Experimental and Numerical Analysis of Dynamic Behavior of Cork Material 55 Table 2 Prony series with 10 terms parameters τmin τmax g1 g2 g3 g4 g5 g6 g7 g8 g9 g10 g∞ 1E-5.608 1E1.322 0.140 0.703 0.046 0.023 0.012 0.006 0.007 0.009 0.006 0.005 0.042 Table 3 Mullins damage parameters r m β 1.067 0.740 0.628 Compression tests were performed at different strain rates on cork block, in order to reproduce as faithfully as possible the experimental tests. The cork is modeled as a 2D model costrained to the bottom side. The plate that load the cork is discretized as a rigid surface and a constant velocity equal to the experimental values. The strain rate analyzed are 10−3, 10−1, 101, and103 s−1. The results of both the experimental tests and the analytical modeling, expressed in terms of stressstrain curves, are shown in Fig.3a and in Fig.3b. The blue curves represent the experimental points, while the curves in red represents the total stress predicted by the constitutive model. (a) (b) Fig. 3 a) Compression stress strain curves at 10−3, 101 and103 s−1 strain rate; b) Compression stress strain curves at 10−1 s−1 strain rate The Fig.3a presents the results for the compression tests at 10−3, 101 and 103 s−1. The stress-strain curve at the lowest strain rate validates the hyperelastic model, while the two curves corresponding to the highest strain rates confirm the accuracy of the viscoelastic model. The Fig.3b illustrates the validation of the complete model, including damage, which is captured through the Mullins effect. This test was performed at a strain rate of 10−1 s−1. TestCase In the previous sections, we defined the constitutive models that best describe the behavior of agglomerated cork. We then validated the model through the simulation of an impact test at different strain rates. In this section, we present a test case: puncture tests performed using a hemispherical rigid indenter. Puncture tests were performed on cylidrical slabs of cork by means of a drop tower machine. This kind of test is very popular as it provides immediate information on the energy absorption. However, here it has been used for verifying the material models calibration. The specimen is placed between two supports with a 40 mm hole, and is deformed by a falling punch having a
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