Loading...
2 results
Search Results
Now showing 1 - 2 of 2
- Numerical study of in-plane biaxial fatigue crack growth with different phase shift angle loadings on optimal specimen geometriesPublication . Baptista, R.; Cláudio, R. A.; Reis, L.; Madeira, JFA; Freitas, M.Nowadays for real world applications, mechanical components in the automotive, aerospace, aeronautical and other industries are subjected to multiaxial loading conditions. Although the fatigue behavior of materials like steel alloys, aluminum alloys or even magnesium alloys is fairly well established for uniaxial loading, one should not use this knowledge for biaxial loading. Developing new testing machines and new specimen geometries have been the previous goal of several authors. A new generation of smaller and more efficient biaxial fatigue testing machines has arrived on the market. Using electrical motors these machines are not able to achieve the higher loads as their hydraulic counterparts can, and therefore the cruciform specimen needs to be optimized. The authors have previously optimized the cruciform geometry for biaxial fatigue initiation, using a revolved spline to reduce the specimen center thickness. For crack initiation experimental results have proven that the obtained design detail is effective, but there are no studies about the behavior of these specimens for crack propagation. In this paper the authors firstly set out to determine the conditions for crack initiation using traditional criteria like Findley, Brown-Miller, Fatemi-Socie, Smith, Watson and Topper (SWT), Liu I and Chu, as a function of different biaxial loading with phase differences. On a second stage the authors compared the biaxial fatigue crack propagation on the optimal specimens, with the behavior of notched specimens, using the stress intensity factors for mode I and mode II. Several crack and loading parameters were studied, including the starting crack length and angle, and different loading paths. Different biaxial loadings were applied to the model, including 30°, 45°, 60°, 90° and 180° out-of-phase angles. Very similar small crack propagation parameters were obtained for both specimens, although as the crack growths the stress intensity factor for the optimal specimen do not behave as expected. Therefore limiting the use of this specimen for crack propagation.
- Optimal cruciform specimen design using the direct multi-search method and design variable influence studyPublication . Miguel Gomes Simões Baptista, Ricardo; Cláudio, R. A.; Reis, L.; Madeira, JFA; Freitas, M.Nowadays the development of new testing machines and the optimization of new specimen geometries are two very demanding activities. In order to study complex material stress and strain distributions, as in-plane biaxial loading, one must develop new technical solutions. A new type of testing machine has been developed by the present authors, for the fatigue testing of cruciform specimens, but the low capacity of the testing machine requires the optimization of the specimen in order to achieve higher but uniform stress and strain distributions on the specimen center. In this paper, the authors describe the procedure to optimize one possible geometry for cruciform specimens, able to determine the fatigue initiation life of material subjected to out of phase in-plane biaxial fatigue loadings. The high number of design variables were optimized using the direct multi-search method, considering two objective functions, the stress level on the specimen center and the uniformity of the strain distribution on a 1.0 mm radius of the specimen center. Several Pareto Fronts were obtained for different material thickness, considering the commercially available sheet metal thickness. With the optimal solution, the influence of every design variable was studied in order to provide others with a powerful tool that allows selecting the optimal geometry for the desired application. The results are presented in the form of design equations considering that the main design variable, the material thickness, was chosen from a Renard series of preferred numbers. The end user is then able to configure the optimal specimen for the required fatigue test.