Impact and dynamic response of high-density structural foams used as filler inside circular steel tube

Structural foams have good energy absorption properties and are effective in reducing the vulnerability of sandwich structures. This research investigated the impact and dynamic response of three different high-density polymeric structural foams; designated A, B and C for proprietary reasons. Foam-C had the lowest density out of the three; density of foam-B was approximately twice the density of foam-C, while the density of foam-A was about three times the density of foam-C. The cylindrical foam samples were initially impacted at different velocities in a DYNATUP Model 8250 instrumented impact test machine and their energy absorption was characterized from the resulting load-deflection data. Each of the three foams was then modeled as filler inside a circular steel tube of 0.8 nun thickness. Non-linear finite element analysis was performed under displacement controlled quasi-static compressive monotonic loading using PATRAN as pre-processor and ABAQUS Standard commercial software. The area under the load-deflection curve was calculated to obtain the absorbed energy and the crush loads for the three foam fillers were compared. Results indicate that foam-A having the highest density was more effective as filler inside the circular steel tube, with the intermediate density foam-B performing equally well under uni-axial compressive loading. Foam-C, which had the lowest density, was found to be ineffective as filler in this application due to large differences in stiffness between this foam and the enclosed steel tube. A TA Instruments Model 983 DMA (dynamic mechanical analyzer) was used for obtaining the storage and loss modulus along with the damping and glass transition properties of the different density structural foams. Frequency multiplexing was also used in conjunction with the time-temperature superposition principle for characterizing the long-term behavior of these viscoelastic foams. (C) 2003 Elsevier Science Ltd. All rights reserved.