Mechanical Engineering 37100: Computer-Aided Design Fem Modeling

Mechanical Engineering 37100: Computer-Aided Design FEM Modeling Project #2: Evaluation of a Steel Pulley-and-Shaft Design

OVERVIEW

In this project, you are asked to evaluate the design of a machine part. Here, no analytical solution is known, so the only sources of information will be your own intuition and experience, and the results of the FE analysis. The part selected for this project is a steel pulley with attached shaft, shown below in Figure 1. The shaft is connected to a motor, which continues attempting to turn, even though an obstacle has penetrated one of the holes, preventing an inside face from moving. The primary purpose of the analysis is to determine whether the pulley-shaft system would deform permanently under these circumstances. If it does, your task will be to redesign it to prevent this failure. To get you started, the solid model is provided and boundary conditions are suggested, but these should be considered only as a first approximation. Both the design of the part and the boundary conditions may change as you conduct your analysis.

BACKGROUND

In order to use FEM software as a design tool, you will first need to verify that (1) the model is consistent with the physical situation it is supposed to represent; and (2) the FEM solution is valid. This section provides some background material to assist you in both of these steps.

In evaluating your results, consider the purpose of the pulley, and how it must be supported to accomplish its task. The pulley transmits force to a belt, which transmits torque to another pulley. What would happen if one pulley and its shaft were allowed to translate toward or away from the other pulley? What must be included in the system to prevent these outcomes?

No complex computer program, such as SolidWorks Simulation, should be trusted. It is essential to conduct an independent analysis to check whether the solution is valid. In FEM Project #1, an analytical solution was available as an outside check on the FEM results. Here, as in most FEM studies, the geometry is too complex to allow a solution by hand. Consequently, convergence studies are the only available means for testing of validity.

PROCEDURE

1. Finite Element Model: The solid model is available as a SolidWorks Part Document, pulley_w_shaft large. Download this part and open it in SolidWorks. As the material, use 1020 steel, cold rolled. Yield strength for this material is approximately 350 MPa. Apply a torque of 100 N-m to the outer face of the shaft, which is outlined above in orange. The yellow line labeled "Axis 1" should be used for the direction of the torque. (Recall that a torque vector is always perpendicular to directions of the forces causing the torque). Restrain one of the inner rectangular surfaces of the cutouts in the wheel, so it will not be able to move when the torque is applied. Use Preview to see the direction of the torque. If necessary, reverse the direction of the torque to make it push against the restraint.

2. Evaluation of the model: Displacements are usually easier to visualize than stresses. Before running the study, consider how a real pulley would displace if it was being turned by a motor against an obstruction inside one of its holes. Then run the study. Look at the displacements first. Use animate or vector plot to show direction as well as magnitude. Did they agree with your prediction? If not, discuss the discrepancies. What did you learn? Are there boundary conditions that need to be added or modified to make the model conform to the physical situation? If these are not valid, consider