Based on the governing equations of linear elasticity, this paper develops a novel boundary value method to study the singular behavior of elastic stress fields at the corners of bimaterial wedges and junctions by using the eigenfunction expansion technique. The resulted one-dimensional differential system, which consists of the reduced equilibrium equations and boundary conditions, just relates to an angular coordinate in the polar coordinate system. Implementing discretization of this differential system by the finite cloud method, we readily derive the so-called generalized eigenproblem in the singular eigenvalue. The performance of the methodology is subsequently verified through the well-known crack and interface crack problems, demonstrating high accuracy and quick convergence characteristics. In addition, a selected set of practically useful models is numerically analyzed to examine the angular variations of the displacement and stress fields, and the influences of wedge-side boundary conditions to singular behavior are also studied.

The fatigue crack growth tests of compact tension (CT) specimens of 2024-T4 aluminum alloy were conducted under constant amplitude loading with differentR-ratios, 0.05, 0.1, 0.5, 0.75, respectively. The thickness of the specimen is 3.8mm. All the fatigue crack growth experiments were carried out in ambient air without a pre-crack. The early crack growth region reflects the influence of the notch. An optical reading micrometer with a magnification of 40 was used to measure the crack length. The size of the notch together with the loading conditions has a great influence on the early crack growth within the notch influenced region. Beyond the notch influenced zone, the stable fatigue crack growth is reached and can be characterized by the Paris law. The experimental results indicate that fatigue crack growth rate increases with theR-ratio for a given stress intensity factor amplitude.

The fatigue crack growth experiments of 2024-T4 aluminum alloy were carried out to study the thickness effects on the fatigue crack growth rate. Round compact specimens with two different thickness, 3.8mm and 12.5mm, were subjected to Mode I loading with fourR-ratios (0.05, 0.1, 0.5 and 0.75) and loading amplitudes. An optical reading microscope with a magnification of 40 was used to measure the crack length. Stable crack growth is characterized by the standard form of the Paris law, material constants of the Paris law corresponding to eachR-ratio were obtained by fitting the experimental data. The fatigue crack growth rate of specimens with a thickness of 12.5mm is apparently higher than that of specimens with a thickness of 3.8mm whenR-ratio is equal to 0.1, 0.5 and 0.75. While the effect of thickness is relatively less significant for the case of. It can be concluded that the fatigue crack growth rate increases with R-ratio or thickness when one of them is identical.

Fatigue crack growth was simulated by using a newly developed unified model on the fatigue initiation and crack growth based on an incremental multiaxial fatigue criterion. The cyclic elastic-plastic stress-strain field was analyzed using the general-purpose finite element software (ABAQUS) with the implementation of a robust cyclic plasticity theory. The fatigue crack growth rates with respect to three different stress ratios were selected as the benchmark to check the unified model. The predicted results agreed with the experimental data very well. The insensitivity of the crack growth rate to the stress ratio is due to the fast mean stress relaxation.

The fatigue crack growth behavior of one compact tension specimen of 16MnR steel under high-low sequence loading was investigated. The symmetric half finite element model under plane-stress state was used to calculate the elastic-plastic stress-strain responses, in which the Armstrong-Frederick type cyclic plasticity model was implemented as a user material subroutine UMAT of ABAQUS. A recently developed dynamic crack growth model was used to simulate the effects of high loading step on the successive low loading step. The detailed evolution process of the crack closure and cyclic plastic zone within the retardation region of fatigue crack growth was obtained. The extend of the crack closure, the size of cyclic plastic zone and the stress gradient have significant influence on the fatigue crack growth rate. The predicted fatigue crack growth rate is in good agreement with the experimental data.