1,721,013 research outputs found
Energy-assisted forming: theory and applications
No full textMany advanced high strength metals developed for automotive and aerospace applications exhibit poor formability at room temperature. This has led to the development of high temperature processes such as warm forming and hot forming that are expensive in terms of cost and time. It is possible to utilize the viscoplastic nature of the material to enhance the room temperature formability. The use of servo press, ultrasonic-assisted forming, and electrical-assisted forming are few such representative processes. This chapter will explore the fundamentals that govern these processes and also describe the application with case studies from literature. Since all the processes are based on similar principles, the mechanical behavior during processing can be modeled under a common framework. In this chapter, a dislocation density model is proposed as a common model for energy-assisted forming processes
Analysis of mechanical performance and energy consumption of microwave cured GFRP composites: A low-energy footprint manufacturing process
No full textThermo-mechanical finite element modeling of the laser treatment of titanium cold-sprayed coatings
No full textThis paper implements a thermo-mechanical model to simulate the laser treatment effects on a cold-sprayed titanium coating and aluminum substrate. The thermo-mechanical finite element model considers the transient temperature field due to the laser source and applied boundary conditions, using them as input loads for the subsequent stress-strain analysis. Numerical outcomes highlighted the relevance of thermal gradients and the presence of thermally-induced stress-strain fields responsible for promoting damage in the coating
A semi-analytical model to predict infusion time and reinforcement thickness in VARTM and SCRIMP processes
No full textIn 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
Hybrid technique to assess the fatigue performance of multiple cracked FSW joints
No full textIn this paper a numerical-experimental procedure useful to numerically assess the fatigue performance of friction stir welded aluminium joints is presented. The impact of manufacturing residual stresses on crack propagation in the joint driven by a remote fatigue load can be predicted. The proposed sequential procedure starts with the experimental residual stress assessment by the contour method and proceeds through the multiple crack growth simulation by the Dual Boundary Element Method. In the frame of Linear Elastic Fracture Mechanics, the superposition principle is invoked to provide the mathematical foundation supporting the proposed modelling strategy. In order to validate the proposed procedure, simple specimens are fatigue tested, obtaining multiple crack propagation scenarios that are monitored, in order to compare experimental and predicted crack growth rates
An integrated numerical approach to simulate the filler deposition and the shape distortions in gas metal arc welding
No full textUltrasonic welding of glass reinforced epoxy composites using thermoplastic hybrid interlayers
No full textA 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
Permeability analysis of natural and artificial fiber textiles for liquid composite molding process
No full textIn liquid composite molding (LCM) processes a catalyzed resin is forced to flow through a dry fibrous preform, opportunely arranged within a mold. The pressure gradient, positive or negative depending on the particular process, drives the uncured liquid flow at a flow rate which relies on fluid viscosity and preform porosity and permeability. Nowadays, sustainability reasons are pushing the market to the wider usage of natural fibers, such as hemp, jute, flex among others, as an interesting alternative to traditional glass and carbon artificial textiles. This manuscript describes an experimental/numerical approach to analyze the preform permeability and the impregnation flow in the LCM process using different textiles, based on glass, carbon and natural fibers. Unidirectional flow tests were performed using a laboratory scale LCM setup, constituted by a sensed mold in order to dielectrically monitor impregnation and saturation flows. The position of the unsaturated flow front was detected also by means of a camera monitoring the resin flow though milled eyelet sealed using transparent material. The permeability was also numerically inferred using the FlowTex software for all the investigated cases. Numerical and experimental outcomes were finally compared and discussed
DBEM crack propagation in friction stir welded aluminum joints
No full textThis paper deals with the simulation of multiple crack propagation in friction stir welded butt joints and the aim is to assess the influence of process induced residual stresses on the fatigue behavior of the assembly. The distribution of the process induced residual stresses is mapped by means of the contour method; then, the computed residual stress field is superimposed, in the DBEM environment, to the stress field due to a remote fatigue traction load and the crack growth is simulated. A two-parameters crack growth law is used for the crack propagation rate assessment. The Stress Intensity Factors are evaluated by the J-integral technique. Computational results have been compared with experimental data, provided by constant amplitude crack propagation tests on welded samples, showing the subdivision of the overall fatigue life in the two periods of crack initiation and crack propagation
A FEM based methodology to simulate multiple crack propagation in friction stir welds
Full text linkIn this work a numerical procedure, based on a finite element approach, is proposed to simulate multiple three-dimensional crack propagation in a welded structure. Cracks are introduced in a friction stir welded AA2024-T3 butt joint, affected by a process-induced residual stress scenario. The residual stress field was inferred by a thermo-mechanical FEM simulation of the process, considering temperature dependent elastic-plastic material properties, material softening and isotropic hardening. Afterwards, cracks introduced in the selected location of FEM computational domain allow stress redistribution and fatigue crack growth. The proposed approach has been validated by comparison with numerical outcomes provided by a consolidated FEM-DBEM procedure, available in literature. The discussed procedures are substantially equivalent in terms of SIFs evaluation along the crack front at the cracks insertion, as well as with respect to crack sizes measured in three different points for each propagation step. This FEM-based approach simulates the fatigue crack propagation by considering accurately the residual stress field generated by plastic deformations imposed on a structural component and has general validity. © 2017 Elsevier Lt
- …
