Compression and Instrumented Indentation Measurements on Biomimetic Polymers

Report No. ARL-RP-135
Authors: Thomas F. Juliano; Paul Moy; Tusit Weerasooriya; Mark R. VanLandingham; Aaron M. Forster
Date/Pages: September 2006; 14 pages
Abstract: The mechanical response of living tissue is important to understanding the injury-risk associated with impact events. Unfortunately, currently used materials are not optimal surrogates and present several experimental challenges. Bulk measurement techniques, such as compression and shear tests, do not necessarily represent the type and rate of loading experienced in an actual impact event. Indentation testing may induce surface loading at stress states and strain rates not available to bulk measurement equipment. In this work, a ballistic gelatin and two styrene-isoprene triblock copolymer gels are tested and compared using both macro-scale and micro-scale measurements. A methodology is presented to conduct instrumented indentation experiments with a flat punch on materials with a modulus far below 1 MPa. The synthetic triblock copolymer gels are shown to be much easier to test than the ballistic gelatin. Compared to ballistic gelatin, both copolymer gels were found to have a greater degree of thermal stability. All of the materials exhibit strain-rate dependence, although the magnitude of dependence is a function of the loading rate and testing method.
Distribution: Approved for public release
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Last Update / Reviewed: September 1, 2006