Marcelo Leite Ribeiro

Computational methodology of damage detection on composite cylinders: structural health monitoring for automotive components

A numerical investigation of the damage effects on the structural response of the composite cylinders damaged by impact loading was performed. A computational methodology, which consists of carrying out four-step finite element (FE) analyses in progressive sequence, was used. Firstly, modal analyses were carried out for the intact structure to determine the natural frequencies and modal shapes. Then, vibration analyses were performed for intact structure to obtain the frequency response function (FRF). After that, impact analyses were performed by using a material model, which is accessed to predict the damage. Based on damaged FE model, vibration analyses, again, were carried out to determine the new FRF. Thus, the results of the damaged structure were combined to intact model results by using a specific metric in order to indicate the damage or not in the composite cylinders. Finally, it was discussed about the advantages and limitations of SHM systems, which use vibration-based methods and piezoelectric sensors.

Experimental and numerical analysis of single lap bonded joints: Epoxy and castor oil PU-glass fibre composites

ABSTRACT Currently, there is a growing concern for the environment. Several studies of new materials to reduce environmental impact have been carried out by different research groups, and many companies have replaced parts made of fossil sources by renewable materials. The use of polyurethane (PU) derived from castor oil as a matrix for composite materials and adhesives is one example. Hence, the present work aims to compare the numerical and experimental analyses of castor oil PU and epoxy resin not only as a matrix of composite materials, but also as an adhesive of bonded joints. The joint coupons were manufactured by using castor oil PU-glass fibre and epoxy-glass fibre as adherents, which were bonded by epoxy or castor oil PU. Thus, four combinations of adherents and adhesives were investigated. Specimens with identical geometry were used in all tests, which were based on guidelines for single lap bonded joints. Computational simulations via Finite Element Method were performed for predictions of the adhesive layer stresses and strength. In addition, a material model is proposed to predict the failure of the adhesive layer. The experimental and numerical results showed that PU derived from castor oil has good mechanical performance, making this material a feasible alternative for bonded joints, mostly nowadays when environment is a major concern.

Computational analyses for carbon-epoxy plates damaged by low velocity impact

The usage of composite materials on new design structures is still very conservative, mainly due to its very complex failure behavior. Therefore, the prediction of these mechanisms requires computational analysis. Thus, a damage model based on CDM concepts is applied in order to predict intra-ply failure mechanisms in impacted carbon-epoxy laminate structures. The damage model was implemented as VUMAT (User Material Subroutine for explicit integration analyses) and linked to ABAQUSTM. Several numerical analyses were performed, and the results were compared to experimental tests in order to evaluate the potentialities and limitations of the damage model application.

A Delamination Propagation Model for Fiber Reinforced Laminated Composite Materials

The employment of composite materials in the aerospace industry has been gradually considered due to the fundamental lightweight and strength characteristics that this type of materials has. The science material and technological progress reached matched perfectly with the requirements for high-performance materials in aircraft and aerospace structures; thus, the development of primary structure elements applying composite materials became something very convenient. It is extremely important to pay attention to the failure modes that influence composite materials performances, since these failures lead to a loss of stiffness and strength of the laminate. Delamination is a failure mode present in most of the damaged structures and can be ruinous, considering that the evolution of interlaminar defects can carry the structure to a total failure followed by its collapse. The present work aims at the development of a delamination propagation model to estimate a progressive interlaminar delamination failure in laminated composite materials and to allow the prediction of material’s degradation due to delamination phenomenon. Experimental data, available at literature, was considered to determine some model parameters, like the strain energy release rate, using GFRPs laminated composites. This new delamination propagation model was implemented as subroutines in FORTRAN language (UMAT-User Material Subroutine) with formulations based on the Fracture Mechanics and Continuum Damage Mechanics. Finally, the UMAT subroutine was complemented with an intralaminar model and compiled beside the commercial Finite Element (FE) software ABAQUS™.

A computational framework for predicting onset and crack propagation in composite structures via eXtended Finite Element Method (XFEM)

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 in-formation 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.