The thickness and stretch dependence of the electrical breakdown strength of an acrylic dielectric elastomer
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(a) An elastomer sheet is stretched biaxially by an amount denoted as the stretch ratio . (b) Electrical test arrangement consists of a prestretched elastomer sheet with an array of parallel cylindrical wires on either side, all embedded by casting a stiff polymer around them. The polymer blocks on either side of the elastomer sheet were made from a two component polyurethane mixture that, once cross-linking had initiated, was cast around the stretched elastomer to form a stiff plastic layer about 3 mm in thickness after fully curing. The electrodes consisted of high purity (99.99%) copper wires with a diameter of 18 encapsulated in the stiff polymer on either side of the elastomer are arranged at right angles to one another. Electrical connection was made to the individual wires, allowing for a large number of individual tests to be made on the same sheet. For example, 20 tests can be made in the configuration shown in the schematic.
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(a) For each initial dielectric thickness, the breakdown voltages decrease monotonically with increase of stretch. (b) Breakdown electric field as a function of thickness for VHB 4905, two-layer VHB 4905, and VHB 4910 stretched to the values indicated. The lines through the data correspond to a power law dependence on (1/h) with an exponent of 0.57. Data for VHB 4910 and two-layer VHB 4905 are fitted to same line. The vertical displacement between the two lines indicates the dielectric strength also depends on the stretch. (c) Breakdown electric field as a function of stretch. The lines through the data correspond to a power law dependence on with an exponent of 1.13. Again the difference between the two lines indicates the dielectric strength should depend on the thickness. Data from the work of Kofod25 are also included and an exponent of 1.12 is obtained by fitting. (d) Experimentally determined scaling between the breakdown electric field and the parameter .
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