with cover and cut reverse method, but also the displacement field and stress field of surrounding rock are analysed. From the numerical calculation it is shown that the bending moment of diaphragm wall is affected seriously by the distribution and value of the stiffness of horizontal support; the excavation phase of the soil of the second floor underground is the key phase of the construction process because the internal force of structure has large increase; the value of surface settlement, horizontal displacement of diaphragm wall, differential settlement between middle pillar and diaphragm walls all meet the requirements, so the construction is safe and the surrounding buildings are affected slightly.

Abstract: Finite element method is used to calculate the crack-tip stresses of rock specimens under plane compression-shear loading in order to study the mechanism of plane shear(Mode II)fracture. Numerical results show that both the tensile and shear stresses exist at the crack tip and the ratio of maximum shear stress to maximum tensile stress,τ_max/σ₁,is about 3-6. Since the additional compressive can restrain tensile stresses at the crack-tip, τ_max can easily reach its limited value before σ₁ and cause plane shear(Mode II)fracture. Plane shear-box test is a potential method for obtaining Mode II fracture of rock and determining Mode II fracture toughness K_IIC of rock.

Abstract: moving least square meshless method is a numerical approximation based on points that do not generate the grid of cells, as long as the node information. Basis function and weight function meshless method for the calculation of accuracy have a significant impact. In order to compare the order of the base functions and powers of the radius of influence domain function meshless method for computational accuracy and efficiency , this paper selected first, second and third basis function and spline-type weight function in a different influence domain radius, respectively construct the field function. Mindlin plate element is derived based on the format of the plate bending problem meshless discrete equations. Programming examples are calculated with elastic plate bending problems non-grid solutions, and analysis and comparison of their accuracy and efficiency, results show that the meshless method using elastic plate bending problem is feasible and effective.

Abstract: A special method based on the extended finite element method is developed for the simulation of dynamic crack growth. It shows great advantages in the simulations of moving crack and mixed mode crack. The extended finite element method for two-dimensional crack is described in this paper. The crack form of the extended finite element in the homogeneous medium is studied in detail, and the internal detail in crack tip element and crack penetration element is analyzed. At last, the displacement mode is generated.

Abstract: The dynamic strength expressions of materials were reviewed in case of one-dimensional strain shock loadings in this paper, the effects on the strength were suggested to be considered of hydrostatic pressure and high strain rate. A modified form for the Hugoniot Elastic Limits was given associated with the Drucker-Prager yield criterion, the effect of hydrostatic pressure being included. Free surface velocity histories of particle were measured by VISAR system in plate impact experiments on alumina with a Light Gas Gun. The experimental determination of dynamic strengths of alumina was discussed and the open problems were clarified. By comparing the strength expressions of ceramic materials with the experimental results, the evident differences were pointed out. Their analysis and discussion were further given for the experimental phenomenon.

Abstract: Compound crumb rubber modified asphalt is a mixture of crumb rubber powder, SBS modifier and the matrix asphalt that has improved road pavement performances in resisting high temperature deformation and low temperature crack. The application of abandoned auto tire in road construction is significant in environment protection by reducing pollution caused by waster tires and in developing circular economy in China. Based on the experimental results of temperature sweep test for compound crumb rubber modified asphalt and contrast test of bending creep for compound crumb rubber modified asphalt mixture and SBS modified asphalt mixture, the temperature dependent properties of compound modified asphalt and its mixtures are studied. The compound crumb rubber modified asphalt is preferable in improving the pavement performance against fatigue and permanent deformation in both high and low temperatures.

Abstract: Concrete degradation in sulfuric acid environment had been widely recognized and the corrosion mechanism needs be further understood. A long time immersion test of concrete specimens in dilute sulfuric acid is carried out. The experiment is designed by uniform design method and through which eight groups of concrete specimens with water cement ratios (W/C) ranging from 0.35 to 0.70 are soaked in sulfuric acid with pH values ranging from 2.00 to 4.00 for 150 days. The pH meter is used to monitor the pH changing of the soak solution. The titrating sulfuric acid is added to maintain the original pH value of the solution and then acid consumption of specimens is recorded. Based on concentration boundary layer theory, a theoretical reaction rate model is proposed and whose validity is proved by experiment. The comparison shows that the theoretical model can well reflect the experimental results in the early phase of immersion and in later phase of immersion, it will over estimate the corrosion speed due to the gypsum layer effect is ignored.

Abstract: During an earthquake, many construction damage for columns, not for the beam. This does not meet the standard design.This paper, we will study the phenomenon such as any and construction joint. There nine specimens, divided into three groups. Every group has three specimens, the first no construction seam, the second simple processing In construction joints, the third has good processing construction three groups will be loaded axial compression coupling than 0.23, 0.34, 0.46. This paper will study the differece of different processing construction joint limit bearing capacity, energy consumption and stiffness degradation.

Abstract: For the situation that the smoke exhaust vents are located on both sides of the fire source, critical ventilation velocity is not appropriate to evaluate the smoke control effect. “Confinement velocity” is proposed as the characteristic parameter to study the longitudinal ventilation by O.Vauquelin in this situation. However, there have been few studies on confinement velocity. An experimental study was carried out on two reduced scale tunnel models. The main objective is to analysis the relationship between confinement velocity and fire heat release in this situation. Helium and air in different ratio was used as the smoke, and the "cold smoke" produced by smoke generator was put into the mixed gas in order to measure the length of smoke layer. The experimental models were based on the half tunnel as flow field at two sides of fire is symmetrical. The CFD model was created on the basis of the experiment, and the results were basically accord with the experimental results. It was shown from the experimental results that the critical point of the confinement velocity is between L / H = 2 to L / H = 4 in section 1, between L / H = 1 to L / H = 2 in section 2, rather than a fixed value; Two tunnel models had similar dimensionless confinement velocity, but the dimensionless total confinement velocity was different.