Papers by Keyword: J-Integral

Abstract: Three-dimensional (3D) elastic-plastic finite element model (FEM) is adopted to research the effect of side groove on the crack-front J-integral for different size of Compact Tension (CT) specimens. Although the side-grooved CT specimen is widely used in the existing test method, such as ASTM E1820-13, the test data of fracture toughness is varying with the various geometric parameters. Before FE calculation, the material properties of Q345 steel were obtained by uniaxial tensile test, especially for the true stress-strain relationship. In this paper, it focuses on the numerical study of geometric parameter effects on the fracture toughness. Toward this end, the commercial FE software of ABAQUS is adopted to calculate the J-integral. Since the side groove of CT specimen is so important to make the fracture test success, the various parameters of side groove is intensively analyzed for obtaining the accurate J-integral along the crack front, including the effects of the angle, depth and root radius. In fact, the side groove effect is so significant around the crack front that cannot be ignored in the J-integral calculation. Through rigorous FE investigation, the influence of the side groove on the fracture toughness testing is fully disclosed, and the appropriate side groove configuration is recommended accordingly.

Abstract: Plasticity zone at crack tip of aluminum alloy with fcc structure is investigated in order to analyze the effect of crystal orientation to the plasticity distribution on crack tip, as well as the effect to CTOD and J-integral, which is implemented using finite element code in Abaqus with a rate dependent crystal plasticity theory. The results show that the crack tip plasticity, stresses and CTOD are significantly affected by grain orientations. When the grains have single textures, Cube and S orientations have a strong ability to against crack propagation. However, when the grains combine textures, the increasing of misorientation enhances the resistance for crack growth. And when the tilt angle is higher, the crack deflection is promoted to reduce the crack propagation rate.

Abstract: Numerical accuracy in assessing the strong shielding interaction that promotes cracking process based on continuum mechanics is presented in this paper. Crack interaction limit (CIL) and crack unification limit (CUL) are investigated based on strain energy release rate approach. The case of two interacting edge crack in finite body is simulated using finite element analysis and J-integral. As a result, the trend of CIL and CUL is presented to prove the limit and unification of energy release can be numerically shown at higher and lower crack-to-width ratio at two crack interval ratio b = 1 and b = 0. It can be concluded that the CIL and CUL is geometrically dependent.

Abstract: In the last few decades, energy absorption of materials becomes an critical issue in a design process of a vehicle because risks of primary and secondary accidents against pedestrians, other road users and structures can be reduced by a performance of absorbing energy in its support structures. Among various materials used for the structures, TRIP steel with favorable mechanical properties such as excellent formability and higher impact energy absorption is attractive to automotive industries. Huge numbers of research works have been carried out to investigate deformation behavior of TRIP steel. However, just few studies can be found on the performance in TRIP steel, especially, at higher deformation rate during the crash of the vehicle. Kinetic energy by higher speed of the vehicle will be consumed by inelastic bending deformation of components. Thus, a consideration of bending deformation at high impact velocity is required for the evaluation of the performance. In this study, the performance in TRIP steel at high deformation rate is clarified by conducting both quasi-static and impact three-point bending tests for pre-cracked specimen.

Abstract: Determination of fatigue crack growth characteristics under shear-mode loading is a rather complicated problem. To increase an efficiency and precision of such testing, special specimens enabling simultaneous propagation of shear cracks under II, III and II+III loading modes started to be used rather recently. K-calibration of these specimens was performed and, after unique pre-crack and heat-treatment procedures, effective thresholds in several metallic materials could be measured. However, a description of crack growth rate in terms of appropriate fracture mechanics quantities demands a precise assessment of plastic zone size under various shear-mode loading levels. This contribution is focused on the numerical elasto-plastic analysis of stress-strain field at the crack tip in specimens made of a pure polycrystalline (ARMCO) iron. The results reveal that the small scale yielding conditions are fulfilled in the near-threshold region. Starting from ΔK values approximately two times higher than the threshold, however, the ΔK_J or ΔJ approach should already be utilized. Probably the most interesting result of the analysis lies in a simple procedure that enables us to separate individual loading components ΔK_J,II and ΔK_J,III, applied in the mixed-mode II+III part of the specimen, by comparing elasto-plastic and elastic solutions.

Abstract: The effect of aging treatments on the mechanical behavior of Ti-15V-3Cr-3Sn-3Al (Ti153) alloy was evaluated in the present study. Properties of the two-step aged specimens were also compared with those of the one-step aged specimens. The second aging treatment, which was performed at 426^o°C for 24 h, apparently raised the tensile strength at the expense of the notched tensile strength for the specimens previously aged at 426°C or below. On the other hand, the second-step aging had a minor effect on further hardening of the specimens prior to aging at 538°C and 593°C. In general, the J-integral value (fracture toughness) had the same trend as that of the notch brittleness of the specimens. Overall, the specimens subjected to the two-step aging treatment did not show any advantage over the specimens subject to one-step aging treatment.

Abstract: This paper investigates crack interaction of multiple edge cracks in elastic solid finite body under pure Mode I loading. The cracks are located in parallel to another in 2D plate model. The stress intensity factors (SIFs) are determined based on strain energy release rate. The J-integral path independent is employed to study the interaction between cracks in regards to the effect of crack shielding and amplification of various cracks arrangement. The aim of present work is to test several numerical techniques reported in literature. J-integral approach are applied in 2D ANSYS finite element models subjected to different crack-width ratio (a/w) and cracks interval ratio (a/b). For validation, the results are compared to singular finite element approach and related analytical formulation. The results obtained by these methods are found in good agreement with singular finite element. Some discrepancies between analytical solutions are discussed. Nevertheless, since strain energy release is concern to characterize the near crack tip field, the J-integral method seems to be more applicable and accurate for interacting cracks analysis.

Abstract: Crack is one of the major distresses in asphalt pavement. Although epoxy asphalt concrete demonstrates higher distress resistant ability than traditional asphalt concrete, crack initiation and propagation is also inevitable due to traffic and environmental impact. Among the three typical crack modes, the Mode I crack usually appears in epoxy asphalt concrete pavement. In this paper, the model of crack propagation in epoxy asphalt concrete pavement is proposed and simulated through finite element method in conjunction with virtual crack extension approach. The eight-node singularity element was used at the crack-tip. And the node shift/release technique is adopted for modeling propagation of the crack tip. Results show that J-integral is path-independent due to the small plastic zone around the crack tip and suitable to evaluate the fracture behavior for epoxy asphalt concrete pavement. Two inflexions on the curve of J-integral vs. crack length indicate that epoxy asphalt concrete pavement have three phases in crack initiation and propagation: crack initiation, stable crack propagation and unstable crack propagation. Finally, the equation describing the relationship between J-integral and displacement is provided in this paper.

Abstract: The ratio of J-conversion CTOD to CMOD-based CTOD was experimentally evaluated and analytically estimated in shallow crack specimens. It was demonstrated that the low strain hardening exponent in the Ramberg-Osgood relation reduced the CTOD ratio. A CTOD transformation equation, which was proposed by the authors, can transform CMOD-based CTOD into J-conversion CTOD with reasonable accuracy for 0.15≤a/W≤0.5.

Abstract: The proposed paper describes fatigue damage evolution in Eurofer 97 reduced activation ferritic-martensitic steel. The short crack growth study was performed on small cylindrical specimens using an MTS 880 servohydraulic machine at constant strain amplitude. Based on the fatigue crack growth data obtained and corresponding 3D finite element analysis Paris law region of the fatigue curve were estimated. The results obtained were compared with standard determination of the fatigue crack growth rate according to ASTM using CT specimens. The presented results can help to transfer experimental data measured on small specimens to large structures and vice versa.