• A method was developed to introduce origami fold patterns into square hon-eycombs. • The origami honeycombs were realized via 3D printing in thermoplastic poly-urethane. • The crushing behavior of the origami honeycombs was studied via fi nite element analysis and experimental compression testing. • Varying the origami fold parameters allowssigni fi canttailoringofthehoney-comb stress-strain response. • Absorption ef fi ciencies as high as 0.49 were experimentally demonstrated, which rivals that of rigid polyurethane foams.

There is global desire to reduce virgin plastic use and enhance the collection and exploitation of plastics waste. Hence, governments are setting high targets for plastics recycling and using statutory instruments such as the plastic packaging tax as well as offering support to the manufacturing sector to trial increasing use of recycled plastic to stimulate end markets with the aim of reducing the amount of virgin production. The construction sector has much promise in terms of adopting circular economy principles and here we report on the results of a trial project to introduce a closed-loop supply chain model. More specifically, we seek to develop appropriate circular economy business models that manufacturers to the construction sector may adopt to enhance plastics recycling. We identify three potential circular economy models: (1) customers return direct to manufacturer, (2) customers return direct to 3rd party processor, (3) customers return to hubs, with the second chosen for trialling. Several barriers were identified, which have been categorised according to demand (perception of quality), supply (limited specialist suppliers, the provenance of the returned plastic, sourcing quality and consistent recycled material), organizational (internal policies and decision-making factors) and control (concrete contamination of end-of-life plastic products, and a lack of cost incentives). Provisional results from in-situ trials of the recycled content tubs suggest that a circular economy approach is feasible.

American football has a comparatively high rate of sports-related concussions, despite mitigating strategies including the use of protective helmets. The traditional energy absorbing component, elastomeric foam pads, have limited scope for leveraging any further protection. Alternative structures and materials that exhibit novel deformation mechanics have been proposed as a route to increased energy absorption capacity. This study investigated a metamaterial based on the Miura Ori folding pattern. Eighty-one potential structural variations were conceptualised and evaluated via the Taguchi method. Twenty-seven geometries were then additively manufactured using commercially available thermoplastic polyurethane, before being impacted at multiple velocities. Experimental data were then extrapolated to predict the impact behaviour across all 81 variants. An optimised geometry was then proposed, which reduced linear accelerations across the test conditions and performed favourably when compared to current, elastomeric foam solutions. This work provides a promising foundation for future investigation.

In the original version of the book, the author name has been updated from “Khaled Gaisin” to “Khaled Giasin” in the Chapter “Using FFF and topology optimisation to increase crushing strength in equestrian helmets”. The chapter and book have been updated with the changes.

Additive Manufacturing of cellular lattice structures offers opportunities to fine-tune the mechanical response by altering geometric variables. It is known that heat treatment cycles provide an effective way of altering mechanical properties while relieving residual stress. By exploiting the combined influence of these two variables, this study demonstrates the possibility of optimising energy absorption in AlSi10Mg honeycomb lattice structures, manufactured using selective laser melting. This finding indicates that heat treatment and powder quality have a significant influence on the mechanical response of the honeycomb. Additionally, this highlights the opportunity to establish an energy absorption diagram, via mapping the relative performance of variable lattice geometries and heat treatment cycles. At the same time, the consistency of powder quality can be tightly controlled.

International standards ensure that equestrian helmets achieve high performance. Recently, one such standard (PAS 015) was revised to include a lateral deformation requirement, ensuring helmets can withstand the potential crushing forces associated with equestrian. This increased performance needs to be achieved against a minimal mass penalty, which is an important consumer consideration. This paper explores how shell design optimisation can improve crush resistance, validated using additive manufacturing and mechanical testing. This approach achieved a 73% increase in crush force, for only an 11% mass increase.

Honeycomb structures display extraordinary stiffness-to-weight ratio when loaded in the out-of-plane direction. When realized using thermoplastic polyurethane (TPU), the structures offer the potential for repeatable and high specific energy absorption. Varying the cell size and wall thickness of TPU honeycombs facilitates changes in stiffness magnitude, though affords only modest capacity to alter the shape of the stress-strain curve. 3D printing facilitates advanced design exploration, beyond that of straight walls. Origami fold patterns have demonstrated the ability to influence the buckling behavior of tubular structures. Here we demonstrate the incorporation of origami folds into square honeycombs. The fold parameters facilitate significant tailoring of the stress-strain curve, allowing a range of profiles from quasi-rectangular to quasi-linear to be achieved; such structures can find applications in situation-specific energy absorption scenarios.

Additive manufacturing (AM) enables production of geometrically-complex elastomeric structures. The elastic recovery and strain-rate dependence of these materials means they are ideal for use in dynamic, repetitive mechanical loading. Their process-dependence, and the frequent emergence of new AM elastomers, commonly necessitates full material characterisation; however, accessing specialised equipment means this is often a time-consuming and expensive process. This work presents an innovative equi-biaxial rig that enables full characterisation via a conventional material testing machine (supplementing uni-axial tension and planar tension tests). Combined with stress relaxation data, this provides a novel route for hyperelastic material modelling with viscoelastic components. This approach was validated by recording the force-displacement and deformation histories from finite element modelling a honeycomb structure. These data compared favourably to experimental quasistatic and dynamic compression testing, validating this novel and convenient route for characterising complex elastomeric materials. Supported by data describing the potential for high build-quality production using an AM process with low barriers to entry, this study should serve to encourage greater exploitation of this emerging manufacturing process for fabricating elastomeric structures within industrial communities.

Thermoplastic elastomers (TPE) are commonly used to fabricate structures for application in repeatable, energy absorption environments. The emergence of additive manufacturing (AM) means scope now exists to design and build complex TPE components that can mechanically outperform traditionally manufactured equivalents. The ability to efficiently characterize these new TPE AM materials is, however, a barrier preventing wider industrial uptake. This study aims to establish a novel pathway for efficiently characterizing materials used in transient, dynamic applications, to ultimately enable accurate finite element (FE) simulation. A laser sintered TPE powder was characterised by performing low, intermediate and high rate uniaxial tension tests, plus planar and equibiaxial loading states. These data demonstrated significantly different behaviour across strain rates and deformation modes, necessitating fit of an augmented hyperelastic and linear viscoelastic model. FE software was then used to calibrate material model coefficients, with their validity evaluated by comparing the simulated and experimental behaviour of the material in isolated (uniaxial tensile) and mixed modal (lattice-based impact) deformation states. Close correlation demonstrated this novel approach efficiently generated valid material model coefficients, removing a barrier to industry adopting these materials. This creates opportunity to exploit these new technologies for the design optimization and fabrication of high-performance components.

Bicycle helmets are designed to attenuate forces and accelerations experienced by the head during cycling accidents. An essential element of bicycle helmet design is, therefore, the appropriate manufacturing of energy-dissipating components. The focus of this study was to evaluate the feasibility of using thermoplastic elastomer (TPE) cellular structures (Duraform® Flex), manufactured via a laser sintering (LS) process, as the energy-dissipating inner liner of the bicycle helmet. This study is presented in two sections; the optimisation of the LS process capabilities for the manufacture of cellular structures and an evaluation of the effects of cellular structure density on helmet impact kinematics. Through the fabrication and testing of tensile and compressive specimens, each process parameter (laser power, scanning exposure, build temperature and part orientation) was optimised to maximise compressive strength. The energy-dissipating characteristics of helmet cellular structures, made from this optimised material, were evaluated during simulated helmeted headform impact tests. Reduced accelerations and increased pulse durations were reported for decreased structural densities, demonstrating improved energy-dissipating characteristics for this novel technique. This study demonstrates that cellular structure-based inner liners, manufactured via additive manufacturing processes, have exciting potential towards improving bicycle helmet safety.

Laser Sintering (LS) is widely accepted as a leading additive manufacturing process with a proven capability for manufacturing complex lattice structures using a group of specially developed powder based materials. However, to date, very little research has been directed towards achieving greater knowledge of the properties of the elastomeric materials that can be used to produce energy absorbent items such as personalised sports helmets and running shoes via the LS technique. This paper will contribute to addressing this knowledge gap by examining the material properties and characteristics of Duraform (R) Flex, a commercially available elastomeric material used for such LS applications.A 3D Systems HiQ machine fitted with a closed loop thermal control system was employed, together with a number of the advanced processing options available in the operating software. In order to measure the mechanical properties of this material, sets of ISO standard tensile test specimens were fabricated, employing a range of different manufacturing processing parameters. The result shows that varying key LS processing parameters such as powder bed temperature, laser power and the number of scanning exposures has a significant impact on the mechanical properties of the resulting part, including its ultimate strength and elongation at break. As LS is a layer manufacturing process, part properties are found to vary considerably between the horizontal (X-Y) and vertical (Z) build orientations.The paper demonstrates how the measured tensile stress-strain curve can be transformed into appropriate hyperelastic material models employing the data curve fitting process in FTC Creo 2.0 Simulate software, and how these material models can be used practically to match user requirements for the laser sintered parts, leading to design optimisation for both bulky solid and lightweight lattice components. The paper concludes with a discussion examining the potential future direction of the research. (C) 2014 Elsevier Ltd. All rights reserved.

Bicycle helmets are designed to attenuate forces and accelerations experienced by the head during cycling accidents. An essential element of bicycle helmet design is, therefore, the appropriate manufacturing of energy dissipating components. The focus of this study was to evaluate the feasibility of using elastomeric lattice-based structures (Duraform® Flex), manufactured via a laser sintering (LS) process, as the energy dissipating inner liner of the bicycle helmet. This study is presented in two sections; the optimisation of the LS process capabilities for the manufacture of lattices based structures and an evaluation of the effects of lattice structure density on helmet impact kinematics. Through the fabrication and testing of tensile and compressive specimens, each process parameter (laser power, scanning exposure, build temperature and part orientation) was optimised to maximise compressive strength. The energy dissipating characteristics of helmet lattice structures, made from this optimised material, were evaluated during simulated helmeted headform impact tests. Reduced accelerations and increased pulse durations were reported for decreased lattice structure densities, demonstrating improved energy dissipating characteristics for this novel technique. This study demonstrates that lattice-based inner liners, manufactured via additive manufacturing processes, have exciting potential towards improving bicycle helmet safety.

PURPOSE:To report an unusual ocular presentation of Candida glabrata in a patient with chronic granulomatous disease.METHODS:Interventional case report. A 15-year-old boy with chronic granulomatous disease presented with bilateral limbal infiltrates. He had been receiving broad-spectrum systemic antibiotics for recurrent liver abscesses. The keratitis did not respond to antibiotics and did not resolve after a course of topical steroids.RESULTS:Corneal cultures revealed Candida glabrata. The same species was simultaneously isolated from the surgical drainage of the liver abscesses. The ocular and hepatic findings resolved on intravenous amphotericin B.CONCLUSION:Candida glabrata has recently emerged as an important nosocomial pathogen. It may present as a limbal keratitis in the setting of systemic infection.