Design Optimization with 3 rd Generation AHSS

“This material is based upon work supported by the Department of Energy under
Cooperative Agreement Number DOE DE-EE000597, with United States
Automotive Materials Partnership LLC (USAMP).

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor anyagency thereof, nor any of their employees, makes any warranty, express orimplied, or assumes any legal liability or responsibility for the accuracy,completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. 

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Project Goal

To reduce the lead time in developing and applying lightweight third generation advanced high strength steel (3GAHSS) by integrating material models of different length scales into an Integrated Computational Materials Engineering (ICME) model

Project Objectives

─ Identify, validate (within 15% of experiments), and assemble length scale material models for predicting 3GAHSS constitutive behavior for component forming and performance

─ Demonstrate the ability to reduce the mass of a vehicle structure* subassembly (consisting of a minimum of 4 parts) by 35% using the ICME 3G AHSS with a cost impact of no more than $3.18 per pound saved and without compromising structural performance .

Body Side Assembly Selected for Optimization Study

1. Key structural assembly that influences overall stiffness and major crash load cases

2. Will benefit considerably from 3G AHSS applications

3. LWB One Piece Body side inner

4. Several reinforcements in joints and members

5. LH & RH Body Side Assemblies Mass around 105 kg (30% of BIW)

CAE Model

1. Includes BIW, Front and Rear Fixed Glass and Bumpers

2. FEA mesh density 5 mm body side to 10 mm other structure

3. All flanges assumed to be spot welded (35 mm pitch).

4. Parts to be assessed for formability and effect of strain hardening for crash load cases:

a) Rocker Reinforcement

b) B-Pillar Reinforcement

c) Roof Rail Inner

d) Front Body Hinge Pillar (FBHP) Inner

CAE Load Cases Assessed

1. Side Barrier

2. Side Pole

3. Front Impact

4. Rear Impact

5. Roof Crush

6. Seat Belt Anchorage Strength

7. Body Static Stiffness (Torsion / Bending)

8. Body Normal Vibration Modes

Preliminary baseline calibration crash studies were conducted in order to:

─ Appropriately define the load case parameters to account for the analyses being focused only on body structure performance

─ Establish structural performance targets for future optimization analyses using the 3G AHSS developed during the course of the project.

For crash load cases, initial velocities are reduced so that the new internal energy is 70% of the total internal energy using standard regulation velocities. This is because the model is for a BIW only (i.e., not a full vehicle system model). The 30% energy reduction is a judgment based on experience with prior projects.

For the ICME study other sub-systems are represented by lumped mass only (i.e., sub-system structures are NOT included in the CAE model).

The speed is LOWERED to reduce the crash energy to achieve body structure intrusions of similar magnitude of typical Mid-Size Sedan vehicle

Highly sensitive parts to both torsion and bending stiffness per kg change in mass

1.Completed Baseline Crash and NVH assessments and established performance targets for project

─ Defined crash load cases’ parameters to account for the project being focused only on body structure analyses

─ Completed the body side part’s gauge sensitivity with respect to static torsion and bending stiffness.

─ Completed side impact and roof crush assessments with “3G” steel properties

─ Assessed mass reduction potential using the newer grades

─ Assessed NVH degradation due to gauge reduction

2.Generated design iterations using preliminary material grade (not final properties) in order to:

─ Establish a strategy for balancing mass reduction, crash, and NVH performance (prior to receiving final project steel grade properties)

3.Constructed a Baseline Technical Cost Model for future assessment of the cost impact of the optimized solution

1.Generate final design concepts that balance performance and required mass reduction (Geometry / Gauge)

2.Conduct final performance assessments using ICME generated steel grades

3.Finalize on-cost assessments through the established Technical Cost Model