Gaetano Salvatore Palazzo

Pultrusion manufacturing process development by computational modelling and methods

This paper deals with the modelling and development of computational schemes to simulate pultrusion processes. Two different computational methods, finite differences and elements, are properly developed and critically analyzed. The methods are applied to a model, implemented with suitable boundary conditions, proposed in this paper. Simulations, compared with experimental data available in the literature, show a good agreement between theory and experiments.

Influence of Process Parameters on Microstructure and Mechanical Properties in AA2024-T3 Friction Stir Welding

Material stirring and heat generation in friction stir welding processes induce significant microstructure and material properties alterations. Previous studies highlighted the relationship among microstructure, grain size, microhardness, and performance of the joint. In this context, an opportune definition of process parameters, in particular rotating and welding speed, is crucial to improve joint reliability. In this article, results provided by a numerical and experimental investigation on the influence of rotating and welding speed on microstructure, mechanical properties, and joint quality in AA2024-T3 friction stir welded butt joints are reported. Experimental data are presented and discussed considering numerically computed temperature and strain rate distributions, providing useful information for parameters setting. Processing window, i.e., parameters resulting in a successful material deposition, is also individuated.

Pultrusion manufacturing process development: Cure optimization by hybrid computational methods

This paper develops a hybrid approach, based on genetic algorithms and simplex method, to optimize the accuracy of a manufacturing process by material pultrusion. The numerical model, proposed in a recent paper of the same authors, is solved by a finite difference scheme. The analysis technically shows the efficiency of the optimization algorithm.

Finite element analysis of the steel quenching process: Temperature field and solid-solid phase change

This paper deals with a finite element analysis of the steel quenching process; regarding the transient temperature field and the thermally induced solid-solid phase transformations. All the process steps, i.e. heating, holding, and cooling, have been considered, modeling both the austenite formation and decomposition and taking into account nucleation and growth processes. The final hardness distribution into the quenched sample has been predicted according to the rule of mixtures, taking into account the chemical composition of the processing material, the final distribution of each phase and the local cooling rate.

Numerical-experimental crack growth analysis in AA2024-T3 FSWed butt joints

This paper deals with a numerical and experimental investigation on the influence of residual stresses on fatigue crack growth in AA2024-T3 friction stir welded butt joints. The computational approach is based on the sequential usage of the Finite Element Method (FEM) and the Dual Boundary Element Method (DBEM). Linear elastic FE simulations are performed to evaluate the process induced residual stresses, by means of the contour method. The computed stress field is transferred to a DBEM environment and superimposed to the stress field produced by a remote fatigue traction load applied on a friction stir welded cracked specimen; the crack propagation is then simulated according to a two-parameter growth model. Numerical results have been compared with experimental data showing good agreement and evidencing the predictive capability of the proposed method. The obtained results highlight the influence of the residual stress distribution on crack growth.

Longitudinal Residual Stress Analysis in AA2024-T3 Friction Stir Welding

Friction Stir Welding (FSW) is an innovative solid-state joining process, which is gaining a great deal of attention in several applicative sectors. The opportune definition of process parameters, i.e. minimizing residual stresses, is crucial to improve joint reliability in terms of static and dynamic performance. Longitudinal residual stresses, induced by FSW in AA2024-T3 butt joints, have been inferred by means of a recently developed technique, namely the contour method. Two approaches to stress measurement have been adopted; the former is based on the assumption of uniform material properties, the latter takes into account microstructural effects and material properties variations in the welding zones. The influence of process parameters, namely rotating and welding speeds, on stress distribution is also discussed.

Unsaturated and Saturated Flow Front Tracking in Liquid Composite Molding Processes using Dielectric Sensors

Liquid composite molding processes are manufacturing techniques involving the impregnation and saturation of dry fibrous preforms by means of injection or infusion of catalyzed resin systems. Complete wetting of the reinforcement and reduction of voids are key issues to enhance mechanical properties of the final product, as a consequence on line monitoring and control of resin flow is highly desirable to detect and avoid potentialbet macro- as well as micro-voids. In this paper, parallel-plate dielectric sensors were investigated to track the position of unsaturated as well as saturated flow fronts through dual scale porous media. Sensors configuration was analyzed and improved via electromagnetic (EM) finite element simulations. The effectiveness of the proposed system was assessed in one-dimensional impregnation tests. Good agreement was found between unsaturated front positions provided by the considered system and acquired through conventional visual techniques. An indirect verification strategy, based on CFD and EM simulations of the process, was applied to investigate the reliability of dielectric sensors with respect to saturation phenomena. Obtained outcomes highlighted the intriguing capabilities of the proposed method.

Computational Approaches for Modeling the Multiphysics in Pultrusion Process

Pultrusion is a continuous manufacturing process used to produce high strength composite profiles with constant cross section. The mutual interactions between heat transfer, resin flow and cure reaction, variation in the material properties, and stress/distortion evolutions strongly affect the process dynamics together with the mechanical properties and the geometrical precision of the final product. In the present work, pultrusion process simulations are performed for a unidirectional (UD) graphite/epoxy composite rod including several processing physics, such as fluid flow, heat transfer, chemical reaction, and solid mechanics. The pressure increase and the resin flow at the tapered inlet of the die are calculated by means of a computational fluid dynamics (CFD) finite volume model. Several models, based on different homogenization levels and solution schemes, are proposed and compared for the evaluation of the temperature and the degree of cure distributions inside the heating die and at the postdie region. The transient stresses, distortions, and pull force are predicted using a sequentially coupled three-dimensional (3D) thermochemical analysis together with a 2D plane strain mechanical analysis using the finite element method and compared with results obtained from a semianalytical approach.

Inverse analysis of the laser forming process by computational modelling and methods

This paper deals with the development of a computational procedure for the inverse analysis of the laser forming process of three-dimensional metal sheet, characterized by double curvature. The procedure is based on the minimization of a vectorial fitness function, obtained by the comparison of the considered target surface with reference deformed surfaces, represented as sixteen point bicubic patches. An FEM-based computational approach has been adopted to evaluate the reference deformed surfaces for the instruction of the processor.

Experimental Analysis of the Influence of Process Parameters on Residual Stress in AA2024-T3 Friction Stir Welds

Friction stir welding (FSW) is an innovative joining technique, in which a solid state weld is obtained by means of frictional heating and plastic deformation of the processing material. In recent years, an increasing application of the FSW process has been observed, however, for the effective implementation of the technique in safety-critical components and to predict the fatigue behavior of FSWed assemblies, an accurate knowledge of the process-induced residual stress is needed. In this paper results, provided by an experimental analysis on the influence of process parameters on the residual stress in 4mm AA2024-T3 butt joints are reported and discussed. The contour method has been applied to evaluate the residual stress. An asymmetric stress distribution has been found in all samples. A significant dependence of the tensile and compressive stress peaks on the feed rate has been found, while a non monotonic influence of the rotating speed has been evidenced.