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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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• Recommended methodology in Specification UNE 0074:2023 to determine shear properties by means of the biaxial tension-compression test with a cruciform specimen

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

  Materiales Compuestos (Online first).

  
  

  Abstract

  The biaxial tension-compression test with a cruciform specimen on symmetrical angle-ply ±45º laminates is proposed as an alternative that improves the results of existing methodologies to determine the pure shear properties in principal material directions. The method satisfies the main requirements for shear tests: i) it concentrates uniform stresses and strains in the biaxially loaded area, from which the shear response can be extracted; ii) it is possible to observe the linear and non-linear stress-strain evolution up to failure levels higher than those of traditional tests; iii) the failure is triggered in the biaxially loaded region, what allows calculating not only the shear stiffness during the linear stage, but also the shear strength. In addition, in carbon fibre reinforced polymeric matrix laminates, it is possible to increase up to 40% the level of shear strain at the moment of failure using a biaxial anti-buckling accessory that prevents the appearance of instabilities in the arms of the specimen. In this work, the test methodology recommended in Specification UNE 0074:2023, prepared by the Technical Committee CTN 53/GT 8, is shown. The specification is based on the previous research carried out in the COMMUL and BISHEAR projects developed within the framework of the national programs of R&D&I programme oriented towards the challenges facing society 2016 and the "Proof of Concept" projects 2021.

  Abstract
  The biaxial tension-compression test with a cruciform specimen on symmetrical angle-ply ±45º laminates is proposed as an alternative that improves the results [...]

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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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