Papers by Keyword: Damage Variable

Abstract: This paper presents the results of a study on the fatigue damage of high strength concrete under uniaxial compression. Based on the experimental data, the change laws of fatigue strain and fatigue modulus are put forward. According to the experimental requests, the numerical value of fatigue strain and fatigue modulus when the fatigue failure of concrete occurs can be regarded as the criteria for fatigue failure of concrete. Then the paper presents a fatigue damage model. By reference to the concept about the damage variable defined by some scholars, the formula of the damage variable is proposed and the damage variable curves varying with recycle ratio (n%) are mapped. At last, the fitting curves of the damage variable varying with recycle ratio are proposed. The fitting effect is very good and the correlation coefficients are above 0.95.

Abstract: The damage and failure mechanism of quasi-brittle materials is the most fundamental research topic in Damage Mechanics. In this paper, the mesoscopic damage mechanism of concrete under uniaxial tension was discussed. The rupture and yield damage modes in meso-scale were introduced as the two basic parameters to define the damage accumulated variable. The results show that the proposed statistical damage model can accurately predict the whole deformation and failure process of concrete under uniaxial tension, including the two-stage deformation characteristics and the size effect.

Abstract: Based on CT technology, real-time scanning and observing meso-damage evolution of emulsified asphalt concrete was carried out. With methods of visual analysis, CT number analysis and damage variable analysis, the following conclusions were obtained: during the continuous loading, the change of CT average value was little at the upper part of cross-sections, but that of the lower part of cross-sections was significant and its damage was serious. Concrete specimen experienced four stages of compaction, dilatancy, crack propagation and failure. Plastic characteristics was revealed in failure process, which due to the mechanical properties of emulsified asphalt concrete, that is the lower strength and lower elastic modulus.

Abstract: How to quantificationally detect the damage of rocks is a key problem in damage mechanics for rocks, and it determined whether the damage theory of rocks could be brought into action in rock engineering. Detection techniques of rock damage were summarized and grouped into structural analysis approaches and feature measurement approaches, which include SEM analysis, CT detection, stress-strain measurement, wave detection, acoustic emission monitoring, infrared radiation detection, etc. Image processing and fractal theory were introduced to calculate damage variable directly based on images. All kinds of damage variables resulted from different methods are equipollent in thermodynamics, and they are an internal variable to characterize damage state. The difference of each kind of damage variable is that different formations of state equations and dynamic equations would be derived from different variables. It was suggested that the favorable rock damage variables should be selected according to the thermodynamics principle and those convenient to detect and easy to analysis should be adopted preferably.

Abstract: The introduction of can reasonable description of transversely isotropic soil micro-element strength parameters - damage variable, according Mohr-Coulomb strength theory and soil micro-element theory of geotechnical failure to obey normal distribution characteristic,the damage variables can true reflection of transversely isotropic soil softening characteristics.Based on the uniaxial stress-strain curve of the geotechnical rupture process of statistical damage constitutive model of geotechnical, statistical damage variable is adjusted, establishing the reflect the complete process of geotechnical failure of 3D statistical damage constitutive model.Model is simple, easy to use, can better reflect the actual.The model reflects the failure process of geotechnical damage not only with geotechnical micro-unit strength changes, and the effect of geotechnical stress state.

Abstract: Sulfate attack of cementitious materials is closely related to the essential properties of cementitious materials and erosive environments. Therefore, the foundation of service life prediction model becomes very difficult and complicated. In this paper, the temperature and concentration of an erosive solution were taken into account in lab accelerating test, the service life prediction model of sulfate attack based on equivalent time and damage variable was founded by using Arrhenius equation, the concept of maturity, Fick’s law and the theory of damage mechanics. Dynamic elastic modulus value change, and/or mass change, and/or compressive or flexural strength change, et al. can be used as damage variable to show the evolving process of sulfate attack in concrete in this prediction model, and certain changed rate was considered as the damage critical value in concrete in terms of the standard or references or test results. To estimate the possible service life of concrete structures in sulfate attacking condition by lab accelerating test according to this prediction model, it will be benefit to guide the selection of raw materials and design of durability in concrete.

Abstract: The static failure can be seen as a special fatigue failure, which means the static failure is the fatigue failure only bearing one cycle under the ultimate-strength loading. By learning from the analysis of fatigue damage, the stress- strain curve and damage of steel fiber reinforced concrete under uniaxial loading have been studied in this paper. The damage evolution equation can be derived from the damage theory, and it can be used to describe the relationship between the damage variable and strain. According to the strain equivalence principle, the corresponding constitutive equation considering damage can be obtained. Finally, comparisons among test results, the model and ansys simulation results show that the model is suitable to describe the uniaxial stress-strain curves of steel fiber reinforced concrete.

Abstract: The damage evolution laws of high strength and high performance concrete (HSHPC) are obtained by a large number of experiments on mechanical properties. Based on stochastic damage model, a new damage variable with two parameters is proposed to describe the damage constitutive relationship of HSHPC and the damage constitutive equation is established by boundary conditions. Compared mechanical test result of HSHPC with theoretical calculation, it is shown that the damage constitutive equation can reflect the damage characteristics of HSHPC reasonably. The research identifies a certain theoretical basis for further studying on dynamic and stochastic damage constitutive relationship of HSHPC.

Abstract: The distribution and spatiotemporal evolution law of the mining-induced fracture field was studied by means of damage mechanics. The damage variable correlated with the excavation process was introduced, which was used to describe the distribution characteristics of fractures in rock mass. In accordance with the damaged theory, the elastic finite element program was developed, by which the analysis of mining process of one coal seam was made of. The material damage accumulation taken into consideration, the distribution and evolution law of the volumetric strain, stress and damage field was obtained, which provided a theoretic reference for the design of gas drainage and improving the efficiency of gas extraction.

Abstract: The attenuation of ultrasonic pulse velocity in various sized concrete specimens under uniaxial compression loading is tested. Tests were conducted on prisms of 25×25×50 cm fabricated with dam concrete(maximum aggregate of 80mm),and standard 15×15×30 cm prisms,10×10×20 cm prisms which were made with the wet-screened components of dam concrete. Ultrasonic attenuation has been shown to increase significantly as distributed damage in concrete increases. Large changes in attenuation with increasing damage levels were found for all specimens at all power levels. Results also show that the rule of ultrasonic propagation in concrete is apparently affected by the scale effect and the effect of wet screen sieve of aggregate. These conclusions proposed can be applied to determining the extent of damage of mass concrete due to the complex load and other environmental effects.