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Thermoset polymer composites have increased in use across multiple industries, with recent applications consisting of high-complexity and large-scale parts. As applications expand, the emphasis on accurate process-monitoring techniques has increased, with a variety of in situ cure-monitoring sensors being investigated by various research teams. To date, a wide range of data analysis techniques have been used to correlate data collected from thermocouple, dielectric, ultrasonic, and fibre-optic sensors to information on the material cure state. The methods used in existing publications have not been explicitly differentiated between, nor have they been directly compared. This paper provides a critical review of the different data collection and cure state correlation methods for these sensor types. The review includes details of the relevant sensor configurations and governing equations, material combinations, data verification techniques, identified potential research gaps, and areas of improvement. A wide range of both qualitative and quantitative analysis methods are discussed for each sensing technology. Critical analysis is provided on the capability and limitations of these methods to directly identify cure state information for the materials under investigation. This paper aims to provide the reader with sufficient background on available analysis techniques to assist in selecting the most appropriate method for the application.

Real-time determination of the optimum curing time for molded rubber parts is a challenge in the rubber industry. This research focused on the development of an in-situ rubber cure monitoring system (RCMS) capable of real-time monitoring of the natural rubber vulcanization process in a compression molding machine. The influence of vulcanization temperature (150 °C, 160 °C and 170 °C) on the cure characteristic properties, degree of cure and cure rate of a natural rubber compound in a conventional vulcanization system were compared when monitored with both a moving die rheometer (MDR) and the RCMS testing system. The degree of correlation between the measurements of the cure characteristics at the various vulcanization temperatures obtained from MDR and RCMS was established. The study found that RCMS can be used to determine the scorch time and the optimum cure time in a compression mold in real time.

A cure kinetics investigation of a high temperature-resistant phenol novolac cyanate ester toughened with polyether sulfone (CE-PES blend) was undertaken using non-isothermal differential scanning calorimetry. Thin ply carbon fiber prepreg, based on the CE-PES formulation, was fabricated, and plates for further in-situ cure monitoring were manufactured using automated fiber placement. Online monitoring of the curing behavior utilizing Optimold sensors and Online Resin State software from Synthesites was carried out. The estimation of the glass transition temperature and degree of cure allowed us to compare real time data with the calculated parameters of the CE-PES formulation. Alongside a good agreement between the observed online data and predicted model, the excellent performance of the developed sensors at temperatures above 260 °C was also demonstrated.

A non-invasive ultrasonic transmission method was applied to on-line monitor the curing behavior of the nanocomposites based on epoxy matrix. Effects of dispersion and interfacial adhesion of the nanofiller on high frequency dynamic mechanical properties during curing process of the nanocomposites were discussed. The typical nanofillers, multi-wall carbon nanotubes (p-MWCNTs) were selected, which were doped with graphene oxides (GOs), and dispersed in epoxy resin. By measuring the velocity and attenuation coefficient of longitudinal ultrasonic waves throughout the entire curing cycle, the longitudinal storage modulus and loss tangent of the epoxy nanocomposites were obtained. And the curing kinetics of the epoxy matrix nanocomposites was analyzed based on the Hsich non-equilibrium fluctuation theory. The results proved that enhanced dispersion and interfacial bonding of the GO-MWCNTs with epoxy improved dynamic mechanical properties of the epoxy matrix nanocomposites, while made curing process accelerated. The proposed ultrasonic monitoring method could accurately evaluate the curing process of epoxy-matrix nanocomposites. In conclusion, this research offered a practical effective measurement method for monitoring of curing process of the thermosetting resin matrix nanocomposites.

This article reports the development of a novel embedded acoustic waveguide sensor concept for monitoring the curing process and online health of composite structures. A sleeved waveguide embedded in the composite is proposed to confine guided waves in one dimension, with leakage to the surrounding media only through specially created openings, thus enhancing the capability to inspect large structures. The method is first developed using a rectangular copper strip embedded in an epoxy plate structure having an artificial delamination-type defect. Finite element simulations are used to gain insights on parameters and limitations. The approach is also demonstrated on a more practical bi-layer composite plate with an artificial delamination and an embedded wire waveguide sensor.

The increasing demand for low cost consistent quality composite materials, especially of the automotive industry, creates the necessity for fast high quality processes. Pultrusion is one of the processes that can fulfill this demand. While the process is highly automated, manufacturing parameters still have to be chosen manually. The choice of line speed, mould temperature and injection pressure is based on best practice and therefore requires manual optimization that results in cost intensive manufacturing errors and suboptimal machine productivity. This paper presents a possible solution for this problem by providing an on-line cure monitoring approach that allows to overcome this challenge. Resonant Ultrasonic Spectroscopy (RUS) shows a high potential for in-line cure monitoring inside the pultrusion tool. RUS has been adapted for the first time in a pultrusion process. This paper focuses on the successful application of this technique to control the pultrusion process based on the state of cure of the material inside of the tool. As one of the only techniques for in-line cure monitoring which can be used continuously in closed tools despite high abrasion, it provides a new insight into the pultrusion process.

The production process of fiber-reinforced plastic parts must be controlled through sophisticated instruments to warrant high quality standards. The cure degree of matrix, which is representative of the product quality, is in general evaluated by an indirect method, measuring the temperature inside the laminate, or by a direct method, evaluating the dielectric behavior of matrix. The aim of this work was to value the possibility to measure the cure degree of laminates by dielectric coplanar plates substituting a traditional parallel plate sensor that are sensitive to laminate compaction during cure. FEM simulations were executed to develop the sensor, and then some experimental tests were carried out to verify the suitability of the designed sensor to measure the degree of cure in a laminate. The cure degree trend evaluated through the developed sensor was compared with that one noticed through a cure process simulation and with that one measured by a parallel plate sensor.

The optimization of the enzyme-like catalytic selectivity of nanozymes for specific reactive oxygen species (ROS)-related applications is significant, and meanwhile the real-time monitoring of ROS is really crucial for tracking the therapeutic process. Herein, we present a mild oxidation valence-engineering strategy to modulate the valence states of Mo in Pluronic F127-coated MoO 3-x nanozymes (denoted as MF-x, x: oxidation time) in a controlled manner aiming to improve their specificity of H 2 O 2 -associated catalytic reactions for specific therapy and monitoring of ROS-related diseases. Experimentally, MF-0 (Mo average valence 4.64) and MF-10 (Mo average valence 5.68) exhibit exclusively optimal catalase (CAT)- or peroxidase (POD)-like activity, respectively. Density functional theory (DFT) calculations verify the most favorable reaction path for both MF-0- and MF-10-catalyzed reaction processes based on free energy diagram and electronic structure analysis, disclosing the mechanism of the H 2 O 2 activation pathway on the Mo-based nanozymes. Furthermore, MF-0 poses a strong potential in acute kidney injury (AKI) treatment, achieving excellent therapeutic outcomes in vitro and in vivo. Notably, the ROS-responsive photoacoustic imaging (PAI) signal of MF-0 during treatment guarantees real-time monitoring of the therapeutic effect and post-cure assessment in vivo, providing a highly desirable non-invasive diagnostic approach for ROS-related diseases. Nanozymes can mimic the activity of natural enzymes but are limited by poor reaction selectivity due to the lack of enzyme-like molecular recognition units as in natural enzymes. Here, the authors present a mild oxidation valence-engineering strategy to modulate the valence states of Mo in Pluronic F127-coated MoO 3-x nanozymes and show they can exhibit exclusive catalase- or peroxidase-like activities.

Biosensors have potentially revolutionized the biomedical field. Their portability, cost-effectiveness, and ease of operation have made the market for these biosensors to grow rapidly. Diabetes mellitus is the condition of having high glucose content in the body, and it has become one of the very common conditions that is leading to deaths worldwide. Although it still has no cure or prevention, if monitored and treated with appropriate medication, the complications can be hindered and mitigated. Glucose content in the body can be detected using various biological fluids, namely blood, sweat, urine, interstitial fluids, tears, breath, and saliva. In the past decade, there has been an influx of potential biosensor technologies for continuous glucose level estimation. This literature review provides a comprehensive update on the recent advances in the field of biofluid-based sensors for glucose level detection in terms of methods, methodology and materials used.

The ability to measure the degree of cure of epoxy resins is an important prerequisite for making manufacturing processes for fibre-reinforced plastics controllable. Since a number of physical properties change during the curing reaction of epoxy resins, a wide variety of measurement methods exist. In this article, different methods for cure monitoring of epoxy resins are applied to a room-temperature curing epoxy resin and then directly compared. The methods investigated include a structure-borne sound acoustic, a dielectric, an optical and a strain-based observation method, which for the first time are measured simultaneously on one and the same resin sample. In addition, the degree of cure is determined using a kinetic resin model based on temperature measurement data. The comparison shows that the methods have considerable but well-explainable differences in their sensitivity, interference immunity and repeatability. Some measurement methods are only sensitive before and around the gel point, while the strain-based measurement method only reacts to the curing from the gel point onwards. These differences have to be taken into account when implementing a cure monitoring system. For this reason, a multi-sensor node is suitable for component-integrated curing monitoring, measuring several physical properties of the epoxy resin simultaneously.