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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]

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]