Nader Abedrabbo

Optimization of a Tube Hydroforming Process

An approach is presented to optimize a tube hydroforming process using a Genetic Algorithm (GA) search method. The goal of the study is to maximize formability by identifying the optimal internal hydraulic pressure and feed rate while satisfying the forming limit diagram (FLD). The optimization software HEEDS is used in combination with the nonlinear structural finite element code LS‐DYNA to carry out the investigation. In particular, a sub‐region of a circular tube blank is formed into a square die. Compared to the best results of a manual optimization procedure, a 55% increase in expansion was achieved when using the pressure and feed profiles identified by the automated optimization procedure.

Warm Forming of Aluminum Alloys using a Coupled Thermo-Mechanical Anisotropic Material Model

Temperature‐dependant anisotropic material models for two types of automotive aluminum alloys (5754‐O and 5182‐O) were developed and implemented in LS‐Dyna as a user material subroutine (UMAT) for coupled thermo‐mechanical finite element analysis (FEA) of warm forming of aluminum alloys. The anisotropy coefficients of the Barlat YLD2000 plane stress yield function for both materials were calculated for the range of temperatures 25°C–260°C. Curve fitting was used to calculate the anisotropy coefficients of YLD2000 and the flow stress as a function of temperature. This temperature‐dependent material model was successfully applied to the coupled thermo‐mechanical analysis of stretching of aluminum sheets and results were compared with experiments.

LS‐DYNA Simulation of Hemispherical‐punch Stamping Process Using an Efficient Algorithm for Continuum Damage Based Elastoplastic Constitutive Equation

An efficient integration algorithm for continuum damage based elastoplastic constitutive equations is implemented in LS-DYNA. The isotropic damage parameter is defined as the ratio of the damaged surface area over the total cross section area of the representative volume element. This parameter is incorporated into the integration algorithm as an internal variable. The developed damage model is then implemented in the FEM code LS-DYNA as user material subroutine (UMAT). Pure stretch experiments of a hemispherical punch are carried out for copper sheets and the results are compared against the predictions of the implemented damage model. Evaluation of damage parameters is carried out and the optimized values that correctly predicted the failure in the sheet are reported. Prediction of failure in the numerical analysis is performed through element deletion using the critical damage value. The set of failure parameters which accurately predict the failure behavior in copper sheets compared to experimental data is reported as well.

Sheet Hydroforming Simulation of a License‐Plate‐Pocket Panel

The objective of this research was to numerically study the application of the sheet hydroforming process to a real‐world complex automotive part. In sheet hydroforming, one or both surfaces of the sheet metal are supported with a pressurized viscous fluid to assist with the forming of the part where a female die is not required. The pressurized fluid supports the blank during the forming process, delays the onset of material failure and acts as an active blank‐holding force. The commercial finite element analysis code LS‐Dyna was used to simulate the process using Barlat’s anisotropic yield function to represent material behavior during deformation. Pressure and blank holding force profiles were developed for forming this complex part without defects. In addition, it is numerically shown that through the application of an appropriate fluid pressure profile, wrinkles could be eliminated.