Mechanics of Composite, Hybrid and Multifunctional Materials, Volume 5 by Unknown

Author:Unknown
Language: eng
Format: epub
ISBN: 9783319955100
Publisher: Springer International Publishing

We created three different types of variable stiffening composites made of: (1) polyurethane sheets, (2) silicone sheets, and (3) paper, all sealed in a polyethylene pouch with a tube inlet for negative pressure. All three composites were composed of 5 layers of bond paper that were 0.1 mm thick per layer, along with another 5 layers of paper or 5 layers of polyurethane rubber of Shore Hardness 90A or silicone of Shore Hardness 40A, both of thickness 0.8 mm per layer. The jamming materials were tested in a cantilever beam configuration that was 13 cm long and 2.4 cm wide. The composites are stiffened by an 80 kPa vacuum, and a 100 g load is applied at the tip. We could determine the difference in stiffness by the vertical displacements each composite experiences under the same load, and compare it with the predicted values. The properties of the layers and the corresponding vertical displacements that were predicted can be seen below in Table 19.1. The correlation between the predicted and measured displacements indicated that the effects of the jamming material were not accurately captured assuming perfect strain transfer across each layer. Instead, there is an increase in the shear strain between the stiffer paper layers due to the order of magnitude differences in the stiffness of the polyurethane rubber and silicone compared to paper that significantly reduces the shear stiffness between the paper layers. The resulting reduction needed in the predicted curvature of the softer layer to account for these differences is also reported in Table 19.1, and is approximately 50%. Table 19.1The predicted vertical displacements for each jamming layer material, and the associated reduction needed in the predicted curvature to account for the loss of strain transfer across layers due to the orders of magnitude difference in stiffness between the paper and the polyurethane rubber or silicone

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