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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. [ABSTRACT FROM AUTHOR]

Drilling process of fiber metal laminates (FML) requires a proper design of the processing parameters to prevent the occurrence of several issues and minimize defects, which can be detrimental for the integrity of the parts. These aspects become more critical in dry machining used in aeronautic field. In this scenario, the monitoring of process temperature is crucial to obtain useful information for machining optimization since many critical factors, such as matrix burnout, fiber pull‐out and delamination, depend on the heat generated during the machining. The aim of this work is to monitor the temperature measured on the tool and workpiece during dry drilling of Al/GFRP (GLARE) and Al/CFRP (CARALL) hybrid laminates. The influence of the cutting speed on the temperature trends was analyzed. Two different set‐ups were designed to measure the temperature on the tool, near the cutting edge and on the flank, and inside the laminate, in both the metallic and the composite parts. In addition, a numerical model to analyze the process temperature trend during drilling has been developed. The increasing the spindle speed from 1500 to 8000 rpm resulted in a decreasing of maximum temperatures of approximately 10°C on the tool tip and on the flank for the GLARE, and of almost 20°C in the CARALL laminates. The numerical simulation also pointed that the temperature fields is dictated by the thermal properties of carbon and glass fibers: temperature profiles within the CARALL were found smoother than those observed in GLARE. [ABSTRACT FROM AUTHOR]

This 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. [Display omitted] • Cold spray metallization of thermoset composites is achieved by adding a thermoplastic layer. • Tomography evidenced the influence of the composite manufacturing route on coating quality. • Up to 1 mm thick coatings were produced in a single pass by tuning standoff distance and traverse speed. • Inverse dependence between equivalent electrical resistivity and adhesion strength was evidenced. [ABSTRACT FROM AUTHOR]

Purpose: Electron-beam welding has been widely used in industry to join different titanium alloys (Ti-6Al-4V) components. During welding production defects, such as porosity, lack of penetration or thinning are often observed. High-cycle fatigue (HCF) tests have been performed on welded specimens to understand the effect of weld defects on fatigue capabilities. The fatigue life of different types of "defective" welds has been compared against a non-welded reference specimen. Design/methodology/approach: The results of the experimental campaign have been correlated with finite elements models. Findings: It is concluded the geometry produced by the weld process, e.g. toe radius and under-bead shape, and the related stress raisers play a relevant role on fatigue capabilities of welds. This conclusion is valid only for a Ti-6Al-4V T-joint weld and only for flaw initiation. Knock down in materials properties has not been considered. Originality/value: There is a lack of HCF fatigue data for welds of this geometry and material in the open literature. The paper is of relevance for industrial application and practical interest, although a lot more validation tests are required to draw a final conclusion. [ABSTRACT FROM AUTHOR]

This 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 non-invasive 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. [ABSTRACT FROM AUTHOR]

Chromium carbides are widely used as functional coatings on steel structures in high-end applications, from energy to marine and aerospace sectors thanks to their corrosion and wear resistance at elevated temperatures. In the present work, a low-power compact plasma spray (CPS) equipment was used to deposit Cr 3 C 2 -based cermet coatings on carbon steel substrate. Design of experiment was applied to select and optimize the spraying parameters, namely current, stand-off distance, scanning speed, plasma gas rate and powder feeding rate. ANOVA analysis was conducted to estimate the effect of the spraying variables on morphology and mechanical properties of the coatings and evaluate the optimal spraying condition. Dense and compact coatings were fabricated by using the CPS. By optimizing the processing parameters, coating hardness equal to approximately 600 HV and average thickness ranging around 600 μm were obtained, while the adhesion strength was approximately equal to 14 MPa. Intermediate phases of Cr carbides were produced by the dissolution of the primary Cr 3 C 2 induced by melting and re-solidification of the particles. The presence of weaker carbide phase, inter-lamellae different features and porosity also caused the scattered hardness values observed in the coatings. • Low power compact plasma spray technique demonstrated to produce sound chromium carbide-based cermet coatings. • The properties of the Cr 3 C 2 -NiCr coating are mainly influenced by current, stand-off distance and plasma flow rate. • Coating adherence and hardness obtained under optimal configuration meet the requirements for applications in CSP plants. • The inflight dissolution of Cr 3 C 2 and the related porosity led to a decrease in the mechanical properties of the coatings. [ABSTRACT FROM AUTHOR]

A glass fiber/polypropylene semi-impregnated lamina was added to an epoxy laminate, prior to the resin infusion, to overcome its limited weldability. Ultrasonic welding of the hybrid composite was conducted by varying welding pressure, time, and vibration amplitude, and using the thermoplastic layer as adjoining surface. Welded joints were analyzed by visual inspection, X-ray tomography, and lap shear testing. Welding time significantly influenced the lap-shear strength, the weld interface quality, and the process stability, promoting the proper intermixing of the thermoplastic layer and the formation of a weld area with strong adhesion. Amplitude and pressure, on the other hand, mostly affected the power absorption. Lower pressure, intermediate amplitude, and longer duration led to an improvement in the lap-shear strength (approximately 5 MPa in the best case). High strength was linked to high exposed-fiber surface area in the fracture surface, while its reduction was attributed to the presence of unwelded areas within the polypropylene interface. X-ray tomography highlighted the correlation between the occurrence of defects in the weld interface and the power profiles, where multiple peaks indicated the material friction and a progressive intermixing of the polymeric interlayer, while flattened profiles and lower peaks are associated to discontinuous and poorly adherent interfaces. [ABSTRACT FROM AUTHOR]

Sandwich panels with composite laminate skins having [(±45C)2,(0C,0G)4,(±45C)2] stacking sequence (subscript C for carbon fibers, G for glass) and containing barely visible impact damage (BVID) induced on the whole sandwich structure impacted at low energy, were tested in edge after-impact-compression with load direction parallel and transversal to the fibers direction (0-dir.). The morphology of impact damage on the sandwich structure was determined by using ultrasonic C-Scan and visual observation of laminate cross section. A Digital Image Correlation (DIC) system was used to measure the delamination evolution during the test. Two different failure behaviors were observed in two different impacted panels. Panel with fibers oriented transversally to the compressive load showed an opening (Mode-I) propagation of a delamination, while the panel with fibers parallel to the load showed shear (Mode-II) propagation. The static load such to determine local buckling of the composite face and failure was experimentally measured. An analytical model was implemented to predict the static strength of laminate with Mode-I opening. An FE model was instead built to predict the local buckling failure mode of the laminate with BVID, which is the first phenomenon to appear. The results of the analytical model and the numerical simulation correlate well with the test. [ABSTRACT FROM AUTHOR]

In liquid composite molding processes, such as resin transfer molding (RTM) and vacuum assisted resin transfer molding (VARTM), the resin is drawn through fiber preforms in a closed mold by an induced pressure gradient. Unlike the RTM, where a rigid mold is employed, in VARTM, a flexible bag is commonly used as the upper-half mold. In this case, fabric deformation can take place during the impregnation process as the resin pressure inside the preform changes, resulting in continuous variations of reinforcement thickness, porosity, and permeability. The proper approach to simulate the resin flow, therefore, requires coupling deformation and pressure field making the process modeling more complex and computationally demanding. The present work proposes an efficient methodology to add the effects of the preform compaction on the resin flow when a deformable porous media is considered. The developed methodology was also applied in the case of Seeman's Composite Resin Infusion Molding Process (SCRIMP). Numerical outcomes highlighted that preform compaction significantly affects the resin flow and the filling time. In particular, the more compliant the preform, the more time is required to complete the impregnation. On the other hand, in the case of SCRIMP, the results pointed out that the resin flow is mainly ruled by the high permeability network. [ABSTRACT FROM AUTHOR]

Conventional and cooling assisted friction stir welded Al–Mg joints were investigated by visual inspection, optical macro plus microscopy, scanning electron micrographs, energy dispersive X-ray spectroscopy, X-ray diffractions, tensile testing and micro hardness indentation. The nugget zone is characterized by onion rings composed of different phases such as Mg in an Al matrix, Al in an Mg matrix as well as intermetallic compounds, Al 3 Mg 2 and Al 12 Mg 17. A diffusion layer was detected on the Al side of the joint between the nugget and thermo-mechanically affected zones identifying a solid solution of Mg in Al. No diffusion layer was observed on the Mg side. The tensile strength of the dissimilar joints is enhanced by cooling assisted welding process due to the reduction in the amount of intermetallic compounds inside the weld bead. Congruently, higher hardness peaks are reported in the nugget zone of conventional FSW joint with respect to the CFSW joint. [ABSTRACT FROM AUTHOR]