A side-splitting tale

[摘要] Researchers who used a device to simulate human copulation report that more than 90% of condom breakages occur when the sheath is stretched repeatedly in the same place without returning to a relaxed state between stretches. International standards for condom testing require two evaluations of the tensile strength of the condom material. One measures how far a ring of the material elongates when stretched between two rollers; the other involves inflating a condom until it bursts and recording the pressure and volume at which that happens. But a sticky problem remains: clinical trials have reported failure rates of around 1% due to breakage, but the sample sizes were too small to reliably indicate why the devices break. Laboratory tests of condoms made of varying thicknesses and materials have done a poor job of duplicating real-world splitting, making it difficult to design safer condoms. Now, a team led by Nicholas White, head of quality control at SSL International in Cambridge, UK, which owns major condom brand Durex, has attempted a more realistic model of sex with a condom, using a device with an adjustable `thrust- hole' diameter, thrust rate and lubrication. The researchers replicated the breakage pattern by altering the parameters of their device so that the test condoms were progressively stretched at the tip during repeated thrusting.