Abstract

In this work, two methodologies for the analysis of unidirectional fiber reinforced composite materials are presented.

The first methodology used is a generalized anisotropic large strains elasto-plastic constitutive model for the analysis of multiphase materials. It is based on the mixing theory of basic substance. It is the manager of the several constitutive laws of the different compounds and it allows to consider the interaction between the compounds of the composite materials. In fiber reinforced composite materials, the constitutive behavior of the matrix is isotropic, whereas the fiber is considered orthotropic. So, one of the constitutive model used in the mixing theory needs to consider this characteristic. The non-linear anisotropic theory showed in this work is a generalization of the classic isotropic plasticity theory (A Continuum Constitutive Model to Simulate the Mechanical Behavior of Composite Materials, PhD Thesis, Universidad Politécnica de Cataluña, 2000). It is based in a one-to-one transformation of the stress and strain spaces by means of a four rank tensor.

The second methodology used is based on the homogenization theory. This theory divided the composite material problem into two scales: macroscopic and microscopic scale. In macroscopic level the composite material is assuming as a homogeneous material, whereas in microscopic level a unit volume called cell represents the composite (Tratamiento Numérico de Materiales Compuestos Mediante la teorı́a de Homogeneización, PhD Thesis, Universidad Politécnica, de Cataluña 2001). This formulation presents a new viewpoint of the homogenization theory in which can be found the equations that relate both scales. The solution is obtained using a coupled parallel code based on the finite elements method for each scale problem.

Abstract

The failure of adhesion between two polymers is a complex phenomenon involving bulk dissipation (i.e., shear yielding, cavitation and crazing), surface adhesion (through Van der Waals interactions) and connector chain pull-out. This article is concerned with a cohesive model for polymer surface separation, which incorporates connector pull-out since it is attempted to adjust this model on coarse-grained molecular dynamics (MD) simulations. This model is made of a viscoplastic constitutive equation taking inspiration from the works by Anand and Gurtin (2003). The MD simulations performed and here analysed were done in close collaboration with Prof. Erik van der Giessen (MuMec, Zernike Institute for Advanced Materials, University of Groningen, Groningen, the Netherlands).

Abstract

The RPAS (Remote Piloted Air System) MILANO is the largest unmanned aerial system developed by INTA that aims to become a research platform capable of carrying out in-flight tests with many scientific payload, thus complementing the Air Research Platforms (PAIs) of INTA. At the structural level, the RPAS MILANO is made in its entirety in carbon / epoxy composite material that is cured out of the autoclave. Its design has been followed by the airworthiness regulations applicable to the aircraft type (STANAG-4671). In the month of December 2018, the RPAS MILANO flight test phase began and it’s Health and Usage Monitoring System (HUMS) is being used to collect data before, after and during flights, providing very useful information when evaluating and analyzing the state of the structure and the possible appearance of structural overloads not foreseen during the mission. Information about special events, such as forced landing or burst loading, can be provided to maintenance operators after each flight. The simulation model and its predictions have been validated in a real structure of the rear fuselage of the MILANO and in which real damage of larger sizes is introduced by eliminating rivets progressively. In our study, three different damage detection algorithms are used, based on a damage index, PCA and Artificial Neural Networks (ANN).