Papers by Keyword: Damage Variable

Abstract: This paper takes geological conditions of the Li—Jun expressway by Kang JiaGou and Tong De coal mine goaf as prototype, using the simulation experiment of similar material, simulates the formation process and distribution of the mined rock fracture and the damage variable of the mined rock by using the simulation experiment of similar material, At the same time, It researches the evolvement law of rock’s fracture network in caving zone, fractured zone over goaf using fractal geometry theory. It analyses the damage variable law in caving zone, fractured zone using the damage mechanical theory, and found the relationship of damage variable and mined width. The conclusion of the experiment indicates: with the advance of the working surface, the fractal dimension of the mined rock crack goes through small → large →small, and stable process of change. In the identical push distance of the working surface, fractal dimension of caving zone is 1.0—1.2 times of fractured zone. With the advance of the working surface, damage variable increases gradually, under the identical mined width, damage variable of caving zone is greater than fracture zone, caving zone is about 1.04—1.11 times of fracture zone. Damage variable of goaf central zone is greater than edge.

Abstract: By means of the three-point bending impact equipment, with the measurement of ultrasonic velocity, the low velocity impact damage evolution of reactive powder concrete (RPC) with 0, 1%, 2% and 3% volume fraction of steel fiber were tested. In this study, the damage variable D pertaining to ultrasonic velocity had been selected to study the damage evolution process of RPC. The results indicate that the fatigue damage process of RPC is linear. The addition of fibers effectively improves the impact energy absorption behavior of RPC matrix, and the damage variable D of RPC with different fiber dosages increases by 1.1~3.5 times than that of plain concrete when it is ultimately destroyed.

Abstract: The flexural fatigue performance of polyacrylonitrile (PAN) fiber reinforced concrete (PANFRC）was investigated by third-point loading tests. Based on the previous research work, optimum mixture proportions of PANFRC for highway overlays and bridge decks that satisfied both the minimum compressive and bending strengths, and showed excellent mechanical properties, were selected for fatigue testing. The experimental program included a total of 69 flexural specimens, 15 of which were plain concrete specimens, and the remaining 54 specimens were PANFRC specimens. Three mixes containing 0.0%, 0.1 %, and 0.15% of PAN fiber volume fractions were selected. For each mix, 4 different target load ranges were applied: 10–75%, 10–80%, 10–85%, and 10–90% of the ultimate flexural capacity, as obtained from the corresponding control static test. The bending fatigue life of PANFRC specimens under various stress ratios are proved to follow two-parameter Weibull distribution. Both a semi-logarithm and a double-logarithm P-S-N equations with various failure probabilities are derived from the experimental measurements. The denifition of the fatigue damage variable and damage evolution equation for PANFRC are furtherly proposed based on theory of continuum damage mechanics.

Abstract: Through INSTRON1304 electric hydraulic servo fatigue testing machine, the fatigue experiment of soil-cement is done, and the ultrasonic velocity of soil-cement under dynamic loading is obtained. The results show the ultrasonic wave velocity through the cemented soil samples free surface obviously attenuates as the cycles of the dynamic loading increases. Based on the damage variable defined by the ultrasonic wave velocity, the evolution equation of soil-cement accumulated fatigue damage is established. The equation indicates that the fatigue damage of soil-cement l under dynamic loading can obviously be divided into three stages: the initial rapid decay of the initial state, stability decay and rapid damage close to the destruction. The experiment results provide an important reference for non-destructive testing of soil-cement under dynamic loading.

Abstract: Considering with the spatial characteristics of concentrated deformation field caused by the micro-cracks concentration and localization in rock, a new damage variable is defined based on the standard deviation of the strain fields of rock specimen surface during loading. When digital speckle correlation method (DSCM) is used to measure the deformation fields of rock specimen, the damage variable definition in this paper takes great advantages on damage measurement of rock methods. Using the new methods, the damage of rock would be measured for the whole loading process and the experiment is easy to be implemented. The validity of the proposed damage variable is verified by the experimental results on column-shaped marble specimen subject to uniaxial compression.

Abstract: Damage distribution and evolution of the HRR field are characterized by means of a two-scalar damage variable approach under the consideration of isotropic damage. This theory is based on the definition of thermodynamic conjugate forces and the postulation that the plastic damage surface corresponds to the initiation of plastic damage. An asymptotic solution is applied for the non-linear plastic damage evolution equations. It is shown that both the damage variables may be expressed as a function of the accumulated amount of overall damage respectively in exponential and tangential types, which determine the damage characteristics in different areas. It is also revealed that the damage evolution coefficient plays an important role to determine the distributions of the damage variables, effective Young’s modulus and Poisson’s ratio. The obtained largest damage variable, which characterizes the deterioration of the material, and the lowest effective Young’s modulus around the crack tip locate at and respectively for Mode I and II problems.

Abstract: In this paper, the method of continuum damage mechanics is used to construct the damage constitutive equations for the material, and governing equations are obtained based on the assumption of spherical symmetry. Then the stress value is taken as basic unknown parameter to solve these equations, the distribution of materials damage field was also obtained. Finally, the influence of different damage parameters on average distribution is discussed. Thus the paper lays a necessary foundation for research on materials damage evolution law.

Abstract: Structures may enter into nonlinear stage under strong earthquake, so precise prediction of nonlinear behavior for building structure in earthquake is important which can assess the earthquake resistance safety of structures accurately. The exact numerical analysis model is required in actual engineering. In this paper the concept of nonlinear dynamic damage is introduced in steel reinforced concrete (SRC) composite structure, based on the theory of continuous damage mechanics. The damage variable is defined and computed by effective plastic strain of material, furthermore, concrete dynamic constitutive model is derived which considered plastic strain of material. Finally, the damage dynamic balance equation is established. Via comparison with test results of a three-story, two-bay SRC frame model which is tested on a shaking table, it is shown that the results of numerical analysis agree well with test results, indicating that the nonlinear dynamic balance equation is capable of describing the dynamic response of SRC frame structure with satisfactory accuracy. The research supplies theoretical basis for the seismic behavior analysis of SRC high-rise buildings.

Abstract: For many quasi-brittle materials (such as rock, ceramic and concrete) in pure bending state, the material on the tensile side will fail firstly since the compressive strength can be ten times the tensile strength. After tensile strain localization zone is initiated in the midspan of the beam, its propagation direction will be perpendicular to the neutral axis. In the paper, using nonlocal theory or gradient-dependent plasticity, the distributions of local plastic tensile strain and local damage variable in tensile strain localization zone of a pure bending beam are analyzed theoretically. The evolutions of the maximum local plastic tensile strain, the maximum local damage variable and the bending moment with tensile stress acting on the tensile side are presented through examples. The distributions of local plastic tensile strain and local damage variable in tensile strain localization zone are highly nonuniform due to microstructural effect. When the maximum bending moment is reached, the maximum local damage variable is proportional to the ratio of elastic modulus to elastoplastic modulus, while the maximum local plastic tensile strain is inversely proportional to elastic modulus and elastoplastic modulus. For quasi-brittle materials, the elastoplastic modulus that is a constitutive parameter equal to the absolute value of the slope of tensile stress-tensile strain curve in strain-softening stage is much higher. The present theoretical results mean that the precursors to failure are less apparent for extremely brittle materials.