Improving the delamination bridging performance of Z-pins through the use of a ductile matrix

This paper presents a characterisation of the effect of varying the polymer matrix in Z-pin through-thickness reinforcement in pre-preg based laminates. Four matrix systems of increasing elongation at break are considered, namely: 1) a low glass-transition temperature (LTG) epoxy; 2) a high glass-transition temperature (HTG) epoxy; 3) a bismaleimide triazine (BT); 4) a bismaleimide (BMI). The last matrix is that used in commercially available Z-pins. The manufacturing of T300 carbon-fibre Z-pins employing the first three matrices via micro-pultrusion is discussed. The BT resin is considered as a benchmark for the manufacturing process. A preliminary screening of the mode II bridging performance of through-thickness reinforcement manufactured using the three matrix systems is carried out. A novel experimental set-up based on an acrylic glass carrier, which allows the failure mode of the through-thickness reinforcement to be visualised, is introduced. The preliminary tests reveal a 7-fold increase of work-to-failure for the candidates with the highest elongation at break, LTG Z-pins, compared to their baseline BMI-based counterparts. LTG Z-pins were then inserted in quasi-isotropic E-glass epoxy laminates and their bridging performance characterised across the full mode-mixity range. The experimental results indicate that LTG Z-pins provide a peak mode I interlaminar fracture toughness of the order of 40 kJ/m2, compared to the 28 kJ/m2 yielded by BMI Z-pins. Moreover, the transition from full pull-out to rupture for the LTG pins occurs at a mode-mixity of 0.55, whereas BMI Z-pins start failing at a mode-mixity of 0.2. The superior bridging performance of the LTG Z-pins is correlated with the enhanced ductility and toughness of the constituent matrix via detailed fractographic observations

Experimental characterisation of the dilation angle of polymers

Despite the wide use of Drucker-Prager plasticity-based models on polymers, the experimental measurement of the dilation angle, a critical parameter to fully describe the plastic potential, has been rarely reported in existing literature. This paper shows, for the first time, the experimental characterisation of the dilation angle of polymers over a wide range of plastic strain. These measurements were obtained from uniaxial compression experiments conducted on poly(methyl methacrylate) (PMMA) and an untoughened epoxy resin. The calculation of the dilation angle relied on the measurements of the compressive force and the strain components obtained via Digital Image Correlation (DIC). Lower values of dilation angle were obtained for the epoxy resin, suggesting that resistance to volumetric change during plastic deformation could be associated to molecular structure and internal forces. The methodology and results presented in this study can be applied to different types of materials and employed for developing and validating constitutive models that incorporate plastic dilation

Valorisation of Biowastes for the Production of Green Materials Using Chemical Methods

With crude oil reserves dwindling, the hunt for a sustainable alternative feedstock for fuels and materials for our society continues to expand. The biorefinery concept has enjoyed both a surge in popularity and also vocal opposition to the idea of diverting food-grade land and crops for this purpose. The idea of using the inevitable wastes arising from biomass processing, particularly farming and food production, is, therefore, gaining more attention as the feedstock for the biorefinery. For the three main components of biomass—carbohydrates, lipids, and proteins—there are long-established processes for using some of these by-products. However, the recent advances in chemical technologies are expanding both the feedstocks available for processing and the products that be obtained. Herein, this review presents some of the more recent developments in processing these molecules for green materials, as well as case studies that bring these technologies and materials together into final products for applied usage