Figure 12: Force Pulse Used for BU Impact A direct integration approach was used for obtaining the strain solutions for the FEM. The comparison between the FEA strain solution and the strain solution obtained using the proposed technique is made in Figures 13 a, c and e at locations 7, 8 and 4 respectively in the BU. The response shown is after the impact was made at 0.25 seconds for a sample time period of 0.15 seconds. The FEA transient solution was obtained for 400 steps with 0.001 seconds per step. The strain solution obtained from the proposed technique uses the full-field displacement solution. So the displacement sampling rate of 0.005 sec per sample also applies for the strain obtained from proposed technique. The FEA solution was performed at a finer time step to properly obtain an accurate numerical solution. This implies that the FEA and test data have different time increments. The FEA strain response had to be down-sampled to the response data points recorded during experimentation. The comparison of this down-sampled FEA strain solution with the predicted strain response using the expansion technique is shown in Figures 13 b, d and f for locations 7, 8 and 4 respectively. The FEA solution shows contribution of higher order modes because the direct integration scheme was used to obtain the solution. However, a good overall agreement is observed between the predicted and FEA strain solutions for locations 7 and 8 which are higher strain regions in the structure as they are closer to the fixed base. Location 4, which is at the mid-level of the BU does not see as much strain in comparison to locations 7 and 8. There is a slight DC bias that appears on the data but the general trend is reasonable considering the lower level of strain observed at this location. 213
RkJQdWJsaXNoZXIy MTMzNzEzMQ==