Introduction

A key performance indicator limiting the potential of aluminum alloy sheet in automotive body panels is dent resistance. Dent resistance is a function of many coupled influences such as panel stiffness, curvature, support conditions, and strength. In addition, the effects of prior work, that is, thickness reductions and work hardening during panel stamping must be considered. Two types of dent resistance are considered, static and dynamic. The difference being the nature of the applied load, static loading is typified by a hand pushing slowly on a hood, while dynamic loading is driven by inertia and contact forces generated during an impact. This work involves prediction of dent resistance for aluminum panels using the finite element method, and validation of these predictions using experimental testing.

Forming Models

Forming strain predictions from a finite element model are required to accurately predict dent resistance for a given panel.

FE simulation of a formed panel

FE simulation of a formed panel

Structural Models

Real automotive panels have stiffening supports which affect panel dent resistance and therefore must be considered.

This is a manufactured inner panel used in parametric studies of support conditions

This is a manufactured inner panel used in parametric studies of support conditions

Mesh Refinement & Stress/Strain Remapping

The FE models used in industry lack sufficient local refinement for denting analysis. A software tool that refines these models and creates a new FE denting model has been created to minimize the amount of pre-processing.

Dynamic dent simulation of a locally refined FE structural model showing displacement contours

Dynamic dent simulation of a locally refined FE structural model showing displacement contours

Experimental Testing

Both static and dynamic dent testing was performed using a 5-axis test bed.

Experimental Static Dent Testing

Experimental Static Dent Testing

Validation of Numerical Results

For static denting both residual dent depth and stiffness response were compared.

Results for Medium-Scale Formed Panels

Results for Medium-Scale Formed Panels

For dynamic denting the residual displacement was compared.

Results for structural assembly panels

Results for structural assembly panels

Full-Scale Hood Models

The work on the medium scale model was used as a foundation for full-scale models of production automotive hoods.

Finite Element Model of Hood Inner and Outer Panels

Finite Element Model of Hood Inner and Outer Panels

Schematic of dynamic dent sites (Dashed circles represent teacup sites and dashed lines indicate internal supports)

Schematic of dynamic dent sites (Dashed circles represent teacup sites and dashed lines indicate internal supports)

Dynamic Dent Depth Comparisons

Dynamic Dent Depth Comparisons

Mesh Refinement & Stress/Strain Remapping

The FE models used in industry lack sufficient local refinement for denting analysis. A software tool that refines these models and creates a new FE denting model has been created to minimize the amount of pre-processing work.

Mesh Refinement Software Interface (200mm refinement radius, 4 levels of refinement)

Mesh Refinement Software Interface (200mm refinement radius, 4 levels of refinement)