Key Engineering Materials Vols. 385-387

Abstract: By using the intrinsic character of the frame structures, a new direct damage identification method of the frame structures based on residual force vector is presented. The stiffness connectivity matrix is obtained by sensitivity analysis. The stiffness matrix perturbation of the damaged structure can be expanded by the stiffness connectivity matrix, then substituting it into residual force vector equation, the new residual force vector equation expressed by the stiffness connectivity matrix is obtained. This equation can be solved directly, so the stiffness perturbation of layers is got, by it, the damaged locations and the extents of the frame structures are identified. At last, a numerical example of a seven-layer frame structure is given, the identification result shows that, only with the first-order mode of the damaged structure, the damage can be identified accurately. Even in considering of some degreed noise of the mode parameters, the structure damage can be identified well, demonstrating the effectiveness of presented method.

Abstract: In many industrial applications is necessary to predict fatigue lifetime of thin structures, where the stress field near the crack front have a real three-dimensional nature. Due to the existence of vertex singularity in the point where the crack front touching free surface, crack propagation in 3D structures cannot be reduced to a series of plane strain or plane stress problems along the crack front edge. The paper describes the influence of vertex singularity on the distribution of the stresses around the crack front for three-dimensional body. The distribution of the stress singularity through the thickness of the specimen gives us indication of the crack behavior in thin structures. The estimation of the thickness of the specimen where the change of singularity plays an important role on fatigue crack growth rate (in dependence on Poisson’s ratio) is carried out. The results contribute to a better understanding of the crack behavior in thin structures, and can help to more reliable estimates of their residual fatigue life.

Abstract: Under the assumption that the viscosity coefficient is in inverse proportion to the power law of the equivalent plastic strain rate. The friction touch effect between viscosity and crack-tip surfaces is considered, the asymptotic solution is established for elastic-viscoplastic field at the mixed-mode quasi static crack-tip under compression and shear. The numerical solution at crack-tip without stress and stain gap is obtained. The variation of numerical solution is discussed for the mixed-mode under compression and shear according to each parameter. Through numerical results and analysis for the mixed-mode crack-tip field under compressing and shear, it is whole plastic without elastic unloaded section, viscosity effect is an important factor when propagating crack-tip field.

Abstract: Physical properties of element are very complex under fatigue loads.The structural system consisted of elements is not a simple topological structure,which the change of its physical properties is more complex.In order to analyze quantitatively the structural stiffness reliability of different design life,it is important to establish the accurate formula of physical properties decrease. In this paper, the formula of elements’ elastic modulus decrease is deduced by using damage mechanics theory combining with the model of residual strength of element. Moreover, stiffness reliability index of controlling node of truss system is solved by applying the Stochastic Finite Element Method in different service life.

Abstract: The visco-elastic mechanism of particles reinforced composites has been investigated through revised Eshelby equivalent inclusion theory. A visco-elastic model is applied. Furthermore, by introducing Heaviside step function and Laplace transform, the creep constitutional equation related to strain rate effect is achieved. Finally, by equivalent inclusion theory, introducing secant modulus, the material moduli with time and volume fraction concerning Glass/ED6 particles reinforced materials have been given. The results show that the visco-elastic property of composite material is mainly determined by the visco-elastic behavior of the matrix, which meet experiment results well. It can be concluded from the results that there exits close relationship between the inclusion shape, volume fraction and loading path.

Abstract: A computational method for the micro-mechanical material model of woven fabric composite material was developed in this paper based on a repeated unit cell approach and two smooth fibre modes were presented. The stiffness matrix was evaluated with a domain integral by the use of radial basis function interpolations without element mesh. The applications of mesh free method to evaluate woven fabric composite elastic moduli have been presented and good accuracy has been achieved compared with the results by other approaches.

Abstract: The main objective of this study is to evaluate the flexural toughness and crack strength of a cement-based composite under the effect of using recycled polypropylene (PP) fiber and recycled glass. This research study proves the feasibility of the use of glass as aggregates replacement and PP fibers for composite reinforcement.

Abstract: A novel methodology based on a combination of experimental and analytical methods is used for monitoring the stress intensity factor in fatigue cracks subjected to constant amplitude loads. Full-field displacement information is fitted, following a multi-point over-deterministic approach, to an analytical model. This is developed from Muskhelishvili’s complex formulation. The methodology allowed accurate monitoring of the stress intensity factor during three fatigue cycles when small-scale yielding conditions were achieved. Moreover for larger loads where important plastic deformation occurs around the crack tip, Dugdale’s correction accounted for the differences between theoretical and calculated stress intensity factors. Accordingly the tool provides an indirect approach for measuring crack tip plasticity. Due to the fact that image correlation is relatively simple to use and is a non-contacting technique, the approach pioneered in this work seems ideal for monitoring fatigue cracks in industrial applications.

Abstract: In order to calculate the service life as precisely and reliably as possible we need good mathematical models for describing loading, geometry, properties of materials and fracture mechanics parameters. It can be established whether a mathematical model is precise and reliable only by comparison of results of the method such as analytical methods in case of simple problems and experiment when real complex structure are deal with. Since gears and gearing belong to the second group, by correctly selected and developed test pieces and carefully planned experiments we obtained results with which we confirmed and justified the mathematical model for calculating mentioned parameters. To this end we will show in this paper series of experimental methods and test pieces used on the gears.

Abstract: In this study, new moment-resisting precast concrete beam-column joint is proposed for moderate seismic regions. The new joint includes the connection reinforcing bars, penetrated the joint and lap-spliced with the bottom bars of precast U-beam. To evaluate the performance for non-contact lapped splice, experimental and analytical work were conducted, for major variables of the length of lap and the diameter of connection reinforcing bars(D19, D22, and D25). Results of experimental and analytical works show that these variables have much influence on flexural strength and ductility, and deformation of lapped joint. Using nonlinear finite element method, analytic research was performed for investigating crack and fracture patterns, load-deflection curve, comparison of internal force, evaluation of ductility, stains of reinforcement bar.