Finite element modeling of dielectric elastomer actuators for space applications

A special actuator device with passive sensing capability based on dielectric elastomer was studied and specialized to be used in space applications. The work illustrates the research project modeling procedure adopted to simulate the mechanical behavior of this material based on a finite element theory approach. The Mooney-Rivlin’s hyperelastic and Maxwell’s electrostatic models provide the theoretical basis to describe its electro-mechanic behavior. The validation of the procedure is performed through a numerical-experimental correlation between the response of a prototype of actuator developed by the Risø Danish research center and the 3D finite element model simulations. An investigation concerning a possible application in the space environment of dielectric elastomer actuators (DEA) is also presented

Design optimisation of shape memory alloy linear actuator applications

Shape memory alloy (SMA) actuators have drawn much attention and interest in recent decades due to their unique properties; and, are expected to be increasingly integrated within commercial automotive applications. Key advantages of SMA actuators include: potentially simplified construction, whereby the SMA can act as both sensor and actuator simultaneously; compatibility with Joule heating and convective ambient cooling; and, potential mass advantages over competing actuation technologies. These attributes potentially allow for the development of simpler, more reliable and cost effective actuation systems with significant reduction in mechanical complexity and size. SMA is readily available in commercial quantities and exhibits high wear resistance and durability, which make it an ideal candidate for application in automotive grade applications. Despite these identified advantages, SMA actuators are subject to a series of technical challenges associated with:  - Relatively small strain (displacement or stroke)  - Achievable frequency (actuation speed)  - Controllability (and stability)  - Positional accuracy  - Energy efficiency These technical challenges contribute to a relatively low success rate of commercial SMA actuator applications; and, provide motivation for this program to generate relevant research outcomes that enhance the commercialisation of SMA actuators. An extensive literature review of over 500 journal and patent documents was conducted to provide a clear roadmap for the commercial imperatives for SMA design. The formulated research methodology identifies milestones required for achieving the research objectives, which were addressed as research themes. Based on this literature review, the following research themes were identified:  - Design methods to resolve SMA actuator limitations  - Development of simple and practical numerical models for SMA actuator response  - Data for SMA linear actuator design Specific research contributions within these themes are presented within the thesis, with the objective of enhancing the commercial application of shape memory alloy (SMA) linear actuators, and include:  - A comprehensive analysis of SMAs: history, commercial applications, strength and limitations, design challenges and         opportunities.  - A novel investigation of transient heat transfer scenarios for cylindrical systems associated with their crossover and critical radii.  - Development of novel latent heat models for analytical and numerical applications, and proposal of readily applied activation and deactivation charts compatible with the requirements of SMA actuator designers.  - A novel investigation of the morphological effects of SMA-pulley systems (i.e. pulley diameter, SMA and lagging diameter) on structural and functional fatigue

Factories of the Future

Engineering; Industrial engineering; Production engineerin

Factories of the Future

Engineering; Industrial engineering; Production engineerin

Chapter 34 - Biocompatibility of nanocellulose: Emerging biomedical applications

Nanocellulose already proved to be a highly relevant material for biomedical applications, ensued by its outstanding mechanical properties and, more importantly, its biocompatibility. Nevertheless, despite their previous intensive research, a notable number of emerging applications are still being developed. Interestingly, this drive is not solely based on the nanocellulose features, but also heavily dependent on sustainability. The three core nanocelluloses encompass cellulose nanocrystals (CNCs), cellulose nanofibrils (CNFs), and bacterial nanocellulose (BNC). All these different types of nanocellulose display highly interesting biomedical properties per se, after modification and when used in composite formulations. Novel applications that use nanocellulose includewell-known areas, namely, wound dressings, implants, indwelling medical devices, scaffolds, and novel printed scaffolds. Their cytotoxicity and biocompatibility using recent methodologies are thoroughly analyzed to reinforce their near future applicability. By analyzing the pristine core nanocellulose, none display cytotoxicity. However, CNF has the highest potential to fail long-term biocompatibility since it tends to trigger inflammation. On the other hand, neverdried BNC displays a remarkable biocompatibility. Despite this, all nanocelluloses clearly represent a flag bearer of future superior biomaterials, being elite materials in the urgent replacement of our petrochemical dependence