Embedded Sensors to Monitor Production of Composites : From Infusion to Curing of Resin

The need for using light-weight and high-strength fibre reinforced polymer in different applications has increased in the past few decades. The ideal product offers excellent mechanical and chemical properties with much lower weight compared to traditionally used metals. Initially, the fibre-reinforced polymers are being produced by trial and error iterations. This causes a very expensive product, with random quality and lack of reproducibility. There is a need to replace trial and error experiments with knowledge-based approaches. Using sensors for in-situ production to monitor the results in a reliable and repeatable way gives a high-quality composite product and optimizes the time and cost of the process. One of the common manufacturing processes of fibre-reinforced polymer composite is resin infusion in dry fabrics. The resin impregnates the fibrous textile through the existence of a pressure gradient in the fibrous mat, which is generated by a vacuum pump or by a resin injection at high pressure. The impregnation of the dry textile is a result of the pressure gradient between resin inlet and venting point in the mold. Therefore, the most relevant measurement to detect the resin front and the changes of resin hydrostatic pressure is measuring the pressure directly inside the laminate. In this study, pressure sensors provide real-time information about the resin front in laminate and the changes of resin hydrostatic pressure during the infusion. Different pressure sensors and interconnection techniques were examined to minimize the size of the sensing element in the composite. After complete impregnation of the fibres, the curing degree of the resin has to be measured. Microscale interdigital capacitive sensors with a perforated substrate of polyimide are designed and fabricated. The sensors are fabricated on polyimide substrate with a thickness of about 5 micrometers. The polyimide is thermally stable up to 450 degree celsius. Therefore, the sensor can be used for a variety of processes even with high-temperature curing requirements. They have a volume of around 0.1 mm3. The miniaturized dimensions of the sensor enables it to remain in the composite product with the negligible diminishing of mechanical properties. The metallization of the sensor is insulated with metal oxide built up from the metallization itself. This insulation layer enables measurement in electrically conductive carbon fibres. The sensors will remain inside the composite material for structural health monitoring during the life-time of composite. Ideally, the sensors for online process monitoring of composites should be made of the identical fibres or resin in that composite. This will eliminate the wound effect in the host material. To obtain sensorial material, a high-performance resin for aerospace application, type RTM6, is mixed with different plasticizers. The cured mixture of the resin is thin and flexible. An interdigital comb structure is screen-printed on the newly developed substrate. The curing degree of the RTM6 resin in glass and carbon fibres is measured by screen-printed planar interdigital sensor on flexible RTM6. Having sensors for online process monitoring is important for industry 4.0 to autonomously produce fibre reinforced composites in a so-called smart factory . Both, pressure sensors and interdigital capacitive sensors in this thesis can be used for online process monitoring. They will provide a knowledge-based approach for high-quality and low-cost products

Strain state detection in composite structures: Review and new challenges

Developing an advanced monitoring system for strain measurements on structural components represents a significant task, both in relation to testing of in-service parameters and early identification of structural problems. This paper aims to provide a state-of-the-art review on strain detection techniques in composite structures. The review represented a good opportunity for direct comparison of different novel strain measurement techniques. Fibers Bragg grating (FBG) was discussed as well as non-contact techniques together with semiconductor strain gauges (SGs), specifically infrared (IR) thermography and the digital image correlation (DIC) applied in order to detect strain and failure growth during the tests. The challenges of the research community are finally discussed by opening the current scenario to new objectives and industrial applications

Methodologies and Applications Review

Funding Information: The Authors acknowledge Fundação para a Ciência e a Tecnologia (FCT-MCTES) for its financial support via the project UIDB/00667/2020 (UNIDEMI). Pedro M. Ferreira also acknowledges FCT-MCTES for funding the PhD grant UI/BD/151055/2021. Publisher Copyright: © 2022 by the authors.Sensing Technology (ST) plays a key role in Structural Health-Monitoring (SHM) systems. ST focuses on developing sensors, sensory systems, or smart materials that monitor a wide variety of materials’ properties aiming to create smart structures and smart materials, using Embedded Sensors (ESs), and enabling continuous and permanent measurements of their structural integrity. The integration of ESs is limited to the processing technology used to embed the sensor due to its high-temperature sensitivity and the possibility of damage during its insertion into the structure. In addition, the technological process selection is dependent on the base material’s composition, which comprises either metallic or composite parts. The selection of smart sensors or the technology underlying them is fundamental to the monitoring mode. This paper presents a critical review of the fundaments and applications of sensing technologies for SHM systems employing ESs, focusing on their actual developments and innovation, as well as analysing the challenges that these technologies present, in order to build a path that allows for a connected world through distributed measurement systems.publishersversionpublishe

Online flow monitoring system development for the resin transfer moulding process

This work is the initial stage of the development of an online flow monitoring system for the resin impregnation phase of the Resin Transfer Moulding process. Online monitoring of the process is proposed to provide an estimation of the component’s state and to predict the defects, such as voids and dry spots. This paper analyses a dielectric sensor, which integrates to the process and measures the change in the impedance. The main contribution to the changes in the sensor response comes from the resin arrival on to the sensor during the impregnation phase. The proposed sensor consists of two parallel line electrodes embedded in an insulator. The design optimization is performed by analysing and modelling the geometry and the materials of the sensor. In addition, the developed monitoring system involves pressure transducers which measure the composite material state during the infusion phase. The pressure sensors operate as indicators of resin’s state and they are used for the process monitoring. This information will be used for the development of an algorithm for the resin frontal flow and enhance the insight of the flow defects mechanism.EPSRC CDTEI grant EP/L014998/1; European Union’s Horizon 2020 research and innovation programme (Clean Sky 2 Joint Undertaking, grant 686493)

Characterization and Modelling of Composites

Composites have increasingly been used in various structural components in the aerospace, marine, automotive, and wind energy sectors. The material characterization of composites is a vital part of the product development and production process. Physical, mechanical, and chemical characterization helps developers to further their understanding of products and materials, thus ensuring quality control. Achieving an in-depth understanding and consequent improvement of the general performance of these materials, however, still requires complex material modeling and simulation tools, which are often multiscale and encompass multiphysics. This Special Issue aims to solicit papers concerning promising, recent developments in composite modeling, simulation, and characterization, in both design and manufacturing areas, including experimental as well as industrial-scale case studies. All submitted manuscripts will undergo a rigorous review process and will only be considered for publication if they meet journal standards. Selected top articles may have their processing charges waived at the recommendation of reviewers and the Guest Editor

Active thermography for the investigation of corrosion in steel surfaces

The present work aims at developing an experimental methodology for the analysis of corrosion phenomena of steel surfaces by means of Active Thermography (AT), in reflexion configuration (RC). The peculiarity of this AT approach consists in exciting by means of a laser source the sound surface of the specimens and acquiring the thermal signal on the same surface, instead of the corroded one: the thermal signal is then composed by the reflection of the thermal wave reflected by the corroded surface. This procedure aims at investigating internal corroded surfaces like in vessels, piping, carters etc. Thermal tests were performed in Step Heating and Lock-In conditions, by varying excitation parameters (power, time, number of pulse, ….) to improve the experimental set up. Surface thermal profiles were acquired by an IR thermocamera and means of salt spray testing; at set time intervals the specimens were investigated by means of AT. Each duration corresponded to a surface damage entity and to a variation in the thermal response. Thermal responses of corroded specimens were related to the corresponding corrosion level, referring to a reference specimen without corrosion. The entity of corrosion was also verified by a metallographic optical microscope to measure the thickness variation of the specimens

Textile materials

In this specialised publication, the reader will find research results and real engineering developments in the field of modern technical textiles. Modern technical textile materials, ranging from ordinary reinforcing fabrics in the construction and production of modern composite materials to specialised textile materials in the composition of electronics, sensors and other intelligent devices, play an important role in many areas of human technical activity. The use of specialized textiles, for example, in medicine makes it possible to achieve important results in diagnostics, prosthetics, surgical practice and the practice of using specialized fabrics at the health recovery stage. The use of reinforcing fabrics in construction can significantly improve the mechanical properties of concrete and various plaster mixtures, which increases the reliability and durability of various structures and buildings in general. In mechanical engineering, the use of composite materials reinforced with special textiles can simultaneously reduce weight and improve the mechanical properties of machine parts. Fabric- reinforced composites occupy a significant place in the automotive industry, aerospace engineering, and shipbuilding. Here, the mechanical reliability and thermal resistance of the body material of the product, along with its low weight, are very relevant. The presented edition will be useful and interesting for engineers and researchers whose activities are related to the design, production and application of various technical textile materials