Curing Process Of Composites Research Articles

FEATURES FOR OPTIMISING THE PROPERTIES OF COMPOSITE MATERIALS BASED ON ACRYLIC MONOMERS

Further development of research in the field of acrylic composites is aimed at creating modifiers with specified properties that will improve the characteristics of composites in specific application conditions; developing optimal ratios of composite components to ensure the required properties; developing universal mathematical models that will predict the properties of composites depending on the composition and curing conditions; searching for new applications for acrylic composites, such as industrial and civil engineering. Among all organic compounds, acrylic compounds demonstrate the highest rate of strength gain over a wide temperature range. This is due to the low activation energy of the polymerisation process of acrylic monomers, which is triggered by special initiators. Due to this feature, acrylic composites can cure even at low temperatures and gain high strength in a short time. However, despite the obvious advantages, there are a number of questions that require further research: how does the rate of strength gain and other properties of acrylic composites change at different temperatures? How does changing the ratio of composite components (pliable, filler, initiator) affect its properties? How does the curing process of acrylic composites work at the molecular level? Determining the answers to these questions will make it possible to select the optimal ratio of components to obtain a material with the required properties, control the rate of strength gain of the composite by changing the temperature and composition, and use acrylic composites in a wider range of temperature conditions. Thus, a deep understanding of the processes that occur during the curing of acrylic composites is a prerequisite for their effective use in various industries and construction. The aim of the study is to comprehensively study the properties of composite materials based on methyl methacrylate (MMA) for the purpose of their effective use. Research objectives: determination of the optimal temperature regime to achieve maximum composite strength in the shortest possible time (1.5-2 hours). Study the effect of various fillers and other components on the strength, durability and other properties of the material. Identification of effective ways to modify MMA to increase the strength of the composite. Development of methods for controlling the rate of strength gain to ensure optimal operation. Assessment of the durability of the adhesive bond under various operating conditions. Comparison of the properties of the developed composites with existing materials. The results of the study will make it possible to develop new, more efficient composite materials for repair work that will be widely used in construction, industry and other sectors. Keywords: acrylic composites, modification, methyl methacrylate, strength, temperature, curing, repair.

The impact of various curing methods on the curing process of polymer-fiber composites analyzed using analytical approach

Ti/Gf/Cf represents a novel form of hybrid fiber metal laminates (HFMLs) that successfully blend the benefits of titanium alloy, glass fiber reinforced plastic (GFRP), and carbon fiber reinforced plastic (CFRP). These materials have garnered attention in the field of engineering due to their exceptional levels of stiffness, strength, and shear resistance. The quality of HFMLs during the curing process was significantly impacted by the chosen curing method. Moreover, the use of multiple types of fibers complicated the optimization of curing parameters in HFMLs. A comprehensive study was conducted using a multi-physics field coupling finite element method to investigate the impact of various curing methods on the development of temperature distribution, curing degree, and curing stress in HFMLs during the curing process. By integrating thermal transmission equations, curing kinetics, and viscoelastic mechanical models, a detailed curing simulation model was established. Increasing the cooling rate from 1 °C to 5 °C was shown to raise the maximum curing stress by 4.7 MPa. Additionally, higher curing temperatures were found to induce internal curing stress due to variations in thermal properties. Insufficient insulation times were observed to exacerbate non-uniform temperature distribution and curing degree fields in HFMLs, potentially leading to increased internal stress. To mitigate the generation of large residual stress, it is recommended to lower the heating and cooling rates, reduce curing temperatures, and extend the insulation time appropriately during the curing process of HFMLs. The primary goal of this research was to accurately predict the evolution of curing parameters in HFMLs under different curing regimes, which were impacted by the chosen curing method. The results of the study demonstrated that rapid changes in temperature during heating and cooling stages can lead to uneven curing, resulting in the accumulation of residual stress within the laminates.

Particle filter‐based prognostics for composite curing process

AbstractProcess‐induced deformation (PID) arises in thermoset parts due to internal residual stress developed from their anisotropic properties, resulting in distortions. While passive numerical manufacturing control exists, active manufacturing control is crucial for enhancing the manufacturing process. The work focuses on diagnosing the polymerization reaction, known as the curing process, to consider the influence of uncertainties in thermal loading conditions on the behavior of cure kinetics. This is achieved using a Particle Filter approach, wherein a posterior distribution of cure evolution is recursively approximated based on observed measurements from characterization tests. The algorithm is designed to simultaneously perform the diagnosis and prognosis of the Degree of Cure and PID. This approach adopts the augmented cure formulation to address various scenarios with uncertainties in thermal loading conditions. It offers the advantage of providing comparable PID predictions with minimal computational costs. C‐shaped thermoset parts made of epoxy/carbon fibers with varying thicknesses are cured using the Manufacturing Recommended Curing Cycle, and the predictions with the developed algorithm are validated against experimental measures. Upon validation, the converged prognosis capability of the Particle Filter model is employed to assess the impact of thermal loading uncertainty on cure profiles, which, in turn, affects the final PIDs outcome.Highlights A Bayesian sampling approach enables the estimation of cure kinetics parameters. The estimated stochastic parameters forecast the process‐induced deformations. The augmented Degree of Cure accounts for uncertainties linked to thermal loadings. Analysis on AS4/8552 C‐shaped parts shows the cure kinetics impact. The framework reduces the computational costs required for active control.

Effect of injection compound rolling process and curdlan gel on water retention of sauced beef

Research background and significance: Under the current development trend in the field of global food science and technology, consumers' requirements for food safety, nutritional value and sensory quality are increasing, prompting the innovation of food processing and preservation technology to become the core of the industry development. In the production of traditional food spiced beef, how to ensure the yield and quality of spiced beef is the focus of the spiced beef market. By adding edible glue can gain weight, thereby improving the yield, but previous studies have shown that carrageenan, seaweed extract and so on seriously affect the sensory quality of marinated beef, especially causing its juice oozing, colloidal attachments oozing and so on. Research content: Through the systematic study of the application of curdlan gel in the processing of brine injection spiced beef, the specific effects of curdlan gel on the water retention and sensory quality of spiced beef were discussed in this study. (1) Sensory optimization injection rolling composite curing process. The experiment was carried out with beef tendinous meat and a series of auxiliary materials, using fine processes and methods, including saline injection, rolling salting, cooking treatment, etc., and then conducting sensory evaluation. (2) Compare the quality difference of curdlan gel 1 and 2. Determination of gel strength and optimization of water retention of stewed beef were carried out. Single factor ANOVA test was used to determine the optimal dosage of curdlan gel. The results showed that the water retention of beef with brine injection could be enhanced significantly when the dosage was 2%, respectively. Under the optimal process conditions, the sensory score of brined beef was 85.4 points. Through this study, important scientific and technological findings were obtained, which did not mean that the higher the concentration of curdlan gel, the better the water retention, on the contrary, the higher the concentration of its water retention would be affected but would decrease. This research not only expands the application range of curdlan gel in the food industry, but also provides new technical solutions and theoretical support for the innovation and development of meat processing technology, and meets the needs of consumers for high-quality meat products.

Thermally controlled shape programming via image-based optimization towards distortion-reduced composite curing

The complex mechanisms involved in thermosetting composite curing process contribute to the cure-induced distortion (CID) that deteriorates load-bearing capacity as well as in-service life of the assembled component. The emergence of novel approaches for flexible thermal control, such as microwave or self-resistance heating devices, enables shape manipulation through customized temperature field programming, which opens up a new avenue for reducing CID. The determination of such temperature field is however a typical inverse problem that conventionally requires accurate modeling of the forward curing process together with an iterative solver, which becomes intractable due to the high-dimensional space required to identify a temperature field. This paper proposed an image-based optimization scheme to deliver a distortion-reduced temperature field. A simply yet effective thermomechanical relationship is primarily established to generate a grayscale image that encodes a nominal temperature field. The adaptive thresholding algorithm based on image processing is then developed to regularize the temperature field, maintaining global features while eliminating high-frequency outliers, in order to comply with applicable thermal control requirements. Experimental results demonstrate noticeable reduction of the CID distribution, where the mean CID could be reduced by 25–50%, as verified in three typical freeform parts using optimized temperature field.

Computational modeling of micro curing residual stress evolution and out-of-plane tensile damage behavior in fiber-reinforced composites

This paper focuses on revealing the evolution mechanism of micro curing residual stress and its impacts on the mechanical responses of medium-temperature cured composites (T700/7901) under out-of-plane tension. An integrated multi-scale framework is established, the macro-scale thermal-chemical and micro-scale stress–strain models are set up to predict the development of the micro residual stress during curing, and the obtained stress field is further employed as the initial boundary conditions in the micromechanical analysis to explore its effect qualitatively and quantitatively. Experimental and analytical methods are taken to verify and validate the current model. Besides, the impacts of different curing cycles on the micro residual stress and out-of-plane tensile strength are also discussed. The evolution of the micro curing residual stress in T700/7901 composites is intuitively revealed, and the results of the micromechanical model show that the out-of-plane tensile strength increases by nearly 14.4% due to the occurrence of the process-induced stress. Both the interfacial damage and matrix plastic deformation are delayed owing to the residual stress. The work builds the connection between the curing process and mechanical responses of unidirectional composites and demonstrates the necessity of considering curing residual stress in designing and evaluating composites.

Contact electrification of porous PDMS-nickel ferrite composites for effective energy harvesting

Energy harvesting technologies are becoming popular owing to their usage in the operation of low-power consumer electronics and as an alternative power source. Specifically, triboelectric nanogenerators (TENGs) have drawn much attention as they can efficiently scavenge waste mechanical energy into electrical output. Careful material selections can further improve the performance of TENGs. In this work, a spinel ferrite material with the chemical formula NiFe2O4 (NFO abbreviated further) is synthesized using a solid-state reaction route. The structural and magnetic property of the NFO has been studied, showing the cubic symmetry and ferromagnetic nature of the sample. The 3D tomography images of the PDMS-NFO composites were carried out using X-ray tomographic microscopy. To enhance the performance of the TENGs, we adopted a porous media by evaporation of water during the curing process of PDMS-NFO composites. A single-electrode operating mode was adopted for TENG fabrication. The electrical response of the device was carried out using different wt% and frequencies. The 12 wt% of NFO in PDMS (PN12 device) delivered a voltage, current, and charge of 60 V, 300 nA, and 34 nC, respectively. The charge density of the plain and porous composite-based TENG was compared to confirm the enhancement of the charge produced on the triboelectric layers. The commercial capacitors and energy harvesting based on a smart home were demonstrated using the TENG devices.

Simulation analysis of curing of filament wound carbon fiber composite shell

To represent the temperature and degree of cure (DOC) more intuitively during the curing process of fiber-wound composite shell, wrote SDVINI, DISP, FILM, and HETVAL subroutines to characterize the fiber-wound composite curing process in ABAQUS. Comparing the temperature and DOC. The results indicate that the heat released from the resin curing process affects the internal temperature of the material, but the effect is small and can be ignored. The DOC on the surface of the fiber-wound shell during the curing process is slightly larger than that inside, but the difference is small and can be approximated as equal. And when the curing time is the same, the faster the heating rate, the faster the curing rate.

Sensitivity Analysis and Multi-Objective Optimization Strategy of the Curing Profile for Autoclave Processed Thick Composite Laminates.

To mitigate the risk of manufacturing defects and improve the efficiency of the autoclave-processed thick composite component curing process, parameter sensitivity analysis and optimization of the curing profile were conducted using a finite element model, Sobol sensitivity analysis, and the multi-objective optimization method. The FE model based on the heat transfer and cure kinetics modules was developed by the user subroutine in ABAQUS and validated by experimental data. The effects of thickness, stacking sequence, and mold material on the maximum temperature (Tmax), temperature gradient (ΔT), and degree of curing (DoC) were discussed. Next, parameter sensitivity was tested to identify critical curing process parameters that have significant effects on Tmax, DoC, and curing time cycle (tcycle). A multi-objective optimization strategy was developed by combining the optimal Latin hypercube sampling, radial basis function (RBF), and non-dominated sorting genetic algorithm-II (NSGA-II) methods. The results showed that the established FE model could predict the temperature profile and DoC profile accurately. Tmax always occurred in the mid-point regardless of laminate thickness; the Tmax and ΔT increased non-linearly with the increasing laminate thickness; but the DoC was affected slightly by the laminate thickness. The stacking sequence has little influence on the Tmax, ΔT, and DoC of laminate. The mold material mainly affected the uniformity of the temperature field. The ΔT of aluminum mold was the highest, followed by copper mold and invar steel mold. Tmax and tcycle were mainly affected by the dwell temperature T2, and DoC was mainly affected by dwell time dt1 and dwell temperature T1. The multi-objective optimized curing profile could reduce the Tmax and tcycle by 2.2% and 16.1%, respectively, and maintain the maximum DoC at 0.91. This work provides guidance on the practical design of cure profiles for thick composite parts.

Quantitative relations between curing processes and local properties within thick composites based on simulation and machine learning

Overheating is almost inevitable during the curing of thick polymer matrix composite parts, which always induces degradation of the mechanical properties. To explore the relationship between the local process variables and the property distribution of interlaminar shear strengths and compression strengths inside thick composites, experiments and relative simulations were conducted herein. Based on machine learning techniques, a convolutional autoencoder (CAE) was used to evaluate the spatial distributions of temperature, cure degree, and stress during autoclave curing process of thick composites. The results demonstrate a strong linear relationship between the spatial distribution of stress with the property values of interlaminar shear strengths and compressive strengths. This indicates that the stress distribution history strongly impacts the mechanical properties of thick laminates, which is usually neglected in previous studies that only concerns the stress magnitude.

Data-measuring device to determine the thermophysical properties of polymer composites: information support part

This paper deals with the problem of developing an information support subsystem of the data-measuring device for determining the thermophysical properties of polymer composites during cure, designed to identify the parameters of a mathematical model necessary to optimize the curing process of composites. Methods and algorithms for processing experimental data and calculating the thermophysical properties of polymer composites, based on an integral representation of the solution of the inverse heat conduction problem and a Kalman filter, has been developed. The structure of the construction, content, goals, parameters and functionality of the basic modules of the data-measuring device application software are presented. A subsystem of informational decision-making support has been developed for choosing the optimal method and algorithm for calculating the thermophysical properties of polymer composites, which allows minimization of the errors in determining properties under given experimental conditions. The subsystem is built on the alternative use of four algorithms for calculating thermophysical properties and is included as a module into the application software of an intelligent data-measuring device for studying the process of curing polymer composites.

A step-wise numerical thermal control method for advanced composite curing process using digital image based programming

Accurate temperature control is required in advanced heat treatment processes such as composite curing. The crux is how to determine the appropriate heat sources which would result in the required temperature distribution during part heating process. This paper presents a new thermal control method using digital image based programming, which efficiently and accurately estimates required heat sources and controls temperature distribution in a step-wise numerical manner. The method was validated in both simulation and real heating tests for microwave curing of composites, showing excellent temperature uniformity and consistency with given target temperature profiles, compared with existing technologies.

Graphene oxide/epoxy composites with enhanced fracture toughness for liquid hydrogen storage

AbstractGraphene oxide (GO)/epoxy composites cured by aliphatic dibasic acids have been prepared. The influences of structure of aliphatic dibasic acid and loading of GO on curing process and mechanical properties of epoxy composites were studied. The results show that the reaction activities, gel time of corresponding epoxy‐acid system and tensile strength of the formed epoxy resins decrease with the increase of the chain length of aliphatic dibasic acids. Both fracture toughness (>1.96 MPa⋅m1/2) and elongations at break (>6%) increase with the increase of the chain length of aliphatic dibasic acids. The introduction of GO is helpful to increase the mechanical properties and the gas transmission coefficient of GO/epoxy composites. A maximum of tensile strength and elongations at break were obtained when the loading of GO is 0.6 wt%. The gas transmission coefficient of GO/epoxy composite increases with the increase of GO loading. The excellent mechanical properties and gas leakage resistance coefficient of the formed epoxy composites provides potential application in many fields where conventional brittle epoxy resins are inapplicable.

Effects of recycled carbon black generated from waste rubber on the curing process and properties of new natural rubber composites

Effects of recycled carbon black generated from waste rubber on the curing process and properties of new natural rubber composites

A single three-parameter tilted fibre Bragg grating sensor to monitor the thermosetting composite curing process

The unique sensing features of the tilted Fibre Bragg Grating (TFBG) as a single three-parameter optical sensor are demonstrated in this work, to monitor the manufacturing process of composite materials produced using Vacuum Assisted Resin Transfer Moulding (VARTM) process. Each TFBG sensor can measure simultaneously and separately strain, temperature and refractive index (RI) of the material where the optical fibre is embedded. A TFBG embedded in a 2 mm glass-fibre/epoxy composite plate was used to measure the thermomechanical variations induced during the curing process. At the same time, the RI measurements, performed with the same TFBG sensor, can estimate the degree of cure of the resin. The TFBG sensor shows to be a valid and promising technology to improve the state of art of sensing and monitoring in composite material manufacturing.

Wide-Range Motion Recognition Through Insole Sensor Using Multi-Walled Carbon Nanotubes and Polydimethylsiloxane Composites.

High linearity/sensitivity and a wide dynamic sensing range are the most desirable features for pressure sensors to accurately detect and respond to external pressure stimuli. Even though a number of recent studies have demonstrated a low-cost pressure sensing device for a smart insole system by using scalable and deformable conductive materials, they still lack stretchability and desirable properties such as high sensitivity, hysteresis, linearity, and fast response time to obtain accurate and reliable data. To resolve this issue, a flexible and stretchable piezoresistive pressure sensor with high linear response over a wide pressure range is developed and integrated in a wearable insole system. The sensor uses multi-walled carbon nanotubes and polydimethylsiloxane (MWCNT/PDMS) composites with gradient density double-stacked configuration as well as randomly distributed surface microstructure (RDSM). The randomly distributed surface of the MWCNT/PDMS composite is easily and non-artificially generated by the evaporation of residual IPA solvent during a composite curing process. Due to two functional features consisting of the double-stacked composite configuration with different gradient MWCNT density and RDSM, the pressure sensor shows high linear sensitivity (∼82.5 kPa) and a pressure range of 0-1 MPa, providing extensive potential applications in monitoring human motions. Moreover, for a practical wearable application detecting the user's real-time motions, a custom-designed output signal acquisition system has been developed and integrated with the insole pressure sensor. As a result, the insole sensor can successfully detect walking, running, and jumping movements and can be used in daily life to monitor gait patterns by virtue of its long-term stability.

Curing mechanism of resole phenolic resin based on variable temperature FTIR spectra and thermogravimetry-mass spectrometry

To solve the problem that the curing mechanism evolution of phenolic resin catalyzed by Ba(OH)2 remained unclear, the p-p methylene index, o-p methylene index, o-o methylene index, hydroxymethyl index, and ether index were introduced to quantitatively investigate the chemical structure of resin in the curing temperature range of 90–230°C. The chemical structures were investigated by variable temperature FT-IR. The gas products released with the increase of curing temperature were characterized by Thermogravimetry-Mass Spectrometry. The curing mechanism from 90°C to 230°C was concluded finally. The results show that the main reaction is the formation of the p-p methylene group in the range of 90–120°C. It is difficult to form the o-p methylene bridge at this stage. In the range of 120–160°C, the main reaction is the formation of the p-p methylene group. From 160°C to 190°C, the main reactions are the breaking of the ether bond, the formation of the carbonyl group and the propyl bridge. Above 190°C, the main reactions are polycondensation reaction among phenolic hydroxyl groups, and the formation reaction of carbonyl groups. The ether bond breaks completely above 230°C. This work provides a new method to investigate the curing mechanism. It is a benefit for the rational design of the curing process of phenolic resin-based composites.

Space-Filling Curve Resistor on Ultra-Thin Polyetherimide Foil for Strain Impervious Temperature Sensing.

Monitoring process parameters in the manufacture of composite structures is key to ensuring product quality and safety. Ideally, this can be done by sensors that are embedded during production and can remain as devices to monitor structural health. Extremely thin foil-based sensors weaken the finished workpiece very little. Under ideal conditions, the foil substrate bonds with the resin in the autoclaving process, as is the case when polyetherimide is used. Here, we present a temperature sensor as part of an 8 µm thick multi-sensor node foil for monitoring processing conditions during the production and structural health during the lifetime of a construction. A metallic thin film conductor was shaped in the form of a space-filling curve to suppress the influences of resistance changes due to strain, which could otherwise interfere with the measurement of the temperature. FEM simulations as well as experiments confirm that this type of sensor is completely insensitive to the direction of strain and sufficiently insensitive to the amount of strain, so that mechanical strains that can occur in the composite curing process practically do not interfere with the temperature measurement. The temperature sensor is combined with a capacitive sensor for curing monitoring based on impedance measurement and a half-bridge strain gauge sensor element. All three types are made of the same materials and are manufactured together in one process flow. This is the key to cost-effective distributed sensor arrays that can be embedded during production and remain in the workpiece, thus ensuring not only the quality of the initial product but also the operational reliability during the service life of light-weight composite constructions.

Characterization of Joule heating and deconsolidation behavior of continuous carbon fiber reinforced polyamide 6 composites under self‐resistance electric heating

AbstractAs an effective heating method, self‐resistance electric (SRE) heating was applied for welding, hot stamping and curing process of composites. In this study, the characterization of Joule heating and deconsolidation behavior of continuous carbon fiber reinforced polyamide 6 (CFR‐PA6) laminate under SRE heating were investigated. A series of experiments were performed to build the relationship among geometry sizes, current density and temperature response. Then the relationship between the temperature rising rate and current density of CFR‐PA6 laminate with twill weave fabric was determined. The temperature evolution of specimen with a hole under SRE heating was also discussed. Furthermore, the deconsolidation behavior of CFR‐PA6 specimens under SRE heating as well as oven heating was characterized through macroscopic and mesoscopic properties. The interlaminar shear strength (ILSS) tests of specimens were also conducted. The results indicate that the temperature response of CFR‐PA6 laminate is mainly determined by the current density and their relationship can be described by a quadratic function. It is found that voids appear both inside the fiber bundles and resin‐rich areas owing to the thermal mismatch between the resin and carbon fibers after SRE heating, while no voids inside the fiber bundles were observed after oven heating. The deconsolidation behavior of laminate after SRE heating reduces the ILSS.

Spatial and temporal changes in physical properties of epoxy during curing and their effects on the residual stresses and properties of cured epoxy and composites

This study presents modeling and analyses of epoxy curing incorporating gradual changes in the thermal and mechanical properties of epoxy due to the cross-linking process. The model includes an exothermic process from the cross-linking, heat conduction across the specimen, and deformations of the specimen during curing. The study examines the influence of volumetric changes from the thermal expansion and shrinkage effects and gradual changes in the thermal and viscoelastic properties of epoxy on the deformation of the epoxy and the formation of stresses. The effects of curing temperatures and pressure on the formation of stress during curing and residual stress after complete curing are also investigated. The temporal and spatial changes in the physical properties of epoxy during curing affect the elastic modulus of the cured epoxy specimens. Furthermore, this study also investigates the existence of fiber reinforcements on the curing process of unidirectional fiber composites comprising carbon fibers in an epoxy matrix. A unit-cell model is generated and used to examine the formation of residual stresses in the composites and their influences on the mechanical properties of the composites.