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• Application of agroforestry residues in polymeric composite materials

  X. Pedras, G. Piñeiro, . M.R.Castilla

  Materiales Compuestos (2022). Vol. 04 - Comunicaciones Matcomp19 (2020), (Núm. 3 - Materiales bioinsipirados), 119

  
  

  Abstract

  The lignocellulosic materials can be employed in the manufacturing of materials compound by a polymeric matrix due to its characteristics and peculiarities. Especially, to come from a natural sustainable resource, abundant and local character, with a low environmental impact and also low cost. In the present it is possible to find in the market industrial solutions, however, usually these materials come of byproducts generated in wood transformation industry and that enter in competence with other industry process like wood board manufacturing. Nevertheless, these materials can also be obtained from the valorisation of different residues generated in local agroforestry crops, which besides it have a low level of exploitation. They are evaluated to the Galicia Euroregion North Portugal, the different natural sources of these materials and its analysed the availability that exists and the technology available to its collection. They are analysed too, the different phases and processes required to do the preparation of these materials to its use in injection, extrusion and rotomolding composites and, especially, in relation to material moisture content and its morphological characteristics. In most of the cases, these residues present difficulties to be valorised so that, in many cases it is resorted to its direct burning, generating environmental problems. Even though, the most part of these materials are susceptibles too to be energy valorised, it is possible to combine in the same industrial process the combined production of natural fibres and material to energy production. 

  Abstract
  The lignocellulosic materials can be employed in the manufacturing of materials compound by a polymeric matrix due to its characteristics and peculiarities. Especially, to [...]

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• Study of the influence of surface treatments in kraft paper for the compatibilization with thermoplastic polymers

  F. Leite, . C.Mota, . L.Nobre, . J.Bessa, . F.Cunha, . C.Costa, . J.Teixeira, . R.Fangueiroc

  Materiales Compuestos (2022). Vol. 04 - Comunicaciones Matcomp19 (2020), (Núm. 3 - Materiales bioinsipirados), 126

  
  

  Abstract

  The transports industry has been presenting a set of solutions that integrates natural fibers and their compatibility with structural materials, like polymers. However, it is fundamental to ensure the fulfillment of mechanical requirements. One of the main reasons that is driving the use of this type of fibers, instead of synthetic fibers, is related with the some actual trends, such as weight reduction, which is linked with its lower density. Moreover, weight reduction also contributes, indirectly, to the sustainability and decrease of greenhouse gases emissions, since it makes possible to reduce the fuel consumption of transports.However, due to the different polarities verified between apolar thermoplastic polymers, such as polypropylene (PP), and natural fiber reinforcements, such as kraft paper, a study of the effect of physical and chemical surface treatments was carried out in order to verify their influence on the fiber-matrix interface properties. The physical process, corona treatment, was applied in the kraft paper with different discharge dosages, while the chemical treatment was performed through the use of several alkali solutions with different concentrations of NaOH. The obtained results from the performed tests shows that the alkali solution treatments improved, up to 57%, the mechanical properties of tensile strength and Young Modulus of the composite material, comparatively with the effect of corona treatment on its surface. These results induce an increase of interface compatibility between the matrix and kraft paper.

  Abstract
  The transports industry has been presenting a set of solutions that integrates natural fibers and their compatibility with structural materials, like polymers. However, it [...]

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• Viabilidad del uso de corcho aglomerado como núcleo de estructuras sandwich sometidas a impacto

  C. Sergi, S. Sánchez-Saez, E. Barbero, J. Sarasini, F. Sarasini

  Materiales Compuestos (2022). Vol. 04 - Comunicaciones Matcomp19 (2020), (Núm. 3 - Materiales bioinsipirados), 131

  
  

  Abstract

  En la fabricación de estructuras sándwich de material compuesto, unas de las opciones más utilizadas como núcleo es el uso de espumas poliméricas. Debido al cada vez mayor esfuerzo en reducir el impacto medioambiental de los procesos industriales, existe un gran interés en incorporar materiales de origen natural que permitan disponer de fuentes renovables y que faciliten los procesos de reutilización y de reciclado. Una de las posibilidades para sustituir a las espumas poliméricas es el corcho aglomerado que presenta unas buenas propiedades mecánicas. No obstante, para que sea posible su uso como núcleo en estructuras sandwich es necesario conocer su comportamiento frente a cargas de impacto, tanto de baja como de alta velocidad. En este trabajo se compara el comportamiento de una espuma de PVC comercial con corchos aglomerados de diferentes densidades. Se ha analizado la fuerza, desplazamiento, energía absorbida y velocidad de perforación. Se ha observado que el comportamiento del corcho aglomerado puede ser similar al de una espuma polimérica convencional, aunque con un incremento de peso. Adicionalmente se ha puesto de manifiesto que el corcho aglomerado puede ser una alternativa mejor a las espumas poliméricas en aquellas aplicaciones que puedan verse sometidas a varios impactos sucesivos.

  Abstract
  En la fabricación de estructuras sándwich de material compuesto, unas de las opciones más utilizadas como núcleo es el uso de espumas poliméricas. [...]

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• Manufacturing and testing of a new CFRP node bonded by adhesives for its use in bus structures

  P. Gálvez, A. Quesada, J. Abenojar, . M.A.Martínez

  Materiales Compuestos (2022). Vol. 04 - Comunicaciones Matcomp19 (2020), (Núm. 2 - Procesos de Fabricación y Técnicas de Unión), 111

  
  

  Abstract

  In recent years exponential increase in the use of adhesives in industrial processes is observed. Nowadays these materials are used in applications as diverse as aerospace industry, automotive industry, railway industry or even civil construction. In the same way, the use of composite materials has grown enormously, especially in the aerospace industry, thanks to the benefits that this type of materials are able to provide, even as reinforcement. Current bus structures present serious problems of fatigue due to their rigidity, resulting in unexpected failures in certain nodes where stresses are concentrated. This work is part of a project that it is trying to provide more elasticity to the structure through the use of a new CFRP node joined by adhesives to the bus structure using polyurethane. The complex design of the node has caused numerous manufacturing problems. PLA node was manufactured using 3D printing for being used as a core. PLA node was covered layer by layer with CFRP by hand lay-up. In order to know the behavior of the whole set (CFRP node, adhesive and steel beams), four prototypes were manufactured and tested. Four point flexural test was carried out on the prototypes to validate the assembly. Results show the suitability and capacity of this new node concept to be used in bus structures. In recent years exponential increase in the use of adhesives in industrial processes is observed. Nowadays these materials are used in applications as diverse as aerospace industry, automotive industry, railway industry or even civil construction. In the same way, the use of composite materials has grown enormously, especially in the aerospace industry, thanks to the benefits that this type of materials are able to provide, even as reinforcement. Current bus structures present serious problems of fatigue due to their rigidity, resulting in unexpected failures in certain nodes where stresses are concentrated. This work is part of a project that it is trying to provide more elasticity to the structure through the use of a new CFRP node joined by adhesives to the bus structure using polyurethane. The complex design of the node has caused numerous manufacturing problems. PLA node was manufactured using 3D printing for being used as a core. PLA node was covered layer by layer with CFRP by hand lay-up. In order to know the behavior of the whole set (CFRP node, adhesive and steel beams), four prototypes were manufactured and tested. Four point flexural test was carried out on the prototypes to validate the assembly. Results show the suitability and capacity of this new node concept to be used in bus structures.

  Abstract
  In recent years exponential increase in the use of adhesives in industrial processes is observed. Nowadays these materials are used in applications as diverse as aerospace [...]

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• Failure prediction in the neighbourhood of the hole in riveted joints with composite materials

  A. Barroso, I. Silva

  Materiales Compuestos (2022). Vol. 04 - Comunicaciones Matcomp19 (2020), (Núm. 2 - Procesos de Fabricación y Técnicas de Unión), 105

  
  

  Abstract

  In riveted joints, typically two groups of failure mechanisms must be verified, those that affect the joining elements and those that affect the parts that must be drilled to be joined. In this last group, at least, three failure mechanisms must be taken into account: tension, shear and bearing. In each of these failure mechanisms, it must be verified that the component of the stress state responsible for the failure does not exceed a certain critical value that causes the failure. In the case of riveted joints with composite materials, the task is doubly complex. On the one hand, the stress state in the neighbourhood of the hole is complex, not only because of the non-linearity of the problem (the contact of the rivet with the walls of the hole) but also because of the non-isotropic nature of the material. This makes the stresses to have a strong dependence on the type of fiber, stacking sequence, and in general, on the mechanical properties (non-isotropic) of the laminate. On the other hand, the determination of the critical values, associated with each component of the stress state, responsible for each failure mechanism, is difficult to obtain, due to the fact that these strength values also depend on the particular orientation along the hole contour, where they are evaluated. In the present work, the stress state in the neighbourhood of the hole is evaluated in riveted joints with composite materials, analyzing different types of laminates, to serve as a basis for the prediction of the different failure mechanisms potentially acting.

  Abstract
  In riveted joints, typically two groups of failure mechanisms must be verified, those that affect the joining elements and those that affect the parts that must be drilled [...]

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• Effects of dynamic fibre failure in unidirectional composites

  I. Tena, I. Saenz-Dominguez, . J.Torre, L. Aretxabaleta, M. Sarrionandia, J. Aurrekoetxea

  Materiales Compuestos (2022). Vol. 04 - Comunicaciones Matcomp19 (2020), (Núm. 1 - Avances en Materiales Compuestos. Nuevos Campos de Aplicación.), 37

  
  

  Abstract

  The stress redistribution around a broken fibre is a substantial issue in longitudinal strength analysis of unidirectional (UD) composites. Most investigated models are based on a regular fibre packings and classical shear lag theory (static failure) that considers pre-broken fibers, where the dynamic aspects of brittle fiber failure are not considered. In the present work, Representative Volume Elements with random fibre packings were modeled by means of 3D finite element analysis, and simulated considering the event of dynamic fibre failure. Significant effects were observed on the stress concentration factor (SCF) and ineffective load length which are related to the fibre debonding length and the volume of matrix damage-plasticity zones. Hence, it can be concluded that an accurate representation of the stress redistribution after a fibre breakage event requires consideration of dynamic effects.

  Abstract
  The stress redistribution around a broken fibre is a substantial issue in longitudinal strength analysis of unidirectional (UD) composites. Most investigated models are based [...]

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• Experimental evaluation of the coefficients of thermal expansion in a composite laminate using digital image correlation

  J. Justo, E. Graciani, P. Zumaquero

  Materiales Compuestos (2022). Vol. 04 - Comunicaciones Matcomp19 (2020), (Núm. 1 - Avances en Materiales Compuestos. Nuevos Campos de Aplicación.), 74

  
  

  Abstract

  A procedure for measuring simultaneously the coefficients of thermal expansion (CET) in the in-plane and the thickness directions in L-shaped composite laminated samples is presented. Measurements are carried out using digital image correlation, from which the displacements in one of the faces of the samples are measured when de sample undergoes a temperature increment inside an oven. From the in-plane displacement measurements, the in-plane strain tensor components and the corresponding CTE are determined. Results show that the presented technique is capable of determining these CTE with high accuracy. Displacement measurements in the direction normal to the face, enables determining the rotation of the face and consequently the difference between the CTE in the thickness direction and the CTE in the in-plane direction affected by the curvature. Results obtained for the CTE in the thickness direction show, first, values significantly higher than the CTE of the material in the in-plane direction normal to the fibres and, second, a high dispersion from one stacking sequence to another. These discrepancies were expected and are caused by the misalignment of the fibres in the corner zone of the samples.

  Abstract
  A procedure for measuring simultaneously the coefficients of thermal expansion (CET) in the in-plane and the thickness directions in L-shaped composite laminated samples is [...]

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• Polyethylene/boron composite materials in X-ray attenuation

  J. Abenojar, S. Armentia, P. Gálvez, M. Martínez

  Materiales Compuestos (2022). Vol. 04 - Comunicaciones Matcomp19 (2020), (Núm. 1 - Avances en Materiales Compuestos. Nuevos Campos de Aplicación.), 73

  
  

  Abstract

  Currently, lead is used as radiological protection due to its high density in both, personal protection and shielding of equipment.. Iron, concrete or water can also be used to stop X-rays and gamma radiation. Shielding thicknesses are different since these materials have different densities. The used measurement is expressed in values of HVL (hemirreductor thickness in cm). In the case of lead, calculations to stop a photon with an energy of 3000 keV, give a shield of 1.5 cm in thickness. Therefore, a plate of 30x40 cm2 will weigh 20 kg, taking into account its density. LDPE and B composite materials are used as neutron shields: polyethylene, because of its high hydrogen content and boron for its ability to absorb neutrons. For this reason, the objective is to replace lead or other heavy materials by boron PMCs with lower densities for the manufacture of radiological shields. For this purpose, low density polyethylene films and LDPE composite films with 15-30 and 60% wt. of boron were made. Films have been manufactured by hot extrusion and compression. The test that has been carried out is to calculate the shielding effect on the aluminum of these films using X-rays provided by a laboratory equipment used for the characterization of materials. The results have shown a greater shielding for a multilayer system, than a single one with the same thickness.

  Abstract
  Currently, lead is used as radiological protection due to its high density in both, personal protection and shielding of equipment.. Iron, concrete or water can also be used [...]

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• Homogenization procedures for the numerical analysis of eco-composites

  L. Barbu, X. Martínez, S. Oller

  Materiales Compuestos (2022). Vol. 04 - Comunicaciones Matcomp19 (2020), (Núm. 1 - Avances en Materiales Compuestos. Nuevos Campos de Aplicación.), 62

  
  

  Abstract

  Homogenization procedures have been gaining more and more emphasis in the field of numerical analysis of composite materials. A homogenization procedure is based on the assumption that a set of equations or a representative element that can provide a response equivalent to the one provided by the actual material exists. A numerical multiscale homogenization will be shown where the behavior of the whole composite is obtained by a micromechanical study of the material components and their interaction within of the composite microstructure through an RVE model. The proposed formulation uses a non-linear activation function in the structural scale and its task is to predict if a material point in the structure is in linear or non-linear range. Because of this, the developed strategy only solves the microscopic Boundary Value Problem using the RVE for the non-linear integration points found. The procedure will be used in the nonlinear numerical simulaction of an eco-composite sanwich panel subjected to a four point bending test.

  Abstract
  Homogenization procedures have been gaining more and more emphasis in the field of numerical analysis of composite materials. A homogenization procedure is based on the assumption [...]

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• Effect of hole interaction in the initiation of damage in laminates

  A. Solis, S. Sánchez-Saez, E. Barbero

  Materiales Compuestos (2022). Vol. 04 - Comunicaciones Matcomp19 (2020), (Núm. 1 - Avances en Materiales Compuestos. Nuevos Campos de Aplicación.), 38

  
  

  Abstract

  In open-hole laminates, when a second hole is made, the stresses and the damage evolution are modified. The main failure mechanisms in laminates subjected to compressive loads are fibre microbuckling and matrix breakage. In this work, the influence of the presence of a second hole in these mechanisms is analysed for two distances between holes. The Serial/Parallel Mixing Theory was used to model the elastic behaviour of the material and a Continuum Damage Model to represent the fibre microbuckling and matrix failure. The equations were implemented in a FEM code developed by the authors. The proposed model has been validated with results from the literature for a laminate with two holes positioned transversally to the applied load. In this problem, it was shown that the growth of the fibre damage is different from that of the matrix.  The laminate is damaged mainly in the zone between the holes. When the distance between holes is reduced, both types of damage around the holes increase.

  Abstract
  In open-hole laminates, when a second hole is made, the stresses and the damage evolution are modified. The main failure mechanisms in laminates subjected to compressive loads [...]

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