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• Analysis of Delamination Behavior in Mode I under Thermal Environment Exposure in Adhesive Joints of Carbon-Epoxy Composite Materials

  P. Vigón, A. Argüelles, M. Lozano, J. Viña

  Materiales Compuestos (Online first).

  
  

  Abstract

  This study analyzes the delamination behavior in mode I, under static and fatigue loading, in adhesive joints on a composite material with an epoxy matrix and unidirectional carbon fiber reinforcement (CFRP). The samples were exposed in a climate chamber at 60°C and 70% relative humidity for different periods (no exposure, 1, 2, and 4 weeks). Subsequently, standardized DCB tests were performed to evaluate the effect of environmental aging on interlaminar fracture toughness and adhesive strength. After an initial static characterization, reference parameters for fatigue tests were defined, obtaining initiation (ΔG–N) and crack growth (G–da/dN) curves. The initiation data were analyzed using a Weibull probabilistic model. The results show a change in the epoxy adhesive behavior with exposure time, evidenced by a reduction in the fatigue limit and an increase in crack propagation rates.

  Abstract
  This study analyzes the delamination behavior in mode I, under static and fatigue loading, in adhesive joints on a composite material with an epoxy matrix and unidirectional [...]

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• Effect of Environmental Degradation on the Fatigue Resistance of Mode II Adhesive Joints in Carbon/Epoxy Composite Materials

  P. Vigón, A. Argüelles, M. Lozano, J. Viña

  Materiales Compuestos (Online first).

  
  

  Abstract

  This study analyzes delamination in CFRP adhesive joints under mode II loading in both static and dynamic regimes. The ENF test was used to evaluate the effect of exposure to salt spray and a climatic chamber over various periods—one, two, four, and twelve weeks—as well as for unaged specimens. Based on the experimental data, fatigue initiation curves (ΔG-N) and fatigue crack growth curves (G-da/dN) were constructed to analyze both degradation processes. In the fatigue initiation phase, the data were analyzed using a probabilistic model based on a Weibull distribution. The most relevant findings of this study are as follows: regarding the fatigue limits obtained for the adhesive joint under mode II fracture, a decrease in load-bearing capacity was observed due to degradation processes—around 20% under static loading conditions for salt spray exposure, and 25% for hygrothermal degradation. As for the fatigue crack growth phase, the crack propagation rates were found to depend on the specific environmental degradation process to which the tested specimens were subjected.

  Abstract
  This study analyzes delamination in CFRP adhesive joints under mode II loading in both static and dynamic regimes. The ENF test was used to evaluate the effect of exposure [...]

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• Influence of aging type on adhesive joints in carbon fiber-reinforced epoxy composites

  P. Vigón, A. Argüelles, V. Mollón, M. Lozano, J. Bonhomme, J. Viña

  Paula Vigón's personal collection (2023). 1

  
  

  Abstract

  This study analyses on comparing the static delamination behavior and mode I fracture toughness of two types of adhesives (one epoxy and one acrylic) used in a composite material with an epoxy matrix and unidirectional carbon fiber reinforcement. The material was subjected to two different degradation processes (hygrothermal and salt spray chamber), and then mode I fracture was evaluated for both materials. The results suggest that hygrothermal exposure may have a moderate impact on the delamination behavior of the epoxy adhesive, while exposure to the salt spray environment may result in a significant loss of its delamination resistance. For the acrylic adhesive, hygrothermal exposure improved its delamination behavior, while exposure to the salt spray environment had a minor impact on its behavior. Overall, it is concluded that the type of aging has influence on the fracture behavior of both adhesives.

  Abstract
  This study analyses on comparing the static delamination behavior and mode I fracture toughness of two types of adhesives (one epoxy and one acrylic) used in a composite material [...]

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• Study of delamination behavior in adhesive joints with epoxy-based adhesive under Mode II

  P. Vigón, A. Argüelles, I. Viña, M. Lozano, J. Viña

  Materiales Compuestos (2024). Vol. 08 - COMUNICACIONES MATCOMP21 (2022) Y MATCOMP23 (2023), (Núm. 3 - Caracterización - Daño, Fractura y Fatiga), 12

  
  

  Abstract

  This study experimentally analyses the phenomenon of delamination under static and fatigue loading in mode II using the standardized End-Notched Flexure (ENF) test. Adhesive joints made of two epoxy matrix laminates reinforced with unidirectional carbon fiber are studied, bonded with an epoxy adhesive, and subjected to environmental degradation in a saline environment for exposure periods of 1, 2, 4, and 12 weeks. By conducting initial static tests on the joints, we identified crucial values for the rate at which energy is released under mode II conditions. These values served as a benchmark to establish the approach for dynamic fatigue testing. Our objective was to generate characteristic curves that illustrate how these adhesive joints behave when fatigue delamination begins, while also assessing the impact of varying exposure periods on their performance. To enhance result interpretation, we employed a probabilistic model rooted in the Weibull distribution to analyse the experimental data. The results show that adhesive joints experience a decrease in their delamination resistance when exposed to a saline environment.

  Abstract
  This study experimentally analyses the phenomenon of delamination under static and fatigue loading in mode II using the standardized End-Notched Flexure (ENF) test. Adhesive [...]

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• Use of digital image correlation to quantify the different fracture modes in the Longitudinal Half Fixed Beam (LHFB) test

  M. Lozano, A. López, A. Argüelles, J. Viña, P. Vigón

  Materiales Compuestos (2024). Vol. 08 - COMUNICACIONES MATCOMP21 (2022) Y MATCOMP23 (2023), (Núm. 3 - Caracterización - Daño, Fractura y Fatiga), 6

  
  

  Abstract

  One of the failures with significant practical repercussions in structural elements made of laminated composite materials is the formation and growth of interlaminar cracks (delamination) under static and dynamic loading. Although the cracks can be subjected to three different modes of stress, the material toughness in mode III is higher than in the other two, so delamination mainly occurs in modes I or II. This is true when there is more than one fracture mode acting in the element. However, by using a testing methodology that allows testing in pure or nearly pure mode III, such as the Longitudinal Half Fixed Beam (LHFB) method, it is possible to characterize the material against this mode. Therefore, the degree of purity of mode III, compared to the residual modes I and II, will be an important indicator of the adequacy of the testing methodology. In this research work, the degree of purity of mode III in LHFB-type tests has been determined by using a digital image correlation (DIC) system. This technique allowed for the analysis of displacements in the X, Y, and Z directions in specimens with initial crack lengths of 1, 5, 10, 15, 20, 25, and 30 mm, using AS4/8552 and AS4/3501-6 materials. Considering the displacements measured with DIC during the different tests, it has been possible to determine the level of combination of modes I, II, and III achieved during the tests.

  Abstract
  One of the failures with significant practical repercussions in structural elements made of laminated composite materials is the formation and growth of interlaminar cracks [...]

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