Lightweight mechanical metamaterials designed using hierarchical truss elements

Rotating unit systems constitute one of the main classes of auxetic metamaterials. In this work, a new design procedure for lightweight auxetic systems based on this deformation mechanism is proposed through the implementation of a hierarchical triangular truss network in place of a full block of material for the rotating component of the system. Using numerical simulations in conjunction with experimental tests on 3D printed prototypes, the mechanical properties of six types of auxetic structures, which include a range of rotating polygons and chiral honeycombs, were analysed under the application of small tensile loads. The results obtained show that there is almost no difference in the Poisson's ratios obtained from the regular, full structures and the ones made from triangular truss systems despite the latter, in some cases, being 80% lighter than the former. This indicates that these systems could be ideal candidates for implementation in applications requiring lightweight auxetic metamaterial systems such as in the aerospace industry

Stress concentrations in skew pressurized holes: A numerical analysis

This work provides a numerical analysis of the stress concentration factor in an elastic solid containing non-aligned and non-concurrent circular holes subjected to an internal pressure. Using Finite Element Analysis, a variety of systems with a range of geometric configurations and loading conditions were simulated and the trends observed were analysed using a qualitative and statistical analysis in order to determine the correlation between these factors and the maximum stress concentration in these systems. Furthermore, simple empirical models were calibrated on the simulation results and used to plot reference graphs which may be employed to predict the stress concentration factor of these systems according to several geometric parameters and loading conditions. The numerical results and the empirical models presented here also show good agreement with previously derived analytical results based on 2D models and are expected to provide a useful tool for the designer of such systems especially for fatigue problems in fluid-power systems, where a straightforward evaluation of the stress concentration factor in pressurized hole systems is needed

Experimental Investigations On Falling-Film Absorbers With Horizontal Tubes – A Review

It is necessary to improve the energy efficiency of all technical processes due to the uncertainties associated with climate change. One possibility to achieve higher energy efficiency is to utilize waste heat which occurs in many different applications. This heat may be used to replace compression chillers by heat driven absorption chillers which leads to a lower consumption of primary energy. Thus, research on heat driven absorption chillers is important to gain higher energy efficiency. In most cases the absorber is the limiting component of absorption chillers which is often designed as a falling-film absorber with horizontal tubes. This paper gives a brief overview on the latest experimental results of absorption on horizontal tubes published in the literature. All important design parameters and their influence on the efficiency of absorbers are considered. This includes the different working fluids and their additives as well as the various geometrical parameters. Thereby, a special focus is put on the different surface structures of the tubes that are used in absorbers. Also recent trends in research as ionic fluids and nanoparticles are examined. As an important result it can be concluded that some design parameters and their effects on the efficiency of absorbers are still not completely understood. Due to this, possibilities for further investigations are given

Design of shape memory alloy sandwich actuators: an analytical and numerical modelling approach

Shape memory alloy (SMA)-based actuator composites are characterised by a high force output which is activated by a temperature increase. In this work we exploit this property to design sandwich structures with SMA-matrix composite actuator skins capable of exhibiting a reversible, tailored flexural response. A theoretical model which predicts the resultant deflection and flexural moment produced as a result of selectively actuating one of the system skins was developed and confirmed using a multi-step Finite Element (FE) analysis which takes into account the fabrication pathway through which these systems may be manufactured. The model correlates the geometric parameters and material properties of the various components making up the system and provides a quantitative description of the role which each variable plays in determining the overall sandwich actuator performance. This is necessary for the future production and implementation of such systems in real-life applications

Mechanical properties and failure modes of additively-manufactured chiral metamaterials based on Euclidean tessellations: an experimental and finite element study

Purpose The “chiralisation” of Euclidean polygonal tessellations is a novel, recent method which has been used to design new auxetic metamaterials with complex topologies and improved geometric versatility over traditional chiral honeycombs. This paper aims to design and manufacture chiral honeycombs representative of four distinct classes of 2D Euclidean tessellations with hexagonal rotational symmetry using fused-deposition additive manufacturing and experimentally analysed the mechanical properties and failure modes of these metamaterials. Design/methodology/approach Finite Element simulations were also used to study the high-strain compressive performance of these systems under both periodic boundary conditions and realistic, finite conditions. Experimental uniaxial compressive loading tests were applied to additively manufactured prototypes and digital image correlation was used to measure the Poisson’s ratio and analyse the deformation behaviour of these systems. Findings The results obtained demonstrate that these systems have the ability to exhibit a wide range of Poisson’s ratios (positive, quasi-zero and negative values) and stiffnesses as well as unusual failure modes characterised by a sequential layer-by-layer collapse of specific, non-adjacent ligaments. These findings provide useful insights on the mechanical properties and deformation behaviours of this new class of metamaterials and indicate that these chiral honeycombs could potentially possess anomalous characteristics which are not commonly found in traditional chiral metamaterials based on regular monohedral tilings. Originality/value To the best of the authors’ knowledge, the authors have analysed for the first time the high strain behaviour and failure modes of chiral metamaterials based on Euclidean multi-polygonal tessellations

Near-to-planar three-jet events at NNLL accuracy

We extend the ARES method for next-to-next-to-leading-logarithmic (NNLL) QCD resummations to three-jet event shapes in e+e− collisions in the near-to-planar limit. In particular, we define a NNLL radiator for three hard emitters, and discuss new features of NNLL corrections arising specifically in this case. As an example, we present predictions for the D-parameter, matched to exact next-to-leading order (NLO). After inclusion of hadronisation corrections in the dispersive approach, we compare our predictions with LEP1 data

Personal development, resilience theory and transition to university for 1st year students

[EN] Aim The study aimed to determine whether an outdoor orientation programme (OOP) could increase personal development, develop resilience and aid transition and adaptation in 1st year university students. OOPs are thought to aid transition through adventure experience. Based on student development theory, outdoor orientation programmes accelerate psychological growth (Vlamis et al., 2011). Method Semi structured interviews were conducted with 14 students who attended an outdoor orientation programme to investigate the experience of attending an OOP and transition to university. The data was analysed following Braun and Clarke (2006) Six phase approach to thematic analysis. Results Thematic areas discovered included ‘Personal development – Building more than a raft’. This theme described the way in which students developed self-worth and self-efficacy through the OOP experience. ‘The fine line between challenge and fear’ describes how delivery of an intervention such as an OOP needs to be carefully delivered to enhance the benefits and limit any possible detrimental experiences. Discussion These first year students developed in terms of self-worth and self-efficacy through overcoming challenge. This development was also linked to the students surprising themselves about their capacities for handling adversity. Keywords: Adaptation; transition; 1st year students; outdoor orientation program; resilience; personal development.Pickard, L.; Mckenna, J.; Brunton, J.; Utley, A. (2017). Personal development, resilience theory and transition to university for 1st year students. En Proceedings of the 3rd International Conference on Higher Education Advances. Editorial Universitat Politècnica de València. 293-302. https://doi.org/10.4995/HEAD17.2017.5172OCS29330

Soil Sensor Network

Water management during crop irrigation is a problem for the agricultural industry. To help farmers better maintain water usage, a wireless soil sensor network comprised of a sensor pod and wireless communication has been designed and implemented. It was proven that the sensor pod can be installed 6-8 inches below the ground and communicate up to at least a 6km distance back to the gateway. The senor pod shells have a 2 mm thick shell to prevent the pod from shattering when coming into contact with the ground after being released from the planter, as calculated through the force of impact equations. The sensor pod contains a capacitive soil moisture sensor with an accuracy of 90% and a temperature sensor with an accuracy of ±0.2ºC. Lithium-ion batteries with a 2800 mA-H rating were chosen to ensure the sensor pods would be power-efficient in order to last an entire growing season. The sensor data is transmitted wirelessly through LoRaWAN communication using a RN2903 transceiver and a quarter wavelength, 3” monopole antenna. A Sentrius Laird gateway was used to collect and forward sensor pod data to the Senet dashboard. The Senet dashboard then forwarded the data to a web-based application that farmers can reference to check the status of their fields

Public interest litigation: making the case in Australia

Litigation is widely and appropriately recognised as an important component of the public interest advocacy \u27toolkit\u27. Yet, little attention has been paid in Australian research and scholarship to an important question: under what circumstances is public interest litigation (PIL) an effective way to bring about progressive social change? Informed by a review of the international literature on PIL, the authors of this article argue for the importance of drawing on Australia\u27s rich history with PIL to develop a solid empirical evidence base which can inform future decision about the strategic employment of PIL in campaigns to address the concerns and needs of disadvantaged and marginalised sections of Australian society