Xuan-Tan Pham

Simulation of Compression Resin Transfer Molding with Displacement Control

In this paper a mathematical model of two-dimensional resin flow through fiber reinforcements in compression resin transfer molding (CRTM) is presented. The preform is partially filled by resin during the injection phase. Then it is compressed by the mobile upper part of the mold. The resin flow in the fiber bed is governed by Darcys law according to the theory of flows in saturated porous media. The consolidation of the saturated preform is described by the total mass conservation equation. A filling algorithm based on resin conservation on a deformable grid is used to advance the flow front at each time step. Resin pressure and velocity are calculated by the finite element method. The accuracy of the model is verified by evaluation of the resin mass balance, calculation of the resin pressure and progression of the flow front in time. Comparison of predicted results with analytical solutions is also presented.

THEORETICAL AND EXPERIMENTAL INVESTIGATION OF FAILURE AND DAMAGE PROGRESSION OF GRAPHITE-EPOXY COMPOSITES IN FLEXURAL BENDING TEST

Predicting failure stress and failure modes in composite laminates is very difficult. The choice between failure criteria is complex and there is a lack of experimental study to validate the results obtained. In this paper, a theoretical and experimental study of damage progression and failure modes of graphite-epoxy laminates in three points bending tests is presented. A quasi-isotropic [(± 45/9010)]5 graphite-epoxy composite is investigated. C-scan method and microscopic sectioning permit to monitor damage progression and failure modes during the experiment. Specimens at different failure levels are used to determine damage progression and the effect of geometrical parameters on the successive failures and on failure modes is studied. The progression of damage has been followed experimentally and identified in detail. The theoretical study is based on the classical laminate theory in the case of in-plane loads. A software program has been elaborated for post-failure treatment and experimental results are compared with numerical predictions.

Two-Dimensional Rosenthal Moving Heat Source Analysis Using the Meshless Element Free Galerkin Method

The quasi stationary-state solution of the two-dimensional Rosenthal equation for a moving heat source using the meshless element free Galerkin method is studied in this article. Node-based moving least square approximants are used to approximate the temperature field. Essential boundary conditions are enforced by using Lagrange multipliers. A Gaussian surface heat source is used for the modeling of the moving heat source. The results obtained for a two-dimensional model are compared with the results of the finite-element method.

Modeling of thermoforming of low-density glass mat thermoplastic

The glass mat thermoplastic (GMT) is made from random-chopped glass fibers and polypropylene in a sheet form. This low-density compressible material is used extensively in the automotive industry for making panels. The mechanical behavior of this material in large deformation and at thermoforming process temperature is far from being well understood. The objective of this research is to determine a constitutive law of this Azdel thermoplastic composite used for thermoforming process. A series of biaxial tests was performed to study the stress-strain behavior of the low-density thermoplastic sheet reinforced with 55% glass fiber. Different strain rates and temperatures were employed to study their effects on the mechanical behavior. Pressure-thickness model parameters were obtained using a laboratory press. A nonisothermal hyperelastic model was used for modeling this material. The results of the simulation are compared with data from a laboratory thermoforming machine and a small, simple mold.

Analysis of the Consolidation in Flexible Bladder Process for Thin Composite Parts by Finite Element Method

The consolidation of a saturated preform under pressure by means of a flexible bladder is studied in this paper. This phenomenon occurs in several composite manufacturing processes such as compression resin transfer molding (CRTM) for example. The resin flow in the fiber bed is governed by Darcys law. The consolidation of the saturated preform is described by the total mass conservation. Mechanical behavior of the fiber network is analyzed. A two-dimensional numerical model is developed based on the finite element method. The numerical model allows the calculation of the resin pressure distribution in the preform, the reaction force of the preform and the prediction of the evolution of the preform thickness as a function of time and space.

Simulation Of Compression Resin Transfer Molding

In this paper, a mathematical model of resin flow through fiber reinforcements in compression resin transfer molding (CRTM) is presented. Before complete closing of the mold, the preform is partially filled by resin during the injection phase. Then it is compressed by the mobile part of the mold. The resin flow in the fiber bed is governed by Darcys law. The consolidation of the saturated preform is described by the total mass conservation. It is assumed that in the resin-saturated domain the total stress is equal to the sum of the fiber bed stress and the resin pressure. A filling algorithm based on resin conservation on a deformable grid is used to advance the flow front at each time step. The model presented in this paper permits to analyze the resin pressure during compression. The resin pressure and the compaction stress on the preform allow to determine the total reaction force applied on the mobile part of the mold. The accuracy of the model is verified by evaluation of the resin mass balance, calculation of the resin pressure and progression of the flow front in time.

Technical challenges in narrow-gap root pass welding during tandem and hybrid laser-arc welding of a thick martensitic stainless steel

As part of a collaborative program to develop advanced manufacturing processes for next-generation hydraulic turbines, this study investigated the technological challenges for joining 25-mm thick martensitic stainless steel (MSS) plates using tandem and hybrid laser-arc welding. Although candidate materials for the intended application typically include wrought AISI 415 and cast CA6NM, a martensitic 410 stainless steel (SS) was especially selected in this study due to its greater crack sensitivity. A narrow-gap groove was designed to minimize the amount of 410NiMo filler metal required to fill the groove using a multi-pass single-sided welding technique. All the welding trials were performed using a 5.2 kW fiber laser. The root-pass quality was characterized in terms of weld bead geometry, defects and microstructure. The main technical challenges observed for the root pass were lack of penetration, lack of fusion and cracking, as detailed in this work.

Modeling circular inductors coupled to a semi-infinite magnetic medium considering the proximity effect

Abstract This paper presents a simple 2D electromagnetic model that solves the high-frequency current distribution, considering the proximity effect, in a planar spiral coil above a linear conductive or non-conductive semi-infinite magnetic medium. The conductive regions are divided into axisymmetric elements in which the current is assumed constant. The current flowing in each element depends on its complex impedance and is computed by Kirchhoff’s circuit law. To take the effect of the magnetic medium into account, a new set of mutual inductance formulas are presented. Those formulas are expressed in terms of elliptic integrals and the fast-converging arithmetic–geometric mean iteration of Gauss. The geometric mean distance method is used to deal with elements of arbitrarily shaped cross-section. Elliptic integrals are also used to express the magnetic flux density. The current distribution, the magnetic field and the equivalent impedance computed with the multifilament model agree well with the results obtained using commercial finite element software.

Numerical analysis of turbulent convective heat transfer in a rotor-stator configuration

This paper presents the numerical analysis of convective heat transfer of a rotor-stator configuration, which is typically found in hydro-generators. The Reynolds Averaged Navier Stokes (RANS) turbulence models based on the eddy-viscosity approximation were employed. Different steady and unsteady multiple frames of reference models were used to deal with the flow interaction in the rotor-stator system. The fluid flow and heat transfer analysis were performed using conjugate heat transfer methodology, in which the governing equations for the fluid dynamics, heat conduction with additional constraints on the fluid-solid interface were simultaneously solved. The computed convective heat transfer coefficient was compared against available experimental data to assess the suitability of turbulence models.

Characterization of multilayered carbon-fiber–reinforced thermoplastic composites for assembly process

The aim of this research work is to characterize the mechanical behavior of multilayered carbon-fiber–reinforced polyphenylene sulfide composites with the application to assembly process of nonrigid parts. Two anisotropic hyperelastic material models were investigated and implemented in Abaqus as a user-defined material. An inverse characterization method was applied to identify the parameters of these material models. Finite element simulations at finite strains of a flexible composite sheet were carried out. Numerical results of sheet deformation were compared with the experimental results in order to evaluate the appropriateness of the material models developed for this application.