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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]

Numerical modelling of scaled centre-notched [45/90/−45/0] 4s carbon/epoxy laminates was carried out. The in-plane dimensions of the models were scaled up by a factor of up to 16. A Finite Element (FE) method using the explicit code LS-Dyna was applied to study the progressive damage development at the notch tips. Cohesive interface elements were used to simulate splits within plies and delaminations between plies. A failure criterion based on Weibull statistics was used to account for fibre failure. There is a good correlation between the numerical and experimental results, and the scaling trend can be explained in terms of the growth of the notch tip damage zone. The modelling gives new insights into the damage development in the quasi-isotropic laminates with sharp cracks, specifically, the growth of splits, delaminations and local fibre breakage. [ABSTRACT FROM AUTHOR]

An experimental investigation into size effects in notched [45/90/−45/0]4s carbon/epoxy laminates is carried out. The in-plane dimensions of the quasi-isotropic laminates are scaled up by a factor of up to 8. Larger Scale 16 specimens with only their width and notch length being doubled were also tested as a further comparison. Interrupted tests and X-ray Computed Tomography (CT) scanning are carried out to study the damage at the crack tips. Sharp centre-notched tensile tests are compared to open-hole tests of the same notch length (hole diameter), material and stacking sequence. A similar strength reduction scaling trend is found for both configurations at the small sizes, except with higher tensile strength for the centre-notched specimens than the open-hole specimens. However, there is a cross-over point when the sizes increase, with the sharp notched results approaching an asymptote based on Linear Elastic Fracture Mechanics (LEFM), and the open hole results approaching an asymptote based on Weibull theory. [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]

Defects such as out-of-plane wrinkles are known to strongly affect in-plane strength but there has been very little research on their effect on out-of-plane properties. Experimental and numerical studies of multi-directional curved-beam laminates were thus carried out to understand the effects of out-of-plane wrinkles on through-thickness tensile strength. The initially selected layup saw free-edge delamination interacting with transverse cracking, which is undesirable. After suppressing the free-edge delamination by dispersing the plies near the specimen surfaces, through-thickness tensile failure was observed near the mid-plane. The effects of out-of-plane wrinkles could be studied with this appropriate layup, showing a 16% reduction in strength. A High-fidelity Finite Element Method (Hi-FEM) has been used to distinguish between the different failure modes and to understand the effects of wrinkles. Good agreement was achieved between the numerical and experimental results in terms of through-thickness tensile strengths and delamination locations. Image 1 [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]

In this work, electron irradiation as a novel and simple method was used to fabricate wearable strain sensors with high comprehensive performance. Hydroxylated multi-walled carbon nanotubes (hydroxylated MWCNTs) were uniformly adsorbed on ecoflex etched by hydrofluoric acid (HF). After electron irradiation, a large number of defects and functional groups were successfully introduced into the hydroxylated MWCNTs/ecoflex, leading to a flexible strain sensor with high comprehensive performance such as ultra-low detection limit, fast response, and wide sensing range. Compared with the unirradiated sensors, the irradiated sensors have an ultra-low detection limit of 0.01% and a wide strain range (the maximum strain of 800%), the maximum gauge factor is increased by 344%, and the response time and recovery time are reduced by 50% and 89.2% respectively. The sensors can be used for monitoring the weak physiological movements and large-scale human movements, which has great potential in health monitoring. The electron irradiation as an activate method can provide a way for mass fabrication of flexible sensors with high comprehensive performance such as ultra-low detection limit and wide sensing range. [Display omitted] [ABSTRACT FROM AUTHOR]