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Keywords: mixed mode fracture, asymmetric double cantilever beam, finite element method, composite delamination.

Summary

There are several experimental methods documented in the literature in order to determine mixed mode fracture toughness in laminated composites. In these test methods, the percentage of mode I and II load state at the crack tip are well known and so the corresponding components of the energy release rate. Nevertheless, the required test fixtures are somewhat complex.

Asymmetric double cantilever beam specimens (ADCB) in which the crack plane is out of the laminate midplane, are useful to easily produce a mixed mode load state at the crack tip of the samples. This test configuration is as simple as pure mode I tests. Nevertheless, the mixed mode load state at the crack tip cannot be controlled by means of the test fixtures and then, the different components of the energy release rate are not easy to be calculated. In this test configuration, the position of the crack plane controls the percentage of mode I and mode II load at the crack tip.

In this paper, the finite element method has been used in order to analyze the ADCB specimen. The mode I and mode II components of the energy release rate have been calculated for different crack plane positions and, from these results, an empirical equation has been derived.

These components have been numerically calculated by means of the two-step method. In this method the forces at the crack tip are calculated in a first step when the load reaches a critical value. The displacements are then calculated in a second step where the nodes at the crack tip are released.

The ADCB specimens were modelled by means of the ANSYSR finite element package. Models were prepared with different plane positions. The models were solved as nonlinear models in order to take into account possible nonlinearities derived from the increase in the upper sublaminate compliance as the crack plane moves away from the midplane. The material used in this study was a Hexcel AS4/8552, 6 mm thick unidirectional carbon fibre reinforced epoxy laminate.

The finite element results were plotted as a function of a combination of the sublaminates thicknesses. This curve was fitted by means of an ellipse equation. Numerical results and empirical calculations showed a good agreement as the error between them was always lower than 11%.

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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	Civil-Comp Proceedings ISSN 1759-3433 CCP: 93 PROCEEDINGS OF THE TENTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY Edited by: Paper 86 Using the Finite Element Method to Analyze Asymmetric Double Cantilever Beam Specimens V. Mollón¹, J. Bonhomme², A. Argüelles² and J. Viña¹ ¹Department of Materials Science and Metallurgical Engineering, ²Department of Construction and Manufacturing Engineering, University of Oviedo, Gijón, Spain doi:10.4203/ccp.93.86 purchase the full-text of this paper Full Bibliographic Reference for this paper , "Using the Finite Element Method to Analyze Asymmetric Double Cantilever Beam Specimens", in , (Editors), "Proceedings of the Tenth International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 86, 2010. doi:10.4203/ccp.93.86 Keywords: mixed mode fracture, asymmetric double cantilever beam, finite element method, composite delamination. Summary There are several experimental methods documented in the literature in order to determine mixed mode fracture toughness in laminated composites. In these test methods, the percentage of mode I and II load state at the crack tip are well known and so the corresponding components of the energy release rate. Nevertheless, the required test fixtures are somewhat complex. Asymmetric double cantilever beam specimens (ADCB) in which the crack plane is out of the laminate midplane, are useful to easily produce a mixed mode load state at the crack tip of the samples. This test configuration is as simple as pure mode I tests. Nevertheless, the mixed mode load state at the crack tip cannot be controlled by means of the test fixtures and then, the different components of the energy release rate are not easy to be calculated. In this test configuration, the position of the crack plane controls the percentage of mode I and mode II load at the crack tip. In this paper, the finite element method has been used in order to analyze the ADCB specimen. The mode I and mode II components of the energy release rate have been calculated for different crack plane positions and, from these results, an empirical equation has been derived. These components have been numerically calculated by means of the two-step method. In this method the forces at the crack tip are calculated in a first step when the load reaches a critical value. The displacements are then calculated in a second step where the nodes at the crack tip are released. The ADCB specimens were modelled by means of the ANSYSR finite element package. Models were prepared with different plane positions. The models were solved as nonlinear models in order to take into account possible nonlinearities derived from the increase in the upper sublaminate compliance as the crack plane moves away from the midplane. The material used in this study was a Hexcel AS4/8552, 6 mm thick unidirectional carbon fibre reinforced epoxy laminate. The finite element results were plotted as a function of a combination of the sublaminates thicknesses. This curve was fitted by means of an ellipse equation. Numerical results and empirical calculations showed a good agreement as the error between them was always lower than 11%. purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £145 +P&P)
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