PSI - Issue 17

C P Okeke et al. / Procedia Structural Integrity 17 (2019) 596–601 C P Okeke et al / Structural Integrity Procedia 00 (2019) 000 – 000

598

3

3. Experiments

The material used in this study was vacuum cast polyurethane supplied by Ogle Models. The rectangular specimens of dimensions 100mm x 10mm x 4mm were cut from material plaques. A U-type notch of 2mm diameter and 6mm depth was introduced at the centre of the specimen as shown in fig 1. The clamping of the sample to the support and loading masses to the sample was done with 0.7Nm torque. The dynamic response was measured by performing a sine sweep test using V721 electrodynamic vibration shaker. The specimen mounted on a test fixture was base excited from 30Hz to 100Hz frequency with variable input load of 1m/s 2 to 60m/s 2 acceleration in 10m/s 2 increments. Miniature accelerometer (PCB 352C22) was placed on the centre of the beam to measure the response. The fatigue life curve was characterised using the resonant fatigue test system developed by Okeke et al (2018). The testing was based on three load levels - 80%, 60% and 40% material yield strength. At every load level, five specimens were tested and the number of cycles to failure was logged for every specimen. The input acceleration for all three load levels was obtained by taking the ratio of the calculated specimen response acceleration to the experimentally obtained transmissibility of the first resonance. The loading was achieved by inertia effect of two small masses mounted on the test specimen. A V721 electrodynamic vibration shaker was used to base excite the specimen at the first resonance frequency until was broken. Both dynamic and fatigue testing were conducted at the room temperature. The complete test set-up is shown in fig 2.

100mm

10mm

6mm

2mm

4mm

Figure 1: Test specimen

Figure 2: Experimental set-up

4. Results and discussion

4.1. Dynamics properties

The dynamic response characteristics of the vacuum cast polyurethane polymer material are shown in fig 3. The drive acceleration was varied from 1m/s 2 to 60m/s 2 at frequency range of 30Hz to 100Hz. It can be seen in fig 3 (a) that the peak frequency decreases with increasing input loading, the rate of decrease is significant up to 30m/s 2 input loading before it starts to flatten out. The transmissibility in fig 3 (b) also shows similar behavior to the peak