207 research outputs found
Multi-scale modeling and online monitoring of resin flow through dual-scale textiles in liquid composite molding processes
No full textThis paper discusses a multi-scale approach for the simulation of preform impregnation and a dielectric flow monitoring system in liquid composite molding processes. A mesoscale unit cell was built based on image analysis of the microstructure of manufactured composite laminates. Bulk permeability and saturation rate were computed at the mesoscale and then introduced in the macroscale model modifying the governing mass and momentum equations. The model was used to simulate a unidirectional infusion test, in order to compare numerical results with experimental data from pressure measurements. Moreover, a noninvasive dielectric monitoring system for unsaturated and saturated flow tracking was developed. The good agreement exhibited by the numerical and experimental results points out the capability of the multiscale model as well as of the dielectric monitoring system
Impregnation and saturation analysis of microwave‐preheated reactive resin in liquid composite molding
No full textIn liquid composite molding processes, resin preheating is a strategy to reduce the viscosity, which consequently improves resin flow and reduces impregnation time. However, the provision of heat to thermoset systems must be carefully calibrated since polymerization is activated by thermal energy, and premature resin curing would determine a sharp increase in viscosity and ineffective impregnation of the reinforcement. This work aims to study the resin flow in the realization of thermoset matrix composites through microwave-preheated liquid composite molding. Experimental and numerical analyses have been conducted to compare the microwave-preheated and the unheated resin infusion in closed molds. The impregnation and saturation were detected by dielectric sensing. The numerical simulation of the process evidences the effects related to the reactivity of the thermoset resin system. The experiments conducted highlight a reduction in filling time of 20% and in saturation time of 15% due to the beneficial effects of preheating in the analyzed cases. Highlights: Microwave preheating accelerates the unsaturated flow in resin infusion. A numerical model was implemented to replicate the reactive resin flow. Reinforcement permeability and resin reactivity have been characterized. The saturation rate of the reinforcement is not sensibly influenced by preheating. Preheating determines higher pressure gradients, improving the flow advancement
Thermoplastic Pultrusion Process of Polypropylene/Glass Tapes
No full text: The present work focuses on the pultrusion of pre-impregnated glass-reinforced polypropylene tapes. An appositely designed laboratory-scale pultrusion line, consisting of a heating/forming die and a cooling die, was used. The temperature of the advancing materials and the pulling force resistance were measured by using thermocouples embedded in the pre-preg tapes and a load cell. From the analysis of the experimental outcomes, we gained insight into the nature of the material-machinery interaction and the transitions of the polypropylene matrix. The cross-section of the pultruded part was analyzed by microscope observation to evaluate the distribution of the reinforcement inside the profile and the presence of internal defects. Three-point bending and tensile testing were conducted to assess the mechanical properties of the thermoplastic composite. The pultruded product showed good quality, with an average fiber volume fraction of 23% and a limited presence of internal defects. A non-homogenous distribution of fibers in the cross-section of the profile was observed, probably due to the low number of tapes used in the present experimentation and their limited compaction. A tensile modulus and a flexural modulus of 21.5 GPa and 15.0 GPa, respectively, were measured
Injection Pultrusion of Glass-Reinforced Epoxy: Cure Kinetics, Rheology, and Force Analysis
No full textPultrusion is a highly efficient continuous process to manufacture advanced fiber-reinforced composites. The injection pultrusion variant permits a higher control of the resin flow, enabling the manufacturing of a high reinforcement volume fraction. Moreover, it reduces the emission of volatile compounds that are dangerous for the operators and for the working environment. The present study proposes an experimental analysis of injection pultrusion in three different operative conditions. In particular, the activity focused on the effects of the temperature setup on the thermochemical and rheological behaviors of the resin system and on the interaction between the processed materials and the pultrusion die wall. The setup of the parameters was selected to evidence the behavior of the viscous interaction during the thermoset transition to the solid state, which is particularly challenging due to the localization of high adhesive forces related to the sharp increase in resin viscosity. Microscope observations of the cross-sections were performed to discuss the effects of the process parameters
Defects Reduction in the Robotic Layup Process
No full textRobotic layup is a novel process developed to face the increasing demand for automation, flexibility, repeatability, and achieving high-quality composite materials in relevant industry fields, such as aerospace and automotive. This process is based on laying prepreg tissues on a mold using the action of a robotic arm equipped with a specific end-effector, which is usually composed of rollers and punches. The main drawback of the robotic layup is the occurrence of wrinkles and defects while moving, placing, and processing the pre-impregnated tissues. This issue is particularly evident in the processing of complex-shaped surfaces. The robotic arm cannot replicate exactly the movement of a human operator, following the geometry of the surfaces with a proper angulation like a human wrist. Moreover, operator hands can be set in a different shape just changing the configuration of the fingers, adapting themself in different curvatures. The demand of the industry to improve automation requires that the robotic manufacturing systems replicate as much as possible the gesture of the operator. Following these requirements, this study has focused on the recognition and discretization of the surfaces to be processed, in order to allow a robotic arm to better reproduce the movements of the laminators thanks to a better management of the end-effector. Moreover, an end-effector capable of replicating one of the techniques most commonly used by professional laminators on molds with complex geometries has been designed
Analysis of spring-in deformation in L-shaped profiles pultruded at different pulling speeds: Mathematical simulation and experimental results
No full textPeculiarities of the pultrusionmanufacturing process lead to the occurrence of spring-in deformations, whereas their value depends on the pulling speed. In this article experimental and numerical analysis was carried out for glass fiber/vinyl ester resin 75 × 75 × 6mmL-shaped profiles pultruded at pulling speeds of 200 and 600 mm/min. Spring-in angles of produced profiles were determined on the same day of manufacturing when profiles cooled down to room temperature. Higher pulling speeds provoked increased values of spring-in. 2D numerical model accounting for thermo-chemical and mechanical composite’s behavior during pultrusion was implemented in ABAQUS software. Cure Hardening Instantaneous Linear Elastic (CHILE) constitutive law was used to describe matrix resin Young’s modulus evolution. Since both unidirectional (UD) rovings and fabric material were utilized, effective mechanical properties of UD and fabric layers were calculated in accordance with Self-Consistent Field Micromechanics (SCFM) approach. Spring-in angles determined within experimental and numerical studies were compared and a good correlation was found: the errors were 12.6% and 6% for the pulling speed of 200 and 600 mm/min, respectively
Filling Time Reduction in Liquid Composite Molding Processes
No full textThe quality of Liquid Composite Molding (LCM) manufactured components is strictly related to the fibrous preform impregnation. As Darcy’s law suggests, the resin flow is influenced by the pressure gradient, geometrical features of the reinforcement, and resin viscosity. The former two parameters are dictated by the requirements of the component and other constraints; therefore, they are hardly modifiable during the process. Resin preheating increases its fluency, thus enhancing the impregnation and saturation flow, and reducing the mold filling time. In the present work, a microwave heating system has been integrated within a vacuum bag resin infusion process, to analyze the effect of the online preheating on the fiber impregnation. To monitor the resin flow a dielectric sensors-based system is used. Results from resin infusion tests conducted with and without the resin pre-heating were compared: the outcomes indicated an advance of approximately 190 s of the flow front when microwave heating is applied with respect to the unheated tests
Erosion behaviour of low-pressure cold-sprayed Ni coatings for concentrating solar power receivers
No full textNickel-based coatings provide outstanding wear and erosion resistance making them particularly suitable for several applications, from aerospace and naval to automotive, energy, and electrical. Cold spray (CS) is encountering a growing interest as a promising technology to deposit thick and dense coatings for components used in energy power generation systems, such as the concentrating solar power (CSP) plants. In this article, nickel coating was deposited onto steel substrates by using a low-pressure CS. The erosion behaviour of the coating was evaluated by a solid particle impact test at two different impact angles. The coating erosion rate was 10 x 10-4 at a 60 degrees impact angle, showing a combination of ploughing and cutting mechanisms
Pulling force analysis in injection pultrusion of glass/epoxy composites
No full textThe present article studies the resistance opposed to the pulling force in injection pultrusion processes and its dependence on polymerization of the resin. A methodology to evaluate and analyze the local resistance to the advancement of the composite is proposed. Injection pultrusion processes were conducted adopting four different advancing speeds, equal to 100, 140, 180, and 220 mm/min. The interaction of the traveling material with the die has been analyzed and discussed referring to the temperature distribution and resin transitions evaluated by a finite element model. Numerical and experimental outcomes highlighted that the kinetic and rheological aspects in pultrusion are strictly dependent on the advancing velocity. Higher speeds determine an increase of the resistant force and reduction in the final degree of cure of the resin system. Detrimental effects on the quality of profiles pultruded at higher speed are demonstrated as well
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