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# A Finite Element Analysis Method for the Evaluation of an Automobile Body Joint

IP.com Disclosure Number: IPCOM000007785D
Publication Date: 2002-Apr-23
Document File: 2 page(s) / 215K

## Publishing Venue

The IP.com Prior Art Database

## Abstract

The concept of the coefficient of joint stiffness and the force distribution ratio are developed to evaluate an automobile body joint design. The coefficient of joint stiffness reveals whether a joint is stiff enough compared to its joining components and gives design directions on how to make further improvement.

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A Finite Element Analysis Method for the Evaluation of an Automobile Body Joint

The concept of the coefficient of joint stiffness and the force distribution ratio are developed to evaluate an automobile body joint design. The coefficient of joint stiffness reveals whether a joint is stiff enough compared to its joining components and gives design directions on how to make further improvement.

Figure 1: A Body Joint.          Figure 2: A joint within a joint frame.      Figure 3: A Joint frame within a body

# Definition

JOINT - A joint is defined as the junction of the members surrounded by sections which are located at the starting point of the transition radius of its members. The section should be perpendicular to the centerline of the member and should not intersect the transition radius on the other side of the member. The highlighted portion of figure 1 is an example of a joint.

JOINT FRAME - A joint frame is defined as the joint and its members until the next joint. Figure 2 shows a joint frame which contains the B-pillar to roof rail joint. Figure 3 shows how the joint frame is cut from the body structure.

COEFFICIENT OF JOINT STIFFNESS C - The coefficient of joint stiffness is defined as the ratio of the stiffness of the joint frame to the stiffness of the same joint frame with a rigid joint. The coefficient of joint stiffness is greater than zero and less than one. If a joint is very stiff, the coefficient of joint stiffness is close to one. Otherwise, if a joint is very soft, the coefficient of the joint stiffness will be close to zero.

FORCE (MOMENT) DISTRIBUTION RATIO - The force distribution ratio is defined as the ratio of the reaction force (moment) at the end of the member of a joint frame to the input force (moment) from another member. The force distribution ratio actually describes the loading path.

COEFFICIENT OF FORCE DISTRIBUTION RATIO OF A JOINT - The coefficient of force distribution ratio is the force distribution ratio of the joint frame divided by the force distribution ratio calculated using the same model but with a rigid joint. This coefficient describes how the force distribution ratio is altered by the joint design either intentionally or unintentionally. If the coefficient is close to one, the loading path is dominated by the stiffness of the members. Otherwise, the loading path is more controlled by the joint.

Method

The finite element model of a joint frame is used for the study of the coefficient of joint stiffness and the force distribution ratio. The joint at the center of the joint frame should be modeled according to the joint definition. Different part ID and material ID are assigned to the components of the joint, so that the material property could be easily changed. To study the coefficient of joint stiffness, a unit rotation is applied at the end section of one mem...