No abstract

The eXtended Finite Element Method XFEM has been reliably used for analyzing crack growth in 3D structural elements over last years. In fact, many researchers have worked in this field, but it is scarce to find scientific contributions about 3D XFEM models applied to the failure of non-standard composite parts, such as tapered structures and thick laminated composites. Thus, a new computational framework is developed, which is based on a new enhanced golden section search algorithm and 3D Puck's action plane principle in order to define the crack initiation direction. This information is integrated into a XFEM and used to enrich elements, which have failed during analysis. Compared to the traditional algorithm, the new methodology has convergence one order higher than the traditional one; and it is 20 times more efficient computationally. Therefore, if more precision is needed, then higher gains are achieved combined to lower computational cost by using the proposed framework. Moreover, thick laminated composites with layers mainly oriented to 90o were simulated under tension and compression via the computational framework, displaying results as reported in the literature. Also, compact tension tests with 0°, 90° and 45° specimens were evaluated, and numerical results were qualitatively coherent with experimental data.

This work aims to provide a computational tool to calculate composite aeronautical structures such as fuselage and rotor blade, considering large damage capabilities. The computational tool developed was based on the theories proposed by Puck and Matzenmiller. The damage propagation is carried out by progressive failure analysis via a phenomenological approach. The material model separates the mechanisms concerning the fibre and the matrix and addresses them under different perspectives. Some parameters related to the material model were obtained from standardized experimental tests, while the identification of others required the development of special procedures. The material model was implemented as subroutines in FORTRAN language, which were linked to ABAQUS by UMAT/URDFIL. A non-local criterion was used to provide spatial regularization, avoiding numerical convergence problems. In order to perform an automatic identification of the parameters related to the material model, another computational tool was developed. After the identification process, a parametric sensitivity study was carried out using a composite plate with a circular hole. The investigated parameters -finite element mesh size, load step and characteristic radius were selected considering that their influences were supposed to be material independent. Finally, a damage analysis of the same composite plate under a specific loading condition was carried out using the "optimal" values for the investigated parameters. Based on the convergence between the numerical results and experimental data, it can be concluded that the theories and methods applied in this work consisted a good strategy to simulate composite structures in the industry environment.

No abstract