Papers by Keyword: Damage Model

Abstract: A FE beam model to perform static and dynamic analysis of fiber-reinforced masonry arches is presented. Based on a constitutive equation formulated for no-tension masonry beams, the model accounts for a limit to the material deformability and provides for irreversible damage occurring under compression. In order to capture any possible FRP debonding, a procedure is also formulated to reduce the performance of the fiber when the tangential and normal stresses at the masonry-composite interface reach a critical value. Some dynamic analyses are performed on a case study with the aim of evaluating the effectiveness of FRP-retrofitting in improving seismic performances.

Abstract: As the action mechanisms of various factors affecting concrete durability are different, it is difficult to understand the durability of concrete exposed to multiple factors using only mechanism analysis. Converting each action mechanism to an appropriate macroscopic mechanical effect can simplify complicated durability problems. Here we study concrete beams exposed to common environmental factors: cyclic freezing and thawing, bending stress and chloride attack. By converting each mechanism into a mechanical process and analyzing its effect on concrete, a damage model based on strain was established. Freezing-induced tensile stress is essentially a low-cycle fatigue tensile stress, as represented by a saw-tooth model. The maximum strains when the maximum freezing-induced tensile stress coupled with the four-point bending stress in every freeze-thaw cycle were measured, and found to increase with freeze-thaw cycling. Our damage model provides a new approach to predict the service life of concrete, and guidance for durability design of concrete.

Abstract: The thin-walled shell axial impact deformation of one-leg electric detonator with different density charge was studied. The impact stress was analyzed, and on the basis of kinetic theory the impact deformation model was established for the thin-walled shell filled with explosive. The experiments were verified at 60 000g, 80 000g, 100 000g and 120 000g by gas gun. The results show that shell length decreases and the plastic deformation zone diameter increases after impact. Damage deformation degree decreases with increased shell strength, reduced shell and internal charging mass summation and reduced impact velocity square. The model calculated value agrees well with the test data. The deformation model can be used to predict overload damage deformation for such detonator.

Abstract: For exploring the attenuation law of limestone dynamic elastic modulus (DEM) under fatigue cyclic loading, 24 limestone specimens were used to conduct dynamic uniaxial cyclic compressive tests under different loading frequencies and stress amplitudes on MTS Test System. The tests results confirmed that the decrease of DEM goes through three different stages with the increase of cyclic numbers. And, there is no distinct correlation between three-stage evolution rule of DEM and frequencies as well as stress amplitudes. The degeneration of DEM is caused by accumulation of micro-cracks and damage increase in rock specimen. Thus, based on attenuation rule of DEM, a fatigue damage evolution model which can depict the first two stages of limestone fatigue damage development was proposed.

Abstract: The simulation of the metal forming processes requires accurate constitutive models describing the material behaviour at finite strain, and taking into account several conditions. The choice of a rheological model and the determination of its parameters should be made from a test that generates such conditions. The major difficulty encountered is that there is no experimental test satisfying all these criteria. The use of more than one test seems well adapted, and is utilized to characterize the rheological behaviour at operating conditions corresponding to metal forming applications. Inverse analysis is then considered. Therefore, the difficulty lies with the long computing time that was taken when an optimization procedure is coupled with a finite element computation (FEC) to identify the material parameters. In order to solve the computing time problem, this paper proposes a hybrid identification method based on an artificial neural network and a genetic algorithm (ANN-GA). The proposed strategy is applied to identify the damage material parameters of the AISI 304 steel and using the bulge test.

Abstract: In the traditional Norton-Bailey model, the stress exponent is a constant value when the temperature keeps constant, But for some materials, this situation can’t be suitable. Based on the analysis of the experimental data, a secondary creep constitutive model which can be used in the stress exponent changing situation has been proposed. By introducing Kachanov-Rabotnov damage equation, the modified creep model has been established for P92 steel at 610°C and 670°C, which can describe the second and tertiary stage. And the method to determine creep parameters of tertiary stage has been derived. The new model was embedded into ANSYS interface program, and used for calculating the creep life of P92 steel. The results show that the model is in agreement with the experimental data.

Abstract: Based on the least squares theory and a damage variable , a damage model is formed for the freeze-thaw degradation of the layered hybrid fiber reinforced concrete (LHFRC). By the model the degradation equations for the LHFRC and the plain concrete(PC) are regressed with the experimental data, which are identical in the initial phase and different in the damage propagation phase and the is used to describe the damage process of concrete subjected to freeze-thaw cycles. The of LHFRC is smaller than that of PC in the damage propagation phase. Furthermore, the frost resistance of LHFRC is stronger than that of PC due to steel fibers and polypropylene fibers having retarded the degradation of concrete.

Abstract: This paper proposed a composite damage model including the damage initiation and evolution based on strain to predict the composite intralaminar damage under impact loading. In the numerical simulation, the user material subroutine VUMAT and the cohesive-zone model are chosen to describe the composite damage model and the delamination of interfaces between different plies. ABAQUS software is used to simulate the low-velocity impact of different thickness composite laminates. It is found that the delamination shape and area, the contact force and the deflection of the impactor obtained by the numerically simulation agree well with the experimental results.

Abstract: In order to describe the stability of borehole face and the theory of hydraulic fracture fissure stretch in real, the stress field of adjacent rock in the hole should be constituted exactly .The article is based on the damnification dynamics theory, meanwhile, considered the rock is fracture-pore dual medium and the damnification characteristic of the rock in hole .Adjacent formation is sectioned three areas: damage-area, damnification-area, elasticity-area. And we have calculated the ambient stress distribution of one oil-well .The results show that the destructive radius of the minimum in-situ stress direction is 1.247m, the damage radius is 8.082m, the destructive radius of the maximum in-situ stress direction is 0.998m, and the damage radius is 6.5865m.

Abstract: Rock strength is closely related to composition and internal structure of water-bearing rock. By using scanning electron microscopy, This paper analyses limestone composition and micro-structural damage mechanisms in the water physical and chemical effects. Besides, By combining with triaxial compression test according to natural state and saturated state of rock samples, and by applying mohr-coulomb strength criterion based on the basic concepts of damage mechanics, The paper obtains the quantitative expression of micro-structural damage by using statistical methods. Finally, The paper establishes the relationship between compressive strength and micro-structural damage and discusses evolution laws of micro-structural damage in limestone under complex stress state, The results show that degree of micro-structural damage increase as the water affection, further more, The correlations between micro structural damage and the compressive strength of water-bearing limestone shows a nonlinear relationship according to different confining pressure.