CAE Driven Body Durability and Upfront Structure Development of the New Ford Edge

Zhonghui (Sean) Ma, Behrooz Shahidi, Michael J. Lee, Suwei Zhou; Ford Motor Company

Martin McNamee, MSC Software Corporation

Contents

• 1. Introduction

• 2. Body NVH Design

• 3. Body Durability Design3.1 Durability Design Process 3.2 CAE Drives the Durability Development3.3 Strength Test Simulation

• 4. VPG (Virtual Proving Ground)

• 5. FMVSS207/210, 225 Development

• 6. Summary

1. Introduction

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The all new Ford Edge sets a bold new direction in Design, Quality and Vehicle Performance. Sporty, versatile and undeniably American, the Edge is the result of high performance product development.

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The body structure was primarily designed to achieve best in market segment levels of comfort in terms of noise, vibration and harshness (NVH), Vehicle Dynamics, Safety and Durability.

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The Ford Edge and its upscale cousin, the Lincoln MKX, have earned the Top Safety Pick rating from the Insurance Institute for Highway Safety (IIHS).

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In order to achieve this intensive usage of CAE (Computer Aided Engineering) methods and tools (MSC Nastran, Adams, LS-DYNA (Solution 700) etc.) was required to drive the design.

2. Body NVH DesignLift-Gate PAC

Tire Tub PAC

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The structural dynamics of the body structure is extremely important to achieve the desired level of comfort in terms of noise, vibration and harshness (NVH).

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The acoustic sensitivity analysis (model shown above) is discussed as an example here with hot spots showing panel acoustic contribution (PAC).

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The acoustic cavity model is coupled with the body structure and excited under the rough road input at a speed of 40 MPH. The contributions of the lift-gate and tire-tub to the rear sound characteristics were identified at several low and middle frequencies.

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Both panel designs were modified to reduce major panel acoustic sensitivity.

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The sensitivity distribution over the frequency range and excited at different attachment locations were examined through acoustic thermal plot (shown in next page).

X Y Z X Y Z X Y Z X Y Z X Y Z X Y Z X Y Z X Y Z X Y Z X Y Z X Y Z X Y Z X Y Z X Y Z X Y Z X Y Z X Y Z X Y Z

200

BETTER <== Below Target === [dB/N] === Above Target ==============> WORSE

8 9 >6 74 52 30 1-2 -1<= -4 -3

Frequency [Hz]

50100

150

Right Left Right LeftRight Left Right LeftRight Left Right LeftRear Front Rear

10

Right Left Right Left Right Left

Front Subframe Front Strut Engine Mount Rear Subframe Rear Shock Rear Trailing ArmFront Middle

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This figure shows an example of acoustic sensitivity measured at the rear passenger ear.

3. Body Durability Design

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Durability is a key attribute of the full vehicle. All components must maintain function during the intended service life.

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Body structure durability has two major specifications: structural strength and fatigue resistance .

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Loads, geometry, material and manufacture process plus environmental conditions determine the durability of a component. These factors interact with each other and make the durability design a very complex and challenging task.

3.1 Durability Design Process

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From CAE, laboratory rig test to proving ground test, all three methods were extensively utilized in the design and development of the new Ford Edge.

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The customer correlated proving ground test is a condensed representation of actual customer usage.

3.2 CAE Drives the Durability Development

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Statistical loads were used as the input in the very early development stage where no prototype was available to provide real measured loads. Statistical loads are developed from historical recorded data for the same vehicle class.

●Later on, when the first prototype is available, measured spindle loads can be obtained from the proving ground test. By using Adams models with rigid suspension components and flexible frame and/or body modal synthesis, time history loads are cascaded to all attachment locations including body mounts.

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MSC Nastran and FDYNAM (Ford's in-house dynamic fatigue software) are used to assess fatigue life. Not only static effects but also dynamic effects of the loading and structure are accurately captured in the analysis. Consideration of the dynamic effects is critical for heavy mass attachment areas.

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Fatigue life assessment used for improvements in seat attachments.

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Fatigue life example in the D-pillar trough area used for design improvements

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Welds life example in the rear floor area used for design improvements.

3.3 Strength Test Simulation

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The curb island event induces a large amount of load and deformation on the body structure. A separate nonlinear analysis

using LS-DYNA (Solution 700) was conducted to calculate the permanent set at the front shock tower to avoid alignment issues

for suspension system.

4. VPG (Virtual Proving Ground)●

VPG was piloted as a new CAE approach in the early development of the new Ford Edge. This new approach has the potential to improve the efficiency of the load acquisition process by simulating the real time running of a vehicle driven on the proving ground.

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A complete body FE model is combined with a multi-

body dynamics model (such as Adams). The ETA/VPG software is then used to create a tire model and position the road surface beneath the vehicle allowing the vehicle to traverse the road surface as in the test.

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The simulations are performed for a period corresponding to the test event duration, and the resulting stress data is obtained. The stress can be used for subsequent fatigue analysis.

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Since the solver for VPG is LS-DYNA (Solution 700) it can also perform nonlinear strength analysis.

5. FMVSS207/210, 225 Development

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FMVSS (Federal Motor Vehicle Safety Standards) 207/210 states the strength requirements for seat and seat belt system. FMVSS 225 requires the child restraint system to maintain structure integrity and also meet compliance target.

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Due to severe loading and large deformation of the structure, the physical test is in nature destructive and non-repetitive.

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LS-DYNA is chosen as the analysis software because it can simulate the highly nonlinear phenomenon as observed in physical test.

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In the full system analysis (including seat, restraint and body), potential failure mode and failure location can be predicted for design improvement.

6. Summary

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The design and development of the body structure driven by CAE have ensured a robust vehicle that has a sporty handling, delivers "hidden quietness" and earns top scores for front, side and rear impact safety with the "Top Safety Pick" award of the Insurance Institute for Highway Safety (IIHS).

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Seamless integration of CAE in the design, engineering and development process is a critical factor for successfully delivering a vehicle with the product integrity of the new Ford Edge at a fast product development time.

Zhonghui(Sean) MaEmail: sma2@ford.com Tel. +1-313-805-7480