Papers by Author: Chun An Tang

Abstract: The periodically distributed fracture spacing phenomenon exists in the failure process of the reinforced concrete prism under uniaxial tension. In this paper, A numerical code RFPA3D (3D Realistic Failure Process Analysis) is used to simulate the three-dimensional failure process of plain concrete prism specimen and reinforced concrete prism specimen under uniaxial tension. The reinforced concrete is represented by a set of elements with same size and different mechanical properties. They are uniform cubic elements and their mechanical properties, including elastic modulus and peak strength, are distributed through the specimens according to a certain statistical distribution. The elastic modulus and other mechanical properties are weakened gradually when the stresses in the elements meet the specific failure criterion. The displacement-controlled loading scheme is used to simulate the complete failure process of reinforced concrete. The analyses focus on the failure mechanisms of the concrete and reinforcement. The complete process of the fracture for the plain concrete prism and the fracture initiation, infilling and saturation of the reinforced concrete prism is reproduced. It agrees well with the theoretical analysis. Through 3D numerical tests for the specimen, it can be investigated the interaction between the reinforcement and concrete mechanical properties in meso-level and the numerical code is proved to be an effective way to help thoroughly understand the rule of the reinforcement and concrete and also help the design of the structural concrete components and systems.

Abstract: This paper presents a new meso-mechanical analysis method of rock failure. The actual inhomogeneity of rock at meso-scale level is represented by processing the image of rock section and incorporated into Realistic Failure Process Analysis code (abbreviated as RFPA2D). Here, this numerical tool is employed to study the fracture phenomena of granite sample considering the interface strength between mineral grains. Numerical results show that interface strength has significant influence on the strength of sample and its failure mode. The larger the interface strength is, the more brittle rock samples become and the strength is bigger. With the interface strength increasing, failure mode gradually varies from intergranular frature to transgranular fracture.

Abstract: Thermal stresses are identified as one of the major causes of concrete failure. In order to consider the heterogeneity of concrete at mesoscopic level, and to simulate its failure processes during temperature change, a coupled thermo-mechanical model, which is on the basis of statistical damage model, is proposed. The model revealed the effect of the heterogeneity on concrete, and by analysis one of the important thermal stresses, i.e. thermal mismatch stresses, which are caused by thermal mismatch between the aggregate and mortar due to uniform change in temperature, it indicate that the presence of thermal mismatch causes stress concentration along the interface between aggregate and mortar, and the superpose of those stresses cause the crack propagation in the line of the two aggregate. The crack patterns, simulated by the proposed model, show a good agreement with the experimental results.

Abstract: The Brazilian splitting tests have been commonly and widely used as a standardized test method on disc or cylinder specimens to measure the indirect tensile strength of rocks in mining engineering and other rock engineering. In this paper, a novel numerical code, 3D Rock Failure Process Analysis code, was applied to implement the splitting tensile failure tests on rock discs. The influences of the heterogeneity on stress distribution in rock are also discussed and the splitting failure patterns of specimens subjected to Brazilian tests are simulated. The simulated splitting results of rock discs were found quite realistic, which indicate that the rock failure analysis method is applicable and practical for the study of rock disc splitting failure.

Abstract: Based on mesoscopic damage mechanics, a numerical code RFPA2D (dynamic version) is developed to simulate the spallation process of inhomogeneous medium induced by reflection of stress wave, and the influence of duration of stress wave on spallation is discussed. For convenience of description and discussion, the failure area in the immediate vicinity of loading position of model is divided into two zones, i.e. comminution zone and fracture zone; and the failure area caused by spalling in model is defined as spalling zone. The comminution zone is affected little by the duration of stress wave, but the fracture zone and the spalling zone are affected to a greater extent by duration, also, the stability of specimen is affected by the duration of stress wave. Furthermore, if the duration becomes significantly long, the fracture zone corresponding to the maximum extension of the radial tensile cracks will be dominant in specimen. If the duration of stress wave becomes short to some extent, the spalling zone corresponding to the maximum extension of the tangential tensile cracks will be dominant in specimen. In addition, if the duration of stress wave is long enough, the specimen may lose stability.

Abstract: With the knowledge of heterogeneous characteristics of thermal barrier coating materials at mesoscopic level, a coupled thermo-mechanical-damage (TMD Model) model was introduced and used to numerically quantify the thermal stresses and crack development of in thermal barrier coatings (TBCs) composite subjected to decreased temperatures. The effect of different surface precrack morphologies, such as precrack length and precrack density, on an interface crack subjected to thermal loading caused by a temperature change is presented. It provides us with a more sensible physical intuition and a more accurate mathematical for optimizing the design and the processing of ceramic coatings subjected to the coupled thermal-mechanical loading.

Abstract: In this paper, a coupled thermal-mechanical-damage model, Material Failure Process Analysis for Thermo code (abbreviated as MFPA-thermo), was applied to investigate the formation, extension and coalescence of cracks in FRCs, caused by the thermal mismatch of the matrix and the particles under uniform temperature variations. The effects of the thermal mismatch between the matrix and fibers on the stress distribution and crack development were also numerically studied. The influences of the material heterogeneity, the failure patterns of FRCs at varied temperatures are simulated and compared with the experimental results in the present paper. The results show that the mechanisms of thermal damage and fracture of the composite remarkedably depend on the difference between the coefficients of thermal expansion of the fibers and the matrix on a meso-scale. Meanwhile, the simulations indicate that the thermal cracking of the FRCs at uniform varied temperatures is an evolution process from diffused damage, nucleation, and finally linkage of cracks.

Abstract: Ductile tearing of brittle solid with initial crack is studied numerically. This work is focused on the simulation and analysis of crack path deviation for the respective configuration and the study of relation between crack length and the fracture resistance, and that the configuration of fracture surface is also observed. The simulating tool is a novel numerical code, 3D Realistic Failure Process Analysis code (abbreviated as RFPA3D). The simulating investigation has shown that the fracture resistance decreases with the increase of the angle between the crack ends and horizontal direction. Due to heterogeneity of materials distribution, crack path deviation towards the softer zone or elements is observed. The topography of the non-planar fracture surface has plotted. Concluding the simulation made in the present study, the problem of crack extension in the brittle solid can be handled by RFPA3D. Fracture resistance can be predicted and the crack path deviation be simulated, if the model parameters have been carefully identified and the mesh design is adequate. So this work is beneficial to choose safe load-spots and predicate the direction of the crack path deviation.

Abstract: A numerical code RFPA3D (Realistic Failure Process Analysis) is used to simulate the crack initiation and propagation in FRP-strengthened concrete beam under external loading. In our model, the FRP-strengthened concrete is assumed to be a three-phase composite composed of concrete, FRP, and interface between them. The displacement-controlled loading scheme is used to simulate the complete failure process of FRP-strengthened concrete the numerical simulation of failure process of the specimens. It is found that the main failure mode is the interfacial debonding and the interfacial debonding may propagate either within the adhesive layer or through concrete layer in the vicinity of bond interface. The simulation results agree well with the experiment observations. The width of the FRP sheet is considered an important factor not only to significantly influence the debonding propagation type and crack distribution but also to control the ultimate load-capacity and ultimate strain. This study is focused on the failure process of the FRP-strengthened concrete beam and the effects of the width of FRP sheet on the failure mode and on the structural load-carrying capacity of concrete structures.

Abstract: Rock and concrete are typical heterogeneous material that the meso-scale heterogeneity may have a significant effect on their macro-scale mechanical responses. In this work, a digital image-based (DIB) technique is employed to characterize and quantify the heterogeneity of concrete, and the obtained data is directly imported into a numerical code named RFPA (Rock Failure Process Analysis) to study the effect of heterogeneity on the failure process of concrete. The upgraded RFPA is capable to simulate the progressive failure of brittle materials such as rock and concrete, representing both the growth of existing fractures and the formation of new fractures, obviating the need to identify crack tips and their interaction explicitly. The simulated results are in reasonable agreement with experimental measurements and phenomenological observations reported in previous studies.