Papers by Author: Zheng Zhao Liang

Abstract: The periodically distributed fracture spacing phenomenon exists in the failure process of the pure bending region of the reinforced concrete beam. A numerical code RFPA3D (3D Realistic Failure Process Analysis) is used to investigate the crack distribution rule of reinforced concrete beam with different shear span ratios. The displacement-controlled loading scheme was used to simulate the complete failure process of reinforced concrete beam. The numerical simulation results were agreed well with the theoretical analysis and experiment observations. The study is focused on the failure process of the reinforced concrete beam and the effects of the shear span ratio on the failure mode.

Abstract: The pre-existing fractures in rock can close, open and growth as it subjected to mechanical or environment loading, which can in turn change the structure of the rock and alter its fluid flow properties. In order to study the crack growth processes of pre-existing fracture in rock under the condition of hydraulic and mechanical coupling, a numerical tool, named F-RFPA2D which takes into account the growth of existing fractures and the formation of new fractures, is used for this purpose. By considering the effect of hydraulic pressure filling into the wing crack, the behavior of fluid flow, damage evolution and their coupling action in the pre-existing and the newly formed fractures are studied in detail. The modeling results suggest that the hydraulic pressure in the crack enhanced the tensile stresses at the crack tips, resulting in crack growth path is different from that without hydraulic pressure loading. The wing crack growth mechanism under the coupling of hydraulic and mechanical is discussed, which provides a good reference for studying on the hydraulic fracturing in rock masses.

Abstract: Based on the microscopic damage mechanics, the finite element method is applied to investigate theinfluence of the inclined joint on the rock fragmentation under impact loading.The viscous boundary is considered to elimilate the influence of the reflected stress waves from the boundary. The result shows the inlcined joints change the direction of crack propagation. The lateral cracks appeare first, and thenthe main cracks tend to propagate to theleft side.

Abstract: A numerical method RFPA-T (Thermal Induced Rock Failure Process Analysis) code is used to study the thermal cracking processes of quasi-brittle materials subjected to high or low temperature. The numerical results indicate that thermal stress concentrating along the interface between the matrix and the embedded grains due to their different coefficient of thermal expansion (CTE). The modeling results indicate that θ-crack is generated during temperature increment as the CTE of the embedded grain is smaller than that of the matrix. However, radial-cracks emerged when the temperature decrease. The results obtained from RFPA-T code show a good agreement with experimental evidence of crack patterns caused by thermal expansion mismatch.

Abstract: Based on the mesoscopic damage theory and the finite element method, a numerical code RFPA was applied to investigate the rock fragmentation by three TBM cutters loaded one after another in different time interval. The whole process of crack initiation and propagation was successfully simulated by the cutters loaded with different step intervals. The time interval of the disc cutters has significant influence on the fracture patterns and the rock breaking efficiency. The simulated results show that there are three types of breakage mode of the rock subjected to compression by the cutters.

Abstract: Based on dynamic contact force and FEM, the contact – separation process of collision was investigated. Compared with other methods, the dynamic contact method needn’t modify the general stiffness matrix, and increase any additional iterative computation. So there should be less computation and high efficiency. By building simulation model LECEI(the technique of loading edge cracks by edge impact), the propagation of branching cracks were simulated. Compared with existing research results, the method can be suitable to the impact model such as LECEI.

Abstract: Parallel fracture formation on surfaces of bi-layered columnar materials like growing tree trunk has been previously studied numerically. In this paper, numerical results of a continuous transition from parallel to polygonal fracture patterns with principal stress ratio provides the clear convincing theoretical explanation for fracture spacing. We perform three-dimensional simulations of fracture growth in a bi-layered columnar model with an embedded heterogeneous layer under inner radial expansion and terminal tension by finite element approach. As a result of this expansion, the bark stretches until it reaches its limit of deformation and cracks. A novel numerical code, 3D Realistic Failure Process Analysis code (abbreviated as RFPA3D) is used to obtain numerical solutions. In this numerical code, the heterogeneity of materials is taken into account by assigning different properties to the individual elements according to statistical distribution function. Elastic-brittle constitutive relation with residual strength for elements and a Mohr-Coulomb criterion with a tensile cut-off are adopted so that the elements may fail either in shear or in tension. The discontinuity feature of the initiated crack is automatically induced by using degraded stiffness approach when the tensile strain of the failed elements reaching a certain value. Numerical results of a continuous transition from parallel to polygonal fracture patterns with principal stress ratio are obtained by varying simulation parameters, the thickness of the material layer. We find that, except for further opening of existing fractures after they are well-developed (saturation), new fractures may also initiate and propagate along the interface between layers, which may serve as another mechanism to accommodate additional strain for fracture saturated layers.

Abstract: A numerical test code is used to study the matrix-inclusion interfacial debonding for particulate reinforced composites. In our numerical model, It is assumed to be a three-phase composite composed of matrix, particulate and the interfaces between them. The finite element program is employed as the basic stress analysis tool when the elastic damage mechanics is used to describe the constitutive law of meso-level element and the maximum tensile strain criterion and Mohr-Coulomb criterion are utilized as damage threshold. A single inclusion of gradually interfacial debonding and a complex structure with 20 inclusions of the interfacial damage were studied under plane stress conditions. Results of stress distribution and interface debonding type obtained by numerical method agree well with the MARK and ABAQUS. The influence of heterogeneity of the matrix materials on the resulting process and the stress distribution of the failure process are also studied in the paper. It is found that the numerical test code can help to understand the failure mechanism of the model and it is an effective way to investigate the interfacial damage of composite materials. Keywords: Numerical test, interface, particulate reinforced composite, crack

Abstract: The goal of the present work is to investigate the influence of concrete on failure mode and stress distribution of the reinforced concrete specimens under axial tension by using a numerical test code named Realistic Failure Process Analysis. It can be found that, the periodically distributed fracture spacing phenomenon and tension stiffening phenomenon exist in the failure process of the reinforced concrete structure. Besides, the effect of concrete characteristics on the mechanical behavior and crack spacing of reinforced concrete was also studied in three samples with different concrete strength. The concrete strength value is considered to be an important factor not only to significantly influence the average crack spacing but also to influence the initial peak load of the specimen. In addition, the average fracture spacing is increased and the initial peak load is also increase with the increasing of the concrete strength value, but the mechanical capacities of the concrete has little influence on the ultimate load capacities of the specimen. Keywords: Numerical test; reinforcement concrete, crack distribution, 3D

Abstract: In this paper, a ring shaped numerical specimen is used to studying the failure process in brittle materials. The ring specimen is subjected to a compressive diametral load and contains two angled central cracks. Numerical modeling in this study is performed. It is shown that the obtained numerical results are in a very good agreement with the experiments. Effect of the crack orientation angle on the failure modes and loading-displace responses is discussed. In the range of 0°~40°, the fracture paths are curvilinear forms starting from the tip of pre-existing cracks and grow towards the loading points. For the crack orientation angle 90°, vertical fractures will split the specimen and the horizontal cracks do not influence the fracture process.