April 5, 2012

Carleton University students have designed a type of crash test dummy not seen before: a cyclist, designed to go over the handlebars at 25 km/h.

On Wednesday, after eight months of hard labour creating the nameless dummy, they had the satisfaction of loading it on a cart and launching it into trouble.

“We’ve been trying to simulate whether you would get a concussion from an over-the-handlebars-type accident,” said Evan Hayes, a fourth-year student in mechanical engineering. The 21 students in the group also come from aerospace and biomedical engineering.

Car-testing dummies, it seems, don’t tell what happens to people who are thrown off bicycles. The Carleton dummy is built to suffer in more ways than the conventional model, a Thor-NT device used widely in industry.

“The idea is that we should be able to throw this crash test dummy into whatever situation and get a reasonably accurate result, regardless of whether we know (in advance) what injuries we’re going to have,” Hayes said.

When engineers crash a car, they use one type of dummy for a frontal crash and a different type for a side impact. Neither is considered right for a cyclist who hits something or slams on the front brakes hard and flies over the handlebars.

This year the student team has concentrated on what happens to the head and neck of the cyclist. Arms and legs can break in a crash, but head injuries are a more serious risk.

The dummy wears a helmet. Like a human cyclist, though, it keeps the important stuff inside its head.

This includes one sensor that deforms under the force of impact, to show the stress that a real cyclist would endure.

There are also two accelerometers, devices that can measure any change in speed, either faster or slower.

In this case, they measure the sudden deceleration from 25 km/h to zero. Deceleration can cause concussions because the skull slows, but the brain’s momentum is still moving, making it slam against the skull.

There has been recent research suggesting that a helmet with a visor on the front may force the head to snap backward when it hits the ground, and that may contribute to a concussion. One of the accelerometers measures this movement as well.

The year was full of surprises: dummy parts from a factory that didn’t quite fit together, budgets that changed unexpectedly, insufficient time in the machine shop.

“Most people enjoy it. It is difficult, but it is a culmination and practical test of what we’ve been learning for the past four of five years,” Hayes said.

Besides, he says, it’s fun to make things crash.