Abstract: The dynamics stress intensity factor of fixed specimen with several notches was analyzed by semi-analytic method. The semi-analytic formula was taken as the interpolation function near notch tip and the degrees of freedom near notch tip were transformed into a small set of generalized coordinates by means of the series expansion formulas of the displacement field. The dynamics stress intensity factor for fixed specimen with two notches or cracks under centralized loading and well-proportioned loading was obtained. The results show that the KI and KII are existed at the same time for fixed specimen with several notches under dynamics loading.
Abstract: Two-dimensional (2D) finite element analyses have been carried out to study the crack opening displacement and stress intensity factor of a cracked centre-hole plate. With the different interference levels (2%, 4%, 6% and 8%) and acted by residual stress caused by cold expansion, the crack opening displacement, the stress intensity factor and J-integral around the crack tip is presented. With the different interference levels and acted by different applied loads , the crack opening displacement, the stress intensity and J-integral around the crack tip is also presented. The results of the 2D FEM analysis show, 1) with the different interference levels and acted by residual stress caused by cold expansion, the crack mouth is throughout closed and the middle part is open, but the opening displacement is constant; 2) under some applied loads, with the interference levels up, the stress intensity factor on the crack tip and J-integral, become weak gradually, then they keep constant values; 3) with the interference increases, the stress intensity factor and J-integral decreases. When the interference increases a certain value, the stress intensity factor and J-integral do not decrease and keep constant values.
Abstract: The Baling River Bridge is a single-span simply-supported suspension bridge with a main span of 1088 m. The steel stiffening truss is employed as its main girder and comprises the integral joints connecting the chord members. The integral joint is a key structure and determines the safety of the bridge, but it is very complex in detail and has an undefined fatigue resistance. In order to investigate its mechanical behavior and fatigue reliability, a fatigue test was performed on a 1:1.4 scale model of the integral joint of the main truss of the Bridge. With an assumption of the load spectra represented by the standard fatigue vehicle in BS 5400, the test fatigue load was derived accounting for the multiple vehicle effect and the model scale. The test result shows that no cracks were detected in the model when subjected to two million stress range cycles, and the structure has an reliable fatigue resistance satisfying the design requirement. This type of integral joint is an alternative for long-span truss bridges.
Abstract: How to judge the rockburst proneness of rocks is one of the key works to predict rockburst. A preliminary approach is made to the relationship between the rockburst proneness and the spectrum characteristic of the rocks by means of experiments in the present paper. The following conclusions are obtained. Firstly, under the condition without loading, there is not any regular relation between the rockburst proneness and the spectrum characteristic of the tested rocks. And secondly, under the condition of uniaxial loading, the spectrum curves of the tested rocks with different rockburst proneness all change with the increase of stress. These curves possess similar tendencies, but different shapes, inflexions and developing rates.
Abstract: Ceramic – metal interfaces are often present in composite materials. The presence of cracks has a major impact on the reliability of advanced materials, like fiber or particle reinforced ceramic composites, ceramic interfaces, laminated ceramics. The understanding of the failure mechanisms is very important, as much as the estimation of fracture parameters at a tip of the crack approaching an interface and crack propagation path. The asymptotic solution of the stress field at the tip of a crack normal to a bi-material interface is presented. A cracked sandwich plate loaded by uniform normal stress was numerically investigated using Finite Element Analysis. The numerical results of the circumferential stress distribution were compared with the analytical solutions. The results for the non-dimensional stress intensity factors show that at lower crack lengths the influence of material mismatch is lower but this influence increases with increasing the crack length.
Abstract: The objective of this investigation was to develop a test methodology to assess the fatigue performance of cold patch asphalt mixtures, potentially usable in the field as a quality control method.The methodology was developed by identifying the relationships between the parameters from a Laboratory Fatigue Test (IDT,according to ASTM D4123 ), and the penetration rate (NPR) from a lighter version of the Dynamic Cone Penetrometer (DCP) at various densification levels. Multiple linear regression analysis (MLRA) was used to develop equations to estimate number of load cycles to fatigue, and critical tensile strain. The fatigue equations were satisfactorily validated after comparing the measure stability parameters from two mixtures not used in the regression analysis. Cross-validation using SPSS procedure was also implemented.
Abstract: The use of gneiss as aggregates might help meet the pavement constructing demands. However, the study of the pavement performances of gneiss asphalt mixture is few. In this paper, the microstructure of gneiss aggregate was studied by Scanning Electron Microscopy (SEM). And the pavement performances of gneiss asphalt mixture with different improving measure were characterized by means of Indirect Tensile Strength Test and Four-Point Bending Fatigue Test. Gneiss is flaky, surface texture rougher and imporosity characteristic in microstructure, resulting to its adhesion and processing property are poor. Experiment results indicate that the use of hydrated lime replacing limestone power partly in filler can improve pavement properties of the gneiss asphalt mixtures distinctly.
Abstract: This paper presents a computational framework for simulation of delamination that combines the features of the discontinuous Galerkin methods with the versatility of the cohesive zone models. Within the finite element formulation of the discontinuous Galerkin methods, displacement discontinuities (jumps) are allowed across the element boundaries. Thus, the cracks are naturally included in the model without modifying the initial mesh. The displacement discontinuities across the element boundaries are used to compute the separations in the cohesive fracture law. The delamination initiation occurs when the traction across the element boundaries reaches its maximum; when the separation exceeds a critical value, total decohesion occurs. Numerical example is presented to illustrate the validity and effectiveness of the present methodology.
Abstract: Adhesively bonded connections involving pultruded FRP typically fail in a brittle manner, making their analysis a case study for the application of statistical size effects. For brittle materials, in which failure is often caused by a single critical defect, statistically based size effects on strength are adequately explained by probabilistic theories such as the Weibull strength theory. A previously implemented probabilistic dimensioning method for adhesively bonded balanced joints is extended to a complex joint involving a tube and a lamella, both made of pultruded FRP. Instead of the previously used 2d approach the extension requires a 3d formulation. The entire joint is idealized as being constituted by n elements; its survival depends on the simultaneous survival of all elements. By the means of a 3d FEA, failure triggering stress components in all n elements were determined; a probability of failure is associated to each element using the corresponding combination stresses combined into an appropriate failure criterion, hence defining a theoretical joint strength.
Abstract: High-performance concrete will undergo severe damage under fire conditions. It is well known that vapor pressure induced by high temperatures plays an important role in the damaging process. This paper presents a method of vapor pressure modeling, called equivalent expansion method, which can be implemented in FEM analysis. The modeling procedure consists of two parts, i.e. vapor pressure determination and vapor pressure modeling incorporated in FEM analysis. In order to make analysis more accurate, steam table is employed instead of ideal gas equation.