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• Effect of Relative Fiber Angles and Distances in Microscale Modelling of Crack Initiation and Propagation under Transverse and Shear Loading

  S. Horta Muñoz, M. Serna Moreno

  Materiales Compuestos (Online first).

  
  

  Abstract

  This work investigates the behavior of unidirectional composite materials through a microscale modeling approach, with a particular focus on crack initiation and propagation under transverse and shear loading. Representative Volume Elements (RVEs) are used to model unidirectional plies with varying geometrical configurations, altering both the relative angles between fibers and the distances between them. Simulations are carried out in ABAQUS/Standard, applying periodic boundary conditions (PBCs) to accurately represent the microstructure and integrating cohesive surfaces at the fiber–matrix interfaces to model interactions and failure at these junctions. Additionally, the Extended Finite Element Method (XFEM) is employed to analyze in detail the initiation and propagation of cracks associated with matrix fracture. This study advances the understanding of the relationship between microstructure and failure mechanisms, offering tools for the design and optimization of composite materials with improved fracture resistance under multiaxial loading conditions. The results show that the relative angle between fiber centers plays a critical role in determining failure mechanisms at the ply level.

  Abstract
  This work investigates the behavior of unidirectional composite materials through a microscale modeling approach, with a particular focus on crack initiation and propagation [...]

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• Buckling analysis of laminates subjected to biaxial loads using cruciform specimens

  M. Serna Moreno, S. Horta Muñoz

  Materiales Compuestos (Online first).

  
  

  Abstract

  This study presents the compression-compression test with cruciform specimens (test CC) as a viable methodology to assess the geometric instability of a ∓45° symmetric laminate. The central region of the specimen, subjected to biaxial loading, exhibits a geometry similar to that of a square plate fixed along its entire perimeter. The bifurcation of the strains recorded at the top and bottom surfaces of the laminate is considered to be the threshold between the in-plane biaxial response and the response dominated by bending and torsional moments. The nonlinearities observed in the evolution of the stress-strain relationship in the region subjected to biaxial loading are confirmed to be independent of the response of the specimen arms. The bending-torsion coupling effects at the beginning of the bifurcation are observed experimentally in the deflection surface recorded by Digital Image Correlation. The results obtained suggest that the test CC is potentially suitable for the observation and measurement of buckling modes under various boundary conditions. However, more work is needed to reduce the quantitative dispersion. Specifically, the research should focus on minimizing geometric imperfections and load misalignments.

  Abstract
  This study presents the compression-compression test with cruciform specimens (test CC) as a viable methodology to assess the geometric instability of a ∓45° symmetric [...]

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• Analysis of the pure shear stress-strain state obtained by biaxial tension-compression test

  S. Horta Muñoz, M. Serna Moreno

  Materiales Compuestos (2024). Vol. 08 - COMUNICACIONES MATCOMP21 (2022) Y MATCOMP23 (2023), (Núm. 3 - Caracterización - Daño, Fractura y Fatiga), 1

  
  

  Abstract

  Characterization of shear properties in unidirectional fibre composite materials can be a complex process due to the difficulty in obtaining uniform and pure shear stress-strain states at the moment of failure. This limits the range of application of the most commonly used standardized methods, as they focus on small deformations. Therefore, this work proposes an alternative solution: the tension-compression test applied to cruciform specimens with ±45° symmetric laminates for the characterization of lamina in-plane shear properties. By using a test method that provides uniform and pure shear stress-strain states, the accuracy of the results can be improved, and the range of application of the method can be expanded. The analysis is based on experimental tests, supported by simulations performed using the finite element method. Special attention is paid to verifying the achieved shear state, and the obtained response is compared with standardized tests that generate non-pure shear stress-strain states on the principal material directions. Additionally, Digital Image Correlation is used during the test to verify the appearance of nonlinear response in different regions of the cruciform specimen, which allows ensuring the validity of the test.

  Abstract
  Characterization of shear properties in unidirectional fibre composite materials can be a complex process due to the difficulty in obtaining uniform and pure shear stress-strain [...]

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• Metodología recomendada en la Especificación UNE 0074:2023 para determinar propiedades de cortadura mediante el ensayo biaxial tracción-compresión con probeta cruciforme

  M. Serna Moreno, S. Horta Muñoz, J. lopez cela

  Materiales Compuestos (1970). Vol. 08 - COMUNICACIONES MATCOMP21 (2022) Y MATCOMP23 (2023), (Núm. 7 - Caracterización - Sostenibilidad y Reciclaje), 3

  
  

  Abstract

  El ensayo biaxial tracción-compresión con probeta cruciforme sobre laminados angle-ply ±45º simétricos se propone como una alternativa que mejora los resultados de las metodologías existentes para determinar las propiedades de cortadura pura en direcciones principales del material. El método satisface los principales requisitos exigidos a los ensayos de cortadura: i) concentra tensiones y deformaciones uniformes en la zona cargada biaxialmente, de las que se puede extraer la respuesta a cortadura; ii) es posible observar la evolución tensión-deformación lineal y no lineal hasta niveles de fallo superiores a los de los ensayos tradicionales; iii) el fallo se desencadena en la región cargada biaxialmente, lo que permite calcular no solo la rigidez a cortadura durante la etapa lineal, sino también la resistencia a cortadura. Además, en laminados de matriz polimérica reforzados con fibra de carbono, se consigue alcanzar hasta el 40% el nivel de deformación de cortadura en el momento de fallo utilizando un accesorio antipandeo biaxial que evita la aparición de inestabilidades en los brazos de la probeta. En este trabajo se muestra la metodología de ensayo recomendada en la Especificación UNE 0074:2023, que ha sido elaborado por el Comité Técnico CTN 53/GT 8. La Especificación se basa en la investigación previa realizada en los proyectos COMMUL y BISHEAR desarrollados dentro del marco de los programas estatales de I+D+i Orientado a los Retos de la Sociedad de 2016 y los proyectos “Prueba de Concepto” de 2021.

  Abstract
  El ensayo biaxial tracción-compresión con probeta cruciforme sobre laminados angle-ply ±45º simétricos se propone como una alternativa que [...]

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• Pseudo-ductility under tensile and compressive loading in ±45º laminates

  M. Serna Moreno, S. Horta Muñoz

  Materiales Compuestos (2022). Vol. 07 - COMUNICACIONES MATCOMP21 (2022), (Núm. 2 - Aplicaciones Industriales - Caracterización), 176

  
  

  Abstract

  This work focuses on analyzing the uniaxial response of carbon fiber reinforced polymer matrix laminates with the configurations [±45]2S under tension and [±45]4S under compression. These present non-linear stress-strain evolutions that allow them to withstand large deformations before losing their load-carrying capacity. Both responses are characterized by a first linear stage, followed by a plateau in which the strain grows without increasing the stress level, and finally by a re-stiffening phase. But there are quantitative differences that lead to different failure patterns, which are explained with the help of the state of stress in the plane of maximum shear stress. For a better understanding of the process, tensile load-unload-reload tests are performed to verify if the energy recovered in each cycle could be related to the loss of the apparent stiffness. During the first two stages of the mechanical response, the laminate suffers a progressive damage with a reduction in stiffness related to the dissipated energy, but this pattern is not repeated in the last stage of strain hardening. Based on the experience of other authors, it is assumed that the re-stiffening stage follows a different pattern due to possible microstructural changes in the matrix during the plateau. These are promoted by a narrowing process under tensile loads and a local widening of the test zone under compression. The dimensional changes perpendicular to the load direction are observed thanks to the strain fields obtained by Digital Image Correlation.

  Abstract
  This work focuses on analyzing the uniaxial response of carbon fiber reinforced polymer matrix laminates with the configurations [±45]2S under tension and [±45]4S [...]

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• Micromechanical modeling of the non-linear behaviour of angle-ply laminates under different plane-stress states

  S. Horta Muñoz, M. Serna Moreno, D. Garoz, R. Sevenois, W. Paepegem

  Materiales Compuestos (2023). Vol. 07 - COMUNICACIONES MATCOMP21 (2022), (Núm. 3 - Materiales y Estructuras - Modelos Numéricos), 5

  
  

  Abstract

  The non-linear behaviour ocurring in symmetrical angle-ply laminates formed by unidirectional layers of carbon fiber reinforced polymeric matrix (CFRP), known as pseudo-ductility, has been previously studied numerically and experimentally under different uniaxial, biaxial and bending loads. This phenomenon is associated with different mechanisms which affect the mechanical behaviour of the material: large permanent strains, fiber reorientation and matrix cracking. The present study is based on a microscale approach through simulations based on the Finite Element Method (FEM), with the aim of predicting the homogenized response of these laminates subjected to multiaxial in-plane. The micromechanical model is based on a Representative Volume Element (RVE) where Periodic Boundary Conditions (PBC) are applied, together with a non-linear material model of the matrix and a cohesive interface between fibre and matrix. In addition, the implementation of the model is updated to be able to reproduce any plane stress state in a [±45]S laminate, without the need to add other meso- or macroscale models.

  Abstract
  The non-linear behaviour ocurring in symmetrical angle-ply laminates formed by unidirectional layers of carbon fiber reinforced polymeric matrix (CFRP), known as pseudo-ductility, [...]

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