A mesh-independent framework for crack tracking in elastodamaging materials through the regularized extended finite element method

We propose a formulation for tracking general crack paths in elastodamaging materials without mesh adaptivity and broadening of the damage band. The idea is to treat in a unified way both the damaging process and the development of displacement discontinuities by means of the regularized finite element method. With respect to previous authors’ contributions, a novel damage evolution law and an original crack tracking framework are proposed. We face the issue of mesh objectivity through several two-dimensional tests, obtaining smooth crack paths and reliable structural results.

Fracture and Fatigue Analyses of Cracked Structures Using the Iterative Method

It is a quite challenging subject to efficiently perform fracture and fatigue analyses for complex structures with cracks in engineering. To precisely and efficiently study crack problems in practical engineering, an iterative method is developed in this study. The overall structure which contains no crack is analyzed by the traditional finite element method (FEM), and the crack itself is analyzed using analytical solution or other numerical solutions which are effective and efficient for solving crack problems. An iteration is carried out between the two abovementioned solutions, and the original crack problem could be solved based on the superposition principle. Several typical crack problems are studied using the present method, showing very high precision and efficiency of this method when making fracture and fatigue analyses of structures.

Research on crack evolution law and macroscopic failure mode of joint Phyllite under uniaxial compression

In order to explore the fracture mechanism of jointed Phyllite, the TAJW-2000 rock mechanics test system is used to carry out uniaxial compression tests on different joint inclination Phyllites. The influence of joint inclination of Phyllite failure mode is discussed, and the progressive failure process of Phyllite is studied. The test results show that the uniaxial compressive strength anisotropy of jointed Phyllite is remarkable. As the inclination increases, it exhibits a U-shaped change; When 30° ≤ α ≤ 75°, the tensile and shear failures along the joint inclination mainly occurs. the joint inclination controls the failure surface form of the Phyllite; The crack initial stress level of the joint Phyllite is 0.30–0.59σf, the crack failure stress level is 0.44–0.86σf. When α = 90°, the σcd value is the largest, and σcd with α = 90° can be used as the maximum reliable value of uniaxial compressive strength of Phyllite. Using the theory of fracture mechanics, it is analyzed that under uniaxial compression of the rock, the crack does not break along the original crack direction, but extends along the direction at a certain angle to the original crack. The joint effect coefficient is proposed to show the influence of the joint inclination on the uniaxial compressive strength of the phyllite. Both the test and simulation results show that when the joint inclination is 60°, the joint effect coefficient is the largest. The compressive strength is the smallest. Numerical simulation analyses the crack evolution law of phyllite under different joint inclination under uniaxial compression, which verifies that there are different failure modes of joint phyllite under uniaxial compression.

Study of the Growth Process of Original Crack in the Surrounding Rock of Tunnel under the Adjacent Explosive Load

The surrounding rock damage of a tunnel under adjacent explosive load is often manifested as the growth of the original crack. In order to thoroughly understand the crack growth mechanism, in this study, the growth process of the original crack was investigated in detail by the dynamic caustics experiment. The experimental study shows that the growth of original crack is the result of the combined action of explosion stress wave and explosive gas. The quasi-static stress generated by the explosive gas was superimposed on the weakened stress field, resulting in the formation of the peak of the main stress difference in the surrounding rock, moving towards the adjacent tunnel in the form of an arc wave. With the arc wave moving towards the original crack, the growth rate of the original crack increases rapidly. During the period of 200 μs to 250 μs, the crack growth rate oscillates at the peak, and its size is approximately equal to the moving speed of the arc wave. Based on the experimental results and microscopic damage mechanics, the high stress concentration at the original crack tip under the stress wave first causes damage localization and the weakest chain is formed by the penetration of the damage localization zones by microcracks by special distribution law. Subsequently, the original crack starts to initiate and grow along the direction of the weakest chain.

Predictions of Tensile Strain Capacity for Strain-Based Pipelines With a Circumferential and Internal Surface Flaw

Strain-based design assessment (SBDA) has been known for suitable assessment concept for pipelines subjected to displacement-controlled load and high plastic deformation rather than conventional stress-based design assessment. Tensile strain capacity (TSC) has been used for one of important factors to indicate limit state in strain-based design, so that it is main concern to predict accurate TSC to ensure the structural safety and integrity of pipelines. For the pipeline containing a flaw, especially a girth weld flaw, TSC based on fracture mechanics can be determined. Crack-tip opening displacement (CTOD) has been widely used for typical elastic-plastic fracture parameter, representing crack-driving force and crack-resistance curve, which are required to assess unstable crack propagation. The one of the main principles of crack assessment is that the definitions of crack-driving force and crack resistance curve should be coincident. However, there exist two kinds of the definitions of CTOD, which are based on 90° and original crack-tip concept, and these have been not unified in practical regions until now. Moreover, it is reported that the deviations of crack-resistance curve can occur in the same specimen and experiment, caused by the different definitions of CTOD. Therefore, CTOD solutions based on each of different definitions of CTOD should be highly required since inaccurate TSC would be assessed when using not the identical definition of that. In the present study, CTOD solutions of pipelines with a circumferential and internal surface flaw are suggested by using two kinds of definitions of CTOD based on 90° and original crack-tip concept. For this purpose, FE analyses were systematically carried out considering various pipe geometries and material properties. And single-edge notched tension (SENT) specimen was used for representing resistance curve of API X70/X65 material. Moreover, the effect of the choice of each CTOD definitions on TSC was investigated through crack-driving force diagram (CDFD) assessment.

Influence of Traffic Load on the Crack Widths of Full Jointless Bridges

Traffic load not only increases the original crack widths of the reinforced approach pavement of full jointless bridges, but also generates the development of new small cracks. Using lab experiments, this paper mainly studies the influence of traffic load on the crack width of the approach pavement of full jointless bridges. The results show that the load of traffic not only increases the crack width, but also increases the vertical settlement. In order to control the crack width we need to consider the influence of the traffic load. And the traffic load influence factor here we choose to be equal to 1.45.

Study on Stress Increment of Externally Strengthened Prestressed Box Beams

With different original status including crack, controlled stretching stress and reinforcement ratio, five reinforced concrete box beams strengthened with external prestressed tendons were designed. The stress increment of external tendons was studied by indoor test and Finite Element Method analysis. The study shows that the less the controlled stretching stress is, the more rapidly the prestressed stress increment increases. There is no clear difference between the beam with original crack and without crack. In the test, the measured ultimate stress of external prestressed tendon agrees with the calculated result based on deflection method, and the stress in serviceability stage agees with the result based on structural mechanics method. In Finite Element model, the change of effective prestress, concrete strength, the area and depth of external tendons will result in a little change of stress in serviceability stage, but obvious change in ultimate status. the change of tendons lateral distance to the web results in litlle change of stress in the whole loading stage , no matter it is inside or outside the box at cross section.

Control Conditions for the Second–Class Crack of Concrete Based on Different Modulus Theory

Many engineering materials exhibit different elastic properties under the extension and compression. Among these materials, the concrete is a typical material which has different extension modulus and compression modulus. Based on different modulus theory, mechanical analysis was performed in this paper for reinforced concrete beams, stress formula was deduced, and the corresponding formula was applied to concrete structures with second-class crack control, which has improved the original crack control conditions in the code for design of concrete structures in China based on the classical modulus theory.

Solution of the boundary value problem for a kinking crack in a bulk compression field

The solution of the boundary value problem for a macroscopic crack with a small wing crack, in a linear elastic brittle material, due to a bulk compressive stress field is considered. The crack, initially subject to pure mode II loading, propagates by kinking at its end and extending along a new trajectory, in the classical opening mode. The innovations of this paper are, firstly, the introduction of a free surface into an infinite plane solution, so that the original crack is an edge crack in a half-plane, and, secondly, the ability to consider rapidly varying stress gradients on both segments of the kinked crack. Solutions are presented for (a) an inclined crack in a uniform compressive field and (b) cracks subject to contact loading from a rigid punch loading the half-plane via a linear elastic interlayer.