The Society of Automotive Engineers sponsors the Mini Baja design competition as part of their collegiate design series.  The purpose of the event is to have teams of engineering students design, build, and race a prototype of a four-wheel, one passenger, off-road vehicle intended for off-road recreation.  North Dakota State University has participated in this competition for numerous years.

The most important aspect of the vehicle design is the frame.  The frame contains the operator, engine, brake system, fuel system, and steering mechanism, and must be of adequate strength to protect the operator in the event of a rollover or impact. The roll cage must be constructed of steel tubing, with minimum dimensional and strength requirements dictated by SAE.

The frame shown below was designed and constructed by a recent NDSU Mini-Baja team.  All tubes are round and made of steel (E = 30 Msi, ν = 0.30).  All tubes with the exception of the diagonal braces have a 1 in OD with a 0.083 in wall thickness.  The diagonal braces have a 1 in OD with a 0.065 in wall thickness.

In this example, we will use ANSYS to investigate the response of the frame (e.g., stresses and

deflections) under various types of impact.  Specifically, we will consider a direct frontal impact that results in an 8g horizontal loading (deceleration), and a one-wheel impact that results in a simultaneous

4g horizontal loading, 6g vertical loading, and 2g lateral loading.  The applied forces are obtained by multiplying the deceleration value by the overall weight of the vehicle and driver, assumed here to be

500 lb.  The impact loading is simulated by restricting displacements at certain locations, and applying discrete forces at various points on the frame where the weight is concentrated.  The frame will be modeled in ANSYS using 3D elastic beam elements (BEAM4).

The BEAM4 element (shown below) requires the following cross-sectional properties to be calculated and entered as Real Constants:  cross-sectional area, area moment of inertia about the z-axis (Izz), area moment of inertia about the y-axis (Iyy), thickness along the z-axis (outer edge-to-edge), and thickness along the y-axis (outer edge-to-edge).

The details are attached in PDF


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