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Azevedo J.M.C.,University of Porto | Belinha J.,Institute of Mechanical Engineering and Industrial Management | Dinis L.M.J.S.,University of Porto | Natal Jorge R.M.,University of Porto
Engineering Analysis with Boundary Elements | Year: 2015

Abstract One of the most challenging problems in computational mechanics is the prediction of the crack propagation path. In this work, the Natural Neighbour Radial Point Interpolation Method (NNRPIM), an efficient meshless method, is extended to the field of fracture mechanics. Since the NNRPIM relies on the Natural Neighbour mathematical concept to obtain the integration mesh and establish the nodal connectivity, the NNRPIM only requires a computational nodal distribution to fully discretise the problem domain. The Radial Point Interpolators (RPI) are used to construct the NNRPIM interpolation functions. Taking advantage of the unique features of the NNRPIM, in this work, the crack propagation path is numerically simulated using an adapted crack path opening algorithm, in which the crack is iteratively extended in line segments. In each iteration, using the obtained stress field, the crack propagation direction is determined using the maximum circumferential stress criterion. Due to the flexibility of the natural neighbour concept, the increase of the domain discontinuities do not represent a numerical difficulty. In the end, several crack opening path benchmark examples are solved in order to show the efficiency of the proposed numerical approach. © 2015 Elsevier Ltd.

Belinha J.,Institute of Mechanical Engineering and Industrial Management | Azevedo J.M.C.,University of Porto | Dinis L.M.J.S.,University of Porto | Jorge R.M.N.,University of Porto
International Journal of Applied Mechanics | Year: 2016

In the present work, the Natural Neighbor Radial Point Interpolation Method (NNRPIM) is used to simulate the crack growth phenomenon in brittle materials. In order to discretize the problem domain, the NNRPIM only requires an unstructured nodal distribution. With the spatial information of the computational nodes, the NNRPIM is capable to automatically establish the nodal connectivity and to construct the interpolation functions. Additionally, using the natural neighbor geometrical concept, the NNRPIM is able to obtain, from the unstructured nodal distribution, the integration background mesh required to numerically integrate the integro-differential equations ruling the studied physical phenomenon. In this work, a crack opening path algorithm is adapted and combined with the NNRPIM. The developed algorithm is able to predict the crack growth by relocating iteratively the crack tip. The stress field in the vicinity of the crack tip is determined in each iteration and then, using the maximum circumferential stress criterion, the direction of the crack propagation is calculated. Here, the repositioning of the crack tip requires a local re-meshing. However, due to the flexibility of the natural neighbor concept, the local re-meshing do not represent a numerical difficulty. Additionally, in order to show the efficiency of the proposed approach, several demanding crack growth benchmark examples are solved. © 2016 World Scientific Publishing Company

Abdiwi F.,University of Glasgow | Harrison P.,University of Glasgow | Koyama I.,University of Glasgow | Yu W.R.,Seoul National University | And 3 more authors.
Composites Science and Technology | Year: 2012

Variability of tow orientation is unavoidable for biaxial engineering fabrics and their composites. Since the mechanical behaviour of these materials is strongly dependent on the fibre direction, variability should be considered and modelled as exactly as possible for more realistic estimation of their forming and infusion behaviour and their final composite mechanical properties. In this study, a numerical code, 'VariFab', has been written to model realistic full-field variability of the tow directions across flat sheets of biaxial engineering fabrics and woven textile composites. The algorithm is based on pin-jointed net kinematics and can produce a mesh of arbitrary perimeter shape, suitable for subsequent computational analysis such as finite element forming simulations. While the shear angle in each element is varied, the side-length of all unit cells within the mesh is constant. This simplification ensures that spurious tensile stresses are not generated during deformation of the mesh during forming simulations. Variability is controlled using six parameters that can take on arbitrary values within certain ranges, allowing flexibility in mesh generation. The distribution of tow angles within a pre-consolidated glass-polypropylene composite and self-reinforced polypropylene and glass fabrics has been characterised over various length scales. Reproduction of the same statistical variability of tow orientation as in these experiments is successfully achieved by combining the VariFab code with a simple genetic algorithm. © 2012.

Freitas D.R.S.,University of Porto | Tavares J.M.R.S.,University of Porto | Tavares J.M.R.S.,Institute of Mechanical Engineering and Industrial Management
Journal of Voice | Year: 2011

Objectives/Hypothesis: The most recent and significant magnetic resonance imaging (MRI) improvements allow for the visualization of the vocal tract during speech production, which has been revealed to be a powerful tool in dynamic speech research. However, a synchronization technique with enhanced temporal resolution is still required. Study Design and Methods: The study design was transversal in nature. Throughout this work, a technique for the dynamic study of the vocal tract with MRI by using the heart's signal to synchronize and trigger the imaging-acquisition process is presented and described. The technique in question is then used in the measurement of four speech articulatory parameters to assess three different syllables (articulatory gestures) of European Portuguese Language. Results: The acquired MR images are automatically reconstructed so as to result in a variable sequence of images (slices) of different vocal tract shapes in articulatory positions associated with Portuguese speech sounds. Conclusions: The knowledge obtained as a result of the proposed technique represents a direct contribution to the improvement of speech synthesis algorithms, thereby allowing for novel perceptions in coarticulation studies, in addition to providing further efficient clinical guidelines in the pursuit of more proficient speech rehabilitation processes. © 2011 The Voice Foundation.

Meira Castro A.C.,Polytechnic Institute of Porto | Ribeiro M.C.S.,University of Porto | Ribeiro M.C.S.,Institute of Mechanical Engineering and Industrial Management | Santos J.,Polytechnic Institute of Porto | And 5 more authors.
Construction and Building Materials | Year: 2013

In this paper the adequacy and the benefit of incorporating glass fibre reinforced polymer (GFRP) waste materials into polyester based mortars, as sand aggregates and filler replacements, are assessed. Different weight contents of mechanically recycled GFRP wastes with two particle size grades are included in the formulation of new materials. In all formulations, a polyester resin matrix was modified with a silane coupling agent in order to improve binder-aggregates interfaces. The added value of the recycling solution was assessed by means of both flexural and compressive strengths of GFRP admixed mortars with regard to those of the unmodified polymer mortars. Planning of experiments and data treatment were performed by means of full factorial design and through appropriate statistical tools based on analyses of variance (ANOVA). Results show that the partial replacement of sand aggregates by either type of GFRP recyclates improves the mechanical performance of resultant polymer mortars. In the case of trial formulations modified with the coarser waste mix, the best results are achieved with 8% waste weight content, while for fine waste based polymer mortars, 4% in weight of waste content leads to the higher increases on mechanical strengths. This study clearly identifies a promising waste management solution for GFRP waste materials by developing a cost-effective end-use application for the recyclates, thus contributing to a more sustainable fibre-reinforced polymer composites industry. © 2013 Elsevier Ltd. All rights reserved.

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