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Abstract The thickness dependency of trans-laminar fracture toughness was studied in centre-notched quasi-isotropic IM7/8552 carbon/epoxy laminates with central double 0° plies with thicknesses between 1 and 8 mm. A reduction in trans-laminar fracture toughness with thickness was measured experimentally in the specimens with a 25.4 mm notch. For specimens with a shorter 12.7 mm notch, no significant dependency on specimen thickness was found. The thickness dependency was captured in detailed Finite Element (FE) models with cohesive interface elements for sub-critical damage and a Weibull criterion for fibre breakage. The reason for the thickness dependency is explained through the damage states of the individual plies which determine whether or not premature fracture occurs before the damage process zone is fully developed. [ABSTRACT FROM AUTHOR]

Mode II fracture energy, G IIC , is a critical parameter for determining the propagation of delamination in composite laminates. Its value can be affected by Through-Thickness Compression (TTC) stress acting on the crack tip and here this effect has been studied using IM7/8552 carbon/epoxy laminates with cut central plies. External TTC loads were applied through bi-axial testing. Unidirectional (UD) cut-ply specimens were used to determine the TTC enhancement factor, η G , for G IIC . A similar enhancement effect was also found in Quasi-isotropic (QI) specimens with 2 extra cut central 0° plies inserted into the layup. The TTC enhancement factor was implemented in a Finite Element Analysis (FEA) framework using cohesive interface elements, showing that the determined η G can be successfully used to model the effect of TTC on delamination. [ABSTRACT FROM AUTHOR]

This paper presents a novel X-ray Computed Tomography (CT) image analysis method to characterize the Fracture Process Zone (FPZ) in scaled centre-notched quasi-isotropic carbon/epoxy laminates. A total of 61 CT images of a small specimen were used to fine-tune a pre-trained Convolutional Neural Network (CNN) (i.e., VGG16) to classify fibre orientations. The proposed CNN model achieves a 100% accuracy when tested on the CT images of the same scale as the training set. However, the accuracy drops to a maximum of 84% when tested on unlabelled images of the specimens having larger scales potentially due to their lower resolutions. Another code was developed to automatically measure the size of the FPZ based on the CNN identified 0 °plies in the largest specimen which agrees well with the manual measurement (on average within 3.3%). The whole classification and measurement process can be automated without human intervention. [Display omitted] • A novel method was proposed to characterise Fracture Process Zone (FPZ). • A Convolutional Neural Network (CNN) was developed to identify fibre orientations. • The CNN model showed a test accuracy of 100% for classification. • The CNN was applied to unlabelled CT images achieving an accuracy of up to 84%. • The estimated FPZ size of the largest scale was within 3.3% from actual measurement. [ABSTRACT FROM AUTHOR]

In this paper, a set of initial R-curves were measured for three different in-plane sizes using scaled Over-height Compact Tension (OCT) specimens and two different stacking sequences. The data reduction scheme was based on a Virtual Crack Closure Technique which is informed by the measured failure load and effective crack length. The R-curve effects were studied by using X-ray Computed Tomography to measure the crack length throughout fracture propagation. It was found that the initial R-curves measured from all three specimen sizes follow the same linearly increasing trend, with similar results for both stacking sequences. However, no plateau was seen on any of the measured R-curves, implying that even the largest specimens are not large enough to generate a full R-curve. a) Scaled OCT tests with two quasi-isotropic stacking sequences b) Initial R-curves showing the same linearly increasing trend but no plateau yet. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper presents prediction of the high velocity, oblique impact response and quasi-static residual tensile strength of thin [45/90/−45/0] 2s carbon/epoxy laminates using finite element (FE) models. A High-Fidelity Finite Element Method (Hi-FEM) with an automated unit cell meshing technique was employed. The predicted impact damage, characterised by the extent of fibre failure and delamination area, was validated against results from gas-gun tests for a range of impact velocities. The numerical results captured the trend of increasing impact damage with impact energy as observed from the tests. Changes in projectile orientation before impact were shown to increase the extent of fibre failure at high impact energies, up by 38% in edge impact cases. The residual tensile strength of the impacted laminates was then investigated, where the numerical results for edge-impacted laminates agreed with the test data within 8%. On the other hand, the residual strength modelling results of centre-impacted laminates were found to be unconservative, mainly due to the extent of fibre failure predicted during impact. Machined notches were also studied for their residual tensile strength in comparison to impact induced damage. The predicted strength of edge-notched laminates was found to be in close agreement with the experimental results for edge-impacted laminates, differing by an average of 9%. [ABSTRACT FROM AUTHOR]

Composite components are required to be resilient against Foreign Object Damage (FOD) induced by localised high velocity impact events. Here an experimental investigation into high velocity oblique impacts and residual tensile strength of thin quasi-isotropic carbon/epoxy laminates is reported. Oblique (45°) impacts between 100 m/s and 350 m/s were carried out using 3 mm steel cubes on the edge and the centre of the laminates, mounted as a cantilever beam. Impact induced damage was characterised using X-ray Computed Tomography (CT) and the residual strength of impacted laminates was determined through quasi-static tensile tests. The residual strength shows a strong dependence on the impact damage size, characterised in terms of fibre fracture width and delamination area. Machined notches were then investigated and compared to impacted laminates in terms of residual strength. [ABSTRACT FROM AUTHOR]

[Display omitted] • A multifunctional heterostructure additive (CuP-MXene) has been prepared. • 5 wt% of CuP-MXene increases antibacterial efficiency of EP up to 99.99%. • 5 wt% of CuP-MXene endows EP with a self-extinguishing behavior. • The presence of CuP-MXene improves mechanical strength and impact toughness of EP. • The peak heat release rate and total smoke release are reduced by 64.4% and 40.5%. The ongoing Covid-19 pandemic has raised the need for urgent antibacterial requirements for many commercially important polymers, e.g., Epoxy resins (EPs). Meanwhile, intrinsic flammability and poor impact toughness are two big obstacles that greatly impede the practical applications of EPs. Hence, it has been imperative but highly challenging to create advanced EPs combining satisfactory antibacterial, fire-retardant and mechanically robust performances so far. Here, we report a reactive multifunctional heterostructure, copper-organophosphate-MXene (CuP-MXene) by rational design. Our results show that with 5.0 wt% of CuP-MXene, in addition to achieving a high antibacterial efficiency above 99.9%, the resultant EP nanocomposite exhibits satisfactory flame retardancy (UL-94 V-0 rating, peak heat release rate decreased by 64.4%) and improved mechanical properties (tensile strength, elastic modulus and impact strength increased by 31.7%, 38.9%, and 25.0%, respectively) relative to virgin EP, outperforming its previous counterparts. Such a desirable performance portfolio arises from multiple synergistic effects between CuP and MXene. This work provides a general strategy for the design of multifunctional nanoadditives and advanced functional polymers, and creates more opportunities for industrial applications of EP in the areas of coatings, medical devices and furniture. [ABSTRACT FROM AUTHOR]