Methods of ANSYS Analysis

The Ansys analysis was conducted by first creating a model of the beam. This was by defining the volume of the beam by the required dimensions.

The material properties of the beam now had to be entered into Ansys. This was done by first selecting the model that required analysing. The material properties could then be entered. E (Young’s modulus of elasticity) was entered as 70 GPa, and n

(Poisson’s ratio) was entered as 0.35. Both of these values were obtained from a materials web site, and are the accepted values of aluminium.

A mesh then had to be put onto the model so that Ansys could calculate the stresses and deflections on the beam when forces were applied. It was decided that Tet 10 node 187 elements would be used, as there are no restrictions on the type of model that these can be used on. 0.5mm elements were used as it was thought that this size would be able to generate accurate enough results. A smaller size would have slowed down the analysis because there would be more calculations to be performed. A diagram of the Tet 10 node 187 element can be seen to the right:: -

As shown in the diagram, the element is defined by ten nodes, having three degrees of freedom at each node. This makes it very flexible, and capable of distorting to fit into most volumes. More information on this element can be found in the appendix.

A picture of the full meshed beam, and a close up of the mesh can be seen below : -

FULL MESHED BEAM

CLOSE UP OF MESH

One end of the beam now had to be restrained. This was done by selecting the area on one end, and then entering a value of 0 displacement for this area.

The three different forces could now be applied to the beam. The loads were applied to one of the nodes on the unrestrained end of the beam. They were applied as a minus value in the y-axis.

The deflection in the y-axis and the stress in the x-axis were then plotted out for each of the forces applied. The directions of the axis’s can be seen in the picture of the full meshed beam (above). The plots obtained from Ansys are shown in the appendix.

After closer inspection of the beam, it was discovered that when a force was applied to the unrestrained end, a non-uniform stress pattern emerged on the restrained end (see picture below) : -

It was decided that this strange stress pattern was probably because the beam was restrained by the end face, meaning this end of the beam could not flex at all. In the true experiment, the beam was still able to flex a small amount. This is because this was not the very end of the beam; it protruded both sides, and was restrained by clamping the top and bottom faces.

To account for the probable inaccuracies described above, it was decided that graphs should be plotted showing the stresses in this area for each of the forces. The line on the graph could then be continued past where it changes, to give truer results. The modified graphs can be seen on the following page : -

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