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My lab and I are looking to conduct tensile test experiments on polymer samples with integrated planes of bubbles or voids (see image). The goal of this is to see how well we can manipulate crack propagation during tensile testing with the induced bubbles by varying the angle this plane makes with the predicted crack plane.

Preparing the currently tested polymer (Ecoflex) involves mixing two liquid components together, pouring the mixture into a petri dish, putting the dish in a vacuum chamber to remove bubbles, and setting the dish out on a level surface to cure for several hours.

Our current ideas on creating this integrated bubble plane:

  • manually inputting bubbles in a curing solution on a petri dish using a syringe
  • creating a layer of polymer which we let cure without placing in a vacuum chamber. Once cured, pour another layer of uncured liquid polymer on one side of the cured (non-vacuumed) polymer, place the combined polymer in the vacuum chamber to remove bubbles from the uncured part, and allow to cure. Repeat process for the other side of the non-vacuumed part

Samples are cut from the cured polymers to achieve tensile specimens with desired orientations of the bubble plane and the initial crack is created by cutting the specimen with a razor blade.

We are still experimenting with these processes and are looking for other ideas as well. Any input on how to create this bubble/void plane would be appreciated.

Sample Concept

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You might try to vacuum the entire sample and then, once cured to a (to be determined) stage, superheat the plane with laser or high frequency ultrasound until bubbles form.

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