Digital Theses Archive


Tesi etd-09102019-000526

Type of thesis
Reliability assessment and predictive diagnosis of Dielectric Elastomer Transducers - Stochastic models and experimental analysis
Scientific disciplinary sector
INGEGNERIA - Ph.D. Programme in Emerging Digital Technologies (EDT)
Presidente Prof. VERTECHY, ROCCO
  • damage modeling
  • dielectric elastomer transducer
  • dielectric losses
  • dielectric strength
  • electrical fatigue
  • lifetime
  • reliability
Exam session start date
Dielectric Elastomer Transducers (DETs) represent an emerging technology in the field of soft electroactive polymers capable of converting electrical energy into mechanical energy and vice – versa. Generally, in their most uncomplicated layout, these devices form an electrostatic system, composed by a Dielectric Elastomer (DE) membrane, embedded between two opposite compliant electrodes, constituting a highly deformable capacitor. Their principle of operation and the rapid and straightforward prototyping process allow us to design and fabricate DETs for many different applications, such as actuators, sensors, and generators for energy harvesting. Thanks to their electromechanical properties and their propensity to combine self-sensing features into the system, i.e., the identification of their constitutive state, DEs are usually referred to as smart materials.<br>Systematic research on DEs dates back to the 1990s and early 2000s, with the primary purpose of developing modeling approaches of their electromechanical behavior and exploiting control strategies of their operational features. At present, many different DETs design and prototypes have been explored and proposed, demonstrating the numerous advantages of this technology for industrial use, like high energy density, manufacturing flexibility, silent operation, and low cost. However, even though it is possible to find some innovative commercial solutions for DE-based devices, especially as actuators and sensors, widespread industrial application of this technology is still under evaluation. Indeed, despite the potential of these devices for several mechatronic systems, DETs practical applicability is strongly affected by their failure modes and lifetime, which depend on both environmental conditions and electro-mechanical loads. <br>To make a step forward, this thesis focuses on the reliability assessment of DETs based on theoretical and experimental observations of the DE materials. With this goal, a detailed research of the principal electromechanical failure modes, obtained through the analysis of their underlying physics, has been carried out. Furthermore, a novel modeling approach for damage evolution in DEs, caused by degradation phenomena as dielectric losses or electromechanical fatigue mechanisms, has been developed and discussed in this work. The reliability theory for physical systems is adapted to DETs, integrating their principal failure modes into a stochastic model and defining a standard procedure for their predictive reliability assessment. <br>The experimental activities focused on silicone membranes made of Wacker ELASTOSIL® 2030 material, which represents one of the principal commercially available solutions as a dielectric material for DETs. Several experimental tests have been executed on this silicone, in order to identify the needed electrical and mechanical material parameters for the reliability assessment procedure. These tests regarded the full identification of the silicone DE, in terms of hyperelastic electromechanical constitutive relations and for the intrinsic dielectric properties, such as the conductivity at different electric fields, the permittivity at different frequencies and the Pulse ElectroAcoustic (PEA) analysis of eventual free charges dispersed or injected in the dielectric matter. Moreover, dedicated test campaigns on the strength and lifetime of this silicone are reported and discussed, determining its dielectric strength and observing a lifetime in the order of million cycles under accelerated test conditions. <br>Finally, reliability evaluation examples of DETs made with Wacker ELASTOSIL® 2030 silicone are presented, defining a standard guide to assess the reliability and predictive diagnosis of this technology.