A novel route for volume manufacturing of hollow braided composite beam structures

This work investigates the application of a rapid variothermal moulding process for direct processing of a braided thermoplastic commingled yarn. The process uses locally controllable, responsive tooling which provides opportunities for optimum part quality and significantly reduced cycle times compared with conventional processes. The proposed process was used to directly manufacture hollow beam structures from dry commingled braided preforms. It was demonstrated that the cycle time using the rapid process was reduced by more than 90% as compared to a conventional bladder moulding process, resulting in a total cycle time of 14 min. Additionally, initial three point flexure test results indicated an improvement in the mechanical performance of the resultant parts as compared to the benchmark

Three-point flexural performance of tailor-braided thermoplastic composite beam structures

This work investigates the potential of improving the mechanical performance of braided composite beams through the introduction of local braid angle variations. Tubular braided beams with a 45°/60°/45° length-wise (axial) braid angle variation were manufactured and tested in quasi-static three-point flexure and their performance was compared with beams having a layer-wise (radial) [±60°/±45°/±45°] variation. Compared to beams having uniform braid angles, axial braid angle tailoring resulted in equivalent flexural performance with a 24% reduction in part weight. In contrast, tailoring in the radial direction did not yield any improvement in mass-specific performance. Deformation analysis of the beams using an extensometer and digital image correlation showed that an axial braid angle variation in each layer resulted in a comprehensive shift in deformation characteristics. Changing the braid angle in the outer layer across the whole beam showed partial change in deformation mode, but did not match the modification observed through axial variation

The effect of braid angle on the flexural performance of structural braided thermoplastic composite beams

Thermoplastic braided composite tubular beams were manufactured using commingled hybrid yarn with braid angles 30°, 45° and 60° and tested in static three-point flexure. Two principal deformation modes were observed during the flexural loading: global flexure and localised crush. The extent of each mode occurring in the three braid angle variants was measured using a linear deflectometer as well as 3D digital image correlation. Localised crushing was found to decrease significantly with increasing braided angle, accounting for 63%, 45% and 19% of the total applied deflection for the 30°, 45° and 60° beams respectively. Further, surface strain measurements obtained from 3D DIC showed increasing the braid angle led to a global flexure-dominated deformation. In addition, the stiffness and peak load increased with increasing braid angle. The observed differences in deformation modes were due to a combination of multiple braid angle-dependent properties of braided composites such as modulus, thickness etc

A precautionary public health protection strategy for the possible risk of childhood leukaemia from exposure to power frequency magnetic fields

<p>Abstract</p> <p>Background</p> <p>Epidemiological evidence showing a consistent association between the risk of childhood leukaemia and exposure to power frequency magnetic fields has been accumulating. This debate considers the additional precautionary intervention needed to manage this risk, when it exceeds the protection afforded by the exposure guidelines as recommended by the International Commission on Non-Ionizing Radiation Protection.</p> <p>Methods</p> <p>The Bradford-Hill Criteria are guidelines for evaluating the scientific evidence that low frequency magnetic fields cause childhood leukaemia. The criteria are used for assessing the strength of scientific evidence and here have been applied to considering the strength of evidence that exposures to extremely low frequency magnetic fields may increase the risk of childhood leukaemia. The applicability of precaution is considered using the risk management framework outlined in a European Commission (EC) communication on the Precautionary Principle. That communication advises that measures should be proportionate, non-discriminatory, consistent with similar measures already taken, based on an examination of the benefits and costs of action and inaction, and subject to review in the light of new scientific findings.</p> <p>Results</p> <p>The main evidence for a risk is an epidemiological association observed in several studies and meta-analyses; however, the number of highly exposed children is small and the association could be due to a combination of selection bias, confounding and chance. Corroborating experimental evidence is limited insofar as there is no clear indication of harm at the field levels implicated; however, the aetiology of childhood leukaemia is poorly understood. Taking a precautionary approach suggests that low-cost intervention to reduce exposure is appropriate. This assumes that if the risk is real, its impact is likely to be small. It also recognises the consequential cost of any major intervention. The recommendation is controversial in that other interpretations of the data are possible, and low-cost intervention may not fully alleviate the risk.</p> <p>Conclusions</p> <p>The debate shows how the EC risk management framework can be used to apply the Precautionary Principle to small and uncertain public health risks. However, despite the need for evidence-based policy making, many of the decisions remain value driven and therefore subjective.</p