Papers by Keyword: Initial Damage

Abstract: The inverse analysis method based on genetic algorithm has been widely applied, but the general genetic algorithm is not applicable to the objective function as a non-analytic formula, so that the clear target function formula is often difficultly been obtained in the practical engineering. In order to solve the problem, the historical data are studied by neural network with the neural network embedded into the genetic algorithm, so as to establish the effective neural network model to replace the target function formula. At the same time, the corresponding fitness function is constructed for the optimal calculation. This method has been used for the inversion analysis on the initial damage of concrete, and the mechanical parameter inversion method is put forward based on the uniform design-genetic algorithm-neural network ensemble theory. Moreover, the method is verified by a calculation example, the results show that the initial damage value of concrete can effectively be obtained.

Abstract: Based on the stress characteristics of freeze shinking shaft lining at construction and operation stages, it is set up that The anisotropic damage model including initial damage, which suit to make Damage and Fracture Mechanics analysis for the shaft lining. A 3 dimensional anisotropic damage program is compiled using FEPG software, which take the following factors into consideration: temperature, conduction conditions, concrete facture energy and its aggregate gradation. Take the liangbosi mine shaft lining for example, its damage evolutionary process under complicated stresses such as permanence field stress, the gravity and vertical additional stress changed with time is obtained. It is discussed that the facture’s position and its development process, and the mechanical mechanics of the shaft lining structure failure.

Abstract: The bearing capacity decreases continuously along with the deterioration of material property under the action of external effects. It is important to evaluate the damage of concrete, and the damage parameter plays an important role in this process. An experimentation method has been designed, which can simulate the initial damage by mixed initiator into concrete. Using the elastic modulus of axial compression experimentation, the initial damage D0 and damage threshold value Df have been gained. The Size effect of concrete compress damage parameters is verified.

Abstract: The Johnson-Cook yielding criteria model, the initial damage model and the progressive damage and failure constitute model have been introduced into the constitutive equations of the rotating band. By using the penalty function method, the dynamic contact model has been introduced and an explicit dynamics finite element model has been established. The process of the rotating band impacting the throat bore was molded based on the elastic-plastic contact finite element theory. The rotating band pulling in and impacting the throat bore was simulated by the numerical computation. The dynamic responses of the rotating band and the projectile were obtained. And the stress distribution of the throat bore was studied. The influences of the engraving process on the interior ballistics were studied through the numerical computation.

Abstract: Many damage models of concrete have been put forward till now, of which some models are applied in engineering practices. The damage parameters play an important role in the calculations of damage with these models, which is determined during experiments. However, the tests of damage on concrete are rarely made, especially about the measuring method of initial damage. The initial damage is an essential parameter to study on the damage of concrete. Being based on the theory of damage, this paper analyze of the damaged and undamaged elastic modulus of concrete. The new method of determining undamaged elastic modulus from test results has been put forward, and then the initial damage has been quantified.

Abstract: Damage parameter of concrete is widely used in design and construction of concrete structures. An experimentation method has been designed, which can simulate the initial damage by mixed initiator into concrete. Damage parameter can be obtained in laboratory with standard specimens. But practical structure is very large. It is not rational to use this parameter in practical structures. So size effect on damage parameter is studied. It is concluded that initial damage and summit damage grow with the increase of structure size, but the growth rate becomes gentle with size increasing. When the size is larger than 500 mm×500 mm, the growth rate is less than 15‰, so the results obtained from specimen in 500 mm×500 mm can be used for mass concrete structures.

Abstract: A damage detection method reflecting initial damage of the elastic structure is presented. It is based on the idea that the damage will decrease the structure stiffness. From eigenvalue issue, regard Poison ratio and elastic modulus as a constant and a random variable, respectively, and in terms of known data and a combination of the FEM, then equations solving random modulus of the undamaged and the damaged structure are obtained, respectively. Based on the element damage indicator, initial damage of the structure can be detected. At last, a five-storey shearing structure is simulated, and the results indicate that initial damage situation can be accurately calculated, and initial damage locations can be estimated based on the proposed method, which is simple and effective, and contributes to the application in Engineering.