1,721,004 research outputs found
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
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
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
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
Manufacturing and cold spraying of hybrid composites — A path for metallizing thermoset matrix composites
No full textThis study aims to realize and metallize the hybrid thermoset-thermoplastic fiber reinforced composites for aerospace applications. Two variations in the manufacturing route including cocuring and hybrid interlayer were adopted for realizing the RTM6-PEI-CF composite. Low pressure cold spray metallization technique is applied by varying the processing parameters stand-off distance and traverse speed. Microstructural analysis and mechanical tests (roughness check, nanoindentation tests) were performed on sprayed composites. Overall, manufacturing routes affected the inherent structure of the composite and subsequent coating quality. Mechanical interlocking induced close contact of PEI-aluminum (Al) particles characterized into uniform coating with surface morphology variation shown in cocured composites. Coating adhesion strength increment up to 18 MPa was noted by using the PEI-carbon fiber (CF) semi-preg in manufacturing. The tomography scan highlighted the structural integrity of the manufactured and coated composites, revealing coating-thermoplastic contact, interphase, and porosity in the inter-tow fiber region. An increase in the traverse speed to 2 mm/s reduced the electrical conductivity and adhesion strength of the coating with the hybrid composite. Within the limits of this investigation, opting for lower stand-off distance and traverse speed (here, 10 mm and 1 mm/s) reflected in improved adhesion and approximately 1.5 mm coating thickness
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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