Baxter makes a peritoneal dialysis kit that includes something along those lines. The kit includes a bag of saline that's plugged by a little colored plastic, well, doohickey, that's shaped sort of like a potato masher, but much smaller. It's hollow, but the hole inside doesn't go all the way through. The big end inserted into a nipple in the bag. A hose is attached to the outside of the bag's nipple. After the patient has made the proper connections to the apparatus that's been surgically inserted in their body, they start the fluid flowing by bending the tube at the nipple until the doohickey breaks in two. The smaller end of it is a loose fit in the hose, so once the doohickey has fractured, the saline can flow axially into the big end, radially through the fracture, and axially along and past the small end. The tube that encloses the doohickey is a loose fit around it, and has a smaller host bonded into its distal end, so the fractured part is captured.
Okay, it's sort of the reverse of what you seem to be asking for, but maybe it will get you thinking. I think it's a nice bit of material selection; the doohickey breaks like highly loaded glass- reinforced ABS. The plastic is strong but not tough. The tubing and the bag appear to be polyurethane; tough but not strong. The assembly withstands normal handling but the doohickey can be fractured by a patient's fingers.
-Mike-
