Accurate stress intensity factors for kinked interface crack in bonded dissimilar half-plane

In this study, the stress intensity factor (SIF) of an interface kinked crack is analyzed by the singular integral equation of the body force method. The problem can be expressed by distributing the body force doublets of the tension and shear types along all the boundaries of the kinked and interface crack parts. The SIFs can be obtained directly from the densities of the body force doublets at the crack tips. Although the problem has already been calculated using the crack connection model, the accuracy of the analysis has not been clarified. From the analysis results in this study, it can be seen that the SIFs calculated by the crack connection model have a nonnegligible error, and the present method gives more accurate results. The advantage of the present method is that the SIFs of the kinked and the interface crack tips can be obtained at the same time with high accuracy.

Numerical Modeling of Plasticity-Induced Fatigue Crack Growth Retardation Due to Deflection in the Near-Tip Area

This article studies the retardation effect in plasticity-induced fatigue crack growth rate for a low-medium strength steel, due to the appearance of microdeflections in the crack path. To this end, the finite element method was used to model the crack with its kinked tip under several stress intensity factor (SIF) ranges. The results allowed a calculation (after a small number of cycles) of the fatigue crack propagation rate for the multiaxial and uniaxial fatigue configurations at the microscopic level. It was observed that the retardation effect rose with an increase in the initial kinked crack tip angle, an increase in the initial projected kinked crack tip length, and with a decrease in the SIF range.

CRACK PROPAGATION UNDER INITIAL MODE II CONDITIONS

Series of tests for compact tension shear specimens under mode II and following mixed mode was carried out. Compact tension shear specimens made of steels 34X and P2M, Ti-6Al-4V titanium and 7050 aluminum alloys. During experiments the behavior of the inclined crack angles, kinked crack angles and crack propagation angles, as a function of dimensionless crack length for the curvilinear paths was obtained. The influence of elastic-plastic material properties on the form the curvilinear crack path is established.

Investigation of Systems Weakened by Kinked Cracks

Прочность летательных аппаратов любых типов — важнейший вопрос безопасности полетов. Наличие скрытых дефектов в материале существенно влияет на прочность при различных нагрузках. Важными характеристиками прочности материалов с дефектами являются скорость и направление роста трещины, а также величина критической нагрузки (коэффициента интенсивности напряжений), при которой начинается рост трещины. В данной работе исследуется трехмерная упругая среда, ослабленная системой плоских трещин и одной трещиной с изгибом. В качестве численного метода был выбран метод граничных элементов, а именно метод разрывных перемещений. Код реализован на C++. Было проведено сравнение с известными аналитическими результатами. Изучено поведение трещин при изгибе при различных нагрузках. Structural strength of aircraft is a key aspect of flight safety. Hidden defects in the material significantly affect its strength under various loads. The crack growth rate and direction, and the crack growth threshold load (stress intensity factor) affect the strength of the damaged material. This study investigates a 3D elastic structure weakened by a system of flat cracks and a kinked crack. The numerical method used was the boundary element method, specifically, the displacement discontinuity method. The code was developed with C++. The results were compared against the available analytic results. The behavior of cracks under bending and a range of loading conditions was studied.

Numerical Study of the Progression of the Micromechanical Debonding Damage in Composites

This paper deals with the study of the actual progression of the damage in the 90 degrees lamina of a composite. It has been proved and observed that isolated debondings between fibres and matrix are the first manifestation of damage in the weakest lamina, the 90 degrees lamina in a [0,90]S laminate. It was also numerically supported that this first phase was independent of the thickness of the 90 degrees lamina, not being then affected by the “scale effect”. The continuation of this first phase of damage is the objective of the present paper. To this end, a multiscale model is created involving the debonding between fibre and matrix and studying the kink of this crack, abandoning the fibre-matrix interface and entering into the matrix to produce a meso-transverse crack in the 90 degrees ply. The study is based on the application of Fracture Mechanics to an incipient kinked crack that starts from a debonding between fibre and matrix. It is concluded that this second phase of damage, playing with the thickness of the 90 degrees lamina, is not affected by the scale effect, as the variation of the energy release rate of the kinked crack is not significantly influenced by the variation of the thickness of the lamina.