Abstract
The aim of this study is to propose a simplified calculation of the Mode I stress intensity factor K for the cruciform specimen design proposed by Brown and Miller. To calculate K, both cracks have to grow with a similar crack growth rate and the crack paths of the two single cracks with the length a should also be similar. The calculations are carried out on an aluminum specimen and a steel specimen. For all load cases and materials, the stresses resulting from the forces are first considered. It was found that the elastic constants E and ν have only a small influence of less than 3 %. In addition, the coupling between the forces of the load axes, which should be minimized by the slotted arms, is considered. Furthermore K-factors are calculated by FE for different crack lengths. These K-values together with the transmission factor allow to find a K-factor formula for cruciform specimens, which is based on the prescribed forces. Finally, the results of the FE calculation of the exact straight crack paths were compared to experimentally determined crack paths.
Highlights
Many components are subjected to multi-axial stress conditions during their service life
The aim of this study is to propose a simplified calculation of the Mode I stress intensity factor K for the cruciform specimen design proposed by Brown and Miller
Three common specimen designs can be found in the literature: (i) flat specimen design with large radii between the loading arms, see e.g. Refs. [1, 2], (ii) flat specimen design with small radii between the loading arms, see e.g. Refs. [3,4,5,6,7], and (iii) specimen design with thickness-reduced measuring area and slotted arms, see e.g. Refs. [7,8,9,10,11,12,13,14,15,16,17]
Summary
Many components are subjected to multi-axial stress conditions during their service life. The estimation of fatigue crack growth is often based on uniaxial data. Biaxial fatigue crack growth investigations are an important link between the uniaxial small-scale tests on the one hand and the complex component tests on the other hand. Difficulties in investigating fatigue crack growth under planar biaxial loading arise from the different specimen types, as there are many different testing machines and no standardized specimen design. (i) flat specimen design with large radii between the loading arms, see e.g. Refs. [1, 2], (ii) flat specimen design with small radii between the loading arms, see e.g. Refs. [3,4,5,6,7], and (iii) specimen design with thickness-reduced measuring area and slotted arms, see e.g. Refs. As a result of the different specimen designs, the K-solution has to be computed for each specimen design by FE-calculations considering the individual crack paths and the material
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