Studying the creep behaviour of strechable capacitive sensor with barium titanate silicone elastomer composite

In this paper, the creep behaviour of stretchable interdigital capacitive (IDC) large strain sensors is studied. A generalized Kelvin-Voigt (GKV) model is used to study the creep behaviour of the sensor's substrate material, manufactured from silicone elastomer (Ecoflex 00−30) with barium titanate (BTO) filler. Creep experiments are performed on sensors with 10, 20, 30 and 40 wt% BTO nanoparticles with dimensions of 100 nm and 200 nm dispersed in the elastomer. The BTO was used to increase the overall permittivity of the substrate, hence raising the capacitance of the IDC sensor. The effect of BTO on the GKV model parameters was studied in detail through analysis of the creep response. The pristine Ecoflex silicone elastomer is predominately a hyperelastic material, which shows negligible creep, while the addition of BTO particles led to the composite exhibiting creep such that the composite behaves like a visco-hyperelastic material. Hence, this behaviour results in the creep affecting the electrical sensing performance of the capacitive strain sensors during static loading conditions. This information provides insights on the impact of composite composition on creep-resistance and output signal of the sensor (capacitance).</p

Studying the creep behaviour of strechable capacitive sensor with barium titanate silicone elastomer composite

In this paper, the creep behaviour of stretchable interdigital capacitive (IDC) large strain sensors is studied. A generalized Kelvin-Voigt (GKV) model is used to study the creep behaviour of the sensor's substrate material, manufactured from silicone elastomer (Ecoflex 00−30) with barium titanate (BTO) filler. Creep experiments are performed on sensors with 10, 20, 30 and 40 wt% BTO nanoparticles with dimensions of 100 nm and 200 nm dispersed in the elastomer. The BTO was used to increase the overall permittivity of the substrate, hence raising the capacitance of the IDC sensor. The effect of BTO on the GKV model parameters was studied in detail through analysis of the creep response. The pristine Ecoflex silicone elastomer is predominately a hyperelastic material, which shows negligible creep, while the addition of BTO particles led to the composite exhibiting creep such that the composite behaves like a visco-hyperelastic material. Hence, this behaviour results in the creep affecting the electrical sensing performance of the capacitive strain sensors during static loading conditions. This information provides insights on the impact of composite composition on creep-resistance and output signal of the sensor (capacitance).</p

The effect of barium titanate ceramic loading on the stress relaxation behavior of barium titanate-silicone elastomer composites

The stress relaxation behavior of barium titanate (BTO)-elastomer (Ecoflex) composites, as used in large strain sensors, is studied using the generalized Maxwell-Wiechert model. In this article, we examine the stress relaxation behavior of ceramic polymer composites by conducting stress relaxation tests on samples prepared with varying the particle loading by 0, 10, 20, 30, and 40 wt% of 100 and 200 nm BTO ceramic particles embedded in a Ecoflex silicone-based hyperelastic elastomer. The influence of BTO on the Maxwell-Wiechert model parameters was studied through the stress relaxation results. While a pristine Ecoflex silicone elastomer is predominantly a hyperelastic material, the addition of BTO made the composite behave as a visco-hyperelastic material. However, this behavior was shown to have a negligible effect on the electrical sensing performance of the large strain sensor.</p

HOMOGENISATION OF COMPACTION BEHAVIOUR AND PERMEABILITY FOR MULTI-LAYERED COMPOSITE STRUCTURES MANUFACTURED VIA LCM PROCESSES

International audienceModern composite structures make use of the possibilities offered by composite materials to add stiffness and strength only where they are needed and in the direction required. This ability to tailor material properties to the needs of the structure have led to significant weight reductions; they have also allowed one to develop new architectures and design shapes, as composites materials are usually formed at the same time as the part they form. The Liquid Composite Moulding (LCM) family of processes, comprising RTM, CRTM, RTMLight and Resin Infusion VARTM, involves the placement of dry fibrous reinforcement into a mould and then, after closing the mould, injection of liquid resin to impregnate the reinforcement before resin-cure. LCM processes have a number of advantages over other processes; these include control over harmful volatiles, the ability to achieve high and consistent final fibre volume fraction (V f) and their potential for automation, greatly reducing labour costs [1, 2]. During manufacture with an LCM process, the operator typically has little control. Successful process development by trial and error, on the other hand, requires experience and can be time consuming and expensive. Reduction of development costs requires a good understanding of the process physics, and can benefit from development of an accurate simulation tool. Significant effort has been placed into establishment of RTM and CRTM simulations that accurately predict process outcomes, such as fill time, flow front advancement and dry spot formation [3, 4]. SimLCM is a simulation software developed at the University of Auckland to simulate LCM processes. Incorporation of the compaction behaviour of the fibrous reinforcement into the simulation allows for calculation of the tooling forces. Modelling of the reinforcement compaction also allows one to calculate the changes in permeability which occur during compaction, which is necessary for providing accurate simulation of the CRTM process. To determine the compaction and permeability behaviour, a set of experimental characterisation is required. Experimental procedures for reinforcement characterisation were devised and presented in [5-8] and [8, 9], respectively, for the compaction and permeability. Using thes

A 2.5D Model of the Resin Infusion Process, Experiments and Simulation

International audienceResin Infusion (RI) is one of the Liquid Composite Moulding processes, and is increasingly being used to manufacture high performance composite structures. Application of a flexible bag as one part of the mould results in laminate thicknesses varying significantly during filling, and in the period after filling, during which final laminate quality is reached. A 2.5D RI simulation has been developed, and is compared to detailed experiments for three moderately complex preform shapes. Evolution of resin pressure is predicted with good accuracy, and laminate thicknesses changes are moderately underestimated. SimLCM is demonstrated to be superior to a constant thickness Resin Transfer Moulding simulation, and is currently being extended to model the post-filling period

Resin infusion/liquid composite moulding (LCM) of advanced fibre-reinforced polymer (FRP)

International audienc

A 2.5D Model of the Resin Infusion Process, Experiments and Simulation

Resin Infusion (RI) is one of the Liquid Composite Moulding processes, and is increasingly being used to manufacture high performance composite structures. Application of a flexible bag as one part of the mould results in laminate thicknesses varying significantly during filling, and in the period after filling, during which final laminate quality is reached. A 2.5D RI simulation has been developed, and is compared to detailed experiments for three moderately complex preform shapes. Evolution of resin pressure is predicted with good accuracy, and laminate thicknesses changes are moderately underestimated. SimLCM is demonstrated to be superior to a constant thickness Resin Transfer Moulding simulation, and is currently being extended to model the post-filling period.status: publishe

A surrogate model based evolutionary game-theoretic approach for optimizing non-isothermal compression RTM processes

The Compression Resin Transfer Moulding (CRTM) process is a variant of the traditional RTM process and permits significantly faster fill times. However, the design parameters of CRTM processes must be carefully chosen in order to reduce cycle time, capital layout and running costs, while maximizing final part quality. These objectives are principally governed by the filling and curing phases which are strongly coupled in the case of non-isothermal processes. In this work the composites manufacturing cycle is modelled as a static Stackelberg game with two virtual decision makers (DMs) monitoring the filling and curing phases, respectively. The model is implemented through a Bilevel Multiobjective Genetic Algorithm (BMOGA), in conjunction with the Cascade-Correlation Learning Architecture Neural Network (CCA-NN) for function evaluations. The obtained results are efficient with respect to the objectives of both DMs and provide the manufacturer with a diverse set of solutions to choose from

Thermal-Mechanical Behaviour of Road-Embedded Wireless Charging Pads for EVs

Road-embedded inductive power transfer (IPT) systems have the potential to accelerate the electrification of the transportation sector. For these systems to be economically viable, however, they need to have a similar durability and lifespan to those of asphalt roads. One area that has lacked investigation is thermally induced stresses in a primary IPT pad, which are caused by the increase in the temperature of the pad when it is energized and the differing thermal expansion of the materials within. This paper presents an experimental and a finite element-based methodology for investigating the thermal–mechanical behaviour of a ¼-scale double-D pad, which was energized while suspended in air, as well as energized when embedded in pavement. A focus was placed on the measurement and prediction of strains in the magnetic ferrite cores because of their brittleness. Ferrite strains were measured using a combination of resistive strain gauges and non-metallic fibre Bragg grating (FBG) sensors. Coupled electromagnetic–thermal–structural simulations were conducted to predict temperature and strains in the system, with temperature-dependent properties obtained through physical testing. At an ambient temperature of 50 °C, the temperature in the middle of the copper litz wire coil was predicted to be 100 °C in both the suspended and embedded case. There was an excellent correlation with the experimental results, with a difference of less than 10% for most temperature measurements. When energized, the pad was predicted to experience an upward bow due to its temperature rise, resulting in bending strains in the ferrite cores. At an ambient temperature of 50 °C, the maximum tensile strain in the ferrites of the embedded pad was measured to be 62 microstrains (με), with a root-mean square error that was 18 με across three sensors. The experimental and validated numerical methodology can be applied to full-scale operational IPT pads to analyse and improve their thermal–mechanical performance

A 2.5D simulation of the filling and post-filling stages of the resin infusion process

The Resin Infusion process (RI, also known as VARTM) is a subclass of the Liquid Composite Moulding (LCM) collective, which is increasingly applied in industry. As opposed to the other LCM processes, RI utilises only one rigid mould half, the upper mould half of the mould being a flexible plastic bag. This greatly reduces tooling costs, and makes the process suitable for medium to very large sized parts. However, the interaction between a flexible bag and the infusion of the laminate within, presents a significant challenge to model and understand. The University of Auckland LCM research group is developing SimLCM as a generic LCM mould filling simulation. SimLCM has recently been extended to simulate RI, focusing on resin flow and laminate thickness predictions throughout the process. To accurately predict filling times, and the evolution of fluid pressure and laminate thickness during filling and post-filling phases, a detailed knowledge is required of the complex compaction response of the fibre reinforcement. While significant research has been published on modelling of the filling in RI, the post-filling period has received much less attention. This phase is, however, significant as spatial variations in laminate thickness are removed, preferably before the infused resin gels. Extending on previous work on rectilinear filling, this paper will present a program of RI experiments in a range of 2D flow geometries and the results will be compared to the predictions made using SimLCM. Special attention is given to the post-filling stage, and the validation of the new models developed for SimLCM. A selection of radial, peripheral and more complex filling situations have been addressed.status: publishe